ML20140E769
| ML20140E769 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/02/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20140E745 | List: |
| References | |
| NUDOCS 9706120198 | |
| Download: ML20140E769 (4) | |
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UNITED STATES l,-
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't WASHINGTON, D.C. 20565 0001 l
SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0. 136 TO FACILITY OPERATING LICENSE NO. NPF-10 AND AMENDMENT NO. 128 TO FACILITY OPERATING LICENSE NO. NPF-15 SOUTHERN CALIFORNIA EDIS0N COMPANY SAN DIEGO GAS AND ELECTRIC COMPANY TBE CITY OF RIVERSIDE. CALIFORNIA THE CITY OF ANAHEIM. CALIFORNIA SAN ON0FRE NUCLEAR GENERATING STATION. UNITS 2 AND 3 DOCKET NOS. 50-361 AND 50-362
1.0 INTRODUCTION
By application dated April 15, 1997, Southern California Edison Company (SCE or the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License Nos. NPF-10 and NPF-15) for San Onofre Nuclear Generating Station, Unit Nos. 2 and 3.
The proposed changes would revise Surveillance Requirement (SR) 3.8.1.8 to Technical Specification (TS) 3.8.1, "AC Sources - Operating." This change will allow the licensee to credit overlap testing to validate the capability of the alternate offsite power source.
2.0 BACKGROUND
The engineered safety features (ESF) buses are normally supplied from the offsite source. through the reserve auxiliary transformer (RAT) of its associated unit.
The credited alternate offsite source per Limiting Condition for Operation (LCO) 3.8.1 at any given time is dependent upon the ESF bus alignment in the companion unit. This source may be from either the companion unit's RAT or unit auxiliary transformer (UAT) via the unit 4.16 kV train-aligned cross-tie.
At present, SR 3.8.1.8 states in part, " Verify automatic and manual transfer of AC power sources from the normal offsite circuit to each alternate required offsite circuit." To meet this statement, the licensee periodically tests the l
capability of the offsite power source of one unit, normally in Modes 1 to 4, to provide power to the ESF buses of the other unit while it is in Mode 5 or 6 1
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l (typically during refueling outages).
By performing the transfer test of AC power to the ESF bus while the associated unit is in Modes 5 or 6, the challenges to the safety buses are minimized.
However, the offsite power source for the operating unit is the RAT for that unit, and the complete transfer test is performed with the RAT as the alternate offsite power source, l
not the UAT.
In order for the UAT to be credited as the alternate offsite l
power source and meet the current version of SR 3.8.1.8, either both units need to be in Modes 5 or 6 during the transfer test with the UAT as the alternate offsite power source, or the transfer test will unnecessarily challenge the operating unit's ESF buses.
The unnecessary challenge results from the need to strip the loads from the operating unit's ESF buses during the transfer test and verify that these buses are successfully loaded by the shutdown unit's VAT.
To avoid shutting down both units or adversely affecting the ESF buses on the operating unit in order to use the UAT as the alternate offsite power source, the licensee has proposed to revise SR 3.8.1.8 to state, " Testing to satisfy this SR shall include actual automatic and manual transfer to at least one alternate offsite circuit.
The other alternate offsite circuit may be verified by overlapping circuit tests." This will permit the companion Unit's UAT to be credited as the alternate offsite power source for the other unit, without either performing an actual transfer of the safety related buses or declaring the alternate offsite power source inoperable for the other unit.
This will allow the licensee to perform maintenance activities of the RAT dur rg its unit's refueling outage in excess of the allowed outage times specified in TS 3.8.1.
In a letter dated April 29, 1997, the staff requested further information on this issue, and the licensee provided its response in a letter dated May 5, 1997.
3,0 EVALUATION The staff evaluated the ability of the companion unit's UAT to adequately perform as the alternate offsite power source for the other unit, and also evaluated the adequacy of the licensee's proposal to credit overlapping circuit tests in lieu of performance of an actual transfer test for the second alternate offsite source (the UAT).
In its May 5,1997, response to the staff questions, the licensee stated that the UAT is capable of supporting the loss-of-coolant accident loads of one unit and the safe shutdown loads of the other unit. The licensee further stated that adequate voltage at safety-related load terminals is ensured by the degraded voltage protection scheme when the ESF buses are aligned to the UAT of the opposite unit. The licensee considers the UAT of the shutdown unit as a delayed-access preferred power source for the ESF buses of the operating unit; hence, the UAT is not credited as a power supply to the ESF buses of the operating unit under safety-injection-actuation-signal / loss-of-voltage-
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l i l signal condition: in the operating unit. The frequency at the load terminals is the same as the offsite power system frequency (60 Hz nominal).
Additionally, adequate protection for bus incoming breakers from the UAT and the RAT and the bus tie breakers is provided.
Protective relays and relay settings for bus tie breakers are selected to coordinate with upstream bus incoming breakers and downstream load feeder breakers. Under a fault condition on the ESF bus of the companion unit, the tie breaker will isolate the faulted bus from the system. The licensee stated that the control power for operation of the required breakers when the UAT will be used as the second source of offsite power for the opposite unit is supplied from their respective de sources. Additionally, in order to declare the ac sources operable, the de control power to the associated breakers must be operable.
Based on the above considerations, the staff concludes that the UAT is capable of maintaining frecuency and voltage within their limits for the required loads under accident conditions, and is an acceptable alternate offsite power source.
In reviewing the licensee's proposal to credit overlapping circuit tests to satisfy LC0 3.8.1 when using the UAT as the alternate offsite power source, the staff evaluated the adequacy of the overlap test to substitute for an actual transfer test. The proposed surveillance would include a complete functional test of the two alternate offsite sources by performing the following activities:
1)
Verification of the cross-tie connection to the ESF bus of the companion unit (with the ESF bus aligned to the RAT).
This functional test verifies that the cross-tie is available and that a manual and an automatic transfer to one alternate source is possible.
2)
To complete the surveillance, performance of a test on that portion of the circuit that permits the cross-tie breaker of the companion unit to close with the ESF bus aligned to the UAT.
The functional test detailed in Item I will adequately test the portion of the circuit that is common to both the RAT and the VAT. Testing the portion of the circuit that is unique to the UAT configuration adequately demonstrates that the UAT will perform its intended function as the alternate offsite power source. Therefore, the staff finds acceptable the licensee's proposal to credit overlapping tests to demonstrate the acceptability of the UAT as the alternate offsite power source.
4.0 EXIGENT CIRCUMSTANCES
Pursuant to 10 CFR 50.91(a)(6), the licensee requested the proposed amendment on an exigent basis. The proposed changes would revise the Technical Specifications to allow the RATS to be removed from service in order to perform maintenance during refueling outages, and allow the UATs to be l
credited as the alternate source of offsite power. The licensee requested
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. approval on an exigent basis based on the refueling outage schedule for SONGS Unit 3 that began on April 12, 1997.
Subsequent to-the request for an exigent review by the staff, the licensee has determined that issuance of the this TS amendment after the 30 day notice has expired in the Federal Reaister will not adversely impact the refueling schedule for SONGS Unit 3, and therefore has withdrawn the exigent aspect of its license amendment request.
Notice of the staff's proposed determination that this proposed amendment involves no significant hazards consideration was published in the Federal Reaister on May 1, 1997 (62 FR 23811). Given that this notice has provided 30 days notice as required by 10 CFR 50.91(a)(2), there is no need for the Comission to make a final determination that the proposed amendment does not involve a significant hazards consideration.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the amendment.
The State official had no comments.
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6.0 ENVIRONMENTAL CONSIDERATION
i The amendment 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 (62 FR 23811). 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.
7.0 CONCLUSION
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: Amar Pal, EELB/NRR Date:
June 2, 1997 i
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