ML19341B903
| ML19341B903 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 02/11/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19341B901 | List: |
| References | |
| TAC-12746, NUDOCS 8102280098 | |
| Download: ML19341B903 (3) | |
Text
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NUCLEAR REGULATORY COMMISSION
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SAFETY CVALUATION PANCHO SECO NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. 50-312 DEGRADED GRID VOLTAGE PROTECTION FOR THE CLASS 1E POWER SYSTEM INTRODUCTION AND
SUMMARY
The criteria and staff positions pertaining to degraded grid voltage protection were transmitted to Sacramento Municipal Utility District (SMUD) by NRC generic letter dated June 3,1977.
In response to this, by letters dated July 19, 1977, June 20,1978 August 1,1980 and September 22, 1980, the licensee proposed certain design modifications and draft changes to the Technical Specifications. A detailed review and technical evaluation of these proposed modifications and draft changes to the Technical Specification was performed by Lawrence Livermore Laboratory (LLL), under contract to the NRC, and with general supervision.
by NRC staff. This work is reported by LLL in a report, " Technical Evaluation of the Proposed Design Modifications and Technical Specifications Changes on Grid Voltage Degradation (Part A) for the Rancho Seco Nuclear Generating Plant" (attached). We have reviewed this technical evaluation report and concur in its conclusions that the proposed design modifications and draft Technical Specification changes are acceptable.
Proposed Changes and Evaluation Criteria The following design modifications and draft Technical Specification changes were submitted by SMUD:
a.
The existing undervoltage protection is integrated into one loss of voltage and degraded voltage protection scheme. The proposed scheme 8102280098 t
. will consist of three undervoltage relays, and will be arranged in a 2-out-of-3 coincident logic. The setpoint is selected such that it will take 12 seconds to trip for 90.6% of ncminal bus voltage and less than one second upon complete loss of voltage.
b.
The licansee has included draft-changes to the Technical Specifications:
These include addition of trip setpoint, limiting conditions for operation and surveillance requirements associated with the design modifications.
The present design blocks the undervoltage trip load shedding feature on the Class 1E buses when the diesel generators are supplying these buses.
If the diesel generator circuit breaker is tripped, the load-shedding logic circuitry will be automatically reinstated.
The criteria used by LLL in its technical evaluation of the above proposed changes include GDC-17 " Electric Power Systems," of Appendix A to 10 CFR 50; IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations;" IEEE Standard 303-1974, "Cisss 1E Power Systems for Nuclear Power Generating Stations," and the staff positions defined in NRC generic letter to Si1UD dated June 3,1977, CONCLUSIONS We have reviewed the Lawrence Livermore Laboratory's Technical Evaluation Report and concur in its findings that (1) the proposed modifications will protect the Class lE equipment and systems from a sustained degraded voltage of the offsite power source, and (2) the draft changes to the Technical
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Specifications meet the criteria for periodic testing of protection systems and equipment. Therefore, we conclude that the pmposed design modifications are acceptable, and the draft Technical Specifications, once fonnally sub-mitted to the NRC, would be satisfactory.
I Dated: FEBRUARY 1 1 1981 i
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