MIGRATION OF CS-137 AND SR-90 FROM CHERNOBYL FALLOUT IN UKRAINIAN, BELARUSSIAN AND RUSSIAN SOILS

Studies carried out inside the 30-km restriction zone of the Chernobyl Nuclear Power Plant (ChNPP) and in other contaminated regions of Ukra ine, Belarus and Russia have shown that much of the Cs-137 and Sr-90 d eposited by the accident in 1986 has been retained in the superficial layers of the soil and is likely to remain there for a long time, Howe ver, in wet organic soils, there has been considerable downward moveme nt. Between 1987 and 1993, laboratory and field experiments were carri ed out in order to determine the vertical distribution profiles of Cs- 137 and Sr-90 in undisturbed soils at various locations and in various soil types. The data from these experiments were then used to calcula te the vertical migration rates of the two radionuclides by two types of model. The experimental results showed that the type of soil and it s water content had a significant influence on the radionuclide distri bution pattern in the soil profile. In undisturbed well-drained sandy and sandy loamy soils, the radionuclides were retained in the upper so il layers. However, in peaty boggy soils and flooded meadows, there wa s a greater downward migration. In tilled soils, the radionuclides wer e distributed more or less homogeneously within the cultivated soil la yer: the depth and homogeneity of the nuclide distribution depended on the soil texture and the way that the soil had been managed. The vert ical migration rates of the Sr-90 were always higher than that of Cs-1 37. In a comparison of migration rates between Cs-137 and Sr-90 in dif ferent types of soils, Sr-90 appeared to migrate fastest in sandy loam and sandy soils, and Cs-137 migrated fastest in peaty, boggy soils. T he limitations in usage of the models are discussed, and predictions a re made for the next years. Copyright (C) 1996 Elsevier Science Limite d.