ML20035E480
| ML20035E480 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/08/1993 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 93-076, 93-76, NUDOCS 9304160059 | |
| Download: ML20035E480 (3) | |
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a VIRGINIA ELECTRIC AND Powrn COMPANY RicnMoxo VIRGINIA 23201 April 8, 1993 U.S. Nuclear Regulatory Commission Serial No.93-075 Attention: Document Control Desk NL&P/RMN R3 Washington, D.C. 20555 Docket Nos. 50-338 50-339 License Nos. NPF-4 NPF-7 i
Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 RESPONSE TO ELEQTRICAL DISTRIBUTION SYSTEM FUNCTIONAL INSPECTION ISSUES UNDER REVIEW We have reviewed your letter dated February 2,1993 which pertains to two issues related to Emergency Diesel Generator (EDG) design and operating practices which were identified for further review in Electrical Distribution System Functional Inspection (EDSFI) Report No. 50-338,339/91-17. Our response to the two issues is attached.
Should you have any questions or require additional information, please contact us.
Very truly yours, Air /
! Tj'q~~3
& Q ) b.jkj W. L. Stewart Senior Vice President - Nuclear Attachment cc:
U.S. Nuclear Regulatory Commission Region 11 i
l 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. M. S. Lesser NRC Senior Resident inspector North Anna Power Station
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s' RESPONSE TO NORTH ANNA ELECTRICAL DISTRIBUTION SYSTEM FUNCTIONAL INSPECTION (EDSFI) ISSUES UNDER R F;"lEW i
A review of the two issues related to Emergency Diesel Generator (EDG) design and operating practices, that were identified during the EDSFI, has been performed. A response to each of the two issues is provided below.
BYPASS OF EMERGENCY DIESEL GENERATOR AIR START TIMER CIRCUIT The first issue is related to the EDG design which provides for the bypass of the air start timer circuit in the emergency mode. The concern is that there is not enough air conserved in the air start receiver tank to allow a minimum of one engine start if the EDG fails to start during the emergency mode of operation. We have considered this point and determined that the current system configuration is adequate. The basis for our conclusion is:
- 1) The EDGs are tested frequently and show a high degree 3 reliability. Currently, North Anna's EDG reliability is greater than 99%. The Technical Specifications provide adequate assurance that a start failure would be detected. The EDG reliability and testing frequency demonstrate that a modification is not necessary.
- 2) Each EDG at North Anna has two air compressors that can be used to recharge the start air receivers. Each compressor can be drive.1 by either an electric motor or a diesel engine (Lister Diesel), Although the EDG is considered operable as long as one of its two air receivers has sufficient air pressure to provide the design number of starts, the Lister Diesels are performance tested periodically.
The availability of the Lister Diesels is also high. Although these Lister Diesels must be manually started following drive belt installation, this is acceptable, since some manual actions and maintenance will be needed to correct the problem that caused the EDG start failure. The time needed to recharge the start air receivers is expected to be significantly less than the time needed to correct the problem that caused the EDG to initially fail to start.
- 3) This issue has been addressed by the NRC in the Final Safety Analysis Report, Regulatory Position 8.2.
Specifically, the NRC staff took the position that all diesel generator trips except the engine overspeed, generator differential, and overcurrent breaker trip should be bypassed during an emergency start.
- 4) Our plans to comply with 10 CFR 50.63 include the installation of an additional diesel generator that can be connected to any emergency bus. This will enhance our ability to restore power to an emergency bus. This diesel is currently scheduled to be installed by 1995.
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EDG AUTOMATIC START SURVEILLANCE TEST ACCEPTANCE CRITERIA The second issue is related to the EDG automatic start test acceptance criteria which accommodates overshoot of EDG voltages and frequency during an unloaded emergency start. A review of the acceptance criteria in EDG test procedures by Engineering has determined that the criterion is fully acceptable. The basis for our conclusion is:
- 1) The EDG is verified operable once every month by Technical Specification Surveillance Requirement 4.8.1.1.2.A. This surveillance requirement ensures the overallintegrity of the EDG and that the EDG is capable of starting and carrying loads.
- 2) The EDG is started by an automatic start signal every six months in accordance with Technical Specification Surveillance Requirement 4.8.1.1.2.c. The basis for performing this surveillance requirement is to prove that the EDG is capable of accepting its emergency loads within 10 seconds of an emergency start signal.
The permissive to close the output breaker requires a minimum voltage. There is no maximum voltage or frequency. ' A temporary overshoot will, theref are, not affect the EDG's ability to accept emergency loads within 10 seconds.
- 3) The design conditions are verified every 18 months in accordance with Technical Specification Surveillance Requirement 4.8.1.1.2.d.4 and 4.8.1.1.2.d.6. These surveillance requirements actually start the EDG by de-energizing the emergency bus, and verifies that the EDG energizes both its permanently connected load within 10 seconds and its subsequent loads which are automatically sequenced on the bus.
- 4) IEEE 387, Regulatory Guide 1.108 and' Regulatory Guide 1.9 do not have acceptance criteria stated for a maximum voltage during an unloaded emergency start.
- 5) Currently, voltage and frequency are stable in the 10 second band without i
overshoot on any of the four EDGs.
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