ML20059F217

Safety Evaluation Supporting Amends 137 & 120 to Licenses NPF-4 & NPF-7,respectively

ML20059F217
Person / Time
Site:	North Anna
Issue date:	08/27/1990
From:	Office of Nuclear Reactor Regulation
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Shared Package
ML20059F209	List: ML20059F204 ML20059F217
References
NUDOCS 9009110145
Download: ML20059F217 (3)

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UNITED STATES E

NUCLEAR REGULATORY COMMISSION WASHINGTON. D. C. 20666

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMEN 0 MENT N05.137 AND 120 TO FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY OLD DOMINION ELECTRIC COOPERATIVE NORTH ANNA POWER STATION. UNITS NO. 1 AND NO. 2 DOCKET N05. 50-338 AND 50-339 l

INTRODUCTION By letter dated June 8, 1990, as superseded June 13, 1990, the Virginia Electric and Power Company (the licensee) proposed changes to the Technical S:ecifications (TS) for the North Anna Power Station, Units No. I and No.' 2 (1A-182). The changes will reduce the minimum residual heat removal (RHR) flow rate from 3000 gpm to 2000 gpm during reactor coolant system (RCS) partial drainage (mid-loop) operation for which the temperature is maintained below 140'F and the reactor has been shut down for at'least 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />. The 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> requirement is consistent with the typical ~ time from power operation to mid-loop operation. At the currently required flow rate of 3000 gpm, the RHR system is more susceptible to vortex formation at the RHR pump suction' piping during RCS partial drainage operation. Vortexing can cause RHR system air i

entrainment and pump cavitation and subsequent loss of RHR system heat removal capability. The changes will increase the margin to safety operate RHR pumps and also increase plant operational flexibility.

6 DISCUSSION Mid-loop operation (operation with the-RCS partially drained) is necessary for.

required inspection and maintenance of RCS components such as reactor coolant pumps and steam generators. As indicated in NUREG-1269, reduced. flow rates provide greater margin against vortex formation and can' help preclude an in-i advertent loss of decay heat removal capability due to air entrainment and cavitation of the RHR pumps. A Westinghouse Owners' Group (WOG) project eval-uated the effects of-system geometry, RHR flow rate and water level within the RCS hot leg piping, in order to predict the. onset of detrimental vortexing.

For the NA-1/2 RCS configuration (at a 2000 gpm RHR flow rate), the WOG evalua-tion predicts that vortexing begins at an RCS hot leg water level of ab it 0.25 inch above reactor vessel nozzle centerline.

Since the~ normal RCS hot'.eg water i

level at NA-182 during mid-loop operation is 10 inches above reactor vessel nozzle center, the proposed minimum RHR flow rate of 2000 gpm provides adequate operational flexibility and margin to vortexing for normal plant mid-loop operation.

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i As the time after plant shutdown increases, decay heat removal and thus the RHR flow rate requirements are reduced.

The licensee performed an energy balance calculation utilizing a decay heat power curve based upon ANSI /ANS-5.1-1979. The analysis indicated that at.100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> after reactor shutdown the pro-posed minimum RHR flow rate provides sufficient heat removal capability to main-tain the RCS temperature below 140*F as required for refueling (Mode'6) operatien.

In addition, a minimum RHR flow rate is required to prevent flow stratification and localized variations in boron concentration in the RCS. The analysis.showed the-proposed minimum flow of 2000 gpm would provide the necessary turbulence in-the RCS cold leg to ensure adequate boron mixing. Also, the functional perfor-mance of the mechanical equipment in the RHR system trains from the RCS hot leg.

piping to the RCS cold leg piping was evaluated. This evaluation confirmed that the minimum RHR flow through any one RHR pump discharge check valve was sufficient to keep the check valve fully open.

The TS changes in the proposed amendments are itemized below:

(1) Addition of TS 3/4.1.1.3.1 to the NA-2 TS -- The addition of this TS-requires that a minimum RCS flow of 3000 gpm be maintained whenever a reduction in the RCS boron concentration is being made. This speci-fication provides assurance that adequate boron mixing will be main,

tained when the RCS boron concentration is being changed. The proposed specification is consistent with the existing NA-1 TS and Standard TS-and is acceptable.

(2). Renumbering of TS 3/4.1.1.3 to 3/4.1.1.3.2 for the NA-2 TS -- The change will enhance consistency between the NA-182 TS. The change is an administrative change, and is acceptable.

(3) TS 4.4.1.3.4, 3/4.9.8.1 and 3/4.9.8.2 (NA-182) -- The proposed changes rev,ise the current minimum RHR system flow rate of 3000 gpm to 2000 gpm during mid-loop operation when the RCS temperature is maintained below 140*F and the reactor has been shut down for at least 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />. The proposed changes are consistent with the licensee's analysis as discussed above, and are therefore acceptable.

(4) TS 4.4.1.3.1 (operability requirements per TS 4.7.9.2) -- The current TS requires the RHR system to be " Operable per Specification 4.0.5."

The TS is changed to be " Operable per Specification 4.7.9.2."

Since Specifi-cation 4.7.9.2 includes the operability requirements for Specification l

4.0.5, the change does not effect the plant operation, is an administrative change, and is acceptable.

(5) TS 3/4.9.8.1 (applicable to " Normal Water Levels") -- The LCO (Limiting Condition for Operation) for this specification is changed to. read "At least one RHR loop shall be OPERABLE and at least one RHR loop shall be.

in operation." The revised TS is a more conservative requirement in that it now requires at least one RHR loop to be operable, in addition to operation of at least one RHR loop. The staff finds this change to be acceptable, i

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'(6). TS 3/4.9.8.2 (applicable to." Low Water Level") -- The TS is revised from "Two independent RHR loops shall be OPERABLE" by adding "with at.least one loop in operation" to the LCO..The change imposes a more restricted operating condition'and the proposed TS is consistent with the. Standard TS, and is therefore acceptable.

EVALUATION The staff has reviewed the proposed TS changes which include e reduction in the RHR flow rate during mid-loop o)eration when the RCS-temperature is main-taineo below 140"F and the reactor las been shut down for at least'100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />.

The_ staff finds these changes 'are consistent with the position of NRC GL 88-17 and supported by the licensee's analysis.

Therefore, the staff finds.the-changes to be acceptable.

ENVIRONMENTAL CONSIDERATION.

These amendments involve a change to a requirement with respect to installation or use of a facility component located wit *'n the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. We have determined that the amendments, involve no>significant increase in the amounts, and no significant change'in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Comission has previously issued a proposed finding that these amendments involve no significant hazards consideration and.there has been no public comment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b), no environmental impact' statement or environmental assessment need be prepared in connection with the issuance of these amendments.

CONCLUSION Wehaveconcluded,basedontheconsiderationsdiscussedabove,that(1)there is reasonable assurance that the health and safety of the public will not be L

endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendments will not be inimical to the common defense and' security or to the health and safety of the public.

Date: August 27, 1990 Principal Contributors:

S. Sun L. Engle J

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