Regulatory Guide: Design-Basis Floods for Nuclear Power Plants and Guidance for Assessment of Flooding Hazards due to Water Control Structure Failures and Incidents

Regulatory Guides: Design-Basis Floods for Nuclear Power Plants and Guidance for Assessment of Flooding Hazards Due to Water Control Structure Failures and Incidents

DATES:

RG 1.59, Revision 3 and RG 1.256, Revision 0 are available on September 22, 2026.

SUPPLEMENTARY INFORMATION:

I. Discussion

The NRC is issuing two related RGs in the NRC's "Regulatory Guide" series. This series was developed to describe methods that are acceptable to the NRC staff for implementing specific parts of the agency's regulations, to explain techniques that the staff uses in evaluating specific issues or postulated events, and to describe information that the staff uses in its review of applications for permits and licenses.

RG 1.59, Revision 3, reflects lessons learned from the review of large light water nuclear power plant applications under part 52 of title 10 of the Code of Federal Regulations (10 CFR) since the issuance of RG 1.59, Revision 2, in August 1977, as well as additional lessons learned from staff reviews of licensees' responses to the NRC's "Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near Term Task Force Review of Insights from the Fukushima Dai-ichi Accident." The body of this RG applies to large light water reactors. In view of the emerging innovations taking place in nuclear engineering science, Appendix K is presented as an alternative approach for advanced reactors, which may be used in conjunction with the guidance in RG 1.247, "Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities."

RG 1.256, Revision 0 provides guidance to applicants for new nuclear power plants on acceptable methods for evaluating design-basis flooding hazards due to failure or other incidents at man-made water control structures including, but not limited to, dams and levees. The RG was developed primarily for use by new nuclear power plant applicants, but current licensees may also find it useful. It incorporates NRC interim staff guidance JLD-ISG-2013-01 "Guidance for Assessment of Flooding Hazards Due to Dam Failure," into the NRC's regulatory framework. Upon issuance of Revision 0 of RG 1.256, JLD-2013-01 will be withdrawn.

II. Additional Information

The two RGs were released for public comment via a notice in the Federal Register on July 15, 2024 (89 FR 57372) as Draft Guide (DG)-1290, Revision 1 for RG 1.59, Revision 3, and DG-1417 for RG 1.256, Revision 0. The comment period was originally for 30 days and was subsequently extended to September 13, 2024. Comments were received from the Nuclear Energy Institute. The comments on DG-1290, Revision 1 and the staff response to them are available in ADAMS under Accession No. ML26246A471. The comments on DG-1417 and the staff response to them are available in ADAMS under Accession No. ML26258A151.

III. Congressional Review Act

These RGs are both considered to be a rule as defined in the Congressional Review Act (5 U.S.C. 801-808). However, the Office of Management and Budget has not found them to be a major rule as defined in the Congressional Review Act.

IV. Backfitting, Forward Fitting, and Issue Finality

The NRC staff may use RG 1.59, Revision 3, and RG 1.256, Revision 0, as references in its regulatory processes, such as licensing, inspection, or enforcement. However, the NRC staff does not intend to use the guidance in RG 1.59 and RG 1.256 to support NRC staff actions in a manner that would constitute backfitting as that term is defined in 10 CFR 50.109, "Backfitting," and as described in NRC Management Directive (MD) 8.4, "Management of Backfitting, Forward Fitting, Issue Finality, and Information Requests," (ADAMS Accession No. ML18093B087); nor does the NRC staff intend to use the guidance to affect the issue finality of an approval under 10 CFR part 52, "Licenses, Certifications, and Approvals for Nuclear Power Plants." The staff also does not intend to use the guidance to support NRC staff actions in a manner that constitutes forward fitting as that term is defined and described in MD 8.4. If a licensee believes that the NRC is using these RGs in a manner inconsistent with the discussion in this Implementation section, then the licensee may file a backfitting or forward fitting appeal with the NRC in accordance with the process in MD 8.4.

V. Submitting Suggestions for Improvement of Regulatory Guides

A member of the public may, at any time, submit suggestions to the NRC for the improvement of existing RGs or for the development of new RGs. Suggestions can be submitted on the NRC's public website at https://www.nrc.gov/reading-rm/doc-collections/reg-guides/contactus.html . Suggestions will be considered in future updates and enhancements to the "Regulatory Guide" series.

VI. Executive Order (E.O.) 12866

The Office of Management and Budget, Office of Information and Regulatory Affairs determined that RG 1.59, Revision 3 and RG 1.256, Revision 0 are not a significant regulatory action under E.O. 12866.

Authority: 42 U.S.C. 2011 et seq.