05000336/LER-2008-003, Millstone. Unit 2, Regarding Failed Pilot Wire Causes Reactor Trip
| ML082060054 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/14/2008 |
| From: | Price J Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 08-003-00 | |
| Download: ML082060054 (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 |
| 3362008003R00 - NRC Website | |
text
5Domiinioin Dominion Nuclear Connecticut, Inc.
Millstone Power Station Rope Ferry Road, Waterford, CT 06385 f JUL 1 4 2008 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.
MPS Lic/BAK Docket No.
License No.
08-0349 RO 50-336 DPR-65 DOMINION NUCLEAR CONNECTICUT. INC.
MILLSTONE POWER STATION UNIT 2 LICENSEE EVENT REPORT 2008-003-00.,
FAILED PILOT WIRE CAUSES REACTOR TRIP This letter forwards Licensee Event Report (LER) 2008-003-00 which documents a condition identified at Millstone Power Station Unit 2 on May 22, 2008. 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, edAltn Price ite ice President - Millstone I --T _E,; ý a
Serial No. 08-0349 Licensee Event Report 2008-003-00 Page 2 of 2 Attachments:
1 Commitments made in this letter: None.
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
Attachment I LICENSEE EVENT REPORT 2008-003-001 FAILED PILOT WIRE CAUSES REACTOR TRIP Millstone Power Station Unit 2 Dominion Nuclear Connecticut, Inc. (DNC)
Abstract
On May 22, 2008 at 1359 with the Millstone Power Station Unit 2 (MPS2) at 100% power in Mode 1, the reactor automatically shutdown following a loss of load and subsequent turbine trip. Investigation determined that a lightning strike on a transmission line created an over current condition to which the unit responded.
The 345 kV main generator output breakers in the transmission switchyard opened causing a turbine trip on loss of load. A pre-existing mechanical failure of a connecting wire lug created an open circuit in the pilot wire circuitry.
The power surge from the lightning strike coupled with this open circuit caused the pilot wire relay to act as an over current protection device which opened the breakers. The transmission switchyard breakers and associated interlocks operated as designed protecting station equipment.
During the event, the in-house electrical buses were automatically transferred from the Normal Station Service Transformer (NSST) to the Reserve Station Service Transformer (RSST) causing a momentary loss of the non-safety grade 120 volt power supplies (VR-1 1 and VR-21). This affected multiple components which required additional operator actions. The systems functioned as expected based upon the signals received. The operators took actions as trained and in accordance with procedures. No equipment was damaged as a result of this event.
The unit was brought to a stable condition in hot-standby (Mode 3) and the lug was repaired.
This event is being reported pursuant to 10CFR50.73(a)(2)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed in 10CFR50.73(a)(2)(iv)(B).
NRC FORM 366 (9-2007)
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
- 4.
Corrective Action
Short term corrective action was to repair the circuit by installing a new lug on the pilot wire, recalibrating the relay, and performing additional testing.
An investigation into this event was conducted and other appropriate corrective actions are being addressed in accordance with the Millstone Corrective Action Program.
- 5.
Previous Occurrences
No previous similar events/conditions were identified.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].