ML20085L525

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

ML20085L525
Person / Time
Site:	Point Beach
Issue date:	10/28/1991
From:	Zach J WISCONSIN ELECTRIC POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-91-124, REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, GL-91-6, VPNPD-91-375, NUDOCS 9111040204
Download: ML20085L525 (12)

Text

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e Wisconsin Electnc POWER COMPMN m w Mc89voc occ4suvur-auntit mumi ne VPNPD 37 5 NRC 12 4 October 28, 1991 Document Control Desk U. S. NUCLEAR REGULATORY COMMISSION Mail _ station Pi-137 Washington, DC 20555 Gentlemen:

DQCKET NOS. 50-266 AND 5.9.1.q1 lifffQllSE TO GIHERLCJETTER 91-D1 AD10UACY OP_ SAFETY-REIATED _ DC POliER SUPPLIES POINT ltFACH NUCLEh8 PLAllTm UNITS 1 k_2 NRP Generic Lotter (GL) 91-06, dated April 29, 1991, requested that licenuces answer a series of questions regarding the adequacy of nafety-related do power supplies. An enclosure to GL 91-06 listed the specific questions to which we were to respond. Attachment 1 to'this letter provides our response to al? questions that were included in the enclosure to GL 91-06.

Please contact us if you have any questions concerning the information provided in this response. _

Veryqtruly yours, /

% No "

Jamt . J.=Zach Vico President Nuclear Power Copy to: NRC Resident Inspector NRC Regional Administratou Subscribed and sworn to before me this2v0 day of /A\ ybc . , 1991.

.t at w / k rs -t t+a

_ Notary Public, StatY of Wisconsin

'My Commission expires G - 2 ? '/ Z.  :-.

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ATTACHMENLA The following information, regarding the adequacy of cafety-related de power nupplien at Point Beach Nuclear Plant, Unita 1 and 2, is provided in renponre to Generic 1,etter (Gb) 91-06. GI, 91-06 requented that licensees renpond to a serien of questions that were provided an Enclosure 1 to the generic letter. Our renponne to each of the subject quentionn in detailed below.

Figures 8.2.8, 8.2.9, 8.2.10, and 8.2.11 in the Point Beach Pinal Safety Analynis Report (PSAR) are electrical schematica of point Beach electrical syntems. These figuren uhould be consulted to provido a description of the basic de syntom configuration.

1. U n i t s .L.o n(LL ._l'pj nt_hcAch_ N y tlea r_l'liu1L t

2. a. The number of independent redundant divisions of Class 1E or safety-related de power for the plant, is t w o_,_

Two battery buses are used to supply each of the two safety-related dc power divisions. The iirot division of dc power, which in designated "A" train, in aupplied by station battery busco D01 and D03. The redundant division of de poser, which in designated "B" train, in powered by station battery busen 002 and D04. *l t ene redundant divisions of de power are independent.

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

3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division of de power?

The below linted annunciatora provide indications in the control room for the name de power train from which they are powered, no the annunciatorn are not independently energized. Consequently, upon loan of an entire de power train all unnunciators anuociated with that train Will also lose power. Each train, however, han an independent lous of power annunciator that la powered by 120V ac power. This design war established to provide independence of the de bunen and to ensure that the loss of power to one de train would not affect the operation of the second de train.

a. alarms

1. Dattery dinconnect or circuit breaker open? _.yepu Two train specific annunciatorn are provided in the control room to alarm when their annociated

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battery breakern open. One annunciator nerven the "A" train battery breakern (for batterieu DOS and D105) and the necond annunciator serven the "h" train battery breakern (for batterien D06 and D106). Upon receipt of the annunciator alarm, the operator must check the control room battery breaker statun 11ghts to determine which breaker han opened.

2. Dattery charger disconnect or circuit broaker open (both input ac and output dc)? ,_ _H h _

The position of the ac input breaker to the battery charger is not monitored by an annunciator circuit. Instead, an undervoltage sensor on the ac input to each battery charger will canno the renpective battery charger trouble annunciator to alarm when the ac input power in lont. The ac undervoltage coil will adequately alert the operator upon the lona of ac power into the charger.

The battery charger de output breakern, which are installed within the battery charger cabinet, have contactn installed that will cauno the battery charger trouble annunciator to alarm woon tlm breaker openn.

A neparate breaker in installed in serien in between each battery charger de output breaker and its renpoetive de bus. These breakern are located in the anccciated de bun cabineta (D01, D02, D03, and D04). There are no alatms annociated with thene breakern. In the control r o o ") , however, there in currently breaker position indication for the de input breakers to the D03 and D04 bunen.

Additionally, au part of our de syntem upgrado, which will involve the addition of a nafety-related swing battery, we are planning to install control room breaker position indication for the de input breakers to the D01 and D02 banon. This modification in scheduled to be completed in mid-1993.

3. DC system ground? _,_Yres _

A de ground will cause the battery charger trouble annunciator to alarm. Because the de ground detection cir.:uitry in an integral part of the battery charger circuitry, the ground detector in available only when the battery charger in on line. We believe that this ground detection

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capability is adequate because the de buses are normally energized by a battery charger at all times.

4. DC bus undervoltage? Yes.

Two annunciators are provided for de system

> undervoltage. One serves the "A" train (D01 and D03 buses), and tne other serves "B" train (D02 and D04 buses). Upon receipt of the alarm, the operator must use the associated control room bus voltmeters to determine which bus has the low voltage condition.

The D03 and 004 dc bus undervoltage coils sense voltage dire .ly on the D03 and D04 buses, respeccively.

The D01 and D02 de bus voltage is sensed by undervoltage coils that are on the D11 and D13 buses, respectively. Because D11 and D13 buses are energized by the D01 and D02 buses, respectively, we believe that this undervoltage annunciation is adequate for the D01 and D02 buses. We are, however, currently investigating the feasibility of installing control room undervoltage annunciators that sense voltage directly on the D01 and D02 buses.

5. DC bus overvoltage? Yes.

Two annunciators are provided for de system overvoltage. One serves the "A" train (D01 and D03 busea), and the other serves "B" train (D02 -

and 004 buses). Upon receipt of the alarm, the operator must use the associated control room bus voltmeters to determine whir aus has the overvoltage condition.

The D03 and D04 de bus overvoltage coils sense voltage directly on the D03 and D04 buses, respectively.

The D01 and D02 dc bus voltage is sensed by overvoltage coils that are on the D11 and D13 buses, respectively. Because D11 and D13 buses are energized by the D01 and D02 buses, respectively, we believe that this overvoltage annunciation is adequate for the D01 and D02

buses. We are, however, currently investigating the feasibility of installing cont rol room overvoltage nnnunciatora that nrna voltage directly on 1.he n01 a C D02 bus s

6. Battery charger failuro? Ves.

?. Dattery discharge?  !{g, No battery discharge annunciators are installed.

A charge / discharge ammeter, however, is installed in the control room for each battery. This meter -

will indicate a discharge when the battery in nupplying its respective bun.

If the bette.y charger doea fall, resulting in a battery dicchargo, the operator will normally be alerted by the battery charger troubic annunciator. Additionally, the de bun undervoltage annunciators are set to alarm at a voltage slightly below the normal f' oat voltage of -

the charger / battery. Consequently, the de bus undervoltage annunciator will alarm shortly after its respective battery begins to discharge. The battery charger output voltage le normally set at approximately 134 volta. The D01 and D02 undervoltage annunciator alarma at 128 volto and the D03 and LO4 undervoltage annunciator alarms at 131 volts.

b. Indications

1. Battery float charge current? Yng.

This battery charge / discharge ammeter is a wide range meter that shows the current flow into or out of the battery. While the battery la on a float, the meter will indicate a smal) current flow into the battery. The meter, however, is calibrated and scaled for the large discharge currents that would be expacted if the charger failed and the battery was supplying all of the de loads. Consequently, because the scale on the charging side of the meter is so Inrgo, operators are unable to quantitatively measure the magnitude of the relatively small charging currents.

Nonetheless, the small deflection of the meter is adequate to allow operators to qualitatively determine whether or not the battery is on a floot.

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We do not maint ain battery floatn by establinhing a specific float current. Inntead, our battery floatn are entablinhed by maintaining a specific battery charger or.tput voltage. To maintain the proper float current, the charger output voltage in readjusted monthly baned on the temperature of the pilot cell.

2. TVIary circuit output current? Y e p.,

An doneribed in question 3.b.1 above, a battery charyo/ discharge meter in provided in the control room. This meter will give an accurate indication of the battery bun current if the battery in supplying power to the de bus.

3. Dattery discharge? _ _Yenn_._

An doncribed in quention 3.b.1 above, a battery charge /dincharge ammeter in provided in the control room.

4. Dus voltage? Yea, The D03 and D04 bunen have voltmetern located in the control room that nenne voltage directly on the respective bunen.

The D01 and D02 bunen do not have voltmeters that sense voltage directly from the respective bunen.

Instead, voltmeters are provided in the control room for the D11 and D13 bunen, which are supplied by the D01 and D02 bunen respectivolv. If the input breakern to the D11 or D13 b s are opened, voltage indication for the respe- '

c.ource bun will be loc.t. Nonethclenn, the

• 4 .m' D13 voltmetern provide an accurate c w.lon of the voltagen on the D01 and D02 bunen .aapectively.

We are, however, currently investigating the fennibility o; installing control room overvoltage annunciatorn that nenne voltage directly on the D01 and D02 bunen.

c. Does the unit have written procedures for renponso to the above alarms and indications? Yes2 The Alarm Response Book describen the renponse to individual annunciators and refern operatorn to the atpropriate proceduren. Although no proceduren are written specifically for the above mentioned indicationn, abnormalition in these indicationn are adequately addrenced in our operation and maintenance proceduren.

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4. 'Does the 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 do bus and the battery charger from its ac power source during maintenance or testing? Yes The battery breakers have position indications in the control room, opening the de output breakers of the battery charger will cause the battery charger trouble annunciator to alarm. As described in question 3.a.2 above, opening the ac input breaker to the charger will cause the battery charger trouble annunciator to alarm due to the resulting ac undervoltage condition.

As described in question 3.a.2 above, the de input breakers to the D03 and D04 buses have position indicators in the control room. Additionally, we are planning to install position indicators in the control room for the dc input breakers to the D01 and D02 buses.

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 the individual questions abo _ve.

6. a. Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one de division to be unavailable?

No.

We currently do not have any operational or maintenance procedures that make a division of de power unavailable. Consequently, we have not conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one dc division to become unavailable. The procedure for paralleling battery chargers, however, has been written to preclude the inadvertent loss of a division of de power.

We are currently planning to install a swing safety-related battery by mid-1993. This project is described below in more detail in our responce to question 7.c.4.

As part of this installation we will be upgrading associated procedures that involve the de system. As we rewrite these procedures, we will incorporate human engineering factors to minimize the potential for human errors.

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'b. Do plant procedures prohibit maintenance or testing on redundantado divisions at the same time? l{p .

Current plant maintenance does not' result in the doonorgization of a de power division. Consequently, our procedures do not specifically prohibit maintenance on redundant de divisions of power. Wo would not,

-however, typically perform maintenance on redundant de divisions at the same time.

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 f d 'owing verified to be within acceptable limits:

At Point Beach, monthly battery maintenanco is performed in accordance with the requirements for i monthly maintenance found in ANSI /IEEE Std 450-1987, the Point'Boach Technical Specifications, and the manufacturer's recommendations. All of the maintenanco:

described in this question 10 included in our monthly battery maintenance proceduro. Wo believe that the monthly periodicity for this maintenance is adequato and that it providos us with sufficient scatus of the battery condition. q i

1. Pilot cell electrolyte level? No .

Pilot cell electrolyto lovel is checked during monthly maintenance.

2. Specific gravity or charging current? No .

Pilot coll specific gravity is checked during monthly maintenance.

3. -Float voltage? No .

The float voltage is checked during monthly maintenance. Additionally,-during the monthly maintenanco, a new float voltage is determined based on the temperature of the pilot coll. The float voltage is then roadjusted as necessary, d

4. Total bus voltags on float chargo7 Mo .

Total battery voltage is determined during monthly maintenance.

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5. The float voltage of each cell? No .

9 The voltage of each cell is measured during monthly maintenance.

6. Visually inspect or measure resistance of terminals and connectors (including the connectors at the do bus)? No .

Each month all battery connections (including -

cable to lug connections) are checked for excessive corrosion or deterioration. Battery cells are also chceked for signs of leakage and cracks.

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 day surveillance requirements are the following verified to be within acceptable limits:

At Point Beach, the following battery maintenance is performed on a monthly or quarterly basis. Our Technical Specifications, however, do not require us to perform this maintenance after a discharge, overcharge, or if the pilot cell readings are outside the monthly surveillance requirements. Nonetheless, our-procedures require us to investigate and correct problems when readings are outside normal specifications'. In such cases, our good engineering practices would dictate that-we conduct-the quarterly maintenance, as appropriate.

1. Electrolyte level of each cell? No.

-This-is performed on a quarterly basis only.

C. The average specific gravity of all cells? No.

This is performed on a quarterly basis only.

3 . -- The specific gravity of each cell? No.

l This-is performed on'a quarterly bacis only..

4. The average electrolyte temperature of a representative number of cells? No.

This is performed on a quarterly basis only.

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5. The float voltage of each cell? __Not Thin in portormed on a monthly banin only.

6. Visually innpect or measure resintance of terminals and connectors (including the connootors at the do bun)? No,_

The vluuni innpoetion in performed on a monthly banin. Tho roulutanco mennuromonto of terminnlo and connector i nro performed on an nnnuni bania.

c. At loant ovary la months are the fe'. lowing verified

1. Low resistance of each connection (by tout)?

12On-Thic tout in conducted annually.

2. Physical condition of the battery? Ypa t__

The phynical condition of the Enttery in checkod during both the monthly and quarterly maintenanco.

3. Battery charger capability to deliver rated ampore output to the do bus? _ Nq, Wo are currently purnuing tho fonulbility of purchasing a land tout call that would allow un to perform charger capacity touting.

4. The capability of the battery to deliver its design duty cycle to ti.e do bun? _ _ Ngu _

We currently do not perform thin toat on a periodic bania. The tonting would involvo the manual dinconnection of the bnttory, connection of the battery to n ronintor bank, and the subsequent tonting, rocharging, and reconnection of the battery. Unned on our experience with touting bnttoriou DIOS and D106 in 19119 (72-hour LCO'n),

we determined that tonting of thin naturo cannot

.o completed within the 24-hour LCO currently upocifiod for batterion DOS and D06. We nre planning to install n fifth nnfoty-related swing battery that will allow un to tnko one battery off-lino to conduct battery nervice tenta.

By letter dated May 10, 1991, we proposed a change to the point llench Technlen1 Spocificatlona that includon a now ourvallianco requiremont for o battory acrvice tout that in to be conducted ovory

18 monthn. Thin tent will verify that the battery capacity in adequate to nupply and maintain in operable statun all of the actual or nimulated emergency londo for the design duty cycle. Thin nervice tenting in to begin nubsequent to the mid-1993 inntallation of the swing natety-related battery. We conducted the S-year required performance tents f or batterien D10's and D106 in tall 1989 (they were installed in 1984), and wo installed batterien D05 and D06 in 1989. An indicated in our May 10, 1991 letter, because of the relative newncon of the batterien, we bellove that it in acceptable to delay further battery nervice tenting until the owing nafety-related battery in inntalled.

5. Each individual call voltage is within acceptablo limito during the service tost? __t{m__

Ao part of the nervice tent that we are planning to establish (an discunned in question 7.c.4 above), individual cell voltagen will be monitored for acceptability during the tent.

d. At least ovary 60 months, is capability of each battery verified by performance of a dischargo test? ,_ _ lea,_

natterien D10S and D106 were tested in 1989, five yearu after their installation. Because batterien DOS and D06 were not installed until 1989, they have not yet been tested other than their initial acceptance tent in 1989.

o. At least annually, is the battery capacity verifiod by performanco discharge test, if the battery shows signs of degradation or has reached 85% of the cupacted servico life? ___R h In our Technical Specification change requent, dated May 10, 1991, we propound a new surveillance requirement that will require un to perform the discharge tent annually on a battery that shows signs of degradation or that han reached 85% of its nervice lite. This requirement in to be implemented subsequent to the installation of the noing nafety-related battery.

8. Does this plant have operational features such that following loss of one safety-related de power supply or bust

a. capability is maintaino$ for ensuring continued and adequato reactor cooling? _ _ yew _ _ _

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At Point Beach there are two redundant de systems. As

_a-result,-_the loss of.one safety-related do power supply will not affect our ability to maintain reactor cooling.

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

At Point Beach there are two redundant de systems. As a result, the loss of one safety-related de power supply will'not affect reactor coolant system integrity

'and isolation,

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

-adequate to initiate systems as required to maintain adequate _ core cooling. Yes.

-At Point-Beach there are two redundant de systems. As a result. the loss of one safety-related de power supply will'not affect our ability to initiate core cooling.

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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 procedures described and/or the bases

'for not including the operational features cited.

See individual questions above.

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