Licensing Safety Analysis for Loss-of-Coolant Accidents

NUCLEAR REGULATORY COMMISSION <CFR>10 CFR Part 50</CFR> <DEPDOC>[Docket No. PRM-50-124; NRC-2022-0178]</DEPDOC> <SUBJECT>Licensing Safety Analysis for Loss-of-Coolant Accidents</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Nuclear Regulatory Commission. <HD SOURCE="HED">ACTION:</HD> Petition for rulemaking; denial. <SUM> <HD SOURCE="HED">SUMMARY:</HD> The U.S. Nuclear Regulatory Commission (NRC) is denying a petition for rulemaking (PRM), dated August 1, 2022, submitted by Ralph O. Meyer. The petition requested that the NRC amend its regulations regarding the licensing safety analysis for loss-of-coolant accidents. The petition was docketed on August 1, 2022, and was assigned Docket No. PRM-50-124. The NRC is denying the petition because the NRC is addressing emergency core cooling system performance with a risk-informed and performance-based regulatory approach rather than a deterministic approach as suggested by the petitioner. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> The docket for the petition for rulemaking, PRM-50-124, is closed on July 28, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> Please refer to Docket ID NRC-2022-0178 when contacting the NRC about the availability of information for this action. You may obtain publicly available information related to this action by any of the following methods: • <E T="03">Federal Rulemaking Website:</E> Go to <E T="03">https://www.regulations.gov</E> and search for Docket ID NRC-2022-0178. Address questions about NRC dockets to Helen Chang; telephone: 301-415-3228; email: <E T="03">Helen.Chang@nrc.gov.</E> For technical questions, contact the individual listed in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section of this document. • <E T="03">NRC's Agencywide Documents Access and Management System (ADAMS):</E> You may obtain publicly available documents online in the ADAMS Public Documents collection at <E T="03">https://www.nrc.gov/reading-rm/adams.html.</E> To begin the search, select “Begin Web-based ADAMS Search.” For problems with ADAMS, please contact the NRC's Public Document Room (PDR) reference staff at 1-800-397-4209, at 301-415-4737, or by email to <E T="03">PDR.Resource@nrc.gov.</E> For the convenience of the reader, instructions about obtaining materials referenced in this document are provided in the “Availability of Documents” section. • <E T="03">NRC's PDR:</E> The NRC PDR, where you may examine and order copies of publicly available documents, is open by appointment. To make an appointment to visit the PDR, please send an email to <E T="03">PDR.Resource@nrc.gov</E> or call 1-800-397-4209 or 301-415-4737, between 8 a.m. and 4 p.m. eastern time, Monday through Friday, except Federal holidays. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Denise Edwards, Office of Nuclear Material Safety and Safeguards, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001; telephone: 301-415-7204, email: <E T="03">Denise.Edwards@nrc.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> <HD SOURCE="HD1">Table of Contents</HD> <EXTRACT> <FP SOURCE="FP-2">I. The Petition</FP> <FP SOURCE="FP-2">II. Public Comments on the Petition</FP> <FP SOURCE="FP-2">III. Evaluation of the Petition</FP> <FP SOURCE="FP-2">IV. Reasons for Denial</FP> <FP SOURCE="FP-2">V. Availability of Documents</FP> <FP SOURCE="FP-2">VI. Conclusion</FP> </EXTRACT> <HD SOURCE="HD1">I. The Petition</HD> Section 2.802 of title 10 of the <E T="03">Code of Federal Regulations</E> (10 CFR), “Petition for rulemaking,” provides an opportunity for any interested person to petition the Commission to issue, amend, or rescind any regulation. On August 1, 2022, the NRC received and docketed a PRM filed by Ralph O. Meyer. On November 23, 2022, the NRC published a notice of docketing requesting comment on the petition in the <E T="04">Federal Register</E> (87 FR 71531). The petition requested that the NRC amend its regulations in 10 CFR 50.46, “Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors.” The regulations in 10 CFR 50.46 require the calculation of emergency core cooling system (ECCS) performance following postulated loss-of-coolant accidents (LOCAs) to demonstrate that the acceptance criteria in 10 CFR 50.46(b) are met. The petition requested the elimination of the acceptance criteria for peak cladding temperature (PCT) and maximum cladding oxidation (commonly referred to as maximum local oxidation, or MLO) in 10 CFR 50.46(b). As a replacement for these criteria, the petition requested that the NRC regulations be revised to limit the number of fuel rod ruptures to 1 percent for small-break LOCAs and 10 percent for large-break LOCAs. The petition stated that nuclear power reactors in Germany must show that the proposed fuel rod rupture limits are met. The NRC identified two issues in the petition, as follows: <E T="03">Issue 1:</E> The petition asserted that the current acceptance criteria for the calculated PCT and MLO in 10 CFR 50.46(b) do not ensure an easily coolable geometry at moderate and higher fuel burnups due to fuel dispersal. <E T="03">Issue 2:</E> The petition asserted that the calculations of temperature and oxidation within the burst region of a fuel rod are prone to large uncertainties, and the technical bases for the acceptance criteria on these two parameters are complex and misunderstood. Specifically, the petition stated that the beliefs that the temperature limit prevents autocatalytic oxidation and that a reduction in cladding thickness causes embrittlement are incorrect. <HD SOURCE="HD1">II. Public Comments on the Petition</HD> The NRC invited interested persons to submit comments on the petition (87 FR 71531; November 23, 2022). In response to a request by the Nuclear Energy Institute (NEI), the comment period was extended to March 8, 2023 (88 FR 7012; February 2, 2023). The NRC received 12 comment submissions on the petition. The petitioner submitted eight comment submissions in support of the petition, including submittals after the closure of the public comment period. Westinghouse Electric Company LLC (Westinghouse), Framatome Inc., the Pressurized Water Reactors Owners Group (PWROG), and NEI each provided a comment submission opposing the petition. A summary of the significant comments and NRC responses is provided below. The NRC evaluation of the petition is provided in Section III, “Evaluation of the Petition.” Several comments on the petition mentioned the then-pending draft final rule commonly referred to as “10 CFR 50.46c.” This draft final rule was provided to the Commission in SECY-16-0033, “Draft Final Rule—Performance-Based Emergency Core Cooling System Requirements and Related Fuel Cladding Acceptance Criteria (RIN 3150-AH42),” dated March 16, 2016. On April 11, 2024, the Commission returned the 10 CFR 50.46c draft final rule to the staff in a staff requirements memorandum (SRM) for SECY-16-0033, “Staff Requirements—SECY-16-0033—Draft Final Rule—Performance-Based Emergency Core Cooling System Requirements and Related Fuel Cladding Acceptance Criteria.” The NRC comment responses below include responses to the comments on the petition that mentioned the 10 CFR 50.46c draft final rule. <E T="03">Comment:</E> The petitioner stated that it is appropriate to consider fuel fragmentation, relocation, and dispersal (FFRD) as part of the rulemaking for “Increased Enrichment of Conventional and Accident Tolerant Fuel Designs for Light-Water Reactors” (Increased Enrichment rulemaking). <E T="03">NRC Response:</E> The NRC agrees with this comment. The Increased Enrichment rulemaking plan was provided to the Commission in SECY-21-0109, “Rulemaking Plan on Use of Increased Enrichment of Conventional and Accident Tolerant Fuel Designs for Light-Water Reactors,” dated December 20, 2021. In an SRM dated March 16, 2022, SRM-SECY-21-0109, “Staff Requirements—SECY-21-0109—Rulemaking Plan on Use of Increased Enrichment of Conventional and Accident Tolerant Fuel Designs for Light-Water Reactors,” the Commission approved this plan and further directed the staff to consider FFRD issues relevant to higher enrichment and fuel burnup levels as part of the rulemaking. <E T="03">Comment:</E> Framatome stated that the range of burnups meant by “moderate fuel burnup” in the petition is not clear. <E T="03">NRC Response:</E> The NRC agrees with this comment. The term “moderate fuel burnup” lacks specificity. The NRC interpreted “moderate fuel burnup” to encompass currently authorized fuel burnups above which FFRD could potentially occur. <E T="03">Comment:</E> The petitioner stated that licensees should report the number of fuel rod ruptures during a LOCA so the NRC may determine if near-term action is needed to limit the amount of loose material in the core. <E T="03">NRC Response:</E> The NRC disagrees with this comment. The NRC has reasonable assurance that the extent and consequences of fuel dispersal during a LOCA, for currently authorized fuel burnup levels, would be limited such that core coolability would not be challenged on a large scale. This conclusion is based on research and analyses summarized in SECY-15-0148, “Evaluation of Fuel Fragmentation, Relocation and Dispersal Under Loss-Of-Coolant Accident (LOCA) Conditions Relative to the Draft Final Rule on Emergency Core Cooling System Performance During a LOCA (50.46c),” dated November 30, 2015. <E T="03">Comment:</E> The petitioner stated that, based on engineering judgment, setting rod rupture limits to 1 percent of the core for a small-break LOCA and 10 percent of the core for a large-break LOCA is reasonable and practical. The petitioner stated that FFRD research should focus on establishing a technical basis for these limits and refine these limits as needed. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 34k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━