05000423/LER-2008-004, Gas Void Discovered in the Emergency Core Cooling System Suction Line
| ML090070031 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/19/2008 |
| From: | Jordan A Dominion, Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 08-0764 LER 08-004-00 | |
| Download: ML090070031 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 4232008004R00 - NRC Website | |
text
- 11111k, 410gIPomjfljoWl Dominion Nuclear Connecticut, Inc.
Millstone Power Station Rope Ferry Road, Waterford, CT 06385 DEC 1 9 2000 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.
MPS Lic/GJC Docket No.
License No.
08-0764 RO 50-423 NPF-49 DOMINION NUCLEAR CONNECTICUT. INC.
MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2008-004-00 GAS VOID DISCOVERED IN THE EMERGENCY CORE COOLING SYSTEM SUCTION LINE This letter forwards Licensee Event Report (LER) 2008-004-00 documenting a condition discovered at Millstone Power Station Unit 3 on October 20, 2008. This LER is being submitted pursuant to the following: 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(v)(B) and (D), and 10 CFR 50.73(a)(2)(vii).
If you have any questions or require additional information, please contact Mr. William D. Bartron at (860) 444-4301.
Sincerely, A. J. Jordan Site Vice President - Millstone Attachments: 1 Commitments made in this letter: None
Serial No. 08-0764 Docket No. 50-423 Licensee Event Report 2008-004-00 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 Mail Stop 08B3 One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No. 08-0764 Docket No. 50-423 Licensee Event Report 2008-004-00 ATTACHMENT LICENSEE EVENT REPORT 2008-004-00 GAS VOID DISCOVERED IN THE EMERGENCY CORE COOLING SYSTEM SUCTION LINE MILLSTONE POWER STATION UNIT 3 DOMINION NUCLEAR CONNECTICUT, INC.
Abstract
On October 20, 2008, with Millstone Unit 3 at 0% power in Mode 5, as part of Generic Letter 2008-01 activities, ultrasonic testing (UT) performed on a portion of the common suction line from the refueling water storage tank to the suction of the emergency core cooling system (ECCS) pumps indicated the accessible portion of the 24" diameter pipe was 85% full. No immediate actions were necessary since ECCS is not required in Mode 5.
Engineering determined for break sizes that would result in low head safety injection there was the potential to transport the gas void/water mixture to specific ECCS pumps during the injection phase of an accident. Of the scenarios with the potential to transport the gas void/water mixture, only those scenarios with a low reactor coolant system pressure were determined to adversely impact the accident mitigation capability of affected ECCS pumps.
The cause of this condition was determined to be a latent design error. The original design of the plant did not include a vent path for this section of piping. Subsequent to the discovery of the gas void, the plant was modified to install a vent valve on this line to provide a venting location. The operators utilized this vent valve upon returning the unit to service to fill the common suction line and confirmatory UTs were performed to verify the line was full.
This condition is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) as any operation or condition prohibited by the plant's Technical Specifications, 10 CFR 50.73(a)(2)(v)(B) and (D) as any condition or event that could have prevented fulfillment of a safety function, and 10 CFR 50.73(a)(2)(vii) as any event or condition where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system.
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)
- 3.
ASSESSMENT OF SAFETY CONSEQUENCES
Past ECCS operability was affected for postulated accident scenarios for the ECCS pumps. However, the combination of available systems and system performance during postulated accident conditions with the identified gas void indicates there would be adequate ECCS flow for core cooling.
Thermal-hydraulic and void size modeling was used as the basis for the conclusion that the SIH pumps would have been able to perform their safety function for all postulated accident scenarios. For postulated scenarios when the charging pumps were rendered inoperable, the RHR system pumps were determined to remain functional. Also, when the RHR system pumps were determined to be inoperable, the charging system pumps remained functional.
Adequate ECCS pump functionality has been demonstrated to support required core cooling such that this condition is of low safety significance and the health and safety of the public was maintained for postulated accident scenarios within the MPS3 design basis.
- 4.
CORRECTIVE ACTION
Subsequent to the discovery of the gas void, a modification to the plant was implemented. This modification installed a vent valve on the 24" diameter section of this line to provide a venting location. The operators utilized this vent valve to vent the line upon returning the unit to service and confirmatory UTs were performed to verify the line was full. Additional corrective actions have been included in the station's 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].