ML20196F212

Application for Amends to Licenses DPR-77 & DPR-79,to Change TS Allowing Use of Fully Qualified & Tested Spare Inverter in Place of Any of Eight Required Inverters

ML20196F212
Person / Time
Site:	Sequoyah
Issue date:	06/24/1999
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20196F215	List: ML20196F212 ML20196F221
References
TVA-SQN-TS-99, TVA-SQN-TS-99-0, NUDOCS 9906290161
Download: ML20196F212 (8)

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• RA Tennessee Valley Authonty, Post Othee Box 2000. Soddy-Damy Tennessee 37379 June 24, 1999 TVA-SON-TS-99-06 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen:

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT (SQN) - UNITS 1 AND 2 - TECHNICAL SPECIFICATION (TS) CHANGE No. 99-06, " ADDITION OF SPARE INVERTERS TO THE ONSITE POWER DISTRIBUTION SYSTEMS REQUIREMENTS" l l

In accordance with the provisions of 10 CFR 50.4 and 50.90, TVA is submitting a request for an amendment to SON's Licenses DPR-77 and 79 to change the TSs for Units 1 and 2. The If proposed change provides an allowance to use a fully  !

qualified and tested spare inverter in place of any of the l eight required inverters. TVA is installing eight new i inverters and updating four of the current inverters to i provide a spare inverter for each of the four channels of vital instrument power. This change will add a footnote to ]

the requirements of Specifications 3.8.2.1 and 3.8.2.2 that describes the acceptability to utilize the spare inverters. 1 77 TVA has dete- ad that there are no significant hazards ,

considerat.' s. is

sciated with the proposed change and that l the change _ <' at from environmental review pursuant to

, the provisio. o' 10 CFR 51. 22 ( c) ( 9 ) . The SON Plant ]

Operations Re> Committee and the SQN Nuclear Safety Review i Board have rev swed this proposed change and determined that operation of 9906290161 990624 PDR ADOCK 05000327 P PD'A

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'U.S.: Nuclear. Regulatory Commission Page 2 June 24, 1999 SON. Units 1 and 2, in accordance with the proposed change, will not endanger the health and safety of the public.

Additionally, in accordance with,10 CFR 50. 91 (b) (1) , TVA is sending a copy of this letter to the Tennessee State Department of Public Health.

Enclosure 1 to this letter providesithe description and evaluation of the proposed change. This includes TVA's determination that the proposed change does not involve a significant hazards consideration, and is exempt from environmental review. Enclosure 2 contains copies of the appropriate TS pages from Units 1 and 2 marked up to show the j proposed change. Enclosure 3 forwards the revised TS pages for' Units 1 and 2 which' incorporate the proposed change.

- TVA plans to implement the modifications to the inverters in September 1999 and requires the approval and issuance of this amendment request to support these activities. Therefore, TVA' requests review and approval of the proposed TS change by September 1999, and that the revised TSs be made effective within 45 days of NRC approval. If you have any questions about this change, please telephone me at (423) 843-7170 or J. D. Smith at (423) 843-6672.

Sincerel ,

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Lice sin nd' Industry Affairs Manager Subscribed this'c N yd sworn

- day of t9-tpfore U/Mff, me

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AQ 41 Nota'rf 96blic l J.

My Commission Expires October 9, 2002 Enclosures l

cc: See page 3

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U.S. Nuclear Regulatory Commission Page 3 June 24, 1999-

'cc ~'(Enclosures) :

Mr. R. W. Hernan, Project Manager Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 Mr. Michael H. Mobley, Director (w/o Enclosures)

Division of Radiological Health Third Floor L&C Annex 401 Church Street Nashville, Tennessee 37243-1532 l

. NRC Resident Sequoyah Nuclear Plant 2600.Igou. Ferry Road Soddy-Daisy,. Tennessee 37384-2000

' Regional Administrator U.S. Nuclear. Regulatory Commission Region II Atlanta Federal Center  ;

61 Forsyth St., SW, Suite 23T85 ,

Atlanta, Georgia 30303-3415 h

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ENCLOSURE 1 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT (SQN)

UNITS 1 AND 2 DOCKET NOS. 327 AND 328 PROPOSED TECHNICAL SPECIFICATION (TS) CHANGE 99-06 DESCRIPTION AND EVALUATION OF THE PROPOSED CHANGE I. DESCRIPTION OF THE PROPOSED CHANGE TVA proposes t le addition of a new footnote to Specifications 3.8.2.1 and 3.8.2.2 for Units 1 and 2. This footnote atlows the substitution of the spare inverter of a specifiec channel as a replacement of one of the two required inverters of the same channel. The footnote applias to the limiting condition for operation associated with the 120-volt alternating current (VAC) vital instrument power board channels and the associated inverter requirements. The proposed package also contains typographical corrections for the existing footnote for Specification 3.8.2.1.

II. REASON FOR THE PROPOSED CHANGE TVA is proposing the above described changes to incorporate a design change that will provide a spare inverter for each of the four channels of 120-VAC vital instrument power board channels. The design change will upgrade the eight required inverters with new inverters that have additional capabilities and improved reliability. In addition, TVA will utilize four of the current inverters, after installing updated features, as spares for each of the required channels. The system will be designed such that each spare inverter can be aligned to provide the power requirements for one of the two associated 120-VAC vital instrument power board channels. The new footnote will allow TVA to utilize the spare inverters for maintenance or testing activities without having to rely on the TS action provisions and will provide improved safety function availability.

III. SAFETY ANALYSIS The SON vital ac and de control and instrument power system consists of four 125-V batteries, four battery chargers and eight 120-VAC inverters with their respective safety-related loads. TVA is adding four spare inverters that have the equivalent features and capability. The El-1 ,

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? I spare inverters will be designed to allow for manual replacement of one of the two inverters in the same channel. The 125-VDC distribution system is a safety-related system, which receives power from four independent battery chargers and four 125-VDC batteries and distributes it to safety-related loads of both units. The 120-VAC distribution system receives power from eight independent inverters and distributes it to the safety-related loads of both units. The inverters provide a source of 120-V, 60-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 (preferred power supply), or the station batteries which assure continued operation of instrumentation systems in the event of a station blackout.

The system incorporates features which serve to increase the overall reliability. Each channel has access to three power sources; a 480-VAC source, a 125-VDC 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-V shutdown boards. This source will provide a more stable and consistent voltage level for the 120-V vital instrument power boards when on the maintenance source. Each inverter has an auctioneered solid-state transfer switch between the 480-VAC and 125-VDC sources. Transfers between the output of the inverter and the 120-VAC maintenance supply is being modified to utilize a static switch that sill transfer loads automatically for a loss of inverter output. The new design will 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

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self-protection from load faults. The inverter and instrumentation power board are monitored to alert the i

operator of abnormalities. The eight inverters are located in the Auxiliary Building at Elevation 749. Channels I and II inverters are located in the Unit 1 area and Channels III and IV inverters are located in the Unit 2 area. Channels I and II inverters are separated from Channels III and IV inverters by reinforced concrete block wall, extending to the ceiling. Channel I and the Channel III inverters are separated from Channel II and Channel IV inverters, respectively, by a distance of about 60 feet.

The spare inverters will be located with the required inverters of the same channel.  !

l The normal supply of ac power to the distribution panels is from the inverter in each channel. The inverter consists of three major subassemblies: a de power supply, an auctioneering circuit, and an inverter circuit. The dc El-2

3 4 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 dc output of the auctioneering circuit is converted to ac by the inverting circuit.

J The modified system will meet or exceed these system features and capabilities. The addition of a regulated maintenance source and the automatic static switch provides l additional capability to provide reliable power to the vital instruments boards and minimize the potential for a unit trip. The regulated maintenance source will 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 will 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 will 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 automatically switch to a regulated maintenance power supply. This ability will improve unit operation and reliability when the spare is in service by providing a reliable source of power to the 120-V vital instrument power boards, in the event.of inverter failure. When the normal inverter is replaced by the spare all required safety functions will 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 will provide enhanced maintenance opportunities while providing an improved source of power to maintain required safety functions.

IV. NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION-TVA has concluded that operation of SON Units 1 and 2, in accordance with the proposed change to the technical specifications (TSs), does not involve a significant hazards consideration. TVA's conclusion is based on its evaluation, in accordance with 10 CFR 50.91(a) (1), of the three standards set forth in 10 CFR 50.92(c).

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r A. The proposed amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated.

The proposed changes to the onsite power distribution systems of the SQN TSs will not alter the safety function of the inverters or the 120-V vital instrument power boards. While additional automatic and manual transfer capabilities have been added, the function of the inverters will remain the same and'the availability of a spare inverter will provide improved capability to tolerate inverter failures and support maintenance activities. These improvements will reduce the potential for unit trips and required shutdowns as a result of inverter failures. The new design, along with the operating requirements, have been evaluated and determined to not present the potential to increase the probability of an accident.

In addition, the inverters and the associated 120-V vital instrument power boards are utilized to support instrumentation that monitor critical plant parameters to aid in the detection of accidents and to support the mitigation of accidents, but are not considered to be an initiator of a design basis accident.

Therefore, the probability of an accident is not increased by the proposed changes to the TSs and the potential for unit shutdowns will be minimized.

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The functions of the inverters remain the same based on the proposed change to the TSs. Other design changes, that are independent of the requested change, will improve the ability of the inverters to supply power for the identification and mitigation of accidents. Since the inverter functions and their operation will not be affected by the proposed TS change, the consequences of an accident will not be )

increased although the consequences should be further ,

minimized as a result of the inverter design changes. l B. The proposed amendment does not create the possibility of a new or different kind of accident from_any accident previously evaluated.

The inverters and the 120-V vital instrument power boards are not considered to be an initiator of a design basis accident. These features provide power to instrumentation that support the identification and mitigation of accidents as well as system control functions during normal plant operations. The functions of the inverters are not altered by the proposed TS change and will not create the possibility of a new or different accident.

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C. The proposed amendment does not involve a significant reduction in a margin of safety.

The plant setpoints and limits that are utilized to ensure safe operation and detect accident conditions are not. impacted by the proposed TS change. The inverters and 120-V vital instrument power boards will continue to provide reliable power to the safety-related instrumentation for the identification and mitigation of accidents and in support of plant operation. The ability to utilize spare inverters that can provide the desired level of redundancy will enhance the safety functions during periods of inverter maintenance or failure that would otherwise have to rely on a single power source without a backup source. Therefore, the margin of safety is not reduced based on the additional capability to utilize a spare inverter that enhances the level of safety without change to plant safety limits.

V. ENVIRONMENTAL IMPACT CONSIDERATION The proposed change does not involve a significant hazards consideration, a significant change in the types of or significant increase in the amounts of any effluents that may be released offsite, or a significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed change meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22 (c) (9) .

Therefore, pursuant to 10 CFR 51.22 (b), an environmental assessment of the proposed change is not required.

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