ML20079L949

Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, Adequacy of Safety-Related DC Power Supplies, Per 10CFR50.54(f)

ML20079L949
Person / Time
Site:	Peach Bottom, Limerick
Issue date:	10/28/1991
From:	Beck G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
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 9111070207
Download: ML20079L949 (21)

Text

_

PillLADELPIIIA ELECTRIC COMPANY

, NUCLEAR GROUP llEADQUARTERS 955-65 CilESTERBROOK BLVD.

WAYNE, PA 19087 5691 (215) 640-6000 NUCL 1R ENGINEERING & SERVICES DETARTMENT october 28, 1991 Docket Nos. 50-277 50-278 50-352 50-353 License Nos. DPR-44 DPR-56 NPF-39 NPF-85 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

Peach Bottom Atomic Power Station, Units 2 and 3 Limerick Generating Station, Units 1 and 2 Response to Generic Letter 91-06, " Resolution of Generic Issue A-30, " Adequacy of Safety-Related

'DC Power Supplies," Pursuant to 10 CFR 50.54(f)"

Dear Sir Enclosed is our response to Generic Letter 91-06,

" Resolution of Generic Issue A-30, " Adequacy of Safety-Related DC -

Power Supplies,." pursuant to 10 CFR 50.54(f)" dated April 29, 1991. Enclosure 1 provides the response for Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3. Enclocure 2 provides the response for Limerick Generating Station (LGS), Units 1 and 2.

If you have any questions, please contact us.

Verytrulyyoury,/

0 / (.

/ /; /

, p m-w2'-

G. J. Bo , Manager Licensing Section Enclosures cc: T. T. Martin, Administrator, Region I, USNRC J. J. Lyash, USNRC Senior Resident Inspector, PB T. J. Kenny, USNRC Senior Resident Inspector, LGS t A\

\0 9111070207 911028 l PDR ADOCK 05000277 l P PDR

__________________________________________________________j

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, COMMONWCALTH-OF PENNGYLVANIA:

o i ss.

COUNTY OF CHESTER  :

D. R. Helwig, being first duly sworn, deposes and says:

That he is Vice President, Nuclear Engineering and Services Department of Philadelphia Electric Company, the Applicant herein; that he has read the enclosed response to Generic Letter 91-06 for Peach Bottom Atomic Power Station, Units 2 and 3 Facility Operating License Nos. DPR-44 and DPR-56 and Limerick Generating Station, Units 1 and 2 Facility Operating License Nos.

NPF-39 and NPF-85 and knows the contents thereof; and that the statements and matters set-forth therein are true and correct to the best'of his knowledge, information and belief.

\ \) '

m s Vice Presiden Subscribed and sworn to before me this:E<,bLday of October 1991 UC SO c~

Nota'/

ry Public NaaM Sed w=~wd%

T

. Peach Bottom Atomic Power Station, Units 2 and 3' ENCLOSURE 1 10 CFR 50.54(f) REQUEST - GENERIC ISSUE (GI) A-30 " ADEQUACY OF SAFETY-RELATED DC POWER SUPPLIES"

Background

The specific area of concern of GI A-30 " Adequacy of Safety-Related DC Power Supplies" is the adequacy of the safety-related de power in operating nuclear power plants, particularly with regard to multiple and common cause failures.

Risk analysis and past plant experience support conclusions that failure 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 de power systems.

During the development of plans to resolve GI A-30, it was obsc ved that several previously issued regulatory notices (IENs), bulletins (IEBs) and letters (GLs) submitted to licensees include recommendations similar to those that have been identified te resolve G1 A-30. More specifically, it has been determined that recommendat~ ions contained in notifications IEN 85-74, " Station Battery Problems", IEB 79-27, " Loss of Non-Class 1E Instrumentation and Control Power System Bus.during Operation," and separate actions being taken to resolve GI 49, " Interlocks and LCOs for Class IE Tie Breakers" include the elements necessary to resolve GI A-30. It is therefore concluded that licensees that

,have implemented these recommendatious and actions will have resolved GI A-30.

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

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

1. (( nit i'each Bottom Atomic Power Stations (PBAPS). Units 2 and 3 ,

2. a. The . number of independent redundant divisions of Class 1E or safety-related de power'for thir plant is 2 per Unit # . (Include any separate Class 1E or safety-related dc, such as any dc 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 3 of 4 divisions per site ##

s (See Page 5 for # and ##)

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

a. alarms

1. Battery disconnect or circuit breaker open? No

2. Battery charger disconnect or circuit breaker open (both input at and output dc)? No

P,each- Bottom Atomic Power Station, Units 2 and 3

3. de system ground? Yes

4. de bus undervoltage? Yes

5. dc bus overvoltage? Yes

6. Battery charger failure? No

7. Battery discharge? No

b. Indications

1. Battery float charge current? No

2. Battery circuit output current? No k

e

3. Battery discharge? No

[ ,4. Bus voltage? Yes

c. Does the unit have written procedures for res ,;ns > L' tms and indications? Yes - alarms (except for oservo . .tions

4. Does this unit have indication.of bypassed and ir.c.pe,ab b circuit breakers or other devices that can be used to " .x .

• battery and battery charger from its de bus and the b .t ry c > - ' Trom its a power source during maintenance or testing? No

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design ft itures of the f acility's safety-related de systems. *See note below.

6. (1) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing mo're than one de division to be unavailable? No and (2) do plant procedures prohibit maintenance or testing on redundant dc 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 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 tall electrolyte levei? Yes

__ _-__ _ _ _ _ _ _ ____ _ _____ --- - - - - - - - - - - - - - - - - - - ^ - " - - - - - - - - - - - - - - - - - - - " - ' - - - -

Peach Bottom Atomic Power Station, Units 2 and.3 9

Specific gravity or charging current? Yes 2.

3. Float voltage?' Yes

4. Total bus voltage on float charge? Yes

5. Physical condition of all cells? Yes

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 requirements are the following verified to be within -

acceptable limits:

1. Electrolyte level of each cell? Yes The average specific gravity of all cells? yes 2.

3. The specific gravity of each cell? Yes 4, The average electrolyte temperature of a representative nunber of cells? _ Yes

5. The ficat voltage of each cell? Yes

6. Visually inspect or measure resistance of terminals and -

connectors (including the connectors at the de bus)?

Yes (except at de bus)

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

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

2. Physic'al condition of the battery? Yes-

3. Battery charger capability to deliver rated ampere output to the de bus? No

4. The' capability of the bz.ttery to deliver its design duty ,

cycle to the de bus? Yes

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

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

e. '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? yes

Peach Bottom Atomic Power Station. Units 2 and 3

- 4. .

8. Does this- plant have operational features such that following loss of one safety-related de 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 sustems as required to maintain adequate core cooling? Yes

-9. .. 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 note below.

• 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 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) 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."

e n

4

.- . . .~ .. . .

., Poach Bottom. Atomic Power Station Supplemental Response Units 2 cnd 3 Page 5

1. There are two independent redundant divisions of Class-lE 125/250V de three-wire systems per unit. Each system is comprised of two 125V batteries, each with its own charger.

-There are a total-of four Class-lE 125/250V de systems in the station, two for Unit 2 and two for Unit 3. The Class-lE 125/250V de systems are described in Section 8.7 of the Peach Bottom Atomic Power Station (PBAPS) Updated Final Safety Analysis Report (UFSAR).

An exception to this system description is discussed in Appendix F, paragraph-3.2.3 of the PBAPS UFSAR. The Unit 2 and Unit 3 batteries supply de power to the four shared diesel generators and their associated 4kV Emergency Auxiliary switchgear.

1. 1. Per Appendix F, parr"- 1.2.3 of the PBAPS UFSAR, the four 125/250V de systemt w ".ored support systems for the  ;

shared diesel gene ~ m three out of four diesel generators are requ.; - , shutdown of one Unit or both Units,-then thre. '

125/250V dc systems are required for safe shut r it or both Units.

Except for the items in h_, ,

eragraph 3.2.3 of the PBAPS UFSAR, the number of .. . . . safety-related divisions of de power necessary to u.tain safe shutdown is 1 of 2 per Unit.

Peach Bottom Atomic Power Station Supplemental Response Units 2 and 3 Page 6 Question 5 Response As requested in Question 5, the following additional information is being provided for those sections of Questions 3 and 4 which were answered "No." This additional information justifies the existing design features of the safety-related de system.

3.a.1 PBAPS does not have battery disconnect switches or circuit breakers between the 125V batteries and their de distribution panels. Between each battery and their de main distribution panels is a bolted removable link on one pole and a bolted removable fuse on the other pole. The battery fuses are located in metal enclosures. Normally, these enclosures are latched shut and are accessed only to perform maintenance and testing activities. Removal of these devices requires definite operator action that is administratively controlled. The batteries, battery fuse boxes, and the de system main distribution panels are located in the limited access areas protected by security card readers and electrically enabled doors. The security computer vital area access control provides access only to those personnel who are authorized with a need for access, thereby limiting the potential for tampering or inadvertent disruption.

The de system motor control centers and distribution panels each have undervoltage alarms that provide for detection of an open battery fuse or an open battery link under certain conditions (e.g., disconnection of the battery chargers).

We are continuing to evaluate improvements and will concluda our evaluation no later than the submittal of the Individual Plant Examination (IPE) submittal which is currently scheduled for September 1, 1992.

3.a.2 PBAPS does not have an independent battery charger circuit breaker open alarm. An open battery charger circuit breaker (i.e., input or output) would be annunciated by the battery charger trouble alarm. The battery charger trouble alarm is activated by more than one abnormal condition, and is separately and independently annunciated for each charger.

Upon receipt of a battery charger trouble alarm in the Main Control Room, personnel are dispatched to visually inspect the battery charger and the motor control center (MCC) circuit breaker that provides ac input power to the battery charger.

- - . , . __ . - .. -- -.- . - - -~.

1 Prach Bottom-Atomic [ Power Station. Supplemental Response

. Unita 2 and 3 Page 7 i

The_ battery charger circuit breakers are located on the front panels-of the battery chargers which allows operators to determine if those devices are opened or closed. The operators can easily determine if the MCC circuit breakers are opened or closed by visual inspection.

The battery chargers are located in limited access areas protected by security card readers and electrically enabled doors. The security computer vital access control provides access only to those

-personnel who are authorized for access, thereby limiting the potential for tampering or inadvertent disruption.

3.a.6 A battery. charger failure would be annunciated via the battery charger trouble alarm. The battery charger trouble alarm is activated by more than one abnormal condition, and is separately and independently annunciated for each charger.

Upon receipt of a battery charger trouble alarm in the Main. Control Room, Operations personnel are dispatched to determine the cause for the alarm and to initiate the appropriate corrective actions.

The battery chargers are located in limited access areas protected by security card readers and electrically enabled doors. The security computer vital area access control provides access only to those personnel who are authorized for access, thereby limiting the potential for tampering or inadvertent disruption.

3.a.7 PBAPS does not have a battery discharge alarm.

However, if a battery were to experience a severe (abnormally high) discharge, the battery charger would not be able to maintain the battery voltage at or above 125V dc which causes a battery charger trouble alarm-in the Main Control Room.

We are continuing to evaluate improvements and will conclude our evaluation no latir than the submittal of tha Individual-Plant Examination (IPE) submittal which is-currently scheduled for September 1, 1992.

3.b.1 The Main Control Room does not have battery float charge current indication. This data is obtained during weekly surveillance tests.

We-are continuing to evt'uate improvements and will conclude our evaluation no later than the submittal of

1 f

• Pacch Bottom Atomic Powar Station Supplemental Responso 1 -

Unita 2 and 3 Page 8 the Individual Plant Examination (IPE) submittal which is' currently scheduled for September 1, 1992.

3b2 The Main Control Room does not have battery circuit output current indication.

We are continuing to evaluate improvements and will conclude our evaluation no later than the submittal of the Individual Plant Examination (IPE) submittal which is currently scheduled for September 1, 1992.

3.b.3 The station 125V batteries do not have an indication of battery die- ge. In normal operating and shutdown scenarios, L.e battery chargers provide power to the de systems while providing a float charge to the batteries.

If a battery were to experience a severe (abnormally high) discharge, the battery charger would not be able to maintain the battery voltage at or above 125V de which would cause a Main Control Room alarm indicating battery charger trouble. Therefore, the addition of a battery discharge indicator is not necessary.

We are continuing to evaluate improvements and will conclude our evaluation no later than the submittal of the Individual Plant Examination (IPE) submittal which is currently scheduled for September 1, 1992.

3.c Written procedures are provided for the alternate alarms discussed in supplemental responses 3.a.2 and 3.a.6. In the case of response 3.a.1, since no separate battery disconnect or circuit breaker open alarm exists, no procedures are required.

There are no written procedures for response to overvoltage alarms or the items listed in paragraph 3.b. These items are a few of the indications used at PBAPS to monitor system conditions and assess battery performance. Operating experience, knowledge of de system conditions, and other indicators such as specific gravity readings, electrolyte temperature, electrolyte level, and battery cell sediment, which are surveilled by procedures that specify acceptance criteria, are used to initiate corrective actions when necessary. Upon receipt of an alarm in the Main Control Room, written procedures are used to respond.

The de system monitoring scheme is shown in Section 8.7 of PBAPS UFSAR.

4. There are no specific hardware indications of the bypassed or inoperable status of circuit breakers or other devices used to disconnect the batteries and battery chargers from the dc buses during maintenance

l Peach Bottom Atonnic Power Station Supplemental Rosponso '

-Units 2 and 3 Page 9 and testing. However, at PBAPS, the Reactor Operator Log, Chief Operator Log, Shift Supervisor Log, Blocking Permits, Equipment Status List, etc. in the Main control Room shows the status of this equipment during maintenance and-testing.

Undervoltage relays are connected to all of the main de system distribution buses. These relays provide separate, independently annunciated alarms during abnormal (low) voltage conditions.

We are continuing to evaluate improvements and will conclude our evaluation no later than the submittal of the Individual Plant Examination (IPE) submittal which is currently scheduled for September 1, 1992.

Question 9 Responso As requested in Question 9, the following additional information is being provided for those sections of Question 6, 7, or 8 which were answered "No " This information provides the basis for not performing the maintenance, surveillance and test procedures described and/or the basis for not including the operational feature-cited.

6.(1) Plant maintenance and testing procedures were written to minimize the potential for human errors. When cerors occur as a result of maintenance and testing, a root cause analysis or a task evaluation is performed in accordance with procedures to define problem areas and to provide for reduction of errors in future tasks by making the appropriate changes to the pertinent procedures. ,

7.b.6 The connections between the copper conductor lugs and the copper de busbars are bolted-type and do not warrant or require visual inspections. Also, the dc bus connections are in metal cabinets (i.e., main distribution panel) and the probability of creating a fault is minimized by limiting access to this equipment. The batteries, battery fuse boxes (metal enclosures), and the dc system main distribution panels are located in limited access areas protected by security card readers and electrically enabled doors.

The security computer vital area access control and authorization list provides access only to those personnel who are authorized-for access thereby limiting the potential for tampering or inadvertent disruption.

Each de system has fuses in metal enclosures which are located between the batteries and the main dc distribution buses. -Normally, these enclosures are

-1 i

, Pcach Bottom Atomic Power Station Supplemental Response j Units 2 and 3 Page 10 i i

latched shut and are' accessed only to perform maintenance and testing activities.

7.c; 3- -There is no procedural stop that specifically documents j the battery = chargers' capability to deliver rated j ampere output. The capability of the batteries to i deliver design duty. cycles to the de buses is veriflod' l I

at'least every 18 months. This verification consists of a test which loads the batteries to a simulated station specific discharge duty cycle. The simulated station specific dischargo duty cycle is the actual de system design duty cycle for the batteries.

After the batteries have-demonstrated this capability, the procedure requires that the batteries be recharged.

This step in the proceduro causes the battery chargers to deliver about 110% of their rated ampere output l (current limit) for a few hours. Station personnel l provide constant surveillance while the battery 1

' .~ -chargers are in current limit operation.

2195b. doc I

i

'l1

Limerick Generating Station, Units 1 and 2 ENCLOSURE 2 10 CFR 50.54(f) REQUEST - GENERIC ISSUE (GI) A-30 " ADEQUACY Of SAFETY-RELATED DC POWER SUPPLIES" B_a c kg round_

The specific area of concern of GI A-30 " Adequacy of Safety-Related DC Power Supplies" is the acequacy of the safety-related dc power in operating nuclear power plants, particularly with regard to multiple and common cause failures.

Risk analysis and past plant experience support conclusions that failure 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 de power systems During the development of plans to resolve GI A-30, it was observed that reviously issued regulatory notices (IENs), bulletins (IEBs) and several letters p(GLs) submitted to licensees include recommendations similar to those that have been identified to resolve G1 A-30. More specifically, it has been determined that recommendations contained in notifications IEN 85 74, " Station Battery problems", IEB 79-27, " Loss of Non-Class 1 Instrumentation and Control Power System Bus during Operation," and separate actions being taken to resolve GI 49, " Interlocks and LCOs for Class 1E Tie Breakers" include the elements necessary to resolve GI A-30. It is therefore concluded that licensees that have implemented these recommendations and actions will have resolved GI A-30.

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

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

1. Unit Limerick Generating Station (10S), Units 1 and 2

2. a. The number of independent redundant divisions of Class 1E or safety-related de power for this plant is 4 ner Unit # . (Include any separate Class 1E' or safety-related dc, such as any de 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 2 ne u nit.##

(See Page 5 for # and ##)

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

a. aiarms

1. Battery disconnect or circuit breaker open? No

2. Battery cn ger disconnect or circuit breaker open (both input ac and output dt)? No

L1:nerick Generating Station, Units 1 and '2

'. 9

3. de system ground? Yes

4. dc bus undervoltage? Yes

5. de bus overvoltage? yes >

6. Battery charger failure? _No

7. Battery discharge? No

b. Indications

1. Battery float charge current? yes

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 - alarras, No - indications

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 de bus and the battery charger from its ac power source during maintenance or testing? __

No . .

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) Have you conducted a review of maintefiance and testing activities to minimize the potential-for human error causing more than one.de division to be unavailable? No and(2)doplantproceduresprohibit maintenance or testing on recundant de divisions at the same time?

Uo 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 electrolyte level? Yes

Limerick Generating Station. Units 1 and 2 p

Specific gravity or charging current? Yes 2.

3. Float voltage? Yes

4. Total bus voltage on float charge? yes Y'S

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 requirements are the following verified to be within acceptable limits:

1. Electrolyte level of each cell? Yes The average specific gravity of all cells? yes 2.

3. The specific gravity of each cell? Yes

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

5. The float voltage of each cell? Yes

6. Visually inspect or measure resistance of terminals and connectors (includin,g the connectors at the de bus)?

Yes. eXCept at dc bus *

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

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

2. Physical condition of the battery? Yes

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

4. The capability of the battery to deliver its design dcty cycle to the de bus? Yes

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

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

e. 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? Yes

1,imerick Generating Station, Units 1 and 2

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

a. Capability is maintained for ensuring continued and adequate recctor 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 procedures described and/or the bases for not including the operational features cited. *See note below.

• 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 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) So state in response to these questions, and (2) Connit 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."

, Limsrick Gunerating Station Supplemental Responbr Units'l and 2 Page 5

1. - The Class-1E 125/250V and 125V de systems are described in Section 8.3.2 of the Limerick Generating Station (LGS)

Updated Final Safety Analysis Report (UFSAR). .There are four independent redundant divisions of Class-1E de systems forfeach Unit: two 125/250V three-wire dc systems each with two 125V batteries; two 125V two-wire de systems each with a 125V battery. Each 125V battery has its own charger.

1. 1. Each Unit requires a 125/250V de system and a 125V de system to safely shutdown in the event of a design basis event described in Chapter 15 of the LGS UFSAR.

Limerick Generating Station Supplemental Bosponse Units 1 and 2 Page 6 Question 5 Response As requested in Question 5, the following additional information is being provided for the sections of Questiona 3 and 4 which were answered "No." This additional information justifies the existing design features of the safety-related de system.

3.a.1 LGS does not have battery disconnect switches or battery circuit breakers. Each positive pole and each negative pole has a bolted removab}e fuse between the battery and the dc bus. Each neutral pole has a bolted removable link between the battery and the de system main distribution panels. Removal of these devices requires definite operator action which is administratively controlled. Also, the batteries and the de system main distribution panels are located in limited access areas protected by security card readers and electrically enabled doors. The security computer vital area access control provides access only to those per.sonnel who are authorized for access, thereby limiting the potential for tampering and inadvertent disconnection of the battery fuses or links.

As found acceptable by the NRC in NUREG-0991, " Safety Evaluation Report Related to the Operation of Limerick Generating Station, Units 1 and 2," dated August 1983, the battery fuse integrity is monitored in the Main Control Room by the battery ammeter and by the plant process computers. Additionally, the de system motor control centers and distribution panels each have undervoltage alarms that provide for detection of an open battery iuse or an open battery link under certain conditions (e.g., disconnection of the battery chargers). Therefore, a separate battery disconnect open alarm is not required.

3.a.2 LGS does not have an independent battery charger circuit breaker open alarm. An open battery charger circuit breaker (i.e., input or output) would be annunciated by the battery charger trouble alarm. The battery charger trouble alarm can be activated by more than one abnormal condition, and is separately and independently annunciated for each cherger. This was found acceptable by the NRC in NUREG-0991.

Upon receipt of a battery charger trouble alarm in the Main Control Room, Operations personnel are dispatched to visually inspect the battery charger circuit breakers and initiate the appropriate corrective actions based on the LED indicators located on the front panel of the battery chargers.

l

- Limsrick Gonorating Station Supplemental Response

.V,nito-1 and 2 Page 7 Additionally, the battery chargers are located in limited access areas protected by security card readers and electrically enabled doors. The security computer vital area access control provides access only to those personnel who are authorized for access, thereby limiting the potential for tampering and inadvertent ,

disconnection of the battery charger circuit breakers.

3.a.6 LGS does not have an independent battery charger fai' lure alarm. However, a battery charger failure -

would be annunciated by the battery charger trouble alarm. The battery charger trouble alarm would be activated by any of the following abnormal conditions:

1) dc undervoltage or overvoltage, 2) low de-current,

3) low ac current, and 4) battery charger output breaker open. A trouble alarm is separately and

-independently annunciated for each charger. This configuration and the de system monitoring scheme was reviewed and fuund to be acceptable by the NRC as discussed in NUREG-0991. >

Upon receipt of a battery charger trouble alarm in the Main Control Room, Operations personnel are dispatched to determine the cause for alarm and to initiate the appropriate corrective actions based on the LED  :

indicators located on the front panel of the battery chargars.

Additionally, the battery chargers are located in limited access areas protected by security card readers and electrically enabled doors. The security computer vital area access control provides access only to those personnel who are authorized for access, thereby limiting the potential for tampering and inadvertent disconnection of the battery chargers.

3.a.7 LGS does not have a battery discharge alarm. A high discharge can occur only if there is an undervoltage on the,dc bus or a ground fault between the bus and the battery. Because both of these conditions are alarmed,

-the addition of a battery discharge alarm is not c

required. This was reviewed and found acceptable by the NRC as discussed in NUREG-0991.

Additionally, shunts are connected between the i batteries and their main dc distribution buses. The

! shunt outputs are connected to the plant process l computers and are used to monitor the battery. When j

the charger output current is less than the current required by the connected de system, the differential current between the charger output current and the de load current will flow through the shunt as battery discharge current. The plant access computers provide l

Limerick Generating Station Supplemental Response

' Units 1 and 2 Page 8 indication of the battery current magnitude and indication of battery discharge.

3.c Written procedures are provided for the alternate alarms discussed in supplemental responses 3.a.2 and 3.a.6. In the case of response 3.a.1, since no separate battery disconnect or circuit breaker open alarm exists, no procedures are required, There are no written procedures for responsen to the items listed in paragraph 3.b (" Indications") of the Generic Letter. These items are a few of the indications used at LGS to monitor system conditions and assess battery performance. Knowledge of de system conditions, operating experience, and other indicators, -

such as, specific gravity readings, electrolyte temperature, electrolyte level, and battery cell sediment which are surveilled on a weekly basis by procedures that specify acceptance criteria, are used to initiate corrective actions when necessary.

4. There are no specific hardware indications of the bypassed or inoperable status of circuit breakers or other devices used to disconnect the batteries and battery chargers from the de buses during maintenance or testing. However, at LGS, the Reactor Operator Log, Chief Operator Log, Shift Supervisor Log, Maintenance Request Forms, Blocking Permits, etc., in the Main Control Room show the status of this equipment during maintenance and testing. Additionally, battery fuse integrity la monitored in the Main Control Room by the plant process computers and associated metering.

Also, the tripping of the battery charger output circuit breaker is alarmed in the Main Control Room by the battery charger trouble alarm. Undervoltage relays are connected to all of the main dc system distribution buses. These relays provide separate, independently annunciated alarms in the Main Control Room during abnormal (low) voltage conditions.

These alternate indications are used to determine the bypassed and inoperable status of circuit breakers or other devices used to disconnect the batteries and battery chargers from their dc buses and the battery chargers from their ac power sources.

Question 9 Response As requested in Question 9, the following additional information is being provided for those sections of Questions 6, 7, or 8 which were answered "No." This information providea the basis for not performing the maintenance, surveillance and test procedures described and/or the basis for not including the operational feature cited.

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'l 4..: LimDrick Generating Station. Supplemental Response

]j L'Unitsi1'and 2 Page.9 -- i m ,

The? plant maintenance and.ttsting procedures were

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6.(1): '

q~ written to' minimize the potential for human errors.

- Whenierstors' occur as a result of maintenance'and

-testing, a root cause analysis or a task evaluation is h -

performed in accordance with procedures to define problem areas and to provide for reduction of orrors in future tasks by making:the appropriate changes to the pertinent procedures.

6.(2) - The LGS Technical' Specifications (TS) require that all

14. divisions of de power be operable during start-up and operation of'a Unit.- With one division.of dc power ,

inoperable, the TS' require that Unit' shutdown be  !

initiated within eight:(8) hours. With more=than one division of de power inoperable,_ the-TS require that-Unit shutdown be initiated within one.(1) hour. During shutdown and refueling conditions, TS state that two divisions of dc' power may be inoperable. Several administrative controls and procedures are used to perform activities-(e.g., maintenance,_ testing, troubleshooting, plant modifications, etc.) associated -

with the de systems;to ensure.that-TS are not violated duringithese activities. These procedures were

' developed in accordance with the TS requirements.

7.b.6 The; connections between the copper conductor lugs and the copper de busbars are the bolted type and do not warrant or require visual 3 inspections. Also, the de-bus'connectionsfare in-metal cabinets (i.e., the. main distribution panels) and the-probability of creating a fault is minimized.by limiting access to this,

-equipment. .The. batteries,L battery _ fuses, and.the dc

- system. main-distribution panels are located in limited-access areas protected by: security card' readers and electrically enabled doors. The security. computer <

vital area. access control provides access only.to those personnel-who are-authorized fariaccess, therebyL ylimiting~ tampering and inadvertent disconnection of this equipment.-

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