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Overview of State-of-the-Art Reactor Consequence Analyses (SOARCA)

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SOARCA's Plant-Specific Basis
SOARCA Process and Schedule

The NRC is conducting a project to estimate the possible public health and safety consequences in the unlikely event of a commercial nuclear power plant accident releasing radioactive material into the environment. The results from this project will replace NUREG/CR-2239, entitled “Technical Guidance for Siting Criteria Development.” The intent of this 1982 study was to develop generic, bounding criteria for siting (locating) reactors that were unrelated to any specific plant designs using a set of hypothetical severe accident releases for a reactor. The use of these bounding criteria and conservative assumptions allowed the NRC to identify comparative impacts of releases in terms of potential public health effects to support the development of siting regulation. The NRC never intended this study to be used as a site-specific consequence analysis. The report acknowledges very large uncertainties associated with the results and states that “the results presented in this report do not represent nuclear power risk.” The report clearly noted that the report must be used in a manner consistent with the stated objectives; to provide technical perspective on siting related issues.

The SOARCA will be based on site-specific designs, operations, and emergency response. It will utilize the latest site-specific design and configuration information and advanced computer modeling to assess the different reactor and containment designs currently in use in the U.S., as well as consider the operational and emergency response features that are most important to safety. SOARCA will take maximum advantage of hundreds of millions of dollars of national and international reactor safety research, as well as improved NRC regulatory requirements and nuclear industry initiatives over the past 25 years. The NRC will use the project’s computer models and simulation tools to develop a set of realistic consequence estimates of very unlikely accidents at U.S. reactor sites. Research into accident phenomena, such as core damage and containment performance, has provided the basis for industry procedures to mitigate such accidents. This project supports the NRC's strategic goals of realism and openness in the regulatory process by making its results and supporting information publicly available in plain language.

SOARCA’s Plant-Specific Basis

The NRC will focus the plant-specific evaluations on event and failure scenarios with at least a once-in-a-million-years chance of core damage. The staff will gain valuable experience in performing such evaluations and in using these evaluations when communicating with stakeholders. The NRC will present the results to inform the public on the extent and value of safety defense features (i.e., defense-in-depth) and current mitigative strategies.

SOARCA Process and Schedule

The NRC will use state-of-the-art information and calculation tools to develop best estimate radioactive material released into the environment based on the reactor/containment classes and assess those releases to determine best estimate offsite radiological consequences including uncertainties in those results. Some areas to be considered in these new assessments include: (1) design-specific reactor accident sequence progression, (2) design-specific containment failure timing, location, and size, (3) site-specific emergency planning assumptions including evacuationand sheltering, (4) credit for operator actions based on Emergency Operating Procedures (EOPs) and Severe Accident Management Guidelines (SAMGs), and (5) site-specific meteorological conditions, and updated population data.

Using a computer code (MELCOR code), the NRC will model accident progression and quantify the radioactvie material released into the environment for each scenario. The NRC will also model offsite consequences using a computer code (MACCS2 code) to generate site-specific consequence estimates that account for site-specific weather conditions, population distribution and emergency planning assumptions. The NRC and Sandia National Laboratory staff members will work together to complete this project.

For more information, please see our SOARCA project plan.