05000333/LER-2024-001-01, EDG Lube Oil Check Valve Bonnet Cap Leak Due to Failed Gasket

EDG Lube Oil Check Valve Bonnet Cap Leak Due to Failed Gasket

ML24234A140
Person / Time
Site:	FitzPatrick
Issue date:	08/21/2024
From:	Sterio A Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
JAFP-24-0039 LER 2024-001-01
Download: ML24234A140 (1)

LER-2024-001, EDG Lube Oil Check Valve Bonnet Cap Leak Due to Failed Gasket

Event date:
Report date:
3332024001R01 - NRC Website

text

James A. FitzPatrick NPP P.O. Box 110 Constellation Lycoming, NY 13093

Alexander Sterio Site Vice President-JAF

JAFP-24-0039 August 21, 2024

United States Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555-0001

James A. FitzPatrick Nuclear Power Plant Renewed Facility Operating License No. DPR-059 NRC Docket No. 50-333

Subject: LER: 2024-001-01, EOG Lube Oil Check Valve Bonnet Cap Leak due to Failed Gasket

Dear Sir or Madam:

This report is being submitted pursuant to 1 O CFR 50.73(a)(2)(i)(B) and 10 CFR

50. 73( a) (2) (v) (A).

There are no new regulatory commitments contained in this report.

Questions concerning this report may be addressed to Mr. Mark Hawes, Regulatory Assurance, at (315) 349-6659.

Sincerely,

Alexander Sterio Site Vice President

ADS/MH

Enclosure: LER: 2024-001-01, EOG Lube Oil Check Valve Bonnet Cap Leak due to Failed Gasket

cc : USNRC, Region I Administrator USNRC, Project Manager USNRC, Resident Inspector INPO Records Center (IRIS)

Abstract

On April 24, 2024, at 1948, with James A. FitzPatrick Nuclear Power Plant at 100% power, the B Emergency Diesel Generator (EDG) was being operated for surveillance testing when lube oil leaked from the bonnet cap of check valve 93EDG-57B. The leak originated when a gasket between the body-to-bonnet connection failed. The gasket was installed on October 11, 2023. The cause of the gasket failure was uneven compression during installation when the bonnet cap was over tightened and yielded the thread root. Work planning instruction and the technical evaluation did not identify a change to the metal-to-metal tightening standard when installing a gasket as a corrective action on October 11, 2023.

This deficiency would have prevented the fulfillment of the B EDG subsystem safety function due to not meeting the lube oil inventory requirement. The other 3 EDG units were not affected by this deficiency, no gaskets were installed.

This condition was prohibited by Technical Specifications (TS), which is reportable per 10 CFR 50.73(a)(2)(i)(B). In addition, during this period, when A EDG subsystem was inoperable for planned maintenance, both subsystems were inoperable, a condition reportable per 10 CFR 50.73(a)(2)(v)(A). The condition was corrected by replacing the check valve on April 25, 2024. A case study will be developed and shared.

NRC FORM 366 (04-02-2024)

Background

The Emergency Onsite Power Supply System [EIIS identifier: EK] consists of two redundant Emergency Diesel Generator (EDG) subsystems. Each EDG subsystem consists of two EDG units. The capability of the two units in the subsystem to start, force parallel, and attain rated voltage and frequency together within 10 seconds, and run the necessary engineered safeguard loads, meet s the requirements for the Emergency AC Power System.

The EDG lubrication system [LA] is designed to provide sufficie nt lubrication (lube oil) to permit proper operation by circulating the lube oil to the diesel engine work ing surfaces and to remove excess heat generated by friction during operation. The lube oil inventory volume required to ensure 7 days continuous operation is 168 gallons based on the manufacturer's consumptio n values and without reaching the recommended minimum level.

In standby, the system circulates warmed oil through the EDG en gines to promote successful quick starts.

This is accomplished by a 5/8-inch line with a swing check valv e (93EDG-57B for B EDG unit), which closes during EDG operation to prevent bypassing flow. The check valve has a bonnet cap to access internals for preventive maintenance.

Event Description

On April 24, 2024, with James A. FitzPatrick Nuclear Power Plan t (JAF) at 100% power, a surveillance test was started at 1912, involving an operational test of the B E DG subsystem. Operators were monitoring the performance when they discovered lube oil spraying from the top of check valve 93EDG-57B. At 1948, the B EDG unit was declared inoperable. Operators secured the EDG as well as the circulating and turbocharger lube oil pumps. The leak originated from the bonnet cap.

With the engine in standby, the leak rate was approximately 60 drops per minute (dpm). A leak rate could not be observed with the system pressurized during the event; howev er, it was estimated that 11.5 gallons of lube oil was lost due to the leak. The operations staff estimated th at the engine was running for approximately 5 minutes with the leak before the engine was secured. Therefore, the leak rate was approximately 2.3 gallons per minute (gpm), or 138 gallons per hour (gph). The magnitude of the lube oil leak would have exhausted the lube oil supply and this deficiency would have prevented the fu nction of B EDG unit to fulfill its mission time.

The A, C, and D check valves did not have any similar leaking c ondition. The A EDG subsystem remained Operable and the D EDG unit remained available during this ev ent.

The check valve 93EDG-57B was replaced on April 25 by 1300. The re was no leakage following the repair.

The Post Maintenance Testing was completed satisfactory restori ng the B EDG subsystem to Operable. NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024)

1. FACILITY NAME 050 2. DOCKET NUMBER 3. LER NUMBER NUMBER NO.

James A. FitzPatrick Nuclear Power Plant 05000333 052 2024 - 001 - 01

Event Analysis

On October 11, 2023, a planned preventive maintenance task was performed to open the bonnet cap and inspect the check valve internals, per industry Operating Exper ience. During post maintenance testing, with B EDG operating, an oil leak was identified. A temporary repa ir to install a gasket and use thread sealant was evaluated and installed to prevent oil leakage.

The failed check valve 93EDG-57B was sent to a laboratory for i nvestigation. Examination revealed uneven compression of the gasket and a crack in the thread root. A gas ket installed in the bonnet cap showed damage and delamination.

Normal installation is bonnet cap to body metal to metal contac t to tightness standard, with no visible gaps.

Adding a gasket to the joint would make that abrupt torque spik e less likely to detect. With no guidance on how much to tighten the gasketed joint and no guidance on a specifi c torque for the gasketed joint, the bonnet cap was tightened until the leak was stopped. The installation of t his gasket also resulted in less thread engagement and would require more tightening to compress the ga sket to ensure a sealed pressure boundary. The bonnet cap would be tightened enough to stop the leak to fulfill the role of the temporary leak repair. This continued tightening, yielded the bonnet thread ro ot which led to an uneven compression on the gasket which led to the eventual gasket failure.

This deficiency existed between when the repair was performed o n October 11, 2023, and when the check valve was restored to operable on April 25, 2024. During this p eriod, the gasket repair maintained operating lube oil system pressure temporarily, but it would not be expec ted to perform its function through the EDG mission time. The required lube oil inventory of 7 days require d per Technical Specification (TS) surveillance requirement (SR) 3.8.3.2 would not be met based on the increase d rate of consumption cause by this oil leak.

This deficiency renders the B EDG subsystem inoperable. The a llowed restoration time required by TS 3.8.1 for one inoperable EDG subsystem would be exceeded. This event is being reported as a condition prohibited by TS in accordance with 10 CFR 50.73(a)(2)(i)(B). During this period, when A EDG subsystem was inoperable due to testing, both subsystems were inoperable, and these events are reportable per 10 CFR 50.73(a)(2)(v)(A).

Cause

The lube oil leak from check valve 93EDG-57B was caused by a fa iled gasket installed on the bonnet connection. Over tightening of the bonnet cap with the gasket i nstalled yielded the thread root and caused uneven compression of the gasket which led to the failed gasket.

First contributing cause was work instructions to install a gas ket leak repair did not provide adequate detail regarding how to tighten the bonnet cap. This is a standard pra ctice for brass fittings; however, it does not apply to joints modified to use a gasket. If a specified torque value was identified in the work instructions than the over tightening of the bonnet cap would have been prevented.

Second contributing cause was insufficient technical rigor for installation of the gasket for use in this temporary corrective maintenance. NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024)

1. FACILITY NAME 050 2. DOCKET NUMBER 3. LER NUMBER NUMBER NO.

James A. FitzPatrick Nuclear Power Plant 05000333 052 2024 - 001 - 01

Similar Events No previous similar events.

FAILED COMPONENT IDENTIFICATION:

Manufacturer: Jenkins Brothers Manufacturer Model Number: 92-A Manufacturer Code: J036 Component Code: V FitzPatrick Component ID: 93EDG-57B

Corrective Actions

Completed Actions On April 25, 2024, check valve 93EDG-57B was replaced and the B EDG subsystem restored to Operable.

Planned Actions Create and Present Teaching and Learning Case Study of the even t and cause identified to Engineering, Maintenance, and Supervisors and above. Case study to include t echnical rigor of Engineering products and work packages.

Safety Significance

Nuclear safety - There were no actual nuclear consequences.

From October 11, 2023, until the failure of the gasket on April 24, 2024, there were 9 successful surveillance tests performed (approximately 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> total loaded on the ele ctrical bus). The gasket repair would have held pressure and EDG would operate until the gasket failure; theref ore, both EDGs units in the B EDG subsystem would have started and automatically powered the emer gency bus. Operators could have responded to a B EDG unit lube oil leak by securing it, but d uring a Loss of Coolant Accident (LOCA) event the low lube oil pressure trip signal is bypassed so B EDG un it would not automatically trip until it failed.

The D EDG unit, in the B EDG subsystem, remained available to supply power to the emergency bus.

References Issue Report - IR 04708722, Oil Leak Identified at 93EDG-57B, d ated October 11, 2023 Issue Report - IR 04769343, 93EDG-57B (lube oil gallery check v alve) Failure, dated April 25, 2024 Engineering Change - EC 639982, Install Gasket to Seal Bonnet C ap Leak on 93EDG-57B Check Valve, dated October 13, 2024