ML20085N754

Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.'

ML20085N754
Person / Time
Site:	Calvert Cliffs
Issue date:	11/08/1991
From:	Creel G BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, GL-91-6, NUDOCS 9111180123
Download: ML20085N754 (10)

Text

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BALTIMORE GAS AND ELECTRI CHARLES CENTER.

• P.O. BOX 1475

• BALTIMORE, MARYLAND 21203 1475 GEORGE C CnEEL vect Pwsotwf NUCLEAR int RGY (301) 260-4455 November 8,1991 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATI'ENTlON: Document Control Desk SUlHECT: Calver? Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Ncs. 50-317 & 50-318 Response to Generie Letter 91-06, Resolution of Generic issue A-30,

" Adequacy of Safety-Related DC Power 'lupplies " Pursuant to 10 CFR 50.54(h

REFERENCE:

(a) Letter from Mr. J. G. Partlow (NRC) to all lloiders of Operating Licenses, dated April 29,1991, same subject Gentlemen:

Generic Letter 91-06, Reference (a), addresses the resolution of Generic Issue A-30," Adequacy of Safety-Related DC Power Supplies" The specific area of concern in GI A-30 is the adequaev of safety-related DC power in operating the nuclear pow:r plant with regard to multiple and comrunn cause failures. Failure of the minimum DC power system could represent a significant contribution to the unreliability of shutdown cooling.

Reference (a) requests information pursuant to 10 CFR 50.54 (f) regarding the implementation of plant specific maintenance, surveillance, and monitoring provisions related to safety-related DC systems. Our written responses to the questions in Enclosure 1 of Generic Letter 9106 are provided in Attachment (1) to this letter. Attachment (2)is a single line diagram of the 125V DC system.

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l ' Document Control Desk Novemner 8,1991 Page 2 l

Should you have any further questions regarding this matter, we will be pleased to di.; cuss them with you.

Very truly yours, ,

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)( -l ) k 4%i foi e G. C. Cree:

Vice President - Nuclear Energy STATE OF MARYLAND :

TO WIT :

CITY OF BALTIMORE  :

. I hereby certify that on the 7 day of "///7&m /2ro 19_94 before me, the subscriber,

-a' Notary Public of the. State of h1aryland in and for /bn n < d a<,- /z/ (cwM, personally appeared G. Dowell Schwartz, Jr., being duly sworn, and states that he is Vice President.jf the Baltimore Gas and Electric Company, a corporation of the State of hiaryland; that he provides the foregoing response for the purposes therein set forth; that the statements made are true and correct to the best of his knowledge. information, and belief; and that he was authorized to provide the response on' behalf of said Corporation.

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WITNESS my lland and Notarial Scal: I'/(72u'IcrEA 'b< cdC .-

p / Ndtary Public hly Commission E' - ires: /C '//9V /bWr:/rt 7 , / 9 f/

Date' GCC/Lh1D/Imd/ dim Attachment cc: D. A~ Brune, Esquire J. E. Silberg, Esquire R. A. Capra, NRC D. G. hicDonald, Jr., NRC T.T htartin, NRC L E. Nicholson, NRC R. I. hicLean, DNR J. H. Walter, PSC

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A'ITACilMENT 1 IIAll!'IMORE t;AS & ELECTRIC COMPANY'S RESPONSES TO GENERIC 1.E'ITElt 9106 OUESTIONS SYSTEM DESCRIPTION The 125V DC power supply system at Calvert Cliffs is common to Units 1 and 2. As described in the Updated Final Safety Analysis Report (UFSAR), the DC power supply system is designed to provide

- uninterruptible power to the plant vital instrumentation and control systems. The system is designed in accordance with "IEEE Criteria for Class 1E Electric Systems for Nuclear Power Generating Stations," IEEE No. 308-1974.

The DC power supply system is comprised of four independent and redundant isolated channels, and a reserve 125V DC system. Each of the four channels consists of one battery, two battery chargers, a battery monitor, one DC bus, multiple DC unit control panels, and two inverters.

The reserve 125V DC system for the plant is completely independent and inlateo .;om the four separation groups, yet is capable of replacing any one of the 125V DC batteries. This system consists of one battery, one battery charger, one battery monitor, and the assoc.ated DC switching equipment.

There is one battery chara,er fed from Uni 1 and another battery charger fed from Unit 2 connected to each 125V DC bus. The reserve battery is connected to its own charger when it is not connected to a safety-related 125V DC bus.

Each of the four 125V DC power sources is equipped with the following instrumentation in the control room to enable continual c erator assessment of system status:

a. DC bus undervoltage alarm

b. Battery current indication

c. Charger current indication G. Charger malfunction alarm (includes input AC undervoltage, output DC undervohage, and output DC overvoltage)

e. DC bus voltage indication

f. DC ground indication In addition to the above instrumentation, continuous monitoring of the battery's connection to the

~ bus and of battery circuit continuity is provided.

REOUESTED ACTION Provide written responses to the questions in Enclosure 1 of the generic letter.

' OUI'STIONS AND llG&E RESPONSES

1. The plant name is Calvert Cliffs Nuclear Power Plant Units 1 aad 2 1

NITACIIMENT I IIAlli'IMOltE GAS & El.ECTitlC COMPANY'S HESPONSES TO GENEltlC 1,lslTEll 91-06 OUESTIONS

2. 'a. The number of independent redundant divisions of Class IE or safety-related DC power for this plant is fots (Include any separate Class 11: or safety-related DC, such as any DC dedicated to the diesel generators.)

b. The number of functional safety-related divisions of DC power necessary to attain safe shutdown for this unit is ihree. This assumes a single failure of any one division.

3. Does the control room at this unit have the following separate, independently annunciated '

alarms and indications for each division of DC power?

a. Alarms

1. Battery disconnect or circuit breaker apen? No. There are no separate alarms for each bus to indicate the battery disconnect is onen. Ilowever, there are separate battery monitors which provide a common open disconnect or circuit breaker alarm for batteries 11 and 12. There is a common battery monitor alarm for batteries 21. 22 and reserve batterv 01 also.

2. Battery charger disconnect or circuit breaker open (both input AC and output DC)? No. Thne are no separate alarms for each battery charcer disconnect or circuit breaker, llowever. a batterv charcer alarm will indicate an open input AC circuit breaker An alarm would be an indication for an open DC output only if one of the two chargers were aliened to the bus.

There is a common charger alann for charcers 11.12. 23 and 24. and one for charcers 01,13.14. 21 and 22,

3. DC system ground? No. There is only one continuous alarm for the DC cround system. This alarm is for DC buses 11 and 21 oniv. Additionally. all

-four buses have a manually operated cround detection s3 tem which is checked once ner shift by niant operators.

4. DC bus undervoltage? No. Ilowever, buses 11 and 12 have a common undervoltace alarm. There is also a common undervoltage alarm for buses 21,22 and reserve battery bus 01.

5. DC bus overvoltage? No. There are no separate alarms dedicated strictiv for pC bus overvoltacc. A DC but overvohace would cause the battery charcer to trip resultine in a battery charcer alarm. There is one battery charcer alarm for chargers 01.13.14. 21 and 22. and one battery charter alarm for chat eers 11.12,23 and 24.

6. Battery charger failure? No. There are two alarms: one for charcers 01,13.

14. 21 and 22. and one alarm for charcers 11.12. 23 and 24. This alatni would annunciate if the charcers have an undervollace on the input / output or an overvoltage on the output of the charter.

7. Battery discharge? No. There are no alarms for battery discharce. Battery monitor will alarm with DC bus undervoltacc.

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T 4 A'ITACilMENT I IIAlli'IMORE GAS & ELECTRIC COMPANY'S RESPONSES TO GENEltlC 1 FTTER 9106 OUESTIONS y

b. - Indications:

1. Battery float charge current? No. There is a current meter on the outnut of the battery which could be used for indication of float charge current.

1-lowever, the meter accuracy readine range is not small enouch to be able to read the float charce current value.

2. Battery circuit output current? Yes

3. Battery discharge? Yes

4. Bus voltage? Yes

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

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 its DC bus and the battery charger from its AC power source during maintenance or testing? No. There is no direct indication of bypassed circuit breakers or disconnect switches. However, an open circuit will be indicated by the battery monitor alarm (described in 3.a.Q

5. If the answer to any part of Questions 3 or 4 is no, then provide information justifying the existing design features of the facility's safety-related DC system.

The existine design features of the safetv-related DC system are consisient with the oricinal design requirements to which this system was built. The NRC has reviewed and approved this design as part of the licensine basis and modification 1have been implemented under the authority cranted by 10 CFR 50.59. The answers to Questions 3 and 4. with the exception of the overvoltace alarm m would all be ves if it were not for the stipulation of channel independence. The Calvert Cliffs control room alarms conform to IFEE-308-1974. as reviewed and annroved by NRC. IEEE-308-1974 does not require channelindependence for alarms. With the common alarm system installed at Calvert Cliffs, control room operators are promptiv alerted to faulted conditions. The operators can auickly diacnose the problem and

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Identify the affected channel by consultine tiie alarm manual and other indications in the control room, as descril,ed in Questions 3 and 4. above,

6. (1) Iw e jou conducted a review of maintenance and testi ; activities to minimize the potentitj .or human error causing more than one DC division to be unavailable? Yes and

-(2) do plant procedures prohibit maintenance or testing on redundant DC divisions at the same time? ' Yes. This is controlled by the limitine conditions for operation in the plant technical specifications. In fact Plant Operations does not allow even a r.:ncle division to be removed from service for testine or maintenance without substituting the reserve battery for ita 3

NITACllMENT I IIA!!!'IMOltE GAS & ELECTitlC COMPANYS RESPONSES TO GENEltlC LF'ITElt 9106 OUESTIONS If the facility Technical Specifications have provisions equivalent 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.

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 c!cctrolyte level? h

2. Specific gravity or charging current? h

3. Float voltage? h

4. Total bus voltage on float charge? Yes

5. Physicalcondition of allcells? Yes

b. At least once per 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? Yes

2. The average specific gravity of all cells? h

3. The specific gravity of each cell? Yes

4. The average electrolyte temperature of a representative number of cells?

Yes

5. The float vohage of each cell? Yes

6. Visually inspect or measure resistance of ternunals and connectors (including the connectors at the DC bus)? h

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

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

2. Physicalcondition of the battery? Yes

3. 13attery charger capability to deliver rated ampere output to the DC bus? h

4. The capability of the battery to deliver its design duty cycle to the DC bus?

Yes

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

Yes -

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NITACllMENT 1 IIAlli'IMOltE GAS & ELELTIllC d -MPANY'S ItESI'ONSES TO GENEltlC LE'ITElt 9. 36 OUESTIONS

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

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 expectea senice life?

g Yes 8.- Does this plant have operational icatures 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 c.;pability 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 Questions 6, 7 or 8 is no, then provide your basis for not performing the maintenance, survei!!ance and test procedures described and/or the bases for not including the operational features cited. N/A l-5

NI'l'ACilhlEN'I' 2 SINGLE 1,1NE DIAGRAM VITALS 120V AC & 125V DC EMEltGENCY 250V DC l

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