BECO-91-147, Responds to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies

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

ML20079K874
Person / Time
Site:	Pilgrim
Issue date:	10/25/1991
From:	Gina Davis BOSTON EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR BECO-91-147, GL-91-06, GL-91-6, NUDOCS 9111050191
Download: ML20079K874 (10)

Text

.

10CFR50.54(f)

. BOSTON EDISON Pilgum Nuclear Power Station ,

Rocky Hill Road l Plymouth, Massachusetts o2360 i

George W. Davis october 25, 1991 sena v.ce prescent - Nuclur BECo 91- 147 U.S. Nuclear Regulatory Commission l Document Control-Desk l Hashington, DC 20555 l License DPR-35 Docket 50-293 l Response to Generic Letter 91-06, Resolution of Generic l

Issue A-30. "Adeauacy of Safety-Related DC Power Supplies" l

This letter responds to NRC questions asked in Generic Letter (GL) 91-06.

Attachment I contains a list of the GL 91-06 questions with our responses.

If you have any further questions regarding this response, please contact our ,

Licensing staff. j

^

/ /

',/ , )'{P % w

' G. H. Davis BRS/cic/6291 Attachm nt cc: (See page 2) l l Commonwealth of Massachusetts)

County of Plymouth )

i Then personally appeared before me, George H. Davis, who being duly sworn, did state that he is Senior Vice President - Nuclear of Boston Edison Company and that he is duly authorized to execute and file the submittal contained herein in the name and on behalf of Boston Edison Company and that the statements in said submittal are true to the best of his knowledge and beller.

My commission expires: Oc 84,z f # f - 7'M  ! ~

DATE NOTARf PUBLIC

\

\

i 9111050191 011025 rh i PDR ADOCK 05000293 l

l

/ -

t ,- P PDR {\

BOSTON EDISON COMPANY O. S. Nuclear Regulatory Connission Page 2 cc: Mr. R. Eaton, Project Manager Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation Mail Stop: 1401 U. S. Nuclear Regulatory Commission 1 White Flint North 11555 Rockville Pike Rockvilla, MD 20852 U. S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406 Senior NRC Resident Inspector Pilgrim Nuclear Power Station

ATTACHMENT 1

l. Unit Pilarim Nuclear Power Station

2. a. The number of independent redundant divisions of Class lE or safety-related dc power for this plant is two . (Include any separate Class IE 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 one .

3. Does the control room at this unit have the following separate, independentiy annunciated alarms and indications for each division of dc 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)? Yes and N_Q resoectivelv - See resconse to question 5

3. dc system ground? Yes

4. dc bus undervoltage? Yes

5. dc bus overvoltage? No

6. Battcry charger failure? No.

7. Battery discharge? No

b. Indications

1. Battery float charge current? No

2. Battery circuit output current? No

3. Battery discharge? No (local)

4. Bus voltage? No (local)

c. Does the unit have written procedures for response to the above alarms and indications? Yes - See resPDDie to agestion 5

4. Does this unit have indication of bypassed and inoperable statuslof 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. See rejponse to aues tions 3.a.J_and 3.a ._1

_1_

. _ . - _. _ _ _ _ . . . ~ _ _ . _ _ . _ . _ _ _ _ _ . _ . _ _ _ _ . _ ,

1 E.; -j

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 dc systems.

Question 3.a.1 There are no alarms to indicate if the battery circuit breaker or the disconnect is open. Presently, the circuit breaker.is verified to be in the correct position three times a day during performance of the Nuclear Power Plant Tour procedure and the battery disconnect is key locked in the closed position. The battery breaker and disconnect are only opened during performance of maintenance. This activity is administratively controlled in accordance with approved maintenance procedures that require independent verification to ensure the system is restored to its proper alignment following maintenance. ,

l Based on our existing design features and the described l administrative procedural controls,_ correct breaker position is '

assured at all times.

J Question 3.a.2 The battery charger input ac supply is monitored and annunciated in  ;

-the control room. -The alarm is a common alarm for the A and B chargers and monitors ac supply voltage and annunciates if supply voltage to the charger is lost.

The output breaker of the :harger is not directly monitored. There is, however,-an undervoltage alarm that monitors de bus-voltage and-will annunciate when the bus voltage decreases below the setpoint.

The setpoint-is conservatively set to annunciate before the battery voltage decreases below a level at which the safety objective of the

~ battery could not be met.

Also, the circuit breaker is verified to-be inlthe correct position three times a day during the performance of the Nuclear Power Plant

~ Tour procedure. The charger supply breaker to the de bus is only

- opened during. performance of maintenance. = This activity is administratively controlled in accordance with approved plant- '

procedures that-require independent verificationLto ensure the system-is. restored toLits proper alignment. . In addition, battery voltage is monitored'during the Nuclear Power Plant. tour. Any significant drop below normal float voltage would indicate = a problem-with the charger.

Based on our existing design: features and the administrative

. procedural: controls described above, correct alignment of the battery charger input and output'circult breakers are assured at all times.

F -If a-breaker were to open or the battery charger become disconnected this would be quickly detected and corrective action taken.

s

l 1

Question 3.a.5 The de bus voltage is monitored by the EPIC computer which provides an alarm on high or low voltage. This alarm is associated with the EPIC system and is logged on the alarm printout. On receipt, the alarm is validated oy checking the local voltage indicator at the battery bus. If the high voltage condition is confirmed corrective action would be taken in accordance with plant procedures.

Question 3.a.6 As discussed in response to Question 3.a.2 the battery charger initiates a common alarm for the A and B chargers when ac input power is lost. If the battery charger fails and output dc power is lost the batteries will begin to discharge. As the battery discharges and the voltage decreases the low voltage setpoint will cause an alarm in the control room. Alarm response procedures provide clear direction for corrective action to be taken. Additionally, the battery is equipped with an ammeter that monitors battery discharge. This ammeter reading is checked and logged three times a day during performance of the Nuclear Power Plant Tour procedure.

Based on our existing design features, the plant tour walkdown procedure verifying the batteries are not discharging, the loss of at input power alarm, and the undervoltage alarm on the dc bus, a battery charger failure would be detected and corrective action promptly initiated.

Question 3.a.7 Battery discharge is not directly monitored or alarmed in the Control Room. The battery bus is equipped with a local dual directional ammeter which is monitored and logged three times a day during the performance of the Nuclear Power Plant Tour procedure.

Also, the batterv is equipped with an undervoltage alarm. This alarm is set conservatively high and when tripped would be indicative of a discharging battery. In addition to the alarm the battery bus voltage is monitored three times a day. Any battery float voltage significantly lower than normal would also be indicative of a discharging battery.

These existing design features and plant tours assure the battery condition is being monitored to ensure it is properly charged.

Question 3.b.1 There is no indication in the Control Room for battery float charge current. There is a local dual directional ammeter which monitors battery current magnitude and direction. This ammeter is checked and logged three times a day during performance of the Nuciear Power Plant Tour. This ammeter is not sensitive enough to measure float charge current but would measure any large float current and/or a battery discharge current.

+

Question 3 b.2 There is an ammeter on the battery charger that provides indication of bus circuit output current plus battery float charge current which is usually very small during normal operation. This indication ,

provides information that is useful when determining if the charger is operating properly and the total load on the bus. During abnormal conditions when bus load is high the battery circuit output current can be obtained by summing the charger output and battery output currents.

Question 3.b.3 Battery discharge is indicated locally by the battery output ammeter that is monitored three times a day. Also, if the batteries were discharging the undervoltage alarm setpoint would soon be reached providing annunciation in the Control Room. The alarm response procedure provides clear direction for corrective action to be taken.

l Question 3.b.4 The battery voltage is indicated locally and is monitored and logged three times a day during performance of the Nuclear Power Plant Tour. If the battery voltage were significantly less than normal float voltage it would be indicative of a failed battery charger and corrective action would be taken. The dc bus undervoltage alarm provides backup to the Nuclear Power Plant tour surveillance.

Monitoring the dc bus voltage and the battery circuit ammeter provides assurance the battery is charged and the charger is operating properly.

Question 3.c There are specific written alarm response procedures for a dc system ground, battery charger failure (loss of ac power to charger), and dc bus undervoltage condition.

The battery output current and the dc bus voltage are monitored and logged. Also, as discussed in response to Questions 3.a.1 and 3.a.2 there are no alarms to indicate if the battery circuit breaker or the disconnect is open; however, the circuit breaker is verified to be in the correct position three times a day and the disconnect is key locked in the closed position. If these devices were found to be incorrectly positioned it would be brought to the attention of the Watch Engineer who would make an operability determination and initiate corrective action. Any anomalies would be evaluated in accordance with plant procedures. The dc bus overvoltage. condition, which is monitored and alarmed on the EPIC system, would be evaluated in a similar manner.

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? See resoonse_to auestion 9 and (2) Do plant procedures prohibit maintenance or testing on redundant dc divisions at the same time? Yes

_4

i'

\

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. __Eg1 acolicable

7. Are maintenance, surveillance and test procedures regarding station batteries conducted teutinely at this plant? Specifically:

I

a. At least once per 7 days are the following verified to be within acceptable limits:

1. Pilot cell electrolyte level? Yes

2. Specific gravity or charging current? Yes

3. Float voltage? Yes

4. Total bus voltage on float charge? Yes

5. Physical condition of all cells? No

b. At least once per 92 days, or within 7 days after a battery discharg6, 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 - See resconse to_ question 9

2. The average specific gravity of all cells? _Yes - See response to auestion 9

3. The specific gravity of each cell? Yes - See rest.onse to gu stion 9

4. The average electrolyte temperature of a representative number of cells? Yes - See resoonig lo auestion 9

5. The float voltage of each cell? Yes - See resoonse to ayestion 9

6. Visually inspect or measure resistance of terminals and connectors (including the connectors at the dc bus)? Yes - Sea resconse to auestion 9

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

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

2. Physical condition of the battery? Yes

3. Battery charger capability to deliver rated ampere output to the dc bus? Yes - See resoonse tq_ question 9

4. The capability of the battery to deliver its design duty cycle to the dc bus? Yes - See resoonse to auestion 9

~ . . - _ _ _ _ _ _ _

5. Each individual cell volisge is within acceptable limits during

. the 5ervice test? ligLApplinble. _$ec_rliponie__to_qutitipIL9

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test? leim41ei_10Ad_dischAL9L.ifilli per f ormed_ty.ery._11Lt9nthi.

e. At least ennually, is the battery capetity serified by performance discharge test, if the battery shows signs of degradation or has reached 85% of the expected service life? _SsLte}conse to queltica 9

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

a. Capability is taaintained for ensuring continued and adequate reactor cooling? _Yes

b. Reactor coolant system integrity and isolation capability are riiaintained? Yes

c. Operating procedures, instrumentation (tr-luding 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, ther, stovide your basis for not performing the maintenance, surveillance and test procedures described and/or the bases for not including the operational features cited.

Question 6 Procedures Faye not been specifically reviewed to ensure maintenance and testing activities minisize the notential for human error ciusing more than one dc division f be unave lable. However, maintenar.e and testing on redundant de divisions at tM m e time is prohibited by our plant maintenance procedures. Since md atenance and testing on more than one dc division at a time is not allowed, the potential for concurrent human error affecting more than one dc division is inherently minimized.

Question 7.a.5 The phyd u l condition of all cells are verified during the monthly battery surveillance procedure. Additionally, during performance of the weekly and quarterly battery surveillances any degradation of the cells would be observed and corrective action taken.

Question 7.b The items specified in Question 7.b are verified once per 92 days and following a battery discharge test as part of our battery surveillances.

The batteries are not suojected to random over charging or discharging, however, if they were observed to be discharged or overcharged appropriate corrective action would be taken. Also, battery electrolyte level is

d monitorM three times a day during performance of the Nuclear Power Plant

. Tour. If the 7-day surveillance requirements for the pilot cell readings are outside the acceptance criteria corrective action is immediately taken by performing single cell charging during which the electrolyte level, specific gravity, electrolyte temperature, and cell voltage of the pilot )

l cell are monitored. l Question 7.b.6 i

The resistance of the battery terminals is measured (ductor test) on a i semi-annual basis in accordance with the PNPS preventive niaintennte schedule.

There is also a monthly battery surveillance procedure that specifically performs a visual inspection of the battery terininals as well as checking the battery racks, battery room ventilation, and general appearance of the battery rooms. The battery terminals are visually inspected for degradation during the performance of system walkdowns that are performed weekly. Maintenance personnel are trained to look for any signs of physical degradation and/or corrosion of battery terminals during performance of weekly and quarterly battery surveillances although not specifically required by procedure.

The connectors at the de bus are not inspected at this time as there have not been any failures associated with these connections. The battery terminal connections are considered more significant for inspection purposes due to historical evidence of corrosion. He will review the pctential need to incorporate the provisions to inspect the bus connections into our maintenance procedures.

Question 7.c.3 There is not a specific test presently performed that verifies the battery charger capability to deliver rsted arnpere output. However, following the 18 month battery discharge test the charger is required to recharge the batteries. The charger is operated at close to rated output thus functionally verifying the charger output capability. This test will be revised to include a verification of the charger's capability to deliver its rated output.

Questien 7.c.4.

The duty cycle of the battery h verified 'y using the manufacturer's duty cycle test in conjunction ide the battery load discharge test to prove the batteries have sufficient capacity to fulfill their safety function.

Question 7.c.5.

He do not perform a service test. PNPS Technical Specifications require i

the performing of a rated load discharge test once/ cycle. During this

! test cell voltage is monitored to be within acceptable limits.

l l

l . . .-. - . . . ..,

i

. l l

1 Question 7,e

. Present)y the batteries are at 80% of the expected service life. The .

batteries are being evaluated to determine an optimum replacement schedule j based on past battery surveillances and future expected loss of service  :

life.

?

1 I

d E

[

t 3

h t

t l-

' i.

, , ,.r.,-.._.-- , -.,-....,_,,.m.. ., , ,, _ .. , . , . ~ - - - , , . - , . . . , . . , _ . - , . . , _ . , _ _ , _ _ . . . _ . . _ . . . . - - . . _ . . , . . , . . - . , .