Approach to numerical safety guidelines based on a core melt criterion. [PWR; BWR]

A plausible approach is proposed for translating a single level criterion to a set of numerical guidelines. The criterion for core melt probability is used to set numerical guidelines for various core melt sequences, systems and component unavailabilities. These guidelines can be used as a means for making decisions regarding the necessity for replacing a component or improving part of a safety system. This approach is applied to estimate a set of numerical guidelines for various sequences of core melts that are analyzed in Reactor Safety Study for the Peach Bottom Nuclear Power Plant

Risk-based plant performance indicators

Tasked by the 1979 President's Commission on the Accident at Three Mile Island, the US nuclear power industry has put into place a performance indicator program as one means for showing a demonstrable record of achievement.'' Largely through the efforts of the Institute of Nuclear Power Operations (INPO), plant performance data has, since 1983, been collected and analyzed to aid utility management in measuring their plants' performance progress. The US Nuclear Regulatory Commission (NRC) has also developed a set of performance indicators. This program, conducted by NRC's Office for the Analysis and Evaluation of Operational Data (AEOD), is structured to present information on plant operational performance in a manner that could enhance the staff's ability to recognize changes in the safety performance. 4 refs., 1 fig., 1 tab

Safety system function trend indicator: Theory and test application

Methods for formulation, interpretation, and validation of dynamic risk and reliability indicators are studied. The use of these indicators for monitoring various levels of safety performance in nuclear power plants, as identified by probabilistic risk assessments (PRAs), such as safety system unavailability, safety system failure frequency, and core-damage frequency, are explored. Simplified indicators for detecting trends in the unavailability of safety systems in nuclear power plants not requiring PRA models and extensive data collection effort are being developed for possible NRC use. These indicators, called safety system function trend indicators (SSFT), are designed because they are easy to implement to display trends in system unavailability which can be detected through their visual inspections. The characteristics of these indicators are studied and optimized through simulation studies to assure sufficient capability in displaying a trend. To further substantiate the findings from visual examination of these indicators, statistical trend tests for sparse data are developed to aid the interpretation of these indicators. To evaluate the indicators from a safety point of view (rather than pure statistical sense) methods for comparing these indicators to a given alert level are being explored. Finally, approaches for engineering interpretation of these indicators are being studied by identifying the major contributors and causes for anomalies in indicator behavior. A preliminary pilot application/validation of these indicators, based on data from a sample of eight units, was completed in FY89. The findings are promising and warrant further refinement in the methodology. 5 refs., 3 figs