Scientech has recently developed Fire PRAs (FPRAs) for about 20% of the units in the US transitioning to an NFPA-805 licensing basis. This paper provides a summary of insights gained in conducting these studies. A summary of the methods, results and insights is provided. These evaluations are identifying cost beneficial enhancements and identifying the need for improvements in methods and data. The identification of plant enhancements should not be surprising, as the mitigation portion of the fire protection design basis provides for a single safe shutdown path. Most design basis events, e.g., loss of coolant accidents (LOCAs) require at least 2 safe shutdown paths. There are credible fire scenarios which can either fail both trains or result in the need for local manual actions to bypass fire induced failures to align a safe shutdown path. In addition, the safe shutdown path may have lower than expected reliability, if several actions are needed, actions have limited time margin, or the resulting safe shutdown path is subject to single failures, such as failure of an emergency diesel generator.
The paper will discuss insights, plant modifications, and defense in depth. Further, key uncertainties which point to the desirability of methods and data enhancement will be discussed. The paper concludes that fire risk is not low and defense in depth can be compromised.
