05000352/LER-2023-001, Emergency Diesel Generator Lube Oil Pressure Sensing Line Leak Resulting in a Condition Prohibited by Technical Specifications
| ML23177A232 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 06/26/2023 |
| From: | Gillin M Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LG-23-057 LER 2023-001-00 | |
| Download: ML23177A232 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3522023001R00 - NRC Website | |
text
Constellation 10 CFR 50.73 LG-23-057 June 26, 2023 U.S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 1 Renewed Facility Operating License No. NPF-39 NRC Docket No. 50-352 Subject: LER 2023-001-00 Unit 1 Emergency Diesel Generator Lube Oil Pressure Sensing Line Leak Resulting in a Condition Prohibited by Technical Specifications In accordance with the requirements of 10 CFR 50.73(a)(2)(ii)(B), Limerick Generating Station hereby submits the enclosed Licensee Event Report.
There are no commitments contained in this letter.
If you have any questions, please contact Jordan Rajan at (610) 718-3400.
Respectfully, Michael Gillin Vice President - Limerick Generating Station Constellation Generation Company, LLC cc: Administrator Region I, USNRC USNRC Senior Resident Inspector, Limerick Generating Station
Abstract
On February 27, 2023, approximately 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> into a planned 24-hour endurance run for the 011 Emergency Diesel Generator (EOG), an oil leak was identified at a threaded fitting for an oil pressure indicator instrument line. The 011 EOG was emergently secured and declared inoperable. Subsequent investigation identified a crack in a threaded pipe nipple for the affected oil pressure indicator instrument line. Forensic analysis of the removed pipe nipple identified a crack initiated in the threaded fitting.
The corrective action was to move the connection to a different location that does not experience high vibration. Although D11 EOG was not inoperable for greater than the allowed out of service time a second EOG was inoperable for greater than the allowed out of service time for two EDGs. This event is being reported as a condition prohibited by Technical Specifications (TS) in accordance with 10 CFR 50.73(a)(2)(i)(B).
Unit Condition Prior to the event, Unit 1 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power.
There were no structures, systems, or components out of service that contributed to this event.
Description of the Event On February 27, 2023, during planned 24-hour endurance run of the D11 Emergency Diesel Generator (EOG) [EIIS-EK],
an oil leak was identified at a threaded fitting for an oil pressure indicator instrument line. The one-quarter inch instrument line threaded connection tees off the 4-inch main lube oil piping near the discharge of the engine driven lube oil pump.
The D11 EOG was started at 09:35 and fully loaded at 10:05. A dirty drip pan alarm came in at 19:42 and subsequently the lube oil leak was identified at 19:47. The EOG was secured and declared inoperable. Prior to the failure there was no leaks or degradation observed from the connection.
The component was sent for failure analysis. The failure analysis identified a crack in a threaded pipe nipple for the affected oil pressure indicator instrument line. Forensic analysis of the removed pipe nipple concluded that the pipe nipple showed fatigue fracture that started from one side at the root of the last engaged thread, consistent with unidirectional cyclic bending loads due to vibration. The D11 EOG was determined to be inoperable from the last completed surveillance test on January 31, 2023, until restored to operable status following repair of the identified oil leak on February 28, 2023.
Following the D11 EOG failure on February 27, 2023, vibration data was again collected on the 4-inch engine driven lube oil pump discharge piping. Comparison of this vibration data to vibration data previously collected for the D11 EOG in February 2020 concluded that the vibration signature of the piping had changed and that the D11 EOG was now susceptible to the same failure mechanism previously identified for the D24 EOG. Inspection of the pipe clamp on the 4-inch engine driven lube oil pump discharge piping adjacent to the instrument line connection identified that the nuts of the U-bolt clamp were not tight. A work order history review was completed, and no maintenance activity was identified that altered or adjusted the 4-inch engine driven lube oil pump discharge piping since vibration data was previously collected in February 2020. No engine operating data or maintenance activity could be cited as the cause for the change in the vibration signature of the 4-inch engine driven lube oil pump discharge piping other than vibration causing loosening of the U-bolt nuts.
Analysis of the Event
The failure analysis of the instrument line on the D11 EOG concluded the EOG was inoperable from the last completed surveillance test on January 31, 2023, until restored to operable status following repair of the identified oil leak on February 28, 2023. During the period that the D11 EOG was inoperable, the D13 EOG was also inoperable for approximately 7 days between, February 12, 2023, and February 19, 2023, for a planned system outage window. Based on the completion of the failure analysis and the component history review the condition was determined to reportable on April 27, 2023.
Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1.1 Condition b requires all four diesel generators to be capable of supplying the onsite Class 1 E AC electrical power distribution system. With one diesel generator inoperable, TS 3.8.1.1 Action a requires several actions to be completed at varying frequencies, including restoring the diesel generator to operable within 30 days. Although D11 EOG was restored to operable within 30 days, the other required actions were not performed. Additionally, TS LCO 3.8.1.1 Action b also requires several actions to be completed at varying frequencies when two EDGs are inoperable, including restoring at least one diesel generator to operable within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. These actions were not completed during the required time. This event is being reported as a violation of Technical Specifications in accordance with 10 CFR 50.73(a)(2)(i)(B).
Safety Consequences
The EOG and Auxiliary Systems are safety-related standby emergency power systems and consist of four diesel generator sets per unit. The operability of the AC power sources and associated distribution systems during operation ensures that sufficient power will be available to supply the safety-related equipment required for (1) the safe shutdown of the facility and (2) the mitigation and control of accident conditions within the facility. The TS action requirements specified for the levels of degradation of the power sources provide restriction upon continued facility operation commensurate with the level of degradation.
Due a planned system outage for the D13 EOG, both the D11 and D13 EDGs were inoperable concurrently from February 12, 2023, to February 19, 2023; therefore, the TS 3.8.1.1.b action to restore at least one of the inoperable diesel generators to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> was not met. There were minimal safety consequences associated with the condition since there were no events during this period that required the D11 and D13 EDGs to perform their safety function. The remaining Limerick Unit 1 EDGs were operable during this period.
Cause of the Event
The cause of the failure was determined to be high cyclic fatigue driven by the change in the vibration of the 4-inch engine driven lube oil pump discharge piping.
Corrective Actions Completed
- 1. Replaced failed oil pressure indicator instrument line on the D11 EDG in kind on 2/28/23 to restore operability.
- 2. Relocated the affected oil pressure indicator instrument line on all EDGs with exception of the D24 EOG.
Corrective Actions Planned
- 1. Relocate the affected oil pressure indicator instrument line on the D24 EOG.
Previous Similar Occurrences Failure of the same oil pressure indicator instrument line has occurred on two other Limerick EDGs. The D13 EOG experienced a failure of the same oil pressure indicator instrument line in 2016. The D24 EOG has experienced three failures of the same oil pressure indicator instrument line, once in 2013 and twice in 2019, the second failure resulted in LER 2019-002-00. The design of the D24 EOG oil pressure indicator instrument line was modified after the July 2019 failure.
Component Data System: EK Emergency On-Site Power Supply System Component: PSF Pipe Fitting Manufacturer: N/A I YEAR B -I SEQUENTIAL NUMBER 001 Page 4
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