Current and Future Applications of Thermal-Hydraulic and Neutronic Best- Estimate Methods in Support of the Swiss Licensing Process

Best-estimate methods are employed within the STARS project at PSI. The project provides independent technical expertise primarily to HSK in support of the Swiss licensing process in the area of deterministic safety analysis, and covers applications ranging from operational occurrences as well as beyond-design-basis transients. Some examples are presented: an assessment of the coolability of a PWR for reduced availability of ECCS, timing studies for an MSIV-ATWS event in a BWR in order to quantify the effect of delayed operator actions, predictions of planned start-up tests and research on BWR-stability to deepen the understanding of the phenomenon. Future work will include an extensive use of 3D-kinetics in transient analysis and the development of a comprehensive uncertainty methodology. Calculations on high burnup fuel behavior for RIA- and LOCA-scenarios are planned; also CFD applications will be developed to assess mixing problems in reactor geometries on a rigorous basis. (authors)