ML13316B338
| ML13316B338 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/14/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13316B334 | List: |
| References | |
| NUDOCS 8905010122 | |
| Download: ML13316B338 (4) | |
Text
RE Go0 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.124TO PROVISIONAL OPERATING LICENSE NO. DPR-13 SOUTHERN CALIFORNIA EDISON COMPANY SAN DIEGO GAS AND ELECTR1C COMPANY SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO. 1 DOCKET NO.
50-206
1.0 INTRODUCTION
In a letter to NRC dated October 4, 1985 (Ref. 1), the licensee committed to install dn ESF switchover automatic trip feature to the Safety Injection (SI) system to terminate primary system injection on low RWST level.
This modification will resolve the staff concern identified during the Systematic Evaluation Program (SEP) Integrated Plant Safety Assessment for Sai Onofre Unit 1, as documented in NUREG-0829.
The licensee, in its letter dated November 11, 1988 (Ref. 2), provides the description of the system modification and proposed Technical Specifications associated with the implementation of the automatic trip feature to the SI system. The licensee indicates that this system modification is scheduled to be implemented during the Cycle X refueling outage.
2.0 EVALUATION During our review uf the subject system modification, the staff fourd that the licensee did not include the required low RWST level setpoint in its pruposed Technical Specifications.
In response to the staff request, the licensee, in its letters dated January 13 (Ref. 3) and February 25, 1989 (Ref. 4), provided the results of the setpoint analysis of this automatic trip. The switchover from injection to recirculatiur modes is a two part process, which consists of the automatic termination of the flow from SI/FW pumps including automatic pump trip and automatic closure of NUV's 850 A, B arid C followed by manual realignment to recirculation from the containment sump. The automatic trip setpoint is bounded by the minimum water level in the cuntainment sump to support recirculation for long-term post-LOCA core ecoling and the minimun RWST level to support charging and containment spray during the switchover. The minimum wdter volume required to be pumped from the RWST into the containment sump via the broken RCS piping following a LOCA to meet recirculation mode NPSH requirements is approximately 187,000 gallons. With the RWST Technical Specification level of 240,000 gallons, the 8905010122 890414 PDR ADOCK 05000206 P
PNU
-2 upper limit of the automatic trip setpoint is approximately 53,000 gallons remaining in RWST, which correspond to approximately 21% RWST level.
The minimum water volume required in the RWST is approximately 44,400 gallorns, This is required to prevent the potential cavitation of charging and contain rnent spray pump considering a 5-minute time period to manually complete recirculation realignment, and an allowance of 10 seconds equivalent full flow to bound SI/FW pump coastdown. This lower limit of the automatic trip setpoint of 44,400 gallons correspond to approximately 17% RWST level.
The staff considers that the licensee calculated band of the required automatic trip setpoint is reasonably conservative and acceptable.
The licensee proposed Technical Specification 3.3.1 requires that the ESF switchover automatic trip channel is operable with the setpoint less than or equal to 20% and greater than or equal to 18% of RWST level.
These proposed Technical Specification values include instrument uncertainties of level switches to prevent both premature and delayed terminations of the SI/FW flow. The proposed Technical Specification 3.3.1 also specifies the maximum time limit of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for allowing one train of ESF switchover automatic trip for maintenance during reactor critical operation or when the RCS temperature is above 2000F. This is consistent with the Technical Specification requirement applied to other ESF equipment.
The proposed change also revises the emergency diesel generator (EDG) concurrent load rejection of the feedwater and safety injection pump motors on low-low Refueling Water Storage Tank (RWST) level.
This concurrent load rejection represents the largest load on the EDG.
Due to this tripping, the load which will be rejected by the Emergency Diesel Generator (EDG) will be 4000kW instead of 3220kW.
SCE completed a load rejection test on EDG No. 2 on January 2, 1989 by tripping the EDG circuit breaker while the unit was in parallel with the outside source and the load on the EDG was 4300kW. The EDG accelerated to 470RPM, nominal is 450RPM, and the unit did not trip on overspeed which is set at 513RPM. 'However in SCE's procedure no voltage and frequency measurements were required.
SCE in their letter of March 4, 1989 (Reference 5) revised the testing procedure to include a limit on the voltage not to exceed 4800 volts during arid following the load test. This overvoltage condition is consistent with industry standards for operating limits of electrical equipment. This is acceptable to the staff.
The technical specification now requires the generator capability to reject a load of 4000kW without tripping. The generator voltage shall not exceed 4800 volts and the generator speed shall not exceed 500 RPM (nominal speed plus 75%
of the difference between nominal speed and the overspeed trip setpoint) during and following the load rejection. The limitation on overspeed is consistent with Regulatory Guide 1.9 (Reference 6). The licensee has agreed to this additional restriction.
By letter dated January 13, 1989, the licensee provided design details and implementation information. Six safety-related pressure switches, three per train, will be mounted as Seismic Category A level switches on the anchor ring
"e g
-3 of the RWST. Each train of safety injection/feedwater pump circuits is electrically independent and physically separated from the other trains.
Output contacts of these level switches will be configured to provide the two out of three coincident logic to automatically trip the feedwater and safety injection pumps upon a low-low RWST level signal and a concurrent Safety Injection Signal (SIS). Thus, failure of a single level switch will not prematurely terminate the safety injection. Memory relays will be provided to ensure that the low-low RWST level trip capability is not disabled by the expected manual block/reset of the SIS that may take place prior to reaching a low-low RWST level POST-LOCA.
Stainless steel piping will be added to the existing RWST single instrument nozzle to maintain train separation of the level switches by providing separate taps and root valves. Each level switch will have individual isolation and drain valves for the purposes of maintenance, calibration and testing. Cables from the RWST level switches to the 4160V switchgear associated with the safety injection and feedwater pump will be routed through new conduits and junction boxes.
Internal electrical modifications at the 4160V switchgear cubicles consist of the installation of relays, test switches, and indicating lights to modify pump control circuits to provide the two out of three low-low RWST level trip logic to the safety injection and feedwater pump motors circuit breakers. Test switches will be connected in parallel to the level switches for surveillance testing of the low-low RWST level auxiliary relays and the 2 out of 3 low-low RWST level trip logic in accordance with Technical Specification criteria.
'The staff concludes that the licensee proposed system modification is consistent with the NRC recommendation in the San Onofre Unit 1 SEP Topic VI-7.B to install the automatic trip to terminate the SI/FW flow on a low RWST level.
The proposed Technical Specification 3.3.1 contains adequate trip setpoints and maintenance restriction, and therefore is acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact have been prepared and published in the Federal Register on February 3, 1989 (54 FR 5566). Accordingly, based upon the environmental assessment, the Commission has determined that the issuance of this amendment will not have a significant effect on the quality of human environment.
4.0 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: C. Liang, S. Rhow, S. Saba and C. Trammell Dated:
April 14, 1989
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-4 REFERENCES
- 1. October 4, 1985; Southern California Edison Company letter to NRC.
- 2. November 11, 1988, Southern California Edison Company letter to NRC.
- 3.
JanuIry 13, 1989, Southern California Edison Company letter to NRC.
- 4.
February 25, 1989, Southern California Edison Company letter to NRC.
- 5. March 4, 1989, Southern California Edison Company letter to NRC.
- 6. Regulatory Guide 1.9, "Selection, Design and Qualification of Diesel-Generator Units Used as Standby (On-site) Electric Power Systems at Nuclear Power Plants, December 1979.