Application of Probabilistic Safety Analysis (PSA) Approach to Structuring Accident Mitigation Systems of a PWR.

The safety evaluation technology of PWRs has already been improved substantially because of large-scale safety verification tests and improvement of accuracy in analyses. However, for structuring accident mitigation systems(AMS), the selection of appropriate systems from various AMS candidates mainly depends on engineering judgements by design engineers. So systematic designing process should be established. Reliability of each AMS forms the basis for reliability of safety plant design as a whole. Therefore, explicitly understanding characteristics of each AMS's reliability is very important for safety design. Based on these facts as a background, the limitation of improving reliability by strengthening redundancy of AMS mainly consisting of active components was clarified by applying PSA. At the same time, reliability and other characteristics of AMS mainly consisting of passive components were also clarified with PSA. Through these studies, it is proved that the application of PSA for structuring AMS is efective.