ML20113G199

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

ML20113G199
Person / Time
Site:	Wolf Creek
Issue date:	10/28/1991
From:	Rhodes F WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR ET-91-0202, ET-91-202, GL-91-06, GL-91-6, NUDOCS 9111040221
Download: ML20113G199 (7)

Text

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• i LF CREEK W@ NUCLEAR OPERATING C:

Fotrtist T Hhodes Yg.e bevocol t estrieering & les brutal hee.ges October 28. 1991 ET 91-0202  :

U. S. Nuclear Regulatory Commission ATTN Document Control Desk Hail Station Pi-137 Washington, D. C. 20555 Subjects Docket No. 50-482: Response to Generic Letter 91-06 Gentlemens The purpose'of this letter is to provide Wolf Creek Huclear Operating Corporation's response to information requested in Generic Letter 91-06

' Resolution of Generic Issue A-30 ' Adequacy of Safety-Related DC Power l Supplies.' Pursuant to 10 CF' 50.54(f).' The Generic Letter requests {

information to determine if plant specific maintenance, surveillanco and monitoring provisions are appropriate and that these provisions have been ,

implemented. Enclosure 1 from the Generic Letter has been utilized. In i accordance eith the instructions provided, and is provided as an attachment to this letter.

Based on our responses to these questions, no further action is required to resolve Generic Issue A-30 at the Wolf Creek Generating Station. [

i If you have any questions, please contact me or Mr. T. E.'Cribbe of my staff. _

)

Very truly yours.

w /

Forrest T.-Rhodes .

Vice President '

Engineering & Technical Services

, FTR/aem-Attachment i

cca L. L. Gundrum (NRC), w/a A. T. Howell-(NRC) w/a R. D. Martin (NRC), w/a W. D. Reckley (NRC). w/a g T 1

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STATE OF KANSAS )

) SS COUNTY OF COFFEY )

Forrest T. Rhodes, of lawful age, being first duly sworn upon oath says that he is Vice President Engineering and Technical Services of Wolf Creek

!!uclear Operating Corporations that ne has read the forego:.ng document and knows the content thereof: that he has executed that same for and on behalf of said Co.poration with full power and authority to do aos and that the facts therein stated are true and correct to the boet of his knowledge, iniormat*.on and belief.

w] [ d Forrest T. Rhodes Vice President Engineering & Technical Services SUBSCRIBED and swarn to before me this 2 [ day of [f[. , 1991.

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. 1 At,tactpent to E1 91-0202

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(~ hcl O W RI 1 it. CIR t0.54(f) Of 00iSi GtNi kiC 155Uf (GI) A-30 "ADiquACY Of W fly-PftAliD DC POWIR SUPPL 115" E8C}fpund The specific area of concern of Gl A-30

• Adequacy of Safety-Related DC power Supplies

• is the adequacy of the safety-related dc power in operating nuclea power plants, particularly with regard to multiple and comon cause f ailures.

Risk analysis and past plant experience support conclusions that f ailure of the de power supplies could represent a significant contribution to the unreliability of shutdown cooling. Analysis indicates that inadequate maintenance and surveillance and failure to detect battery unavailability are the prime contributors to failure of the dc power systems.

During the development of plans to resolve G1 A-30, it was observed tnt several previously issued regulatory notices (IL4s), bulletins (IEus) and letters (GLs) submitted to licensees include reconomndations similar to those that have been identified to resolve G1 A-30. More specifically,_it has been determined that recomendations contained in notifications IEN 85-74, " Station Battery problems",- 1[Il 79-27, "Less of Non-Chss 1E Instrumentation ard Control power System Bus during Operation," and separate actions being taken to resolve GI 49, " Interlocks and LCOs for Class 1E Tie Dreakers" include the elements necessary to resolve G1 A-30. It is therefore concluded that icensees that

-have implenented these recommendations and actions will have resolved G1 A-30.

The response to the questions that follow is necessary to provide the staf f with information to determine whether any further action is required for your facility.

Questions The following information is to be provided for each unit at each site:  !

1. Uni t _Wo1LCreeL______

2. a. The number of independent redundant divisions of Class 1E or safety-related de power for this plant is tw . (include any separate Claas ![ or safety-relatedTc';pEu W as any dc dedicated to the diesel <.enerators.)

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b. The number of ft.ictional safety-related divisions of dc power '

necessary to attain safe shutdown for this unit is __o_qt_,_.

3. Does the control room at this unit have the follewing separate, independently anriunciated alarms and indications for each division of dc power?

a. alarms

1. Battery disconnect or circuit breaker open? __Seelage _5 _

?. Battery charger disconnect or circuit breater open (both input at and output de)? See page 5

Attachment to El 91-0202

. P' age 2 of 5 p.

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3. dc system ground? _50e_p;agqj _ l

4. dc bus undervoltauc? See [ggq_5

5. dc bus overvoltage? Seepagel

6. Batterv charger failure? Seejagel

7. Bettery discharge? Jeggage_5,,,

b. Indications

1. Battery float charge current? Jee Jiage 5_

2. Battery circuit output current? See paqe_5

3. Battery discharge? See page 5

4. Bus voltage? _S_e_elaae_5_

c. Does the unit have written procedures for response to the above alarms and indications? See_page ,5

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 f ron its ac power source during maintenance or testing? Yes

5. If the answer to any part of question 3 or 4 is no,' then provide informatior, justifying the existing design fee' of the facility's safety-related dc systems. *See note below.

6. (1) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one dc division to be unavailable? Yes and (2) do plant procedures prohibit maintenance or testiii^gTn~ii~dundant de divisions at the same time?

_Yes If the facility Technical Specifications have provisions equivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specifications for maintenance and survetilance, then question 7 may be skipped and a statement to that effect may be inserted here. Wo_lLCreek _Technj_caj_SpecjfjiS3tions have provisions equivalent to Westinghouse standard technical specifications

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? ___

1

Attacijment to ET 91 0202 Page 3 of 5 2. $pecific gravity or charging current?

3. Float soltage?

4 Total bus voltage on float charge?

5. Physical condition of all cells?

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

1. Electrolyte level of each cell?

2. The average specific gravity of all cells? _

3. The specific gravity of each cell?

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

5. The flohl voltage of each cell?

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

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

1. l.ow 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 de 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? _

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs _ of- degradation or has reached 851 of the expected service life?

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Attachment to,ET 91-0202 Page 4 of 5 4,

8. Does this plant have operationil features such inat followir,g loss of one safety-related dc pcwer supply or bus:

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

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

Ye r, c, Operating precedures, 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 s oJr basis for not performing the maintenance, surveillance and test procedures described and/or the bases for not including the operational features cited. *See note below.

• Note: For questions involving supportinc type information (question numbers 5 and 9) instead of developing and supplying the informatlun in response to this letter, you may commit to further evaluate the need for such provisions during the performance of your individual plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required to:

'(1) 10 state in response to these questions, and (2) Commit to-explicitly address questions 5 and 9 in your IPE submittal cor the guidelines outlined in NUkEG-1335 (Section 2.1.6, Subitem 7),

" Individual Plant Examination: Submittal Guidance."

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Attachment to ET 91-0202 Page 5 ot 5 Lips.3a Wolf Creek Generating Station (WCGS) has two separate and independent divisions of safety related DC power each with two separate and independent DC systems consisting of a battery and charger. The Main Control Board (MCB) does not have a separate and independent annunciator for each of the alarms listed for each division of safety related power. However, WCCS has a espurate and independent annunciator (annunciatoro 25C, 260, 27C and 28C) for -

each safety related DC source. These are generic trouble annunciators that indi ste that there is an abnormal condition associated with the respective saf ety related battery or charger. Once the annunciator alarms, the control room operator would dispatch a Nuclear Station Operator to that particular DC syste.n to determine the actual problem. At the DC bus distribution panel, there are a group of individual annunciators for each safety related DC system ta whleh the operator would respond with the appropriate approved procedure.

71e local annunciators agree with the list provided in Item 3a of the Generis Letter with tna axception of " Battery Discharge." However, using a ecmbination of annunciators, MCB indication, and local indication, this condition can be easil/ determined.

in addition to the loca?. annunciators, the Nuclear Plant Information System (NPIS) computer will automatically display certain alarm conditions on the alarm CRT so that the control room operators would have an immediate indication of the problem on the affected DC system. Also, the HCB has ona annunciator which is commo.) to all four safety related battery rooms and is able to indicate a high hydrogen concentration in the battery room.

WCGS does not have separate MCB annunciation, however, there are separata and independent local annunciators for each safety related bus for these conditions. With the local annunciation, individual MCB trouble alarm, HCB indication, and the aid of the NPIS computer, the control room operators are able to adequately mor.itor the candition of the catet y related batteries and chargers.

Itee 3b The MCB has three (3) aeparate meter indications for each safety related DC source. These are battory DC volts, charger amps, and battery amps

(+ o~ -h. From these three indicators, toere is indication of float current, battery output current, battery discharge, 2nd bus voltage.

1, tag _Jf; WCGS has writt6n proceduros for reoponding to each local annunciator alarm and procedures f or ths MCB trouble alarms and Battery Room H2 Hi Alarm.

There la also an offnormal procedare, OFN 00-0020, " Loss of Vital 125VDC Bus NK01, NKO2, NK03, NK94" and OFN 00-021 " Loss of Vital 220VAC Inutrument Bus".

These procedures give guidance to the operators in the case that a vital bus f ailta. In the emergency condition of loss of all AC power, WCGS has a contingency procedure C-0, that has a step and an attachment as to which DC loads may be isolated to reduce the amp /hr discharge rate.

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