Consideration of long-term aspects and low-probability events in assessment of nuclear waste disposal systems

The radiological safety assessment of nuclear waste disposal systems involves difficulties regarding both long-term aspects and probabilistic considerations. In the safety analyses and optimization studies that have been performed of various disposal systems for different types of radioactive waste, useful practical insights have been gained on the feasibility of the safety assessment methodology and the cost-effectiveness approach. As regards individual risk limitation, the safety assessments have to take into account the uncertainties related to both the long-term evolution of environmental conditions and disruptive events. A comprehensive view of the differences in safety between various alternative concepts can best be obtained by employing, in addition to individual and collective dose estimates, other parallel impact indicators which also provide a perspective on the risk levels of similar natural risks. Results from a practical case study on different repository concepts for activated metal waste disposal demonstrate the importance of realistic models and data for reducing the uncertainties and facilitating the intercomparison of alternative solutions. (author). 9 refs, 1 tab