Intercomparison and Validation Exercises in the Southern Urals and the Kazakh Polygon

Abstract

The military nuclear activities in the former Soviet Union led to unique contamination and resulted in high cumulative exposures. A proper assessment is needed for mitigation and for the further development of radiation protection. Environmental samples from areas affected by large radioactive releases into the Techa river starting in 1948 and by fall-out from the explosion of a tank containing high level waste in 1957, were independently analysed by two Russian groups and by our team in 1992-93. Soil, sediments, milk and fish samples were split into three aliquots and analysed for 90 Sr, 137 Cs and plutonium. Soil values in areas accessible to the local population were up to 16 kBq kg -1 for 90 Sr, up to 26 kBq kg -1 for 137 Cs and up to 12 Bq kg -1 for 239 Pu, respectively. Milk generally contained low levels ranging from to 25 Bq kg -1 for 90 Sr, 1 to 14 Bq kg -1 for 137 Cs and Bq kg -1 for plutonium. Pike from the Techa river, however, showed 15,000 Bq kg -1 90 Sr. In 1993, 750 in vivo measurements of 90 Sr/ 90 Y were performed in individuals of communities situated downstream of Majak which had incorporated large activities of 90 Sr from using the Techa river as drinking water supply. To help validate a large body of Russian measurements, a transportable body counter which measures the scull content of 90 Sr/ 90 Y directly from high energy β 's emitted from the front of the head and also indirectly via Bremsstrahlung was developed. Although the highest activities (37 kBq) were found in persons having lived at the river Techa during the early releases, considerable 90 Sr contamination, often accompanied with elevated 137 Cs burdens, were also found in younger persons indicating recent ingestion. Chronic and recent contamination will add to the uncertainties involved in the assessment of bone marrow doses from 90 Sr as a crucial element in dose reconstruction for the Techa river cohort. A first visit to the medical school and health institutions in Semipalatinsk and to a village having been heavily contaminated by an atmospheric bomb test at the Polygon yielded sometimes contradictory information but indicated high cumulative exposures in several Kazakh settlements adjacent to the test site.