ML24327A026

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ISTOG- NRC Snubber ASME OM Code and Issues December 2024-Bedi R4
ML24327A026
Person / Time
Issue date: 11/21/2024
From: Gurjendra Bedi
NRC/NRR/DEX/EMIB
To:
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Download: ML24327A026 (38)
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Snubber Inservice Testing Issues and Updates Inservice Testing Owners Group Meeting December 9-10, 2024 Gurjendra S. Bedi, PE Mechanical Engineering and Inservice Testing Branch Division of Engineering and External Hazards Office of Nuclear Reactor Regulation

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

  • Title 10 of the Code of Federal Regulation (10CFR) Section 50.55a, Code and standard and Snubber Program.
  • Snubber Program Code of Record (COR) and Interval Update
  • Visual Examination
  • Conclusion 3

10 CFR 50.55a Rulemaking Ahuja

  • 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 4

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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ASME OM Code-2022 Edition and Snubber Program

  • 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.

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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 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.

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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, 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 11

Snubber Program, ASME OM Code, Subsection ISTD

  • Snubber IST Program shall contain snubber (1) visual examination; (2) testing and; (3) service life monitoring as follows:
  • General Examination Requirements (ISTD-3100)
  • Specific Examination Requirements (ISTD-4000)
  • General Testing Requirements (ISTD-3200)
  • Specific Testing Requirements (ISTD-5000)
  • General Service Life Monitoring Requirements (ISTD-3300)
  • Service Life Monitoring Requirements (ISTD-6000) 12

ASME OM Code, ISTD-4200, Visual Examination

  • ISTD-4210 Method and Objective. Snubber visual examination to identify:
  • physical damage,
  • leakage,
  • corrosion, or degradation
  • Nonmandatory Appendix B, Snubber Examination Checklist Items List
  • ISTD-4231 Restrained Movement. Snubbers visual examination to observe
  • loose fasteners, or members that are corroded or deformed
  • disconnected components or other conditions that might interfere with the proper restraint of movement
  • ISTD-4232 Thermal Movement. Snubber visual examination to verify
  • if no indication of binding,
  • misalignment, or

Visual Examination

  • ISTD-4233 Design-Specific Characteristics.
  • snubbers shall be free of defects (design)
  • fluid supply or content for hydraulic snubber
  • fluid level is equal to or greater than the minimum specified amount
  • fluid is less than the minimum amount, the installation shall be identified as unacceptable, unless a test establishes that the performance of the snubber is within specified limits.

Tests shall be performed in accordance with ISTD-5210.

  • ISTD-4240 Operational Readiness Test Evaluation.
  • snubber that requires further evaluation or is classified as unacceptable during inservice visual examination may be tested in accordance with ISTD-5210.
  • results that satisfy the operational readiness test criteria of ISTD-5210 shall be used to accept the snubber, provided the test demonstrates that the unacceptable condition did not affect operational readiness.
  • ISTD-4280 Inservice Examination Corrective Action.
  • unacceptable snubbers shall be adjusted, repaired, modified, or replaced.

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Nonmandatory Appendix B, Snubber Examination Check List

  • Examples for of unacceptable attributes:
  • Inadequate reservoir fluid level
  • Loose, missing, or incorrectly installed structure connections or fasteners
  • Vented reservoir oriented such that fluid cannot gravity to snubber
  • Corrosion or solid deposit that could result in unacceptable performance
  • Deformed structure attachment or piston rod
  • Weld arc strikes, paint, weld slag, adhesive, or other deposit on piston rod or support cylinder that could result in unacceptable snubber performance
  • Spherical bearing not fully engaged in attachment lug
  • Inadequate position setting.

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Visual Examination

  • Visual indication does not mean failure.
  • Functional testing should be performed to determine if the snubber is degraded or UNSAT.
  • Snubbers can be evaluated to determine operational readiness
  • Issue Corrective Action (CA) to correct the deficiency
  • Issue reports for indications.

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Examples of Visual Indication 1.

Inadequate position setting.

  • Verifying that thermal movement is acceptable. Will the snubber top out or bottom out?

2.

Loose, missing or incorrectly installed structural connections or fasteners.

  • Are all the fasteners tight? Are any fasteners missing? One fastener loose but 3 are tight? Missing washers? Missing cotter pins?
3. Degradation of fluid reservoir Fluid reservoir is cracked or damaged.
4. Inadequate fluid reservoir level.
  • Low fluid or no fluid.
5. Corrosion or solid deposits that result in unacceptable snubber performance.
  • Any deposits that can adversely affect the performance of the snubber.

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Example 1-A Inadequate position setting.

Snubber extension piece not fully connected to snubber body due to wrong size bolts (and missing bolts)

Result = UNSAT Justification = Without the 2 bolts attached and the existing bolts the wrong size, the snubber is not capable of restraining dynamic movements. A SAT functional test per ISTD-4240 will not change the results of this exam.

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Example 1-B End Pin Missing Snubber end pin (bolt) missing Result = UNSAT Justification = Without end bolt, the snubber is not capable of restraining dynamic movements. A SAT functional test per ISTD-4240 will not change the results of this exam.

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Example 2 Loose, missing or incorrectly installed structural connections or fasteners.

Example 2A: Anchor bolts for attachment of snubber rear bracket to the concrete structure are loose/missing. No other issues noted on the exam.

Result = SAT Justification = The issue is not within the examination boundary. The issue exists with design of structural attachment, not with snubber. Corrective actions shall be initiated to tighten the bolt, investigate the cause, and analyze the structural attachment. No test per ISTD-4240 is required to determine if snubber meets operational readiness because no issues are noted with the snubber.

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Example 2 Loose, missing or incorrectly installed structural connections or fasteners.

Example 2B: Anchor bolts for attachment of snubber rear bracket to the concrete structure are loose/missing. Snubber setting is outside of the expected range.

Result = Degraded Justification = See above for bolt issue. An anchor bolt issue combined with a snubber out of normal travel range is indicative of a transient event. A functional test may be required per ISTD-4240 to determine if snubber meets operational readiness 21

Example 3 Fluid Level Example 3A: Snubber is found with a fluid level between recommended level and unacceptable level.

Result = Degraded Justification = Snubber still has adequate fluid to perform its design function. Corrective actions shall be implemented to address the fluid level.

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Example 3 Example 3B: Snubber is found with a fluid level below unacceptable level.

Result = UNSAT or Degraded (depends on test result)

Justification = A functional test per ISTD-4240 is required to determine if the snubber can perform its design function.

If the test is SAT, the exam is considered degraded. If the test is UNSAT, the exam is considered UNSAT. Corrective actions shall be implemented to address the fluid level.

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Example 4 Snubber reservoir is cracked or damaged Result = UNSAT or Degraded (depends on test result)

Justification = A functional test per ISTD-4240 is required to determine if the snubber can perform its design function. If the test is SAT, the exam is considered degraded. Corrective actions shall be implemented to address the damaged reservoir.

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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 27

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) 32

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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Conclusion

  • 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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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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