ADVANCING PERFORMANCE-BASED AND RISK-INFORMED DESIGN METHODS FOR THE SEISMIC DESIGN AND REGULATION OF SSCs IN NPPs

摘要

The current NRC regulations for design and analysis of nuclear power plants to resist large earthquakes use a framework that is partially risk-informed, in the sense that a target performance goal of 10"5 per year is the design target for the design of every individual SSC (structure, system, or component) that contributes significantly to the safety performance of the plant. However, the current framework does not admit design-specific or plant-specific PSA information directly as a part of the technical basis used to determine whether an SSC should be approved. Instead, the design rules and analysis provisions have used information from the body of seismic PSAs already in the literature to inform how the design process and analysis provisions themselves are framed. This is "risk informed" but not fully so, and it is also not fully performance-based because although the target is framed in probabilistic terms, most of the design rules are prescriptive, rather than allowing the designer to choose his/her own design approach. This paper will discuss a group of several proposals, any one of which could advance the situation significantly toward a more fully performance-based and risk-informed framework. This paper will discuss the technical basis for each of the several proposals, what valid reasons stand in the way of their early implementation, and what research could be undertaken to help move the seismic design and approval process along toward a more nearly risk-informed and performance-based framework.