A RISK-INFORMED APPROACH TO ADDRESS DIVERSITY REQUIREMENTS IN THE DESIGN OF NEW REACTORS

摘要

Diversity is defined as the presence of two or more systems or components to perform an identified function, where the different systems or components have different attributes so as to reduce the possibility of common cause failure (CCF). By eliminating CCF an adequate level of diversity between redundant systems or components contributes to improve safety function reliability. Thus it plays an important role in the respect of both qualitative and quantitative high safety objectives for new Nuclear Power Plants, as independence between Defense in Depth (DiD) levels, and respect of quantitative safety goals. This paper presents the main stages of an approach to address diversity requirements for redundant components involved in several DiD levels: Identification of diversity requirements for the main safety functions; Preliminary system reliability analysis for determining the components that need to include diverse provisions; Detailed Failure Mode and Effects Analysis of these components taking into account operating experiences and focusing on the identification of coupling factors amongst critical redundant parts leading to CCF. This approach allows characterizing diversity provisions to limit CCF to consider in future component design. Insights of the application of this approach on redundant safety injection pumps are briefly given in this paper.