ML25255A053
| ML25255A053 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute |
| Issue date: | 09/08/2025 |
| From: | Basso T Nuclear Energy Institute |
| To: | Office of Administration |
| References | |
| NRC-2024-0036, 90FR38512 00003, DG-1422, Rev 1, RG-1.245 | |
| Download: ML25255A053 (1) | |
Text
PUBLIC SUBMISSION As of: 9/12/25, 8:41 AM Received: September 08, 2025 Status: Pending_Post Tracking No. mfb-gmft-j77b Comments Due: September 08, 2025 Submission Type: Web Docket: NRC-2024-0036 Preparing Probabilistic Fracture Mechanics Submittals Comment On: NRC-2024-0036-0005 Draft Regulatory Guide: Preparing Probabilistic Fracture Mechanics Submittals Document: NRC-2024-0036-DRAFT-0006 Comment on FR Doc # 2025-15049 Submitter Information Organization:Nuclear Energy Institute General Comment See attached file(s)
Attachments 09-08-25_NRC_NEI Comments on DG-1422 Docket ID NRC-2024-0036 9/12/25, 8:41 AM NRC-2024-0036-DRAFT-0006.html file:///C:/Users/BHB1/Downloads/NRC-2024-0036-DRAFT-0006.html 1/1 SUNI Review Complete Template=ADM-013 E-RIDS=ADM-03 ADD: Vance Petrella, Trish Walker Webb, Mary Neely Comment (3)
Publication Date:
8/8/2025 Citation: 90 FR 38512
Thomas Basso Sr. Director, Engineering & Risk Phone: 202.739.8049 Email: tbb@nei.org September 8, 2025 Office of Administration Mail Stop: TWFN-7-A60M U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
NEI Comments on Draft Regulatory Guide (DG)-1422, Revision 1, Preparing Probabilistic Fracture Mechanics Submittals, 89 Fed. Reg. 14782 (August 5, 2025) Docket ID: NRC-2024-0036 Project Number: 689
Dear Program Management,
Announcements, and Editing Staff:
The Nuclear Energy Institute (NEI)1, on behalf of its members, appreciates the opportunity to provide comments on Draft Regulatory Guide DG-1422, Revision 1, Preparing Probabilistic Fracture Mechanics Submittals, which proposes a revision to Regulatory Guide 1.245.
NEI supports the NRCs ongoing effort to improve clarity and consistency in technical submittals. However, we have several substantive concerns with DG-1422, particularly the expectation that applicants using probabilistic fracture mechanics (PFM) must now address each principle of the integrated decision-making process described in RG 1.174 in their submittals. The staff clearly stated this position, this revision would explain that PFM analyses are only one part of a risk-informed regulatory application, and that RG 1.174 (which provides a framework for integrated risk-informed decision-making) is also applicable to regulatory applications that use PFM as part of their technical basis. NEI disagrees that all PFM applications are risk-informed.
The industry has long-used fracture mechanics in its design and analyses, and the state-of-the-art has advanced significantly in recent years. The industry historically used a deterministic fracture mechanics (DFM) approach when evaluating whether a component will fail under a certain stress level. With the advent of probabilistic fracture mechanics (PFM), more information is available, and the results are expressed as a likelihood of failure (e.g., probability of rupture of a component over a given time) rather than a binary answer of yes/no. Neither DFM nor PFM is a risk-informed approach.
In contrast, a risk-informed approach does not focus on whether or not (or the likelihood that) one component fails but considers the entire plant response to an initiating event, such as a pressure boundary failure in the case of a loss-of-coolant accident, and assesses the change in core damage frequency (CDF) or large early 1 The Nuclear Energy Institute (NEI) is responsible for establishing unified policy on behalf of its members relating to matters affecting the nuclear energy industry, including the regulatory aspects of generic operational and technical issues. NEIs members include entities licensed to operate commercial nuclear power plants in the United States, nuclear plant designers, major architect and engineering firms, fuel cycle facilities, nuclear materials licensees, and other organizations involved in the nuclear energy industry.
Office of Administration September 8, 2025 Page 2 Nuclear Energy Institute release frequency (LERF). Unfortunately, DG-1422 fails to distinguish between PFM and a risk-informed approach. If the NRC has modified its approach to require that all applications of PFM include a risk-informed argument, this decision raises forward-fitting concerns that have not been evaluated.
On another topic, language added to Section 2.1 of DG-1422, Revision 1, implies that PFM, when used along with a risk-informed argument, will be exclusively used to support changes to a plants licensing basis and that an additional performance monitoring plan will always be needed. This position may stem from the fact that PFM has been recently used in risk-informed submittals to optimize inspection frequencies. However, this neglects the history over the last 15 years of using PFM as part of a risk-informed argument to resolve emergent issues.
Example issues pertaining to reactor pressure vessel integrity include the following:
Quasi-Laminar Indications (Hydrogen Flaking) - EPRI developed report, Materials Reliability Program: Evaluation of the Reactor Vessel Beltline Shell Forgings of Operating U.S. PWRs for Quasi-Laminar Indications, Revision 1 (MRP-367). EPRI, Palo Alto, CA: 2013. 3002000647, which was submitted to the NRC for information and to assist in their independent review and assessment of this issue. The NRC issued a technical assessment (ML15282A218) in which they referred to the EPRI report and said that it was considered in determining the recommendations offered in the technical assessment.
Carbon Macrosegregation - EPRI developed report, Materials Reliability Program: Evaluation of Risk from Carbon Macrosegregation in Reactor Pressure Vessel and Other Large Nuclear Forgings, Revision 1 (MRP-417, Rev. 1). EPRI, Palo Alto, CA: 2018. 3002012328, which was submitted to the NRC for information and to assist in its independent review and assessment of this issue. The NRC issued a technical disposition of this issue in ML18017A441 in which the EPRI report is utilized.
Potential non-conservatism of Branch Technical Position (BTP) 5 EPRI developed report, Assessment of the Use of NUREG- 0800 Branch Technical Position 5-3 Estimation Methods for Initial Fracture Toughness Properties of Reactor Pressure Vessel Steels (MRP-401 and BWRVIP-287). EPRI, Palo Alto, CA: 2015. 3002005348, which was submitted to the NRC for information and to assist in its independent review and assessment of this issue. The NRC ultimately issued a closure memorandum in ML16364A285 which included a review of the EPRI report.
In each of the instances cited above, the NRC evaluated the issue using the LIC-504 process, Integrated Risk-Informed Decision-Making Process for Emergent Issues, and concluded that it posed a negligible increase in risk such that no new performance measures were needed.
A further example where PFM is used to evaluate an issue and where additional performance monitoring was not justified is the use of xLPR to assess compliance with GDC 4 for Alloy 82/182 butt welds that have been approved for leak-before-break (LBB). The acceptance criteria for application of xLPR documented in ML16271A436 includes acceptance criteria consistent with the core damage frequency (CDF) and large early release frequency (LERF) risk metrics in RG 1.174 and requires that defense in depth and safety margins be addressed. However, the xLPR acceptance criteria do not require the implementation of a performance monitoring plan.
PFM has also been used by the NRC to develop regulatory positions, such as the Alternate Pressurized Thermal Shock (PTS) Rule, 10 CFR 50.61a. The technical basis for 10 CFR 50.61a, as documented in NUREG-1806, describes that the through-wall cracking frequency value on which the screening limits are
Office of Administration September 8, 2025 Page 3 Nuclear Energy Institute based is partially based on the CDF and LERF metrics in RG 1.174. However, NUREG-1806 makes no mention of performance monitoring, and 10 CFR 50.61a contains no such requirements.
Therefore, the NRC should not impose the burden of new or increased performance monitoring simply because a risk-informed approach is used and instead should require changes to performance monitoring only when warranted by a holistic evaluation of the five risk-informed principles, consistent with existing NRC guidance.
In summary, NEI respectfully requests that the NRC either withdraw DG-1422 or revise it with additional public comment period to:
Make a clear distinction between applications using PFM to inform a technical basis and those where PFM is included in a risk-informed argument; and Clarify that when PFM is used as part of a risk-informed argument, the five principles of risk-informed decision making should be applied in context and with a balanced understanding that includes risk insights from plant probabilistic risk assessment (PRA), along with other engineering inputs, as expected from a risk-informed approach, and as described in existing NRC guidance, such as RG 1.174.
Alternatively, the NRC should justify its change in position with a forward-fitting analysis. The industry has other comments related to the recognition of approved industry codes which are included in the attachment.
We appreciate the NRCs engagement with stakeholders and welcome the opportunity to further support this effort. If you have any questions or require additional information, please contact Thomas Basso at tbb@nei.org or 484-366-7534.
Sincerely, Thomas Basso Sr. Director, Engineering & Risk
Attachment:
Table of Detailed Comments on DG-1422, Rev. 1 cc:
Christopher Nellis, RES, NRC Vance Petrella, RES, NRC John Tappert, RES, NRC Marissa Bailey, RES, NRC Michael A. Eudy, RES, NRC Patrick Raynaud, RES, NRC Michele Sampson, DNRL, NRR, NRC Meena Khanna, DRA, NRR, NRC
NEI Comments on DG-1422, Revision 1 Page 1 DG-1422 Rev. 1 Text Comment/Question Recommendation Related Guidance:
PFM is likely to be used to risk-inform licensing applications.
The statement in the Related Guidance is speculative and unnecessary and creates ambiguity about scope and applicability.
The need for and applicability of this RG must be uniquely clarified from when RG 1.174 applies as that guidance already exists and does not need to be different for RIDM applications involving PFM if it truly is a regulatory RIDM.
Delete or replace with clear applicability statement (e.g.,
This RG applies when PFM is used to support a risk-informed application.)
Reason for Revision:
The revisions made to RG 1.245, Revision 0 clarify guidance for applications that leverage risk insights, such as PFM. [Bolded for emphasis.]
This is an incorrect characterization: PFM is not itself a risk insight but an analytical tool. This statement may be misleading for reviewers when equating any use of PFM to risk insights/risk informed decision making because it has the word probability is not accurate.
Delete phrase or clarify that PFM supports risk-informed applications but is not itself a risk insight.
Background:
The heightened focus on PFM is partly due to the increased emphasis on risk-informed regulation, but also because plant aging and new degradation mechanisms This statement is speculative and hyperbolic; it implies NRC action is driven by aging or unknown unknowns not being addressed. There are robust programs with decades of operating experience which manage aging and monitor degradation mechanisms. This is not appropriate for regulatory guidance for what is needed in a PFM submittal.
Delete entire sentence.
NEI Comments on DG-1422, Revision 1 Page 2 2.1 Regulatory Context Either way, PFM results provide risk insights into the impacts of the proposed change, therefore, applicants using these tools to justify a submittal, such as an alternative to the codes and standards requirements, should consider not only the PFM analysis results but also other factors when developing the basis. [Underlined for emphasis.]
To reduce uncertainty in the application of this guidance, specifically what is meant by other factors should be clarified. Are they the items discussed in the latter paragraphs of section 2.1? The text is open ended and leaves licensees vulnerable to subjective interpretations of what other factors need to be considered and included in a submittal.
The Regulatory Guide should be more precise in the content of the submittal.
2.1 Regulatory Context First, a licensees proposed change may affect safety margins and layers of defense incorporated into the current plant design and operation.
Therefore, the licensee should reevaluate the safety margins and layers of defense to support the proposed change. Second, careful consideration should be given to implementation of the proposed change and the associated performance monitoring strategies to ensure that they do not cause any unexpected adverse safety degradation. Therefore, an implementation and DG-1422, Revision 1, Page 11 monitoring plan should be developed to ensure that the PFM analysis conducted to examine the impact of the proposed changes continues to reflect the actual reliability and availability of the component evaluated. These considerations ensure that the conclusions drawn from the analyses remain valid.
In response to NEIs comments on DG-1422, Rev. 0, that the text in Section 2.1 imparted the requirements of RG 1.174 on PFM applications, the NRC revised the bulleted text into a paragraph of requirements that still imparts the RG 1.174 concepts onto all applications involving PFM. These requirements without the context of the full RIDM framework and can lead to misuse by reviewers outside RG 1.174.
As qualified in the referenced EPRI report (Ref. 17); When information from the plant probabilistic risk assessment (PRA) is used along with the PFM results to propose a risk-informed change to the plant licensing basis, explicitly address each of the five items identified below, i.e., include sufficient discussion how each is ensured. It is not correct to interpret this to mean that the RG 1.174 principles need be addressed for every application of PFM.
DG-1422 Rev. 1 applies the referenced EPRI report out of context.
The requirement to address the five principles in RG 1.174 should only apply to PFM submittals that use information from plant probabilistic risk assessment (PRA). There should be clear exceptions or clarity when PFM is not used to support a risk-informed approach.
Moreover, this RG should simply refer to RG 1.174 if the PFM application is risk-informed and not embedded parts of RG 1.174 which would be missing the full context of RG 1.174.
NEI Comments on DG-1422, Revision 1 Page 3 2.1 Regulatory Context regulatory submittals using PFM analyses should explain why a probabilistic approach is appropriate and how the probabilistic approach is used to demonstrate compliance with the regulatory criteria. When no specific regulatory acceptance criteria exist, the submittal should explain how the probabilistic approach informs the regulatory action and regulatory compliance demonstration.
Applicants should be aware that this RG focuses only on the supporting PFM information needed for the staff to make an informed decision regarding the acceptability of the PFM methodology.
These statements seem to contradict the intent of this RG.
It is unclear whether the intent is to determine the acceptability of the PFM methodology or approval of a RIDM application.
The text should be revised or deleted such that the information being requested meets the intent of RG 1.245 to determine the acceptability of the PFM methodology.
2.1 Regulatory Context Application specific guidance may be needed to develop the remaining basis needed for integrated decision making.
Although performance monitoring is cited as an example, this statement is vague and open to interpretation as to when specific guidance is required and what that guidance may entail.
The Regulatory Guide should be more precise in the content of the submittal.
2.2 Information Made Available As mentioned above, this includes not only the information described in this RG, but also the information on safety margins, defense in depth, and performance monitoring.
It is not clear why this information would be needed if PFM is used as additional supporting analysis for an application that is not using information from the plant PRA.
DG-1422 should not assume all PFM applications are risk-informed and use information from the plant PRA. Revise to clarify and qualify when such information should be included in a submittal.
NEI Comments on DG-1422, Revision 1 Page 4 Table C-2: SQA and V&V Code Categories Footnote a:
As of the publication of this RG version, PFM codes used in NRC-approved applications or having received general approval within a validated range include xLPR, FAVOR, and SRRA.
Other industry PFM codes have been used in multiple NRC submittals and approved for use in those submittals should be included in Footnote a, e.g.,
EPRIs VIPER, VIPER-NOZ, or PROMISE codes. There are several other industry codes that have been approved for use in industry applications that have received NRC approval such as reactor pressure vessel weld examinations and risk-informed methods to piping inservice inspection.
Update the referenced PFM codes to all those that have been NRC-approved.
Reference 14:
NRC, RG 1.99 Revision 2 Update FAVOR Scoping Study, Technical Letter Report TLRRES/DE/CIB-2020-09, Washington, DC, October 2020 (ML20300A551). References 14 and 16 are Technical Letter Reports, so their references in this list should have the same format. See edits in Ref. 16.
This appears to be a note that should have been deleted.
Correct the text of Reference
- 14.
2.3. Quantities of Interest and Acceptance Criteria The use of previously approved acceptance criteria is encouraged but should be appropriately justified and explained.
This statement is problematic; requiring licensees to re-justify already approved criteria undermines efficiency.
Revise to: Use of previously approved acceptance criteria is acceptable without further justification.
Glossary definitions of:
risk-informed sensitivity analysis sensitivity studies Unnecessary and inconsistent with established definitions (e.g.,
NUREG-2122). Creates risk of conflicting terminology.
Delete redundant/conflicting definitions. Reference NUREG-2122 as the authoritative source for terminology.