ML20245J515

Ro:On 890309,differential Settlement Between Svc Bldg & Unit 2 Main Steam Valve House Indicated That 110% of Current Allowable Differential Settlement Occurred.Differential Settlement Result of Inaccuracies in Survey Rod Utilized

ML20245J515
Person / Time
Site:	North Anna
Issue date:	04/28/1989
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
89-319, NUDOCS 8905040151
Download: ML20245J515 (2)

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( i VinoxNIA ELECTRIC AND Powsu COMPANY RicarMoNo,VIHOINIA 20261 Iw.n.ciarw=mur. April 28,s1989 Vaca Panamawr Nucom Am .

Y U.-S. Nuclear Regulatory Commission- Serial No.89-319 Attention: ' Document Control Desk' NAPS /DEQ/11:

Washington, D.C. 20555 Docket Nos.50-33S 50-339

, License Nos. NPF-4 NPF-7 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 VOLUNTARY REPORT ON THE DIFFERENTIAL SETTLEMEh"r BEWEER THE SERVICE BUILDING AND THE UNIT 2 MAIN STEAM VALVE HOUSE On March 9, 1989, the differential settlement between the Sw " ce Building and the Unit 2 Main Fieam Valve, House (MSVH) was calculated during the performance of 1-PT-112, Category 1 Structures - Settlement Monitoring. Results of the survey indicated that 110 percent. (0.033 feet) of the current allowable differential settlement, 0.03 feet, specified in Table 3.7-5 of To :hnical Specification 3.7.12.1 had occurred. At this time, the Action Statement. of Technical Specification 3.7.12.1 was entered.

Previously,. the differential settlement between the Service Building and the Unit 2 MSVH had been calculated from survey results obtained utilizing a Philadelphia Rod, However, since a Philadelphia Rod was not available on March 9, 1989, a folding Engineers' Rule (a non-standard surveying technique) was utilized to survey the differential settlement between the Service  !

Building and the Unit 2 MSVH.

Additional surveys were conducted on March 13 and' March 16, 1989 to determine if inaccuracies were present in the March 9, 1989 survey results due to the use of different surveying methods. An Invar Rod, a standard surveying technique, was used for these surveys. Also, a comparison of the results among the three survey rods was performed. It was found that the Philadelphia i Rod and Engineers' Rule being us d were shorter than the Invar Rod by 0.009 and 0.012 feet, respectively. The results of these additienal surveys and measurement technique comparisons, which were submitted to the NRC on March 23, 1989, (Serial No.89-175), confirmed that a more accurate measurement of ,

the differential settlement between the Service Building and the Unit 2 MSVH {

is obtained by utilizing the Invar Rod and that only 67 percent (0.020 feet) of the current allowsble differential settlement specified in Technical Specification 3.7.12.1 has actually occurred. )

i 8905040151 890428 PDR ADOCK 05000319 f l

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On April .5, 1989, the differential settlement between the Service Building and the Unit 2 MSVH was again determined to be 67 percent (0.020 feet) of the allowable differential settlement. This differential settlement of 67 1~ percent, calculated from survey results obtained utilizing the Invar Rod, l further confirmed that the differential settlement of 110 percent, calculated on March 9, 1989, was a result of inaccuracies in the survey rod utilized.

The above information, the Technical Specification change request submitted on bbrch 10, 1988, and the additional supporting information submitted on March

! 23, 1989, confirms that increasing the allowable differential settlement from 0.030 feet to 0.047 feet is justified, the Unit 2 MSVH is stable and not rising as the previous survey data had indicated, and the Service Building is continuing to settle at a very slow rate, as are other soil founded structures throughout the site. As a result, the Action Statement of Technical l

Specification 3.7.12.1 has been cleared and the differential settlement between the Service Building and the Unit 2 MSVH will no longer be monitored monthly, as previously committed, but will only be monitored semiannually as requ!. red by the Technical Specifications.

Very truly your ,

- /

W. R. Cartwr ght r

cc: U.S. Nuclear Regulatory Commission 101 Marietta Street, N. W.

Suite 2900 Atlanta, Georgia 30323 Mr. J. L Caldwell NRC Resident Inspector North Anna Power Station