05000414/LER-2021-003, Re Containment Penetration Failure Resulting in Integrated Leak Rate Test Failure

Re Containment Penetration Failure Resulting in Integrated Leak Rate Test Failure

ML21207A238
Person / Time
Site:	Catawba
Issue date:	07/26/2021
From:	Simril T Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-21-0222 LER 2021-003-00
Download: ML21207A238 (7)

LER-2021-003, Re Containment Penetration Failure Resulting in Integrated Leak Rate Test Failure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(v), Loss of Safety Function
4142021003R00 - NRC Website

text

( ~ DUKE ENERGY RA-21-0222 July 26, 2021 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Duke Energy Carolinas, LLC Catawba Nuclear Station, Unit 2 Docket No. 50-414 Licensee Event Report (LER) 414/2021-003-00 Tom Simril Vice President Catawba Nuclear Station Duke Energy CN01VP 14800 Concord Road York, SC 29745 o: 803. 701.3340 f 803.701.3221 10 CFR 50.73 Pursuant to 10 CFR 50.73(a)(1) and (d), attached is LER 414/2021-003-00, entitled "Containment Penetration Failure Resulting in Integrated Leak Rate Test Failure."

This report is being submitted in accordance with 10 CFR 50.73(a)(2)(ii)(A) and 10 CFR 50.73(a)(2)(v)(C)

There are no regulatory commitments contained in this letter or its attachment.

This event is considered to be of no significance with respect to the health and safety of the public.

If questions arise regarding this LER, please contact Ari D. Tuckman of Regulatory Affairs at (803) 701-3771.

Sincerely, Tom Simril Vice President, Catawba Nuclear Station Attachment

United States Nuclear Regulatory Commission Page 2 July 26, 2021 xc (with attachment):

L. Dudes Regional Administrator U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303 K. Cotton NRC Project Manager (CNS)

U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mailstop O-8G9A Rockville, MD 20852 J. Austin (without enclosure)

NRC Senior Resident Inspector

United States Nuclear Regulatory Commission Page 3 July 26, 2021 bxc (electronic copy)(with attachment):

Melodee Jensen (NRC)

Melodee.Jensen@NRC.gov S.E. Andrews S.J. Andrews A. Linker J. Constant (INPO-IRIS)

R.T. Simril, Jr.

B.C. Carroll M.C. Nolan A.H. Zaremba ELL-EC02ZF NCMPA-1 NCEMC PMPA bxc (hard copy)(with attachment):

LER File RGC Date File

Abstract

At 1751 on May 25, 2021, it was determined the local leak rate test (LLRT) for the 2EMF-IN containment penetration did not meet 10 CFR 50 Appendix J requirements for both the inboard and outboard containment isolation valves. The LLRT was performed during the C2R24 refueling outage at which time primary containment was not required to be operable. The leakage assigned to the penetration also resulted in total containment leakage exceeding the allowed overall leakage (La). The valves were repaired and retested satisfactorily prior to entering the mode of applicability.

The most likely cause of the leakages from 2MISV5230 and 2MISV5231 is the degradation of the elastomer seat aggravated by the presence of a buildup of debris in the seating area and overly conservative testing methodology.

This event was reported to the NRC as an eight-hour, non-emergency Event Notification 55275 on May 25, 2021, per 10 CFR 50.72(b)(3)(ii)(A), event or condition that the nuclear power plant, including its principal safety barriers, being seriously degraded.

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BACKGROUND The following information is provided to assist the readers in understanding the event described in this LER.

Applicable Energy Industry Identification [EEIS] system and component codes are enclosed within brackets and Catawba Nuclear Station unique system and component identifiers are contained within parentheses.

On April 15, 2021, with Unit 2 of Catawba Nuclear Station (CNS) at 0 percent power (Mode 6) due to a refueling outage for cycle 24 (C2R24), the Unit 2 reactor building radiation monitor sample line containment penetration (2EMF-IN) failed its local leak rate test. The penetration failed to pressurize to the required test pressure due to excessive leakage through both the inboard and outboard containment isolation valves, 2MISV5231 and 2MISV5230 respectively (Valcor Model 04D-232 1 inch solenoid valves). Due to both primary containment isolation valves (PCIVs) in this penetration flow path failing to pressurize, a leakage value of La was assigned to each valve, which represents a failure of the associated penetration, 2EMF-IN, to maintain containment integrity per Technical Specification 3.6.3, Containment Isolation Valves and specifically SR 3.6.3.8, to "Verify the combined leakage rate for all reactor building bypass leakage paths is less than or equal to 0.07 La when pressurized to greater than or equal to 14.68 psig."

Catawba Technical Specification 5.5.2, Containment Leakage Rate Testing Program requires a program shall be established to implement the leakage rate testing of the containment as required by 10 CFR 50.54(o) and 10 CFR 50, Appendix J, Option B, as modified by approved exemptions. This program shall be in accordance with the guidelines contained in NEI 94-01, "Industry Guideline for Implementing Performance-Based Option of 10 CFR Part 50, Appendix J," Revision 3-A dated July 2012, and the conditions and limitations specified in NEI 94-01 Revision 2-A, dated October 2008.

The As-Found LLRT minimum pathway leakage value for any penetration not vented and exposed to containment pressure during the Integrated Leak Rate Test (ILRT) must be added as a penalty to the results of the ILRT to obtain the As-Found Overall Integrated Leakage Rate per NEI 94-01, Rev 3A. Due to the failure of the As-Found local leak rate test for penetration 2EMF-IN and its associated impact on the Containment ILRT, this event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A), any event or condition that results in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded and 10 CFR 50.73(a)(2)(v)(C), Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

EVENT DESCRIPTION

During the scheduled C2R24 refueling outage, a containment integrated leak rate test (ILRT) was performed on March 30, 2021 with no apparent issues identified. As part of the ILRT, penetration 2EMF-IN was isolated by closing both containment isolation valves as well as downstream isolation valves. Leakage through this penetration was not measured during the ILRT as the penetration was to be tested locally and the as found local leakage measured from this penetration as well as other penetrations isolated for the ILRT would be added to the Type A containment leakage as prescribed in in NEI 94-01--Rev 3A.

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U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

3. LER NUMBER Catawba Nuclear Station, Unit 2 05000-414 YEAR SEQUENTIAL NUMBER REV NO.

2021

- 003

- 00 On April 15, 2021, while still in the C2R24 refueling outage, an as found leakage test was performed on penetration 2EMF-IN. During performance of this test, the penetration was unable to pressurize greater than 11 psig compared to a required test pressure of 15.1 to 15.7 psig. The credited containment isolation valves, 2MISV5231 and 2MISV5230, were tested individually and the penetration would not pressurize utilizing either valve, indicating gross leakage for each valve. Since the required leak rate could not be measured, a leakage value equal to La was assigned to each valve, resulting in an as-found overall integrated leakage rate of greater than 1.0 La.

After failure of the local leak rate test, repairs were made to valves 2MISV5231 and 2MISV5230 and the penetration was successfully retested while the unit remained in a mode in which containment integrity is not required. The result of the completed retest for 2MISV5230 was erroneously entered into the Appendix J testing database as As-Found test data as opposed to As-Left data. As stated previously, penetration As-Found minimum path leak rate data is added to the Type A leakage measured by the ILRT to determine overall containment leakage. This mis-labeling of the data resulted in the false impression the ILRT initially met all acceptance criteria as defined in NEI 94-01--Rev 3A-Section 8.0, to which CNS is licensed. This error was discovered while performing a Maintenance Rule evaluation for the failed penetration after the unit returned to power operation. Subsequently, all data was reviewed by the Containment/IST engineer and it was concluded that the penetration did fail the As-Found leakage test. This review confirmed a failure of the As-Found Overall Integrated Leakage Rate Test.

CAUSAL FACTORS The most likely cause of the leakages from 2MISV5230 and 2MISV5231 is the degradation of the elastomer seat aggravated by the presence of a buildup of debris in the seating area. Additionally, the test methodology which test the valves in a reverse flow direction can contribute to additional leakage. Based on the valves' design, testing in the reverse flow direction is a worst-case test scenario and reduces closing margin and seating loads. Testing in this manner is conservative relative to actual valve performance if called upon to perform its containment isolation function.

CORRECTIVE ACTIONS

Immediate Actions:

1.

Repair and retest valves 2MISV5230 and 2MISV5231 Planned Actions:

1.

Rebuild and inspect select valves of the same application to determine if this similar O-ring damage and debris accumulation has occurred in other valves of similar age.

2. Evaluate long term adjustments to the PM (as needed based on action 1 above)

3. Revise LLRT test procedures to include additional troubleshooting actions including testing in the forward flow direction to provide additional data and to ensure timely communication to Engineering for review of leak rate test failures.

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I I~ Page 4 of 4 (08-2020)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

3. LER NUMBER Catawba Nuclear Station, Unit 2 05000-414 YEAR SEQUENTIAL NUMBER REV NO.

2021

- 003

- 00

SAFETY ANALYSIS

Inboard and outboard containment isolation valves 2MISV5231 and 2MISV5230 respectively were found to be functioning as designed when performing the containment ILRT on March 30, 2021 and these valves have successfully passed their local leak rate testing requirements each outage for the past eight refueling outages.

In addition, no external leaks in the process piping or components installed in the flow path of these containment isolation valves was identified. The failure of the valves is determined to have occurred during the local leak rate test performed on April 15, 2021. This failure occurred in an operating mode where their safety function of preventing the release of radioactive material from the containment structure was not required and these valves were repaired and retested satisfactorily prior to entering such an operating mode. There were no safety consequences for this event as the valves failed in a mode in which the containment isolation function is not required.

This condition was a safety system functional failure (SSFF) as defined in accordance with NEI 99-02, Regulatory Assessment Performance Indicator Guideline.

ADDITIONAL INFORMATION

There have been no previous Licensee Event Reports at Catawba Nuclear Station in the last 3 years with the same cause as this issue.

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