05000336/LER-2006-006-01, Regarding Scaffolding Built for Work on Main Steam Isolation Valve (2-MS-64A) Prevented the Valve from Closing

Regarding Scaffolding Built for Work on Main Steam Isolation Valve (2-MS-64A) Prevented the Valve from Closing

ML070650411
Person / Time
Site:	Millstone
Issue date:	02/21/2007
From:	Price J Dominion Nuclear Connecticut
To:	Document Control Desk, NRC/NRR/ADRO
References
07-0010 LER 06-006-01
Download: ML070650411 (6)

LER-2006-006, Regarding Scaffolding Built for Work on Main Steam Isolation Valve (2-MS-64A) Prevented the Valve from Closing

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3362006006R01 - NRC Website

text

J9"IDominion-Dominion Nuclear Connecticut, Inc.

Millstone Power Station Rope Ferry Road Waterford, CT 06385 FEB 2 12007 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Serial No.

MPS Lic/GJC Docket No.

License No.

07-0010 RO 50-336 DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 LICENSEE EVENT REPORT 2006-006-01.

SCAFFOLDING BUILT FOR WORK ON MAIN STEAM ISOLATION VALVE (2-MS-64A)

PREVENTED THE VALVE FROM CLOSING This letter forwards Licensee Event Report (LER) 2006-006-01.

This is revision 1 to LER 2006-006-00, which documented an event that occurred at Millstone Power Station Unit 2, on October 7, 2006. This LER is being submitted pursuant to 50.73(a)(2)(i)(B),

as an operation or condition prohibited by Technical Specifications.

If you have any questions or require additional information, please contact Mr. David W.

Dodson at (860) 447-1791, extension 2346.

Very truly yours, 44D !;-

L k

A Site President - Millstone 1~e~

Serial No. 07-0010 Licensee Event Report 2006-006-01 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 Mr. V. Nerses Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 8C2 Rockville, MD 20852-2738 Mr. S. M. Schneider NRC Senior Resident Inspector Millstone Power Station Licensee Event Report 2006-006-01, Scaffolding Built For Work On Main Steam Isolation Valve (2-MS-64A) Prevented The Valve From Closing Millstone Power Station Unit 2 Dominion Nuclear Connecticut, Inc. (DNC)

Abstract

On October 7, 2006, with the plant in Mode 3, scaffolding built on August 25, 2006 to support work on the #1 steam generator main steam line isolation valve 2-MS-64A prevented the valve from fully closing during surveillance testing. The obstruction was removed within approximately one hour of discovery. An immediate report per 10 CFR 50.72(b)(3)(v)(D) was made to the NRC. A review of valve closure under design basis conditions with the scaffolding interference in place concludes that the valve would not have closed for small steam line breaks downstream of the MSIV and steam generator tube rupture conditions due to insufficient pressure drop across the valve disc. An engineering evaluation determined the area around the MSIV would remain accessible to the operators and the scaffolding interference could be removed intime to complete the safety function.

The root cause investigation for this event determined that supplementary instructions provided for the construction of scaffolding in the vicinity of the MSIV lacked sufficient specific information to ensure MSIV operability was not impacted. The station's scaffold evaluation process will be modified to ensure specific information is provided to maintain operability of safety related and other critical safety related systems, structures or components potentially impacted by the proposed scaffold.

The scaffolding was in place for more than the TS allowed outage time, therefore this event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B), as an operation or condition prohibited by Technical Specifications.

I 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) downstream of the MSIV in the enclosure building would be equivalent to that of a break upstream of the MSIV.

For small steam line breaks in the turbine building, the equipment required to isolate auxiliary feed water to the affected SG and to maintain the RCS decay heat removal and vital auxiliaries safety functions would continue to function. In addition, for small steam line breaks in the turbine building, and in the event of a SGTR, the area around the MSIV would remain accessible to the operators and the scaffolding interference could be removed to close the MSIV and isolate the break.

In summary, for full flow conditions within the main steam system, the load on the MSIV disc would be sufficient to close the MSIV despite the scaffolding interference. The radiological consequence of a SGTR with the MSIV open was assessed. Using the RCS activity at the time the scaffolding was installed, it was determined that even after 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> with the SG not isolated, the affected release would not exceed the dose limits to the EAB, LPZ, and MP2 Control Room specified in Regulatory Guide 1.183 and 10 CFR 50.67. It was also concluded that the MSIV would remain accessible to the operators and the scaffolding interference could be removed to allow closure of the MSIV. Within approximately one hour of discovery of the condition, the scaffold was modified to remove the interference. Based on the above, the safety function of the MSIV was never lost.

4.

Corrective Action

Upon discovery, the scaffolding was modified to remove the interference. The scaffold evaluation process will be modified to ensure specific information is provided to maintain operability of safety related and other critical safety related systems, structures or components (SSCs), potentially impacted by the proposed scaffold. As a compensatory measure, for scaffolding built near safety related SSCs, a pre-construction walkdown by Operations with the Scaffold Lead will be required. Pre-and post construction walkdowns will be conducted by Engineering and Operations for all scaffolding that has the potential to impact safety related SSCs. These walkdowns will continue until the revised process is in place. Additional corrective actions are being taken in accordance with 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].

1