ML20092B964

Responds to Generic Ltr 91-11, Resolution of Generic Issues 48, 'Lcos for Class 1E Vital Instrument Buses' & 49, 'Interlocks & LCOs for Class 1E Tie Breakers.'

ML20092B964
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	02/06/1992
From:	Pelletier J VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-048, REF-GTECI-049, REF-GTECI-NI, TASK-048, TASK-049, TASK-48, TASK-49, TASK-OR BVY-92-10, GL-91-11, NUDOCS 9202110201
Download: ML20092B964 (4)

Text

VEllhiONT YANKlil?

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7syy February 6,1992 BVY 9210 United States Nuclear Ro0ulatory Commisslor.

Attention: Document Control Desk Washington, DC 20555

References:

a) License No. DPR 28 (Docket No 50 271) b) Letter, USNRC to all Licensees, (NVY 91 137), dated July 18,1991; Generic Letter 9111, Resolution of Generic issues 48, "LCOs for Class 1E Vital Instrument Buses" and 49, " Interlocks and LCOs for Class 1E Tio Breakers"

Subject:

Response to Generic Letter 9111, Resolution of Generic issues 48, "LCOs for Class 1E vital Instrument Buses" and 49,

" Interlocks and LCOs for Class 1E Tio Breakers"

Dear Sir:

The following information is provided in responso to Generic issuo 48, "LCOs for Class 1E VitalInstrument Buses" and Generic lasuo 49, " Interlocks and LCOs for Class 1E Tio Breakers," Reference b). These generic safety issues raise concerns over the operation of the Class 1E 120V oc vitalinstrument busos and the Class 1E tio breakers at some nuclear power plants. The NRC staff identified conditions that indicate that the licensees at some plants may be violating the single failure criterion for a substantial period by lining up vital buses to alternato sources and by maintaining tle breakers closed 'or excessive times. The primary objectivo of the generic issues are to verify that plants are not being operated in violation of appilcablo regulations.

The generic letter concludes that, unless licensees provide adequate justification that such provisions are not needed, aill!censees should have appropriato procedures that include timo limitations and surveillanco requirements for:

1) Vital instrument buses (typleally 120V ac buses),

2) Inverters or other on sito power sources to the vital instrument busos, and

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i VERMONT YANKCC NUCLE AR POWER CORPOR ATION United Statos Nuclear Regulatory Commission February 6,1992 Pago 2

3) Tio breakers that can connect rodundant Class 1E buses (ac or de) at ono unit or that can connect Class 1E buses between units at the same sito.

The following discussion describes how Vermont Yankoo addressos the concerns of the generic lotter. The concerns are addressed onnor by dolormining that Vermont Yankee has the required timo limitations and surveillanco incorporated into tholt existing procedures; or that justification exists that such provisions are not neodod.

Qtnotic_ Issue 48 Generic Issuo 48, "LCOs for Class 1E Vitalinstrument Buses," raised concerns over the operation of no vitalinstrument buses. The "vitalinstrument busos" described in the generic Issue are the ac buses that provido power for the Instrumentation and controls of the engineered safety features (ESP) systems and the teactor protection system (RPS) which are designed to provide continuous power during postulated events including the loss of normal off sito power. The NRC found that some operating nuclear power plants do not have any administrativo controls governing operational restrictions for their 120V ac vital instrument buses and associated inverters.-

The 120V ac buses at Vermont Yankee that were reviewed for applicability to this generic issue are the 120/240V Uninterruptible (Vital) AC Distribution Panel (" vital bus"), the 120/240V AC Instrumentation Distribution Panel (" Instrument bus"), the RPS Bus A and the RPS Bus B.

The original design basis of the " vital bus" at Vermont Yankoo was to provide uninterruptibio power for non safetyloads such as the station computer and feedwater system controls. An alternate supply Is available from a diesel generator backed bus, in addition to the non safety loads which require an uninterruptible supply, certain Safety Class Electricalloads are connected to the " vital bus" at Vermont Yankee. The Safety Class Electricalloads can withstand the interruption of power associated with the time necessary for tha start of the diesel generator. Because the Safety Class loads can be interrupted for the timo necessary to start the diesel generator during a loss of off site power, the requirement for a time limitation on use of the alternate supply for the " vital bus" is not applicable to Vermont Yankeo.

The'" Instrument bus" at Vermont Yankeo is not provided with any uninterruptible power but is connected to buses provided with power from the diesel generators.

Generic Issue 48 is not applicable to these buses because they do not meet the definition of " vital instrument buses" provided in the safety issue.

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United States Nuclear Regulatory Cor ilselon February 6,1992 Page 3 The RPS busos are designed to provido power to RPS loads during reactor operation but the busos are designed to " fall safe" under loss of power. In addition the design of the RPS buses at Vermont Yankoo is such that only ono RPS bus can be connected to its alternato source of power at one time. Thus the concerns of Generic Issuo 48 do not apply to the RPS busos at Vermont Yankoe.

G9MLS_l1WD i 4R Generic issuo 49, " Interlocks and LCOs for Class 1E Tio Breakers," was writton to assure that licensoos have procedures which provido administrativo controls and time limitations on the use of tio breakers which connect redundant omorgency power systems tegother. These restrictions are necessary to assure the plants are operating within tholt design basis.

The breakers at Vermont Yankoo that woro dolormined to be applicable to this genoric issue are Breakers 3V and 4V in the 4 kV system, Breakers BT9 and 9T8 in tho 480 Volt system and the breakers between buses DC 1 and DC 2 in the 125V de system, in the 4 (V system at Vermont Yankoo there are two manual breakors,3V and 4V, which are normally used only to connect olther of the two redundant safety class electrical busos to the Vernon Hydroelectric Station in the unlikely event of a loss of off sito power and failure of one or both diosol generators, Interlocks provent the connection of Vernon Hydroelectric Station to both 4 kV buses simultaneously. A review of the 4 kV circuitry has dolormined that interlocks would not provent the operators from closing breakers 3V and 4V during a beyond design basis event. The control circuitry permits closure of the breakers if closure occurs in the proper sequenco with one 4 kV bus dead. Plant procedures do not provido for uso of this connection. Wo believe that the concerns of Generic issuo 49 are addressed because plant procedures do not provido for simultaneous closure of those breakers at all, thus providing administrativo control and a time limit on their uso; and interlocks provent the breakers from being closed unless an emergency bus is dead, thus providing assurance that the breakers cannot be Inadvertently closed.

In the 480V system, tio breakers 8T9 and 9TP can connect the two redundant safety busos, Bus 8 and Bus 9. Those breakers are normally left opon; however they can be

. closed during refuelin0 outages for equipment maintonance, testing and inspection.

The surveillance required for monitoring status of breakers 8T9 and 9T8 is provided by plant procedure AP 0155, " Current Valvo and Breaker Lineup and Identification."

Time limilations exist which govern the closure of theso breakers during reactor power operation. The time limitations applicable to these breakers are the Technical Specificatlor. t!mo limits associated with operation with inoperable buses as described in T.S.3.10 B.1 and T.S.3.5.H.1, t i

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VERMONT YANKEE NUCLEAR POWCR CORPORATION United States Nuclear Regulatory Commission February 6,1992 Page 4 in the 125V DC system, Bus DC 1 and DC 2 can be connected together by closing two breakers. Under normal operation the breakers are left open. The breakers are currently used only when it is necessary to feed one of the de buses from the spare battery charg]r, Charger CAB, which is connected between the two breakers. Only one breaker is closed to connect the charger. Operating procedures currently prevent closing both breakers at the same time; thus, the two systems remain independent at all times. Vermont Yankee is currently revising its operating procedures to permit closure of both breakers during cold shutdown. This change will provide a connection

- from the battery of the opposite redundant division during battery discharge testing.

The surveillance required for monitoring status of the de tie breakers is provided by plant procedure AP 0155, " Current Valve and Breaker Lineup and Identification."

Time limitations exist which govern the closure of these breakers during reactor power operation. The time llmitations applicable to these breakers are the Technical Specification time limits associated with operation with inoperable buses as described in T.S.3.10.B.2 and T.S.3.5.H.

We trust that the information supplied above is satisfactory in answering the concerns raised in subject generic letter. Should you have any questions .r require additional information, please do not hesitate to contact us.

Very truly youcs, Vermont Yankee Nuclear Power Corporation ral $

ames P. Pelletier Vice President - Engineering cc: USNRC, egion I Administrator USNRC Resident inspector - VYNPS USNRC Project Manager - VYNPS STATE OF VERMONT )

)ss WINDHAM COUNTY )

Then personally appA J befc e me, James P. Pelletier, who, being duly Swe'n, did state that he e 'l Engineering of Vormont Yankee Nuclear Power Corporation, that he is duly authorized to execute

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file rggcr document in the name and on the behalf of Vermont Yankee Nuclear Power Corporation, and that sthwents t Mpe true to the best of his knowledge f/id belief, y

.{ G die N WASb Gina M. Fontaine. Notary Public My Commission expires February 10, Irl95 4 b OTARY 1

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