ML25189A239

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Snug - NRC Liasion Report July 2025-R2
ML25189A239
Person / Time
Issue date: 07/16/2025
From: Gurjendra Bedi
NRC/NRR/DEX/EMIB
To:
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Download: ML25189A239 (38)
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NRC Liaison Report & Updates Snubber User Group (SNUG) 2025 Meeting Sananah, GA Gurjendra S. Bedi, PE Mechanical Engineering and Inservice Testing Branch Division of Engineering and External Hazards Office of Nuclear Reactor Regulation July 14-16, 2025

Disclaimer

  • This presentation was prepared by staff of the U.S. Nuclear Regulatory Commission (NRC). It may present information that does not currently represent an agreed upon NRC staff position. NRC has neither approved nor disapproved the technical content.

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Topics for Discussion

  • Current Part 10 Code of Federal Regulation (CFR) 50.55a Code and standard, Regulatory Requirements.
  • Commercially Dedicated Snubber Valve Not Properly Heat Treated

Topics for Discussion (continued)

  • NRC/ASME O&M Fifteenth Symposium
  • ASME QME-1-2023 and Reformatted QME-1
  • Plant Restarts
  • Conclusion 4

10 CFR 50.55a Rulemaking ja

  • Inservice Inspection (ISI)/Inservice Testing (IST) Program Code of Record (COR) Interval and Code Case Final Rule (Revision 40)
  • ASME Operation and Maintenance of Nuclear Power Plants (OM Code), 2022 Edition, and ASME BPV Code, 2021 Edition, Final Rule
  • Note:

ISI/IST COR Program COR Interval includes Snubber Program Interval 5

ISI/IST Program including Snubber Program COR Interval and Code Case Rule (Rev. 40)

Ahuja

  • Editorial correction issued in Federal Register on July 29, 2024 (89 FR 60795).
  • Final rule specifies licensees required to update IST/ISI Program COR every two consecutive IST/ISI intervals if licensee implementing 2017 Edition (or later) of OM Code and 2019 Edition (or later) of BPV Code.
  • Final rule includes RG 1.192, Revision 5, to accept OMN-28, 29, and 30 without conditions, and OMN-31 with conditions.

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Transition at the End of Current IST Interval to 20/24-Year Interval

  • IST Program Interval 1 (after end of current interval)
  • Apply 2017 or later edition of OM Code as COR.
  • Submit relief and alternative requests for NRC review.
  • Implement ISTA-3120 10-year interval or OMN-31 12-year interval.
  • IST Program Interval 2
  • May apply same COR as Interval 1
  • Submit relief and alternative requests for NRC review.
  • Implement ISTA 10-year interval or OMN-31 12-year interval
  • Update COR at end of Interval 2 to begin next IST interval
  • FRN specifies 25-year maximum for same COR.

7

ASME OM Code -2022 Edition

  • Final rule includes changes to 10 CFR 50.55a to reflect 2022 Edition of OM Code and clarifications.
  • Changes to specific IST conditions (only snubber) indicated on next slides.

8

ASME OM Code-2022 Edition and Snubber Program Condition

  • Clarifies when implementing ISTD-4253, and Note 7 of Table ISTD-4252-1 in 2022 Edition, licensees prohibited from applying OMN-15, Revision 2 or Revision 3.

Notes:

1.

ASME OM-2020 and earlier Editions: Code Case OMN-13, which allows to extend the visual examination of snubber once every 10 years, shall not be used in conjunction with Code Case OMN-15, which allows to extend inservice testing of snubbers once every 10 years.

2.

ASME OM-2022 incorporates Code Case OMN-13. Therefore, 10 CFR 50.55a includes condition 10 CFR 50.55a(b)(3)(vii), while using ASME OM-2022.

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10 CFR 50.55a 2023 BPV Code and Code Cases Rulemaking (Revision 41)

  • 2023 ASME BPV Code Rulemaking in progress
  • Direct Final Rule (DFR) planned to incorporate by reference acceptable of noncontroversial and unconditioned Code Cases in 10 CFR 50.55a
  • Proposed/final rule process will continue for biennial incorporation by reference of ASME Code editions and conditionally-approved Code Cases in 10 CFR 50.55a.
  • First DFR for Code Cases in process 10

10 CFR 50.55a and Snubber Program

  • 10 CFR 50.55a(f)(4) and (g)(4) clarify relationship between 50.55a(f)(4) and (g)(4) regarding Inservice Testing (IST) and Inservice Inspection (ISI) programs for snubbers.

11

10 CFR 50.55a and Snubber Program

  • The NRC regulations require that the snubber program be updated and aligned with the plants IST or ISI program interval.
  • Snubber program alignment with the ISI or IST program interval should be clearly specified in the snubber program, along with start and end dates.
  • NUREG-1482, Guidelines for Inservice Testing at Nuclear Power Plants, describes a method to align the snubber program with the IST program.
  • Snubber Program alignment with the IST program interval in lieu of the ISI interval should be carefully evaluated, and any extension beyond the requirements of ASME OM Code, ISTA-3120, or ASME BPV Code,Section XI, IWA-2430, must be submitted as a request to NRC for authorization before implementation.

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10 CFR 50.55a and Snubber Program

  • While using the ASME OM Code for inservice examination and testing of snubbers (pin-to-pin), the examination of support structure and attachments must be performed by use of ASME BPV Code,Section XI, 2006 Addenda or later Editions as described in Figure 1300-1(f).

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Boundary between Snubber (pin-to-pin) and support structure Figure 1300-1(f),

ASME BPV Code,Section XI, 2006 Addenda and later Editions 14

Failure to Make an Interim 10 CFR Part 21 Report Notification of Anomaly:

  • NRC inspector completed an inspection March 31, 2024, at Diablo Canyon Power Plant (DCPP) (ML24113A066). One of the inspection report related to snubber is reportable under 10 CFR Part 21.

Reporting of Defects and Noncompliance, for the DCPPs failure to make an interim report within 60 days after identification of a potential deviation in installed pipe snubbers.

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Failure to Make an Interim 10 CFR Part 21 Report

==

Description:==

  • During refueling outage 1R24, the DCPP discovered test anomalies associated with pipe snubbers installed in the plant starting on October 4, 2023.
  • DCPP discovered that snubber had loose locking washers, excessive grease, out of tolerance parts, components installed incorrectly, loose tie-wires, and anomalies in the ball nut screw assembly. The licensee completed onsite troubleshooting on October 16, 2023.
  • Due to the snubbers being contaminated, the licensee experienced delays in shipping the snubbers to the vendor for evaluation.

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Failure to Make an Interim 10 CFR Part 21 Report

==

Description:==

  • The DCPP initiated Notification 51214999 on November 16, 2023, tracking the vendors task for testing the suspect snubbers for a Part 21 evaluation to be completed on April 16, 2024.
  • The DCPP held an internal meeting on March 4, 2024, and determined they failed to make an interim Part 21 report to the NRC. The DCPP completed making the interim report on April 4, 2024.

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Event Notification 57271-Part 21 Commercially Sourced Part Not Properly Heat Treated for snubber Notification of Anomaly:

  • NRC received notification on August 15, 2024, from Pacific Gas and Electric (PG&E) Company for Diablo Canyon Power Plant (DCPP) and a letter dated September 9, 2024 (ML24255A090) that a manufacturing non-conformance associated with snubber valve assemblies identified with ALCO (valve company) part number 2402466 is reportable under 10 CFR Part 21.
  • PG&E evaluation has determined the upper body of these valves did not meet material and heat treatment requirements (AISI 1117 resulfurized carbon steel vs. AISI 8620/8630 low ally steel.

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Event Notification 57271-Part 21 Commercially Sourced Part Not Properly Heat Treated Summary:

  • PG&E documented in the DCPP corrective action program. The subject snubber valve assemblies were purchased as a commercial grade item under ALCO Part No. 2402466 and dedicated for a safety-related application. Utilities that perform this dedication should consider specific tests for case-hardening and correct material verification.
  • Based on the snubber valve history, licensees should review their purchase order and installation history for snubber valves purchased ahead of and during the 2008 timeframe for similar vulnerabilities.

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Steam Generator Snubbers and 10 CFR 50.69 10 CFR 50.69 Regulation

  • A nuclear power plant licensee or applicant may request implementation of 10 CFR 50.69, Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Plants. Implementation of 10 CFR 50.69 allows for risk-informed treatment of structures, systems, and components (SSCs) as an alternative to certain special treatment requirements STRs) in the NRC regulations.
  • RISC-1 SSCs: safety-related SSCs that perform safety significant functions.
  • RISC-2 SSCs: nonsafety-related SSCs that perform safety significant functions.
  • RISC-3 SSCs: safety-related SSCs that perform low safety significant functions.
  • RISC-4 SSCs: nonsafety-related SSCs that perform low safety significant functions.

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Background - Snubber

  • Snubbers are used to support various piping systems and components along with rigid and spring hangers in nuclear power plants. In plant normal operation mode, the snubber permits slow, normal movement (thermal), but becomes rigid and holds the piping and components when it senses sudden motion, such as seismic events or a line break or a water hammer.

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Background - Snubber and Steam Generator

  • Hydraulic snubbers are used in SG upper support systems because of the snubbers ability to accommodate the large thermal movement of a SG during plant heatup and cooldown while providing restraint to the Reactor Coolant Loop (RCL) for dynamic events, such as postulated pipe ruptures and earthquakes.
  • Because of the complexity of the design of the SG upper support system, several factors can significantly affect the performance of the hydraulic snubbers and contribute to the continuing need to monitor and test the functionality of the snubbers. In some cases, snubber malfunctions have caused extended plant outages.

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=

Background===

  • In the past, system functional safety significance was deemed to be an adequate surrogate measure of the safety significance of snubbers.
  • Regulatory Guide 1.29, states that at the interface between seismic Category I and non-seismic Category 1 SSCs, the seismic Category 1 dynamic analysis requirements should be extended to either the first anchor point in the non-seismic system or a sufficient distance into the non-seismic Category 1 system so that the seismic Category 1 analysis remains valid.

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Background -Safety Significant of Snubber

  • ASME OM Code Case OMN-10 (2000), Requirements for Safety Significant Categorization of Snubbers Using Risk Insights and Testing Strategies for Inservice Testing of LWR Power Plants, which the NRC has not accepted. RG 1.193 provides a statement of concerns:
  • The method used for categorizing snubbers could result in certain snubbers being inappropriately categorized as having low safety significance.
  • These snubbers would not be adequately tested or inspected to provide assurance of their operational readiness.
  • In addition, unexpected extensive degradation in feedwater piping has occurred which would necessitate a more rigorous approach to snubber categorization than presently contained in this Code Case OMN-10. [ASME Code Case OMN-10 was developed by EPRI TR 110381 (May1998) 24

Background -Safety Significant of Snubber ASME OM Code Case OMN-10, Section: 4.2.3 Expert Panel Decision Criteria, states (a) Level A Inclusion Criteria. Any of the following contributors to snubber importance above stated threshold will potentially make the snubber HSSC [high safety significant component]:

(1) Level A-1. All snubbers protecting the following components:

(-a) PWRs: steam generators, reactor coolant pumps

(-b) BWRs: recirculation pumps Definitions from Code Case OMN-10:

  • Level 1 PRA: a PRA that identifies accident sequences that can lead to core damage, calculates the frequency of each sequence, and sums those frequencies to obtain CDF.
  • high safety significant components (HSSCs): components that have been designated as more important to plant safety by a blended process of PRA risk ranking and Expert Panel evaluation.

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Background -Safety Significant of Snubber

  • EPRI TR 110381 (May 1998), Risk-Based Snubber Inspection and Testing Guidelines-Pilot Project Studies, which references EPRI TR 105396, PSA [Probabilistic Safety Assessment ] Application Guide, dated August 1995.
  • EPRI TR 110381 was developed to provide a cost-effective, risk-informed inservice testing (RI-IST) strategy for snubbers and to deliver guidelines, pilot demonstrations, licensing evaluations, and a proposed ASME code case on RI-IST acceptance of nuclear piping snubbers.

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=

Background===

ASME/BPVC Case N-660, Risk-Informed Safety Classification for Use in Risk-Informed Repair/Replacement ActivitiesSection XI, Division 1, Section I-3.2.2 Classification Considerations part (d), states, A component support or snubber shall have the same classification as the highest-ranked piping segment within the piping analytical model in which the support is included. The Owner may further refine the classification ranking by more extensive application of the process defined in these requirements. These analyses shall be documented.

  • ANO-2 method ANO2-R&R-004, Revision 1, Request to Use Risk-Informed Safety Classification and Treatment for Repair/ Replacement Activities in Class 2 and 3 Moderate Energy Systems, dated April 7, 2007 (ML071150108) Section I-3.2.2 Classification Considerations part (d), states, A component support, hanger, or snubber shall have the same classification as the highest-ranked piping segment within the piping analytical model in which the support is included.

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Summary

  • Licensee is not required to categorize the snubbers associated with a Class 1/RISC-1 component under 10 CFR 50.69.
  • In that case, the snubbers would retain their original design classification, and any special treatments would continue to apply.

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Update of Snubber Program

  • NRC staff has learned that after implementing 10 CFR 50.69 treatment program for pumps, valves, and snubbers, the licensees failed to update plants IST Program and Snubber Program to reflect the changes.
  • The licensee should update IST Program and Snubber Program after implementing 10 CFR 50.69 treatment program for pumps, valves, and snubbers, the licensee is responsible to update IST program, as applicable.

29

NUREG-1482, Revision 4 Update

  • NRC staff has issued Draft Revision 4 of NUREG-1482, with public comment period closing April 14, 2025.
  • 46 comments received from 4 separate commenters
  • Staff is preparing responses to comments and finalizing NUREG for publication 30

NRC/ASME O&M Fifteenth Symposium

  • NRC/ASME O&M (formally Pumps, Valves, and Snubbers)

Fifteenth Symposium is being planned for July 28 and 29, 2025, with ASME OM Code committee meetings on July 30, 31, and August 1, 2025.

  • Symposium and ASME OM meetings are planned to be held in person at Bethesda North Marriott (across from NRC Headquarters While Flint building) in Washington, DC.

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ASME OM-2 Code

  • ASME has issued OM-2-2024, an IST Code for pumps, valves, and dynamic restraints (or components that perform similar functions) in new and advanced reactors.
  • NRC staff is considering a new Regulatory Guide (RG) for acceptance of the OM-2 Code with applicable conditions.

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ASME QME-1-2023 and reformatted QME-1

  • ASME QME-1 Standard for Qualification of Active Mechanical Equipment in Nuclear Facilities issued in 2023
  • ASME is preparing a reformatted QME-1 standard to be more applicable for new and advanced reactors that might not use water-cooled systems
  • NRC staff plans to revise RG 1.100 to accept QME-1-2023 and reformatted QME-1 with conditions when available 33

Plant Restarts

  • Few plants are considering returning to operation from a permanent shutdown or ceasing operation or decommissioning status
  • There are various unknown:
  • Where did the plant leave off?
  • What records were maintained?
  • Physical condition of snubbers: hardened or dry grease, snubber settings, service life, how long-ago service life performed
  • Preventative maintenance, if performed 34

Plant Restarts (cont.)

  • New baselining
  • Conditions of piping and its supports
  • Stagnant conditions in piping system
  • Reconfirmation/reestablishment of piping system, various components (i.e., pumps, valves and snubbers)
  • All snubbers should be visually examined per ASME OM Code requirements and snubber settings should be examined and compared with snubber drawings
  • Hardening of grease, degradation of soft materials, seals other detrimental effects likely occurred
  • Preventive Maintenance was not performed at operation frequencies
  • Degraded or non-conforming service life possible due to nonoperational conditions
  • This would be more than just IST scope of plant 35

Plant Restarts (cont.)

  • Preparation:
  • Engage NRC earlier
  • NRC staff is planning to propose a ASME Code Case to the ASME OM Code Committee specifically for IST activities and IST Program
  • For IST Program, Restart plant date shall not be considered from the time the plant was permanently shut down or decommissioned until a decision was made to restart the plant (which could have been many years), the equipment and snubbers in the plant was basically ignored.

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Licensees who believe that some of the items discussed are applicable to their facilities may wish to review their current snubber program and modify their program as appropriate.

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