05000455/LER-2011-001, Regarding Emergency Diesel Generator Inoperable for Longer than Allowed by Technical Specifications Due to Inadequate Work
| ML110871903 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 03/28/2011 |
| From: | Tulon T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2011-0056 LER 11-001-00 | |
| Download: ML110871903 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vi) 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) 10 CFR 50.73(a)(2)(x)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4552011001R00 - NRC Website | |
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n.6o 994 March 28, 201 1 10 CFR 50.73 Byron Ltr 2011-0056 File 1.10.0101 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Unit 2 Facility Operating License No. NPF-66 NRC Docket No. STN 50-455
Subject:
Licensee Event Report 2011-001-00, Unit 2 Emergency Diesel Generator Inoperable for Longer Than Allowed by Technical Specifications Due to Inadequate Work Instructions The enclosed Licensee Event Report (LER) is being submitted in accordance with 10 CFR 50.73, Licensee event report system, paragraph (a)(2)(i)(B), as a condition prohibited by Technical Specifications. The LER involves a Unit 2 Emergency Diesel Generator that was unknowingly inoperable for approximately six months due to loose bolting on its upper lubricating oil cooler.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. David Gudger, Regulatory Assurance Manager, at (815) 406-2800.
Respectfully, Tin)Othy J. Tulon SWe Vice President Bron Station
Enclosure:
LER Number 455-2011 -001 -00
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES 10/31/2013 1O-2OrO
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- 3. PAGE Byron Station, Unit 2 05000455 1
OF 4
- 4. TITLE Unit 2 Emergency Diesel Generator Inoperable for Longer than Allowed by Technical Specifications Due to Inadequate Work 5, EVENT DATE
- 6. LER NUMBER
- 7. REPORT D4TE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR N/A N/A i.
FACILITY NAME DOCKET NUMBER 11 17 2010 2011 001 00 03 28 2011 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
C 20.2201(b)
C 20.2203(a)(3)(i)
C 50.73(a)(2)(i)(C)
C 50.73(a)(2)(vi) 1 C 20.2201(d)
C 20.2203(a)(3)(ii)
C 50.73(a)(2)(ii)(A)
C 50.73(a)(2)(viii)(A)
C 20.2203(a)(1)
C 20.2203(a)(4)
C 50.73(a)(2)(ii)(B)
C 50.73(a)(2)(viii)(B)
C 20.2203(a)(2)O)
C 50.36(c)(1)(i)(A)
C 50.73(a)(2)Oii)
C 50.73(a)(2)(x)(A)
- 10. POWER LEVEL C 20.2203(a)(2)(ii)
C 50.36(c)(1)(ii)(A)
C 50.73(a)(2)Ov)(A)
C 50.73(a)(2)(x)
C 20.2203(a)(2)(iii)
C 50.36(c)(2)
C 50.73(a)(2)(v)(A)
C 73.71(a)(4) 100 C 20.2203(a)(2)(iv)
C 5D.46(a)(3)(ii)
C 50.73(a)(2)(v)(B)
C 73.71(a)(5)
C 20.22D3(a)(2)(v)
C 50.73(a)(2)(i)(A)
C 50.73(a)(2)(v)(C)
C OTHER C 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B)
C 50.73(a)(2)(v)(D)
Specify in Abstract below or in An evaluation was initiated to assess the 2A DG TS operability status from January 17, 2010, to November 17, 2010. Based on the results of this evaluation, on January 25, 2011, Exelon Generation Company, LLC (EGC) concluded that on May 19, 2010, the 2A DG would not have been able to fulfill its 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> mission time and therefore was unknowingly inoperable since this date until November 17, 2010.
TS 3.8.1, Condition B requires an inoperable DG to be restored to operable status within 14 days, otherwise Condition G requires the Unit to be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Consequently, the condition of Unit 2 not in compliance with Condition G on June 2, 2010, is a condition prohibited by TS and reportable to the NRC in accordance with 10 CFR 5073 (a)(2)(i)(B).
In addition, during the time period the 2A DG was unknowingly inoperable, the 2B DG was also inoperable due to emergent conditions or planed work activities. These situations will be reviewed to determine if other reporting requirements apply and will be reported in a supplement to this report.
The 2A DG was repaired and returned to operable status on November 22, 2010. An extent of condition check of lubricating oil coolers bolted connections found no other loose bolting.
C.
Cause/s of the Event The cause was determined to be an inadequate work instructions provided for the January 17, 2010, 2A DG work activities in that it did not contain sufficient directions to re-torque the bolted connections after initial torquing as recommended by EPRI and the gasket manufacturer. This was caused by a lack of a formal process to ensure EPRI documents are systematically reviewed for good practices and then incorporated into maintenance procedures.
D.
Safety Significance
There were no actual safety consequences as a result of this condition. Safety bus 241 is normally supplied by off site power via its System Auxiliary Transformer (SAT) 242-1 and was available throughout the time frame that the 2A DG was unknowingly inoperable. Safety bus 242 was available and capable of being powered by its offsite power source and would have supplied power to B train components to safely shutdown the plant as designed.
The DGs are designed to provide emergency power to the safety buses in the event of a Loss-Of Offsite-Power (LOOP). Had a LOOP occurred, the 2A DG would potentially not have run for the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> mission time. The Unit 2 safety bus 241 would have become de-energized. Operating procedure would be utilized to energize bus 241 from Unit 1 safety bus 141. This source of power was available during this time frame.
In the event of a Station Blackout, either one of the two emergency DG for each unit serves as an alternate a-c power source for the opposite unit. The alternate a-c power source is available within 10 minutes of the onset of the Station Blackout event and has sufficient capacity and capability to operate equipment necessary to bring and maintain the station in a safe shutdown condition.
Equipment required for Station Blackout is capable of being powered from a single remaining DG.
The capability for providing power to the blacked-out unit is possible with manual operation of cross-tie switchgear breakers from the Main Control Room.
NRC ORM 366A 15-2010)
A probability risk assessment performed for this condition concluded it to be of low to moderate significance.
The safety significance of the instances when the 2B DG was also inoperable will be reported in a supplement to this report.
E.
Corrective Actions
The maintenance procedure governing assembly of bolted connections has been revised to address the assembly of equipment with multiple joints.
The model work orders for DG oil coolers assembly will be revised to require final torque checks after assembly and to include a requirement to ensure torque verification is performed within three months.
The maintenance procedure for assembly of bolted connections will be revised to incorporate EPRI recommendations.
The operating experience review process has been revised to include EPRI documents to ensure good practices are incorporated into EGCs procedures.
Training will be conducted for appropriate maintenance personnel concerning the assembly of multiple joints configurations.
F.
Previous Occurrences
Several DG oil cooler flange leaks have been documented in the Corrective Action Program over the past 10 years. The leaks were minor in nature and did not result in the DG being declared inoperable. The repair typically involved re-torquing the flange bolts. No investigations were conducted into determining the cause involving the need to re-torque bolts.