Assessment of the frequency of failure to scram in light-water reactors

Bayesian methods are used to construct a distribution for the probability of failure of the reactor protection system (RPS) per demand inlight-water reactors. This distribution expresses quantitatively the current state of knowledge as formed by analysis of the RPS, by the available statistical evidence, and by the work of the Electric Power Research Institute, and the Nuclear Regulatory Commission staff on anticipated transients without scram. The distribution can be summarized by the following values: 5th percentile: 6 x 10/sup -6/ per demand; median: 2.8 x 10/sup -5/ per demand; mean: 5.4 x 10/sup -5/ per demand; 95th percentile: 1.2 x 10/sup -4/ per demand.