Migration of 90Sr and 137Cs in the Soil After Radiation Accidents

Abstract

Studying the principles of vertical migration and radionuclides distribution in soil is essential for a prediction of their transport dynamics into the root uptake area as well as for the planning of measures for decreasing contamination of agricultural and forest goods. A study of 90Sr and 137Cs distribution in a soil profile, as a result of radioactive contamination due to operation of radiochemical plant, Production Association (PA) “Mayak” was carried out on the territory of northeastern part of Chelyabinsk region in 2008–2012. In forest and meadow soil, the bottom part of forest litter and the upper soil layer (0–5 cm) are the most contaminated with 90Sr and 137Cs. The radionuclides contamination at a depth >20 cm is nearly undistinguishable for different soil types. In alluvial swamp soil, 90Sr is distributed through the whole soil profile, whereas 137Cs is concentrated in the depth of 20–40 cm. Annual plant fallout contributes to a lower extent into contamination of the litter and upper soil layer. In the experiment with a decay of plant fallout, a 90Sr distribution and contamination level in the profile of a model soil was similar to a natural soil, whereas a 137Cs contamination was 10 times lower for the model soil. In the forest-steppe area of Chelyabinsk region, a change of an upward and downward water flow in soil takes place several times in a season, during certain years a fallout and evaporation vary a lot. That is the reason for constant and unpredictable change of vertical radionuclides migration. A computer program for imitation modeling of radionuclides mobility in soil has been developed in our group. The radionuclides behavior in soil is determined by a probability of decay during certain period of time and by a probability of transport up and down within profile for a different distance independent of displacement mechanism. In a certain period of time, a position of a radioactive particle is defined by the sum of opposite directed vectors, each of which in a natural stochastic system is randomly determined, considering probabilities characteristic for given natural system.