ANS Standards Committee publishes joint ASME/ANS standard for level 1/large early release frequency PRA

March 22, 2024, 7:01AMANS News

ANSI/ASME/ANS RA-S-1.1-2024, Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications, has just been published by the American Nuclear Society. The document, which is a joint standard developed with the American Society of Mechanical Engineers by the ANS/ASME Joint Committee on Nuclear Risk Management, received approval of the American National Standards Institute on February 29, 2024, and was issued on March 15, 2024.

This standard states requirements for a Level 1 probabilistic risk assessment (PRA) of internal and external hazards while at power for the evaluation of core damage frequency. It also states requirements for a limited Level 2 PRA sufficient to evaluate large early-release frequency. The only hazards explicitly excluded from the scope are accidents resulting from purposeful human-induced security threats (e.g., sabotage, terrorism). These requirements are written for operating light water reactor power plants (i.e., plants with designs and features similar to the plants operating when this standard was published). They may be used for LWR plants under design or construction or for advanced LWRs, but revised or additional requirements may be needed.

The current edition, ANSI/ANS RA-S-1-1-2024, presents only minimal editorial modifications and reference corrections from the 2022 edition and further enhances the internal consistency of the previous version. Expanded requirements are only provided for Supporting Requirements HR-H2 and HR-G3 for the Human Reliability Analysis technical element in Part 2. The 2022 edition was a substantial revision of ASME/ANS RA-Sb-2013, Addenda to ASME/ANS RA-S-2008 Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications. Changes made in the 2022 version included a major reformatting and inclusion of lessons learned. Significant changes included the following:

  • Greater consistency among technical elements that are cross-cutting through different hazards.
  • Addition of back references from part to part to facilitate the peer review process.
  • Removal of Capability Category III.
  • Addition of a new section to assess the technical adequacy of newly developed methods.
  • Removal of “PRA maintenance” and “PRA upgrades” examples now addressed by the Pressurized Water Reactor Owners Group.
  • Addition of a new appendix that provides the meanings of action verbs used in requirements.
  • Addition of new and revised definitions for clarity.
  • Deletion of Part 10, on seismic margin assessment.

The ANS/ASME Joint Committee on Nuclear Risk Management is a collection of committees animated by the passion of more than 200 professionals in the industry, from four continents and spanning the extensive interdisciplinary breadth needed for the development of multihazard, full-scope, comprehensive risk assessments.

Check out a preview of ANSI/ASME/ANS RA-S-1.1-2024, or purchase the standard in the online ANS standards store.

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