Behaviour of long-lived Chernobyl radionuclides in a soil–water system

Abstract

Field and laboratory experiments have been used to study the behaviour of long-lived radionuclides in the zone affected by the Chernobyl accident. Speciation of ⁹⁰Sr and ¹³⁷Cs in soils and bottom sediments was determined. The principal distinction of the Chernobyl fallout was that it contained a relatively small proportion of exchangeable forms because a considerable fraction of the radionuclides was incorporated as part of the insoluble fuel particles. Disintegration of fuel particles in soils and bottom sediments results in transition of non-exchangeable forms into exchangeable forms. Radionuclide species have different pathways and rates of migration in soils and bottom sediments. Migration of each chemical form was described by a convective–dispersive equation taking into account transformation processes of radionuclide species in soils or bottom sediments. Adsorption of ⁹⁰Sr and ¹³⁷Cs in the environment is controlled by the cation-exchange capacity and the selectivity of the solid phase (i.e., soil, bottom sediments and suspended matter) and the cationic composition of the liquid phase (i.e., soil solution, surface run-off and river or lake water). The corresponding parameters for the processes were obtained.