Radiological Conditions at Bikini Atoll: Prospects for Resettlement Radiological Conditions at the Semipalatinsk Test Site, Kazakhstan: Preliminary assessment and recommendations for further study

Autor: Dennis Woodhead
Rok vydání: 1999
Předmět:
Zdroj: Journal of Radiological Protection. 19:386-387
ISSN: 1361-6498
0952-4746
DOI: 10.1088/0952-4746/19/4/701
Popis: Radiological Conditions at the Semipalatinsk Test Site, Kazakhstan: Preliminary assessment and recommendations for further study Radiological Assessment Reports Series 1998 (Vienna: IAEA) 43 pp 200 Austr. Sch. ISBN 92 0 104098 9 These two reports stem from requests to the IAEA, from the local Government Authorities, for help and advice in assessing the radiological situations at two former nuclear weapons testing sites. Both reports have similar general structures - a discussion of the geographical context of the sites; a summary of the weapon tests, and their continuing impacts on the local populations; the basis for the IAEA programme; radiological concepts and criteria in the context of the residual contamination arising from the tests, and specifically the bases for intervention and remediation; assessments of the present and future radiation exposures of the actual/potential residents of the areas; and conclusions and recommendations. Because the indigenous Bikinian population is at present relocated elsewhere in the Marshall Islands archipelago, the report for Bikini Atoll is essentially concerned with an assessment of the current radiological situation, the prospects for resettlement, and the justification and available strategies for remedial action to reassure the Bikinians that it would be safe to return. Since the cessation of testing at the atoll in July 1958, there have been continuing radiological surveys of the local environment - the latest being the Marshall Islands Nationwide Radiological Study under an International Scientific Advisory Panel. The Panel report was not accepted by the Marshall Islands Government, who then requested the IAEA to carry out an independent peer review. The IAEA assessment (with some corroboratory data from a monitoring mission) confirmed the estimate of 15 mSv a-1 for the total potential dose rate to individuals relying entirely on locally produced foodstuffs, mainly from 137Cs in coconuts and other fruits. An examination of existing guidelines and practice concluded that 10 mSv a-1 is an appropriate generic action level to trigger consideration of remediation strategies prior to resettlement. From five potential remedial measures, two were considered in more detail - removal and disposal of the surface 40 cm of the topsoil, and treatment of the soil with high potassium fertilizers. It was concluded that the former, although reducing the dose rate from the residual contamination to less than 0.1 mSv a-1, would entail unacceptable environmental and social consequences. Experimental investigation of the latter showed that it would reduce the uptake of 137Cs significantly, with the total dose rate rapidly declining to about 1.2 mSv a-1; it was also found that the application of fertilizer would have to be repeated every 4-5 years to sustain the reduction. The latter was, therefore, the preferred option together with some localised soil removal in the living areas of the village to reduce both the external exposure and the inhalation pathway. The sole remaining concern of the Bikinians appears to relate to the identification of a reliable authority to assume responsibility for maintaining the implementation of the countermeasure to reduce the 137Cs uptake into foodstuffs for the foreseeable future. If this concern can be resolved, it appears that the way is open for the resettlement of the Bikinian people on the atoll. The situation at Semipalatinsk is somewhat different in one respect - the site, although large, has unrestricted access and small numbers of people already live within the boundaries. After the request to the IAEA from the Kazakhstan Government for assistance, the initial objective was to determine the magnitude of the problem. This was achieved on the first mission to the site when the main areas of contamination were identified using information available from the local authorities, and radiation measurements and sample collections were made at identified places both within, and external to, the site. A second mission extended the range of measurements and sample collections; in addition, local people were interviewed to determine dietary habits relevant to the radiological assessment. Two main areas of enhanced, but relatively localised, contamination were identified on-site: the ground zero area of the surface and atmospheric tests (Technical area `') and the site of a peacetime nuclear test that produced the excavation now forming Lake Balapan. (In passing, it may be noted that it is indicated that there are inconsistencies in the primary sources of information on the numbers of tests carried out within the site, and that data were, therefore, taken from a single source. The inconsistencies appear, however, to have been carried over into this report and there is not complete correlation between the data on numbers of tests given variously in Fig. 2, Table I and the text.) There are people living close to (but not in) these two areas and it is feasible that permanent occupation of these two sites could occur in the future; there is also evidence that both people and animals currently visit them. Radiation dose assessments were, therefore, made on the basis of a number of conservative assumptions for visitors and permanent inhabitants. The results, at 14 and 140 mSv a-1 respectively (largely from external sources), were above the generic action level of 10 mSv a-1 (produced from the same considerations as for the Bikini Atoll) and it was concluded that restrictions on access would be the most appropriate countermeasure at the present time. Outside the test site, the measured concentrations of activity were of the same order as, to several times greater than, those typical of global fallout; an exception was the settlement of Dolon where significantly higher concentrations of 239+240Pu were found. The estimated dose rates from the contamination were 0.14 mSv a-1 at Dolon and 0.06 mSv a-1 at the other settlements. It was concluded, therefore, that no intervention action was justified. Although present drinking water supplies show no evidence of enhanced radioactivity, it was recommended that a hydrological study be made to determine the potential future implications of the radionuclides from the underground tests. Overall, it was noted that the results were of a preliminary nature and more extensive surveys would be necessary to produce more robust estimates of the radiation exposure. Taken together, these two reports provide useful examples of the application of the Basic Safety Standards of the IAEA to situations of chronic radiation exposure from contamination arising from human activities. They should find a place on the health physicist's bookshelf.
Databáze: OpenAIRE
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