ML20147F214
| ML20147F214 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/29/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20147F194 | List: |
| References | |
| TAC-66967, NUDOCS 8803070277 | |
| Download: ML20147F214 (4) | |
Text
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- smouqk, UNITED STATES g
NUCLEAR REGULATORY COMMISSION C.
j WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 107 TO FACILITY OPERATING LICENSE NO. NPF-3 TC;~AG EDIS0N COMPANY AND THE CLEVELAND ELECTRIC ILLUMINATING COMPANY DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NO. 50-346
1.0 INTRODUCTION
By letter dated January 20, 1988, ToledoEdisonCompany(TEDorthelicensee) requested a change to Facility Operating License No. NPF-3, Appendix A Technical Specifications (TS's), for the Davis-Besse Nuclear Power Station Unit No.1.
The change proposed would permit extension of the next due date for Surveillance Requirement (SR) 4.8.1.1.1.b which would otherwise be required to be performed not later than March 1,1988. Specifically, the extension would extend the surveillance due dates for demonstrating the operable status of the required independent electrical circuits between the offsite transmission network and 4
onsite Class 1E distribution system.
The surveillance requirements extended by the proposed amendment are to demon-strate operable the manual ano automatic transfer of unit power supply to each of the 345 kV transmission lines.
2.0 DISCUSSION SR 4.8.1.1.1 b requires that the manual and automatic transfer capability of the unit power supply to each of the 345 kV transmission lines be demonstrated operable. These surveillances must be performed at least once each 18 months while the unit is shut down. Specification 4.0.2 requires the performance of each SR within the specified time interval; however, any one interval is allowed to be as much as 1.25 times the specified surveillance interval, and the i
combined interval for any three consecutive surveillances is allowed to be as much as 3.25 times the surveillance interval.
SR 4.8.1.1.1 b must be performed no later than March 1,1988, to comply with SR 4.0.2 a and not later than July 24, 1988, to comply with SR 4.0.2 b.
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' The Davis-Besse Nuclear Power Station is currently operating at power. Shutdown is scheduled for March 11, 1988 to enter the fifth refueling outage. To perform the scope of work necessary to satisfy SR 4.8.1.1.1 b, it would be necessary to shut uown the station 11 days sooner than planned.
Shutdown for the refueling outage was previously scheduled for mid-February 1988, but in early January 1988 it was rescheduled for March 11, 1988. This later date for shutdown has created the need to consider the extension of the due date for the subject surveillance tests.
3.0 EVALVATION In Modes 1 through 4, the Davis-Besse TS's require two operable, independent circuits between the offsite transmission network and the Class 1E distribution system. SR 4.8.1.1.1 b. requires that these circuits be demonstrated operable at least once per 18 months by transferring unit power supply to each of the 345 kV transmission lines. The transfer is to be demonstrated for both the manual transfer capability and the automatic transfer capability. The TS requirement further specifies the test to be done while the unit is shut down because performing this test while the unit is at power potentially could challenge plant safety systems should a failure occur. Shutdown is considered to be while the unit is in Modes 5 or 6.
The licensee states that this SR was last done on April 14, 1986, and, therefore, the tests must be done not later than March 1,1988. This due date is 687 days from the last surveillance and complies with TS 4.0.2 a.
The 18-month test interval for the 13.8 kV bus transfer was selected to be consistent with the maximum anticipated interval between refueling outages; and the interval is based on engineering judgment to achieve the dual goals of the need to conduct periodic surveillance tests (to verify operability within a time interval which does not exceed the mean time to failure for the subject equipment) but not not so frequent as to interfere substantially with unit availability. The tolerances on the individual and consecutive intervals are intended to ensure that the reliability of the equipment associated with the surveillance activity is not likely to be significant:y degraded beyond that obtained from the nominal specified interval.
In its application, TED asserts that the operability of the manual transfer capability for the 13.8 kV breakers has been demonstrated successfully several times since the surveillance requirement was last performed. Additionally, the licensee asserts that, as a result of several plant trips, the automatic transfer capability from the normal source to the selected offsite source has also been demonstrated.
The A.C. power supply is designed to provide reliable redundant sources of power to the onsite power distribution system in the event of a turbine trip or when the plant is shut down. The 13.8 kV buses are normally supplied power from the auxiliary transformer connected to the station generator.
In the event of a turbine generator trip, the 13.8 kV buses are fast-transferred to the preselected 345 kV offsite power source through a startup transformer, j
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. If the preselected power supply is not available, the 13.8 kV bus goes dead and the corresponding emergency diesel-generator automatically starts _and picks up the safety-related loads. The 13.8 kV bus will not shift to the alternate startup transformer.
If a 13.8 kV bus is being supplied through a startup transformer and the offsite power fails, the 13.8 kV bus will automatically fast-transfer to the alternate startup transformer if preselected by the operator.
On September 6,1987, following a plant trip, the fast transfer feature on one of the Class 1E distribution system 13.8 kV breakers failed. Because the trip and subsequent plant recovery was complicated by a sequence of unrelated malfunctions, the NRC sent an Augmented Inspection Team (AIT) to the site to investigate the circumstances related to that event. The AIT reported its findings in Inspection Report 50-346/87025(AIT)datedOctober1,1987.
The AIT investigations revealed that the procedures in effect for conducting surveillance testing of the fast transfer features described above would only demonstrate operability of the transfer from one startup transformer to the other but would not demonstrate operability of the transfer from the auxiliary transformer to the selected startup transformer as required by SR 4.8.1.1.1.b.
Prior to restart after this event, post-maintenance testing of the breakers and other controls related to the fast transfer capability was performed.
This testing did demonstrate both fast transfer features. On December 7, 1987, the fast transfer from the auxiliary transformer to the correct offsite power source functioned successfully in response to a plant trip.
TED is requesting an extension to the current due dates for the surveillances discussed above of 31 days. This extension would permit the unit to continue operation at power until the scheduled refueling outage of March 11, 1988.
The staff believes that an extension of 31 days will not increase significantly the probability of undetected degradation of equipment related to the fast transfer capability.
4.0 FINDINGS Based upon the details discussed above, the staff has concluded that the proposed extension of no more than 31 days represents a small increase in the currently allowable 687 days interval between surveillance tests.
- Further, since the prior surveillance tests were not conducted such as to demonstrate the fast transfer of power from the auxiliary transformer to the offsite transmission system, the length of the interval since the last surveillance test has no significance. Following the September 6, 1987 event the licensee conducted a successful post maintenance demonstration of the fast transfer of power from the auxiliary transformer to the startup transformer.
Following the December 7,1987 trip this same fast transfer capability functioned properly.
Therefore, the staff finds the licensee's request to extend the due date for SR 4.8.1.1.1.b. until April 1, 1988, is acceptable.
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5.0 ENVIRONMENTAL CONSIDERATION
This amendment involves changes to a surveillance reoutrement. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration, and there has been no public comment on such finding. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10CFR51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement nor environmental assessment need be prepared in connection with the issuance of this amendment.
6.0 CONCLUSION
The staff has 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, and (2) such activities will be conducted in compliance with the Commission's regulations, and 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 Contributor:
A. De Agazio Dated: February 29, 1988
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