ML20209B429

Safety Evaluation Supporting Util Proposed Rev to Tech Specs Re Drywell Leakage Test Interval

ML20209B429
Person / Time
Site:	River Bend
Issue date:	04/22/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20209B420	List: ML20209B416 ML20209B429
References
NUDOCS 8704280435
Download: ML20209B429 (2)

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~g UNITED STATES

! c NUCLEAR REGULATORY COMMISSION

{ I WASHWGTON. D. C. 20555 l'

\*****) SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION TECHNICAL SPECIFICATION CHANGE REQUEST GULF STATES UTILITIES RIVER BEND STATION UNIT 1

. DOCKET NO. 50-458

1.0 INTRODUCTION

, By letter dated January 28, 1987, Gulf States Utilities (GSU), the licensee

for River Bend Station Unit 1, proposed a Technical Specification (TS) change to Appendix A to Facility Operating License NPF-47. The proposed change involves the deletion of Specification 4.6.2.2.b from the overall i Drywell Bypass Leakage Surveillance Requirements as specified in Specifi-cation 4.6.2.2. Currently the drywell bypass leakage rate tests are

required at intervals no greater than 18 months. This time interval is

sufficient to allow testing during the refueling outage.of an average fuel

! cycle. The present cycle, however, has been extended to August 1987 while

the drywell test is required to be performed no later than April 25, 1987.

I Without a TS change, compliance would require a station outage in April 1987 to perform this test.

Deletion of Specification 4.6.2.2.b will allow an individual extension not

to exceed 25% of the surveillance interval but the combined interval for three consecutive intervals should not exceed 3.25 times the surveillance interval. Therefore, approval of the proposed TS change would allow the l River Bend Station to continue to operate until August 1987 which is the approximate schedule for the next refueling outage.

2.0 EVALUATION I

Specification 4.6.2.2 requires that the drywell be leak tested at periodic i intervals. This test is conducted to insure that the bypass flow area l

.! between the drywell and the containment airspace is always less than the '!

maximum allowable area the containment can accommodate without exceeding

the design pressure in the event of a LOCA. The acceptance criteria for the allowable tested bypass flow area is given in Specification 3.5.2.2.

This tested value is 10% of the maximum allowable area. As discussed in i FSAR Section 6.2.1.1.3.4, the design value of A/8 or'the allowable bypass area is given as 1.0 square feet.

1 The intent of the above surveillance requirements, as stated in the SRP i Section 6.2.1.1.C Appendix A, is to require'a leakage test during each refueling outage. The refueling outage was selected because it repre-sented a time period which occurs at regular time intervals throughout i

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the life of the plant and is of sufficient duration to accommodate'this complex test without requiring a unique plant shutdown. For the River Bend Station, this time interval was referred to in the TS as a maximum

• time interval of 18 months rather than each refueling outage.

Providing a certain degree of scheduling flexibility by referring to the time interval as each refueling outage was deemed appropriate'for two reasons. First of all, the major penetrations, where leakage is most likely to occur, are surveilled and/or leak tested at least every 31 1 days. Therefore, all significant suppression pool bypass pathways are verified to be in the correct configurations on at least a monthly inter-val. ' Secondly, the drywell structure .is not expected to significantly 4 change between refueling outages. The philosophy of a flexible testing..

schedule is further supported by the results of the drywell leakage tests conducted at River Bend. The pre-operational test conducted in February 1985 showed that at the design pressure of 24 psig, the measured leakage was about 25% of the allowable limit. The next test occurred in October

1985, where.the test results showed a leakage area of about 14% of the

allowable limit of 0.1 square feet.

The proposed deletion of Specification 4.6.2.2.b is consistent with the abovestated.staffobjectives. Deletion of this specification would allow Specification 4.0.2 to be applicable for the determination of the drywell leakage test interval. The provisions of Specification 4.0.2 allow the licensee to extend the test interval from the nominal 18 months to as much as 22.5 months as long as the combined interval for three .

consecutive intervals does not exceed 3.25 times the surveillance interval.

This flexibility has been shown to be needed for continued operation until the next scheduled refueling outage. Therefore, the proposed change would reduce the unnecessarily restrictive requirement currently contained

! within the TS.

3.0 CONCLUSION

i Based on the reasons provided above, the staff concludes that the proposed

! TS change is acceptable.

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