MACCS is a fully integrated, engineering-level computer code developed at Sandia National Laboratories (SNL) for the Nuclear Regulatory Commission (NRC). MACCS simulates the impact of severe accidents at nuclear power plants (NPPs) and other nuclear facilities on the surrounding environment. As the only code used by the NRC to support Level-3 a probabilistic risk assessments (PRAs), MACCS can use a site’s weather data to determine hypothetical land contamination levels, doses to individuals, health effects and risks on populations based on protective action recommendations, and economic losses resulting from a NPP accident. A list of references can be located on the left-hand side of this webpage.

Release of MACCS Version 4.2
MACCS v4.2 is now available! Major enhancements for version 4.2 include the following:

  • License key: The "Product.key" is provided with the "WinMACCS 4.2.0 Setup.exe" file and is no longer locked to a specific computer. This allows MACCS to run on multiple computers with the same license key, including for cloud computing.
  • Cleanup criterion: A new dose-dependent cleanup criterion allows users to model the acceptable cleanup level of contaminated areas. This now allows users to model decontamination in lightly contaminated, habitable areas in addition to interdicted areas.
  • Dual dose criteria: Users now have the ability to model two relocation criteria in the long-term phase. This allows users to model two dose criteria (e.g., 2 rem in the first year, 0.5 rem in the second year) to make a single relocation decision, reflecting the US Environmental Protection Agency’s protective action guides.
  • Hotspot and normal relocation: Users now have two additional ways to model dose projections for early phase hotspot and normal relocation, "TOTAL" and "AVOID". "TOTAL" evaluates the total dose from all air and ground concentrations and "AVOID" evaluates the avoidable dose from ground pathways. These options are intended to mirror how decision-makers would evaluate doses during a radiological emergency using Turbo-FRMAC.
  • RDEIM economic model: The new RDEIM model outputs have been updated to differentiate between gross domestic product losses and offsetting recovery gains.
  • TEDE dose coefficients: MACCS now includes two sets of dose coefficients to estimate the effective dose, "ICRP60ED" (based on ICRP-60) and "TEDE" (based on ICRP-30).
  • Radionuclide list: The limit to the number of radionuclides defined in MACCS has been changed from 150 to 999.

Additionally, the MACCS Code Suite will be undergoing a modernization effort in the next several years to update the underlying programming languages as well as expanding capabilities to consider new reactor designs.


  • User activates modules only as needed to determine results of interest
  • Activated modules determine input files that are required
  • Some required input files may be used as transmitted with MACCS (without user modification)


The MACCS user community includes both domestic and international users, to include the NRC, DOE, several research organizations, nuclear industry licensees/applicants, and academic institutions. Primary uses of MACCS include performing regulatory cost-benefit analysis, environmental analyses of Severe Accident Mitigation Alternatives (SAMAs) and Severe Accident Mitigation Design Alternatives (SAMDAs), evaluations for emergency planning, Level 3 PRA studies, consequence studies, and other risk-informed activities.