BIOSPHERE MODEL FOR ASSESSING DOSES FROM NUCLEAR WASTE-DISPOSAL

The biosphere model, BIOTRAC, for predicting long term nuclide concent rations and radiological doses from Canada's nuclear fuel waste dispos al concept of a vault deep in plutonic rock of the Canadian Shield is presented. This generic, boreal zone biosphere model is based on scena rio analysis and systems variability analysis using Monte Carlo simula tion techniques. Conservatism is used to bridge uncertainties, even th ough this creates a small amount of extra nuclide mass. Environmental change over the very long assessment period is mainly handled through distributed parameter values. The dose receptors are a critical group of humans and four generic non-human target organisms. BIOTRAC include s six integrated submodels and it interfaces smoothly with a geosphere model. This interface includes a bedrock well. The geosphere model de fines the discharge zones of deep groundwater where nuclides released from the vault enter the biosphere occupied by the dose receptors. The size of one of these zones is reduced when water is withdrawn from th e bedrock well. Sensitivity analysis indicates I-129 is by far the mos t important radionuclide. Results also show bedrock-well water leads t o higher doses to man than lake water, but the former doses decrease w ith the size of the critical group. Under comparable circumstances, do ses to the non-human biota are greater than those for man.