05000353/LER-2019-002, Emergency Diesel Generator Lube Oil Pressure Sensing Line Leak Resulting in a Condition Prohibited by Technical Specifications
| ML19263A648 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 09/20/2019 |
| From: | Sturniolo F Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LG-19-094 LER 2019-002-00 | |
| Download: ML19263A648 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3532019002R00 - NRC Website | |
text
Exelon Generation LG-19-094 September 20, 2019 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 2 Renewed Facility Operating License No. NPF-85 NRC Docket No. 50-353 10 CFR 50.73 Subject: LEA 2019-002-00, Emergency Diesel Generator Lube Oil Pressure Sensing Line Leak Resulting in a Condition Prohibited by Technical Specifications Enclosed is a Licensee Event Report (LER) that addresses an Emergency Diesel Generator (EOG) being inoperable for greater than 30 days, resulting in a condition prohibited by Technical Specifications (TS) at Limerick Generating Station, Unit 2.
This LEA is being submitted pursuant to the requirements of 1 O CFR 50.73(a)(2)(i)(B).
There are no commitments contained in this letter.
If you have any questions, please contact Robert B. Dickinson at (61 O) 718-3400.
Respectfully,
'J?f~ ~
f'ra.nk S-lva1iclo Frank Sturniolo Vice President - Limerick Generating Station Exelon Generation Company, LLC cc: Administrator Region I, USNRC USNRC Senior Resident Inspector, Limerick Generating Station
NRC FORM 366 U.S. NUCLEAR REGULA TORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (02-2018)
Estimated blrden per response to comply with this mandatoiy collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
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LICENSEE EVENT REPORT (LER)
Reported lessons leirned are inccrpatated into the ieensing process and fed bacl< to indusby. Send comments regarding burden estimate to the lnf<xmation SeMces Branch
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to lnfocollecis.Resoi.rce@nrc.gov, and to the Desi< Officer, Office of Information and
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(See NUREG-1022, R.3 for instruction and guidance for completing this form Regulatory Attairs, NEOB-10202, (3150--0104), Office of Management and Budget,
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3.Page Limerick Generating Station Unit 2 05000 353 1
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- 4. Title Emergency Diesel Generator Lube Oil Pressure Sensing Line Leak Resulting in a Condition Prohibited by Technical Specifications
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rev Facility Name Docket Number Month Day Year Year Number No.
Month Day Year 05000 Facility Name Docket Number 07 22 19 2019 -
002 -
00 09 20 2019 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 1 O CFR §: (Check all that apply)
D 20.2201(b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D 20.2203(a)(1)
D 20.2203(a)(4)
D 50. 73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x) 1 O. Power Level D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50. 73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50. 73(a)(2)(v)(C)
D 73.77(a)(2)(ii)
D 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(iii)
D 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in The failure on 1/21/2019 was due to high-cyclic fatigue due to the instrument line vibrating at its resonant frequency. The threaded pipe was replaced and the EOG was returned to an operable status. The corrective actions were to install a clamp to support the one-quarter inch instrument line and to modify the instrument line design to reduce the vibration at the threaded connection.
On 3/19/19 during a walkdown of EOG 024 during the 24-hour endurance run, a broken U-bolt was identified on the four-inch main header in a location near the threaded connection. The U-bolt was repaired following the completion of the 24-hour endurance run.
On 4/25/19 a clamp was installed from the four-inch main header to the one-quarter inch instrument line. The running vibration data showed an improvement in the magnitude. It was believed that the cause of the 1/21/19 failure was due to the broken U-bolt, and with the repair of the U-bolt and the addition of the support, the cause of the failure had been addressed.
On 7/22/19 the threaded connection failed. Although the new support was installed, the threaded connection was still experiencing vibration, albeit at a reduced level. The threaded pipe was not replaced when the support was added. The threaded pipe had already experienced fatigue since it was installed several months prior to the installation of the new clamp. The modification to change the piping configuration had not yet been implemented.
Based on past operating history, threaded pipe failures have occurred during engine starts and have been known to worsen during engine runs following crack initiation. Since the failure that occurred on 7 /22/19 was a sudden shear of the threaded pipe with no signs of leakage prior to failure, it is concluded that the crack initiated during the engine start on 7/22/19 and the rapid propagation of the crack occurred during the subsequent engine run-time. Therefore, 024 EOG was conservatively determined to be inoperable following the completion of the last run of the EOG on 6/18/19.
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 A.C. 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.
The 024 EOG was conservatively determined to be inoperable from 6/18/19 through 7/25/19 therefore, the TS 3.8.1.1.a action to restore the diesel within 30 days was not met. There were minimal safety consequences associated with the condition since there were no events during this time period which required the 024 EOG. The remaining LGS Unit 2 EOGs were only inoperable but available for surveillance testing during this period.
Cause of the Event
The cause of the failure of the threaded pipe connection was due to high-cyclic fatigue. A contributing cause was the modification to change the piping configuration had not been installed prior to the failure.
Corrective Actions
- 1. A temporary configuration change was implemented to remove the threaded pipe and valve, plug the lube oil piping hole, and cap off the small diameter copper instrumentation tubing. This temporary change eliminates the threaded pipe vulnerability in this location.
- 2. A design change is being implemented to change the configuration of the connection between the four-inch main header and the one-quarter inch instrument line.
Previous Similar Occurrences On 3/21 /13, a 1-2 drop per minute (OPM) leak was identified on the threaded connection for the EOG 024. On 4/27/13, the 1-2 OPM threaded connection leak became a 140 OPM leak, resulting in EOG 024 inoperability. The investigation performed for this failure determined that the cause to be high-cycle fatigue from engine vibration exacerbated by a missing grommet on one of the downstream supports.
On 1/21/2019, the threaded connection developed a leak and the EOG 024 was declared inoperable due to a leak on the fitting that was replaced on 5/23/18. The replacement was a proactive replacement as part of an extent-of-condition action from a failure of this threaded connection on a different EOG.
System:
Component:
Manufacturer: EK Emergency On-Site Power Supply System PSF Pipe Fitting NIA Page 4
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