Alternative Method for Calculating Embrittlement for Steel Reactor Vessels

NUCLEAR REGULATORY COMMISSION <CFR>10 CFR Part 50</CFR> <DEPDOC>[Docket No. PRM-50-120; NRC-2019-0180]</DEPDOC> <SUBJECT>Alternative Method for Calculating Embrittlement for Steel Reactor Vessels</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, dated August 19, 2019, submitted by Thomas A. Bergman on behalf of NuScale Power, LLC. The petition was docketed by the NRC on September 11, 2019, and was assigned Docket No. PRM-50-120. The petitioner requested that the NRC revise its regulations to add an alternative formula for calculating the mean value of the transition temperature shift described in American Society for Testing and Materials Standard E900-15 to the NRC's regulations and guidance documents. The NRC is denying the petition because the petitioner did not demonstrate the immediacy of any safety issues in the concerns raised in the petition and did not provide any new information that would warrant revision of the NRC's regulations. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> The docket for the petition for rulemaking PRM-50-120 is closed on July 23, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> Please refer to Docket ID NRC-2019-0180 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-2019-0180. 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 individuals 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 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> Aaron Kwok, Office of Nuclear Material Safety and Safeguards, telephone: 301-415-1371, email: <E T="03">Aaron.Kwok@nrc.gov;</E> or Dan Widrevitz, Office of Nuclear Reactor Regulation, telephone: 301-415-2620, email: <E T="03">Dan.Widrevitz@nrc.gov.</E> Both are staff of the U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001. </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. Reasons for Denial</FP> <FP SOURCE="FP-2">IV. Availability of Documents</FP> <FP SOURCE="FP-2">V. 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—requirements for filing,” provides an opportunity for any interested person to petition the Commission to issue, amend, or rescind any regulation. On August 19, 2019, the NRC received a petition for rulemaking (PRM) from Thomas A. Bergman on behalf of NuScale Power, LLC (NuScale). The petitioner requested that the NRC revise its regulations to add an alternative formula for calculating the mean value of the transition temperature shift described in American Society for Testing and Materials (ASTM) E900-15, “Standard Guide for Predicting Radiation-Induced Transition Temperature Shift in Reactor Vessel Materials.” On November 19, 2019 (84 FR 63819), the NRC published a notice of docketing and request for comment for PRM-50-120. The petitioner requested that the NRC amend its regulations in § 50.61(c)(1)(iv), with the first paragraph to read as follows: “ΔRT <E T="52">NDT</E> is the mean value of the transition temperature shift, or change in RT <E T="52">NDT</E> , due to irradiation, and must be calculated using Equation 3. As an alternative, ΔRT <E T="52">NDT</E> may be determined in accordance with ASTM E900-15 instead of Equation 3, and Tables 1 and 2 of this section.” Further, the petitioner requested that the formula for calculating the mean value of the transition temperature shift described in ASTM E900-15 be added for use as an alternative to Equation 2 in Regulatory Guide (RG) 1.99, Revision 2, “Radiation Embrittlement of Reactor Vessel Materials.” The petitioner requested that the following text be added to paragraph 2 in Section 1.3 of RG 1.99, to read as follows: “For new plants electing to use ASTM E900-15 as allowed by Regulatory Position 3 for determining ΔRT <E T="52">NDT</E> , the correction factor is not required, provided that the irradiation temperature is within the ASTM E900-15 applicability range.” The NRC identified the following five main issues raised in the petition: <E T="03">Issue 1:</E> The methodology for calculating the mean value of the transition temperature shift (ΔRT <E T="52">NDT</E> ) in § 50.61, “Fracture toughness requirements for protection against pressurized thermal shock events,” and RG 1.99 is overly conservative and is based on outdated information. <E T="03">Issue 2:</E> The 1 °F/1 °F adjustment methodology requires excessive compensation for irradiation temperatures less than 525 °F and has significant drawbacks. <E T="03">Issue 3:</E> The staff required NuScale to comply with § 50.61 and RG 1.99 and use the 1 °F/1 °F adjustment methodology. <E T="03">Issue 4:</E> ASTM E900-15 more accurately models the effects of irradiation temperature and does not suffer the drawbacks of the 1 °F/1 °F adjustment methodology. <E T="03">Issue 5:</E> The current methodology for determining embrittlement in § 50.61, with 1 °F/1 °F adjustment, is unnecessarily burdensome for reactors like NuScale, in that it would: (a) result in unnecessarily restrictive heat-up and cool-down rates during startups and shutdowns, and (b) cause surveillance capsules to be withdrawn and tested prematurely. <HD SOURCE="HD1">II. Public Comments on the Petition</HD> The notice of docketing for PRM-50-120 requested interested persons to submit comments. The comment period closed on December 19, 2019. The NRC received 6 comment submissions consisting of 38 comments. The comments were received from private citizens, individuals affiliated with advocacy groups, and an individual affiliated with an industry group. The comments received on PRM-50-120 and the NRC's responses to them are available in ADAMS under Accession No. ML20304A003. <HD SOURCE="HD1">III. Reasons for Denial</HD> The NRC is denying the petition because the petitioner did not demonstrate the immediacy of any safety issues in the concerns raised in the petition and did not provide any new information that would warrant revision of the NRC's regulations. The NRC concludes that Issue 1 does not warrant rulemaking because the petitioner did not provide any new information that would warrant the expenditure of limited NRC resources for rulemaking. Specifically, the NRC found that while a significantly larger body of data for neutron embrittlement is now available, the core assertion that RG 1.99, Revision 2, with the use of the 1 °F/1 °F adjustment methodology, provides an overly conservative prediction is not correct in cases the NRC has evaluated such as the NuScale design certification application (DCA). The petition presents no additional information or data to demonstrate that the current regulation is overly conservative. The NRC concludes that Issue 2 does not warrant rulemaking because the petitioner did not provide any new information beyond what is approved in the NRC's final safety evaluation for the NuScale DCA. The steels proposed to be used in the NuScale DCA, as well as those proposed in other light-water designs known to the NRC, are represented in the operating fleet. The petition did not present any pertinent new information regarding embrittlement performance characteristics of these materials. The NRC determined that the NuScale design presented no unusual characteristics justifying a unique temperature-embrittlement relationship for that design. In addition, RG 1.99, Revision 2, does not prescribe a temperature adjustment; rather, it states that any correction factor for operating conditions below 525 °F should be “justified by reference to actual data.” Embrittlement was previously evaluated by the staff for the specific case of a NuScale design, whose operating conditions include a relatively low operating temperature (the embrittlement impacts of which the 1 °F/1 °F adjustment compensates), for 40 years of operation. The NRC verified, during its review of the NuScale DCA, that a combination of the methodology in 10 CFR 50.61 and RG 1.99, Revision 2, together with the 1 °F/1 °F adjustment provides an appropriate estimate of RT <E T="52">NDT</E> based on a comparison to the publicl ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 22k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━