ML22040A180
| ML22040A180 | |
| Person / Time | |
|---|---|
| Issue date: | 03/08/2022 |
| From: | Mark Thaggard Office of Nuclear Regulatory Research |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| Download: ML22040A180 (13) | |
Text
Perspective on Safety Improvements for Commercial Nuclear Power Plants Mark Thaggard, Director Division of Risk Analysis Office of Nuclear Regulatory Research, U.S. NRC
2 Overview
- The NRC uses various means to monitor changes in reactor safety
- Both quantitative and qualitative measures are used to assess safety
- The NRCs assessment of safety focuses on public health and safety
3 RES Considerations in Looking at Different Measures of Performance
- What timeframe should we consider?
- 20 years (2000+)
- 30 years (1990+)
- Advancements make it difficult to compare performance measures over time
- Measures of performance may need to be interpreted using engineering judgment
4 1988-2000 Plant Safety Improvements The period of interest impacts overall conclusions Many safety-significant actions/changes were made
5 1988-2000 Plant Safety Improvements Significant Events
2000-Present: Plant Safety Improvements 6
Improvements made during this period are not as significant as those in the 1990s Not all changes have been fully realized
7 RES Categories of Performance Measures Operational trends Plant risk due to internal events/internal floods Plant risk due to other hazards NRC studies, orders, models, etc.
Industry studies, standards, models, etc.
Other
Safety Measure Trends 8
51 measures Negative Trends Loss of offsite power (LOOP) recovery time Positive Trends Annual scrams NRC reactive inspections Accident sequence precursor (ASP) results Radiation exposure Performance indicators Internal events core damage frequency (CDF)
Reactor coolant pump (RCP) seal performance Loss of offsite power (LOOP) frequency 1
measure 8
measures
Remaining Safety-Related Measures 9
Apparent favorable trends Lower conditional probability that a radiological release would lead to prompt or latent health effects Improvements related to flooding and seismic hazard reevaluations Mitigating strategies improvements (FLEX)
Risk insights from the State-of-the-Art Reactor Consequence Analyses (SOARCA)
Generic Issues Program improvements B.5.b improvements Improvements in consensus standards and regulatory guidance Pressurized-water reactor steam generator performance improvements Improvements in PRA development tools 32 neither favorable or negative trend 9
Some Observations 10
- Limited to contributions from internal events
- External event hazards can add significantly to plant risk, so it is important to include in discussion of safety trending
- Reduction in performance issues
- Risk below NRC safety goals
- Both the uncertainties and external hazards need to be considered when looking at the safety goal impacts
Conclusions 11
- Performance measures appear to show improvements in nuclear power plants Could be attributed to initiatives and rules addressing key safety issues (e.g., station blackout (SBO) rule, greater use of risk-informed decisionmaking)
- Plant safety improvements implemented since the year 2000 have shown a gradual increase in safety, but to a smaller extent than during the previous 10 years
- Not all safety measures moved in the same positive direction
- External event impacts are important, and significant uncertainties still exist
Questions 12
13 Mehdi.Reisifard@nrc.gov Branch Chief, Division of Risk Analysis, RES Matthew.Humberstone@nrc.gov Senior Reliability and Risk Analyst Division of Risk Analysis, RES