The Use of Risk Information in Nuclear Regulatory Decision Making

The traditional approach to regulation of nuclear reactor safety in the United States has been achieved, for the most part, using conservative methods and acceptance criteria.  From a safety perspective, a set of licensing-basis events has been established that is intended to ensure conservatism in design and protection from a wide spectrum of postulated events, up to and including design basis accidents.  One key concept that emerged early in the licensing history of U.S. nuclear power reactors was “defense in depth,” i.e., the use of multiple barriers or multiple means to accomplish safety functions to prevent the release of radioactive material.  A limited number of stylized design-basis events traditionally have been associated with mechanistic analyses.  In contrast to the traditional methods used for analysis of design basis events, a probabilistic risk assessment (PRA) models thousands of credible accident sequences by considering the facility or operation as a “system of systems” consisting of structures, systems, components, and personnel.  The NRC has been using PRA insights to inform certain regulatory actions and is currently pursuing increased us of PRA in several areas.