Release of radionuclides to the geosphere from a repository for high-level waste

A mathematical model is described which enables calculation of the rates of removal of nuclide ions from high level waste by groundwater flow. The model, which is incorporated into a computer code, DREG, takes into account release of the nuclides by dissolution from their stabilising matrix, the solubility of each nuclide and where several isotopes of the same element are present, the sharing amongst them of the water's total solution capacity for that element. A running mass balance, which includes the effects of chain-decay, is built into the code. Examples are given of the use of the model in conjunction with a selection of fission products and the four actinide decay chains. (author)