05000424/LER-2010-001, For Vogtle Electric Generating Plant, Regarding Breaker Failure Results in 1B Train Containment Cooling System Being Declared Inoperable
| ML103560023 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 12/16/2010 |
| From: | Tynan T Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-10-2274 LER 10-001-00 | |
| Download: ML103560023 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 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)(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 |
| 4242010001R00 - NRC Website | |
text
Tom Tynan Southern Nuclear Vice President -Vogile Operating Company. Inc.
7821 River Road Waynesboro, Georgia 30830 Tel 706,826.3151 Fax 706.826.3321 December 16, 2010 Docket Nos.: 50-424 NL-10-2274 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant - Unit 1 Licensee Event Report 1-2010-001 Breaker Failure Results in 1 B Train Containment Cooling System Being Declared Inoperable Ladies and Gentlemen:
In accordance with the requirements of 10CFR50.73(a)(2)(i)(b) Southern Nuclear Operating Company (SNC) is submitting the enclosed Licensee Event Report.
This letter contains no NRC commitments. If you have any questions, please contact Doug McKinney at (205) 992-5982.
Respectfully submitted, T. E. Tynan Vice President - Vogtle TET/TMH/sdc Enclosure: Unit 1 Licensee Event Report 1-2010-001 cp:.
Southern Nuclear Operating Company Mr. J.-T. Gasser, Executive Vice President Ms. P. M. Marino, Vice President - Engineering RType: CVC7000 U. S. Nuclear Regulatory Commission Mr. L. A. Reyes, Regional Administrator Mr. R. E. Martin, NRR Project Manager - Vogtle Mr. M. Cain, Senior Resident Inspector - Vogtle Mr. P. G. Boyle, NRR Project Manager
Enclosure Vogtle Electric Generating Plant-Unit 1 Licensee Event Report 1-2010-001 Breaker Failure Results in 1 B Train Containment Cooling System Being Declared Inoperable
I4RC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED UY OV11v NO..l5sp-m04, EXPIRtES: 10!1,'2013
, the NRC may not coit ducI or sponsor, and a person is net iequired to respond to, the infumlair hitiorn collectiop.
- 3. PAGE Vogqle Electric Generating Plant - Unit 1 05000424 I1 OF 5
- 4. TITLE Breaker Failure Results in 113 Train Containmenl Cooling System Betin g Declared Inoperable
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED 1SEQUENTlAL REV Iiii'* lANE DOCKAET "E1,l00 MON r; hi DAY YEAR YEAR NUMBER NO, V
ION I I I
)AY YEAR 0500 FACInITY NAM PDOCKET NUMEHR 1(
24 2010 2010 001 00 12 16 2010 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C) 0l 50.73(a)(2)(vii)
M El 20.2201(d) 0l 20,2203(n)(3)(ii)
[I 50.73(a)(2)(ii)(A) 0l 50.73(a)(2)(viii)(A)
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l 20.2203(b)(4)
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El 50,73(a)(2)(iii) 17 50.73(a)(2)(ix)(A) 10, POWER LEVEL El 20.2203(a)(2)(ii)
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50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A) 0l 50.73(a)(2)(x) 0l 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50,73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71 (a)(5) 100 El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A) l 50.73(a)(2)(v)(C)
E OTHER El 20.2203(a)(2)(vi)
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50.73(a)(2)(i)(B)
El 50D73ia)(2)(v)(D)
Specify in Abstract below or in
C. DESCRIPTION OF EVENT
Technical Specification Surveillance Requirement SR 3.6.6.2 requires that each Containment Cooling train fan unit be operated for greater than or equal to 15 minutes at a frequency of every 31 days., On September 26, 2010 each of the IB train Containment Cooling fan units were successfully started in low speed and operated for greater than 15 minutes satisfying this surveillance requirement. Once all four of the 1B train fans had successfully passed the surveillance test, all four 1B train fans were placed in normal (high speed) alignment and continued to operate in high speed until October 24, 2010. On October 24, 2010 as part of the next scheduled surveillance test, all four 1B train fans were stopped. During the subsequent attempted start in low speed of the 1 B train Containment Cooling fans, one of the fans failed to start. Due to the failure of the fan to start, the lB train Containment Cooling system was declared Inoperable. As a result, Operations personnel entered Technical Specification LCO 3.6.6 Condition B.
D. CAUSE OF EVENT
Investigation into the failed start attempt of one of the lB train Containment Cooling fans determined that the cause of the failure was due to the breaker that provides power to the low speed winding, being mechanically bound. This condition prevented the breaker from closing and hence the fan from starting. The likely cause of the breaker binding was due to a screw that holds a molded plastic face cover in place contacting the closing mechanism. During the previous breaker closure, when the closing mechanism contacted the screw, the mechanism became bound, which prevented the closing mechanism from functioning during the close attempt. During the investigation it was also noted that the molded plastic cover tab, that the screw bears against was broken which allowed the screw to be inserted further than designed.
The breaker (trade name Emax) that failed was rated for 480 volts, was manufactured by ABB and was installed in this location on April 7, 2008 as part of a Design Change Package (DCP).
The DCP was initiated due to obsolescence of the General Electric 480 volt AKR breakers that had been inservice since plant startup. Prior to installation in the plant, the breaker was inspected and the set up verified by plant electricians. Part of the set up verification requires that the molded plastic cover to be removed and reinstalled. There are four screws that hold the plastic cover in place. Neither the vendor manual nor the plant procedure required that the screws be torqued to a specific value, only that they be tightened. Additionally, maintenance was performed on the breaker May 7, 2010 to replace the closing coil which also required removal and reinstallation of the cover. The investigation concluded that one potential cause for the screw tab on the molded plastic cover being broken was due to the screw being over kt NR*
tightened during installation of the plastic cover. The breaker manufacturer confirmed that with an intact molded plastic cover, there was sufficient design clearance present such that the screw should not be able to contact the breaker closure mechanism. It was also noted that the breaker had been successfully closed on at least 32 occasions as part of the monthly surveillance test from the time the breaker was installed on April 7, 2008 and at least 6 times from when the maintenance was performed on May 7, 2010 until the failure occurred on October 24, 2010.
However, it could not be conclusively determined if the screw had further inserted as a result of the breaker operating (e.g. vibration) or if the opening and closing of the breaker combined with a stack up of tolerances of the internal mechanisms ultimately led to the screw contacting and binding the closing mechanism. In either case, the failure of the breaker was most likely due to the cover being damaged which allowed the screw to be inserted further than the design allowed, which in turn allowed the screw to contact and bind the closing mechanism.
E. ANALYSIS OF EVENT
The Containment Cooling system at Vogtle Electric Generating Plant is comprised of two trains, each of sufficient capacity to supply 100 percent of the design cooling requirement.
During the time period from September 26, 2010 until October 24, 2010 the lB train Containment Cooling system was rendered Inoperable due to the malfunctioning breaker.
However, the 1A train Containment Cooling system remained Operable and capable of providing 100 percent of the design cooling requirement. Therefore, the event did not result in a loss of safety system function. Additionally, a risk assessment of this condition was performed for the time period the configuration existed, and the increase in core damage frequency (CDF) and large early release frequency (LERF) were found to be low. Also, there were no events which required a Containment Cooling system actuation during the time the configuration existed. Based on these considerations, there was no adverse affect on plant safety or on the health and safety of the public.
F. CORRECTIVE ACTIONS
- 1. Temporary modifications for both Unit I and Unit 2 were initiated that allowed removal of the top right hand screw on all of the I E and certain non-I E ABB Emax breakers. The top right hand screw is one of four screws that hold the molded plastic cover in place and is the only one that could potentially interfere with the closing mechanism. An engineering evaluation was performed and it was determined that removal of the screw would not compromise the.seismic qualification of the breaker.
- 2. All of the IE and certain non-IE ABB Emax breakers were inspected in place to determine if the molded plastic cover was damaged and to remove the top right hand screw as allowed by the Temporary Modifications. All but six of the breakers had the screw removed. The NRC FORMI W
(10-2010)
six breakers that remain were found to have damaged covers and all of these breakers are energized to support current plant operation. For the breakers found with damaged covers, the breaker should be de-energized to remove the screw. Otherwise the potential to introduce foreign material from the damaged cover into the breaker internal operating mechanism exists. However, based upon the inspection performed, it was concluded that these breakers would open and reclose if demanded. Therefore, the screw will be removed during the upcoming refueling outages (Spring 2011 for Unit 1 and Fall 2011 for Unit 2) when the breakers can be de-energized.
- 3. A permanent change will be implemented that will preclude the possibility of the top right hand screw from contacting the closing mechanism on all IE and certain non-lE 480 Volt ABB Emax breakers. The expected completion date for this activity is November 1, 2011.
G. ADDITIONAL INFORMATION
- 1. Failed Components:
480 Volt Breaker, Manufactured by ABB, Model E2N-A 16 (Trade name Emax)
- 2. Previous Similar Event:
A review of events reported within the last 3 years did not identify a similar event that was caused by a breaker malfunction.
- 3. Energy Industry Identification System Codes:
Containment Fan Cooling -[BK]
ISSIONI L4 NRCI, FORM ;366Am (10IU2010)