An engineering-level computer code developed in 2021 at U.S. Sandia National Laboratories to simulate the impact of nuclear power plant accidents on the surrounding environment has been updated. The MACCS code is used by the U.S. Nuclear Regulatory Commission to support Level-3 probabilistic risk assessments and determine hypothetical land contamination levels, doses to individuals and other health, environmental and economic impacts of such events.

The code, developed to also evaluate the potential health and environmental risks posed by advanced nuclear reactors and small modular nuclear reactors, can now model accident consequences much closer to the reactor building. Previously, MACCS was not recommended for modeling consequences closer than five football fields from the reactor. The revised version can model consequences starting much closer to the reactor building as well as options to improve the model’s results out to 1,000 miles.

With the inclusion of the HYSPLIT atmospheric transport model developed by the U.S. National Oceanic and Atmospheric Administration, MACCS is better equipped to predict the fate of radioactive material after an accident under very specific weather conditions, or under random representative collection of weather conditions.

In addition to totaling the costs for evacuating and relocating people within a certain area, as well as for environmental remediation, MACCS can now estimate gross domestic product-based losses incurred by a potential accident.

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