A mathematical model for the behaviour of Se-79 in soils and plants that takes account ofseasonal variations in soil hydrology

Abstract

Se-79 is a long-lived radionuclide of potential radiological significance in relation to thedeep geological disposal of solid radioactive wastes. In the context of release to theterrestrial environment, its main radiological impact is delivered through food chainpathways. Therefore, its accumulation in soils and uptake by plants is an importantconsideration in post-closure safety assessment studies. However, representation of itsbehaviour in the soil–plant system requires consideration of the multiple valencestates that it can exhibit under different redox conditions and its susceptibility tovolatilisation. A simple model is described that includes seasonal variations in soilhydrology and their effects on the mobility and root uptake of Se-79. Illustrativecalculations are undertaken with the model, to demonstrate its capabilities forinterpreting experimental data on the behaviour of Se-79 in soils and plants, and formaking projections on the long-term behaviour of Se-79 transported to soils.