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The Medical Implications of Nuclear War, Institute of Medicine. @) 1986 by the National Academy of Sciences. National Academy Press, Washington, D.C. Radioactive Fallout CHARLES S. SHAPIRO, PH.D. San Francisco State University, San Francisco, California Lawrence Livermore National Laboratory, Livermore, California TED F. HARVEY, PH.D., alla KENDALL R. PETERSON, M.S. Lawrence Livermore National Laboratory, Livermore, California OVERVIEW Potential radiation doses from several scenarios involving nuclear attack on an unsheltered United States population are calculated for local, in- termediate time scale and long-term fallout. Dose estimates are made for both a normal atmosphere and an atmosphere perturbed by smoke produced by massive fires. A separate section discusses the additional doses from nuclear fuel facilities, were they to be targeted in an attack. Finally, in an appendix the direct effects of fallout on humans are considered. These include effects of sheltering and biological repair of damage from chronic doses. RADIOACTIVITY FROM NUCLEAR WEAPONS Introduction In this paper the potential doses associated with the radionuclides created by nuclear explosions are assessed. Our focus is on the areas outside the zone of the initial blast and fires. Prompt initial ionizing radiation within the first minute after the explosion is not considered here, because the physical range for biological damage from this source for large-yield weapons is generally smaller than the ranges for blast and thermal effects. The contributions from local (first 24 hours) and more widely distrib- uted, or global fallout, will be considered separately. Global fallout will 167

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168 PHYSICAL EFFECTS AND ENVIRONMENTaL CONSEQUENCES be further subdivided into an intermediate time scale, sometimes called tropospheric, of 1 to 30 days, and a long-term (beyond 30 days) strato- spheric component. Mainly the dose from gamma-ray emitters external to the body is considered. Contributions from external beta emitters are not estimated because of the limited penetration ability of beta radiation, but there is the possibility that in areas of local fallout, beta radiation can have a significant impact on certain biota directly exposed to the emitters by surface deposition (Svirezhev, 19851. Potential internal doses from ingestion and inhalation of gamma and beta emitters are estimated in only an approximate manner, as these are much more difficult to quantify. The total amount of gamma-ray radioactivity dispersed in a nuclear exchange is dominated by the weapon fission products whose production is proportional to the total fission yield of the exchange. Exposure to local fallout, which has the greatest potential for producing human casualties, is very sensitive to assumptions about height of burst, winds, time of exposure, protection factor, and other variables. For global fallout, the dose commitments are sensitive to how these fission products are injected into various regions of the atmosphere, which depend on individual war- head yield as well as burst location. For local fallout, aspects of the baseline scenario outlined in the Sci- entific Committee on Problems of the Environment-Environmental Effects of Nuclear War (SCOPE-ENUWAR) Study (Pittock et al., 1985) are considered. For global fallout, both the 5,300-megaton (Mt) baseline scen- ario reported by Knox (1983) and the 5,000-Mt reference nuclear war scenario described by Turco et al. (1983; also known as the TTAPS study) are considered. Local Fallout Local fallout is the early deposition of relatively large radioactive par- ticles that are lofted by a nuclear explosion occurring near the surface in which large quantities of debris are drawn into the fireball. For nuclear weapons, the primary early danger from local fallout is due to gamma radiation. Fresh fission products are highly radioactive and most decay by si- multaneous emission of electrons and gamma rays. An approximate rule of thumb for the first 6 months following a weapon detonation is that the gamma radiation will decay by an order of magnitude for every factor of seven in time (Glasstone and Dolan, 19771. If the implausible assumption is made that all of the radioactivity in the fresh nuclear debris from a 1-Mt, all-fission weapon arrives on the ground 1 hour after detonation and is uniformly spread over grassy ground

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RADIOACTIVE FALLOUT 169 such that it would just give a 48-hour unshielded dose of 450 reds, then approximately 50,000 km2 could be covered. Given such a uniform dep- osition model, it would require only about 100 such weapons to completely cover Europe. In reality, because of a variety of physical processes, the actual areas affected are much smaller. Most of the radioactivity is airborne for much longer than an hour, thus allowing substantial decay to occur before reaching the ground. Also, the deposition pattern of the radioactivity is uneven, with the heaviest fallout being near the detonation point where extremely high radiation levels occur. When realistic depositional pro- cesses are considered, the approximate area covered by a 48-hour un- shielded 450-rad dose is about 1,300 kin2, i.e., nearly a factor of 40 smaller than the area predicted using the simplistic model above. This large factor is partially explained because only about one-half of We radioactivity from ground bursts is on fallout-sized particles (Defense Civil Preparedness Agency tDCPA] 1973~. The other portion of the radioactivity is found on smaller particles that have very low settling velocities and therefore contribute to global fallout over longer times. Portions of this radioactivity can remain airborne for years. For airbursts of strategic-sized weapons, virtually no fallout-sized particles are created, and all of the radioactivity contributes to global fallout. Lofted radioactive fallout particles that have radii exceeding 5 to 10 ,um have sufficient fall velocities to contribute to local fallout. Some particles can be as large as several millimeters in radius. Settling velocities range from a few centimeters per second to many tens of meters per second for these particles. They are lofted by the rising nuclear debris cloud and are detrained anywhere from ground level to the top of the stabilized cloud. Horizontal wind speeds usually increase with height up to the tropopause, and frequently, wind directions have large angular shears. Nuclear clouds disperse due to atmospheric shears and turbulence. The arrival of radioactivity at a given location can occur over many hours, with large particles from high in the cloud usually arriving first at a downwind location. Rainout effects have been suggested as being potentially significant contributors to local fallout effects from strategic nuclear war (Glasstone and Dolan, 19771. The inclusion of rainout processes would probably not significantly affect the answers to generic questions pertaining to large- scale nuclear war phenomena (for example, What percentage of Western Europe would suffer lethal levels of gamma radiation from local fallout in a large-scale nuclear exchange?), especially if a substantial portion of the weapons are surface burst. This is particularly true for strategic weapon yields of greater than 30 kilotons (kt), because the radioactivity on the small particles most affected by rainout rises above all but the largest

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170 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES convective rain cells. Thus potentially lethal doses from rainout should occur only from large convective rain cells, and this should occur only over relatively small areas (i.e., beneath moving convective cells). How- ever, for any given radioactive air parcel, the overall probability of rainout the first day from a convective cell is quite low for yields greater than 30 kt. Rainout also may occur over large areas associated with frontal sys- tems, but in the case of strategic weapons yields, the radioactivity on small particles must diffuse downward from levels that are often above the top of the precipitation system to produce rainout. As a result, ra- diological doses from debris in precipitation would be substantially lower than early-time doses associated with local fallout. In either case (frontal or convective rainout), for a large-scale multi-burst exchange, the size of the expected lethal-dose rainout areas should typically be small (i.e., well within the range of modeling uncertainty) compared to the size of the fallout areas created by particles with large settling velocities. Thus, to first order rainout areas can be ignored in calculating the radiological hazard from a large-scale nuclear war scenario. However, for lower yield (~30 kt) tactical war scenarios, or for scenarios at specific locations, rainout could lead to important and dominant radiological effects. Single-Weapon Fallout Model For this work the KDFOC2 computer model (Harvey and Serduke, 1979) was used to calculate fallout fields for single bursts, which in turn were used to develop a semiquantitative model for preparing rough esti- mates of fallout areas for typical strategic weapons. A wind profile (in- cluding shear) characteristic of midcontinental Nor~em Hemisphere summer conditions was selected from observations, and baseline fallout calcula- tions were performed for several explosion yields under the assumption that all-fission weapons were used. As an example of the results, a 1-Mt fallout pattern is shown in Figure 1. Figure 2 gives the area versus min- imum dose relationship for several different yields. Fallout areas are shown rather than maximum downwind extents for various doses since areas are less sensitive to variations in wind direction and speed shears and should be more useful for analysis. These areas correspond to unshielded doses associated with external gamma-ray emissions. All of the local fallout estimates given below are based on the KDFOC2 model and the wind pattern used for Figure 1. To convert from areas for the 48-hour curves shown in Figure 2 to areas for minimum doses over longer times, an area multiplication factor, AMP, is given in Figure 3. For example, if the 2-week, 300-rad area is needed, first the 48-hour, 300-rad area is found from Figure 2 and then the ap

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RADIOACTIVE FALLOUT it;) {/J ~ :~300-~- ~100 reds of\ ~ ~ 3000 1 0,000 50 km 171 FIGURE 1 48-hour dose predictions for a 1-Mt all-fission weapon detonated at the surface. A m~dcontinental Northern Hemisphere summer wind profile was used. The double-lobed pattern is due to a strong directional wind shear that is typical during this season. For a 1-Mt weapon, the lofting of radioactivity is so high that topographic features are not expected to play a large role in pattern development; thus, a flat surface has been used. The protection factor is 1. The local terrain is assumed to be a rolling grassy plain. Source: Pihock et al. (1985, p. 2424. Repnnted with permission from the Scientific Committee on Problems of the Environment (SCOPE). propriate AMP is read from Figure 3. The 2-week, 300-rad area is the product of the 300-rad, 48-hour area and the 2-week, 300-rad AMP. For example, a 1-Mt, all-fission weapon, has a 2-week, 300-rad area of ~2,000 km2 x 1.30 ~ 2,600 km2. There are two scaling laws that allow weapons design and various sheltering to be factored into dose calculations. The first scaling law permits consideration of weapons that are not all fission. Most large-yield weapons (~100 kt) are combined fission-fusion explosives with approx- imately equal amounts of fusion and fission (Fetter and Tsipis, 19811. The fission fraction (p) is the ratio fission yield P= ~ total yield

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172 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES 1 0,000 ,= 1 000 - CC ~ 100 oo i . _ - \\\\/ 11111! 111111111 lilllI_ ,5 Mt r3 Mt 300 kt :\>~\\\\\\\~1 It 200 kt ~ - 100 kt: 1 1 1111111 1 1 1111111 1 1 1111111 1 1 11 301 OCR for page 167
RADIOACTIVE FALLOUT 173 activity becomes a significant factor. For such cases, careful consideration of surrounding materials may be necessary to produce accurate fallout estimates. The second scaling law accounts for protection factors (K) against ion- izing radiation that would be provided by sheltering. The 48-hour mini- mum dose areas given in Figure 2 are appropriate for a person or other organism located on a rolling grassy plain. In other configurations, ra- diation exposure varies according to how much shielding is obtained while a person remains in the area. For example, a person leading a normal life- style is likely to achieve an average K of 2 to 3 for gamma radiation from time spent inside buildings and other structures. Basements can provide K values of 10 to 20. Specially constructed shelters can provide K values of 10 to 10,000 (Glasstone and Dolan, 1977~. To determine the radiation area for a dose of D when shielding with a protection factor K is available, the scaled dose KD from Figure 2 should be used. For example, for those in an undamaged basement win K = 10 for the first 48 hours, Figure 2 indicates that the effective dose area of 450 reds or more from a 1-Mt, all-fission weapon is about 130 km2. This is obtained by using a scaled dose of 4,500 reds. For comparison, the 2.3 o 2.0 o ._ Cal - Q - 1.5 3 Hi: 1.0 1 1 1 1~1111 1 1 1 111111 ' 1 ~ 1 00 reds 300 ~ \ 1 000 At/\ /~/~ ~ 2 weeks 410,000 - . I I I Illlli I ,l'l,,,ll ,, Illl,,l I, I,lllil I, I Illll 1o6 10 100 1000 104 105 Hours FIGURE 3 Area multiplication factors to extend the dose integration time from 48 hours to longer times. These factors must be used in conjunction with the areas given in Figure 2. Source: Pittock et al. (1985, p. 244). Reprinted with permission from the Scientific Committee on Problems of the Environment (SCOPE).

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174 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES 450-rad minimum dose area is about 1,300 k=2 for people with no shelter, greater by a factor of 10 than the area for those with a K of 10. Other factors that could reduce the effects of fallout on the population over long time periods ('1 month) include weathering (runoff and soil penetration), cleanup measures, relocation, and the ability of the body to repair itself when the dose is spread over time or occurs at lower rates. These considerations can be taken into account with existing computer models but are not treated here. Several factors that could enhance the effects of fallout are mentioned below. Dose Estimation from Multiple Explosions In a major nuclear exchange, thousands of nuclear warheads could be detonated. For such an exchange, realistic wind patterns and targeting scenarios could cause individual weapon fallout patterns to overlap in complicated ways that are difficult to predict and calculate. Even though acute doses are additive, a single-dose pattern calculated for a weapon cannot be used directly to add up doses in a multiweapon scenario, except under limited conditions. For example, if the wind speed and direction are not approximately the same for the detonation of each weapon, then different patterns should be used. In addition, the number of possible fallout scenarios far exceeds the number of targeting scenarios. This is because, for each targeting scenario that exists, the possible meteorological situations are numerous, complex, and varying. Thus, only under limited conditions may a single dose pattern be moved around a dose accumulation grid to obtain the sum of total doses from many weapons. Two relatively simple multiburst models can be developed for use in conjunction with the semiquantitative model presented here. These cases can provide rough estimates of fallout areas from multiple weapons scen- arios; however, their results have an uncertainty of no better than a factor of several, for reasons explained below, and are neither upper nor lower case limits. The no-overlap (NO) case is considered first; this could occur when targets are dispersed, there is one warhead per target and the fallout areas essentially do not overlap. Second, the total-overlap (TO) case is examined where multiple bursts are assumed to be at the same burst location. This approximation would arise when targets are densely packed and warheads of the same size are used against each. A large number of warheads used against, say, a hardened missile field site would be more closely modeled by the TO model than the NO model. As an example of the use of the NO and TO approximations, a case with 100 1-Mt, 50 percent fission, surface-detonated explosions is con- sidered, and estimates are developed for the 450-rad, 48-hour dose areas

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RADIOACTIVE FALLOUT 175 for both cases. For the NO case the fallout area can be obtained by determining the area for a single 1-Mt weapon (900-rad scaled dose from Figure 2) and multiplying by 100. This gives 7.2 x 104 km2 for the 450- rad, 48-hour dose contour. For the TO model, the area is obtained for a single 1-Mt weapon, 9-red scaled dose from Figure 2. One hundred of these, laid on top of each other, would give 450 reds for 50 percent fission weapons. The area in this case is 3.3 x 104 km2. These results differ by about a factor of two, with the NO case giving a larger area. Although these models are extremes in terms of fallout patter, overlap, neither can be taken as a bounding calculation of the extremes in fallout areas for specified doses. It is very possible that a more realistic calculation of overlap would produce a greater area for 100 weapons than either of these models. Such a result is demonstrated by a more sophisticated model prediction that explicitly takes overlap into account (Harvey, 1982~. In this study, a scenario was developed for a severe case of fallout in a countervalue attack on the United States where population centers were targeted with surface bursts. Figure 4 shows the contours of a 500-rad minimum 1-week dose where overlap was considered. The 500-rad area , , 4[ (Oo ~ ~''_ _ G. lo or to ~T fox 0 ~3 0~_~:- - He 1;,) at:' .. _' _ r \ ~~ \0' , ~ ~ ~ , I, 1 1 1 , I I ~ FIGURE 4 A fallout assessment that explicitly takes fallout pattern overlap into account. Shown are SOO-rad, 1-week minimum isodose contours. This scenario was intended to emphasize population dose. Approximately 1,000 population centers in the United States were targeted, each with a 1-Mt, 50 percent fission weapon. The assumed winds were westerly with small vertical shear and were nearly constant over the continent (taken from Harvey, 19821. Reprinted with permission from Lawrence Livermore National Laboratory.

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176 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES is about three times greater than that predicted by the NO model and six times that of the TO model. Note also that the distribution of radioactivity is extremely uneven. About 20 percent of the United States is covered with 500-rad contours, including nearly 100 percent of the northeast, approximately 50 percent of the area east of the Mississippi River, 10 percent of the area west of the Mississippi River, and only a few percent of the area in the Great Plains. Results of these scenarios, as well as those postulated by others, clearly show that such estimates are very scenario dependent and that detailed estimates should be made with care. For example, the regional results shown in Figure 4 could be significantly different if military targets (e.g., intercontinental ballistic missile [ICBM] silos) were included as well. Although the NO and TO cases presented in this paper are simple to apply, they must be used only to develop rough estimates of total area coverage within regions with relatively uniformly dispersed targets. When the den- sity of targets of one area is as large as that in the northeastern United States and another is as dispersed as that in the western United States, regional models should be used to develop specific regional estimates. Even then, multiple-weapon fallout estimates should be considered to have uncertainties no smaller than a factor of several, with the uncertainty factor increasing as the model sophistication decreases. Sample Calculation of Multiple-Weapon Fallout To illustrate the fallout prediction method presented here, an escalating nuclear exchange scenario, which is consistent with that described in the SCOPE-ENUWAR study (Pittock et al., 1985), is used to estimate fallout areas. In this scenario there are four sequential phases of attack against five different regions. The five regions are Europe (both east and west), western USSR (west of the Ural Mountains), eastern USSR, the western United States (west of 96 W latitude), and the eastern United States. The four phases of attack are initial counterforce, extended counterforce, in- dustrial countervalue, and a final phase of mixed military and countervalue targeting. The weapon yields and the number of warheads that are em- ployed for just the surface bursts during each phase are shown in Table 1. Airbursts are omitted since they do not produce appreciable local fallout. In the first phase, land-based ICBMs are the primary targets. These are assumed to be located in the western United States and the USSR at sites containing 125 to 275 missiles. The geographical distribution of missile silos in the USSR is assumed to be 50 percent east and 50 percent west of the Ural Mountains. Each missile silo is attacked with a surface-burst and an airburst weapon. For a given site, the TO model is used to calculate

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RADIOACTIVE FALLOUT TABLE 1 Surface-Burst Warheads in a Phased Nuclear Exchangea 177 Number of Warheads WeaponInitial ExtendedIndustrial YieldCounterforce CounterforceCountervalue Full Baseline (Mt)Phase PhasePhaseFinal PhaseExchange 0.050 3000250550 0.1975 1505081,183 0.20 25050121421 0.3500 2500125875 0.51,000 2000251,225 1.0250 4951601251,030 5.00 5015873 Total surface burst yield ~ 1 ,000 ~ 1 ,000~250~250~2,500 aAll weapons are assumed to have 50 percent fission yield. the fallout pattern. All U.S. ICBM sites are attacked with 0.5-Mt weapons. Each of five U.S. ICBM complexes is presumed to have 200 missile silos, while each of six USSR complexes is presumed to have between 125 and 275 missile silos, with a total of 1,300. The Soviet sites are attacked with 1-, 0.3-, and 0.1-Mt weapons. During this phase, each side employs a total of about 1,000 Mt. Besides the attack on Soviet missile silos, 425 0.1-Mt weapons are assumed to be surface-burst against other Soviet military targets, with approximately 28 Mt west of the Urals and 14 Mt to the east. The 425 fallout patterns from these weapons have been modeled with the NO model. In the second phase of the attack, there are an additional 1,000 Mt of surface-burst weapons employed. These are employed against each region with 20, 40, and 40 percent of the weapons being used against targets in Europe, the United States and the USSR, respectively. Here, Europe includes both the North Atlantic Treaty Organization (NATO) and Warsaw Pact countries. To roughly account for population distribution, the weap- ons employed against the United States are divided up as two-thirds in the eastern U.S. and one-third in the western United States; for Soviet targets it is assumed that two-thirds are detonated west of and one-third are detonated east of the Ural Mountains. For all the weapons employed in the second, third, and fourth phases, the fallout pattern is calculated using the NO model. The results, in terms of percent of land covered by at least a 450-rad, 48-hour dose, are shown

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194 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES Local Fallout For dose estimates from local fallout, two time frames are considered- the short term, where there is acute and potentially lethal radiation, and the long term, when chronic doses become important. In the short term, the gamma radiation is the main hazard. Later, specific radionuclides become important concerns for doses via food pathways. For doses received within the first 48 hours, the nuclear weapon gamma radiation pathway for a high-yield (A 1-Mt) warhead dominates the fuel- cycle gamma radioactivity, even if one assumes a worst case assumption in which all the radioactivity from the attacked nuclear fuel cycle facility is lofted with the weapon products. For lower yields and thermonuclear weapons, the core gamma radiation becomes more important and could be potentially greater than the dose from the nuclear weapons, even at very early times. However, since there are now only approximately 100 nuclear power plants available for targeting in the United States and pos- sibly a few hundred shipboard reactor targets which are dispersed over the globe (Ambio Advisors, 1982), and because there are typically more than 1,000 other U.S. targets in major nuclear-exchange scenarios, the impact of fuel cycle radiation to the total U.S. 48-hour external gamma- ray dose would likely be less than 10 percent. In the long term, the radioactivity from the core and spent-fuel ponds could be a dominant effect, both around the reactor and at substantial distances downwind. After about 1 year, the products from the nuclear fuel cycle could make a substantial contribution to the total gamma-ray dose fallout patterns over the United States. Certainly, if released, fallout gamma radiation from a large reactor would dominate the dose of a 1-Mt weapon over the long term (see Figure 81. In terms of radiological effects, individual radionuclides (e.g., 90Sr) become more important over the longer time frame than the whole-body gamma radiation. Assuming 50 percent fission weapons, it is possible to have more 90Sr in a single reactor and its spent-fuel pond than that produced in a 1,000-Mt attack. Most of the 90Sr is in the spent-fuel pond and thus could be more easily lofted as fallout than the 90Sr in the heavily shielded reactor core. Accordingly, in the long term, the fuel cycle 90Sr contribution can dominate over the weapon contribution. For example, Chester and Chester (1976) calculated levels of 90Sr much higher than the current maximum permissible concentration (MPC) over much of the U.S. farm- land 1 year after an attack on the projected nuclear power industry of the year 2000. Scaling down their results to an attack on a 100-MW(e) nuclear power industry, they calculated that about 60 percent of the U.S. grain- growing capacity would be in areas that exceed current 90Sr MPC levels.

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RADIOACTIVE FALLOUT 195 B A 100 km ~ 1 FIGURE 8 Contours of 100-rad fallout dose during 1 year's exposure, starting 1 month after the detonation of a 1-Mt bomb (A) and a 1-Mt bomb on a 1-GW(e) nuclear reactor (B). Source: Rotblat (1981~. Reprinted with permission from the Stockholm International Peace Research Institute (SIPRI). Global Fallout In calculation of the potential global fallout, assumptions have been made that facilitated calculations and allowed estimation of expected dose. For example, it was assumed that each nuclear facility would be surface targeted by a high-yield, accurately delivered warhead that would com- pletely pulverize and vaporize all of the nuclear materials and that these materials would then follow the same pathways as the weapon materials (a worst-case assumption). It was assumed further that the major nuclear facilities in a 100-GW(e) civilian nuclear power industry would also be attacked. The results should be viewed as providing estimates that ap- proach maximum global fallout for an attack on a commercial nuclear power industry of 100 GW(e). Higher estimates would be obtained, how- ever, using the same assumptions by including military nuclear facilities and a larger civilian industry. This hypothetical reactor attack scenario assumed that, as part of the 5,300-Mt exchange of Knox (1983), some of the warheads would be targeted on nuclear power facilities. Specifically O.9-Mt weapons would be surface burst on 100 light water reactors, 100 10-year spent-fuel storage (SFS) facilities, and one fuel reprocessing plant (FRP). With a O.9-Mt surface burst on each facility, 2 percent of the radioactive fission products would be injected into the troposphere and 48 percent into the stratosphere. The remaining activity (50 percent) would contribute to local fallout. Such large yields were assumed because of the hardness of the nuclear reactor. If smaller-yield weapons were used to target the nuclear facilities, the relative injections of radioactivity into the troposphere would be much greater. While the weapons radioactivity would result in higher doses on

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RADIOACTIVE FALLOUT 197 the ground, this would not be true for the nuclear facility radioactivity. This is because of the relatively slow decay of the facilities' radioactivity. Hence, a faster deposition time would not significantly affect the 50-year dose. The patterns and local concentrations of fallout deposition would, however, be affected. Using GLODEP2 and a Northern Hemisphere winter scenario, the re- sulting unsheltered, unweathered doses are shown in Table 8. The largest value of 95 reds for the total of weapons plus the nuclear power industry occurred in the 30-50N latitude band. The doses obtained for the Southern Hemisphere were about a factor of 30 smaller than in the Northern Hemi- sphere. The majority of the dose contributions came from the spent-fuel storage facilities and the high level waste in the reprocessing plant. Figure 9 is a plot of accumulated dose in the 30-50N latitude band as a function of time to 50 years (200 quarter years) for the 5,300-Mt scenario (Northern Hemisphere winter injection) with and without the targeting of nuclear power facilities. The bulk of the dose from the weapons alone for this scenario resulted from deposition in the first year. The relative con- tributions of the nuclear facilities were minimal in the first year, but 4,, 1 000.0 - in a ~5 100.0 ~5 a Q o 10.0 1.0 - <` 0. 1 1 ' 1 ' 1 ' 1 1 1 1 ' 1 ' A2 A1 -Scenario A1 - 5300 Mt baseline scenario Scenario A2 - - Same as 1 plus targeting of nuclear facilities 1,1, 1 1, 1 -1 2 4 6 10 2 4 6 100 24 Time in quarter years FIGURE 9 Accumulated dose at 30-50N versus time scenario A, with (A2) and without (Al) an attack on nuclear facilities. Source: Pittock et al. (1985, p. 273~. Reprinted with permission from the Scientific Committee on Problems of the Environment (SCOPE).

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98 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES became larger with time. At 50 years, the contribution of the nuclear facilities would be approximately double that of the weapons alone. In addition, while the weapons-only curve at 50 years is almost flat, the nuclear facilities curve has a positive slope with the radioactivity contin- uing to directly affect future generations. An attack on all of the world's civilian nuclear fuel cycle facilities (approximately 300 GW[e]) would scale the above results up by about a factor of 3, although this scenario is even less likely. The potential effect is growing in time; the world's nuclear capacity has been projected to grow to 500 GW(e) by 1995. A significant contribution could also come from the targeting of military nuclear facilities, with results qualitatively similar to those obtained from attacks on power plants. In summary, using some worst-case assumptions for a speculative nu- clear war scenario wherein 100 GW(e) of the nuclear power industry is included in the target list, the 50-year global fallout dose is estimated to increase by a factor of 3 over similar estimates wherein nuclear power facilities are not attacked. If one adds the internal doses necessarily accompanying the external doses (perhaps doubling or tripling the latter) and considers that localized hotspots can be formed with up to 10 times the average dose, it seems that moderate to heavy attacks on civilian and military nuclear facilities could result in significant long-term radiological problems for humans and ecosystems. Many of these problems involving the radiological assess- ments associated with nuclear facilities are unresolved and uncertain but deserve more thorough attention. APPENDIX: THE IMPACT OF FALLOUT ON HUMANS In the main body of this paper the focus was an estimation of unprotected doses due to fallout. The focus of the SCOPE-ENUWAR fallout calcu- lations (Pittock et al., 1985) was on assessing the impact on nonhuman biota; direct effects on humans was specifically excluded. Hence, the calculations made were predictions of the unprotected dose, and it is these that have been reported on earlier in this paper. Here, we are more con- cerned with direct effects of fallout on humans. Consequently, this ap- pendix extends our previous discussion of unprotected doses to focus on the latter subject. We begin with a short discussion about the impact of global fallout on humans. The remainder of this appendix discusses the more serious impact of local fallout. Giabal Fallout As we have reported above, our GLODEP2 calculations for strategic nuclear exchanges of about 5,000 to 6,000 Mt predict that the 50-year

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RADIOACTIVE FALLOUT 199 unsheltered, unweathered, external total body gamma-ray dose levels av- erage about 15 reds in the Northern Hemisphere and about 0.5 reds in the Southern Hemisphere. The maximum longitude-averaged dose of 30 to 40 reds appears in the 30 to 50N latitude band. Values predicted for the global population (chronic) dose are typically about 6 x 10~ person- rads. The dose in rainout hotspots, obtained by using 10 latitude and longitude areas, are a factor of 6 to ~ higher than the Northern Hemisphere averages, or 90 to 120 reds, respectively. These results have an estimated confidence level of a factor of 2. From 50 to 75 percent of the global fallout dose is due to tropospheric injections of radionuclides that are deposited in the first month. Additional calculations, utilizing GRANTOUR and assuming a per- turbed nuclear winter atmosphere, indicate that the above dose assessments would be about 15 percent lower in the Northern Hemisphere and mar- ginally higher (to approximately 1 red) in the Southern Hemisphere than in an unperturbed atmosphere. These calculations have been presented at a number of scientific meet- ings, including the ICSU-SCOPE workshop on radiation held in Paris, October 1984. There, internationally known radiation experts carefully reviewed this work, which subsequently became the basis of the chapter on radioactivity in the SCOPE-ENUWAR report (Pittock et al., 1985~. For radiation exposure that is protracted in time, biological repair of the resulting damage is significant in mitigating the effects. Dose effec- tiveness factors from 0.1 to 0.5 for chronic exposures have been suggested (National Council on Radiological Protection Report 64, 1980~. This means that a large chronic dose will have an effect equivalent to a much smaller acute dose. This phenomenon has particular relevance here in assessing the impact of global fallout, which is chronic, low-dose-rate irradiation received over many decades. The effects of the above levels of global fallout, even including the hotspots referred to earlier,were summarized in the Report of the Paris Commission on Radiological Dose Assessments and Biological Effects (SCOPE-ENUWAR Newsletter, 19841. It concluded that "the long-term increase in genetic and carcinogenic effects on humans from global fallout is of the order of 1% of the natural incidence and should be considered a second order effect." No mention was made of prodromal effects on humans because at these lifetime (50 years) dose levels, and assuming biological repair mechanisms, prodromal effects would not be observed. This result is far from that pictured in the On the Beach syndrome. Local Fallout As we have seen, projections of the intensity and extent of local fallout are highly sensitive to a number of variables, which helps explain why

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200 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES many assessments have produced widely different results. Uncertainties in these projections can be divided into three categories: those due to the targeting scenario, the fallout calculations model, and the selected me- teorological conditions. The targeting scenario contains variables such as the number of weapons and their yield mix, fission fractions, heights of burst, and precise target locations. The height of burst (MOB) is of particular significance because airbursts do not produce significant local fallout, except for rainout of debris from tactical yield weapons. Only when the fireball interacts with the ground (a ground or near-ground burst) does significant local fallout ensue. A widely used and reasonable assumption is that hardened military targets are targeted with ground bursts. For the softer industrial and other military targets, maximum damage is accomplished by airbursts where the HOB can be optimized. The fires hypothesized in urban areas in nuclear winter studies are assumed to be initiated by airbursts since ground bursts are not efficient in initiating large fires. Uncertainties in dose calculations in the best fallout models originate from several sources. These include limited experimental data, whether the modeled radioactivity is rigorously conserved, whether time of arrival is properly accounted for, and other inaccuracies of the model. Assumptions about selected meteorology (e.g., wind velocities, shears, precipitation patterns) affect the results. Hence, local fallout assessments can vary greatly, depending on these many as- sumptions. For assessing the impact of local fallout on humans, additional factors must be considered. By far the most sensitive of these is the protection factor afforded by homes, buildings, basements, and other shelters. These structures can dramatically mitigate the unprotected dose assessments nor- mally cited and used previously in this paper. In Table 9, structure pro- tection factors from fallout gamma rays are listed. An additional important consideration for humans is the assumption of what are the lethal acute external whole-body dose levels (50 percent lethal dose [LDso] values from 220 to 600 reds of external gamma radiation have been reported). Finally, for local fallout delivered over days and weeks, biological repair will reduce the damage from the dose by a sig- nif~cant factor, vis-a-vis an instantaneously delivered dose by a significant amount. Our calculations of the total fatalities produced by large-scale attacks on the continental United States have produced estimates of fallout fatal- ities (after subtracting those already killed by blast and thermal effects) that range over almost 2 orders of magnitude. This large variation in fallout fatalities is well understood in terms of variations in the parameters discussed above.

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RADIOACTIVE FALLOUT TABLE 9 Fallout Gamma-Ray Dose Protection Factors for Various Structures Structure Protection Factor Three feet underground Frame house Basement Multistory building (apartment-type) Upper stones Lower stones Concrete blockhouse shelter 9-inch (23-cm) walls 12-inch (30-cm) walls 24-inch (61-cm) walls Shelter, partly above grade With 2-feet (61-cm) earth cover With 3-feet (91-cm) earth cover 5,000 2-3 10-20 100 10 10-150 30-1,000 500-10,000 50-200 200-1 ,000 SOURCE: Glasstone and Dolan (1977). 201 In one study, fallout fatalities resulting from a massive countervalue attack of 1,000 Mt against U.S. urban population centers was estimated (Harvey, 1982~. The scenario contained 1,000 surface-burst warheads each of 1 Mt. 50 percent fission yield. This population-destroying scenario was not purported to be realistic; rather, it was part of a parameter study to estimate the effects of evacuation and/or sheltering on fatality estimates. In this study, we used realistic overlap of fallout from multiple weapon bursts, the U.S. Census Bureau population distribution, and a probability of death from fallout with 500 reds received in 1 week with no sheltering. The total number of fatalities was estimated at about 160 million, of which 16 million were attributed to fallout. This study illustrated the great sen- sitivity of fallout fatalities to the choice of parameters. Physicians are more concerned with nonfatal injuries. Radiation effects become apparent in humans with acute doses greater than about 100 reds. We can estimate the extent of the areas that are covered with a minimum dose by referring to Figure 2. The slope of the 48-hour dose versus area curves for strategic-sized weapons yield are approximately -1, meaning that the minimum dose area contours are inversely proportional to the 48- hour dose. As an example, the SCOPE-ENUWAR study reported that about 7 percent of the land masses of the United States, the USSR, and Europe would receive a minimum of 450 reds within 48 hours. The figure for the continental United States was about 8 percent. This result assumed no shielding and applied to an unsheltered population. Our inverse ap- proximation would then project that the area covered by a minimum dose

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202 PHYSICAL EFFECTS AND ENVIRONMENTAL CONSEQUENCES of 100 reds would be 4.5 times larger, or 36 percent of the total land area of the contiguous United States. However, minimum dose contours over land areas do not relate in a simple manner to human exposure. Here, both protection factor disai- butions and population distributions must be considered to make a proper assessment. In summary, global fallout is not expected to result in prodromal symp- toms from radiation exposure because of both the magnitude of exposures and the chronic (long-term) exposure rate. Global fallout would result in a small statistical increase, of the order of 1 or 2 percent, above the current incidence of cancers and genetic mutations in the decades following the occurrence of a nuclear war. Local fallout can produce significant numbers of injuries and fatalities from radiation exposure, but numerical estimates are highly uncertain and are very sensitive to the assumptions made to obtain these estimates. Attempts to make these assessments as realistic as possible by including credible population distributions (relocated andJor sheltered) should be made. Superficial attempts at reality will yield an artificially large spread in the results. ACKNOWLEDGMENTS This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. REFERENCES Ambio Advisors. 1982. Reference scenario: How a nuclear war might be fought. Ambio 11 :94-99. Chester, C. V., and R. O. Chester. 1976. Civil defense implications of the U.S. nuclear power industry during a large nuclear war in the year 2000. Nuclear Technol. 31:326- 338. Defense Civil Preparedness Agency (DCPA). 1973. Response to DCPA questions on fallout. DCPA Research Report No. 20, November 1973. Washington, D.C.: U.S. Defense Civil Preparedness Agency. Edwards, L. L., T. F. Harvey, and K. R. Peterson. 1984. GLODEP2: A computer model for estimating gamma dose due to worldwide fallout of radioactive debris. Report UCID- 20033. Livermore, Calif.: Lawrence Livermore National Laboratory. Fetter, S. A., end K. Tsipis. 1981. Catastrophic release ofradioactivity. Sci. Amer. 244(4): 41. Glasstone, S., and P. Dolan. 1977. The Effects of Nuclear Weapons. Washington, D.C.: U.S. Department of Defense and U.S. Energy Research and Development Administra- tion. Harvey, T. F. 1982. Influence of civil defense on strategic countervalue fatalities. Report UCID-19370. Livermore, Calif.: Lawrence Livermore National Laboratory. Harvey, T. F., and F. J. D. Serduke. 1979. Fallout model for system studies. Report

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