05000423/LER-2007-004, Fire Scenario Results in Unanalyzed Condition - Potential Loss of Charging
| ML073450815 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/03/2007 |
| From: | Jordan A Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 07-0780 LER 07-004-00 | |
| Download: ML073450815 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4232007004R00 - NRC Website | |
text
Dominion Dominion Nuclear Connecticut, Inc.
Millstone Power Station Rope Ferry Road, Waterford, CT 06385 0DEC 03 2001 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.
MPS Lic/TGC Docket No.
License No.
07-0780 RO 50-423 NPF-49 DOMINION NUCLEAR CONNECTICUT. INC.
MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2007-004-00. FIRE SCENARIO RESULTS IN UNANALYZED CONDITION - POTENTIAL LOSS OF CHARGING This letter forwards Licensee Event Report (LER) 2007-004-00, documenting a condition identified at Millstone Power Station Unit 3, on October 5, 2007. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(ii)(B).
If you have any questions or require additional information, please contact Mr. William D. Bartron at (860) 444-4301.
Sincerely, A. J.J rdan, Jr.
Plant Manager - Nuclear
Serial No. 07-0780 Licensee Event Report 2007-004-00 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, Mail Stop 08 B3 One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No. 07-0780 Licensee Event Report 2007-004-00 FIRE SCENARIO RESULTS IN UNANALYZED CONDITION POTENTIAL LOSS OF CHARGING MILLSTONE POWER STATION UNIT 3 DOMINION NUCLEAR CONNECTICUT, INC. (DNC)
Abstract
On October 5, 2007 and October 11, 2007 while operating at 100% power, Millstone Power Station Unit 3 (MPS3) identified a vulnerability in the fire safe shutdown strategy in which a fire could disable both the train A and train B charging pumps. In the event of a fire affecting one train of charging with the opposite train charging pump in service, a fire induced circuit failure could produce spurious closure of the Volume Control Tank (VCT) outlet valve, resulting in damage to the operating charging pump. As a result, neither charging pump would be available to provide reactor coolant system inventory control and reactor coolant pump seal injection. Since the station's design basis following a fire in a specific area is that one train of required systems remain free of fire damage, these scenarios result in an unanalyzed condition. The analyses for fire areas, prepared in the 1980s, reviewed spurious equipment operation. However, the report failed to consider the unique interaction between the spurious closure of the VCT outlet valve and the operating charging pump in the redundant train. Compensatory measures have been implemented and will remain in place until a permanent resolution is identified and implemented. The condition resulted in no adverse safety consequences. It is of regulatory significance because it represents an unanalyzed condition. This condition is being reported under 10CFR50.73(a)(2)(ii)(B), "Any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety."
(If more space is required, use additional copies of (If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
In the event of a large scale fire in fire area AB-6, the third charging pump would not be available. However, operators remain in the control room for a fire in fire area AB-6. Although not previously analyzed, safe shutdown could be achieved without relying on the charging system by depressurizing the plant below high head safety injection limits and utilizing high head safety injection to achieve and maintain safe shutdown.
- 4.
Corrective Actions
Compensatory actions were implemented that enhance the defense in depth philosophy to prevent, detect and rapidly extinguish fires to minimize the likelihood of a large scale fire in these areas. These include additional controls of combustible materials, hourly fire watches and increased monitoring of fire detection and suppression systems for the affected fire areas. Additional administrative controls have been implemented to maximize the availability of the third charging pump in the event of a fire.
An extent of condition review was conducted for the circuit routing for the VCT outlet valves and charging pump suction valves. No other similar conditions were found.
Corrective actions for this condition are being addressed in accordance with the station's Corrective action program.
Compensatory actions will remain in place until a permanent resolution is identified and implemented.
- 5.
Previous Occurrences
No previous similar events/conditions were identified.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
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