ML13316B475
| ML13316B475 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/14/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13316B472 | List: |
| References | |
| NUDOCS 9008230239 | |
| Download: ML13316B475 (5) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.134TO PROVISIONAL OPERATING LICENSE NO. DPR-13 SOUTHERN CALIFORNIA EDISON COMPANY SAN DIEGO GAS AND ELECTRIC COMPANY SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO. 1 DOCKET NO. 50-206
1.0 INTRODUCTION
By letters dated April 19 and June 18, 1990, Southern California Edison Company (SCE or the licensee) requested a change to the Technical Specifi cations appended to Provisional Operating License No. DPR-13 for operation of San Onofre Nuclear Generating Station, Unit No. 1, located in San Diego County, California.
During the current Cycle 11 refueling outage, the licensee is modifying the existing 480 volt a.c. electrical system. The modifications will reconfigure the 480 volt a.c. system from three electrical buses and three station service transformers (SSTs) to four electrical buses and four SSTs. This.modification will provide for two electrical buses and two SSTs per train. Previously, the 480 volt a.c. electrical distribution system consisted of one electrical bus and one SST for each train, with a third electrical bus and SST provided as an alternate source which could be aligned to either Train A or Train B via a manual transfer switch.
In order to accommodate the modifications being made to the 480 volt a.c.
electrical distribution system, the licensee has proposed changes to the applicable sections of the Technical Specifications. The system modifi cations and proposed Technical Specification changes are described in detail by Amendment Application No. 180 applicable to San Onofre Unit 1 dated April 19, 1990, as supplemented by SCE letter dated June 18, 1990.
The June 18, 1990 submittal provided a revision to Amendment Application No. 180, reassigning the breaker number for a manual load transfer switch (MTS-8) and providing clarification of fire protection requirements for SST3. The revision was clarifying and editorial in nature and does not alter the action or affect the initial determination hoticed in the Federal Register on May 30, 1990.
9008230239 900150 PDR ADOC-:K 0F-5000206 P
-2 2.0 DISCUSSION In an event notification dated January 30, 1989, the licensee advised the NRC that while evaluating the electrical system and calculating voltage transients, it was determined that the loading on 480V Buses No. 1 and No. 2 main breakers 1102 and 1202, respectively, and 480V Transformers SST1 and SST2, could exceed the design rating assuming the worst case combination of loading (safety injection without loss of power). SCE submitted the details of the potential overload conditions in a letter dated March 17, 1989, which was reviewed by the NRC staff. Based on these SCE submittals, the NRC issued an SER dated April 27, 1989, accepting interim corrective measures and requiring permanent resolution prior to Cycle 11 operation.
In a letter dated April 19, 1990, SCE submitted its long-term solution for the postulated electrical overload conditions, which is to modify the 480 volt a.c. system. Modification of the 480V system will consist of providing two electrical buses per 480V train rather than the existing one bus per 480V train. This will be accomplished during the Cycle 11 outage while in Modes 5 and 6 as follows:
- 1. A new station service transformer (SST3) will be installed. The Train A loads will be divided between SST1 and SST3. A new 480V bus will be formed and will be designated as Bus No. 3. This arrangement will eliminate the potential of overloading SST1 and the 480V Bus 1 main feeder cables and main breaker.
- 2. The existing transformer SST3 will be fed from 4160V Bus 2C and be redesignated as SST4. SST4 will feed a newly designated 480V Bus 4 which will be formed from the existing 480V Bus 3 and a section of Bus 2. This arrangement will eliminate the potential for overloading SST2 and 480V Bus 2 main feeder cables and main breaker.
- 3. Consistent with the new electrical line-up, MCC-1B, 1C, 2B, 3 and 3A will be redesignated as MCC-3B, 3, 4B, 4 and 4A respectively.
- 4. Control room modifications on the main control board and on the diesel generator panels will be carried out to reflect the above changes.
- 5. Nonessential loads on the new 480V Bus 4 will be tripped on a safety injection signal/safety injection signal with loss of power (SIS/SISLOP). The loads have been redistributed in such a manner that all breakers are within their rating under worst case accident conditions.
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- 6. -Normally open tie breaker 1103 will be located on Train A between 480V Bus 1 and new 480V bus 3. The tie breaker can only be closed if one or both source breakers (1102 and 1302) on Train A are open. Similarly, on Train B a tie breaker (1203) between Buses 2 and 4 will be used. Electrical interlocks will be provided so the tie breaker can only be closed if an emergency source breaker (1200) is open and if one or both source breakers (1202 and 1402) are open. These interlocks are to prevent the two transformers from being operated in parallel.
- 7. MCC-4 is not qualified and not required to function during a MSLB. Therefore, a contact from the Train B sequencer will be added to trip the MCC-4 feeder breaker on a SIS/SISLOP. A control switch to reclose the MCC-4 feeder breaker during post LOCA conditions-will be added in the control room.
- 8. A manual load transfer switch (MTS-8) will be installed and will normally be supplied from MCC-4 on Train B. MTS-8 will supply power to existing MOV-883 and the uninterruptible power supply (UPS) for MOV-850C and MOV-358. MOV-883 is the discharge valve from the RWST and must remain open during the safety injection phase and close with initiation of recirculation. MOV-850C and MOV-358 are in the recirculation system. An alternate source from Train A will be available in case Train B power is lost. A SIS or SISLOP signal will trip the normal sources of power to the transfer switch by tripping MCC-4 thus complying with R.G.
1.75 requirements of tripping unqualified equipment during an accident.condition.
After the modifications are completed, the two trains will be as follows:
- 1. Train A 4160V Bus 1C will feed: (a) 480V Bus #1 via Station Service Transformer #1 (SST1) through breakers 11C10 and 1102, (b) 480V Bus #3 via Station Service Transformer #3 (SST3) through breakers IC1I and 1302.
- 2. Train B 4160V Bus 2C will feed: (a) 480V Bus #2 via Station Service Transformer #2 (SST2) through breakers 12C10 and 1202, (b) 480V Bus #4 via Station Service Transformer #4 (SST4) through breakers 12C11 and 1402.
3.0 EVALUATION The NRC staff reviewed the modifications discussed above and concur with the licensee that the modifications/additions will improve the 480 volt electrical distribution system at San Onofre Unit 1 and will eliminate the potential for overloading electrical system for the following reasons:
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- 1. The maximum loading on the main breakers is below 1400A. These breakers are rated 1600A.
- 2. The main feeder cable loading is below 1600A. The allowable ampacity is 1800A.
- 3. The station service transformer loading is below 1250kVA.
Transformers SST1, 2 and 4 are rated 1400kVA, and transformer 3 is rated 1500kVA.
The staff concluded that the breakers, cables and transformers have sufficient capacity for safe operation.
The staff has evaluated each section of the proposed Technical Specification changes. The numbering system used in the following evaluation has been keyed to the numbering system established by SCE.
The TS changes follow the content and format of TS Section 3.7 of the Westinghouse Standard Technical Specifications (STS). The proposed change will revise the minimum required OPERABLE AC systems to include 480V buses and associated transformers in Modes 1, 2, 3 and 4 and will establish STS LCOs and associated action statements. In addition, the change will require entry into the action statement whenever a tie breaker in either train is closed.
With the emergency diesel generator (EDG) inoperable, action statement 3.7.1.D was added to require verification that (1) all required systems, subsystems, trains, components and devices that depend on the remaining operable EDG as a source of emergency power are also operable and (2) the steam driven auxiliary feedwater pump is operable in Modes 1, 2 and 3.
This is acceptable.
When San Onofre Unit 1 is in Modes 5 and 6, TS 3.7.2, "SHUTDOWN," one service transformer and one main breaker will be adequate and sufficient to supply the needed power to the two associated 480V buses without exceeding the ratings of the equipment. Thus the proposed change will require one operable train consisting of two 480V buses and one transformer.
This change is acceptable.
For maintenance purposes, temporary cross connection between the two emergency AC trains is allowed only during outage conditions. This is done by the use of power cables provided between 480V Bus 4 and Bus 1 with two breakers in series to maintain adequate separation. This is acceptable.
The proposed change of TS 3.14, "Fire Protection," is an administrative change as its purpose is to identify the fire area/zone and hazards as well as the minimum fire protection instrumentation. This change reflects the new equipment additions and designations. This is acceptable.
-5 TS 4.1.1, "Operational Safety Items," relocates the surveillance require ments for manual transfer switch MTS-7 from this section of the Technical Specifications to Section 4.4. This is an administrative change and is acceptable.
In a letter dated June 18, 1990, SCE submitted an editorial revision to two pages of their Amendment Application No. 180 reassigning a breaker number and providing clarification of fire protection requirements for the new station service transformer (SST3). Specifically:
- a. Normal power supply breaker 8-1491 for MTS-8 was redesignated as 8-1480B. The breaker remained the same, but the number designation was changed to maintain a consistent numbering system.
- b. The new 1500 kVA SST3 transformer is of the outdoor, ventilated, and dry type design which does not require a fire protection system.
The staff considered this information to be editorial and clarifying in nature, and therefore acceptable.
Based on the evaluation discussed above, the NRC staff has concluded that the proposed revision to the San Onofre Unit 1 Technical Specificaions is acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment involves changes in 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
We have 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 this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: S. Saba J. Tatum Dated: August 14, 1990