ML20235W832

Safety Evaluation Supporting Amends 96 & 91 to Licenses DPR-19 & DPR-25,respectively

ML20235W832
Person / Time
Site:	Dresden
Issue date:	10/09/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20235W830	List: ML20235W827 ML20235W832
References
NUDOCS 8710190051
Download: ML20235W832 (2)

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT N0. 96 TO PROVISIONAL OPERATING LICENSE NO. DPR-19 AND AMENDMENT N0. 91 TO FACILITY OPERATING LICENSE N0. DPR-25 i

COMMONWEALTH EDISON COMPANY DRESDEN NUCLEAR POWER STATION, UNIT NOS. 2 AND 3 DOCKET NOS. 50-237 AND 249

1.0 INTRODUCTION

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By letter dated May 14, 1986, the Commonwealth Edison Company (CECO, the licensee) proposed to amend Provisional Operating License No. DPR-19 and Facility Operating License No. DPR-25 for Dresden Nuclear Power Station, Unit Nos. 2 and 3.

The proposed amendments would impose 4-KV cross-tie l

operability requirements.

On August 16, 1985, normal offsite AC power was lost to Dresden Unit 2.

i The licensee provided a report dated December 13, 1985, which responded to NRC staff concerns over the event. During the August 16, 1985, Dresden 2 event, normal offsite AC power was lost due to tripping of the Reserve Auxiliary Transformer (RAT) which is fed by 138-KV switchyard. Due to transfer circuit deficiency, the two auxiliary power buses normally fed by this transformer failed to automatically transfer to the Unit Auxiliary Transformer (UAT) which is the second normal supply of AC power. This feilure to transfer ultimately led to a reactor scram and loss of AC power feed to UAT. This constituted a complete loss of offsite AC power. As designed, both diesel generators automatically started providing AC power to the essential equipment.

During this t1me, another independent source of offsite power, which is a Unit 2/3 4-KV cross-tie, was available but not utilized. By letter dated May 14, 1986, the licensee requested a revision to the Technical Specification for the 4-KV cross-tie operability.

2.0 EVALUATION GDC 17 of Appendix A 10 CFR 50 requires that the electrical power from the transmission network to the onsite electric distribution system shall be supplied by two physically independent circuits. By letter dated December 13, 1985, the licensee stated that the RAT of the other unit is the second offsite source through a bus tie provided between corresponding safety-related buses of the two units. Although this specific back-up source of offsite power is not automatically transferred, it could be aligned quickly from the control room.

Furthermore, offsite power capability via the cross-tie has been designed with sufficient capacity to operate one plant's total auxiliary loads during normal operation, while supplying adequate power to safely shutdown the other plant and also support all necessary engineered safeguards during an accident.

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However, existing TS 3.9. A only requires the 4-KV cross-tie, for Dresden 2 and 3 to be available if-normal offsite power to one of the two units-is lost.

In a response dated December 13, 1985, to address concerns raised by the staff about compliance with GDC 17, the licensee committed to amend TS 3.9_ for Dresden. Subsequently by letter dated May 14, 1986, the licensee proposed changes to TS 3.9 which would establish operability and surveillance requirements for the common unit 4-KV cross-tie and, thereby,

' assure an alternative source of offsite AC power would be available. This line will only be connected manually after the detection of loss of power condition to the buses.

3.0 -

SUMMARY

t The staff has reviewed the proposed TS and considers them acceptable requirements for ensuring availability of a second independent back-up source of offsite power via the 4 KV bus cross-tie that is consistent with GDC 17.

4.0 ENVIRONMENTAL CONSIDERATION

These amendments involve changes to a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendments involve 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 these amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, these amendments meet the eligibilit criteria for categorical exclusion set forth in 10 CFR 51.22(c)(y9).

Pursuant to 10 CFR 51.22(b) no environmental impact statement nor environmental assessment need be prepared in connection with the issuance l

of these amendments.

5.0 CONCLUSION

The staff has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the

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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 these amendments will not be inimical to the common defense and security nor to the health and safety of the public.

Principal Contributor:

N. Trehan Dated:

October 9, 1987

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