ML20248C532

Special Rept:On 890601,discovered Differential Settlement Between Unit 2 Containment & Main Steam Valve House Exceeding Limit.Caused by Apparent Upward Movement of Point 131 on Unit 2 Containment.Procedure 1-PT-112 Revised

ML20248C532
Person / Time
Site:	North Anna
Issue date:	07/28/1989
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
89-540, NUDOCS 8908100071
Download: ML20248C532 (2)

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VIRGINIA ELECTRIC AND POWER COMPANY RICllMOND, VIRGINIA 23261 W. L. STEW ART )

sosioR vice PRestorxt July 28, 1989 POWER United States Nuclear Regulatory Commission SerialNo.89-540  !

Attention: Document Control Desk NO/DEO/DLDM:deq Washington, D.C. 20555 Docket No. 50-339 License No. NPF-7 Gentlemen:

yjB.GINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT 2 DIFFERENTIAL SETTLEMENT BETWEEN THE UNIT 2 CONTAINMENT AND THE UNIT 2 MA]R STEAM VALVE HOUSE On June 1,1989, the differential settlement between the Unit 2 Containment (survey point 131) and the Unit 2 Main Steam Valve House (survey point 124) was confirmed to exceed 75 percent of the allowable value,0.030 feet, specified in Table 3.7-5 of Technical Specification 3.7.12.1. The differential settlement between survey pointa 131 and 124, calculated during the performance of 1 PT-112, Category 1 Structures .- Sett! ament Monitoring, on May 30,1989, was 0.023 feet , which is 77 percent of the Technical Specification limit of 0.03 feet. This Special Report is being submitted pursuant to the requirements of Technical Specification 3.7.12.1.

The Bases for Technical Specification 3.7.12.1 defines the piping system containing line number 6"-SI-416-1502-01 as the primary concern for the differential settlement between the Unit 2 Containment and the Unit 2 Main Steam Valve House. On June 1,1989, during a field walkdown to determine if there were any signs of overstress in the piping system, it was discovered that line number 6"-SI-416-1502-01 is not located between the Unit 2 Containment and the Unit 2 Main Steam Valve House. Line number 6"-SI-416-1502-01 is located between the Unit 2 Containment and the Unit 2 Safeguards. Consequently, line nurnber 6"-SI-416-1502-01 does not constitute the basis for the 0.030 f.eet allowable differential settlement between the Unit 2 Containment and the Unit 2 Main Steam Valve House. The correct basis for the differential settlement ostween the Unit 2 Containment and the Unit 2 Main Steam Valve House are the Main Steam, Feedwater, Service Water, and Condenser Air Elector lines. Results of an evaluation indicate that the Main Steam, Feedwater, Service Water, and Condenser Air Ejector lines located between the Unit 2 Containment and the Unit 2 Mala Steam Valve House have adequate flexibility to absorb 0.030 feet of differential settlement.

Results of the previous suivey on October 1,1988, indicated that 67 percent (0.020 feet) of the current allowable differential settlement between the Unit 2 Containment and the Unit 2 Main Steam Valve House had occurred. The May 30,1989 survey indicated an apparent upward movement of point 131 on Unit 2 Containment which resulted ir, a calculated differentia'. settlement of 0.023 feet.

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The differential settlement between the Unit 2 Containment and the Unit 2 Safeguards, where line number 6"-SI-416-1502-01 is actually located, is currently monitored under the Settlement Monitoring Program required by Technical Specification 3.7.12. As stated in Table 3.7-5 of Technical Specification 3.7.12, the allowable differential settlement between the survey points for these two structures is 0.070 feet. The maximum differential settlement exhibited between the Unit 2 Containment and the Unit 2 l Safeguards is 0.013 feet.

The next survey required by Technical Specification 3.7.12 is scheduled for October 1989. Prior to October 1989,1 PT-112 will be revised to administratively limit the allowable differential settlement between the survey points for the Unit 2 Containment and the Unit 2 Safeguards to 0.030 feet, based on ,

the location -of line number 6"-SI-416-1502-01. In addition, a Special Report will be submitted if the differential settlement between the Unit 2 Containment and the Unit 2 Safeguards exceeds 75 percent of 0.030 feet.

Based on the above, the structuralintegrity of the limiting safety related lines has not been compromised.

Virginia Electric and Power Company is currently re-assessing the entire Settlement Monitoring Program and upon completion intends to submit a Technical Specification change request. This Technical Specification change request will include the corrections required to resolve the discrepancies in the Bases of Technical Specification 3.7.12 described above.

This Special Report has been reviewed by the Safety Nuclear and Safety Operating Committee. Should you have any questions regarding this report, please contact us at your earliest convenience.

Very truly yours, V. a n W.L. STEWART cc: U.S. Nuclear Regulatory Commission Region 11 ,

101 Marietta Street, N.W. I Suite 2900 i Atlanta, Georgia 30323 Mr. J. L. Caldwell )

NRC Senior Resident inspector  !

North Anna Power Station 1

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