NUCLEAR POWERWatching Trends: Helping the NRC Model Risk and Reliability
Nuclear power accounts for 0.03 deaths per terawatt-hour of electricity generated, when including both accidents and deaths due to air pollution. This fatality rate is a factor of 820 lower than electricity produced using coal. One reason U.S. nuclear power plants have such an impressive safety record is that utilities embrace a safety culture, one that uses probabilistic risk assessments, also known as PRAs.
Supporters of nuclear energy tout the safety and reliability of nuclear power, and data supports their claims. According to detailed studies, nuclear power accounts for 0.03 deaths per terawatt-hour of electricity generated, when including both accidents and deaths due to air pollution. This fatality rate is a factor of 820 lower than electricity produced using coal.
One reason U.S. nuclear power plants have such a stellar safety record is that utilities embrace a safety culture, one that uses probabilistic risk assessments, also known as PRAs. The safety enhancements of PRAs were recognized early on by the U.S. Nuclear Regulatory Commission (NRC), and the NRC championed their use beginning in 1995. This endorsement in regulatory licensing and oversight has resulted in an enhanced understanding and control of commercial nuclear plant risk.
These assessments survey the possible “failure modes,” or sequences, that could lead to failure. Such sequences may involve combinations of equipment problems, external events or human errors. PRAs assign a probability of failure to each component and figure out which problems are most likely to occur. Engineers can then go back and strengthen the weak spots.
The NRC continues to encourage the industry to use PRA to provide a basis for “risk-informed, performance-based” decision-making. But nuclear safety relies on redundancy, checking and double-checking. How can the NRC have confidence that the utility’s analyses are correct?
The answer is to use independent PRA models, known as Standardized Plant Analysis Risk (SPAR) models. Idaho National Laboratory creates these models for the NRC, and they can be used to evaluate a specific plant’s operations risk. Different from a plant-managed PRA model, SPAR models use data from across the industry, rather than just a single plant, to provide a holistic, third-party safety picture.
Decades of Helping NRC Assess Risk
Beginning in the late 1990s, INL began working on the independent SPAR models, which now include 67 models, one for each nuclear power plant or each reactor unit at a plant. There are currently 92 commercial operating reactors in the U.S., some with two or three units per site, e.g., the Vogtle site in Georgia, which will soon have four units.
For the INL-developed SPAR models to be useful for the NRC, they must be updated in three ways. First, the plants are continuously making improvements, replacing components when needed, and reconfiguring systems for better performance.
