From the plant layouts to optimized LP and 3D PWR-KWU containment models for combustion risk assessment with GOTHIC 8.3(QA)

One of the key objectives of the severe accident management strategies is to preserve containment integrity and to prevent a large release of radioactive products into the environment. To evaluate containment response during a severe accident (SA), two GOTHIC 8.3(QA) models (LP and 3D) of a PWR-KWU containment have been developed in the framework of AMHYCO (EU-funded Horizon 2020 project). The LP and 3D models were compared for the in-vessel phase of a total loss of AC power scenario (SBO), with and without considering Passive Autocatalytic Recombiners (PARs). The two models showed consistent global trends, but the 3D model revealed local variations in hydrogen stratification, condensation, and temperature gradients that were not captured by the LP model. 3D results also highlighted the influence of 3D mesh resolution on stratification and flammability conditions, with finer meshes predicting different hydrogen accumulation flow patterns. As expected, PARs effectively reduced flammable volumes in both models, although 3D models yielded lower recombination rates due to local heterogeneities. Last, this study emphasizes the importance of the post-processing choices made by the user to identify safety relevant conditions with the potential to enhance accident management measures and the positioning of safety systems.