Risk-Informed Hazard Barrier Assessment

There are a number of hazard barriers installed in power plants. The removal of hazard barriers from service can currently require substantial plant resources to evaluate. These evaluations are usually performed to assess the impact of an open barrier on a plant’s licensing basis and fire protection program and are deterministic in nature. The risk-informed approach to hazard barrier assessment helps alleviate the constraints and manpower requirements imposed by the deterministic approaches currently used. A two-step approach has been developed for performing a risk-informed hazard barrier assessment. The objectives of the first step “Data Gathering” are to review the previously performed analyses and to perform the plant walkdowns and data collection needed for the study. In the second step “Model Development and Quantification” using the most recent Probabilistic Safety Assessment (PSA) system models and the results of the “Data Gathering” walkdowns, a set of fault tree/event tree models are prepared for each unique scenario or hazard to be evaluated. The overall set of barrier impairment impacts is binned into a smaller number of generic categories for the PSA analysis. The quantification results will enable utility management to manage the risk of taking barriers out of service and to make a determination of which barriers could be candidates for a risk-informed impairment out-of-service limit if desired.