A new joint American Society of Mechanical Engineers/American Nuclear Society (ANS) standard has been issued to establish requirements for probabilistic risk assessments used to support risk-informed decisions for commercial nuclear power plants.

ANS RA-S-1.4-2021 — Probabilistic Risk Assessment Standard for Advanced Non-Light Water Reactor Nuclear Power Plants — supports a diverse mixture of reactor concepts, including high-temperature gas-cooled reactors, liquid metal-cooled fast reactors, molten salt reactors, microreactors and small modular reactors, through the use of established technology-neutral risk metrics common to existing light water

reactor (LWR) Level 3 probabilistic risk assessments. Such risk metrics include frequency of radiological consequences such as dose, health effects and property damage impacts.

To support a wide range of applications defined by the non-LWR stakeholders, the scope of this standard is very broad and is comparable to a full-scope Level 3 probabilistic risk assessment for an LWR with a full range of plant operating states and hazards. Because some of the advanced non-LWR designs supported by this standard include modular reactor concepts, requirements are included that support an integrated risk of multi-reactor facilities, including event sequences involving two or more reactors or radionuclide sources concurrently.

The document supersedes a 2013 version of the standard issued for trial-use and pilot application. This trial-use version was extensively piloted in the development of a number of advanced non-LWR probabilistic risk assessments that were under development and being built around the world.

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