CHANGES IN THE FORMS OF CS-137 AND ITS AVAILABILITY FOR PLANTS AS DEPENDENT ON PROPERTIES OF FALLOUT AFTER THE CHERNOBYL NUCLEAR-POWER-PLANT ACCIDENT

The dynamics of exchangeable and acid soluble Cs-137 content in soils, as well as Cs-137 transfer factors for natural vegetation were studied for different sites within a 50-km zone around the Chernobyl nuclear power plant after the 1986 accident. Changes in Cs-137 forms in soils during the 6 years after the accidental release of radioactive substances and availability of this radionuclide to plants at that time were dependent on the character of radioactive fallout (fuel particles, aerosols of different dispersion) and soil type. Transformation of different Cs-137 species in soils with time after the accident was observed (destruction of fuel particles, ageing of Cs-137 and changes in the Cs-137 sorption strength of the soil solid phase). Behaviour of Cs-137 in the 'near' and 'remote' zones was different. The content of exchangeable Cs-137 in soils was found to have decreased after the accident. The average half-life of Cs-137 in grass stand in dry meadow in the 'remote' zone is 3.5 years, and in the second (slower) period after the accident, this half-life for Cs-137 will amount to about 17 years. The Cs-137 transfer factors for peaty swamped soils were 3.7-6.6 times as high as for soils of automorphous series.