ML13330B408
| ML13330B408 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/18/1988 |
| From: | Medford M Southern California Edison Co |
| To: | NRC Office of Administration & Resources Management (ARM) |
| References | |
| RTR-REGGD-01.075, RTR-REGGD-1.075, TAC-67902 NUDOCS 8810240266 | |
| Download: ML13330B408 (4) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 M. 0. MEDFORD TELEPHONE MANAGER OF NUCLEAR ENGINEERING (818) 302-1749 AND LICENSING October 18, 1988 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Nuclear Instrumentation System Upgrade (TAC No. 67902)
San Onofre Nuclear Generating Station Unit 1
Reference:
Letter, Charles M. Trammell, NRC, to Kenneth P. Baskin, SCE, Nuclear Instrumentation System Upgrade, July 29, 1988 The referenced letter provided SCE with a request for additional information in order to continue the NRC's review of the subject upgrade. In accordance with that request the enclosed information is submitted.
If you have any questions, please let me know.
Very truly y-urs /
Enclosure cc: J. B. Martin, Regional Administrator, NRC R gion V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 8810 240266 881018 PDR ADOCK 05000206 P
PDIC
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON THE SONGS 1 NUCLEAR INSTRUMENTATION SYSTEM UPGRADE
- 1. Provide a description of the proposed design change (i.e., the upgrade replacement of the NIS) as it relates to the DC and AC electric power systems.
RESPONSE
The upgraded NIS receives four channels of independent AC power derived from existing Regulated Buses 1, 2, 3, and 4, consistent with the existing NIS.
Each regulated bus is separately fed from a vital bus source (Vital Buses 1, 2, 3, and 4), through a voltage regulator.
The 120V AC vital bus system is configured such that each vital bus can receive power from either of two redundant sources, via an automatic transfer switch. Normal power is supplied by a Train A source (125V DC Bus 1 thru an inverter), and alternate power is provided by a Train B source (MCC 2 thru a step-down transformer).
- 2. In support of the replacement upgrade of the Nuclear Instrumentation System (NIS), as indicated by letter dated April 15, 1988, the upgrade of the NIS will increase the DC system load. As a consequence of this increased load, the margin of safety for DC system capacity and capability will be reduced. The significant hazards consideration analysis (which states that the revision to the battery test acceptance criterion from 80 to 85 percent will ensure that an existing safety margin is maintained) does not adequately address reduced margin of safety for DC system capacity and capability due to increased load.
For each component part of the DC system (battery, charger, and distribution system components) that will be required to supply the increased load, provide the results of your analysis which demonstrates that the DC system can adequately accommodate the increased load.
RESPONSE
The additional NIS loads (net) on Regulated Bus #1 (RB #1) (8-11R3), RB #2 (8-12R3), RB #3 (8-13R3), and RB #4 (8-14R3) are 3.8, 3.9, 0.37 and 5.46 amps, respectively. To accommodate these additional loads, the existing 5-amp fuses on 8-11R3, 8-12R3 and 8-14R3 will be replaced as part of the scope of the NIS. The fuse on 8-13R3 is adequate for the additional loads; however, it is being replaced along with the other fuses.
The impact of these additional NIS loads on the rest of the Maintained 120V AC and 125V DC distribution system components, from the regulated buses up to and including the battery charger input breakers, was further evaluated for bus capacity, proper fuse/breaker sizing/coordination, component ratings, system voltages and short circuit capabilities. Each component has been found to be adequate to provide for the increased load requirements.
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- 3. The significant hazards consideration analysis states that the battery specification revision (i.e., acceptance criteria for battery capacity revised from 80 to 85 percent) provides assurance that the system is tested in a manner consistent with its recalculated duty cycle. It is not clear how replacing a battery when its capacity reaches 85 percent assures a battery is capable of meeting its duty cycle. Provide the results of an analysis to indicate the extent to which recommendations of IEEE Standard 485-1983 have been followed in assuring adequately sized batteries at San Onofre Unit 1.
RESPONSE
Each section of the revised load duty cycle profile resulting from the additional NIS loads was analyzed to determine the adequacy of the existing battery, using the guidelines of IEEE Standard 485. Based on the IEEE Standard 450 recommendation that a battery be replaced when its actual capacity ages to 80 percent of its rated capacity, IEEE Standard 485specifies that the rated capacity should be initially sized to at least 125 percent of the required load to ensure that the battery at 80 percent capacity will still be capable of meeting this load duty cycle requirement.
The minimum required capacity was calculated to determine if the battery can accommodate the revised load duty cycle criterion. The available ampere-hour corresponding to 80 percent of the battery's 2550 ampere-hour rated capacity is 2040. The revised minimum required load capacity was calculated to be 2116 ampere-hours which corresponds to an 83 percent replacement criterion. Therefore, the revised load duty cycle requirement can still be adequately accommodated when the battery capacity is at the 83 percent value.
- 4. Section 4.2.5 of the Safety Review Report for the NIS indicates that each redundant channel set of the NIS is energized from a separate AC power source. This section, thus implies that there will be four physically and electrically separated AC sources supplying the NIS. Verify that this is so and provide a description of these power sources and their physical and electrical separation. If this is not the case, provide the results of an analysis which demonstrates that the existing electric power system design, which will supply the new NIS design, will not compromise the independence requirement for the NIS.
RESPONSE
The upgraded NIS receives four channels of independent AC power derived from existing Regulated Buses 1, 2, 3, and 4, consistent with the existing NIS. Each regulated.bus is separately fed from a vital bus source (Vital Buses 1, 2, 3, and 4), through a voltage regulator.
-3 The 120V AC vital bus system is configured such that each vital bus can receive power from either of two redundant train sources of power, via an automatic transfer switch. Normal power is supplied by a Train A source (125V DC Bus 1 thru an inverter for each vital bus), and alternate power is provided by a Train B source (MCC 2 thru a step-down transformer).
Regulated Buses 1, 2, 3, and 4, are fed from Vital Buses 1, 2, 3, and 4, respectively, via feeders that share common raceways. This electrical and physical configuration was previously reviewed and accepted by the NRC as part of the Systematic Evaluation Program, and has been further demonstrated acceptable by a subsequent single failure analysis.
The NIS upgrade work will install a new AC power feeder for each of NIS Channels I, II, III, and IV (one per section of the new four-section NIS cabinet) from existing Regulated Buses 1, 2, 3, and 4, respectively. The new AC feeders are routed in accordance with current IEEE Std 384 and Regulatory Guide 1.75 physical separation criteria. This configuration improves the physical separation compared to the existing NIS, and hence remains acceptable relative to the previous NRC review.
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