BWR loss of coolant accident simulation by means of RELAP5

Abstract Application of best estimate codes and methodologies for LOCA simulation can provide the high level of details of the real plant response necessary to assess the adequacy of an emergency core cooling system. The current KKM RELAP5 model developed for the KKM plant (Muhleberg nuclear power station) has been demonstrated to be valid for simulating a wide range of transients including loss of coolant type accidents. Using this model, KKM LOCA analyses have been performed for the recirculation line break. The simulations have been done for the full break size spectrum. The sensitivity to the most important physics phenomena, e.g. CCFL, and model parameters, e.g. nodalization, has also been assessed. Results from the KKM RELAP5 LOCA analyses have been compared to the KKM LOCA results obtained with TRACG code by GEH. The RELAP5 and the TRACG models were both validated and showed very good agreement with the measured plant data. Regarding the LOCA calculations, the plant behavior and PCT results predicted by the RELAP5 model are consistent with those reported by GEH using the TRACG model. The differences observed can firstly be attributed to the diversity in the basic modeling of physical phenomena in the two codes. In addition, differences may originate from varying details in modeling the KKM plant and core parameters. However, considering that completely independent codes and models of the KKM plant predict similar PCT and plant behaviors during a LOCA, both KKM RELAP5 and KKM TRACG models can confidently be used for comparison against safety criteria.