ML20114B586
| ML20114B586 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 08/19/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20114B585 | List: |
| References | |
| NUDOCS 9208280401 | |
| Download: ML20114B586 (4) | |
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FAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS.169 AND 173 TO FACILITY OPERATING LICENSE N05. OPR-44 and DPR-56 PHILADELPHIA ELECTRIC COMPANY PUBLIC SERVICE ELECTRIC AND GAS COMPANY DELMARVA POWER AND LIGHT COMPANY ATLANTIC CITY ELECTRIC COMPANY PEACH BOTTOM ATOMIC POWER STATION. UNIT NOS. 2 AND 3 DOCKET N05. 50-277 AND 50-278
1.0 INTRODUCTION
By letter dated May 18, 1992, as supplemented by letter dated July 9, 1992, Philadelphia Electric Company, Public Service Electric and Gas Company, Delmarva Power and Light Company and Atlantic City Electric Company (the i ncensees) submitted a request for changes to the Peach Bottom Atomic Power Station (PBAPS), Unit Nos. 2 and 3, Technical Specifications (TS).
The requested change would modify the surveillance requirements for the Main Steam Safety Valves and Relief Valves in Section 4.6.D.1 and 4.6.D.2 of the TS.
Specifically, the requested change would modify the frequency at which the main steam safety and relief valves are checked or replaced with bench checked valves and the frequency at which one cf the relief valves is disassembled and inspected from once-per-refueling cycle to once every 24 months.
The proposed changes are part of an effort to modify the-Peach Bottom TS to accommodate a 24-month fuel cycle.
Guidance on TS changes to support a 24-month fuel cycle was provided in NRC Generic Letter 91-04, dated April 2, 1991.
The letter dated July 9,1992, did not change the substance of the original request and did not change the initial proposed no significant hazards consideration determination.
Background
As part of a program to accommodate a 24-month fuel cycle, the licensee has proposed to modify the TS that specify that one main steam safety valve and five main steam relief valves be checked or replaced with bench checked valves once-per-operating cycle.
In addition, the licensee has proposed to change the TS that specify that at least one relief valve be disassembled and inspected each refueling outage.
The licensee proposes to change the frequency for these activities to once every 24 months.
The licensee's basis for extending thS surveillance interval to 24 months is that the Safety and Relief valves installed at Peach Bottom do not experience a time based failure mechanism that would preclude such an extension.
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Section 4.4.2 of the PBAPS Updated Final Safety Analysis Report (UFSAR) describes the design bases of the nuclear system pressure relief system.
The safety and relief valves prevent overpressurization of the nuclear system thus j
preventing failure of the nuclear system process barrier. ASME Boiler and i
Pressure Vessel Code, Section 111, requires that a vessel be protected from j
pressure in excess of design pressure. The Code allowable peak pressure is j
110% of vessel design pressure.
The Code further requires that the lowest safety valve setpoint be at or below design pressure and that the highest safety valve setpoint be below 105% of design pressure.
Section 4.4.6 of the i
UFSAR describes the pressure relieving capacity analysis of the installed safety and relief valves for Peach Bottom.
The analysis concludes that for a l
Fiain Steam Isolation Valve closing event followed by an indirect reactor scram on high neutron flux, the reactor vessel bottom pressure will reach 1260 psig assuming all of the safety and relief valves are operable and actuating at +1%
of their nominal setpoints. The peak pressure of 1260 psig represents a 115 psig uargin to the Code limit of 110% of design pressure (1375 psig).
Design pressure for the nuclear system is 1250 psig.
The safety / relief valves (SRV) (eleven per unit) installed at Peach Bottom are three-stage pilot-actuated valves manuf actured by the Target Rock Company.
In i
the pressure relief or safety mode, the valves operate by steam overpressure causing a pilot valve to actuate which allows steam to actuate a second stage valve which, in turn, allows system pressure to open the main valve disc.
The relief valves can also be operated remotely from the control room by application of pneumatic pressure to a mechanical push rod which actuates the second stage disc.
The safety valves at Peach Bottom (two per unit) are spring safety valves.
l The valve actuates when the force on the disc from system pressure exceeds the
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opposing spring force.
2.0 EVALUATION l
Information submitted in the July 9, 1992 supplement indicated that since 1987, the licensee has experienced ten safety / relief valve tests where the as t
found lift setpoint was outside of the 1% deviation allowed by the Technical Specifications.
Similarly, the licensee experienced two safety valve tests where the as found lift setpoints exceeded the 1% TS allowed deviation.
l The licensee submitted an analysis that described the significance of these failures.
The licensee used the worst case as-found conditions as the basis of their analysis. Of the 11 safety / relief valves tested during the Unit 3, i
1989 outage, 3 SRVs had setpoints that were out of tolerance high (from 2.0 to 4.5% high). Of the remaining eight SRVs, five had setpoints that were within tolerance and three were either not testable or had missing test data.
The two safety valves tested during the same Unit 3,1989 refueling outage had as-found setpoints that were out of tolemnce low (from 2.1 to 4.6% low).
The licensee concluded that sufficient margin to 110% design pressure existed in the UFSAR analysis to accommodate the observed out-of-tolerance setpoints.
Additionally, the licensee described the results of a recent overpressure
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analysis that evaluated increased delay time during safety / relief valve actuation.
The licensee's results showed that for an increase in delay time from 0.4 to 0.6 seconds, which the licensee correlated to a 2-3% setpoint j
increase, peak pressure increased by 19 psig for the MSIV closure with high neutron flux scram event.
This revised peak pressure was still well below the 1375 psig maximum allowable pressure.
1 An April 1992 study by the NRC staff, "AE00/S92-02, Safety and Safety / Relief j
Valve Reliability," indicated that three stage safety / relief valves have not j
experienced the significant number of problems that two-stage pilot-operated l
valves have experienced.
The study was based on a review of Licensee Event Reports and industry data.
No time based setpoint drift mechanisms have been j
identified for the three-stage pilot-operated valves.
Thus the number or magnitude of observed setpoint drift events would not be expected to increase significantly by extending the surveillance interval to 24 months.
j Based on the licensee's analysis which demonstrated that the setpoint drifts observed for Peach Bottom's safety and safety / relief valves did not have a 3
significant impact _ on the ability of the nuclear system pressure relief system to maintain reactor coolant pressure boundary integrity and on the fact that i
three-stage pilot-operated safety relief valves and spring safety valves have not experienced a significant time based setpoint drift mechanism, the staff finds the licenses's proposal to extend the surveillance interval on safety and safety / relief valves to 24 months acceptable.
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3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Pennsylvania State l
official was notified of the proposed issuance of the amendments.
The State l
official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
l The amendments change surveillance requirements.
The NRC staff has determined j
that the amendments involve no significant increase in the amounts, ano no significant change in the types, of an.y effluents that may be released offsite, and that there is no significant increase-in individual or cumulative occupational radiation exposure.
The Commission has previcusly issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (57 FR 28205). Accordingly, the 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 the-amendments.
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5.0 CONCLUSION
i The Commission has concluded, based on the considerations discussed above, i
that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation 4 the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common l
defense and security or to the health and safety of the public.
Principal Contributor:
J. Shea s
Date: August 19, 1992 i
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