LONG-TERM INVESTIGATION OF CS-137 FIXATION BY SOILS

The results of long-term (two years) investigation of Cs-137 fixation in soil suspension are presented. It was shown that the equilibration time in a soil-water system for this radionuclide can be as long as on e year. This means that the total caesium distribution coefficient is nor relevant for mathematical modelling of migration processes with ch aracteristic times less than several months. The distribution coeffici ent of the exchangeable fraction of the radionuclide is recommended fo r modelling of faster processes. Caesium interaction with soils is cha racterised by three phases with distinctly different time scales: init ially rapid uptake, relatively slow intermediate uptake and the third phase with characteristic time about several months. A mechanistic int erpretation of each phase is proposed.