05000423/LER-2009-002, Regarding Automatic Reactor Trip
| ML100541851 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/15/2010 |
| From: | Semancik J Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 10-034, FOIA/PA-2011-0115 LER 09-002-00 | |
| Download: ML100541851 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation 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)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(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 |
| 4232009002R00 - NRC Website | |
text
Dominion Dominion Nuclear Connecticut, Inc.
Millstone Power Station Rope Ferry Road Waterford, CT 06385 FEB 1 5 2010 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.
.MPS Lic/TGC Docket No.
License No.10-034 RO 50-423 NPF-49 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2009-002-00 This letter forwards Licensee Event Report (LER) 2009-002-00 documenting an event that occurred at Millstone Power Station Unit 3, on December 19, 2009. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed in 10 CFR 50.73(a)(2)(iv)(B).
If you have any questions or require additional information, please contact Mr. William D. Bartron at (860) 444-4301.
Sincerely, J. 5. Semancik Plant Manager - Millstone Attachments: 1 Commitments made in this letter: None LA-- Ej(ZA5
Serial No.10-034 Docket No. 50-423 Licensee Event Report 2009-002-00 Page 2 of 2 cc:
U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406-1415 Ms. C. J. Sanders Project Manager U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08B3 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No.10-034 Docket No. 50-423 Licensee Event Report 2009-002-00 ATTACHMENT LICENSEE EVENT REPORT 2009-002-00 MILLSTONE POWER STATION UNIT 3 DOMINION NUCLEAR CONNECTICUT, INC.
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may not conduct or sponsor, digits/characters for each block) and a person is not required to respond to, the information collection.
- 3. PAGE Millstone Power Station - Unit 3 05000423 1 OF3
- 4. TITLE Millstone Unit 3 Automatic Reactor Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED HFACILITY NAME DOCKETNUMBER SEQUENTIAL REV MONTH DAY YEAR 05000 MONTH DAY YEAR YEAR NUMBER NO.
MNH DY YA 50 FACILITY NAME DOCKET NUMBER 12 19 2009 2009- 002- 00 02 15 2010 05000
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR Check all that apply)
- 9. OPERATING MODE 20.2201(b)
- 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A)
X 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. POWER LEVEL 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71 (a)(4) 20.2203(a)(2),,v) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71 (a)(5) 100 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Specify in Abstract below or in
- 1.
EVENT DESCRIPTION
On December 19, 2009 an automatic reactor trip occurred on Millstone Power Station Unit 3 (MPS3) while the unit was in Mode 1, at 100 % power, due to a turbine trip caused by a generator output electrical fault. All control rods fully inserted into the reactor. The auxiliary feedwater pump started as designed.and maintained steam generator level.
All other post trip actions were standard and all systems operated as expected. A post trip walk-down identified damage to 'C' phase main generator breaker and isophase ducting.
There were no radiological challenges as a result of the event.
This event is being reported in accordance with 10 CFR 50.73(3)(2)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed ;n 10 CFR 50.73(a)(2)(iv)(B).
- 2.
CAUSE
The Root Cause Team determined the most probable cause of the ground fault, which resulted in the turbine trip, was a manufacturing defect in the main generator [EL] breaker [BKR], 15G-3U-2, 'C' pole moving contact. This defect was a failure of a "punch mark" to secure a screw-in flange to the moving contact piston. This allowed the flange to unscrew over time. When the breaker closed in November, 2009, the flange had unscrewed sufficiently such that the moving contact was not fully engaged in the fixed contact.
This condition increased contact resistance, causing temperatures to increase, eventually leading the breaker failure, the ground fault, and the turbine trip.
- 3.
ASSESSMENT OF SAFETY CONSEQUENCES
The operating crew responded to the reactor trip by entering Emergency Operating Procedure (EOP) 35 E-0, Reactor Trip or Safety Injection. The reactor trip was not complicated by a safety injection allowing transition to EOP ES-0.1, Reactor Trip Response. The electric plant fast transferred from the normal station services transformer (NSST) [XFMR] to the reserve station services transformer (RSST) [XFMR] due to the loss of the NSST on the generator breaker fault. Initial primary plant cool-down was greater than expected.
The operating crew took action in accordance with plant procedures, stopping the cool-down by turning off the steam dump valves and isolating steam traps and inactive steam dump valves. The normal heat removal path via the main condenser was intact and available.
The auxiliary feedwater system started automatically on the trip as expected and restored the steam generator levels to their normal operating band. Heat removal capability was maintained.
The operator actions and plant mitigating equipment responded as expected with no safety system failures. There were no challenges to any fission product barrier. Therefore, there were no safety consequences due to the reactor trip.
- 4.
CORRECTIVE ACTION
The 'C' pole of the main generator breaker was repaired. All three poles of the breaker will be inspected during the next refueling outage (3R13) scheduled in the spring of 2010 to verify the proper geometry of the contacts (moving and fixed) as well as the security of the fasteners holding the moving contact piston flange in place. Additional corrective actions will be evaluated in accordance with the station's corrective action program.
There is no other use of this type breaker at Millstone.
1
- 5.
PREVIOUS OCCURRENCES
No previous similar events/conditions were identified.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].