ML13330B493
| ML13330B493 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/20/1989 |
| From: | Nandy F SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8903240072 | |
| Download: ML13330B493 (4) | |
Text
e-71 Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 F. R. NANDY TELEPHONE MANAGER OF NUCLEAR LICENSING March 20, 1989 (818) 302-1896 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Response to Miscellaneous Requests for Additional Information San Onofre Nuclear Generating Station Unit 1
References:
A. Letter, F. R. Nandy, SCE, to NRC, dated March 11, 1989 B. LER 1-88-019, dated January 12, 1989 C. Letter, Kenneth P. Baskin, SCE, to 3. B. Martin, NRC dated March 17, 1989 In discussions with members of the NRC staff, requests were made for the following:
- 1. A page change to the Reference A letter to correct a minor error;
- 2. Modified simplified drawing supplied with the Reference B LER; and
- 3. Reference the appropriate section in the Reference C letter to address the use of appropriate standards when considering transformer response associated with the issue of 480 V bus main breaker overloading.
Accordingly, Enclosure 1 is a revised page 23 to the Reference A letter.
Breaker number 152-llCll (line 2) has been corrected to read 152-12C11. A single change bar is provided for the entire page as it was in the previous submittal. A double change bar now appears where the correction has been made.
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Document Control Desk
-2 is a revised simplified drawing of that which was enclosed with the Reference 2 LER. The change consists of adding breaker 12C11 (from 4160V bus 2C to SST #3) to the drawing with a note to clarify its use. No other changes were made to the simplified drawing.
In response to the third request listed above, a discussion of the effect of the potential overload of the 480 V main breaker on the associated transformer is included on page 12 of the report enclosed with the Reference C letter.
Included on that page is a discussion of the overload condition and an indication of the applicable ANSI standard.
If you would like additional information, please let me know.
Very truly yours, cc: 3. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 An administrative control is being implemented to assure that 152-12C11 cannot be used in modes 1 through 4 unless switchgear 2C is declared inoperable. This prevents 480V Bus 3 from being aligned to 4160V Bus 2C through station service transformer number 3. The modifications and administrative controls described above will assure that 480V Bus No. 3/MCC-3 will be isolated.from the redundant trains of ECCS. The miscellaneous ECCS loads powered from 480V Bus No. 3/MCC-3 have been provided with a UPS backup or can be repowered via the operator.actions.
(See Item II, "Recirculation System" above and Sections V.A.2 and V.A.3 of ESF Single Failure Analysis, Revision 1, dated February 1989).
VII. Low Flow Scram
- 1) Current sensing relays will be provided for the reactor coolant pump (RCP) breakers.
Upon a high or low current condition, the relays would open the RCP breakers resulting in a reactor trip from the RCP breaker auxiliary contacts. This configuration provides protection for single loop RCP locked rotor/shaft break events above 50% power within the time frame asssumed in the accident analysis.
As discussed.earlier, SCE identified a single failure susceptibility with the low.flow reactor trip in Revision 0 of RPS single failure analysis. For backup to the low flow reactor trip, credit was taken for two diverse trip functions. The RCP breaker auxiliary contact scram was credited for the RCP shaft seizure event. The variable low pressure trip was credited for the RCP shaft break event.
Subsequently, SCE identified that the RCP breaker auxiliary contact scram would not occur within the time assumed in the analysis. The breaker control circuits have a delay provided to prevent breaker opening on high current during pump startup. Although the RCP locked rotor would result in high pump current almost immediately, the startup delay circuit would result in delaying reactor trip.
Additionally, as part of the Reload Safety Evaluation for Cycle X, Westinghouse discovered that a single variable low pressure setpoint would not provide protection over the entire operating range. At lower power levels, it was found that the variable low pressure setpoint would not be reached in the two unaffected loops.
0 TRAIN "A" TRAIN "B" 4160V BUS 1C 4160V BUS 2C I7 1l 1
c) c)
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S I S/ LOP Loc -our 12 111*
LOCK-OUT SR NSR SR NSR DG #1 DG #2 W
t SST #1 SST #3 The same breaker acts as SST #2 11011 and 12Cll.
Breaker 11011 must be physically LSS-relocated fr Swtchgear IC to Swttchgear 2C to serve as Breaker 12C11.
Nc 1303. uc I-.
4tOV SWITCHGEAR 1
480V SWITCHGEAR 3 480V SWITCHGEAR 2 Ft H-.
o0c.
110 1203N N
c) 0 0
SR SR NS SR N5R In B0 NOTE: LINT IL MID-1988, SLSS-2 SIS/LOP SIGNAL CLOSED BREAKER 1203 AFTER TRIPPING BREAKER 1303 ABBRE.V I AT IONS DG= DI ESEL GENERATOR SLSS= SAFEGUARD LOAD SEQUENC I NG SYSTEM NC= NORMALLY CLOSED SIS/LOP-SAFETY INJECTION SIGNAL/ LOSS-OF-POWER 0
NO= NORMALLY OPEN SR= SAFETY RELATED LOADS NSP= NON-SAFETY PELATED LOADS SST= STATION SERVICE TRANSFORMER 0
l 1t..