ML20212F476

Safety Evaluation Supporting Amends 246 & 237 to Licenses DPR-77 & DPR-79,respectively

ML20212F476
Person / Time
Site:	Sequoyah
Issue date:	09/23/1999
From:	NRC (Affiliation Not Assigned)
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Shared Package
ML20212F452	List: ML20212F450 ML20212F460 ML20212F476
References
NUDOCS 9909280217
Download: ML20212F476 (4)

Text

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't NUCLEAR REGULATORY COMMISSION

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 246 TO FACILITY OPERATING LICENSE NO. DPR-77 AND AMENDMENT NO. 237 TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328

1.0 INTRODUCTION

By application dated June 24,1999, to the U.S. Nuclear Regulatory Commission (NRC), the Tennessee Valley Authority (TVA, the licensee) proposed an amendment to the Technical Specifications (TS) for Sequoyah Nuclear Plant (SON) Units 1 and 2. The requested changes would revise the TS to allow use of a fully qualified and tested spare inverter in place of any of the eight required inverters. Specifically, TVA proposed the addition of a new footnote to TS 3.8.2.1 and TS 3.8.2.2. Consistent with a plant design change, the footnote would allow the substitution of the spare inverter of a specified channel as a replacement of one of the two required inverters of the same channel. The footnote applies to the limiting condition for operation associated with the 120-volt altemating current (VAC) vital instrument power board channels and the associated inverter requirements. The proposed package also contains typographical corrections for the existing footnote for TS 3.8.2.1.

2.0 EVALUATION TVA proposed the above described changes to incorporate a design change that would

- provide a spare inverter for each of the four channels of 120-VAC vitalinstrument power board channels. The design change would upgrade the eight required inverters with new inverters that would have additional capabilities and improved reliability, in addition, TVA would utilize ,

four of the presently installed inverters, after installing updated features, as spares for each of the required channels. The swtem would be designed such that each spare inverter could be aligned to provide the power requirements for one of the two associated 120-VAC vital j instrument power board channels. This plant modification was undertaken to rectify inverter '

operational problems that have occurred in the past. The new footnote in the TS would allow TVA to utilize the spare inverters for maintenance or testing activities without having to rely on the TS action statement provisions (that could require dual plant shutdown) and would provide improved safety function availability and, therefore, improved plant reliability.

The SON vital alternating current (ac) and direct current (de) control and instrument power systems consist of four 125-volt batteries, four battery chargers and eight 120-VAC inverters with their respective safety related loads. TVA is adding four spare inverters that have the l equivalent features and capability. The spare inverters would be designed to allow for manual replacement of one of the two inverters in the same channel. The 125-volt de distribution l j

system is a safety-related system, which receives power from four independent battery 9909280217 990*23 ADOCK 05000327 PDR  ;

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n-2 chargers and four 125-volt batteries and distributes it to safety-related loads of both units. The

120-VAC distnbution system receives ac power from eight independent inverters and i distributes it to the safety-related loads of both units. 'The inverters provide a source af 120-volts,60-Hertz (Hz) power for the operation of the nuclear steam supply system instrumentation. This power is derived from the 480 VAC,3-phase,60-Hz distribution system (the preferred power supply), or the station batteries, which assure continued operation of the

- ac instrumentation systems in the event of a station blackout.

The 120-VAC vital instrument system incorporates features which serve to increase the overall I reliability of the plant. Each channel has access to three power sources; a 480-VAC source, a 125-volt de source, and a 120-VAC maintenance source. TVA is providing a new maintenance ,

source that utilizes a regulated transformer and obtains the power source from the 480-VAC l shutdown boards. This source would provide a more stable and consistent voltage level for l the 120-VAC vitalinstrument power boards when on the maintenance source. Each inverter i has an auctioneered solid-state transfer switch between the 480-VAC and 125-volt de sources.

Transfer switches between the output of the inverter and the 120-VAC maintenance supply  ;

would be modified to utilize static switches that would transfer loads automatically for a loss of inverter output. The new design would continue to provide manual transfer capability so that the inverter may be taken out of service for maintenance without interrupting power to the loads. The current limiting feature of the inverter provides self-protection from load faults. The inverter and instrumentation power board are monitored to alert the operator of abnormalities.  ;

The eight inverters are located in the Auxiliary Building at Elevation 749. Channels I and ll inverters are located in the Unit 1 area and Channels ill and IV inverters are located in the Unit 2 area. Channels I and 11 inverters are separated from Channels lil and IV inverters by a reinforced concrete block wall, extending to the ceiling. Channel I and the Channel lll inverters are separated from Channel 11 and Channel IV inverters, respectively, by a distance of about 60 feet. The spare inverters would be located with the required inverters of the same channel.

The normal supply of ac power to the distribution panels is from the corresponding inverter in each channel. Each inverter consists of three major subassemblies: a de power supply, an auctioneering circuit, and an inverter circuit. The dc power supply converts the 480-VAC normal inverter input to direct current. The auctioneering circuit accepts the de power supply (normal supply) and battery (emergency supply) inputs and permits a switchless bidirectional transfer between them in the event of 480-VAC supply failure and restoration. The de output ,

of the auctioneering circuit is converted to ac by the inverting circuit.

The modified system would meet or exceed these system features and capabilities. The addition of a regulated maintenanca source and the automatic static switch provides additional capability to provide reliable power to the vital instruments boards and minimize the potential

. for a unit trip. The regulated maintenance source would be a more reliable supply to the board

.with better voltage control to support safety-related instrumentation operation during maintenance or inverter failure.: The ability to utilize spare inverters with the equivalent capabilities would allow better opportunities to properly maintain the inverters and minimize the potential to require unit shutdown for an inverter problem.

The new design that includes a spare inverter would provide the ability to remove the normal

. inverters for maintenance without the limitations of TS actions or the potential to require unit shutdown. The proposed TS changes support the use of a spare inverter that has the ability to

n automatically switch to a regulated maintenance power supply. This ability would improve unit operation and reliability when the spare is in service by providing a reliable source of power to the 120-VAC vital instrument power boards in the event of inverter failure. When the normal inverter is replaced by the spare all required safety functions would be retained without a reduction in reliable power to the instrument boards. Therefore, the implementation of the proposed TS change to allow the use of a spare inverter would provide enhanced maintenance opportunities while providing an improved source of power to maintain required safety functions.-

The NRC staff has reviewed the subject amendment application against the guidance contained in NUREG-0800, " Standard Review Plan," Sections 8.3.1 (onsite ac power systems) .

and 8.3.2 (onsite dc power systems). The staff finds that the required General Design Criteria

~ (GDC) of Title 10, Code of Federal Reaulations (10 CFR), Part 50, including GDC-17 (electric power systems), would continue to be met with implementation of the proposed changes to the SQN TS. The staff, therefore, finds the proposed changes to be acceptable.

3.0 STATE CONSULTATION

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

4.0 ENVIRONMENTAL CONSIDERATION

The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC 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 the amendment involves no significant hazards consideration (64 FR 41973), and there has been no public comment on such finding. Accordingly, the amendment meets the siigibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

5.0 ' 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 would not be endangered by operation in the proposed manner, (2) such activities would be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment would not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor: Ronald W. Heman, NRR Dated: SePL M E i

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. Mr. J. A. Scalice Tennessee Valley Authority SEQUOYAH NUCLEAR PLANT cc:

Mr. Karl W. Singer, Senior Vice President Mr. Pedro Salas, Manager Nuclear Operations Licensing and Industry Affairs Tennessee Valley Authority Sequoyah Nuclear Plant 6A Lookout Place Tennessee Valley Authority 1101 Market Street P.O. Box 2000 Chattanooga, TN 37402-2801 Soddy Daisy, TN 37379 Mr. Jack A. Bailey Mr. D. L. Koehl, Plant Manager Vice President Sequoyah Nuclear Plant Engineering & Technical Services Tennessee Valley Authority Tennessee Valley Authority P.O. Box 2000 6A Lookout Place Soddy Daisy, TN 37379 1101 Market Street Chattanooga, TN 37402-2801 Mr. Melvin C. Shannon Senior Resident inspector Mr. Masoud Bajestani Seouoyah Nuclear Plant Site Vice President U.S. Nuclear Regulatory Commission Sequoyah Nuclear Plant 2600 Igou Ferry Road Tennessee Valley Authority Soddy Daisy, TN 37379 P.O. Box 2000 Soddy Daisy, TN 37379 Mr. Michael H. Mobley, Director TN Dept. of Environment & Conservation Division of Radiological Health General Counsel 3rd Floor, L and C Annex Tennessee Valley Authority 401 Church Street ET 10H Nashville, TN 37243-1532 400 West Summit Hill Drive Knoxville, TN 37902 County Executive Hamilton County Courthouse Mr. N. C. Kazanas, General Manager Chattanooga, TN 37402-2801 Nuclear Assurance Tennessee Valley Authority SM Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Mark J. Burzynski, Manager Nuclear Licensing Tennessee Valley Authority 4X Blm Ridge 1101 Market Street Chattanooga, TN 37402-2801 L