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Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests 1 INTRODUCTION BACKGROUND AND CONTEXT Over 500 atmospheric nuclear-weapons tests were conducted at various sites around the world during 1945–1980 (see Table 1). Five nations—the former Soviet Union, the United Kingdom, France, the People’s Republic of China, and the United States—were responsible for the radioactive debris, some long-lived and some short-lived, that those tests injected into the atmosphere. The debris, generally termed “fallout” because eventually some of it falls to Earth, resulted in increased radiation doses (adding to those occurring naturally) to people living throughout the world. The longer-lived nuclides resulted in essentially permanent changes in the ambient or natural radiation background throughout much of the world, whereas the shorter-lived radionuclides contributed to dose primarily in regions near the test sites. The amount of debris injected into the atmosphere and hence the later fallout associated with a particular test and its geographic distribution were functions of local and test-specific factors—such as height, yield, and material in the vicinity3—and of the meteorologic conditions prevailing at the time of the test (see, e.g., Beck and Bennett, 2002, Carter and Moghissi, 1977). 3 That is, materials vaporized by the bomb or activated by neutron bombardment, such as a metal tower on which the bomb was detonated, or soil vaporized in the blast.
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Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests Table 1. Summary of atmospheric nuclear tests by major site and country (Adapted from Table 2, Volume 1, Annex C, UNSCEAR 2000) Country Test Site Number of Tests Conducted Yield (megatons) Total Yield (megatons) China All 22 21 21 France All 45 10 10 United Kingdom Christmas Island 6 7 8 Others 15 1 United States Nevada 86 1 154 Marshall Islands 69 109 Christmas Island 24 23 Johnston Atoll 12 21 Others 6 0.1 Former USSR Novaya Zemlya 91 239 247 Semipalatinsk 116 7 Others 12 1 Totals 543a 440 aIncludes 22 safety tests of the United States, 12 safety tests of the United Kingdom, and five safety tests of France not listed above. The feasibility study under review did not consider all the weapons tests indicated in Table 1 but was restricted to aboveground tests during 1951–1962, so it embraces only the atmospheric weapons tests conducted by the United States, the former USSR, and the United Kingdom. The authors of the draft report offer as a rationale for that restriction the assertion that “it is generally acknowledged that the most important contributions to the radiation doses arose from atmospheric nuclear tests conducted by the United States, the United Kingdom, and the former USSR during the pre-1962 time period.” To support that statement, they note that “the tests considered in this report that were conducted at the NTS account for over 95% of the total 131I produced during the entire testing period at the NTS (NCI, 1997).” Although the detonation of a nuclear weapon produces more than 900 fission products, only about 165 radionuclides have half-lives long enough to contribute to fallout and thus to constitute a potential threat to human health. The threat arises from exposure of a person to radioactive materials deposited on the ground, termed external or ambient exposure, and through the inhalation or ingestion of radioactive materials, called internal exposure. External exposure to fallout from the NTS tests was evaluated in the feasibility study by estimating the deposition density of some 43 radionuclides throughout the United States and
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Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests applying previous methods (Hicks, 1981; Beck, 1980). For evaluating global fallout from other tests, a similar approach was used for the 18 most important radionuclides (for such global fallout, the shorter-half-life radionuclides are much smaller contributors). The committee considers that approach appropriate for a feasibility study. An NTS-weapons-test fallout study before the one under review showed that more than 95% of the dose stemming from ingested radionuclides is attributable to 22 radionuclides,4 and that inhalation generally contributes little to the dose to the general public (Ng et al., 1990). Accordingly, the draft report has ignored inhalation as an exposure route and for estimates of internal dose from fallout from the NTS tests has focused its attention on the 20 major contributing radionuclides (of those listed in Table 2) for which deposition density estimates were available.5 For global fallout, internal dose estimates were made for the five radionuclides considered to be most important (3H, 14C, 90Sr, 131I, and 137Cs). The committee views those approaches as appropriate for a feasibility study. 4 The counting of radionuclides adopted here differs from that in the feasibility study. For example, in Appendixes E and G of the feasibility study, 239+240Pu is counted as a single radionuclide. 5 Appendix E of the feasibility study is based on an electronic database produced from an earlier draft of Appendix D in which deposition-density estimates for 135I and 239Np were not made. The internal dose estimates include the effects of daughter nuclides produced in the body.
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Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests Table 2. Radionuclides for which deposition densities were calculated for NTS weapons tests (adapted from Table 3.2, and Table 2 of Appendix D, of the draft report) Nuclide Half-life (parent) Sr-89, 90 (Y-90a), 91 52, 10400, 0.4 d Y-91, 91m (=0.65* Sr-91), 93 59, a, 0.4 d Zr-95 (Nb-95a), 97 (Nb-97a) 64, 0.7 d Nb-97m (=0.96* Zr-97) a Mo-99 2.8 d Tc-99, Tc-99m (=0.96*Mo-99) 7.8E7da, Ru-103 (Rh-103ma), 105 (Rh-105ma), Ru-106 (Rh-106a) 39, 0.2, 368 d Rh-105 1.5 d I-131, 132 (=1.03* Te-132), 133, 135 8, a, 0.9, 0.3 d Te-132 3.3 d Cs-136, 137 13, 11000 d Ba-140 13 d La-140 1.7 d Ce-141, 143, 144 (Pr-144a) 32.5, 1.4, 284 d Pr-143 14 d Nd-147 11 d Pm-147 956 d Np-239 2.36 d Pu-239, 240, 241 24131, 6569, 14.4 y Am-241 430 y aIn equilibrium with parent
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Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests THE CONGRESSIONALLY REQUESTED FEASIBILITY STUDY As public awareness and concern mounted over the possible health hazards associated with exposure to the fallout from weapons testing, studies were initiated to assess the extent of the hazard. The studies failed to allay public concern, and further studies were begun in the 1980s to reevaluate the radiation exposures of the population after the weapons tests in Nevada. In 1983, Public Law 97–414, Section 7(a) directed the secretary of health and human services to conduct research into, and develop estimates of, the thyroid doses received by the American people from 131I in fallout from the Nevada atmospheric tests. To that end, in 1983 the National Cancer Institute (NCI) established a task group to assist it in a program of technical and scientific work. The work of the task group, which extended for more than a decade, was centered on 131I and the fallout arising from the weapons tests conducted by the United States. Its findings appeared in 1997 as an NCI report titled Estimated Exposures and Thyroid Doses Received by the American People from Iodine-131 in Fallout Following Nevada Atmospheric Nuclear Bomb Tests (NCI, 1997). That publication did not address the risks associated with other radionuclides found in fallout or the contribution to exposures of global fallout stemming from weapons testing outside the US by the US and other nations, and these omissions became a matter of public concern. In 1998, the Senate Appropriations Committee asked the Department of Health and Human Services to assess the feasibility and public-health implications of a detailed study concerning the health consequences for the American people of radioactive fallout from nuclear-weapons tests. The request resulted in a collaborative effort involving staff at the Centers for Disease Control and Prevention (CDC) and NCI to Locate documents related to nuclear-weapons fallout Develop preliminary dose and risk estimates for the population Review the epidemiologic literature Review and outline communication strategies. The feasibility study reviewed here summarizes the findings of that collaborative effort and sets out a series of options related to future work. THE NATIONAL RESEARCH COUNCIL’S INVOLVEMENT On March 27, 2002, the National Research Council was asked by the Centers for Disease Control and Prevention (CDC) to review the CDC-NCI draft of A Feasibility Study of the Health Consequences to the American Population from Nuclear Weapons Tests Conducted by the United States and Other Nations. Specifically, CDC sought a review of all technical aspects of the draft, including answers to the following questions:" Are the methods and sources of information used in the technical report to estimate radiation doses and health effects from fallout appropriate for this study?
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Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests Are the methods and results clearly presented in the main text of the Technical Report? Are the findings presented in the report supported by the data and analyses provided? Do the Options for Future Work presented in Chapter 6 represent an appropriate range of options for public-health activities that could be pursued as a result of this study?” To that end, the National Research Council formed a committee, the Committee to Review the CDC-NCI Feasibility Study of the Health Consequences from Nuclear Weapons Tests, consisting of members of its Committee on An Assessment of the Centers for Disease Control and Prevention Radiation Studies from DOE Contractor Sites and other experts. The committee constituted to review the CDC-NCI draft report has expertise in health physics and dose assessment (pertaining to both external radiation and internal emitters), radiation chemistry, radiobiology, nuclear medicine, ethics, risk communication, epidemiology, biostatistics, modeling, and risk assessment. The review began in April 2002, and the goal was to produce a consensus report by January 30, 2003. The present report contains the results of the review of the CDC-NCI draft report. At the initial meeting of the new National Research Council committee in Washington, DC, on April 26–27, 2002, representatives of CDC (James Smith and Charles Miller) and of NCI (André Bouville, Steve Simon, and Ethel Gilbert) were present. They enlarged on the draft and the methods used in arriving at the conclusions set forth in it, and they responded to questions raised by the committee. Lynn Anspaugh and Harold Beck, consultants for the feasibility study, were also present to address committee questions related to dose reconstruction. The review committee met again in Washington on July 15–16 in closed sessions to begin the drafting of its findings and recommendations. Two further meetings were held: in Des Moines, Iowa, on September 12–13, 2002, and in Washington on November 14–15, 2002. The first of those two meetings involved further fact-finding and was open to the public; the second was closed and involved preparation of the final report. Information obtained from the public and outside experts was used in the committee’s deliberations and is woven into the report.
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