ML20211G206

Safety Evaluation Supporting Amends 228 & 219 to Licenses DPR-77 & DPR-79,respectively

ML20211G206
Person / Time
Site:	Sequoyah
Issue date:	09/23/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20211G203	List: ML20211G198 ML20211G206
References
NUDOCS 9710020150
Download: ML20211G206 (3)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REAC10R REGULATION RELATED TO AMENDMENT NO. 228TO FACILITY OPERATING LICENSE NO. DPR 77 AND AMENDMENT NO.?to TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-327 AND Efd2B

1.0 INTRODUCTION

The Tennessee Valley Authority (TVA, the licensee) requested amendments to Operating Licenses DPR 77 and DPR 79 for Sequoyah Nuclear Plant (SON), Units 1 and 2, respectively, in a letter dated September 21,1996. The amendments would revise the SON Unit 1 and 2 Technical Specifications (TS) to eliminate Surveillance Requirement (SR) 4.8.1.1.1. This SR requires verifying the ability to manually and automatically transfer each unit's main power supply from the unit generator cupported circuit to the " preferred" power circuit.

2.0 BACKGROUND

General Design Criteria 17 (GDC 17),10 CFR Part 50, Appendix A, requires two independent offsite power circuits designed and located so as to minimize to the extent practical the likeli5ood oitheir simultaneous failure under operating and postulated accident and environmental conditions.

The offsite power distribution system at the SON switchyard consists of two 161 kilovolt (kV) buses supplied by eight 161 kV feeders and two 500-kV buses supplied by five 500-kV feeders.

Two of the 161 kV transmission lines connect to TVA's Chickamauga Hydroelectric Plant and one connects to WA's Watts Bar Hydroelectric Plant. The electrical output of SON Unit 1 is fed to the 500-kV buses and the electrical output of SON Unit 2 is fed to the 161-kV buses. Two unit station service transformers are connected to the output of each unit's generator, between the generators and the main transformer banks.

The intent of GDC-17 has been implemented la the GON Preferred Power System (PPS) by providing two physically and functionally independent circuits for energizN safety related load groups. The PPS is supplied from the161 kV switchyard and consists of three 161/6.9 kV common station service transformers (CSSTs), four 6.9-kV start buses, eight 6.9 kV unit boards, and and four 6.9-kV shutdown boards.

As stated in the licensee's submittal, the purpose of SR 4.8.1.1.1.b is to ensure that the power feeds, including those to the shutdown boards, would be transferred to a qualified offsite power circuit in accordance with GDC-17. In the past, these safety-related electricalloads were

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normally supplied from the unit generator output through the unit station service transformers and would be required to transfer to the preferred power source in the event of a main turbine-generator trip. TVA has implemented an operational design change at SQN which results in the safety related loads being normally supplied from the prefarred GDC 17 power supply (161 kV buses) via the CSST's. Because the power supply to the safety related loads is normally now the preferred s0urce because of the design change, TVA claims that this surveillance is no longer necessary.

3.0 EVALUATION As discussed above, the SON 181 kV switchyard is designed with a high degree of diversity to ensure the reliability of offsite power to SON The operational design change using the CSSTs instead of the unit generator supported circuits has improved the reliability of power to the unit safety related electricalloads and has made SR 4.8.1.1.1.b testing irrelevant. The reason is because the purpose of the test was to verify that the safety-related loads would automatically transfer (and could be manually transferred) from the generator output to the preferred power supply upon a degradation of generator output voltage (such as from a turbine trip). Since the loads are now normally aligned to the preferred source, the transfer circuitry that is tested no longer has a safety function and should not be part of the SON TS.

The licensee's submittal also stated that whenever shutdown power may be aligned to other circuits not meeting GDC-17, the TS action statements pertaining to an inoperable offsite circuit will be entered to ensure the circuit will be restored to operable status within the required time or a unit shutdown would be required to a nonapplicable mode.

For the reasons stated above, the staff finds deletion of SR 4.8.1.1.1.b from the SON TS to be acceptable.

4.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendments. The State official had no comments.

5.0 ENVIRONMENTAL CONSIDERATION

The amendments change the requirements with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements. 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 the ameadments involve no significant hazards consideration and there has been no public comment on such finding (61 FR 52968). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmentalimpact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

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criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). FTsuant to 10 CFR 51.22(b), no environmentalimpact statement or environmental assusment need be prepared in connection with the issuance of the amendments.

6.0 CONCLUSION

The Commission 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, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor: R. Heman Dated: September 23, 1997