ML19207B333

Provides Revised Design Groundwater Level Predictions Per 760315 Ltr.Subsurface Drainage Has Not Been Incorporated in Figures Although Appropriate Mods Have Been Made to Assure Adequacy of safety-related Structures & Facilities

ML19207B333
Person / Time
Site:	North Anna
Issue date:	08/21/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
657, NUDOCS 7908240452
Download: ML19207B333 (3)

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{ vinmoi a su r c T sic es o ro a e n coun ^sv. nic. von n. vincinia 232si August 21, 1979 Mr. James P. O'Reilly, Director Serial fio. 657 Office of Inspection & Enforcement PSE&C/RKM/CES:adw:mc U. S. fluclear Regulatory Commission Reaion II Docket Nos. 50-404 10; Marietta Street, Suite 3100 50-405 Atlanta, Georgia 30303 Control flo. F20097H1

Dear Sir:

As stated in our letcer to the Nuclear Regulatory Commission (NRC),

Serial No. 938, dated March 15, 1976, the design groundwater levels used in north Anna Power Station Units 3 and 4 were being reviewed for agree-ment with the latest predicted groundwater levels. These predinted groundwater levels are bas-d on a water surface profile which varic; in the plant area from elevation +250 at Lake Anna to elevation +271 south of the boron recovery tank enclosure. As further discussed in the above referenced letter, this prediction does not include the effects of any subsurface drainage or structures on the groundwater level. Where condi-tions appear capable of producing locally higher groundwater levels appro-priate modifications were made to the general prediction to insure the adequacy of safety related structures and facilities. This review has now been completed and has resulted in the following findings.

The presently predicted maximum groundwater elevations for each safety-related structure are:

Structure Groundwater Elevation Reactor containment Unit 3 268 Reactor containment Unit 4 268 Containment auxiliary structures Unit 3 Ndin steam valve house 266 Quench spray 266 Safeguards 267 Unit 4 Main steam valve house 266 Quench spray 266 Safeguards 267 Auxiliary building 268 Fuel building 268 Decontamination building 270 Service building 265 Emergency diesel generator building 267 Intake structure 259 Service water pump house 315 Fuel oil tanks and pump house 271

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vincm4 ruCTE AM POWER COMPANY TO Mr. James P. O'Reilly SHEET NO.

Structure Groundwater Elevation Boron recovery tank enclosure 271 Discharge tunnel sections T3 and T4 supporting Unit 3 RWST and CST 267 Unit 4 RWST 266 Unit 4 CST 267 Structures with a considerable width in the north-south direction, such as the auxiliary building, may have a variation of 3 or 4 feet in groundwater elevation from the south end to the north end. This variation will be utilized for local design and structure stability. With the exception of the containment auxiliary structure, these groundwater elevations have been a part of the structural design criteria since June 17, 'o70.  : ne ground-water elevation for the containment auxiliary structure was conservative by 2 feet, and the design criteria will be adjusted for this revision.

The containment auxiliary structure, service water pump house, and dis-charge tunnel sections T3 and T4 have been utilizing the appropriate ground-water elevations for stability and structural capacity since the start of design.

The decontamination building, auxiliary building, fuel building, and the service building designs are being revised and will continue to utilize the appropriate groundwater elevations.

The reactor containment was designed for a lower groundwater elevation than is now predicted. The structure has been checked for stability and structural capacity of beneath-grade exterior walls and is adequate for the presently predicted groundwater elevation.

The intake structure groundwater level of el 259 ft is applicable for the south face only. The geometry of the intake tunnels and the turbine building creates an area south of the intake structure where groundwater could be ponded. The groundwater level for the east and west walls of the intake structure is el 251 ft. The stability analysis used groundwater el 259 ft. Structural design of the mat and south wall will be updated for a groundwater level of el 259 f t.

The emergency diesel generator building, the fuel oil tanks and pump house, and the boron recovery tank enclosure do not have completed designs.

These designs will use the appropriate groundwater elevations.

The Unit 4 rerueling water storage tank and the Unit 4 cendensate storage tank have their foundations above the predicted groundwater leval. Therefore, the designs are not affected.

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""SN'A nEC* CAN P WER C MPAN'r T Mr. James P. O'Reilly 3 Structural details at constructions joints, expansion joints, and rattle spaces were reviewed to determine whether water stops and water-proof membrane provided were adequate to prevent groundwater seepage.

As a result of the review, water stops are beino added in portions of the fuel building and in the rattle space between the fuel building and the Unit 3 reactor containment.

Water stops are clso being added in areas where waterproof membrane is the only protection from groundwater seepage. These areas are between the react ir containment and the auxiliary building, the reactor contain-ment and the containment auxiliary structures, and the safeguards area and the quench spray area. These areas apply for both Units 3 and 4.

This summarines the effects of the latest predicted groundwater elevation on the design of Units 3 and 4's structures. This response will thus complete and finalize our committment to review Unit 3 and 4 structural designs discussed in our letter (Serial fio. 938) of March 15, 1976 on this subject.

f Very ru y yours, l h i/ 'Q ,n e v>

vs' SamC.vBro/n,Jr.

Senior Vice President-Power Station Engin ering and Construction cc: Mr. Victor Stello, Directoi Office of Inspection & Enforcement Mr. Harold R. Denton, Director Office of t'uclear Reactor Regulation

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