Prof. D. N. Singh

RAVI RANJAN RAKESH

Ph. D.
Indian Institute of Technology Bombay, Powai, India ravirr@apsara.barc.ernet.in

SIMULATION OF RADIOACTIVE CONTAMINANT TRANSPORT IN UNSATURATED SOILS

Low and Intermediate level radioactive waste is disposed off in different disposal modules (viz. stone lined trench, reinforced concrete trench and tile holes) of the Near Surface Disposal Facility, NSDF, after proper treatment and immobilization. These modules are located in the soil mass which remains either unsaturated or exhibits considerable seasonal fluctuation of the ground water table. In case of any eventuality, release of radionuclides from these modules may occur and may be followed by their migration through the unsaturated soils. Hence, for assessing the safety of the NSDF, prediction of radionuclide migration in the unsaturated soils becomes essential.
With this in view, an attempt was made to develop a methodology for modelling migration of radionuclides in the unsaturated soils. Laboratory experiments were conducted on the soil samples collected from two NSDFs located in India, with totally different site conditions. These samples were characterized for their physical, chemical, mineralogical and geotechnical characteristics. Sorption characteristics of these soils were also established, under different experimental conditions, for radionuclides 137Cs, 90Sr and 60Co. In addition to this, diffusion characteristics of these soils, with different compaction states, were established by conducting experiments using inactive waste containing these cations in different concentrations.
Such a study would be of great help in assessing the extent of radionuclide migration in the unsaturated soils and hence for developing regulatory guidelines for safe and proper functioning of the NSDF.