Nuclear safetyExtending Nuclear Power Accident Code for Advanced Reactor Designs

Nuclear power is a significant source of steady carbon-neutral electricity, making the design and construction of new and next-generation nuclear reactors critical for achieving the U.S.’s green energy goals.

A number of new nuclear reactor designs, such as small modular reactors and non-light water reactors, have been developed over the past 10 to 15 years. In order to help the Nuclear Regulatory Commission evaluate the safety of the next generation of reactors, fuel cycle facilities and fuel technologies, researchers at Sandia National Laboratories have been expanding their severe accident modeling computer code, called Melcor, to work with different reactor geometries, fuel types and coolant systems.

These advancements have been demonstrated at several virtual public meetings this summer. The purpose of these meetings is to show U.S. policymakers, members of the nuclear energy industry, international nuclear energy regulators and members of public interest groups that the NRC has the tools needed to evaluate the safety of new and advanced nuclear reactor designs.

“This computer code really is the Swiss Army knife of nuclear system safety,” said David Luxat, manager for Sandia’s nuclear reactor severe accident modeling group. “It is a flexible toolbox of physics and chemistry that allows us to simulate how a nuclear power plant or another nuclear facility reacts during an accident that could potentially lead to the release of radioactive material into the environment. In my view, the code is central to enabling the innovation of nuclear energy in the U.S. and thus mitigating the worst outcomes from climate change.”

Advancing the Safety Code for the Next Generation
Sandia and the NRC have worked together for decades to advance the understanding of system performance under accident conditions. This research covered areas such as accident progression, combustible gas generation and transport, molten core concrete interaction, fuel coolant interactions and many others. Starting in the 1980s, the NRC directed Sandia to consolidate these capabilities into one software package.

The Melcor code can model a wide array of phenomena including severe accidents that can occur at a nuclear power plant, then estimate the extent of radioactive material release possible due to the accident. Work on the code began after the Three Mile Island accident in 1979.