ML24299A264

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Response to Request for Supplemental Information Needed for Acceptance of Requested Licensing Action Regarding Primary Containment Leakage Technical Specifications
ML24299A264
Person / Time
Site: Limerick  Constellation icon.png
Issue date: 10/25/2024
From: Para W
Constellation Energy Generation
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
Download: ML24299A264 (1)
v • d • e


Text

200 Energy Way Kennett Square, PA 19348 www.constellation.com

10 CFR 50.90

October 25, 2024

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Limerick Generating Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353

Subject:

Response to Request for Supplemental Information Needed for Acceptance of Requested Licensing Action Regarding Primary Containment Leakage Technical Specifications

References:

1. Letter from Wendi Para, Constellation Energy Generation, LLC to the U.S.

Nuclear Regulatory Commission, License Amendment Request for Modification to Technical Specification 3.6.1.2 and Main Steam Isolation Valve Leakage Rate Requirements, dated August 28, 2024 (ADAMS Accession No. ML24241A195).

2. Letter from Audrey Klett, U.S. Nuclear Regulatory Commission to Constellation Energy Generation, LLC, Limerick Generating Station, Units 1 and 2 -

Supplemental Information Needed for Acceptance of Requested Licensing Action Regarding Primary Containment Leakage Technical Specifications, dated October 7, 2024 (ADAMS Accession No. ML24274A237)

By letter dated August 28, 2024, Constellation Energy Generation, LLC (CEG) submitted an application for amendment to the Technical Specifications (TS) for Limerick Generating Station, Units 1 and 2. CEG requested a license amendment to revise TS 3.6.1.2.c (Reference 1). The proposed amendment would modify TS 3.6.1.2, Containment Systems - Primary Containment Leakage, to verify the allowable leak rate through each main steam line and the total leak rate through all four main steam lines. By letter dated October 7, 2024, the U.S. Nuclear Regulatory Commission (NRC) notified CEG that supplemental information is needed to complete the acceptance review of the LAR (Reference 2). CEGs response to the NRCs supplemental information request is provided in Attachment 1.

CEG has reviewed the information supporting the No Significant Hazards Consideration and the Environmental Consideration that was previously provided to the NRC in Reference 1. The information in this response does not impact the conclusion that the proposed license amendments do not involve a significant hazards consideration. The information also does not impact the conclusion that there is no need for an environmental assessment to be prepared in support of the proposed amendments.

U.S. Nuclear Regulatory Commission Response to Request for Supplemental Information - LGS MSIV Leakage LAR October 25, 2024 Page 2

There are no regulatory commitments contained in this response.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b),

CEG is notifying the Commonwealth of Pennsylvania of this response to request for additional information by transmitting a copy of this letter to the designated State Official.

If you have any questions regarding this submittal contact Steve Flickinger at 267-533-5302.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 25th day of October 2024.

Respectfully,

Wendi Para Sr. Manager - Licensing Constellation Energy Generation, LLC

Attachment:

Response to Request for Supplemental Information

cc: Regional Administrator - NRC Region I w/ attachments NRC Senior Resident Inspector - Limerick Generating Station "

NRC Project Manager, NRR - Limerick Generating Station "

Director, Bureau of Radiation Protection - Pennsylvania Department of Environmental Protection ATTACHMENT

Response to Request for Supplemental Information

By letter dated August 28, 2024, Constellation Energy Generation, LLC (CEG) submitted an application for amendment to the Technical Specifications (TS) for Limerick Generating Station, Units 1 and 2. CEG requested a license amendment to revise TS 3.6.1.2.c (Reference 1). The proposed amendment would modify TS 3.6.1.2, Containment Systems - Primary Containment Leakage, to verify the allowable leak rate through each main steam line and the total leak rate through all four main steam lines. By letter dated October 7, 2024, the U.S. Nuclear Regulatory Commission (NRC) notified CEG that supplemental information is needed to complete the acceptance review of the LAR (Reference 2).

Requests for Supplemental Information:

1. The LAR does not have sufficient justification for the NRC to evaluate whether the requested change will ensure that (1) the assumed leakage rates of 200 standard cubic feet per hour (scfh) combined or 100 scfh per steam line (tested at 22 pounds per square inch gauge) will not be exceeded and (2) the MSLs and main steam isolation valves (MSIVs) would be operable when TS 3.6.1.2 is applicable. For example:

The LAR does not describe the test methods for determining leakage and operability, such as the arrangement(s) used for testing MSIV leakage per ANSI/ANS-4[5]6 1994 (LAR Reference 3) and how maximum and minimum pathway leakage rate (MXPLR and MNPLR) are used.

Response

MSIV Local Leak Rate Testing (LLRT) currently uses acceptance criteria for operability of <100 scfh for a single MSIV and <200 scfh total for all four main steam lines (MSL).

The guidance in NEI 94-01, Industry Guideline for Implementing Performance-Based Option of 10 CFR Part 50, Appendix J (Reference 3), calculates the minimum pathway at all times when containment operability is required. This request is to align with the requirements of 10 CFR Part 50, Appendix J to record the leakage through the pathway and not each specific valve in the pathway. To assess the leak rate of the containment the actual leakage is through both the inboard and outboard MSIV. The leakage requirement through the MSIVs should follow the same rational.

NEI 94-01 also requires the maximum pathway to be less than the limit prior to entering a mode where containment integrity is required following a refueling outage or a shutdown that included leak rate testing of the MSIVs. This will ensure margin is maintained to the total allowable leak rate for the MSIVs.

The LAR does not describe the licensing basis (location, content, and acceptance criteria) for how MSIV and MSL leakage are determined, including test methods, analysis requirements, and applicability of 10 CFR Part 50, Appendix J methodology given the exemptions noted in condition 2.D in each units operating license.

Page 1 of 7 ATTACHMENT

Response to Request for Supplemental Information

Response

The licensing basis is documented in the Limerick Generating Station UFSAR specifically UFSAR Table 6.2.25, CONTAINMENT PENETRATIONS COMPLIANCE WITH 10CFR50, APPENDIX J. The table identifies the Main Steam Isolation Valves (MSIVs) as Inboard and Outboard barriers that require Type C testing.

Note 6 is applicable and states:

The primary steam penetrations are tested by pressurizing between the valves.

Testing of the inboard MSIV in the reverse direction tends to unseat the valve and is therefore conservative. The valves are Type C tested at a test pressure of 22 psig.

The exemption for MSIVs is documented in Tech Spec 3.6.1.2.b:

Primary containment leakage rates shall be limited to:

A combined leakage rate in accordance with the Primary Containment Leakage Rate Testing Program for all primary containment penetrations and all primary containment isolation valves that are subject to Type B and C tests, except for: main steam line isolation valves*, valves which are hydrostatically tested, and those valves where an exemption to Appendix J of 10 CFR 50 has been granted.

The TS states that MSIVs are exempt from a combined leakage rate (summation of Type B and Type C leakage related to 0.6La). The TS does not state that MSIVs are exempt from Appendix J (testing).

The leakage requirements for MSIVs (Main Steam Line penetrations) are specifically stated in Tech Spec 3.6.1.2.c:

Where definitions of

  • and ** are as follows:

[Note: The below asterisk is Unit 1 only and is being requested to be deleted]

    • During Unit 1 Cycle 19, one main steam isolation valve may exceed 100 scf per hour provided the leakage is less than or equal to 105 scf per hour.

MSIVs, as Primary Containment Isolation Valves (PCIV) are included in the Scope of the Primary Containment Leakage Rate Testing Program at Limerick as required by 10 CFR 50.54(o).

Page 2 of 7 ATTACHMENT

Response to Request for Supplemental Information

The LAR does not describe how the changes ensure that a single failure of any MSIV, at any time, will not result in exceeding analyzed limits (e.g., how using the MNPLR acceptance criteria is consistent with the offsite dose assumption that a valve in each MSL fails to close).

Response

Maintaining the primary containment OPERABLE in accordance with plant technical specifications requires compliance with the visual examinations and leakage rate test requirements of the Containment Leakage Rate Testing Program. (Ref.- Technical Specification 6.8.4.g). In accordance with the LLRT program ER-AA-380, Step 4.8.3, the minimum path leakage is used for on-line operation. This maintains compliance with Tech Spec 6.8.4.g that states the LLRT program shall be in accordance with NEI 94-01, Industry Guideline for Implementing Performance-Based Option of 10 CFR 50, Appendix J, Revision 3-A, dated July 2012, and the Limitations and Conditions specified in NEI 94-01, Revision 2-A, dated October 2008. Section 8.0 and 10.2 state that minimum path leakage shall be maintained below 0.6La at all times when containment integrity is required.

The maximum path leakage is utilized and verified to be acceptable prior to entering a Reactor Mode where containment is required to be operable. The use of maximum path ensures that a single failure of any MSIV in the MSL will not result in exceeding the TS requirement, supporting analyzed limits.

Minimum path acceptance criterion is only used for As-Found testing and is performed in a Reactor Mode where Containment is not required. For example, when testing the containment penetrations two values are used when assessing the leak rate of the penetration. The As-Found leak rate is based on the minimum pathway and the As-Left leak rate is based on the maximum pathway.

When the unit is shut down and the leak rate is measured, both the inboard and outboard MSIVs are closed. This verifies the valves were operable during the cycle so single failure is not required to be assessed during the As-Fond leak rate measurement. Prior to startup, to address a potential of a single failure, the maximum pathway leakage is used to verify LGS is below the TS allowable leakage.

Sample calculation:

The As-Found leak rate for the inboard MSIV was 110 scfh and the outboard MSIV leak rate was 30 scfh. Since both valves closed and were operable during the cycle, the actual leak rate through the penetration would be 30 scfh (minimum pathway leakage). However, since the current TS is per valve, the inboard MSIV would be assessed for reportability, even though the penetration would be below the allowable limit.

In preparation for start up the maximum pathway leak rate would be used to account for single failure. Since the inboard MSIV was 110 scfh, thus exceeds the LGS TS

Page 3 of 7 ATTACHMENT

Response to Request for Supplemental Information

allowable leakage maintenance will need to be performed to reduce the leak rate below the LGS TS allowable limit of 100 scfh per main steam line.

Additionally, to maintain the MSIV leak rate below the design limit, the LGS TS has a total allowable leak rate for all four MSLs of 200 scfh. The 200 scfh is the limit for both As-Found (minimum pathway) and As-Left (maximum pathway).

The LAR does not describe how the proposed changes would retain the safety function of the MSIVs and MSLs considering that the Limerick TS bases state, Operating experience with the main steam line isolation valves has indicated that degradation has occasionally occurred in the leak tightness of the valves; therefore, the special requirement for testing these valves.

Response

The PCIVs for the Main Steam Line penetrations have Inboard and Outboard MSIVs.

The proposed change does not impact the safety function. The use of minimum pathway to determine the leakage of the MSL is only used when determining the As-Found leakage for each MSL. Verification that the minimum pathway leakage satisfies the TS requirement for leakage validates that the MSL did not exceed the leakage requirement.

2. The LAR states that the proposed changes to TS are consistent with NUREG-1433, Revision 5, Standard Technical Specifications - General Electric BWR/4 Plants (ML21272A357 (specifications) and ML21272A358 (bases)); however, the LAR is missing justification for this assertion. The consistency was not apparent given that the improved standard technical specifications (STS) have leakage requirements for each MSIV, not each MSL as proposed in the LAR. The STS requirements are summarized as follows:

STS surveillance requirement (SR) 3.6.1.3.13 establishes a leakage rate for each MSIV but not each MSL. This is emphasized in the STS bases for this SR.

The required action for STS 3.6.1.3, Condition D requires that MSIV leakage rate, not the MSL leakage rate, be restored in 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

Response (for both bullets):

The intent of referencing NUREG 1433, Revision 5, Standard Technical Specifications - General Electric BWR/4 Plants, was to reference similar BWR/4 plants that currently have the proposed changes within their TS. In this instance, Peach Bottom Atomic Power Station, Units 2 and 3, (PBAPS) TS SR 3.6.1.3.14 (Reference 4) and James A. Fitzpatrick Nuclear Power Plant (JAF) TS SR 3.6.1.3.10 (Reference 5)

The current Limerick Alternate Source Term (AST) Analysis of Record (AOR) for the post-LOCA dose consequences is documented in design analysis LM-0646 (Reference 6) as referenced in Limerick UFSAR Chapter 15.6-23. The MSIV leakage portion of this analysis is unchanged from the original Limerick AST LAR (Reference

Page 4 of 7 ATTACHMENT

Response to Request for Supplemental Information

7).

The analysis conservatively models the tota l MSIV leakage (200 scfh) using only two of the MSLs and each of the lines modeled in the AOR is assumed to pass 100 scfh of leakage. This choice of nodalization of the MSLs in the AOR provides additional conservatism because it neglects the holdup and deposition that would be afforded by the leakage passing in the two unmodelled MSLs. If all four MSLs were credited in the AOR, it would result in a reduction in computed dose, because the lower leakage rate flowing through all four MSLs results in more holdup and deposition in the MSLs.

A MSIV specific leakage limit is not required because:

The Boiling Water Reactor Owners Group (BWROG) issued a topical report on MSIV leakage limits, NEDC-31858P, Revision 2, BWROG Report for increasing MSIV Leakage Rate Limits and Elimination of Leakage Control Systems, dated September 1993 (Reference 8). In this report, the BWROG states that MSIV leakage could increase up to 200 scfh per MSL will not inhibit the safety function of the valve.

Leakage of 200 scfh is bounded by the analyzed AOR leakage per steam line of 100 scfh and combined maximum permissible total leakage for all steam lines of 200 scfh.

With the precedent of PBAPS and JAF, both facilities are similar design BWR 4s and obtained NRC approval to use the per MSL versus per MSIV leakage limit.

Therefore, the proposed change to remove the MSIV specific leakage limit and replace it with an MSL specific limit is justified and acceptable.

3. The LAR did not discuss how the proposed change from MSIV Leakage to Main Steam Line Leakage would be consistent with the regulatory position provided in Regulatory Guide (RG) 1.183, Appendix A Assumptions for Evaluating the Radiological Consequences of a LWR Loss-of-Coolant Accident, Assumptions on Main Steam Isolation Valve Leakage in BWRs. Specifically, per its February 27, 2004, LAR related to application of Alternative Source Term (ML040980153, as supplemented), the licensee used the term MSIV Leakage consistently throughout the entire submittal to be consistent with regulatory position in RG 1.183 which uses MSIV Leakage to perform accident dose analysis, as opposed to Main Steam Line Leakage.

Page 5 of 7 ATTACHMENT

Response to Request for Supplemental Information

Response: The Limerick AST LOCA analysis of record (Reference 6) models only two MSLs with one MSIV open in each, which is conservative for post-accident dose calculations. This is consistent with the AEB-98-03, Assessment of Radiological Consequences for the Perry Pilot Plant Application Using the Revised (NUREG-1465) Source Term, (Reference 9). Since only a single MSIV is closed in each line, MSIV leakage and MSL leakage are equivalent.

Generic Conceptual MSIV Leakage Model (Reference 10)

Page 6 of 7 ATTACHMENT

Response to Request for Supplemental Information

References:

1. Letter from Wendi Para, Constellation Energy Generation, LLC to the U.S. Nuclear Regulatory Commission, License Amendment Request for Modification to Technical Specification 3.6.1.2 and Main Steam Isolation Valve Leakage Rate Requirements, dated August 28, 2024 (ADAMS Accession No. ML24241A195).
2. Letter from Audrey Klett, U.S. Nuclear Regulatory Commission to Constellation Energy Generation, LLC, Limerick Generating Station, Units 1 and 2 - Supplemental Information Needed for Acceptance of Requested Licensing Action Regarding Primary Containment Leakage Technical Specifications, dated October 7, 2024 (ADAMS Accession No. ML24274A237).
3. NEI 94-01 Revision 3-A, Industry Guideline for Implementing Performance-Based Option of 10 CFR Part 50, Appendix J, dated July 2012 (ADAMS Accession No. ML12221A202).
4. Letter from Pamela B. Cowan, Exelon Generation Company, LLC to the U.S. Nuclear Regulatory Commission, License Amendment Request - Application of Alternative Source Term, dated July 13, 2007 (ADAMS Accession No. ML072570156)
5. Letter from David T. Gudger, Exelon Generation Company, LLC, to the U.S. Nuclear Regulatory Commission, License Amendment Request for Application of the Alternative Source Term for Calculating Loss-of-Coolant Accident Dose Consequences, dated August 8, 2019 (ADAMS Accession No. ML19220A043)
6. Limerick Generating Station, Units 1 and 2, LM-646 Revision 2, Re-analysis Of Loss of Coolant Accident (LOCA) Using Alternative Source Terms, dated June 14, 2006 (ADAMS Accession No. ML061780046 and 061780047)
7. Letter from Michael P. Gallagher, Exelon Generation Company, LLC to the U.S.

Nuclear Regulatory Commission, Request for License Amendments Related to Application of Alternative Source Term, dated February 27, 2004 (ADAMS Accession No. ML040980153)

8. Boiling Water Reactor Owners Group (BWROG) Topical, NEDC-31858P, Revision 2, BWROG Report for increasing MSIV Leakage Rate Limits and Elimination of Leakage Control Systems, dated September 1993.
9. NRC, Accident Evaluation Branch (AEB)- 98-03, Assessment of Radiological Consequences for the Perry Pilot Plant App lication Using the Revised (NUREG-1465)

Source Term, Washington, DC, December 9, 1998 (ADAMS Accession No. ML011230531).

10. NRC, Re-Evaluation of AEB 98-03s Aerasol Parameters, Dated July 21, 2021 (ADAMS Accession No. ML21141A006)

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