DETERMINATION OF PROBABILISTIC SOURCE TERMS FOR WASTE DISPOSAL FACILTIES

Probabilistic Safety Analysis (PSA) has proved to be a useful tool for demonstrating the high safety level of Nuclear Power Plants (NPP). However, the methods developed for NPP could not be applied for disposal facilities. With respect to the operational phase of a final repository for radioactive wastes a special approach has been developed taking release behavior of radioactive waste into account. The total spectrum of Low Activity Waste (LAW) and Intermediate Level Waste (ILLW) is grouped into waste streams of similar characteristics. Distributions of release fractions are determined for these distinct waste streams as a function of the incident loads and the waste properties. These distributions are especially suitable for the application in Monte-Carlo-Simulations. In addition to “rolling dice ” regarding the selection of waste, activity inventory and incident scenarios, the release fraction is likewise determined in a realistic way by “rolling dice”. Thus a realistic dose distribution can be determined, which is essential for the adequate safety design of a facility. After determining the probabilistic source term distributions, the PSA can easily be carried out with minor expenditures in terms of costs and time. OBJECTIVE The derivation of waste acceptance criteria is usually supported by a deterministic safety analysis. Within th