State-of-the-Art Reactor Consequence Analyses Project: Uncertainty Analyses for Station Blackout Scenarios

Abstract

This paper provides an overview of the U.S. Nuclear Regulatory Commission’s (NRC’s) project to develop a technical report summarizing the most important insights from its three State-of-the-Art Reactor Consequence Analyses (SOARCA) project uncertainty analyses (UAs). The NRC, with Sandia National Laboratories, has completed three UAs as part of the SOARCA project, for three different operating reactor types in three different locations in the United States. The SOARCA UAs included an integrated evaluation of uncertainty in accident progression, radiological release, and off-site health consequence projections. These three UAs are currently documented in three detailed reports. The NRC is currently developing a technical overview report summarizing the important insights from the three SOARCA UAs. The purpose of the NRC summary is to provide a useful reference for regulatory applications that require the evaluation of off-site consequence risk from beyond-design-basis-event severe accidents. Examples include regulatory and cost-benefit analyses that rely on off-site consequence projections using the MELCOR Accident Consequence Code System (MACCS) code, in conjunction with MELCOR for source term characterization. This paper provides an overview and discusses the overall scope and methodology of the SOARCA UAs and the approach for the summary report currently under development.

Keywords:

• Severe accident consequences
• uncertainty analysis

Acknowledgments

The SOARCA project UAs and reports are the result of the efforts of many NRC staff and the staff of its contractor, SNL. The project team is especially grateful to NRC’s Patricia Santiago for her greater than 8 years of dedicated leadership and managerial oversight of the SOARCA project. The coauthors gratefully acknowledge the contributions of Jonathan Barr, Keith Compton, and Salman Haq at the NRC; Matthew Denman, Christopher Faucett, Randall Gauntt, Troy Haskin, Fotini Walton, and Patrick Mattie at SNL; as well as the many other authors of the original SOARCA project and reports published in 2012, including Richard Chang, Jason Schaperow, Charlie Tinkler, Martin Stutzke, Joseph Jones, Cedric Sallaberry, and Mark Leonard.

Notes

^a https://maccs.sandia.gov/maccs.aspx (current as of Jan. 18, 2021).

^b https://melcor.sandia.gov/about.html (current as of Jan. 18, 2021).

^c https://maccs.sandia.gov/melmaccs.aspx (current as of Jan. 18, 2021).

^d MACCS also models economic and societal consequences such as the population subject to protective actions; however, these were not used in the SOARCA project.

^e These estimated core damage frequency contributions do not consider recent diverse and flexible mitigation capability (FLEX) upgrades that can potentially avert core damage in the given scenario. These numbers are based on existing information and expert judgment at the time each analysis was conducted. No new work was performed in this study to quantify the contribution to core damage frequency. This discussion is included only to provide context of the likelihood of the scenarios studied in this consequence analysis.

^f Estimated risks below 10⁻⁷ per reactor-year should be viewed with caution because of the potential impact of events not studied in the analyses and the inherent uncertainty in very small calculated numbers.

^g The habitability criteria can be more restrictive in certain states, such as in Pennsylvania, where Peach Bottom is located.