An approach to merge PSA-based assumptions and BEPU method - 15556

The adoption by regulators of the risk-informed decision-making philosophy has opened the debate on the role of the deterministic and probabilistic approaches to support regulatory matters of concern to Nuclear Power Plants (NPP) safety. In this respect, a related medium-term challenge is to combine the use of well established Best Estimate Plus Uncertainty (BEPU) methodology and probabilistic-based assumptions on systems availability as proposed in option 4 IAEA SSG-2 guide (DSA for NPP Specific Safety Guide, No. SSG-2). In this paper, an approach is proposed to integrate probabilistic assumptions on the availability of safety systems into deterministic safety assessment, which follows and extends the fundamentals of the BEPU methods to build an Extended BEPU method that follows the principles of option 4 of the above guide. An example of application is provided to demonstrate how this approach performs. The case study focuses on an accident scenario following the initiating event 'Loss Of Feed Water (LOFW)' for a typical three-loops Pressurized Water Reactor (PWR) NPP