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Related Information
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Probabilistic Risk Analysis (PRA) Models
A PRA model of a reactor plant is not limited by assumptions, such as a single failure, so it can represent many events and failures that are possible at one time. PRA models identify the various combinations of these events and failures that could lead to reactor core damage or release of radioactivity. Each scenario is given an estimated likelihood based on the probabilities of each of the individual failures. These events are extremely unlikely, since they represent simultaneous failure of multiple safety defense features, but PRA models can still rank events in order of likelihood. These rankings help identify which of these scenarios is more likely, and which systems or components are most important contributors in these scenarios. The NRC and licensees can then focus attention and resources on the issues that will do the most to ensure safe plant operation.
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Severe Accident (SA) Models
Twenty-five years of extensive U.S. and international research have evaluated “severe” accident conditions that can result in core damage and possible release of radioactive material to the environment. Results of individual research projects have supported NRC regulatory decisions and policy statements. Collectively, they are the basis for the nuclear industry's plant-specific procedures for addressing severe accidents and minimizing possible releases of radioactivity.
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