Integrating Seismic Fragility of ASR-Affected Nuclear Containment Vessel in a Level-II SPRA in Support of Multi-Hazard Risk Assessment

In light of the Fukushima Daiichi accident in 2011, the incorporation of external multi-hazards in probabilistic risk assessments (PRAs) for nuclear power plants (NPPs) has become essential. However, a comprehensive PRA framework that accounts for all potential external multi-hazards has yet to be established. Our current research objective is to develop a time-dependent multi-hazard PRA approach that takes into account the deterioration of structures related to aging. The deterioration of concrete due to alkali silica reaction (ASR) is a well-known issue that affects concrete structures at different rates. Recently, there has been evidence of this deterioration in concrete structures in nuclear power plants, which could affect the seismic capacity of nuclear containment vessels. In this study, we aim at developing a framework for integrating the effects ASR on the early release frequency of radionuclides from a generic pressurized water rector (PWR). of A level-I PRA model was utilized for a generic (PWR) to estimate the frequencies of core damage at different levels of peak ground acceleration (PGA). The output of this analysis is assumed to be the initiating event in a simplified containment event tree (CET) where accident progression in the containment is tracked. The time-dependent ASR impact on the seismic capacity of the containment was captured using fault tree structure. The minimal cut sets for the CET were then quantified in SAPHIRE at each PGA level. The findings revealed a significant increase in Large Early Release Frequency (LERF) mean values at low PGA bins as ASR-induced degradation increases. A small increase in LERF was observed at intermediate PGA levels, while no increase was detected at high PGA level.