ML20207N426

Safety Evaluation Supporting Amend 101 to License DPR-3

ML20207N426
Person / Time
Site:	Yankee Rowe
Issue date:	01/06/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20207N402	List: ML20207N400 ML20207N416 ML20207N426
References
NUDOCS 8701140206
Download: ML20207N426 (3)

Text

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1. • 'o g UNITED STATES I o NUCLEAR REGULATORY COMMISSION 8

,E WASHINGTON, D. C. 20665 l 1

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.101TO FACILITY OPERATING LICENSE N6. DPR-3 YANKEE ATOMIC ELECTRIC COMPANY YANKEE NUCLEAR POWER STATION DOCKET NO.50-029

1.0 INTRODUCTION

By letter dated October 22, 1986, the Yankee Atomic Electric Company (YAEC) submitted a request for changes to the Yankee Nuclear Power Station Technical Specifications (TS).

The amendment modifies the time period that valve CS-MOV-532 may be open from 30 minutes per week to 120 minutes (two hours) per week.

2.0 DISCUSSION On January 3, 1974, a new rule, 10 CFR 50.46, and Appendix K to 10 CFR Part 50, were promulgated, establishing acceptance criteria for emergency core cooling systems. In particular, these rules require that studies be performed to identify the most damaging single failure of ECCS equipment that could affect system performance.

The Yankee Emergency Core Cooling System (ECCS) contains three trains of pumps. Each train consists of one high pressure and one low pressure pump. All six pumps have orificed minimum recirculation lines, which connect to a common header to return the recirculation flow to the safety injection tank (SIT). The common recirculation line is isolated by series valves upon the initiation of recirculation from the containment sump.

In addition, a larger recirculation path (3" diameter) from the low pressure safety injection (LPSI) pump discharge back to the SIT is provided. This path is used for pump flow testing and for SIT mixing.

One valve, CS-MOV-532, provides isolation for this flow path. The valve is signaled to close on a safety injection actuation signal.

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During the single failure reviews, the possible failure of CS-M0V-532 in the open position was identified; such a failure would divert LPSI flow from the core and prevent successful operation of the LPSI system.

Therefore, the licensee de-energized this valve by disconnecting the power cables as they left the motor starter and maintained the valve in a closed position. However, as noted in the staff's December 4, 1975 safety evaluation, supporting Amendment 21 to the license, the valve was allowed to be re-energized and opened for approximately 30 minutes per week for safety injection tank mixing. Subsequently, the valve was modified by addition of dual contactors separating the valve operator motor from the motor control center. This design requires one failure in the control circuitry of the valve contactor, and a second failure in the control circuitry of the dual contactor before the valve would inadvertently open.

Thus, in order for the valve to be open when LPSI system function is required, either the valve must spuriously open (prevented by the dual contactor design), or the valve must be open at the time of the safety injeet..n actuation signal (SIAS), and fail to close on the SIAS.

Oper auon with valve CS-MOV-532 open is limited to minimize this possible failure mode.

However, since 1975, when the 30 minute time period was selected, the inservice testing requirements, such as vibration monitoring and temperature measurements, for the safety injection purrps have changed. These tests require data with the pump running at normal, stabilized operating conditions. In addition, pump start and flow tests are required monthly on a staggered test basis per TS 4.5.2; with 3 trains, the licensee tests one pump a week to meet this requirement. The pump must operate for at least 15 minutes with valve CS-MOV-532 open. Also, following any maintenance of the system, it is desirable to test the system, including a system flow test, prior to returning the system to service.

l The 30 minute time period has restricted such maintenance and testing l procedures. Therefore, the licensee has proposed to increase the time l period that the valve is allowed to be open from 30 minutes per week to 120 minutes per week.

3.0 EVALUATION r

To support this proposed change, the licensee provided an analysis of j the effect on LPSI system unavailability of this change.

I At present, the valve may be open for 30 minutes per week, or .3% of the plant operating time ~( .5 ) 1 Under the proposed change, the valve may be 168 J open 1.2% of the time. In order for the LPSI system function to be affected, the valve must then fail to close on demand. From the Yankee Probabilistic Safet valve is 1.25 x 10-y Study (PSS),

demand. Thisthis probability value for a motor-operated is consistent with that used in nts, such as WASH-1400, the Reactor otherprobabilisticriskassessmg/

Safety Study, which used 1 x 10- demand. Therefore, the f of_3he LPSI system d 5 ue to this failure mode is (1.2 x 10-2)ailure (1.25 x proba

! 10 or 1.5 x 10 1

I

The overall failure rate of the LPSI system from all causes as reported inghelicensee'sPSS,is3.48x10-3, including a contribution of 3.7 x 10~ from the 30 minute opening of the recirculation valve 532. The new failure rate of the LPSI with the proposed change to 120 minutes / week, would only be 3.49 x 10-3 Failure to close of CS-M0V-532 contributes less than 1% to the total system failure probability, even with the proposed change to 120 minutes per week.

Thus, the proposed change would only have a very small effect on LPSI system failure due to this one case and it would provide enhanced capability for LPSI pump testing and system maintenance. Therefore, the staff concludes that the proposed change is acceptable.

4.0 ENVIRONMENTAL CONSIDERATION

This amendment involves a change to a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves 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 .

Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this amendment meets 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 this amendment.

5.0 CONCLUSION

l The staff has concluded, based on the considerations discussed above, l that: (1) there is reasonable assurance that the health and safety of l the public will not be endangered by operation in the proposed manner, l and (2) such activities will be conducted in compliance with the Comission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety i

of the public.

l 6.0 ACKNOWLEDGEMENT Principal Contributor: E. McKenna Dated: January 6, 1987 l

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