Application of PSA for optimization of systems design and backfitting at Siemens/KWU

The systems and plant design of Siemens/KWU pressurized water reactor (PWR) is based on mainly deterministic oriented requirements, with limited practicability for PSA recommendations. The PSA has been used as a supplementary tool for years with increasing importance. The actual licensing for the most recent PWR 1300 MW-Convoy plants required a PSA-Level 1. With respect to the resulting discussions the supplementary character of the PSA should be preferred over direct inclusion, e.g. due to the lack of guidelines. The consequent conversion of findings from safety research including PSA during design development results in very low core damage frequency as demonstrated for the PWR 1300 MW-Convoy. But in general the engineering insights from PSA valuation should be prioritized to absolute frequency numbers. Basing mainly on PSA-findings, an additional fourth safety level has been established to cope with beyond design accidents and/or to mitigate the consequences of severe accidents. To use the inherent safe behavior of the plant, relatively simple accident management measures are developed to prevent severe core damage and to limit the releases to the environment beyond values actually required for advanced plants