A repairable dynamic event tree framework for the safety assessment of a steam generator of a nuclear power plant

Traditional Deterministic Safety Assessment (DSA) and Probabilistic Safety Assessment (PSA) of complex systems have been recently challenged by the excessive conservatism of DSA and the demanding treatment of uncertainties of PSA. In order to deal with these challenges, new methodologies have been developed which result from the integration of DSA and PSA methods for an Integrated Deterministic and Probabilistic Safety Analysis (IDPSA). In this work, we show the capabilities of a Repairable Dynamic Event Tree (RDET) who sets its basis on the traditional static Event Tree (ET) while focusing on the dynamic aspects of accident scenarios thereby described (e.g. timing and magnitude of occurrence of components failure events and repair), as an integrated methodology for IDPSA. We apply the framework of the RDET for the reliability assessment of a U-Tube Steam Generator (UTSG), in which we assume that four components can fail (with different timing and magnitude of failure) and can be repaired. The results of the RDET are benchmarked with those of a traditional ET and of a Repairable ET (RET).