Overview of the SOARCA Project

The State-of-the-Art Reactor Consequence Analyses (SOARCA) project incorporates the results of more than 25 years of research to analyze the realistic outcomes of postulated severe reactor accidents, even though it is considered highly unlikely that such accidents could occur. The SOARCA objective is to develop updated and more realistic analyses of severe reactor accidents by including significant plant changes and updates (e.g., system improvements, training and emergency procedures, and offsite emergency response) that plant owners have made, which were not reflected in earlier assessments conducted by the U.S. Nuclear Regulatory Commission (NRC). These plant changes also include recent enhancements since the terrorist attacks on September 11, 2001.

The initial phase of SOARCA analyzed two plants that are typical of the two basic types of U.S. commercial nuclear power plants. The Peach Bottom Atomic Power Station is a boiling-water reactor (BWR) near Lancaster, Pennsylvania, and the Surry Power Station is a pressurized-water reactor (PWR) near Newport News, Virginia. The NRC has not decided whether to analyze additional plants. To understand the purpose and scope of this project, please see the following topics on this page:

• Foundation for the SOARCA Project
• SOARCA Methodology and Scope

Foundation for the SOARCA Project

In developing realistic consequences of postulated severe accidents, the SOARCA project relies on many years of previous national and international reactor safety research. Through the years, the U.S. Nuclear Regulatory Commission (NRC), the U.S. Department of Energy (DOE), nuclear industry, and international nuclear safety organizations have extensively researched plant responses to hypothetical scenarios that could damage the reactor core or the containment. This research has significantly improved the NRC's ability to analyze and predict how nuclear plant systems will respond to severe accidents, and how accidents progress.

In addition, plant owners have continually improved safety by enhancing their plant designs, emergency procedures, inspection programs, and operator training. Plant owners and local governments have also refined and improved emergency preparedness to further protect the public in the highly unlikely event of a severe accident. Finally, the NRC has incorporated results from studies into health effects from radiation exposure in order to realistically model accident consequences.

The SOARCA project team applied the accumulated research and plant enhancements to integrated computer models. These models are designed to realistically evaluate plant behavior during severe accidents, and the potential public health risk from a hypothetical release of radioactive material. In addition, these models consider onsite and offsite actions — including the implementation of mitigation measures and protective actions for the public (such as evacuation and sheltering) — that may prevent or mitigate accident consequences.

SOARCA Methodology and Scope

The SOARCA project uses computer modeling techniques to understand how a reactor might behave under severe accident conditions, and how a release of radioactive material from the plant might impact the public. Specifically, it uses MELCOR (an integral severe accident analysis code) to model the severe accident scenarios within the plant, and MACCS2 (a consequence assessment code) to model the offsite health consequences of any atmospheric releases of radioactive material.

Using these resources, SOARCA analyzed an example of each major type of operating U.S. nuclear reactor, namely a boiling-water reactor (BWR) and a pressurized-water reactor (PWR). Since this project is a research study and independent of any regulatory action, nuclear power plants are under no obligation to participate. However, Peach Bottom and Surry volunteered for this study. These two plants also took part in earlier accident analyses performed by the NRC, such as those documented in NUREG/CR-2239, "Technical Guidance for Siting Criteria Development" (available through the NRC's Public Document Room), and NUREG-1150, "Severe Accident Risks: Assessment for Five U.S. Nuclear Power Plants." Under the SOARCA project, the NRC staff analyzed one reactor at each of these two sites. (In the future, the NRC may consider extending SOARCA to analyze additional examples of operating U.S. nuclear power reactors.)

The SOARCA project considered postulated severe reactor accidents from internal and external events (such as an earthquake) that begin during full-power reactor conditions. Because this project focused on realistic modeling of select severe accidents during full-power operation, its results are not meant to represent a complete risk analysis. Instead, these best-estimate calculations advance our knowledge of severe accidents, as well as the standard of what is "state-of-the-art."

The NRC's Advisory Committee on Reactor Safeguards (ACRS) and an independent external panel of scientific and technical experts reviewed the SOARCA methods and results to ascertain that they are state-of-the-art and credible.