ML20085K147

Responds to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.' Control Room Indications Available to Alert Operator to Inoperability Affecting Dc Power Sys

ML20085K147
Person / Time
Site:	Seabrook
Issue date:	10/25/1991
From:	Feigenbaum T PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, NYN-91172, NUDOCS 9110300164
Download: ML20085K147 (9)

Text

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• I New Hampshire Ted C. Feigenbaum Yiln- e " ' " * " ' '"

Chief becutne Officer NYN 91172 October 25, 1991 United States Nuclear Regulatory Commission Washingten, D.C. 20555 Attentinn: Document Control Desk

References:

(a) Facility Operating License No NPF 86, Docket No. 50 4 83 (b) USNRC Generic Letter 91-06 dated April 29, 1991, Resolution of Generic issue A 30, ' Adequacy of Safety-Related DC Power Supplies,'

Pursuant to 10 CFR 50.54(f)"

Subject:

Respon e to Generic Letter 91-06 Gentlemen:

Generic Letter 91-06 requested information pursuant to 10 CFR 50,54(f) regarding safety-related DC power systems. In Enclosure 1 to this letter, New llampshire Yankee (N!!Y) provides the specific responses to the questions of Generic Letter 91-06 for Seabrook Station. Explanatory notes accompany the response to several questions.

The Seabrook St. tion Class IE Electrical System is divided into two load groups:

Train A and Train B. Either load group supplies all equipment necessary to safely shut down the reactor under any of the design bash, accident conditions analyzed in the Updated FSAR (UFSAR)c The safety-related DC power system for Seabrook Station, described in UFSAR Section 8.3.2.1, is an integral part of the Class 1E Electrical System . Each train en; ploys two battery banks, two battery chargers and two DC buses. Each ba:tery bank is normally connected to one vital DC bus and can also be simultaneously connected to the other vital DC bus in the same train. Each battery bank has the electrical capacity to handle the full 100 percent load requirements of both vital DC buses withir. its electrical Tr a in.- Therefore, each electrical Train, either A or B has the capability to be powered by a single battery bank. System design precludes any Train A battery, charger or DC bus from being cross. connected to its Train B counterpart.

Control Room indications and alarms are available to alert the operator to conditions of inoperability affecting the DC power system. Technical Specifications require both trains of the DC power system to be operable in Operational Modes 1 through 4 and one train to be operable in Modes 5 and 6. '

i 911Q,3,00lb4 9110 os ADOCK 0500 @- l New Hompshire Yonkee Division of Public Service Company of New Hampshire P.O. Box 300 = Seabrook, NH 03874 = Telephone (603) .t74-9521 f i} l

United States Regulatory. Commission October 25, 1991 Attcution: Document Control Desk Page two ,

New llampshire Yankee believes that at Seabrook Station, the DC power system design, the limitations of the Technical Specifications and the current level of maintenance and surveillance required by procedures ensures a high degree of availability of DC power to safety-related systems.

Should you have any questions on the above information or the specific responses to the Generic Letter 9106 questions set forth in Enclosure 1, please contact Mr. Geoffrey Kingston at (603) 474 9521 extension 3371.

Very truly yours, (pgl2 TH b Ted C. Feigenbaum Enclosure TCF:GK/ss STATE OF NEW ll AhlfSHIRE Rockingham, ss. October 25, 1991 Then personally appeared before me, the above-named Ted C, Feigenbaum, being duly sworn, did state that he _ is President & Chief Executive Officer of the New llampshire -

Yankee Division-of Public Service Company of New llampshire, that he is duly authorized

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. to execute and file _ the- foregoing information in the name and on the behalf of New Hampshire Yankee Division of the' Public Service Company and that the statements therein are true to the best of his knowledge and belief.

\ H$6'/ / N /'d

-Tracy AheCredico, Notary Public My Commission Expires: October 3,1995

4 United States Regulatory Commission October 25, 1991 Attention: Document Control Dest Page thace ec: Mr. Thomas 1. Martin Regional Administrator U. S Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 Mr. Gordon E. Edison, Sr. Project Manager Project Directorate 1-3 Division of Reactor Projects U.S. Nuclear Regulatory Commission Washington, DC 20555 Mr, Noel Dudley NRC Senior Resident luspector P.O.130x 1149 Seabrook, Nil 03874 c

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l New llampshire . Yankee October 25, 1991-

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, ENCLOSURE I TO NYN-91172 4 s

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RESPONSE TO TIIE OUESTIONS OF ENCL.OSURE 1 TO GENERIC 1.ETTER OJ-06 ,

GENERIC 1 ETTER '91-06 OUESTIONS: (NHY's answLrs are in bold typeface)

The following information is provided for the following unit and site:

1. Unit 1. Seabroot. Station.

2. a. The number of independent redundant divisions of Class IE or safety related de power for this plant is 2. (luclude any separate Class IE or safety-related de, such as any de dedicated to the diesel generators).

b. The number of functional safety-related divisions of de power necessary to attain safe shutdown for this unit is 1.

3. Does the co.strol room at this unit have the fo!!owing separate, independently annunciated alarms and indications for each division of de power?

i n. alarms

1. Battery disconnect or circuit breaker open? Yes.

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)? See Note 3.a.2.

3. de system ground? Yes.

4. de bus undervoltage? Yes.

5. 'dc bus overvoltage? Yest (See Note 3.a..y.

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6. Battery charger failure? Yes.

7. Battery discharge? Yes,

b. indications

1. Battery float charge current? Not (See Note 3.b.1).

2. Battery circuit output current? No; (See Note 3.h.2).

3. Battery discharge? Yes.

4.- Bus voltage? Yes.

c. Does the urait have written procedures for response to the above alarms and indications? Yes.

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4. Does this unit have indication of bypassed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from - 4

its de bus and the battery charger from its ac power source during maintenance or testing? No; (See Note 4).

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design features of the facility's safety related de systems. 'See note below. +

6, (1) llave you conducted a review of maintenance and testing activities to minimite the potential for human error causing more than one de division to be unavailable!

See Note 6 and (2) do plant procedures prohibit maintenance on redundant de divisions at the same time? No; (See Note 6).

If the facility Technical Specifications have provisions eq .ivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specifications for maintenance and surveillance, then question 7 may be skipped and a statement to that effect may be inserted here. See Note 7.

7. Are maintenance, surveillance and test procedures regarding station batteries conducted routinely at this plant? Specifically:

a. At least once per 7 days are the following verified to be within acceptable limits:

1. Pilot cell electrolyte level?

2. Specific gravity or charging current?

3. Float voltage?

4. Total bus voltage on float charge?

E - 5. - Physical condition of all cells?

b. At least once pu 92 days, or within 7 days after a battery discharge, overcharge, or if the pilot cell readings are outside the 7-day surveillance requirements are the following verified to be within acceptable limits:

1. Electrolyte level of each cell?

2. The average specific gravity of all cells?

lL 3. The specific gravity of each cell' L 4 'The average electrolyte temperature of a representative number of cells?

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i 5. The float voltage of each cell?

6. Visually inspect or measure resistance ok terminals and connectors (including the connectors at the de bus)?

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c. At least every 18 months are the following verified:

1. Low ' resistance of each connection (by test)? '

2. Physical condition of the battery?

3. Battery charger capability to deliver rated ampere output to the de bus?

4. The capability of the battery to deliver its design duty cycle to the dc.

bus?

5. Each individual cell voltage is within acceptable limits during the service test?

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test?

' c. At least annually, is the battery capacity verified .by performance discharge test, if the battery shows signs of degradation or has reached 85% of the expected service life? '

L8. Does this plant have operational features such that following loss of one safety related dc. power supply or bus:

a. Capability is maintained for ensuring continued and adequate reactor cooling?

Yes,

b. Reactor coolant system integrity and isolation capability are maintained? . Yes,

c. Operating procedures, instrumentation (including indicators and annunciators),

and control functions .are adequate.to initiate systems as required to maintain adequate core ; cooling? ' Yes.

9. If the answer to any part of question 6,7 ;or 8 is no, then provide your basis for not performing the ' maintenance, surveillance and test ptocedures described and/or the F

bases for not including the operational features cited. *See note' briow- .

• Note: For . questions involving supporting type information (question numbers 5 and 9)

.instead of developing and supplying the information in response to this letter, you may .

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. commit to further. evaluate the need for such provisions -during the performance of L your individual plant examination for severe accident vulnerabilities (IPE). If you

. select this~ option, you are required to:

(1) So state in response to these questions, and (2)- Commit to explicitly address questions 5 and 9 in your IPE submittal per the guidelines outlined in NUREG-1335 (Section 2.1.6, Subitem 7), " Individual Plant Examination: Submittal Guidance."

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E.ESPONSE TO GENERIC LETTER 9106 BDTES 3.a.2. Each battery charger has four circuit breakers associated with it: an internal and an external AC input circuit breaker plus an internal and an external DC output circuit breaker. An alarm is associated with the position of the external DC output circuit breaker. The position of the remaining three circuit breakers is not directly associated with an clarm, llowever, UFSAR Section 8.3.2.1.f. describes two alarms which indicate loss of AC input voltage to the charger and loss of DC output current from the charger. These alarms effectively monitor battery charger operability.

3.a.5. As described in UFSAR Section 8.3.2.1.f.5., the DC bus overvoltage alarm is provided by an overvoltage relay at the charger, 3.b 1. UFSAR Section 8.3.2.1.f.1 indicates that an ammeter is located in the Con %d imom and at the DC switchgear to indicate battery charge and discharge, '1 he Control Room ammeter does not have sufficient resolution to read battery float current because it is scaled to display discharge current which can be much higher than float current. .'A local, digital ammeter is provided with sufficient resolution to read normal float charging current, A loss of charging current alarm derived from this digital ammeter is available in the ' Control Room. Technical Specifications require -

verification of battery float charge at least every seven days during Operational Modes 1 through 4. The NRC has reviewed the Seabrook design as described in UFSaR Section 8.3.2.1 and found it acceptable as discussed in NUREG-0896, the Safety Evaluation Report for Seabrcok Station.

3.b.2. It is assumed that this question refers to battery charger output current. As described in UFSAR Section 8.3.2.1.f.2., an ammeter located at the charger provides indication of. battery charger output current. As described above in the Note to question No.

3 b.1., two alarms monitoring charger performance are provided in the Control Room:

- a loss of battery charging current alarm and a charger failure alarm. Charger output current is indicated locally. at the charger. The NRC has reviewed the Seabrook g design as described in UFSAR Section 8.3.2.1 and found-il acceptable av discussed in. NUREG 0896, the Safety Evaluation Report for Seabrook Station.

4, The position of the station battery output fuses and circuit breakers and the charger

AC input - and DC output circuit breakers are not direct inputs to the Bypass Indication . System described in UFSAR Sectior 7.1.2.6, These components are not '

included in the " bypassed and inoperable status" logic because maintenance and testing  !

affecting operability of the batteries and chargers are not expected to be. performed more than once per year. However,- the Bypass Indication System does monitor the availability of. DC control power to the systems listed ~ in UFSAR Section 7.1.2.6.

These systems are required to operate under accident conditions. Loss of DC control:

power to _a- Train of 'any of these systems will actuate the bypass alarm for that particular Train.

6. An evaluation performed in response to IE Bulletin No. 79-27-was described in the UFSAR in the response to RAI 420.50. This review focused on the manner in which electrical power systems could effect the ability to achieve cold shutdown. With 1

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' respect to Class 1B DC power systems, the review concluded that failure of any single bus will 'not-affect the ability to achieve a cold shutdown condition. This review did not' assess the potential for human error causing more than one Train of the' DC power system to be' unavailable.

Potential failure modes- of the DC power system were evaluated as part of the Individual Plant Examination for Severe Accident Vulacrability (IPE). The evaluation concluded that there was no credible, internal, common.cause failure mode affecting the Station batteries and bus work of the DC distribution system.

Technical Specifications require the operability of both Trains of the DC power system.

in Operetional Modes 1 through 4 and one Train in Modes 5 and 6. The concept that redundant Trains- of safety related equipment should not be simultaneously out of .

service (unless permitted by Technical Specifications) is so axiomatic that plant procedures do not specifically prohibit such action. The responsibility to ensure that

- equipment operability status meets Technical Specifications requirements rests with the l Shift Superintendent. Control Room indications and alarms provide equipment status i information' and reminders of out of-service conditions. Procedures provide guidance, specific instructions, notes and cautions supporting the goal of meeting Technical Specifications requirements. - For example, procedures for planning anct scheduling catablish a " system week". concept under which preventive maintenance and surveillance-testing 'is performed.on one designated-Train of safety telated equipment during a calendar week. .Under this concept, if a given week were designated for Train A work, the Shift Superintendent would question t.ny request to perform work on Train '

.B equipment. As anots example, a procedure defines a tracking system to be-used upon er.tering a Technical Specifications action statement. This tracking system can assist the Shiff Superintendent in maintaining cognizance of inoperable equipment and avoiding action . to render the redundant train inoperable. As a final example, procedures for-performing vital battery discharge tests include cautions referring to Technical Specifications to remind involved personnel to maintain the required number of operable DCfpower sources. ,

7. cSeabrook Station Technical Specifications are based on the Westinghouse Standard Technical Specifications. Therefore, as permitted by Generic Letter 91-06, the specific responses to Question No. 7 have been omittedc a

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