ML20034E531
| ML20034E531 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 02/23/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20034E529 | List: |
| References | |
| NUDOCS 9302260294 | |
| Download: ML20034E531 (3) | |
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UNITED STATES
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g NUCLEAR REGULATORY COMMISSION 7;
p WASHINGTON,0. C. 20555 t
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f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.137 TO FACILITY OPERATING LICENSE NO. DPR-36 MAINE YANKEE ATOMIC POWER COMPANY b
i KalNE YANKEE ATOMIC POWER STATION DOCKET NO. 50-309 l
1.0 INTRODUCTION
i By letter dated December 15, 1992, Maine Yankee Atomic Power Company (the j
licensee) submitted a request for changes to the Maine Yankee Atomic Power Station Technical Specifications (TS). The requested changes would:
- 1) Revise TS 4.6.A.2.f Acceptance Criteria by rewording and incorporating t
Condition 1; 2) Delete TS 4.6.A.2.f Acceptance Criteria Conditions 2 and 3; 3) i Reword and incorporate TS 4.6.A.2.f Acceptance Criteria Condition 4 into the Remedial Action for TS 3.19. A.4; 4) Revise the Basis of TS 3.19.A.4 and 4.6 to delete reference to the previous operating position of low pressure safety injection motor operated valves LSI-M-II,. 21, and 31, and their use as t
pressure isoiation barriers; 5) Delete the Exception to TS 4.6.A.I.b; and
- 6) correct a typographical error on Page 4.6-3.
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2.0 BACKGROUND
Maine Yankee's low pressure safety injection (LPSI) system is designed to deliver borated water to the reactor vessel to flood and cool the core upon depressurization of the reactor coolant system (RCS). The LPSI system consists of two high flow pumps, and piping and valves arranged in three separate injection flow paths to each of the three cold legs of the RCS.
Because the RCS operates at high pressure, and the LPSI system is designed as a low pressure injection system, some method is needed to separate these two i
systems and prevent possible overpressurization and damage to the LPSI system.
I Until 1981, there were three barriers between each RCS loop and the corresponding LPSI flow path; a thermal barrier check valve, a pressure isolation check valve, and a motor-operated pressure isolation valve. The motor-operated pressure isolation valve (LSI-M-11, 21, and 31) in each loop remained closed during power operation.
in 1981, Maine Yankee installed an additional pressure isolation check valve in each LPSI injection flow path and revised their Technical Specifications to include requirements for leak testing the pressure isolation barriers during each refueling outage. These modifications were in response to " Event v" 9302260294 930223 PDR ADOCK 05000309 P.
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. (intersystem loss-of-coolant accidents caused by overpressurization) concerns raised in a USNRC letter to all power reactor licensees dated February 23, 1980. Upon completion of these modifications, it was no longer necessary to keep the motor-operated pressure isolation valves closed to provide adequate pressure isolation.
3.0 EVALUATION As presented in the Maine Yankee Final Safety Analysis Report (FSAR), accident analyses involving activation of emergency core cooling systems (ECCS) require eleven separate valves to change position to admit coolant injection flow into the RCS. The proposed amendment would align each LPSI system loop motor operated injection valve (LSI-M-ll, 21, and 31) in the normally open position.
Such positioning will eliminate the chance that a single active failure would degrade the ECCS function, and thus will improve the overall probability of proper ECCS function on demand.
(For example, valves LSI-M-11, 21, and 31 require an eight-foot extension shaft between each valve and its associated motor operator.)
The proposed amendment retains the most conservative leakage limits of TS 4.6.a.2.f (Acceptance Criteria Condition 1) to demonstrate that the leakage barriers are intact.
Acceptance Criteria Condition 4 is reworded for clarity and moved to become the Remedial Action for TS 3.19, Safety Injection System.
(Remedial Action would be required should any barrier not meet the leakage limits of TS 4.6.A.2.f)
Acceptance Criteria Conditions 2 and 3 are deleted because they are less conservative than the requirements of the amendment.
The Exception to TS 4.6.A.I.b is deleted because it was based on valves LSI-M-ll, 21, and 31 being normally closed, and because it referenced Acceptance Criteria Conditions 2 and 3.
The safety class boundary between the RCS and LPSI systems is not affected by the proposed change.
American National Standards Institute (ANSI) Standards N18.2-1973 and N18.2a-1975 (review and addendum), and ANSI /ANS (American Nuclear Society) Standard 51.1, 1983 and reaffirmed in 1988, " Nuclear Safety Criteria for the Design of Stationery Pressurized Water Reactor Plants",
require two, in-line check valves between systems, and periodic leak testing of the valves. Maine Yankee satisfies the boundary standards by providing three, in-series check valves grouped into two separate isolation barriers.
Isolation barrier (a) is comprised of the two check valves closest to the RCS; isolation barrier (b) is formed by the check valve closest to the LPSI system.
Both isolation barriers in each LPSI loop are leak tested each refueling outage.
The leak test history of the pressure isolation barrier (a) and (b) check valves provides a basis for discontinuing the use of LPSI motor operated valves LSI-M-ll, 21, and 31 as backup pressure isolation barriers. The set of leakage test data collected since 1982 shows that neither barrier (a) nor barrier (b) has approached its allowed leakage rate. This leakage test data set shows that these barriers provide adequate overpressure protection for the LPSI system.
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. Isolation of the containment is not affected by changing the alignment of LPSI valves LSI-M-II, 21, and 31. The isolation requirements found in Appendix A to 10 CFR Part 50 (General Design Criteria 55 and 56) remain satisfied by the continuous, positive pressure water seal formed by the LPSI system at each containment penetration.
In the event of an accident, these lines will remain water-filled and pressurized to greater than peak containment pressure for an extended period of time.
As a result of its review, the staff concludes that this amendment may be granted. The proposed action improves the overall probability of proper'ECCS function on demand that accrues with the LPSI injection valves normally open, and eliminates less conservative leakage limits for the LPSI pressure isolation barriers.
In addition, these barriers have a history of satisfactory leakage test data, and the containment isolation requirements of 10 CFR Part 50, Appendix A, (General Design Criteria 55 and 56) remain satisfied for each LPSI penetration.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Maine State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area.as defined in 10 CFR Part 20.
The NRC 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 the amendment involves no significant hazards consideration, and there'has been no public comment on such finding (58 FR 5433). Accordingly, the 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 the amendment.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance th'at the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
E. Trottier Date: February 23, 1993