MOBILITY OF RADIONUCLIDES IN UNDISTURBED AND CULTIVATED SOILS IN UKRAINE, BYELARUS AND RUSSIA 6 YEARS AFTER THE CHERNOBYL FALLOUT

Six years after the accident at the Chernobyl Nuclear Power Plant, the behaviour of radionuclides in soils in rural areas of Ukraine, Belaru s and Russia has been studied. Measurements were made to determine the total radioactive contamination, the fuel particle contribution, and the distribution and extractability of the radionuclides Cs-137 and Sr -90. Inside the 30 km restriction zone around the plant, particles of highly irradiated fuel accounted for most of the radioactive contamina tion. The radioactivity in the soil, in decreasing order, was due to C s-137 > Sr-90 > Ce-144 greater than or equal to Cs-134 > Am-241 > Sb-1 25 > Eu-154 > Eu-155. Outside the 30 km zone, condensed radionuclides were dominant and here the radionuclide content of the soil was Cs-137 > Cs-134 > Sb-125 > Sr-90. The mobility of Cs-137 in the soil increas ed with increasing distance from the reactor: this was in line with th e fact that the Cs-137 in condensed form, relative to that in fuel par ticles, also increased with increasing distance from the reactor. Ther e was greater migration of the gamma-emitting radionuclides Sb-125, Cs -137 and Ce-144 in peaty soils than in soddy podsolic, sandy and loamy soils. In undisturbed soddy podsolic sandy soils, more than 95% of th e Cs-137 was found in the top 6 cm layer. Not surprisingly, in the cul tivated soils, the radionuclides were found more or less homogeneously distributed in the 0-25 cm layer. in the undisturbed soils, the gamma -emitters had all migrated down to about the same depth, except for th e Sb-125 which had moved rather deeper. Considerable amounts of the Cs -137 and Sr-90 were found to be extractable into ammonium acetate solu tion and the Sr-90 was easily the most extractable radionuclide. This probably explains its enhanced migration in the soddy and loamy soils. (C) 1996 Elsevier Science Limited