ML19318B128
| ML19318B128 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 05/22/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19318B124 | List: |
| References | |
| NUDOCS 8006250048 | |
| Download: ML19318B128 (2) | |
Text
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ENCLOSUP O
SAFETY EVALUATION PRAIRIE ISLAND UNITS 1 AND 2 DOCKET NOS. 50-282 AND 50-306 DEGRADED GRID VOLTAGE PROTECTION FOR THE CLASS lE A.C. POWER SYSTEM Introduction and Summary The criteria and staff positions pertaining to degraded grid voltage protection were transmitted to Northern States Power Company (NSP) by NRC generic letter dated June 3,1977. In response to this, by letters dated May 4,1978 and October 12, 1979, NSP proposed certain design modifications and changes to the Technical Specifications. A detailed review and technical evaluation of these proposed modifications and changes was performed by the Lawrence Livermore Labora*:ry (LLL) under contract to the NRC, and with general supervision by NRC staff. This work was reported in LLL report UCID-18654, " Technical Evaluation of the Proposed Design Modifcations and Technical Specification Changes on Grid Voltage Degradation for the Prairie Island Nuclear Generating 9
Plant Units 1 and 2" dated March 1980 (attached). We have reviewed this technical evaluation report and concur in its conclusion that the proposed design modifications and Technical Specification changes are acceptable.
4 Proposed Changes and Evaluation Criteria The following design modifications and Technical Specification changes were proposed by NSP:
a.
Installation of second level undervoltage relays, two on each of the four 4160v Class 1E buses with a drop out setting at approximately 89%
of nominal bus voltage and a six second time delay.
These relays will be part of a modified two-out-of-four coincidence logic scheme. The same logic is used for the existing firs: level of undervoltage protection.
8 0062 500t/F
. b.
Installation of circuitry to block the undervoltage trip load shedding feature on the 4160v Class lE buses when the diesel generators are supplying these buses, and automatically reinstating this feature when the d'esel generator breakers are tripped, Addition of trip setpoint, limiting conditions for operation and c.
surveillance requirements in the Technical Specifications associated with the design modifications cited above.
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 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations;" and the staff positions defined in NRC generic letter to NSP dated June 3,1977.
Conclusions We have reviewed the LLL Technical Evaluation Report and concur in its findings that (1) the proposed modifications will protect the Class lE equip-ment and systems from a sustained degraded voltage of the offsite power source, and (2) the proposed changes to the Technical Specifications meet the criteria for periodic testing of protection systems and equipment. Therefore, we conclude that NSP's proposed design modifications and changes to the Technical Specifications are acceptable.
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