Application of the BEPU safety analysis method to quantify margins in nuclear power plants

Following the progresses in research and development, regulatory requirements and industrial applications, Tractebel has been applying the best estimate plus uncertainty (BEPU) safety analysis method to quantify margins in Belgian nuclear power plants (NPPs) since the 1990's. For design basis accidents like large break Loss-Of-Coolant Accidents (LOCA), Tractebel has supported the vendors in the licensing and application of the BEPU methodologies. For non-LOCA accidents such as the Reactivity Initiated Accidents (RIA), Tractebel has been working on the development and application of a graded BEPU approach based on the best estimate multi-physics code package and the statistical uncertainty and sensitivity analysis method (SUAM) to support the reactor core design and operation. This paper presents a practical definition of margins and associated safety, design and operating limits, the evolution of safety analysis methods for margin quantification, as well as an overview of the Tractebel's activities in licensing of the BEPU LOCA methodologies for LOCA margin quantifi-cation, development and application of the graded BEPU approach for RIA margin quantification.