Demonstration of the E-BEPU methodology for SL-LOCA in a Gen-III PWR reactor

Abstract

The paper presents the first practical application of the alternative Extended Best Estimate Plus Uncertainty (E-BEPU) methodology. The E-BEPU is the systematic risk-informed combined deterministic and probabilistic methodology dedicated to design verification of Nuclear Power Plants. The approach covers applying the best-estimate computer code, realistic input data for initial and boundary conditions with uncertainties, and plant systems availability based on Probabilistic Safety Analysis methods. Furthermore, it extends the scope of the uncertainty analysis to include the availability of safety systems as an additional uncertain item. The approach is characterized by an enhanced Defence-in-Depth; it can detect cliff-edge effects and include risk insights in the deterministic analysis framework. It is an advanced approach to Deterministic Safety Analysis beyond the BEPU approaches and an alternative realization of the Extended-BEPU. In this study, the generic Generation-III Pressurized Water Reactor design was investigated to demonstrate the methodology with a practical example. The Postulated Initiating Event was a surge line double-ended break (SL-LOCA), a variant of the Large Break Loss of Coolant Accident (LB-LOCA), and considered an example of the Design Basis Event. The considered reactor design passed successfully through the procedure with a large margin due to the robustness of its safety systems.