Technical Advances in the Preliminary LERF MPAS Model

Since 2002, KINS has developed a regulatory PSA model named MPAS (Multipurpose Probabilistic Analysis of Safety) which consists of level 1 and level 2 PSA. The LERF (large early release frequency) evaluation model is devoted for level 2 PSA portion since this measure is more useful for risk-informed regulation than those of source term categories. A simplified containment event tree (CET) is structured to estimate the overall LERF. The general attentions in using a simplified CET are: To use the state-of-the-art database for severe accident analysis, To use systematic best-estimate prediction, To keep in mind the uncertainty, and identify the sources of uncertainty, etc. In this paper, we discuss some practical considerations for the development of simplified CET model, and provide preliminary review results for estimating branch fractions of CET headings