Key Issues
Safety Benefits of Risk Assessment at U.S. Nuclear Power Plants
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Background
Risk assessment techniques were first used by the nuclear power industry more than 25 years ago.
Risk assessment studies start by identifying the full spectrum of plant operating events, including events not considered in current NRC regulations. Using the database compiled from plant experience, along with scientific methods for estimating rare plant operating occurrences, the likelihood of nuclear power plant events can be calculated. Potential events include the rupture of a pipe, failure of an electrical system, or any other of literally thousands of "initiating events"-that is, events that might challenge a plant's safety systems.
The next step in the assessment is the construction of a unique computer model for each nuclear plant. The model combines the initiating event data with the performance data for plant systems that are important to safety. Using standard techniques of statistics and probability, thousands of potential accident sequences are modeled, involving practically every combination of equipment failures imaginable.
Critical worker actions also are analyzed, and the likelihood of human error is calculated in the model. The overall approach is called "probabilistic safety analysis," or PSA. All U.S. nuclear power plants have performed these analyses.
Risk analysis techniques have been reviewed by the NRC, U.S. national laboratories and other independent entities, including the worldwide academic community. The analyses techniques have been improved and refined based on this input. In addition, the analyses for individual nuclear plants have been subjected to peer review. The results of the analyses are estimates, but they are state-of-the-art assessments of nuclear plant safety.
The results show a very low risk of damage to a reactor-a one-in-40,000 chance per year. The risk of a large radiation release is even lower because the robust reactor containment building provides protection against radiation release even after a core-dam-aging accident inside a reactor.
Background
Risk assessment techniques were first used by the nuclear power industry more than 25 years ago.
Risk assessment studies start by identifying the full spectrum of plant operating events, including events not considered in current NRC regulations. Using the database compiled from plant experience, along with scientific methods for estimating rare plant operating occurrences, the likelihood of nuclear power plant events can be calculated. Potential events include the rupture of a pipe, failure of an electrical system, or any other of literally thousands of "initiating events"-that is, events that might challenge a plant's safety systems.
The next step in the assessment is the construction of a unique computer model for each nuclear plant. The model combines the initiating event data with the performance data for plant systems that are important to safety. Using standard techniques of statistics and probability, thousands of potential accident sequences are modeled, involving practically every combination of equipment failures imaginable.
Critical worker actions also are analyzed, and the likelihood of human error is calculated in the model. The overall approach is called "probabilistic safety analysis," or PSA. All U.S. nuclear power plants have performed these analyses.
Risk analysis techniques have been reviewed by the NRC, U.S. national laboratories and other independent entities, including the worldwide academic community. The analyses techniques have been improved and refined based on this input. In addition, the analyses for individual nuclear plants have been subjected to peer review. The results of the analyses are estimates, but they are state-of-the-art assessments of nuclear plant safety.
The results show a very low risk of damage to a reactor-a one-in-40,000 chance per year. The risk of a large radiation release is even lower because the robust reactor containment building provides protection against radiation release even after a core-dam-aging accident inside a reactor.
