ML20114D967
| ML20114D967 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/03/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20114D966 | List: |
| References | |
| NUDOCS 9209100230 | |
| Download: ML20114D967 (4) | |
Text
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o UNITED STATES 8"
NUCLEAR REGULATORY COMMISSION g
E WASHit.GTON. D. C. 20555 3
SAFETY EVALUATION BY THE OFFICE OF NVCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.15 TO FACILITY OPERATINC LICENSE NO. NPF-86 NORTH ATLANTIC ENERGY SERVICE CORPORATION SEABROOK STATION. UNIT NO. 1 DOCKET NO. 50-443
1.0 INTRODUCTION
By letter dated May 5, 1992, the Public Service Company of New Hampshire (former licensee) submitted a request for changes to the Seabrook Station Technical Specifications (TSs).
Public Service Company of New Hampshire has transferred management authority for Seabrook Station to North Atlantic Energy Service Corporation (current licensee).
The proposed change would allow relaxation of the Pressurizer Safety Valve (PSV? and the Main Steam Safety Valve (MSSV) setpoint tolerance from 11% to 13%.
The licensee proposes to use the 13% tolerance for the "as-found" acceptance criteria for additional valve testing required by ASME Section X", Article IWV-3513.
The proposed TS changes require that the PSV and M.,SV setpoints be restored to within 11% of their nominal setpoints following testing.
The licensee also proposes to revise the Bases for TS 3/4.7.1.1 to specify the correct Edition of the ASME Boiler and Pressure Vessel Code,Section III applicable to the MSSVs. The proposed relaxation of the PSV and MSSV setpoint tolerances complies with the 1989 Edition of the ASME Code,Section XI and has been evaluated by Yankee Atomic Electric Company (YAEC) (YAEC-1847, "Seabrook Station Code Safety Valve Setpoint Tolerance Relaxation," February 28,1992).
2.0 EVALUATION The Seabrook Station overpressure protection design incorporates three Code safety valves on the primary system pressurizer and a total of 20 Code safety valves on the four main steam lines (five per line)'in the secondary system.
The pressurizer safety valves (PSVs) were designed and manufactured to meet the 1971 Edition, including the Winter 1972 Addenda, of the ASME Code,Section III. The main steam safety valves (HSSVs) were designed and manufactured to meet the 1974 Edition, including the Summer 1975 Addenda, of the ASME Code,Section III. An ASME Code,Section III requirement for both the PSVs and MSSVs is that they be designed to open within 11% of the set pressure.
The current TS Limiting Condition for Operation (LCO) for the PSVs and MSSVs also imposes the tolerance cf 11% on their set pressure.
Currently the TS Surveillance Requirements for the PSVs and the MSSVs requires that testing be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda, as required by 10 CFR 50.55a(g).
i The surveillance requirements indicate that the MSSVs and PSVs should be tested to verify that their lift pressure and seat leakages are acceptable pursuant to the Seabrook Inservice Test (IST) program which complies with the 9209100230 920903 DR ALOCK 0500 3
ASME Boiler and Pressure Vessel Code,Section XI,1983 Edition, through the Summer 1983 Addenda.
This document <4es not indicate the tolerance to be 3
applied to the safety valve lift pressure verification.
The licensee therefore uses the 11% indicated in the LCO as the acceptance criteria for the PSVs and MSSVs during ASME Section XI testing.
Under the current testing requirements, when a PSV or MSSV has a tested lift pressure outside the 11%
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tolerance specified in the LCO, it must be repaired or replaced and additional valves in the system must be tested.
l The 1989 Edition of the ASME Code,Section XI, now requires that the PSVs and i
MSSVs be tested pursuant to the ASME/ ANSI OM-1987, Part 1, " Requirements for Inservice Performance Testing of Nuclear Power Plant Pressure Relief Devices."
This allows the tested lift pressure to exceed the stamped set pressure by up to 3% before declaring a test failure.
It also includes guidelines for testing additional valves when a valve exceeds the 13% tolerance.
Therefore, increasing the PSV and MSSV setpoint tolerance to 13% for testing acceptance criteria is in compliance with the later ASME Code,Section XI requ1rements.
The licensee proposes to use the 3% tolerance for the "as-found" acceptance criteria for additional valve testing required by ASME Section XI Subsection IWV-3513.
The proposed TS revisions require that PSV and MSSV Setpoints be restored to within 11% of their nominal setpoints following testing.
The 1989 Edition of the ASME Code Section III, Subarticle NB-7410/NC-7410 states that "The set pressure of at least one of the pressure relief devices connected to the system not be greater than the Design Pressure of any component within the pressure retaining boundary of the protected system".
The Reactor Coolant System design pressure is 2485 psig, which corresponds to the setpoint of the PSVs.
The Main Steam Supply System design pressure is 1185 psig, which corresponds to the Group 1 MSSVs which have the lowest opening setpoint.
Therefore, the proposed-relaxation of the setpoint tolerances for the PSVs and the MSSVs has been determined to be in compliance with this edition of the Code.
The licensee evaluated each of the transients considared in the Updated Final Safety Analysis Report (UFSAR) to determine the effects of increased safety valve setpoint tolerance.
The UFSAR Departure from Nucleate Boiling Ratio (DNBR) evaluations take credit for operation of the pressurizer PORVs, which have a setpoint pressure of 2400 psia.
Since this is lower than the proposed lower limit of 2425 psia on PSV setpoint, revising the sa S ty valve setpoint tolerance d6es not affect DNBR.
Increasing pressure yields less limiting values of DNBR. Therefore, all further evaluations address peak pressure response.
A margin of 24 psi remains between the Atmospheric Steam Dump Valve (ASDV) setpoints and the relaxed Group 1 MSSV setpoints.
The Group 1 MSSVs, which have the lowest opening setpoint, have a proposed lower limit setpoint (-3%
4 tolerance) of 1164 psia.
This is sufficiently above the ASDV opening setpoint of 1140 psia to prevent unnecessary challenges to the MSSVs.
The licensee also concluded that the proposed lower limit of the PSV setpoint, 2425 psia, will not affect the automatic reactor trip on high pressurizer pressure which occurs at 2400 psia.
2.1 Turbine Trio A detailed analysis was performed for the most limiting pressurization transient, the turbine trip. This event was simulated using the RETRAN01 MOD 5 computer code.
Comparisons were performed with the licensing basis analysis of record to demonstrate that the RETRAN model provides comparable results.
The limiting peak pressure case with minimum reactivity feedback and without pressure control was simulated using RETRAN.
The RETRAN results slightly overpredicted the peak pressure compared to the UFSAR.
Evaluations with revised setpoints were then performed with the RETRAN model to demonstrate ttat the peak pressure remains well below the Condition II limit of 110% of design pressure, or 2750 psia for the primary system and 1320 psia f r the secondary system.
2.2 LOCA Analysis The postulated large break loss of coolant accident (LBLOCA) events in the Seabrook UFSAR do not challenge the MSSVs beccuse the primary system pressure draws down the secondary pressure almost immediately after initiation.
The postulated small breap),LOCA (SBLOCA) events, however, by virtue of their break sizes (less than 1 ft can challenge the MSSVs because the secondary side plays the role of the heet sink early in the transient.
Since the PSVs are not challsnged in a LOCA transient, the proposed PSV setpoint tolerance relaxation does not affect LOCA analyses. Therefore, the LOCA review will only include the effects of SBLOCA on the MSSVs.
The UFSAR SBLOCA defines the limiting event as a cold leg pipe rupture of an equivalent 4-inch diameter at the ECCS injection location.
The UFSAR evaluation of the limiting SBLOCA event yields a Peak Cladding Temperature (PCT of 1790.0*F. The current SBLOCA PCT including margin allocation -is 1973)F.The licensee's evaluation of the Code safety valve setpoint tolerance relaxation specifies an increase in the limiting SBLOCA PCT of about 2.5*F.
The licensee recommends a conservative PCT penalty of 5'F be applied to the SBLOCA PCT results and be tracked in accordance with 10 CFR 50.46 reporting requirements.
Since this increase in PCT is less than 50 F, it is not considered a significant change as defined by 10 CFR 50.46. The revised SBLOCA PCT value of 1978.2'F remains below the 2200'F limit.
Pending approval of this license amendment, the licensee has comitted to report the SBLOCA PCT increase in its annual 10 CFR 50.46 report.
3.0 STATE CONSULTATION
in accordance with the Commission's regulations and past practice, the New Hampshire and Massachusetts State officials were notified of the proposed issuance of the amendment.
The State officials had no comments.
4.0 INVIRONMENTAL 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 and changes surveillance requirements.
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 (57 FR 24677). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR Sl.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.
5.0 CONCLUSION
The staff has reviewed the licensee's evaluation on the impacts of the proposed TS changes, TS 3/4.4.2 and TS Table 3.7-2, to allow a relaxation in the PSV and MSSV setpoint tolerances to i 3% for testing acceptance criteria.
The evaluation concluded that (1) there will be no reduction in the calculated minimum DNBR, (2) overpressurization events do not exceed the safety limits, and (3).the acceptance criteria for ECCS performance were not exceeded for LOCA events.
The staff finds the evaluation and conclusions acceptable.
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that 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:
S. Brewer Date: September 3, 1992 i
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