ML20058L215

Responds to NRC Re Unresolved Item Noted in Insp Repts 50-317/90-80 & 50-318/90-80.Corrective Action: Evaluation of Battery Charger Determined That Provisions Adequately Verify Requirements of Tech Spec 4.8.2.3.2

ML20058L215
Person / Time
Site:	Calvert Cliffs
Issue date:	07/27/1990
From:	Creel G BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9008070064
Download: ML20058L215 (4)

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., BALTIMORE l OAS AND I ELECTRIC ,

CHARLES CENTER e P.O. BOX '1475

• BALTIMORE. MARYLAND -212031475

. GroRot C. CREEL  !

vice Passiocar '

Nocttam Eugnov (300 teo mess I

July 27,1990 a E

i U. S. Nuclear Regulatory Commission Washington,DC 20555

. A'ITENTION: Document Control Desk t 4

SUIMECT: Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50 317 & 50-318  !

Battery Charger Testing Method r

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REFERENCES:

(a). Letter from Mr. M. W. Hodges'(NRC) to Mr. G. C. Creel (BG&E),

Maintenance Team Inspection Report No. 90-80, dated April 4,1990 (b)- Letter from Mr. G. C. Creel (BG&E) to NRC Document Control Desk, dated June 4,' 1990, Response to Maintenance Team Inspection '

Report Gentlemen:

During the NRC's recent Maintenance Team Inspection at Calvert Cliffs, our method of '

demonstrating compliance with the battery charger surveillance testing requirements of Technical Specification 4.8.2.3.2.c was questioned (Reference (a), page 35). This resulted in an unresolved item'(50-317/90-80-04 and 50-318/90-80 03) pending our demonstration to the NRC , Office of Nuclear. Reactor Regulation-(NRR) that the present testing method meets the intent of the Technical Specification.

In Reference (b) we indicated our intent to provide a written response to the unresolved item directly to NRR. This letter provides that response.

i STATEMENT OF UNRESOINED ITEM NO. 90 80 04/03 .i l

Technical Specification 4.8.2.3.2.c states:

l- - "At least once per 18 months, the battery charger shall be demonstrated capable of ,

! recharging the battery at a rate of,s,400 amperes while supplying normal de loads or l equivalent or greater dummy load."

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.. July 27,1990 Page 2 The NRC inspection team observed that after a return from a system blackout the battery charger would pick up the bus load, approximately 180 amperes, as an ins: ant load. The Surveillance Test L Procedure (STP) is written to apply the bus / load in a step profile which is not the same loading the ,

charger would see under actual conditions of return from a blackout.

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HG&E RESPONSE l We have performed an evaluation of the battery charger STP in view of the concern expressed in the unresolved item and have determined that the testing provisions of the STP adequately verify the operability requirements of Technical Specification 4.8.2.3.2.c, in that:

o The surveillance requirement is mainly concerned with returning a battery to se vice following testing, not an accident o The blackout . scenario postulated by the inspector is not required by technicalspecification bases; and i o in any case, the charger has inherent design capability to handle situations well beyond technical specification bases requirements.

l The purpose of the battery charger test performed under Technical Specification 4.8.2.3,2.e is to complement the battery service test performed under Technical Specification 4.8.2.3.2.d. During this l l test, the battery is demonstrated capable of supplying emergency loads for two hours. At the

" completion of this service test, the affected battery is substantially discharged ar.d, in effect, one of i the redundant DC power supplies has been rendered inoperable. As this is an undesirable condition i l'

during most operational modes, it is important to return the battery to full charge in a prompt and orderly fashion. Accordingly, this surveillance test also requires that the battery be recharged to at least 95% capacity in 5,24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

L The capability to accomplish this is provided by the battery chargers, as assured by periodic testing .l l=

under Technical Specification 4.8.2.3.2.e. Note that this surveillance requirement verifies the I capability to recharge the battery while supplying normal DC loads. This is a clear distinction from the test performed under Technical Specification 4.8.2.3.2.d to verify the battery's ability to supply emercency DC loads. Consequently, it is not the intent of Technical Specification 4.8.2.3.2.e to

l. verify the ability of the charger to supply emergency DC loads while recharging a battery. In l l '

addition, it is not necessary to demonstrate that large loads can be instantaneously accepted by the charger in the performance of its function of restoring a discharged t uery to operable status i l

following the twmhour service test. -l 1

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Document Control Dcsk July 27,1990

~ Page 3 Technical Specification Bases 3/4.8 states:

L"The ACTION requirements specified for the levels of degradation of the power sources provide restriction upon continued facility operation commensurate with the level of degradation. The OPERABILITY of the power sources are consistent with the initial condition assumptions of the accident analyses and are based upon maintaining at least one of each of the onsite A.C and D.C power sources and

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associated distribution systems OPERABLE during accident conditions coincident with an assumed loss of offsite power and single failure of the other onsite A.C source."

(emphasis added)

The capability to achieve and maintain safe shutdown is provided by one diesel generator operating in conjunction with a battery charger and a battery bank. Following an accident involving a concurrent k>ss of offsite power and the single failure of one of the emerg:-ncy onsite AC power sources, the station batteries would supply uninterrupted instrument AC power through the inverters while also carrying the loads on the DC bus. This will continue until the remaining emergency dicsci generator has started and is available to accept AC loads. At that time, the battery charger would be energized and would pick up the DC bus loads in parallel with the batteries while it recharged the batteries. The chargers are loaded onto the diesel generator on the first step of the load sequencer -

the charging load resulting from the battery would not be

-significant (about 10 seconds);

as compared consequently,h to that whic would exist following a station blackout. It is not neces the purposes of complying with the Technical Specification Surveillance Requirements to apply an instant load from a system returning from an extended blackout condition, s*nce the Technical Specification Bases do not presently consider station blackout as a design basis event (please note we are aware NRC staff is developing new technical specifications and associated surveillance requirements for station blackout mitigation and/or recovery).

The issue of technical pecification compliance aside,we reviewed the technical characteristics of the battery chargers (Exido Filtered Constant Voltage Float Charger Model UPC 130 3 400) to evaluate their actual design cr.pabilities. We have determined that the charger design provides substantial inherent capability to accommodate charging and system loads under many postulated situations, including recovery from an extended station blackout. ' the chargers come equipped with a DC output

' time delay circuit and a load limiter. The output time delay circuit prevents full charger output for -

20-30 seconds. After this initial delay, the total charger output is restricted by the load limiter to 110% of charger current rating, the exact value being dependent on load and battery condition. The Exide vendor manual specifically states:

"In the event of an AC outage, the battery is most often in a state of discharge, when AC power is restored. The current limit circuitry will prevent heavy AC current overload with subsequent AC breaker tripping. In more precise terms, this means that a fully discharged battery can be put on the charger without the inconvenience of.

the high current demand exceeding the charger rating and tripping the breaker."

In summary, the battery charger surveillance test procedure adequately verifies that the chargers will be capable recharging the batteries while supplying the normal bus loads following battery testing and during the accident conditions described in the Technical Specification Bases.

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~3N We trust the above information adequately resolves this issue. Should you have any questions, please do not hesitate to contact us.

D. .; Very truly yours,

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GCC/BSM/ dim

[ cc: D. A. Brune, Esquire  ;

J. E. Silberg, Esquire .

R. A. Capra, NRC r D. G. Mcdonald,'Jr., NRC T. T. Martin, NRC L E. Nicholson, NRC R. I. McLean, DNR a

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