Radiation Source Use and Replacement Abbreviated Version (2008) / Chapter Skim
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2 RADIATION SOURCES IN THE UNITED STATES AND THEIR USES AND ORIGINS
2 RADIATION SOURCES IN THE UNITED STATES AND THEIR USES AND ORIGINS
Pages 23-42
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From page 23... ...
is also important. Before examining each important radionuclide and the major radiation source devices, it is useful to understand the disposition or disposal paths available for these sources.
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As a practical matter for disposal, however, there are also waste acceptance criteria at the disposal sites and these criteria preclude some high-activity sources because of worker exposure limits. DOE has disposal facilities for and regulatory authority over its own radioactive waste.
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TABLE 2-1 Summary of Radionuclides in Category 1 and 2 Radiation Sources in the United Statesa Typical Total Activity Physical Radioactive Specific in U.S. Typical or Emissions Activity Inventory Major Activity Chemical Radionuclide Half-life and Energies (TBq/g)
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Cobalt-60 undergoes beta decay (emits an electron and a neutrino) and emits two gamma rays with each decay; one at 1.173 MeV and one at 1.333 MeV.6 Cobalt-60 sources are produced as high-specific-activity sources for teletherapy and industrial radiography and industrial sources for irradiators and other applications.
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From page 27... ...
It is supplied as cesium chloride, a crystalline salt (it is chemically and structurally related to table salt, sodium chloride) that can be made in a range of particle sizes, from centimeter-scale blocks to powder, as is used in the manufacture of radioactive cesium chloride sources.
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Cesium chloride is soluble in water at room temperature and so, if it is intentionally or accidentally removed from its container, it can readily be dispersed. If a leak in the stainless steel container were to occur, the cesium chloride could dissolve in water and contaminate the nearby environment, as happened in the water tank of a panoramic irradiator facility used for sterilizing medical devices in Decatur, Georgia, in 1988 when a radioactive cesium chloride source containment failed due to thermal cycling and stress corrosion cracking (Setser, 1990; see Chapter 3 for a description of this incident)
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From page 29... ...
Irrespective of the method of forming pollucite powders, they could be pelletized by warm pressing prior to sealing in stainless steel capsules. Production of cesium-137 pollucite at a facility that currently makes cesium chloride radiation sources would require establishment of a new process line, although the new line might be able to use some of the preexisting equipment.
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Iridium-192 radiation sources are made by irradiating natural iridium in a nuclear reactor. The iridium-191 can capture a neutron to create iridium-192, which has a 73.83-day half-life and has a 95 percent probability of decaying by beta decay to platinum-192 and emitting gamma rays and a 5 percent probability of decaying by electron capture to form osmium-192.
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Once supplied by the DOE Isotopes Program (separated from plutonium at Los Alamos National Laboratory) , americium-241 is now only produced by the Russian radionuclide production facility at the PA Mayak.
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, a factor of nearly 300 million lower than the concentration in a typical radiation source. The only current disposition path for these sources is through the OSRP, which stores them pending approval to dispose of them.
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. Selenium-75 decays by electron capture with a halflife of 119.8 days to stable arsenic-75, emitting an average of 1.75 gamma rays with an average energy of 215 keV each, and a peak energy of 800 keV.
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USES OF CATEGORY 1 AND 2 RADIATION SOURCES IN THE UNITED STATES The major applications for the high-activity sources include large panoramic irradiators for bulk sterilization, self-shielded irradiators for research and blood irradiation, teletherapy and Gamma Knife® machines for cancer therapy, RTGs, radiography cameras, and well logging tools. Each of these device applications is described briefly below.
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There are 1,341 self-contained irradiators that use radionuclide radiation sources in the United States, approximately 85 percent of which use cesium-137, while nearly all of the remaining devices use cobalt-60 (U.S.
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The major manufacturers and distributors for industrial radiography devices include QSA Global, Industrial Nuclear, Source Production and Equipment Company, Agiris, and CIS-US. However, the actual producers of the radioactive material are MDS Nordion, PA Mayak, and the consortium of European reactors.
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NRC Fiscal Year 2006 Interim Inventory of Radioactive Sources Data Analysis, which reports that there are 28,200 civilian Category 1 radiation sources and 25,532 Category 2 sources licensed by the U.S. NRC and Agreement States in the United States.
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NRC licensees who are licensed to hold Category 1 or 2 radiation sources but had not been surveyed in previous years. Only 10 percent of these actually had Category 1 or 2 sources in their possession when surveyed.
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U.S. NRC actions on the use of radioactive cesium chloride sources in panoramic irradiators, even dry source irradiators, indicate the commission's skepticism about the use of such sources in panoramic irradiators.
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. RADIATION SOURCE PRODUCTION AND DISTRIBUTION One can visualize the international supply chain for radionuclides as a pyramid system.
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At the next level of the pyramid are the manufacturers and distributors that manufacture sealed sources from the radionuclide product (unsealed radiation sources) or repackage encapsulated sources and place them into devices for purchase by licensed users.
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FINDING AND RECOMMENDATION Finding: The radionuclide radiation sources examined in this study are used in applications that are important to the nation's health, safety, and economic strength. High-activity radiation sources are used in the United States and other modern societies in a variety of ways: they are used in devices that improve the success of medical procedures -- ensuring that medical devices and implants are sterile, preventing fatal complications from bone marrow transplants, and providing noninvasive techniques for treating brain lesions; they are used in devices for inspecting the integrity of buildings, bridges, and industrial equipment; and they are used to seek out oil and gas resources deep in the ground.
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