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Radioactivity in the Marine Environment (1971)

Chapter: SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS

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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Suggested Citation:"SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS." National Research Council. 1971. Radioactivity in the Marine Environment. Washington, DC: The National Academies Press. doi: 10.17226/18745.
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Chapter Two SOURCES OF RADIOACTIVITY AND THEIR CHARACTERISTICS A. B. Joseph, P. F. Gustafson, I. R. Russell, E. A. Schuert, H. L. Volchok, A. Tamplin Prior to 1942, man's exposure to ionizing radiation was lim- ited, essentially, to natural radioactivity and medical x rays. Since then, the use of atomic energy has become an impor- tant part of the modern way of life. The first controlled, self-sustaining nuclear chain reaction occurred in December 1942, and the first atomic bomb was tested successfully in July 1945. Both kinds of events create man-made radioac- tivity. Over the past 25 years, the uses of atomic energy have grown more numerous, more diverse, and more wide- spread. In only a quarter of a century, man has created more radioactivity than existed naturally in the world in 1942, and the future will see quantum jumps in production. Table 1 indicates the diversity of types and applications of man-made atomic energy. To increase our understanding of radioactivity in man's environment-more specifically, in the oceanic environ- ment-it is helpful to examine the uses of atomic energy, the conditions of the creation of radioactivity, its control and management, and where and how radioactivity is used; these factors bear on the role of radionuclides in the phys- ics, chemistry, and biology of the sea. Not all uses of atomic energy release radioactivity to the environment; some never do, some always do, and some do only under accidental conditions. The spectrum of radioisotopes released into the environment varies with the kinds of applications, the chem- ical and physical form of the radioactive material, and the environmental conditions at the place and time of use. Two sources of atomic energy create fission-product radioactivity—nuclear reactors and nuclear explosives, both of which involve the fission of heavy elements. Nuclear ex- plosives may also involve fusion of light elements. During the fission and fusion process, neutrons are released that may interact with surrounding materials to create new ra- dionuclides. All of the other sources of atomic energy (see Table 1) involve the radioactivity derived from the fission or fusion processes-either fission products or activation products. The greatest future source of radioactivity will be nuclear reactors, assuming that the atmospheric nuclear test- ing moratorium will continue. In 1967, in the United States, there were 17 commercial nuclear-powered generating plants with a total capacity of 2,000 electrical megawatts (MWe). In the early 1970's, the number of U.S. plants will be increased by 32 and power production by 23,000 MWe-a tenfold in- crease in nuclear generating capacity (U.S. Atomic Energy Commission, 1967a). It has been estimated that 145,500 MWe will be generated by nuclear plants by 1980 (U.S. Atomic Energy Commission, 1967b), not including reactors outside of the United States or reactors for ships, research, and special purposes. It is evident that significant amounts of fission products will be generated in nuclear power plants. The fission of 1 g of 235U produces approximately 1 g of fission products and 1,000 kilowatt-days of energy (at 100 percent efficiency). At the end of one MW-year, the "important" fission-product

Sources of Radioactivity and Their Characteristics TABLE 1 Sources and Applications of Atomic Energy Energy Source Output Applications Nuclear reactors (controlled nuclear fission) Nuclear explosives Encapsulated radioisotopes (sealed sources) Encapsulated radioisotopes Radionuclides Steam, electricity Heat, electricity, neutrons Kinetic energy Electricity Gamma and beta radiation Beta and gamma radiation Electric power-stationary or portable plants, desalination, propulsion of submarines and surface ships Spacecraft and satellite power, spacecraft propulsion, research and special materials production Military and civilian applications: large-scale earth moving, subsurface excavation, mineral extraction from underground Marine navigation aids, unmanned weather stations, spacecraft project power, artificial human organs Food preservation, polymerization, sterilization of medical supplies, thickness gauges Medical uses, tracers in scientific research, measures of manufacturing processes activity would amount to approximately 700,000 Ci (U.S. Public Health Service, 1960). However, under normal oper- ating conditions, nuclear reactors release little radioactivity into the environment (see Table 11). To date, the largest source of radionuclides in the ocean has been the atmospheric nuclear weapons testing programs of the United States, the Soviet Union, the United Kingdom, the People's Republic of China, and France. Meteorological processes distribute radioactive test debris throughout much of the stratosphere, which in turn results in worldwide de- position of fallout on the earth's surface. Only China and France continue atmospheric weapons tests and add to the worldwide fallout burden. On the whole, the inventory of nuclear debris in the stratosphere has declined since cessa- tion of widespread atmospheric testing in 1963. Future uses of nuclear explosives are contemplated for large-scale construction projects and for programs in conser- vation of natural resources; the former are to be under- ground explosions with less release to the atmosphere than past nuclear testing programs, and the latter are expected to be contained explosions. Encapsulated radioisotopes release no radioactivity to the environment unless the container is ruptured. However, because of the substantial amounts of radioactivity in- volved, it is important to consider the environmental impli- cations of accidents. Scientific, medical, and industrial uses of controlled amounts of radioisotopes may release some activity to drainage systems that flow to the sea; generally, these quan- tities are small. In the United States, disposal of packaged wastes to the sea has been largely discontinued in favor of land burial. However, other countries still use the sea for disposal of low-level packaged radioactive waste. NATURAL RADIOACTIVITY More than 60 radionuclides occur naturally in the earth's environment. These derive primarily from two sources: the rocks and minerals of the solid earth and cosmic-ray activity. The solid-earth radionuclides include 32 daughters of the long-lived uranium and thorium isotopes. There are 11 other radioisotopes spread across the periodic table whose com- mon characteristic is a long half-life, i.e., between 107 and 1015 years. Some of these isotopes probably originate from the spontaneous fission of uranium in situ (Parker and Kuroda, 1958). The radionuclides of the earth's crust are believed to have been created when the earth was formed. Wind and water erode and leach the radionuclides as part of the pro- cess of rock weathering; they are then carried to the oceans by runoff or by the winds as gases and particulates. In the oceans, the materials are found throughout the water col- umn and in the sediments, according to their physical and chemical states, as described in Chapter 5. Cosmic rays originating in outer space continuously bombard the earth's gaseous envelope. Some of these par- ticles collide with atoms of nitrogen, oxygen, and argon in the atmosphere, producing radioactive elements. These ra- dionuclides are brought down in solution to the earth's sur- face by precipitation, are sorbed on particles that settle out or are carried down by precipitation, or behave as a gas and enter into equilibrium reactions with water and other ma- terials on the earth's surface. At least 14 radionuclides are created in this manner, and a number of these have been measured in seawater and in ocean sediments (see Table 2). Two of these radionuclides, 3H and 14C, also are produced by nuclear detonations.

Radioactivity in the Marine Environment TABLE 2 Concentrations of Natural Radionuclides in the Sea" In Seawater Radionuclide Half-life g/liter dpm/liter In Sediments (g/g) Terrigenous Origin Potassium-40 1.25 X 109yr 4.7 X 10-5 670 (0.8-4.5) X l0"6 Rubidium-87 4.7 X 10ioyr 3.4 X 10-5 64 - Indium-1 I5 6.0 X 1014yr 1.6 X I0-10 - — - Iodine- 129 1.7 x 107 yr 0.06 - Lanthanum-138 2.0 X 10" yr - - - Neodymium-144 5.0 X 1015yr - — - Samarium-147 1.3 x 10nyr - - - Lutetium-176 2.4 X 1010yr - - - Tungsten-180 1014yr - - - Rhenium-187 5.0 X 1010yr — - — Platinum-190 1012 yr <1.2 X 10-23 - — 2.1 X 10-21 - Thallium-207 4.79 min <0.005 Thallium-208 3.10min 4.1 x 10-24 0.003 6.7 X l0'22 Lead-210 19.4 yr 1.1 X 10-15 0.2 4.5 X 10-14 Lead-211 36.1 min <9.0 X 10-23 <0.005 1.6X 10-20 Lead-212 10.6 hr 2.4 X 10-21 0.007 3.9 X 10-19 Lead-214 26.8 min 2.9 X 10-21 0.2 1.2 X 10-19 Bismuth-210 5.01 day 7.8 X l0-19 0.2 3.1 X 10-i7 Bismuth-211 2.16 min <5.6X l0"24 <0.005 1.0 X 10-21 Bismuth-212 60.5 min 2.2 X 10-22 0.007 3.7 X 10-24 Bismuth-214 19.7 min 2.1 X 10-21 0.2 8.8 X 10-20 Polonium-210 138.4 day 2.2 X 10-i7 0.2 8.8 X I0-16 Polonium-211 0.52 sec <6.8 X 10-29 <1.5 X 10"6 1.2 X 10-26 Polonium-212 3.04 X 10-7sec 1.2 X 10-32 0.005 2.4 X 10"29 Polonium-214 1.64 X 10^* sec 3.0 X 10-28 0.2 1.1 X 10-27 Polonium-215 1.83 X 10-3 sec <8.1 X 10"29 <0.005 1.4 X 10-26 Polonium-216 0.158 sec 1.0 X 10-26 0.007 1.7 X 10"24 Polonium-218 3.05 min 3.4 X 10-22 0.2 1.4 X 10-20 Radon-219 3.92 sec <1.7 X 10-25 <0.005 3.1 X 10'23 Radon-220 51.5 sec 3.3 X 10-24 0.007 5.4X 10"22 Radon-222 3.8 day 6.3 X 10-i9 0.2 2.5 X 10-i7 Francium-223 22 min <7.0 X 10-24 <6.0 X I0•4 1.4 X 10-21 Radium-223 11. 68 day <4.4 X I0"20 <0.005 8.5 X 10-18 Radium-224 3.64 day 2.1 X 10-20 0.007 3.4 X 10-i8 Radium-226 1,622 yr 1.0 X 10-13 0.2 4.0 X 10-12 Radium-228 6.7 yr 1.4 X 10-16 0.05 2.3 X 10-15 Actinium-227 21.6 yr <1.0X 10-i5 <0.2 5.9 X 10-15 Actinium-228 6.13hr 1.5 X 10-20 0.075 2.4 X 10-i9 Thorium-227 18.17 day <7.0X 10'20 <0.005 1.3X 10-17 Thorium- 2 28 1.91 yr <4.0X 10-" <0.07 7.0 X l0-16 Thorium-230 7.52 X 104yr <3.0X 10-13 <0.014 2.0 X I0-10 Thorium-231 25.6 hr 8.6 X 10-20 0.1 2.9 X I0-20 Thorium-232 1.42 X 1010yr 1.0 X 10-io 2.4 X 10-i5 5.0 X 10"6 Thorium-234 24.1 day 4.3 X 10-i7 2.2 1.4X 10-17 Protoactinium-231 3.43 x 104 yr <2.0 X l0-12 <0.2 1.0 X 10-11 Protoactinium-234 1.14 min 1.4X 10-i9 220 4.7 X 10-20 Uranium-234 2.48 x 10s yr 1.9X I0-10 2.3-2.9 8.1 X 10-i1 Uranium-235 7.13 X 108yr 2.1 X I0"8 0.09-0.17 7.1 X 10"9 Uranium-238 4.5 X 109yr 3.0 x 10"6 2.0-2.5 1.0 x 10"6 Cosmic Origin Hydrogen-3 12.26yr 1.7X 10-18 0.036 - Beryllium-7 5 3 day <4.9 X 10-17 <38 - Beryllium-10 2.5 x 106yr 2.2 X 10-17 lo-6 (1-3) X 10-13 Carbon- 14 5,570 yr (2-3) X 10-14 0.2-0.3 (0.1-1) X 10-13 Sodium-24 2.6 yr 2.9 X 10-19 - 1.2X 10-8 - - Aluminum- 26 7.4 X 10s yr -

Sources of Radioactivity and Their Characteristics TABLE 2 (Continued) In Seawater Radionuclide Half-life g/liter dpm/liter In Sediments (g/g) Silicon-32 710yr 5.0 X I0-19 2.4 X I0"5 (0-2) X 10-16 Phosphorus-32 14.3 day <1.5 X 10-18 - - Phosphorus-33 25 day <3.1 X 10-18 - - Sulfur-35 87 day <1.8 X l0-18 — - Chlorine-35 3.1 X 10s yr 7.7X 10-17 5.5 X 10-14 - Chlorine-39 Ihr - - - Argon-37 35 day 3.8 X 10"20 — 2.9 X 10"6 — - Argon-39 270 yr - "Compiled from Koczy and Rosholt (1962) and Lai and Peters (1967). TABLE 3 Number of Nuclear Detonations through 1968, by Local Environment and Elevation of Explosion Continental Arctic Islands Coral Islands Open Ocean Surface 58° 79" 16 - Tower 45 — 11 — Air and balloon* 47 - 48 1 High-altitude and rocketc 4 - - 10 Barge and ship - - 35 - Underwater - 1 3 2 Underground 116 - - — "includes Soviet and Chinese shots indicated only as "atmospheric. 6Approximately 1,000-86,000-ft altitude. cApproximately 141,000-ft to 300-mi altitude. NUCLEAR EXPLOSIVES Through December 1968, some 470 nuclear explosives had been detonated in many parts of the world in the testing programs of the United States, the Soviet Union, the United Kingdom, France, and China. All nuclear tests, with the pos- sible exception of contained, underground explosions and those in outer space, result in radioactivity being introduced into the oceans. The kinds, amount, and characteristics of the radioactivity introduced varies with the number, size, and materials of the devices themselves. The environmental media that react with the heat and fission and activation products of the explosion determine the physical and chem- ical characteristics of the debris and its subsequent rate and pattern of distribution. Table 3 is a composite summary of known or detected tests conducted by the five nuclear powers through 1968 (Glasstone, 1964; various press an- nouncements of Chinese and French tests). Through 1968, nuclear weapons tests have been conducted in both hemi- spheres under a wide variety of environmental situations-on, over, and under continental land masses, coral and arctic islands, and the open sea. It has been estimated that there were some 194 megaton equivalents of fission produced by nuclear testing between 1945 and 1963: 139 megatons as air bursts, 54 as coral sur- face or barge bursts, and one megaton as tower bursts (Fed- eral Radiation Council, 1963). The total of 194 megatons corresponds to about 2.8 X 1028 fissioning atoms of uranium or plutonium. Most of the fission occurred in 238U in thermonuclear explosions. Hence, to a good approximation the fission product mass yield curve reported by Hallden et al. (1961) will apply. The half-lives of 137Cs and 90Sr are, respectively, 30 and 28 years. Using the fission yields reported by Hallden et al. (1961), for thermonuclear-induced fission, it is estimated that approximately 21 MCi of 90Sr and 34 MCi of 137Cs have been introduced into the earth's atmosphere and onto the surface of the globe. The production of other fission products can be esti- mated similarly, using the fission yield and half-life data tabulated by Hallden et al. (1961). A few specific nonfission inputs are worthy of mention, such as 18i.185W during Operation Hardtack* in 1958, 102Rh in the high-altitude ORANGE* explosion in 1959, and 109Cd and n^Cd in the STARFISH* 400-km explosion in 1962. The high-yield Soviet explosions in 1961 and 1962 produced much 124Sb, 'Operational code names; a chronology is given in Glasstone (1964).

10 Radioactivity in the Marine Environment 54Mn, and 55'59Fe. The MIKE* thermonuclear explosion in 1952 generated considerable transuranium isotopes, includ- ing higher mass isotopes of plutonium. A sensible fraction of the debris from MIKE was deposited in the Pacific, thus providing a number of unique tracers with fairly localized input, such as 241Pu and 242Pu. It appears that approximately 1028 atoms of 239Pu (and perhaps one tenth as much 240Pu) have been generated by thermonuclear explosions in the course of testing. Nep- tunium-237 has also been produced in quantities compar- able to 239Pu. One hundred and forty megatons, or 72 percent of the total yield, were produced as airbursts, i.e., under condi- tions in which the fireball did not intersect the ground. Documented cases of tower-burst inputs represent a small fraction of the total—in the vicinity of 0.5 percent—and may be taken to be of trivial significance in the context of the marine environment. However, the third category, sur- face bursts, while representing only about 28 percent of the total, deserves special attention because of highly localized input, the majority of which was in the Marshall Islands, in the 1952 Ivy, 1954 Castle, 1956 Redwing, and 1958 Hard- tack series. Characteristics of Radioactive Debris The characteristics of the particles formed in a nuclear ex- plosion are determined by a large number of factors. Among the more important are the yield of the device and the quantity and kind of nearby environmental materials inter- acting with the nuclear explosion. The biological availability of the radioactivity in the debris particles will depend on particle size, the chemical form of the radioelement, and the matrix in which the radioactivity is imbedded or to which it is attached. PARTICLE SIZE DISTRIBUTION Airbursts In general, more than 90 percent of the radio- activity in airburst debris is to be found in very finely di- vided particles, less than 1 n in diameter. The literature on the particle size distribution of debris produced by airbursts is sparse. Nathans suggests a log-normal size distribution with a peak diameter in the differential size distribution be- low 1 n in diameter (M. Nathans, Tracerlab Inc., personal communication). Sherer proposed an exponential form of distribution for particles larger than 1 n, based on micro- scopic sizing of particles of verified radioactivity, e.g., the particle size distribution as a function of its diameter is pro- portional to e~°lb, where b is a parameter having a value of 1-2 ^-i for nominal-size (20-kt) explosions and D is the 'Operational code names; a chronology is given in Glasstone (1964). diameter in microns (J. Sherer, Lawrence Radiation Labora- tory, Livermore, Calif., personal communication). Whatever the true form of the size distribution function, it is clear that the particle population increases rapidly with decreasing particle size to below 1 n. There is considerable indirect evidence that particle size is related to the yield of the device, or more precisely, to the yield to mass ratio. The size distribution curve is shifted to smaller sizes as the yield increases. Since the bulk of the radioactivity in air- bursts resides in submicron particles, and these are slowly acted upon by gravitational forces, the worldwide strato- spheric distribution of airburst debris is relatively insensitive to the exact form of the size distribution. Very few par- ticles in excess of 10 n in diameter are found at any yield. Tower Bursts In tower bursts, a considerable portion of the supporting structure will be volatilized or melted. Few quantitative data have been published that reveal details of the size distribution of tower burst events. It is clear from environmental studies accompanying tests, however, that the particle population contains particles much larger than are found in airbursts of the same yield. For example, Larson (1966) reports that significant fractions of the radio- activity are to be found in particles in excess of 44 p. Hence, a large fraction of the radioactivity is deposited locally, and proportionately less enters the long-range-long-term atmo- spheric distribution system. Coral Island Surface Bursts A number of explosions of moderately high to high yield have been conducted on coral island surfaces or on barges, sometimes in relatively shallow water. In these cases substantial quantities of coral may be melted and vaporized, and, together with the vaporized constituents of seawater, may become major radioactive debris constituents. Data on the size distribution of radioactive debris from multimegaton explosions on coral islands are limited. The sheer magnitude of the event precludes collection of ade- quate samples from the prompt fallout and the residual nu- clear cloud. The samples that have been retrieved and analyzed inevitably suffer from lack of definition concern- ing the precise fraction of the total radioactive particle population the sample represents. Figure 1 gives a composite size distribution of radioactive particles for BRAVO as obtained from prompt fallout re- corded on nearby islands. Note that the maximum observed in the vicinity of 150 n reflects only that particles smaller than 150 n were incompletely deposited at the collection point because of their finite gravitational settling rates. Nathans etal. (1970), in studying the size distribution of cloud samples of nuclear debris of BRAVO and other coral island surface explosions, found that the results for all par- ticles (radioactive and inert) over the range 1-100 n fit a power law of the foimf(d) a CD~", where n may have the value of about 4. Power law distributions are rather com-

Sources of Radioactivity and Their Characteristics 11 £ 10- 10' 10 .-0• —--ex. FIGURE 1 Composite differential particle size spec- trum -BRAVO. 10 i i i 1 i 10' 10 PARTICLE DIAMETER IN MICR0NS 10 monly observed for natural aerosols, for zodiacal dust, and for stratospheric dust. Russell (1964) found a power law description for cloud samples of a low-yield surface explo- sion. Heft (1970) described a cloud from a coral surface ex- plosion as representing the superposition of two log-normal distributions. However, because of the late time of sampling, Heft's samples, similar to Nathans', contained very little of the larger end of the particle size spectrum. In any event, there appears to be a physical basis for a multimode set of particle distribution functions describing the debris as a whole. At the larger end of the particle size spectrum, par- ticles are formed by coalescence of smaller particles charac- teristic of the pre-shot soil. Melting and shock compaction are presumably partly responsible. A second phase, distrib- uted about a smaller median diameter, is attributed to un- melted, still-crystalline debris swept into the nuclear clouds by the strong afterwinds. ACTIVITY CONCENTRATIONS OF RADIOACTIVE DEBRIS Radioactivity per unit mass of particle varies in both kind and amount with the size and shape of the particles of de- bris formed in nuclear tests. A term used to describe the ra- dioactive content of particles is "activity concentration."* Activity of radioactive debris may be reported as atoms of radioactive species per gram of debris, as disintegrations per *In view of a different use and connotation of "specific activity" in subsequent chapters, in this chapter we will use "activity concentra- tion." minute of radioisotope per gram, and so on. In this section, activity concentration is given in units of equivalent fissions per gram of debris. An equivalent fission is the number of fissile atoms (e.g., 235U, 239Pu, or 238U) required to give the observed number of fission product atoms, or, alterna- tively, the number of fissioning atoms associated with a given number of product atoms of any kind. The situation is complicated by a phenomenon called "fractionation." If the debris sample were unfractionated, i.e., representative of the true proportions in which the ra- dioactivity was produced in the device, then equivalent fis- sions calculated for all isotopes in the sample will be'identi- cal. Because of differing chemical and physical properties, the elements may fractionate with respect to each other during the condensation and subsequent cooling phase in the fireball and nuclear cloud, or may fractionate by selec- tive attachment onto pre-existing condensed materials. The elements in the chains that are gaseous at ordinary tempera- tures, or low-boiling, may experience sharp differentiations from elements whose metals or oxides are high-boiling. The more refractory elements or oxides (those condensing above 1500° K) will have condensed out well before 60 sec have elapsed, even for megaton explosions. One can calculate the theoretical population of chain members in the first few minutes by using the charge divi- sion hypothesis of Glendenin et al. (1951), assigning prob- able nuclear charges based on the method of Wahl (1958), and using estimated half-lives after the method of Bolles and Ballou( 1956).

12 Radioactivity in the Marine Environment The average activity concentration of airburst debris is calculable if the fission yield and mass of the device struc- ture are known. Denoting activity concentration as 5, 5= 1.45X1017(M//A/). Here W is the yield in kilotons and M is the mass in tons. The units of S are equivalent fissions per gram. However, because of fractionation of the radioelements during the cooling phase, no specimen of debris may cor- respond to this value, except by chance. Benson et al. (1965) have presented data that imply that the activity concentra- tion of airburst particles over the range of a few to 15 mi- crons in diameter is roughly constant. They found that the 95Zr content of the particles is roughly related to the cube of the particle diameter. Barium-140 shows a radial depen- dence, roughly as D2: 3-2.6 over this size range. These larger particles are strongly depleted in 140Ba and all other volatile or semivolatile chains. Hence, the bulk of their activity is contributed by zirconium and rare-earth nuclides and a few additional refractory or semirefractory species, leading to a quasiconstant activity concentration behavior. Typically, it is found that the fraction of the mass found in particles in excess of 2 n will exceed by a factor of three or more the fraction of the most refractory fission product found in this size interval. Thus, in the above example, 30 percent of the mass might be found in particles larger than 2 ju associated with only 10 percent of the 95 Ar. This result may be attributable to poor mixing between the volatilized device materials and the fission products. It may also arise from concentration effects, insofar as they modify the con- densation temperature of the higher-boiling elements or their oxides. The fission products may represent only 10~3 to 10~4 of the concentration of the structural components in the fireball vapors. In particles smaller than 2-3 n, however, the activity concentration increases sharply for all nuclides, as required by mass and activity balance constraints. There are few pub- lished details on this region, and the general behavior must be inferred from gross beta particle specific activities. In the case of surface or near-surface bursts, the expand- ing fireball will be admixed with inert soil, some of which will have been vaporized, some melted, and some of which will remain essentially unaltered. The extent and time se- quence of mixing between inert debris and fission products will be variable from event to event and would be expected to be dependent upon explosion conditions. Soils are vari- able in composition, and water vapor can represent a signif- icant and undetermined component of the system, particu- larly in coral surface bursts. Despite the complexity of the chemical and physical processes attending a land-surface nuclear explosion, certain consistent patterns of debris behavior are observed. Empirical observations of land-surface nuclear debris sug- gest that a distinction be made among at least three classes of particles. 1. Completely volatilized material that recondenses to finely divided particles consisting of the device structural members, the fission products, and some environmental material. 2. Melted but not completely volatilized environmental material into which fission products may diffuse or onto which they attach. The melted entities may coalesce to form larger particles. 3. Unmelted environmental material, swept into the nu- clear cloud by the afterwinds, to which fission products or small condensed radioactive agglomerates attach by surface impaction. To these may be added a fourth class-spherical particles of very high activity concentration (up to 1016 equivalent fissions per gram) are found. These may represent coales- cence of condensed vaporized soil and fission product drop- lets, with rapid agglomeration to larger particles. Some coalescence of this component with melted inert droplets may also occur, leading to a spherical end product. Figure 2 depicts empirical activity concentration versus particle size data for a 15-megaton coral island explosion. This curve is drawn on the basis of radioactive particles only. It was determined by radioautography that the frac- tion of radioactive particles diminished rapidly with decreas- ing size below 44 ju. This effect is responsible for the steep slopes of both classes of chains, refractory and volatile, be- low 44 n. Consequently, the absolute magnitude of the slopes of the curves below 44 n is not to be taken too liter- ally, since there is some uncertainty in the assessment of the number of radioactive particles. If correction is not made for radioactive particles, the activity concentration curve for chain 89 is flat over the entire range of particle sizes. In Table 4 are assembled some activity concentration data, expressed in equivalent fissions per gram of fallout, collected near the fallout site. Data for a refractory-chain "Mo, a volatile-chain 89Sr, and a chain of intermediate vol- atility 140Ba are given. These data represent activity concen- trations that would be observed if the total yield of the device were due to fission, i.e., they have been normalized to 100 percent fission yield for comparative purposes. No attempt has been made to distinguish between radioactive and nonradioactive particles in the samples, with the excep- tion of the 15-Mt case. An admixture of inert (nonradioactive) debris will in general represent material physically displaced by the energy of the explosion to the sampling position. Some significant points become apparent from a study of Table 4:

Sources of Radioactivity and Their Characteristics 13 10 10 15 10 FIGURE 2 Empirical activity concentration versus particle size data for 15-megaton coral island explosion. Sgg, activity concentration of chain 99; Sgg, activity concentration of chain 89. 10 10' 10- DIAMETER IN M1CRONS 1. The normalized refractory-chain activity concentra- tions from coral surface explosions are relatively insensitive to yield, and, indeed, to particle size between about 50 n and 250n in diameter. The average "F/g for the four events is 6.9 X 1014 over this range of sizes. The average deviation from the average is about 36 percent. The greatest variabil- ity is found at the large-particle end of the spectrum. 2. If columns 2 and 3 are compared, corresponding to fallout near zero and 80 km downwind, the activity concen- tration of the debris transported downwind is seen to be uniformly higher for all classes of isotopes. This suggests a longer opportunity for debris attachment processes to occur when the mean residence time in the cloud is lengthened. (However, absolute fallout intensities downwind will nor- mally be lower because the number of grams of fallout de- posited per unit area is smaller.) 3. Spherical particles (column 5) are uniformly higher in activity concentration for chain 99, a refractory chain, than are the irregular particles. [Tompkins and Krey (1956) re- port that about 25 percent of the total activity at 10 days after the explosion was attributable to spherical particles in the 5.1-Mt explosion, but only a few percent of the mass. Spherical particles were difficult to find in size fractions below 177 n. One should not, however, infer their absence.] 4. Volatile chains show a somewhat greater variability in activity concentration from event to event than do refrac- tory chains. The mean residence time in the cloud exerts a strong influence. (Compare 3.5 Mt near ground zero and 80 km downwind.) Also, the degree of mixing in the cloud appears to have been somewhat more effective in the 5.1-Mt case than in the other instances. Whereas spherical particles were strongly enriched in refractory chains relative to irregu- lars of the same size, this is not the case with volatile chains. 5. An activity concentration maximum in the vicinity of 300 ju is a recurring freature, which is most pronounced for the spherical population. Volatile chains appear to decrease in activity concentration roughly according to D'2 past 300 n; the behavior is more in accord with D~l for refrac- tory chains, with the slope being slightly flatter for spheres than for irregulars. These features, if present in the 15-Mt case, were not revealed by the analysis that grouped all par- ticles larger than 300 n in a single fraction. In summary, few unequivocal statements can be made concerning the activity concentration behavior of coral sur- face debris. However, certain of the observations have at least a partial explanation in the thermal and mixing history to which the debris was subjected. We believe the large, high-specific-activity spheres to represent, in part, fireball condensate that coalesced to large droplets and, in part, melted soil particles that experienced no condensation history but that coalesced with high-activ- ity-concentration droplets of condensate origin. Electron microprobe analysis of spheres from coral island explosions

14 Radioactivity in the Marine Environment TABLE 4 Activity Concentration and Particle Size, Coral Island Surface Explosions (Equivalent fissions X10-14 per gram)" DgW 3.5 Ml (Prompt Fallout near Ground Zero) 3.5 Mt (Fallout Collected 80km Downwind) S.1Mt 5.1Mt (Spheres Only, near Ground Zero) 15 Mt (Radioactive Particles Only, Shot Atoll, Spheres plus Irregulars) 0.04 Mt (All Particles, Shot Atoll, Spheres plus Irregulars) Chain 99 (99Mo) 57 4.8 16.0 10.2" 7.2 2.5 88 4.9 10.6 8.9* - 6.6 4.0 125 5.8 9.8 8.4* - 6.2 4.7 177 6.0 12.5 9.0c 35 6.0 5.7 297 12.4 13.2 15.2c 100 4.8 4.5 594 11.9 21.3 5.7c 68 3.4 1.6 840 3.1 24.3 4.7c 58 - - Chain 89 (89Sr) 57 0.075 0.24 0.36* 0.086 0.063 88 0.065 0.17 0.28* - 0.11 0.074 125 0.046 0.19 0.246 - 0.12 0.082 177 0.042 0.14 0.18c 0.24 0.12 0.062 297 0.043 0.12 0.22c 0.26 0.13 0.044 594 0.044 0.11 0.1 lc 0.063 0.046 0.063 840 0.075 0.070 0.04 2c 0.031 - - Chain 140(140Ba) 57 0.32 1.28 0.676 0.20 0.25 88 0.27 0.74 0.546 0.22 0.28 125 0.20 0.99 0.45 b — 0.22 0.30 177 0.17 0.77 0.39c 0.48 0.23 0.23 297 0.15 0.75 0.49c 0.74 0.25 0.18 594 0.16 0.67 0.31c 0.18 0.13 0.24 840 0.031 0.41 0.1 2c 0.085 — — "Derived from Morgenthau era/. (1960). "irregulars plus spheres, near ground zero. c Irregulars only, spheres removed, near ground zero. show a number of instances in which spheres arose by coalescence of heterogeneous droplets (Norman and Winchell, 1967). The \/D2 behavior observed for volatile isotope chains in particles in excess of 300 /u is explicable on two grounds. Vapor phase controlled diffusion may lead to an activity proportional to the diameter of the particle for a given ex- posure time and hence to an activity concentration inversely as the square of the diameter. Also, larger particles are fall- ing out of the volatile-rich cloud faster than smaller par- ticles, leading to a decrease in activity concentration with increasing diameter. It is of some interest also that the up- take of refractory chains proceeds as \/D, indicating incor- poration as the area for these large particles. The refractory- containing droplets are probably attached very early (in the first few minutes); vapor phase controlled diffusion prob- ably plays no role here. The activity concentration maximum of a volatile chain is understandable in terms of residence time in the cloud. A 100-/J particle found in the prompt fallout pattern could not have originated from so high a position in the cloud as a 300-500-/U particle and hence would have been exposed to volatile chain vapors for a shorter time. Attempts to achieve a basic understanding of fractiona- tion behavior as a function of explosion conditions and yield have been made by a number of workers. The thermo- dynamic model of Miller (1960) was a major step in placing fallout studies on a scientific basis. Norman et al. (1970) have carried the Miller model forward with a number of sig- nificant refinements, both conceptual and experimental. The radial distribution model of Freiling (1961, 1963) leads to considerable systemization in the treatment of debris be- havior. Heft (1970) has achieved considerable success in describing fractionated systems with a nonphenomenologi-

Sources of Radioactivity and Their Characteristics 15 cal model that introduces a minimum number of basic as- sumptions. Laboratory studies by Freiling (1970) and Adams et al. (1967a, 1967b) have recently focused on the kinetic aspects of the pickup of fission-product vapors by molten oxide droplets. Similar studies are under way in a number of other laboratories, using methods of high-temperature chemistry. A satisfactory physical model of debris formation processes must probably include due consideration of vaporization, condensation, and agglomerative processes. Equally impor- tant is a better understanding of the early thermal and mix- ing history within the ball of fire and developing nuclear cloud. RELATIVE VOLATILITIES OF SOME FISSION PRODUCT CHAINS It is appropriate to mention briefly fundamental chemical differences between subclasses of volatile fission product mass chains. Chain 89 is volatile mainly because of the 3.2- min 89Kr; 89Rb, another chain member, will behave as a volatile element during the initial stages of fireball cooling when only the most refractory elements have condensed. On the other hand, if the temperature is well below the boil- ing point of rubidium or its oxides, the latter will quickly attach to a debris particle surface. Similarly, the volatility of chain 131, usually measured as 1311, is conferred by the relatively low boiling properties of Sn, Sb, and Te oxides. When the temperature has fallen to below 1000°C, these elements can be considered to be no longer volatile for the usual range of partial pressures. It is apparent that radiochemical composition of the fall- out must change proceeding downwind from ground zero, becoming more enriched in volatile relative to refractory chains. The Special Case of Underwater Explosions Only an insignificant fraction (less than 0.1 percent) of the total megaton equivalents of fission detonations (see Table 3) has resulted from underwater bursts. These events have the unique characteristic of being point source injections. The initial oceanic distribution is a function of the yield and depth of detonation. Based on limited test experience in oceanic situations, for shallow explosions, from one third to two thirds of the debris may be found in the mixed layer in a pool many hundreds of meters in radius and mixed to the existing thermocline (approximately 100 m). The his- tory of such an injection as it was influenced by currents, turbulent diffusion, and decay, is depicted in Figure 3 as measured from an aircraft and in Figure 4 as measured by an in situ gamma probe (Riel, 1962). FIGURE 3 Surface pattern of distribution of radioactivity from a nominal-yield underwater explosion as measured from an aircraft at 500-ft (150-m) altitude. (Gamma contour values in mR/hr.) Debris from deep explosions deposited in the thermo- cline layer will generally react to the same environmental influences; however, since the subsurface scale of turbulence is small, the predominant activity reduction mechanism is radioactive decay. Discrete lamina of radioactivity were ob- served in the thermocline layer after the WIGWAM test.* The fraction of the debris in these waters, as reported by Isaacs (1962), was estimated to be approximately two thirds of the total debris released by the explosion. Advection and diffusion of radioactivity in the ocean is discussed in detail in Chapter 4. Fractionation of fission products created in underwater detonations is not severe (Freiling and Ballou, 1962). Indi- vidual fission product data from samples collected shortly after detonations indicated a variation of no more than 30 percent in predicted fission product ratios. An exception was 89Sr from a deep burst, which varied by a factor of up to about 10 in relation to other fission product radionuclides. *A 30-kt device detonated at a depth of 2.000 ft (610 m) in the Pacific at 29°N, 126°W,in 1955.

16 Radioactivity in the Marine Environment O GR0UND ZER0 ..-0.03 H + 48 H0URS 20 M1 ...- 0,4 0.04; °.4p'.04 H + 87 H0URS .013 H + 105 H0URS .0013 H + 537 H0URS FIGURE 4 Subsurface pattern of distribu- tion of radioactivity from a nominal-yield underwater explosion as measured by an in situ gamma probe (some lines are dashed for clarity of presentation). (Reprinted from Riel, 1962). O0050 CKO0I3 H +741 H0URS 00050 AB0UT 8O FT DEEP H + 881 H0URS AB0UT 30 FT DEEP \\ //0.0O13 Nuclear Explosion Debris and Its Interaction with Seawater The physical and chemical states of bomb debris in seawater are poorly understood. Some theoretical estimates have been made, a few determinations from actual debris have been reported, and some laboratory studies using stable element counterparts of detonation debris have been undertaken (Freiling and Ballou, 1962; Greendale and Ballou, 1954). Radionuclide physicochemical states are largely deter- mined by their state at the time of addition to the ocean (or by the initial state and the decay of their precursors) and by the effects of their chemical environment. Little is known of the fundamental processes of forma- tion of nuclear debris from an underwater explosion. In the absence of large quantities of bottom material, the initial processes can be visualized as forming debris consisting of vaporized and dissociated water, seawater salts, and device materials. For a 10-kt device detonated underwater, on the order of 7 X 106 kg of seawater will be vaporized. The bubble of debris will then contain, in addition to the vapor- ized device materials and the 7 X 106 kg of H2O, 1.3 X 10s kg of chlorine, 7.7 X 104 kg of sodium and potassium, 1.1 X 104 kg of calcium and magnesium, 6.3 X 103 kg of sulfur, and less than 7 X 102 kg of any other seawater constituent. As this system cools, nucleation of the debris should be

Sources of Radioactivity and Their Characteristics 17 governed by iron, calcium, and magnesium oxides. The ini- tial nuclei would therefore be expected to consist of par- ticles of calcium, magnesium, and iron oxides of less than 20 n diameter. These would contain the refractory-like ra- dionuclides. Upon further cooling, these, in turn, would serve as nuclei for deposition of more volatile radionuclides. The release of fission products to seawater from nuclear debris depends primarily upon particle solubility and leach- ing properties. It has been established that the ease of leach- ing gross beta activity from fallout particles increases in the following order: tower-shot debris, silicate-burst debris, air- burst debris. Some authors report that the solubility in- creases as the size of the debris decreases. The debris from coral surface bursts is reported to be highly soluble in sea- water (Adams et al., 1960). For underwater explosions, release to the seawater would include late-condensing soluble fission products and col- loidal particles bearing most of the activity. Due to the large surface-to-volume ratio of small particles, leaching of soluble radionuclides would occur with high efficiency, leaving the insoluble radionuclides in the colloidal state. It has been shown that the halides, alkali metals, and alkaline earth metals will generally occur as soluble species in their normal oxidation states. Certain other elements, such as B, P, Ce, As, Se, Mo, Tc, and Te, are expected to occur as oxygenated anions that would be found partially in solution and par- tially colloidal or particulate. Nearly all of the remaining elements may be expected to exist as oxides or hydrated oxides associated with colloidal or gross particulate matter. However, our understanding of the interaction of radio- nuclides in such a complex mixture of inorganic compounds and organic and biological material is far from complete. As a result of limited experiments, Freiling and Ballou (1962) summarized the nature of underwater nuclear explo- sion debris in seawater. They found that the total activity in the soluble phase increased from 35 percent at one day after the event to approximately 60 percent after two weeks. This increase was attributed to the slow conversion of some of the constituent elements into soluble material, rather than to the production of new elements through radioactive decay. The percentages of soluble and insoluble fractions of a number of radionuclides were also determined by Ballou (1963), as shown in Table 5. These data generally indicate greater solubility than that earlier reported by Greendale and Ballou (1954). Similar investigations were carried out with waterborne debris from an underwater burst in which the fireball con- tacted the bottom of a coral lagoon. These data, after Ballou (1963), are reported in Table 6. Particle sizes ranged from 0.001 n to 10 £i in diameter. The distribution of radionu- clides in surface water was collected 2 hr after detonation and analyzed 31 hr after detonation. "Solid phase" refers to material remaining in the ultrafiltrate. Standard deviations were calculated from duplicate analyses. Deviation of sums from unity indicates a lack of mass balance or is an indica- tion of sample contamination. For the data in Table 6, radiochemical analysis for se- lected radionuclides was performed on duplicate aliquots of the gross samples, ultrafiltrates, and dissolved membranes. Results from successively separated fractions did not reveal any change in the physical state distribution of any radio- nuclide with time, but mass balance deficiencies prohibit firm conclusions in some cases. The results from successive ultrafiltrations have therefore been averaged. The results for each radionuclide discussed below are compared with the results of the two previous investigations. Included in each discussion is the mass balance achieved and the effect of an TABLE 5 Percentages of Activity of Radionuclides in Ultrafiltrates from Surface Water Samples, Underwater Burst Relative Activity in Ultrafiltrate at Centrifugation Time (%) Sample Centrifugation lime (hr from zero time) «Zr *»Mo «9Np 237JJ RE" 137Te 140Ba 1 1 35 64 - 54 33 0 35 7 - - 42 — - - 19 43 66 44 80 19 0 2 7 - - 41 - - - 19 - - 53 — - - - 3 10 48 67 67 77 42 0 19 - - 52 — - - - 116 43 63 - 71 39 0 Average 42 65 50 71 34 35 Gross rare earths and yttrium.

18 Radioactivity in the Marine Environment TABLE 6 Radionuclide Distributions 31 hr after Detonation in Lagoon Burst; H + 2 Surface Water Sample Radionuclide "Total rare earths. Fraction Distribution Solid Phase Colloidal Phase Soluble Phase 89Sr 0.00 ± 0.00 0.11 ± 0.01 0.99 ± 0.00 95Zr 0.38 ± 0.01 0.16 0.03 ± 0.00 95Nb 0.45 ± 0.00 0.39 ± 0.01 0.00 ± 0.00 "Mo 0.28 ± 0.00 0.06 ± 0.01 0.60 ± 0.00 103Ru 0.60 0.25 ± 0.00 132Te 0.60 ± 0.00 0.1 8 ±0.00 - l^Ba 0.00 ± 0.00 0.01 ± 0.01 0.99 ± 0.01 TRE" 0.83 ± 0.02 0.14 ± 0.06 0.03 ± 0.00 237u 0.02 ± 0.00 0.11 ±0.01 0.04 ± 0.06 "9Np 0.47 ± 0.00 0.46 ± 0.01 0.02 ± 0.00 additional membrane on the physical state distribution and on the mass balance observed. Mass balance deficiency may be taken as a measure of contamination potential, since it presumably arises from adherence of the radioactive species to the walls of the polyethylene container or to the surfaces of the ultrafilter apparatus. 89Sr An average value of 4 ± 1 percent of the 89Sr was found to be in the insoluble phase, and an average mass bal- ance of 116 ± 5 percent was obtained. The results show a somewhat greater solubility than that found in underwater arcing experiments, but not outside the precision of the methods. The results were unaffected by the presence of a second membrane. 95Zr and 95Nb Analyses were performed for both of these radionuclides, and no distinction between their behavior was evident. The presence of a second membrane increased both the mass balance and the percentage of activity appearing in the colloidal fraction. With either a single or double mem- brane, 0-8 percent of the activity was found in the soluble state, in fair agreement with underwater arcing results. With only a single membrane, an average of 48 percent was found to be insoluble, but the results were spread from 34 to 66 percent. The results from the deep underwater burst are within this range. "Mo Mass balance was consistently good, averaging 102 ± 5 percent. Using a single membrane, an average value of 68 ± 5 percent was found to be soluble, in good agreement with the deep underwater burst results. With a double mem- brane, 26 ± 5 percent was found to be soluble, in agreement with underwater arcing results. I03Ru It was found that 82 ± 5 percent of the ruthenium was insoluble, the mass balance being 105 ± 6 percent. No double-membrane effect was noted. The solubility is there- fore greater than indicated by the value of 1 percent from the underwater arcing experiments. l32Te The insoluble fraction was found to contain 64 ± 9 percent of the activity and the mass balance was 81 ± 12 percent. No double-membrane effect was noted. These re- sults are in better agreement with those from underwater arcing than with those from the deeper underwater burst. 140Ba This radionuclide showed a much higher solubility than the single determination made for the deep underwater burst would indicate. Only 5 ± 1 percent was found in the insoluble fraction, the mass balance being 88 ± 4 percent. No double-membrane effect was noted. The results are simi- lar to those obtained for 89Sr. Total rare earths The insoluble fraction contained 67 ± 3 percent of the activity, in accord with the deep underwater burst results, but the mass balance was only 71 ± 3 percent. No double-membrane effect was noted. Cerium-141, 144 was found to behave similarly. This behavior is not inconsis- tent with the results from the underwater arcing experiment, in which it was found to be soluble to the extent of 3 per- cent or less. 237U The insoluble fraction contained 46 ± 5 percent of the activity, but the percentage of activity found in the sol- uble fraction was quite variable. The deep underwater burst results also indicate considerable variability. No double- membrane effect was noted. 239Np With single membranes, 50 ± 2 percent of the activ- ity was found to be insoluble, in agreement with the deep underwater burst results. With a double membrane, how- ever, 93 percent was found to be insoluble. As in the case of 237U, the percentage of activity found in the soluble frac- tion was quite variable.

Sources of Radioactivity and Their Characteristics 19 Radioactive Fallout from Nuclear Weapons Tests The specific character of the oceanic contamination from nuclear explosions depends very directly upon the nature, size, and physical location of the event. Thus, underwater bursts introduce radioactive contamination directly and im- mediately into the sea in a relatively small and well-defined area. Surface or air detonations, depending upon the size of the burst, distribute the debris in the atmosphere to varying altitudes and horizontal distances. The extent of these atmo- spheric dispersions directly influences the rate of fallout of the radioactive material and its ultimate distribution on the earth's surface. The bulk of the nuclear debris from large surface or air bursts enters the stratosphere. Once in the stratosphere, this material is, for practical purposes, insulated from the earth's weather, and the rate and extent of its distribution are deter- mined by meteorological processes in the stratosphere. In general, the stratospheric mixing rate is more rapid within the hemisphere of injection than either the fallout rate or the rate of intrahemispheric mixing. These factors result in a generally characteristic pattern of distribution of the radio- active aerosol within that hemisphere. Removal of radionuclides from the stratosphere occurs by downward mixing and diffusion, with the major entry into the troposphere occurring in the middle and upper latitudes during late winter and early spring, in both hemi- spheres. The rate of stratospheric depletion of nuclear debris depends, to a degree, upon the latitude of the injection and the altitude of stabilization of the particles. This rate, termed the "stratospheric half residence time" has been empirically observed to resemble a simple exponen- tial decay. The minimum rate appears to be about 6 months, for nuclear tests in the lower stratosphere in polar regions. Debris injected into very high altitudes may take 2 years or longer before reaching the ground. It is interesting, however, that since the partial test ban treaty went into effect at the end of 1962, the stratospheric half residence time has re- mained quite constant at about 10 months. The rate of intrahemispheric mixing in the stratosphere is slow, compared to the average observed stratospheric fallout rate; hence, the bulk of the nuclear debris remains within the hemisphere of introduction. Upon leaving the stratosphere, the debris is deposited on the earth's surface primarily as a direct result of precipitation and with a "tropospheric half residence time" of approximately 30 days or less. The seasonal release of stratospheric debris into the tro- posphere, the probable latitudinal distribution of this re- lease, and the indicated precipitation patterns on the ground combine to produce the observed spring maximum in fallout and global distribution with higher values in the mid- latitudes. Figure 5 illustrates a typical latitudinal distribu- tion of stratospheric fallout. Of the many radionuclides produced in the testing of nu- clear weapons, 90Sr has been examined the most intensively and extensively because its relatively high fission yield (~3.5 atoms per 100 fissions) and its bone-seeking character and long physical half-life make it potentially the greatest fallout hazard to man. Measurements of 90Sr in a variety of environmental and biological media, including human speci- mens, have been made since the beginning of weapons test- ing. Atmospheric measurements coupled with the direct assay of 90Sr in soil have made possible the assembly of a 90Sr inventory. Interestingly enough, the inventory of 90Sr in the atmosphere (mainly in the stratosphere) plus that present on the surface matches quite closely the total pro- duction of 90Sr calculated from weapons testing to date. This does not imply detailed knowledge of the precise 90Sr yield, or indeed the explosive yield, of each and every deto- nation, but it does apply to the time average of such events. Hence, we may conclude that we know the production and distribution (on a broad scale) of this particular radionu- clide. The annual production and rate of deposition of 90Sr are indicated in Table 7. Table 8 lists the annual deposition of 90Sr by 10° latitude bands for the period 1958-1966. These values were com- puted from the data of the worldwide sampling network and are based upon the assumption that there is no systematic difference in fallout efficiency between ocean and land sur- faces. With that restriction, the information in Table 8 may be utilized as a direct measure of input to the oceans as a function of time. Table 8 may also be used to derive stratospheric deposi- tion values for other fission product nuclides on the further assumption that the ratio between such nuclides and 90Sr is constant. There is substantial evidence that this can be as- sumed with some confidence for 137Cs; hence, the 90Sr val- ues of Table 8 can be converted to 137Cs values by multi- plying by the constant 1.5. Calculation of amounts of other relatively long-lived fission products, such as 144Ce and 95Zr, from 90Sr ratios should be used with caution and must be TABLE 7 Worldwide Production and Deposition of 90Sr (in MCi) Year Produced Deposited 1945-1958 9.1 S.6 1959 0 1.1 1960 0 0.4 1961 2.5 0.4 1962 7.6 1.6 1963 0 2.6 1964 0 1.9 1965 0 1.0 1966 0 0.4

20 Radioactivity in the Marine Environment FIGURE 5 Latitudinal distribution of 90Sr fallout (1958-1967). 2.0 1.8 1.6 - 0.8 0.6 0.4 0.2 90° 80° 70° 60° 50° 40° 30° 20° 10° N0RTH LATITUDE 10° 20° 30° 40° 50° 60° 70° 80° 90° S0UTH LATITUDE corrected for radioactive decay, since their half-lives are rel- atively short. A calculation of the distribution of 55Fe produced as a product of activation by neutrons presumably on materials of the nuclear devices also was made based upon the 55Fe/ 90Sr ratio. A very substantial amount of this nuclide was made and injected into the stratosphere during the U.S. and Soviet test series in 1961 and 1962. The fallout data for 55 Fe, though sparse, suggest that it had apparently become rather well mixed with the 90Sr in the stratosphere by 1963. On this basis, an average ratio of 55Fe to 90Sr of 9.4 was derived and used for the compilation of Table 9. Future Applications of Nuclear Explosives Some potential peaceful applications of nuclear explosives constitute a potential source for the introduction of radio- nuclides into the marine environment. The proposed appli- cations that could contribute the most radioactivity to the oceans involve the use of nuclear explosives for the con- struction of harbors or canals. The U.S. Atomic Energy Commission's Plowshare Pro- gram for developing potential uses for nuclear explosives is in its early developmental stages. While some experiments have been conducted in terrestrial situations, none has been attempted in the marine environment. Guidelines for the employment of nuclear explosives and for the design of the explosives themselves are still being developed and refined. Environmental contamination resulting from nuclear ex- cavations would differ significantly in at least three ways from that resulting from atmospheric weapons tests. First, most of the radioactivity produced would be retained in the broken rock that falls back into the crater and in the ejecta in the immediate vicinity of the detonation site, and any portion that moves from the detonation site will do so only by surface runoff or groundwater transport. Second, the radioactivity produced per megaton of explosive force will be substantially reduced by employing explosives with low fission yields, by using nonactivating neutron absorbers to reduce the neutron activation of components of the explo- sive and of the soil, and by using explosive components whose activation products are of low biological significance. Finally, because low-fission-yield devices will be employed, activation products will equal or surpass fission products in curies produced and in biological significance. In this re- spect, however, it is important to note that, of the radionu- clides thus far introduced into marine or freshwater environ- ments, the greatest potential hazard to man has involved

Sources of Radioactivity and Their Characteristics 21 TABLE 8 Annual Deposition of 90Sr Since 1958, by 10° Bands of Latitude (in MCi) Latitude 1958 1959 1960 1961 1962 1963 1964 1965 1966 Total 80° -90° N 0.003 0.002 0.001 0.001 0.002 0.007 0.002 0.001 0 0.019 70° -80° 0.025 0.016 0.006 0.006 0.017 0.047 0.014 0.008 0.003 0.142 60° -70° 0.064 0.059 0.011 0.020 0.089 0.200 0.087 0.030 0.012 0.572 50° -60° 0.114 0.157 0.031 0.044 0.168 0.376 0.262 0.109 0.042 1.293 40° -50° 0.153 0.206 0.043 0.065 0.285 0.540 0.354 0.149 0.056 1.851 30° -40° 0.147 0.218 0.043 0.064 0.247 0.358 0.248 0.137 0.051 1.513 20° -30° 0.106 0.192 0.038 0.045 0.214 0.358 0.239 0.091 0.034 1.317 10°-20° 0.024 0.104 0.035 0.035 0.145 0.250 0.180 0.094 0.036 0.903 0°-10° 0.019 0.021 0.025 0.031 0.113 0.184 0.093 0.069 0.026 0.581 0°-10° S 0.044 0.034 0.024 0.021 0.096 0.063 0.073 0.039 0.015 0.409 10° -20° 0.041 0.023 0.018 0.017 0.028 0.033 0.036 0.028 0.011 0.235 20° -30° 0.055 0.031 0.027 0.044 0.048 0.056 0.068 0.062 0.024 0.415 30° -40° 0.067 0.032 0.022 0.033 0.032 0.050 0.075 0.068 0.026 0.405 40° -50° 0.030 0.022 0.028 0.024 0.036 0.049 0.076 0.071 0.027 0.363 50° -60° 0.018 0.015 0.017 0.015 0.017 0.023 0.032 0.026 0.010 0.173 60° -70° 0.010 0.007 0.008 0.008 0.009 0.012 0.016 0.012 0.005 0.087 70° -80° 0.004 0.002 0.003 0.003 0.003 0.004 0.005 0.005 0.002 0.031 80° -90° 0 0 0 0 0 0 0.001 0.001 0 0.002 Total 0.924 1.141 0.380 0.476 1.549 2.610 1.851 1.000 0.380 10.311 TABLE 9 Deposition of 55Fe from Weapons Tests, by 10° Bands of Latitude (in MCi of 55Fe, decay corrected to October 15, 1961) Latitude 1962 1963 1964 1965 1966 Future" Totals 80° -90° N 0.01 0.06 0.01 0.01 0 0 0.09 70° -80° 0.08 0.44 0.13 0.07 0.03 0.01 0.76 60° -70° 0.42 1.88 0.82 0.28 0.11 0.04 3.55 50° -60° 0.79 3.54 2.36 1.02 0.39 0.16 8.26 40° -50° 1.34 5.10 3.32 1.40 0.53 0.20 11.89 30° -40° 1.16 3.36 2.32 1.29 0.48 0.18 8.79 20° -30° 1.00 3.36 2.33 0.85 0.32 0.12 7.88 10° -20° 0.68 2.34 1.68 0.89 0.34 0.13 6.06 0.53 1.72 0.87 0.65 0.25 0.09 4.11 northern hemisphere 6.01 21.80 13.74 6.46 2.45 0.93 51.39 0 ~10 S 0.45 0.59 0.68 0.36 0.14 0.09 2.31 10° -20° 0.13 0.31 0.34 0.26 0.10 0.13 1.27 20° -30° 0.22 0.52 0.64 0.59 0.23 0.12 2.32 30° -40° 0.15 0.47 0.70 0.64 0.25 0.18 2.39 40° -50° 0.17 0.46 0.72 0.66 0.25 0.20 2.46 50° -60° 0.08 0.21 0.30 0.25 0.10 0.16 1.10 60° -70° 0.04 0.11 0.15 0.12 0.05 0.04 0.51 70° -80° 0.01 0.04 0.05 0.05 0.02 0.01 0.18 80° -90° 0 0 0.01 0.01 0 0 0.02 southern hemisphere 1.25 2.71 3.59 2.94 1.14 0.93 12.56 Total, world 7.26 24.51 17.33 9.40 3.59 1.86 63.95 "Based on Stardust 0.2 MCi '"'Sr from pre-1963 tests. This material was evenly distributed over the northern and southern hemispheres; thus, fallout is assumed symmetrical. The ratio of ^Fe to '"'s, changes with time; using a constant ratio of 9.4 for the period 1962-1966 introduces an error.

22 Radioactivity in the Marine Environment activation products such as 32P. 65Zn, and 55Fe. In under- ground explosions, 3H contamination of groundwater may be a biological hazard, depending on the quantity produced. There are three sources of the radionuclides produced in a thermonuclear cratering explosion: fission products, radio- nuclides induced in the device materials, and radionuclides induced in the environmental media surrounding the device. In addition, between 7X 106 and 5X107 Ci of tritium, de- pending upon the nature of the thermonuclear reaction, may be produced. In a thermonuclear explosion, roughly 1027 neutrons will be produced per megaton of yield. In addition, a large number of protons, deuterons, tritons, helium-e nucleii, and alpha-emitting radionuclides will be generated. These neu- trons and charged particles will react with the materials of the device to produce a wide variety of radionuclides. Estimation of the activation radionuclides produced in a nuclear event is difficult because many of the cross-section values necessary for the calculations are unknown. However, using the data that are known, such as Ng's calculations of the activation products in major rock types (1965), and using worst-case assumptions where needed, estimates of the potential biological hazard of a device can be made (Kayeera/., 1969;Tamplin, 1967; Ng and Thompson, 1966; Burton and Pratt, 1967;Tamplin etal., 1968; Martin, 1969). When an explosive is detonated on a tower, all of the ra- dioactivity produced is released to the atmosphere, but when the explosive is detonated underground, only a frac- tion of the activity is released to the atmosphere. When the explosive is buried deep enough, all of the activity remains underground. In cratering experiments, in which the expand- ing cavity ruptures the surface to form the crater, the ma- terial above the explosive acts like a filter bed and removes a large portion of the radioactive material that would other- wise be released to the atmosphere. The efficiency with which a radionuclide is removed depends on its chemical and physical properties or on those of its precursors during the venting process. Fission products such as 137Cs and 90Sr, which have rare-gas precursors during the venting pro- cess, are found in much higher relative concentrations in the cloud than are refractory radionuclides that do not have gaseous precursors, such as 95Zr or 147Nd. Therefore, to the extent that it is possible, the fraction released to the atmo- sphere must be determined for each specific radionuclide of interest. The final physical and chemical forms of the radionu- clides produced in a nuclear cratering explosion are poorly known, except for a few species. The final forms depend, as in the case of fractionation, upon the chemical nature of the species present during cavity expansion and venting. The chemical species present depend upon such factors as the water content of the medium and the overall oxidation- reduction potentials of the mixture. Large quantities of rock are melted and vaporized along with the materials of the device itself. As the cavity expands, the vaporized materials begin to condense, the order of condensation depending upon the volatilities of the materials. It is possible to alter this overall process by placing in the immediate vicinity of the device materials that could, for example, change the overall oxidation-reduction potential of the mixture and, therefore, the chemical species present. Whether such a pro- cedure should be considered, of course, depends upon the associated biological hazard. The U.S. Atomic Energy Commission (1967c) has re- leased the following information concerning the radioac- tivity released to the atmosphere by cratering explosives: In order to plan for major excavation projects, the fol- lowing factors relative to release of radioactive debris should be taken into account: The amount of radioactivity airborne in the cloud and in the fallout is minimized by scavenging during the venting process, by special emplacement techni- ques, by utilizing minimum fission explosives, and by em- ploying extensive neutron shielding. Based on reasonable assumptions about these factors, the following information can be used in planning for cratering events of useful magni- tude. For each individual nuclear explosive detonated, the sum of fission products airborne in the radioactive cloud and in the fallout can be expected to be as low as the equiv- alent of 20 tons. The tritium release may be less than 20 kilocuries per kiloton of total yield. The sum of activation products airborne in the radioactive cloud and in the fallout may be expected to be as low as the amounts shown in the following table: Representative Set of Induced Radioactivities at Detonation Time (Total in Cloud and Fallout) Nuclide Production, Kilocurie for Yield of Nuclide 100 KT 1 MT 10 MT 24Na 200 800 2,000 32,, 0.1 0.4 0.8 0.01 0.03 0.06 54Mn 0.1 0.3 0.7 56Mn 6,000 20,000 50,000 55 Fe 0.04 0.15 0.3 59 Fe 0.04 0.15 0.3 185W 6 10 14 187W 300 500 700 203Pb 1,000 7,000 20.000 Other 15 20 40 NUCLEAR REACTORS Nuclear reactors have been designed and built for a variety of purposes, as indicated by Table 1. Each purpose involves a design concept keyed to the desired form of energy out- put, which in turn depends on the intended application. Reactors are designed to produce power, neutrons, radio-

Sources of Radioactivity and Their Characteristics 23 active isotopes, and fissionable material. Each design pre- sents different operating characteristics and could also influ- ence the amount and type of wastes to be disposed of. All present nuclear reactors are designed to induce fission and to sustain and control the chain reaction. Future nu- clear power sources may include fusion when it is learned how to sustain and control temperatures of about a million degrees. The principle of operation of various fission reac- tors is the same in all reactors, but for different reactor con- cepts the major variants are the composition and construc- tion of the fuel rods, neutron reflectors and moderators, control rod systems, and heat exchange materials and meth- ods. Of special interest is the construction of fuel rods and the manner of their use, because radioactivity is created in and adjacent to the fuel rods.* Typically, fuel rods or ele- ments are fabricated of fissionable uranium in the form of plates or pins that are completely encased (cladded) by a corrosion-resistant metal alloy such as stainless steel or zir- conium alloy (zircaloy). The fuel elements are assembled into a cluster, forming the core of the reactor. The core is immersed in or bathed by a coolant fluid. In the United States, most reactors used for making electricity use iso- topically light water that also acts as a neutron moderator. In the United Kingdom and other nations, nuclear electric- generating reactors having graphite moderation and gas cooling, generally air, are more common. Our discussion, however, will be concerned mainly with U.S. practices. In water-cooled reactors, the core and coolant are con- tained in a vessel called the reactor vessel, usually of heavy steel construction. Heat is generated by fission of the fuel and is conducted through the walls of the cladding to the moderator-coolant. The size of a reactor is measured by its sustained thermal output, usually in kilowatts (kW^). Products created by the fission of uranium are retained within the cladding of the fuel elements unless there is a hole through which they can leak to the coolant. However, some neutrons do escape from the core to interact with im- purities in the coolant and with the reactor vessel and other nearby materials. The neutron activation products in the coolant are the major source of radioactive wastes in reactor operations. Nuclear reactors are generally housed in airtight steeel or concrete shells designed to contain airborne contamination from either normal or abnormal reactor operating condi- tions. The sites on which reactors are located are usually se- lected to restrict the exposure of nearby populations to ra- dioactivity that may be released in a reactor accident.' *This discussion is concerned only with heterogeneous nuclear reac- tors; homogeneous reactors, in which the fuel is in a liquid or fluid state, are not yet beyond the conceptual research stage. 'There have been two known reactor accidents-"Windscale" and "SL-1"-and a preplanned reactor excursion-"Boxax." These are described by Dunster et al. (1958), U.S. Atomic Energy Commission (1961), and Kramer (1958). PUMP B0ILING-WATER TYPE PUMP PRESSURIZED-WATER TYPE FIGURE 6 Schematic nuclear electric power reactors. Nuclear Electric Power Reactors Two systems have been devised for recovering the heat from nuclear reactors in order to generate steam and electricity. One, the boiling-water reactor, is direct; the other, the pressurized-water reactor, is indirect. These systems are illus- trated diagramatically in Figure 6. In the United States, all of the central-station electric power nuclear reactors are either of the boiling-water or the pressurized-water types. Power reactors exported by the United States are also of these types. These contrast with the natural-uranium-fueled, gas-cooled power reactors of the United Kingdom and France. As in the United States, for- eign nations project increasing use of nuclear reactors for electric power generation (Table 10). Thermal electric generating plants discharge some heat via their cooling systems because they are not 100 percent efficient in converting heat to electricity. Modern fossil- fueled generating plants have a thermal efficiency of about 38 percent, while nuclear plants are about 32 percent effi- cient. Future reactor plants, on the average, will have sub- stantially larger generating capacities than those of today, and they will, therefore, require even more coolant flow. Some of this thermal capacity of large nuclear plants will be put to work in desalting seawater in dual-purpose plants. It is expected that, as more generating capacity is installed, more plants will be constructed in coastal locations, where coolant water supply is essentially unlimited. This is already being done in the United Kingdom. Nuclear power stations produce radioactive wastes in gaseous, liquid, and solid forms. Most of the fission products created within the fuel elements remain in the fuel elements until they are removed in chemical processing plants for recovery of the unused fuel. A recent survey by Blomeke and Harrington (1968) of up to 7 years of experience in managing radioactive wastes at six operating nuclear power generating stations revealed that most of the radioisotopes present in the waste gases, liquids, and solids from power reactors originated in the primary reactor coolant. The isotopes appeared in the wastes as by-products of repurification of the coolant from the ac- tivation of corrosion products from chemical additives, from natural impurities in the water and even from the water it-

24 Radioactivity in the Marine Environment TABLE 10 Nuclear Power Plants in Operation, under Construction, or Planned for the Near Future" Through 196 7 1967-1973 Country No. of Plants Capacity (MWe) No. of Plants Capacity (MWe) Belgium 1 10 2 1456 Canada 2 220 5 2282 France 8 1177 5 2885 W. Germany 4 317 8 1891 India - - 5 980 Italy 3 607 2 685 Japan 2 165 6 2662 Netherlands - - 1 47 Pakistan - - 1 125 Spain - — 3 1073 Sweden 1 9 2 593 Switzerland 1 7 4 1756 United Kingdom 27 4125 11 6390 United States 14 2782* 61 46,941c "After U.S. Atomic Energy Commission (1967b). *U.S. Atomic Energy Commission (1967c). c41 having a combined generating capacity of 14,705 MW£ are under construction; projections are through 1974. self, and from fission products that may leak into the coolant through defective cladding. Evidence indicated that some fission-product tritium may have diffused through stainless steel fuel cladding. Gases are removed from the primary coolant stream in a variety of ways. In boiling-water reactors, over 99 percent of the radiolytic and fission gases are removed continuously by passing large volumes of air through the steam turbine air ejector. Short-lived gaseous isotopes are decayed by a 20- to 30-min delay before release. In pressurized-water reactors, gases are normally removed only when the coolant is with- drawn; some may leak out of the pressurized system. Pres- surized-water reactors are provided with gas storage tanks, usually enough to allow several weeks' decay before release, if needed. The primary coolant is treated by demineralization to keep the conductivity of the reactor water below 0.5 /umho/ cm. This reduces corrosion rates within the system and holds down radiation levels in the piping system outside the core. In pressurized-water reactors, corrosion may be further in- hibited by hydrogen overpressure and by addition of hydra- zine, ammonia, or lithium hydroxide. Suspended solids in the coolant stream are removed in part by filters and by the demineralizer beds; depending on the age of the system, suspended solids are also deposited on surfaces throughout the primary system and occasionally may be "bumped" loose. According to Blomeke and Harrington (1968), other sources and kinds of wastes associated with reactor opera- tions are generally of routine importance, but under un- usual circumstances they can be significant problems. Liquid wastes include the large volumes of water used for shielding during refueling operations and the wastes from decontami- nation operations, the laundry, the analytical laboratory, and the fuel storage pool; solid wastes-from replaced reac- tor components and instruments to contaminated tools, laboratory ware, laundry, removable floor coverings, and decontamination materials such as paper (wipes) and rags- have a large radioactivity range. RADIOACTIVITY CHARACTERISTICS Radionuclides in the gaseous wastes consist primarily of the activation products 13N and 41 Ar and isotopes of the noble gas fission products, Kr and Xe, and halogens. Radionuclides found in the coolant waters, and subse- quently in the solid wastes, include most of the fission prod- ucts and activated corrosion products such as 3H, 32P, siCr, 59Fe, 54Mn, 58Co, 60Co, 65Zn, 110mAg, 131I, 134mCs, 137Cs, 138Cs, 139Ba,and140Ba. DISPOSAL PROCEDURES If low in activity, liquid wastes are generally diluted with condenser cooling water to below 10~7 mCi/cc and dis- charged from the plant. Other liquid wastes, particularly from demineralizer regeneration, that contain relatively large amounts of activity and dissolved salts are collected in temporary storage tanks and then treated or decontami- nated by evaporation. Evaporator overheads may be passed through mixed-bed demineralizers and returned to the plant system or discharged from the plant. Evaporator bottoms

Sources of Radioactivity and Their Characteristics 25 containing salt and radioactivity in the form of sludge are mixed with cement, put into drums, and shipped to regional land burial grounds. Solid wastes contain about the same spectrum of radio- nuclides as the liquid wastes. These too are packaged and shipped to land burial sites. Table 11 summarizes the radioactive-waste-management experience at four boiling-water and two pressurized-water nuclear reactor power stations. Alan Preston, of the Ministry of Agriculture, Fisheries and Food of the United Kingdom, summarized in a private communication the annual liquid radioactive waste dis- charges of eight nuclear power stations operating in the United Kingdom in 1966, as shown in Table 12. ing the Pacific Ocean are as indicated in Table 14. In the early years of Hanford operations, methods for identifying and measuring extremely low concentrations of radionu- clides were not yet developed. Consequently, samples were simply analyzed for "total beta" or "total alpha" content. The discrepancy between the "total beta" for 1960 and the sum of the isotopic analysis is explained by the fact that there is a low counting efficiency for 51Cr and 65Zn in a total beta analysis. The effect of decay time and river envi- ronment on the amount of radioactivity reaching the sea is seen in Table 15, which compares the concentrations at Richland, Washington, 34 miles downstream from the reac- tors, with concentrations at Bonneville Dam (the last im- poundment before the sea), some 200 miles downstream. Materials-Production Reactors At one time there were nine plutonium-producing reactors at the Hanford Plant, along the Columbia River approxima- tely 360 miles upstream from its mouth on the Pacific Ocean; six of these were shut down between January 1965 and January 1969. One of the remaining reactors is dual- purpose, producing electric power (790-MWe capacity) as well as plutonium; it was started up in 1963. These produc- tion reactors are designed for low-pressure, single-pass water cooling; the dual-purpose reactor has a closed-cycle coolant system similar to a pressurized-water reactor. In single-pass cooling systems, particulates in the river water are removed by coagulation, sedimentation, and filtration before the water enters the reactor. Sodium dichromate is added to reduce corrosion before the water passes through the reac- tor core and carries away the heat of fission. Impurities re- maining in the water and corrosion products from the piping systems are neutron-radioactivated by the high neutron flux of the reactor core. In addition, fission products occur in the coolant because of natural uranium dissolved in the river water, uranium contamination on the surface of the fuel cladding, and occasional rupture of the fuel cladding. Parker (1959) reports some 61 radioactive isotopes, as listed in Table 13, were detected in the Hanford reactor coolant discharge 4 hr after passage through the reactor. The reactor coolant stream is discharged to the Columbia River, where it mixes with the river water and is carried through four impoundment reservoirs enroute to the Pacific Ocean. The distance is approximately 360 miles, and travel time is 1 to 3 weeks, depending on stage of flow. The time of river flow permits radioactive decay, and interactions with the stream bed, sediments, and biota greatly reduce the spec- trum of radioisotopes reaching the ocean. J. F. Honstead, of the Pacific Northwest Laboratories, Battelle Memorial Institute, Richland, Washington, in a private communica- tion, estimates that annual amounts of radioactivity reach- Naval Propulsion Reactors As of 1968, the United States had 76 nuclear-powered sub- marines in service, 21 under construction, and 8 more planned.* The United States also operated a two-reactor cruiser, an eight-reactor aircraft carrier, and two reactor- powered frigates. Three similar frigates, a deep-sea research vehicle, and a two-reactor aircraft carrier were planned or were being built (U.S. Atomic Energy Commission, 1967d). All nuclear-powered U.S. naval ships use pressurized-water reactors similar to the nuclear electric power stations described earlier. That is, they have closed primary and secondary cooling loops. The principal radionuclides con- sidered as wastes are the neutron-activated corrosion and fission products that may leak through the fuel-element cladding. One major difference between the pressurized- water reactors on ships and on shore is the available physi- cal space for tankage or other purposes. The reactor vessels in operational readiness must be kept full of water-modera- tor. At reactor start-up, the water expands when the reactor is brought up to operating temperature. In land-based plants, this expansion water is stored in tanks, whereas on submarines, it is dumped overboard. When the reactor is shut down and cooled, fresh water is added to keep the coolant system completely filled. On naval ships, reactors may be started up a few times per month on each ship, dis- charging on each heat-up an average of about 500 gallons (1,900 liters) of coolant (Iltis and Miles, 1959). Other wastes that evolve from nuclear-ship operations include demineralizer resins used to decontaminate the cool- ant, reactor shield water, solid wastes from routine decon- tamination and maintenance operations, and laundry wastes. * Janes Fighting Ships (1967-1968) reports that the United Kingdom has 5 nuclear-powered submarines, France has 3 under construction, and the Soviet Union has 50 nuclear submarines and a nuclear- powered icebreaker in service and 2 nuclear-powered icebreakers under construction.

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28 Radioactivity in the Marine Environment TABLE 12 Radioactivity in Liquid Wastes Discharged by Nuclear Power Stations of the United Kingdom, 1964-1966 Radioactivity Discharged (Ci) Generating 1964 1965 1966 Power Station Location Capacity (MWe) 3H Other 3H Other 3H Other Berkeley Bradwell River Severn Estuary 2 X Blackwater Estuary 2 X 138 150 1,008 1 306 471 5 19 225 23 29 37 4 583 Chapelcross Open coast 4X 45 4 - 5 — 28 Dungeness Open coast 2X 275 - 6 0.1 569 2 Hinkley Point Parrett Estuary 2X 250 0.01 174 2 32 18 Hunterston Open coast 2X 260 21 0.004 477 2 477 19 Sizewell Open coast 2x 290 - - - 29 1 Trawsfynydd Lake Trawsfynydd 2x 250 - 2 0.06 222 2 Oldbury - 2X 300 - - - - - Calder Hall Windscale 4X 45 Discharges included in totals for fuel reprocessing operations Windscale AGR Windscale 32 (see Table 18, p. 32) TABLE 13 Hanford Reactor Effluent Isotopes in Order of TABLE 14 Annual Discharges of Radioactivity from the Decreasing Concentration, Four Hours after Irradiation" Hanford Reactor Operations to the Pacific Ocean (Ci)a Major (90%) Minor (8%) Trace (2%) Year Beta 32p 51Cr 65Zn 239Np 56Mn6 69Zn 152Eu 131,6 145pr 1950 2,500 64Cu6 72Ga 153Sm 14lCe 151Pm 1951 3,600 - - - - 24Na* 92Sr 187W 142pr «>Co 1952 7,100 - - 51Cr* 239U 141 La 14C 143pr 1953 Insufficient data - - 239Np6 133(6 149Nd 147Nd 103Ru 1954 Insufficient data - - - - 76As* 92yt * 140La 45Ca6 47Sc 1955 13,000 - - - - 31 Si6 "Nt f> 132j6 1MAg 90Sr6 1956 1 7,000 - 91Sr' > 157Eu 91Y 137Cs 1957 37,000 - - - - 65Zn6 140Ba6 59Fe* 85Sr 1958 44,000 32p6 "Mo 89Sr6 238 jj6 1959 110,000 — - 90Y6 156Sm MMn 239pu6 1960 93,000 6,200 310,000 14,000 26,000 1JSjO ^Sc6 95Zr 227Ac 1961 11,000 310,000 16,000 24,000 93Y 115Cd 149Pm 210p06 1962 - 4,700 240,000 11,000 11,000 143Ce i56Eu 1963 - 4,400 320,000 10,000 18.0006 1964 — 4,400 320,000 16,000 — "After Parker . (1959). 1965 — 4,000 290,000 18,000 — 6Routine measurements made on these isotopes. 1966 - 3,300 160,000 8,000 - The radionuclides commonlv oresen t in discharj :ed reac- 1967 - 4,400 224,000 15,000 — tor coolant are shown in Table 16, along with maximum and average concentrations obtained over 3 years of opera- tions of the USS Nautilus. Similar results have been reported from other naval reactors (Iltis and Miles, 1959). A summary of reported liquid-waste discharges and of amounts of activity discharged into U.S. harbors is given in Table 17. Harbor waters and sediments at shipyards, harbors, and submarine bases are monitored principally for 60Co. In 1967, 55 sediment samples from three locations were re- ported to contain over 100 pCi of 60Co per square centi- meter, and 340 samples contained between 10 and 100 pCi/cm2; the total bottom area with concentrations of 60Co greater than 10 pCi/cm2 was estimated to be approximately 0.6 km2. Waters in the harbors, on the other hand, showed no de- "Since 1960 individual isotopes have been measured; previously, all isotopes were measured collectively. "First 8 months only; analysis was subsequently discontinued. tectable 60Co activity. In 1965, in Holy Loch, Scotland, 60Co was detected in bottom sediment and on mud flats ex- posed at low tide, but none above background level was de- tected in the water. In 1966, levels were reported to have declined (Miles and Mangeno, 1967). Demineralizer resins from shipboard reactors, containing as much as 12.5 Ci of activity, of which 10 Ci are attribut- able to 60Co, are either transferred to shore facilities and subsequently handled as solid wastes or are dumped at sea more than 12 miles from shore while the ship is under way. Solid radioactive wastes are transferred to shore facilities, packaged, and shipped to land burial sites.

Sources of Radioactivity and Their Characteristics 29 TABLE 15 Annual Average Concentration of Several Radionuclides in Columbia River Water, 1966" Richland Radionuclides (pCi/liter) Bonneville Dam6 R.E. + Yc 270 ID 24Na 2,600 ID 32p 140 23 51Cr 3,600 1,300 MCu 1,400 ID 65Zn 200 43 76As 420 ID 90Sr 1 ID 131I 18 3 239Np 770 ID "After Honstead , 1967. "ID, insufficient data. c Rare earth + yttrium: 140La, 152mEu, 153Sm, 165Dy, 90Y 91Y, 93Y, l^Ce, '43Ce, 144Ce, 142Pr, 143Pr, 147Nd. 147Pm, 149Pm. 151Pm, 152Eu, 156Eu. 153Gd. 159Gd. 160Tb. 161Tb. 166Ho. 169Er. 171 Er. TABLE 16 Concentrations of Radionuclides in Reactor Coolant Water, USS Nautilus (^Ci/ml) Nuclide Maximum Average Corrosion Products ISp 2.7 X 10'2 1.5 X 10-2 MNa 6.2X10^* 2.2 X 10-4 51Cr 3.4 X 10"3 3.7 X l0"4 56Mn 9.3 X 10-2 2.1 x 1o-2 59Fe 2.7 X10-3 5.1 x 1o-4 «>Co 2.5 X 10-2 3.2 X l0"3 MCu 4.7 X 10"3 1.0 X 10"3 65Ni 1.5 X I0"3 5.7 x io-4 182Ta 2.9 X 10-2 4.5 X l0'3 187W 9.0 X I0'3 1.5 x io-3 Fission Products ^Sr 5.0 X 10"6 ^Sr 5.0 X l0"8 131, 1.0 X 10•s 140Ba l.o x irr6 137Cs 1.0 Xl0'8 l^Ce 1.0 XI0'7 Civilian Propulsion Reactors As of 1970, there were only two operational nuclear-powered civilian ships-the United States' NS Savannah, a cargo- passenger vessel, and West Germany's Otto Hahn, a 15,000- ton bulk carrier, which was undergoing sea trials. Japan has launched an 8,300-ton nuclear-powered freighter, the NS Mutsu, due for service in 1971. Italy has a nuclear-powered freighter under construction, and Japan and Germany have announced plans for two more freighters. The Savannah has provided experience to many maritime nations in how to deal with nuclear ships in harbors, coastal waters, and on the high seas. The Savannah's reactor is a pressurized-water type with a power rating of 80,000 kW^ and 22,000 shaft horsepower. The reactor vessel and its two primary coolant loops are contained within a vessel designed to withstand an internal pressure of 188 psi. The reactor has a dual shield: The pri- mary shield is an annular water-filled tank around the reac- tor vessel with walls of lead 1 to 4 inches thick. The second- ary shield, which surrounds the containment vessel, is made of concrete and steel in its lower half and lead and poly- ethylene in its upper half. The reactor was first started up in December 1961, and in its first year of operation, the Savannah traveled some 30,000 miles, visiting ports on both U.S. coasts before re- turning to her maintenance base at Galveston, Texas. Since 1961, the Savannah has visited many of the major ports of the world and was in commercial service between U.S. and European ports. Through August 1968, she cruised 335,000 miles on her first fuel loading. Although the Savannah was designed to contain all liquid radioactive wastes, with 1,350 ft3 (38 m3) of storage tank capacity, more wastes are generated than can be held. In its first year of operation, 23,700 ft3 (670 m3) of liquid wastes were evolved, primarily from leakage at the buffer-seal charge pumps, pressurized relief valve, and sampling-system relief valve. The first wastes contained 1.02 Ci of radioac- tivity and ranged in concentration between 3X10~8 and 5.4 X10^ mCi/ml. Of the first year's wastes, 8,300 ft3 (235 m3) were disposed of on land and the remainder dumped at sea. The wastes disposed of at sea were within the limits suggested by the National Research Council in its 1958 report (National Academy of Sciences-National Re- search Council, 1959). It has been reported (Nuclear Safety Information Cen- ter, 1966) that in its first 6 months of commercial service (four round-trip voyages to European ports between August 1965 and March 1966), the Savannah discharged into the sea some 8,100 ft3 (229 m3) of liquid wastes containing 6 Xl0-3 Ci of radioactivity, primarily 54Mn and 60Co. Solid wastes and demineralizer resins were disposed of on land. Off-gases from the containment vessel were passed through a series of filters prior to release to the atmosphere. Aerospace Nuclear Reactors Two classes of reactors are being developed for use in the aerospace program-one to provide electrical or other form

30 Radioactivity in the Marine Environment TABLE 17 Summary of Liquid Radioactive Wastes Discharged into Harbors by U.S. Navy Nuclear-Powered Ships" Shipyard or Naval Harbor6 Liquid Radioactive Waste Discharges0 1966 1967 1961-1965 (Ci) 1,000 gal Ci 1,000 gal Ci Portsmouth, N.H. 0.48 155 0.01 265 0.01 Quincy, Mass. 0.15 0 < 0.005 - <0.005 Groton-New London, Conn. (Electric Boat Div., state pier and submarine base) 7.18 1,274 0.03 606 0.01 Camden, N.J. 0.01 0 <0.005 - - Newport News, Va. 2.31 1,581 0.06 1,533 0.04 Norfolk ,Va. 1.17 1,051 0.03 1,784 0.03 Charleston, S.C. 1.19 369 0.04 320 0.01 Pascagoula, Miss. 0 0 <0.005 - <0.005 San Diego, Calif. 0.99 0 <0.005 - <0.005 Vallejo, Calif. 2.33 270 0.19 - <0.005 Bremerton, Wash. 0.03 0 <0.005 - <0.005 Pearl Harbor, Hawaii 3.20 654 0.03 683 0.01 Apra Harbor, Guam 0.01 0 — — <0.005 "After Miles and Mangeno (1966, 1967, 1968). 6Other U.S. harbors have had less than 20,000 gal and less than 0.1 Ci discharged into them per year. cRadioactivity measurements have been calibrated to 60Co standard; volumes are prior to dilution. of power in the kilowatt range for spacecraft missions, and the other, in the megawatt range, capable of propelling space vehicles into orbit. Both could introduce nuclear fission and activation products into the sea, either directly by launch accident or indirectly by fallout of burn-up materials from the atmosphere resulting from scheduled or unscheduled re-entry of space vehicles. SNAP reactors (Systems for Nuclear A uxiliary Power) are relatively small electrical generating plants designed to produce full power for more than a year without refueling. The aerospace SNAP reactors have fuel elements of ura- nium mixed with a neutron moderator—zirconium hydride (U-ZrHx). The fuel elements have thin-wall steel cladding and are arrayed within a stainless-steel reactor vessel. The neutron flux and chain reaction are controlled by beryllium reflectors located outside the reactor vessel. Heat is con- ducted from the fuel elements to the electrical generating system by a liquid metal, NaK, an alloy of sodium and potassium. SNAP 10A* was launched in April 1965 and operated at full power for 43 days, at which time it was shut down by a spurious command from the satellite on which it was riding. This unit, designed to produce 500 electrical watts, used thermoelectric converters from a heat source of 60 kW^. It is now in a 700-mile-high nearly circular polar orbit. The reactor is designed to break up, ablate, and disperse on re- entry into the earth's atmosphere. If SNAP 10A had oper- *In SNAP terminology, even numbers denote nuclear reactor units, and odd numbers, isotopic-heat-generating units. ated for a year, it would have accumulated approximately 40,000 Ci of fission products. During its 43 days of opera- tion, it accumulated about one tenth as much radioactivity. At the time of re-entry, in about 600 years, essentially only the longest-lived fission products-90Sr and 137Cs-would remain, and these would constitute only a millionth of the original amount. SNAP 8, a 600-kW^ reactor system designed to produce 30 kWe using liquid metal for coolant and a turboelectric generator, is being developed to supply power for manned oribital laboratories, lunar expeditions, communications satellites, or deep space missions. Methods for disposal of the reactor at the end of its operation are being evaluated. These methods include random re-entry and burn-up at high altitudes; intact re-entry into the deep ocean; intact earth impact and recovery; and boost into outer space (Nelson and Detterman, 1967). Entry into the ocean is also possible in the event of a launch abort. If the reactor retains its components and con- figuration up to the time of impact with water, a nuclear excursion of 70 MW-sec (equivalent of 250-kW operation for 280 sec) would result. Although about half a million curies of total fission-product radioactivity would be created, it would consist largely of short-lived isotopes; in 2 hr, the radioactivity would have decayed to several thousand curies, in 4 days to about 40 Ci, and in 40 days to about 3 Ci (Kochendorfer, 1964). In 1964, an experiment was performed to provide data and information for evaluation of the consequences of water immersion of an air-cooled aerospace reactor (Kessler et al.,

Sources of Radioactivity and Their Characteristics 31 1964). A SNAP 10A reactor was injected into a large tank of water. A nuclear excursion of about 45 MW-sec occurred, which resulted in the rupture of all fuel elements in the re- actor core and dispersal of the fuel (within the tank). The fuel lattice retained about 99 percent of the available fission products. Halogens that escaped from the fuel were retained in the water. Primarily noble gases and their daughters es- caped, and these amounted to about 5 percent of the noble gas present in the core. Nuclear rocket engines will be used to propel upper stages or large, advanced space vehicles after conventional chemi- cal rockets have carried the nuclear stage well above the atmosphere. In all mission applications currently foreseen, the nuclear stage will be left in deep space after use and will never return to Earth. Hence, no radioactive materials are scheduled to enter the oceans from flight operations; ocean entry becomes a possibility only after a failure or accident. There are two possibilities for failure. One would result from the booster failing during early ascent.* Since the re- actor would not yet be started, it would not be radioactive when it falls back into coastal waters. However, rapid intro- duction of water into the core could override the control system and cause a nuclear excursion. The magnitude would depend on the water entry rate, which, in turn, would de- pend on the velocity and orientation of the vehicle on im- pact. In the worst case, up to 104 to 10s MW-sec of energy could be generated in a fraction of a second before the reac- tor destroyed itself. One would expect about two thirds of the fission products generated during the excursion to be contained in a low atmospheric cloud of gases and fine par- ticulates and the rest to remain submerged in larger fuel frag- ments. The normal fission product inventory for thermal fission in 235U (e.g., 3-30 Ci of 90Sr) would be expected, plus a much lower number of activation products. The other possibility for introducing radioactive material into the oceans would result from failures after the nuclear reactor is brought to power—about 4,000 MW. In some mis- sions, the reactor would be started before Earth orbit is reached; in others, the reactor would be first started up in orbit. Depending on the start-up point, the reactor would operate from 10 to 20 minutes before reaching mission in- jection velocities-roughly Earth escape velocity. Complete failure at any time during operation would leave the highly radioactive reactor coasting in space. The period of time from failure to atmospheric re-entry and impact is extremely sensitive to the velocity attained at the instant of failure, *Not every ocean impact could result in an excursion. During launch and early portions of the ascent, auxiliary controls (neutron ab- sorbers or poisons) may be used to override the effects of water entry and preclude an excursion. Beyond some point, however, fail- ures could result in ocean impacts of such force as to dislodge the auxiliary poisons. Still later, atmospheric re-entry would cause re- actor disassembly prior to impact, so that an excursion is impossible. and can range from less than an hour to hundreds of years. If the delay time is long enough for normal radioactive decay to reduce the inventory sufficiently, the failed ma- chine will be allowed to remain in orbit. If the time before impact is too short, however, deliberate action will be taken, if necessary, to cause impact and disposal in deep ocean waters. In such cases, impact would occur within an hour. Again, atmospheric re-entry would break up the reactor so that the radioactive fuel elements and other debris would impact over an area of several square miles. No excursion would result, and the fission and activation products would remain within heavy pieces that would sink rapidly. WASTES FROM THE PROCESSING OF REACTOR FUEL ELEMENTS The vast amounts of fission products created in reactor fuel elements remain in the uranium matrix within the aluminum, stainless-steel, or zirconium-alloy cladding or jackets. Spent fuel elements are periodically removed from reactors and are shipped intact to chemical reprocessing plants, after a period of storage in water-shielded tanks to permit the short- lived radioisotopes to decay away. At the reprocessing plants, the cladding is removed, and the fission products are chemically separated from the unfissioned uranium in pro- cesses of two or more stages or cycles. First-stage waste normally contains more than 99 percent of the fission product radioactivity; this material, referred to as high- radioactivity or high-level waste, is kept in underground storage tanks. To our knowledge, no nation deliberately disposes of such high-level wastes to the environment. Second and third stages of reprocessing unfissioned ura- nium result in larger volumes of wastes with significantly less radioactivity content. In the United States, these liquids may be still further decontaminated by evaporation or other process and discharged to underground formations. In the United Kingdom, such low-level wastes are discharged to coastal waters. Table 18 summarizes 11 years of radioactive- waste disposal by the Windscale plant. The Dounreay Ex- perimental Reactor Establishment, in northern Scotland, also disposes of some chemical-processing plant wastes to the sea near Caithness, Scotland; in 1967, it was reported by the Fisheries Radiobiological Laboratory of the Ministry of Agriculture, Fisheries and Food that the Dounreay plant discharged 290 Ci of 90Sr, 12,000 Ci of beta activity, and 14 Ci of alpha activity. Other plants around the coasts of the British Isles, where fuel elements are fabricated or radio- isotopes are processed, dispose of smaller total amounts of activity than the fuel reprocessing plants. In France, the chemical reprocessing plant at Marcoule disposes of about 1,800 Ci in liquid wastes per year to the

32 Radioactivity in the Marine Environment TABLE 18 Mean Activity Discharge Rates (Ci/mo) to the Irish Sea, Windscale Chemical Reprocessing Plant, United Kingdom" Radionuclide "After Howells( 1966). 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 106Ru 2,218 3,522 2,956 3,302 2,095 1,916 2,781 1,924 1,752 2,077 1,436 103Ru 300 492 746 964 265 153 800 100 150 205 186 "OSr 137 210 129 43 41 85 46 81 97 76 116 89Sr 248 72 170 82 114 42 14 16 14 7 12 144Ce 215 497 583 74 180 200 116 267 288 571 1,142 91 Y .Hare earths 300 567 506 83 201 125 90 90 73 75 203 i37Cs 310 516 165 76 91 92 31 111 97 100 132 95Zr 59 210 415 196 140 78 47 1,797 1,479 1,172 1,566 95Nb 535 510 845 523 658 356 272 1,735 2,803 1,947 2,143 Total beta 5,366 6,846 7,659 6,461 3,981 3,742 4,020 5,055 4,560 5,464 6,022 Total alpha 4.8 5.2 5.6 6.8 11.1 15.5 19.0 23.5 33.8 48.8 79.6 Rhone River; in 1965, the amount was 2,584Ci (Rodierefa/., 1966). In addition, there is a new chemical reprocessing plant for irradiated fuel elements at La Hague on the Coten- tin Peninsula with plans for disposal of treated wastes di- rectly to the English Channel (Avargues and Jammet, 1966). RADIOISOTOPIC POWER GENERATORS SNAP isotopic devices are now employed over, on, and in the oceans. Tables 19 and 20 list the characteristics and ap- plications of existing U.S. units. SNAP* units utilize the heat of radioisotopic decay. It has been proposed that in some aerospace units the heat be used directly for thrusters. In terrestrial applications, the heat is converted to electricity by thermoelectric converters. The source of energy for the SNAP devices are the long- lived fission products or trans-uranics recovered from the tank-stored first-stage wastes from the processing of the ir- radiated fuel elements. These are first concentrated and then converted metallurgically to a dense mass most suitable for SNAP units. The isotopic power devices used in the United States are all of similar construction; only their size and output varies with the different fuels and thermoelectric converters. Figure 7 schematically illustrates the configura- tion of an isotopic power unit and the basic materials of construction. The materials of construction are chosen to provide a margin of safety in the event of a damaging accident. Most of the SNAP devices in oceanic applications to date *SNAP is the U.S. designation; in Europe they are called RIPPLE (ftadio/sotopic Power Packages for £lectricity). are fueled with 90Sr in the chemical form of titanate, SrTiO3. The titanate form is an inert ceramic that dissolves quite slowly on exposure to fresh or salt water. Future fuels may include the oxide forms of Sr, or Ce, or Co in metallic form, giving the most dense and efficient power-to-weight ratio. The amount of radioactivity in present SNAP units ranges from 30,000 Ci to 225,000 Ci of 90Sr and is directly pro- portional to electrical output. Future units may contain up to 107 Ci. SNAP units for aerospace units use the most ad- vantageous power-to-weight ratios and are fueled with metallic or oxide forms of somewhat shorter-lived isotopes, i.e., those having higher specific activity. The isotopic fuel forms are jacketed or encapsulated in sealed (welded) corrosion-resistant metals and alloys such as Haynes, Hastelloy, or titanium. These canisters of fuel are completely surrounded by a heat-absorbing metal such as depleted uranium or tungsten. An insulating material around the fuel canister and heat-sink absorber keeps the isotopi- cally generated heat at maximum temperature. The thermo- electric couples, which operate on the principle of maxi- mum temperature drop, are linked at one end to the heat sink and at the other to the outside of the insulator. The insulation package is surrounded by a radiation-shielding material such as depleted uranium or lead, and this is en- cased in a container of heavy steel. For oceanic applications, the outer steel shell is designed to be a pressure vessel, as is the fuel capsule itself. Corrosion Tests of SNAP Components Hastelloy-C, the fuel-encapsulating metal of existing oceanic SNAP devices, has an average corrosion rate in seawater of 0.024 ± 0.008 mils per year (0.00061 ± 0.0002 mm per

Sources of Radioactivity and Their Characteristics 33 TABLE 19 Characteristics and Applications of Oceanic SNAP Systems Power Electrical System Output Fuel Form Fuel Quantity (kCi) Marine Application Status as of November 1968 Past and Present Systems SNAP-7A 10W SNAP-7B 60 W SrTiO3 SrTiO3 41 225 Coast Guard buoy CG lighthouse; then, offshore Post test analysis after 3-yr operation Operating (relocated on oil plat- SNAP-7D 60 W SrTiO, 225 oil platform Navy NOMAD buoy, Gulf of Mexico form in August 1966 after 2 yr on lighthouse) Operating (implanted January 1964) SNAP-7E 7.5 W SrTiO3 31 Sonar transducer at 15,600 ft depth Operating (implanted July 1964) SNAP-7F 60 W SrTi03 225 Offshore oil platform Post test examination of power decrease Future Systems SNAP-21 10W SrTiO3 33 64 Sonar, cable boosters, navigation aid, research Under development (environment test units 1969) 20 W or SrO SNAP-23 25 W 60 W 100 W SrTiO3 or SrO 75 185 275 Weather buoy, navigation buoy, offshore oil platform Under development (environmental test units scheduled 1971) KW 1-10 kW SrTiO3, SrO, Co, orCeO Up to 10,000 Man-in-the-sea research; offshore oil, mining, and exploration; communications Application engineering and design study in progress TABLE 20 Characteristics and Applications of Aerospace SNAP Systems Power System Power Output Fuel Form Fuel Quantity (kCi) Aerospace Application Design Mode of Re-entry Status (1968) NASA Goddard 60Wth I47Pm 170 Space vehicle thruster Intact re-entry Ground tests Microthruster Air Force DART 157 Wth 238pu 4.7 Space vehicle thruster Intact re-entry Ground tests SNAP-19 60 We 238pu 34.5 NIMBUS B auxiliary 960-km orbit; Aborted launch in power intact re- 1968, recovered entry intact from ocean SNAP-27 50 We 238pu 45 ALSEP mission Superorbital; intact re- entry SNAP-3A 3We 238pu 1.6 Navy satellite 800-km orbit; 2 launched 1961 burn-up on re-entry SNAP-9A 25 We 238pu 16 Navy satellite 960-km, 900-yr 2 launched 1963 orbit; burn-up 1 aborted 1964 on re-entry

34 Radioactivity in the Marine Environment Thermoe1ec tr*cs Rad1o*sotope fue1 238Pu 90Sr 242Cm 147pm 244Cm 137Cs Dep1eted U, Hq Insu1at*on Absorber/rtd*ator Dep1eted U Ta-W W Nb Ta Nb-Zf W-Re Re-Mo FIGURE 7 Schematic of SNAP isotopic power generators. year) (Kubose and Cordova, 1966). It has been calculated that it would take some 300 years to corrode through the Hastelloy-C at that rate. Laboratory and oceanic experiments were conducted to determine the dissolution rate of the SNAP fuels in sea- water. Laboratory measurements of strontium titanate in- dicate a high initial release rate, 800/ug/cm2 on the first day, followed by a slower rate of release (Zigman et al., 1964). The release rate for extended periods was expressed as R = 105 (f + 6)-1 /ug/cm2/day (for t - 1), where t (time) is expressed in days. Strontium titanate was also exposed to an oceanic envi- ronment at a depth of 30 m for 1,065 days (Goya et a/., 1966). Biological growth was evident on the fuel specimens. Measured dissolution rates varied from 4 to 14 ^g/cm2/day. Plutonium metal reportedly reacts rapidly and com- pletely with seawater, producing solid reaction products plus hydrogen (Lai and Goya, 1966). The solid reaction products have a solubility of about 1.5 to 2 /ug/day/50-70 mg of solids. In another series of laboratory experiments, plutonium dioxide was immersed in seawater under various temperatures and pressures (Kubose et al., 1967a). The long-term solubility rate was found to be lower at high tem- peratures, and this was attributed to the formation of a coating of calcium sulfate on the fuel-form specimens. The data were as follows: Temperature Pressure (psig) Dissolution Rate (*ig/mg/day) 20 120 190 15 30 180 4X10-3 1.3X10^* 0.6 X10-4 Later experiments indicated that the dissolved plutonium was absorbed from solution by ocean sediments; in one ex- periment, the amount in solution was reduced by a factor of 600 (Kubose era/., 1967b). SNAP isotopic units are also used in aerospace applica- tions. Several are now in orbit, providing electrical energy for a satellite navigation system. FALLOUT OF 238Pu FROM THE SNAP-9A RE-ENTRY In April of 1964, a SNAP-9A nuclear power generator aboard an aerospace vehicle re-entered the atmosphere fol- lowing a malfunction during launch. The generator con- tained about 17 kCi of 238Pu and was estimated to have entered the atmosphere of the southern hemisphere at an altitude of approximately 150,000 ft (45,000 m). (By con- trast, approximately 400 kCi of 239Pu have been dispersed from all nuclear explosions in the atmosphere.) The plutonium of the device was assumed to have com- pletely ablated during the intense heat of re-entry and to have been distributed in the atmosphere as particles of un- known size. In the first 2 years since the re-entry and burn-up of the SNAP-9A, several programs were carried out to find, iden- tify, and characterize the debris. The following conclusions briefly summarize the results of these studies: 1. More than 80 percent, or about 15 kCi, of the original 17 kCi in the device was still in the stratosphere in early 1966. Of this, some 80 percent was in the southern hemi- sphere and 20 percent in the northern hemisphere. 2. Particle size of the stratospheric 238Pu from the SNAP-9A generator probably ranged from 5 to 58 mp in diameter, with the arithmetic mean at 9.7 m/u. 3. By the end of 1966, approximately 1.5 kCi of the SNAP-9A plutonium had been deposited on the earth's sur- face. The southern hemisphere had received approximately 85 percent of this, while only 15 percent had been deposited in the northern hemisphere. 4. The distribution of the 238Pu in the stratosphere over the southern hemisphere in mid-1966 approximated rather well the distribution of 90Sr in early 1965 over the northern hemisphere. The altitude and latitudinal distribution of the highest core of activity in the southern hemisphere for the SNAP-9A materials generally mirror-imaged the older 90Sr picture in the northern hemisphere. Based on these observations, it is assumed that since the beginning of 1967, the fallout pattern of the 238Pu particles from the SNAP-9A burn-up was and will continue to be similar to the pattern of stratospheric 90Sr fallout observed over the past few years. Table 21 is based on the above observations and assump- tions, using a 10-month stratospheric half-residence-time. An additional assumption, based upon very qualitative observa- tion of the 90Sr stratospheric inventories, is that the strato- spheric air of the two hemispheres mixes slowly and achieves

Sources of Radioactivity and Their Characteristics 35 TABLE 21 Projected Deposition of 238Pu from the SNAP-9A Re-entry (in kCi) Latitude 1967 1968 1969 1970 1971 Total 80° -90° N 0 0 0 0 0 0 70° -80° 0.02 0.01 0 0 0 0.03 60° -70° 0.08 0.04 0.02 0.01 0.01 0.16 50° -60° 0.28 0.17 0.09 0.05 0.03 0.62 40° -50° 0.37 0.22 0.11 0.07 0.04 0.81 30° -40° 0.33 0.19 0.10 0.06 0.04 0.72 20°-30° 0.22 0.13 0.07 0.04 0.03 0.49 10° -20° 0.23 0.14 0.07 0.04 0.03 0.51 0°-10° 0.17 0.10 0.05 0.03 0.02 0.37 Total, northern hemisphere 1.7 1.0 0.5 0.3 0.2 3.7 0M0° S 0.68 0.27 0.10 0.05 0.02 1.12 10°-20° 0.93 0.37 0.14 0.07 0.03 1.54 20° -30° 0.89 0.35 0.13 0.07 0.03 1.47 30°^0° 1.32 0.52 0.19 0.10 0.04 2.17 40° -50° 1.46 0.58 0.22 0.11 0.04 2.41 50° -60° 1.14 0.45 0.17 0.09 0.03 1.88 60° -70° 0.30 0.13 0.04 0.02 0.01 0.50 70° -80° 0.07 0.03 0.01 0 0 0.11 80° -90° 0.01 0 0 0 0 0.01 Total, southern hemisphere 6.8 2.7 1.0 0.5 0.2 11.2 Total, world 8.5 3.7 1.5 0.8 0.4 14.9 approximately equal concentrations of 238Pu in about 4 years, which, in fact, was observed. In Table 21, the pre- dicted annual fallout of 238Pu from the SNAP-9 A burn-up is given for each 10° band of latitude. It is interesting to compare the probable sensitivity re- quired for observing the 238Pu deposited on land and in the sea. By the end of 1971, when virtually all of the SNAP-9 A debris will have been deposited on the earth, the average concentration in the surface ocean water (assuming that the 238Pu is homogeneously mixed to a depth of 100 m) will be approximately 0.0005 pCi per liter. Even within the latitude band of maximum deposition, 40°-50° S, and assuming no horizontal mixing, we would not find concentrations much higher than 0.001 pCi per liter. In contrast, the 238Pu de- posited on land in the 40°-50° S band will be about 1 mCi per km2, or about 1,000 pCi per m2. Even in the northern hemisphere, the deposits in mid-latitudes will be in excess of 100 pCi per m2. These projected concentrations on land and in the sea seem to indicate clearly that the 238Pu will be a very useful and practical tool for continental fallout studies. For marine studies, however, the concentrations will prob- ably be beyond the range of practical measurement, using current equipment and technology. Therefore, if we are to make use of this radioactive source as an oceanic tracer, new systems for sampling of the sea-for determining chemical or physical concentrations of plutonium in seawater or for low-level alpha counting (or some combination)-must be developed. PACKAGED RADIOACTIVE WASTE DISPOSAL Any establishment working with radioactive materials prob- ably evolves radioactive wastes, since anything the radioac- tive material comes into contact with is likely to become contaminated—i.e., some of the radioactive material is rubbed off or left behind. Such radioactive waste materials include laboratory ware and furniture; chemical hoods or their air filters; tubing and piping; protective plastics; experi- mental hardware; rags, wipes, and mops used for cleaning up; sludges from evaporators; and demineralizer resins. Uranium refineries, fuel fabrication plants, reactors, fuel reprocessing plants, radioisotope production plants, and laboratories working with uncontained radioisotopic ma- terials all evolve radioactive wastes. In the United States, hundreds of establishments, both government and private, are licensed to use radioactive materials. The volume and level of activity of the wastes they may evolve vary in direct proportion to the amount of radioactivity being manipu- lated. Activity levels of wastes produced per year per estab- lishment range from picocuries to kilocuries. Since wastes occupy space, and since their accumulation may eventually build a radiation hazard, it is desirable to remove them to where they will be out of the way and create no further hazard. Remote, uninhabited places, such as abandoned mine shafts, government-owned and moni- tored sites, specially engineered burial vaults, or selected sites in the deep sea (>1,000 fathoms) have been suggested. Such places are limited in number, however, and as man ex- tends his exploration and exploitation of the deep sea, pos- sible sites for waste disposal there will diminish still further in number and remoteness. It will eventually be necessary to limit the number of sites used for this purpose and to monitor them in order to safeguard users of the sea floor. Currently, in the United States, most of the solid wastes are buried on the sites of the federally owned atomic-energy plants or on state-owned lands. The latter are operated com- mercially and monitored by licensees, subject to government inspection. In the early years of the atomic-energy industry in the United States, several establishments near the coasts used the sea for disposal of radioactive wastes. A few commercial companies were licensed by the AEC to practice sea disposal. However, since 1960, when the AEC adopted a policy lead-

36 Radioactivity in the Marine Environment ing to establishment of licensed regional land burial sites for private industry's radioactive wastes, sea disposal has waned. For sea disposal, containers of wastes were weighted, to assure sinking, and fabricated to accommodate deep-sea pressures. Land burial, on the other hand, requires only structural integrity for transporting; consequently, it is less expensive than sea disposal. The United Kingdom has established two land burial sites in northern England for solid wastes containing small amounts of radioactive contamination. Such wastes consti- tute the largest fraction of all solid radioactive wastes (Morely, 1967). Many other nations do not have available as much remote land with required geohydrological character- istics as the United States. They look upon deep-sea dis- posal, therefore, as a safe and efficient means of getting rid of solid wastes. Their alternative is to use engineered burial vaults, which are more expensive to build and maintain than sea disposal. Packaging for Sea Disposal In the United States, the container most used for packaging radioactive wastes for sea disposal was the 55-gal (200-liter) oil drum. Paper or rag wastes were compressed into small bales, placed in the drum and completely surrounded by high-density material, usually concrete. Solids such as plas- tics and metals were mixed in the drum with concrete, the ratios of concrete to wastes depending directly on the levels of radioactivity. Sludges and demineralizer resins were usu- ally contained within a carboy or smaller drum, then sur- rounded by concrete in the 55-gal drum. Several establish- ments packaged wastes in prefabricated steel-mesh- reinforced concrete boxes that varied in size from 20 X 20 X 44 in. (50X50X110 cm) to 5X7X8 ft (1.5X2.1X2.4 m). Wastes and concrete were mixed together in the box to achieve the desired specific gravity, 1.2. All packages, drums, and boxes were capped with 4 in. (10 cm) or more of clean concrete, and those with internal air spaces were fitted with vents to allow water to enter and equalize pressures on de- scent in the ocean (Joseph, 1957). Other nations package wastes for sea disposal similarly, especially using 55-gal drums. In 1961, the AEC conducted two series of tests on the structural integrity of the various kinds of packages used for sea disposal. These tests provided information that was used to determine optimum combinations of steel and concrete needed to package various configurations of wastes. They also indicated that air spaces within the package of wastes must be pressure-equalized with vents in order to prevent container collapse (Pohlman and Pickett, 1962). Large con- crete boxes with unvented internal air voids were found to be particularly vulnerable to rupture by pressure (Pneumo Dynamics, 1961b). In another test, smaller, unvented con- crete boxes survived immersion to 6,000 ft (Brown et al., 1962). Burns and Dunster (1967) report that the U.K. pack- aging practice also is to use reinforced concrete and pressure equalization devices. Disposal at Sea Tables 22 through 24 summarize the known packaged radio- active waste sea disposal operations conducted through 1967. Locations are approximate because of drifting of the ship during disposal and by the containers during descent through the mile-plus depths. Some of the U.S. disposals were conducted by transoceanic steamship companies that are licensed to dispose of wastes. Numbers of containers in- clude all sizes, large concrete boxes as well as 55-gal drums. However, probably more than 95 percent of all containers were of the 55-gal size. The radioactivity contained in the waste packages can only be estimated on the basis of labels describing the con- tents of waste receptacles coming into the packaging facility. Contaminated heterogeneous solids are the most difficult to assay; homogeneous sludges or slurries are the easiest. Exter- nal radiation readings are marked on each container. The wastes generally include a wide spectrum of radionuclides, ranging from 3H to the transplutonics. Alpha curies as a rule indicate thorium, uranium, or plutonium wastes, the iso- topes having long half-lives. In 1967, the European Nuclear Energy Agency coordi- nated a waste disposal demonstration "experiment" to establish common sea disposal operation principles and safety practices. Five nations participated, as indicated in Table 25 (European Nuclear Energy Agency, 1968). In 1957 and 1960, the United States monitored the waste disposal sites off its Pacific Coast. Samples of water, biota, and sediments were collected and analyzed; none of the disposed radionuclides was detected in any of the samples (Faughn et al., 1957; Pneumo Dynamics, 1961a). MISCELLANEOUS SOURCES OF RADIOACTIVITY There are several other possible sources of radionuclides that reach the oceans. These include low-level liquid wastes from medical and industrial users of isotopes and other re- search establishments (International Atomic Energy Agency, 1965). Such wastes, within established permissible concen- trations of activity, are normally disposed of into municipal sewer systems. The widespread use of radioisotopes and the number of isotope users is becoming quite significant: in

Sources of Radioactivity and Their Characteristics 37 TABLE 22 Summary of U.S. Sea Disposal Operations, 1951-1967 (Atlantic Ocean) Year Approximate Location No. Containers, All Types Estimated Activity at Time of Packaging (Ci) 1951-1958 42°25'N 70°35'W 36°56'N 74°23'W Midocean 37°50'N 70°35'W \ 38°30'N 72°06'W J 4,008 432 97 2,440 6.5 <0.1 23,000 8,000 1959-1960 between and 38°30'N72°06'W 36°44'N 45°00'W 36°50'N 74°23'W Midocean 5,800 228 204 22 68,500" 456 24.5 <0.1 1961-1962 36°56'N 74°23'W 137 15.6 1963-1964 36°56'N 74°23'W 58 5.3 1965 36°56'N 74°23'W 6 4.3 1967 Totals 36°56'N 74°23'W 6 30.5 "Includes pressure vessel of Seawolf reactor -estimated 33,000 Ci of induced activity. 33,998 79,482.9 TABLE 23 Summary of U.S. Sea Disposal Operations, 1946-1966 (Pacific Ocean) Year Approximate Location No. Containers, All Types Estimated Activity at Time of Packaging (Ci) 1946-1958 between and 37°39'N 123°26'W .^/i'^y 40°07'N 135°24'W 54°10'N 141°09'W 24,305 38 14,061 0.5 1959-1960 between and 40°07'N 135°24'W 54°10'N 141°09'W 37°39'N 123°26'W--" 32°00'N 121°30'W 21°28'N 157°25'W 34°58'N 174°52'W 53 0.4 14,311 3,467 39 7 155.7 3.6 0.1 14 1961-1962 between and 40°07'N 135°24'W 54°10'N 141°09'W 32°00'N 121°30'W 37°39'N 123°26'W — 33°39'N 119°28'W 41 0.5 948 8,913 164 30 235.1 47.9 1963-1964 between and 40°07'N 135°24'W 54°10'N 141°09'W 37°39'N 123°26'W --" 175 7.2 1965 between and 40°07'N 135°24'W 54°10'N 141°09'W 37°39'N 123°27'W — 8 16.1 14 <0.1 0.4 4 1966 Totals between and 40°07'N 135°24'W 54°10'N 141°09'W 37°12'N 123°55'W - 40 3 88.7 (3H) 15.4 (3H) 52,530 14,677.3

38 Radioactivity in the Marine Environment TABLE 24 Summary of Sea Disposal of Packaged Radioactive Waste by the United Kingdom, 1950-1967 Estimated Activity (Ci) Year No. Containers Alpha Beta 1951 100 0.5 5 1953 131 2.5 3 1955 2,519 12 33 1957 7,369 955 808 1958 4,330 695 1,085 1961 6,890 563 1,630 1962 648 17 163 1963 8,379 368 7,071 1964 10,634 444 15,090 1965 5,140 114 13,754 1966 3,362 78 2,742 1967" 1,268 91 1,682 50,570* 3,331 44,096 1950-1963c 61,570 390 1,176 "included in European Nuclear Energy Agency packaged radioactive waste disposal operation, 1967. 6Through 1961, the wastes were disposed of in an area near 34° N 20° W; after 1961, except for 1967, they were disposed in a rectan- gular area circumscribed by the coordinates: 40°20'N 13°53'W, 47°56'N 13°27'W, 48°43'N 1 3°05'W, and 48° 19'N 12°39'W. cRelatively low-activity wastes, including some from C.E.N.-Belgium and from Belchim, Belgium, disposed in the "Hurd Deep", an area near 50° N 01° W, by the United Kingdom. TABLE 25 Summary of European Nuclear Energy Agency Packaged Radioactive Waste Disposal Country of Origin Number of Containers Estimated Activity (Ci) Alpha Beta-Gamma United Kingdom" 1,268 91 1,682 Germany 480 0.5 5 Netherlands 501 0.07 2 Belgium 1,945 - 190 l•rance 896 (concrete) 1 10 30,700 160 5,747 Totals 35,790* 253 7,636 "Also included in Table 24. *Disposal area near 42° N 14° W. 1968, there were 8,321 licensees in the United States alone, many of them concentrated in urban population centers. The fate of such wastes is indicated by two recent stud- ies; one, of wastes discharged directly to a river system, and the other, of wastes reaching a sewage treatment plant. The Clinch River environment below the Oak Ridge National Laboratory was surveyed for radionuclides after nearly 20 years of low-level waste discharge that amounted to 1,110 Ci of 90Sr, 660 Ci of 137Cs, 6,600 Ci of 106Ru, 1,240 Ci of rare earths, 270 Ci of 60Co, and lesser amounts of 144Ce, 95Zr, 95Nb, and 131I, totaling almost 14,000 Ci. It was shown that about 200 Ci, principally cesium, were bound up with the sediments and that the remainder of the activity passed through this stretch of river in the aqueous phase (Parkerera/., 1966). Folsom and Mohanrao (1960) studied the amount of gamma-emitting isotopes entering and leaving the sewage treatment plant of a large metropolitan city over a 2-year period. They found that in addition to a steady background level of fallout isotopes and natural radioactivity there were pulses or peaks of isotopes such as 137Cs, 60Co, 65Zn, and 1311 entering the plant. They also found fractionation, caused by the sewage treatment process, i.e., about 55 per- cent of the 137Cs was concentrated with the sludge, which undergoes aerobic bacterial digestion, and the remainder stayed with the liquid phase. In this particular plant, which was on the seacoast, the treated liquids and sludges were piped out to sea, where they were spread out over the sea floor and dispersed slowly. Radioisotopes are also purposefully introduced to the marine environment in the course of scientific research pro- jects, as tracers of physical, chemical, or biological processes. Several experiments have been carried out in the marine en- vironment employing large quantities of short-half-life radio- active tracers to study the distribution of products from underwater chemical explosions (Gurney etal., 1963). In 1961, for instance, four charges were detonated off the coast of California, at San Clemente Island. These shallow explosions of 10,000 pounds of HBX-1 were each seeded with 500 Ci of radionuclide. Three detonations employed 177 Lu (6.8-day half-life) in fine particulate oxide form; the fourth employed the noble gas 133Xe (5.3-day half-life). According to unpublished data of Schuert, samples col- lected on the day of the explosion and the day following it showed significant accumulation of the tracer by plankton (principally copepods). Activity ranging from 10s to 107 d/m/g of wet weight were measured in samples taken from water having no detectable radioactivity. Lower levels of radioactivity were measured in a number of species of fish, including jack mackerel, boccaccio, bonito shark, swell shark, and sheephead. A number of experiments have been conducted along coastlines to study the littoral drift of sand by injecting the surf zone with batches of sand tagged with radioactivity. In these tests, the sand is either tagged directly with 133Xe (similar to the kryptonating process) or coated with other nuclides and sealed with sodium silicate (Acree et al., 1968). Such experiments have proven of great value in understand- ing the dynamics of shoreline coastal waters and harbor erosion or buildup. Some years ago, consideration was given to the use of radioisotopes to study local diffusion and mixing processes,

Sources of Radioactivity and Their Characteristics 39 and several tests of this technique were conducted (Nuclear Science and Engineering Co., 1958). Since then, the tech- nology of fluorometers has advanced considerably, and it is now possible to measure dye concentrations of the same low order as radioisotopes-0.5 parts per billion. Dyes largely have superseded isotopes in the measurement of water mix- ing processes. Selected radioisotopes such as 65Zn and 32P continue to be useful for studies of ecological systems (Pomeroy and Odum, 1966; Hooper and Ball, 1966). SUMMARY Radioactivity in the oceans can result from numerous sources. Natural atmospheric and geologic processes issue discrete radionuclides in certain forms and distributions; these are briefly described. Man's uses of nuclear energy re- sult in another, wider spectrum of radionuclides of varying characteristics. The biological distribution in the ocean of man-made radionuclides depends greatly on the initial phys- icochemical form of the radioactivity, and this, in turn, de- pends on the particular use or application of nuclear energy. Nuclear energy applications are described, indicating the particular radionuclides involved in each application and the form of the radioactivity likely to be introduced into the ocean. The applications include nuclear explosions at various positions relative to the earth's surface; nuclear reactors for electric power, fuel production, ship propulsion, and space vehicle propulsion; nuclear fuel processing; waste disposal; auxiliary power generators; and radioisotopic tracers. ACKNOWLEDGMENTS Many individuals and organizations helped to put this chap- ter together. In particular, the authors are indebted to H. Howells and R. H. Burns of the U.K. Atomic Energy Research Establishment and to A. Preston of the U.K. Min- istry of Agriculture, Fisheries and Food for providing data and information concerning nuclear waste operations in the United Kingdom; to M. Nathans of Tracerlab, Inc., and J. Sherer of the AEC Lawrence Radiation Laboratory for their ideas about particle size determination; to J. Honstead of Battelle Pacific Northwest Laboratory for his recent data concerning radioactivity in the Columbia River; to R. Decker G. P. Dix, and S. Seiken of the AEC for their help with the discussion about SNAP and nuclear aerospace applications; and to E. D. Goldberg of Scripps Institution of Oceanog- raphy, who provided data for the compilations of natural radionuclides in the sea. We are grateful to the many re- viewers at the AEC for their many constructive and helpful suggestions and comments. REFERENCES Acree, E. H., F. N. Case, N. H. Cutshall, and H. R. Brashear. 1968. Radioisotopic sand tracer study, May 1966-April 1968. ORNL- 4341. (Oak Ridge National Laboratory, Tenn.) (Available from National Technical Information Service, U. S. Dep. of Commerce, Springfield, Va. 22151.) Adams, C. E., W. R. Balkwell, and J. T. Quan. 1967a. High tempera- ture measurements of the rate of uptake of MoO3 vapor by selected oxides. USNRDL-TR-67-98. (U. S. Naval Radiological Defense Laboratory, San Francisco.) Adams, C. E., W. R. Balkwell, and J. T. Quan. 1967b. High tempera- ture measurements of the rate of uptake of TeO2 vapor by selected oxides. USNRDL-TR-67-134. (U. S. Naval Radiological Defense Laboratory, San Francisco.) Adams, C. E., N. H. Farlow, and W. R. Shell. 1960. The composi- tion, structures and origins of radioactive fallout particles. Geo- chim. Cosmochim. Acta 18:42-56. Avargues, M., and H. P. Jammet. 1966. Etude du site marin de la Hague en relation avec le rejet d'effluents radioactifs, p. 787-795. In Proceedings of the conference on disposal of radioactive wastes into seas, oceans, and surface waters. International Atomic Energy Agency, Vienna. 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