05000423/LER-2008-002, Unit 3 Failure of Four Main Steam Safety Valves to Lift within the Acceptance Criteria

Unit 3 Failure of Four Main Steam Safety Valves to Lift within the Acceptance Criteria

ML083510753
Person / Time
Site:	Millstone
Issue date:	12/05/2008
From:	Jordan A Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
08-0653 LER 08-002-00
Download: ML083510753 (6)

LER-2008-002, Unit 3 Failure of Four Main Steam Safety Valves to Lift within the Acceptance Criteria

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4232008002R00 - NRC Website

text

B+/-iF.flil~

Dominion Nuclear Connecticut, Inc.

Millstone Power Station Rope Ferry Road, Waterford, CT 06385

'DEC 0 5 2008 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.

MPS Lic/ELA Docket No.

License No.

08-0653 RO 50-423 NPF-49 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2008-002-00 FAILURE OF FOUR MAIN STEAM SAFETY VALVES TO LIFT WITHIN THE ACCEPTANCE CRITERIA This letter forwards Licensee Event Report (LER) 2008-002-00 documenting a condition discovered at Millstone Power Station Unit 3, on October 10, 2008. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B), as a condition prohibited by technical specifications.

If you have any questions or require additional information, please contact Mr. William D.

Bartron at (860) 444-4301.

Sincerely, Site Vice President - Millstone Attachments: 1 Commitments made in this letter: None M(2/f2~

Serial No. 08-0653 Docket No. 50-423 Licensee Event Report 2008-002-00 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. 08-0653 Docket No. 50-423 Licensee Event Report 2008-002-00 ATTACHMENT LICENSEE EVENT REPORT 2008-002-00 FAILURE OF FOUR MAIN STEAM SAFETY VALVES TO LIFT WITHIN THE ACCEPTANCE CRITERIA MILLSTONE POWER STATION UNIT 3 DOMINION NUCLEAR CONNECTICUT, INC.

Abstract

With the plant in MODE 1 at 100% power on October 9 and 10, 2008, set pressure "simmer" testing of Millstone Power Station Unit 3 (MPS3) Main Steam Safety Valves (MSSVs) was conducted per plant procedures. During the testing, four MSSVs (3MSS*RV22C, 3MSS*RV22D, 3MSS*RV24A, and 3MSS*RV25C) failed to lift within the

(+/- 3%) acceptance criteria of Technical Specification (TS) 3.7.1.1.

The failure of four MSSVs to lift within the required set pressure range is attributed to a corrosive oxide locking action between surface layer materials of the disc-seat interface, sometimes referred to as "oxide locking" or "micro bonding".

After testing, all twenty MSSVs were left within +/- 1% of TS acceptance criteria to account for potential future drift.

NRC FORM 366 (6-2004)

(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17) to 1225 psig. The safety valves protect the SG and portions of the main steam [SB] and feedwater systems [SJ] from overpressure conditions. The valves also serve as a heat sink for the reactor coolant system if the main condenser [COND] is unavailable and the atmospheric steam dump valves cannot relieve pressure following a reactor trip or secondary system accident. The limiting FSAR events with respect to main steam and reactor coolant overpressurization are those presented in FSAR Section 15.2, which involve a decrease in heat removal by the secondary system. The accidents presented in FSAR Section 15.2 assume all MSSVs open at a lift setting 3% higher than their nominal set pressure. An additional conservatism is added to this value for accumulation plus a conservative estimate of the pressure drop to the relief valve. For the limiting Section 15.2 event, all the safety relief valves are assumed open at the time of peak secondary pressure. Since the relief valves all opened during the simmer testing, the same relief capacity would exist with all the relief valves open for the event. Therefore, it is concluded the overall MSSV response of the as-found MSSV condition is equivalent to the MSSV response assumed in the FSAR Section 15.2 Safety Analyses.

Additionally, the micro bonding phenomenon has been limited to static, in-situ testing. The EPRI report indicates that under actual transient high pressure conditions, disk movement/flexure breaks the micro bonding allowing the MSSVs to lift uninfluenced by this phenomenon. Additionally, the EPRI Report indicates that, within the limits of detectability, no history of the seat sticking phenomena had been identified during actual plant transients resulting in MSSV lifts.

4.

Corrective Action

All twenty MSSVs were left within +/- 1% of TS acceptance criteria to account for potential future drift.

Additional corrective actionsto address micro bonding will be evaluated in accordance with the station's Corrective Action Program.

5.

Previous Occurrences

LER MPS3 2007-001-00.

On September 30, 2005, during the performance of set pressure "simmer' testing of MSSVs, valve 3MSS*RV25C failed to lift within the +/- 3% acceptance criteria. The allowable as-found set pressure range is 1179-1251 psig. The valve liftedat 1252.9 psig. The valve was lifted two additional times with results within the required as-left criteria of +/- 1% with no adjustments required. Two additional MSSVs were set pressure tested, to meet the American Society of Mechanical Engineers/Operation and Maintenance code requirement for test expansion. These valves (3MSS*RV23C and 3MSS*RV24C) were satisfactorily tested. The as-left "simmer" tests for both valves were within the required as-left criteria of +/-

1%.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].