Mobility of radionuclides in undisturbed and cultivated soils in Ukraine, Belarus and Russia six years after the Chernobyl fallout

Abstract

Six years after the accident at the Chernobyl Nuclear Power Plant, the behaviour of radionuclides in soils in rural areas of Ukraine, Belarus 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 137Cs and 90Sr. Inside the 30 km restriction zone around the plant, particles of highly irradiated fuel accounted for most of the radioactive contamination. The radioactivity in the soil, in decreasing order, was due to 137Cs > 90Sr > 144Ce ⩾ 134Cs > 241Am > 125Sb > 154Eu > 155Eu. Outside the 30 km zone, condensed radionuclides were dominant and here the radionuclide content of the soil was 137Cs > 134Cs > 125Sb > 90Sr. The mobility of 137Cs in the soil increased with increasing distance from the reactor: this was in line with the fact that the 137Cs in condensed form, relative to that in fuel particles, also increased with increasing distance from the reactor. There was greater migration of the γ-emitting radionuclides 125Sb, 137Cs and 144Ce in peaty soils than in soddy podsolic, sandy and loamy soils. In undisturbed soddy podsolic sandy soils, more than 95% of the 137Cs was found in the top 6 cm layer. Not surprisingly, in the cultivated soils, the radionuclides were found more or less homogeneously distributed in the 0–25 cm layer. In the undisturbed soils, the γ-emitters had all migrated down to about the same depth, except for the 125Sb which had moved rather deeper. Considerable amounts of the 137Cs and 90Sr were found to be extractable into ammonium acetate solution and the 90Sr was easily the most extractable radionuclide. This probably explains its enhanced migration in the soddy podsolic, sandy and loamy soils.