ML20091D848

Responds to Generic Ltr 91-06 10CFR50.54(f) Request Re Generic Issue A-30, Adequacy of Safety-Related DC Power Supplies. Battery Circuit Output Current Not Needed to Monitor Battery Status,Per Question 5

ML20091D848
Person / Time
Site:	Summer
Issue date:	10/22/1991
From:	Skolds J SOUTH CAROLINA ELECTRIC & GAS CO.
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 9110290419
Download: ML20091D848 (6)

Text

{{#Wiki_filter:-- -. - - _ _ - -_ . _ _ _ ._ - ee .. th Car: na E6ectric & G:s Comp:,ny hn oo Jenkinovalo. SC 29065 Nuclear Operatens

                                     .                                                                                                  -{

(803) 345-4040

                                           'SCE&G                                                                                            I
                                            ' " ~ ~ '

OCT 2 21991 Document Control Desk U. S. Nuclear Regulatory Commission

                                  . Washington, DC 20555-Gentlemen:

Subject:

VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO.- 50/395 l OPERATING LICENSE NO. NPF-12 RESPONSE TO GENERIC LETTER 91-06 (LTR 910006-0) 1

                                   -Pursuant to 10 CFR.50.54(f), South Carolina Electric & Gas Company (SCE&G) is                         ;

submitting the required responses to the questions in Enclosure 1 of Generic - Letter 91-06 with respect to Virgil C. Summer Nuclear Station (VCSNS). Attached is~the completed questionnaire plus additional justification as required by Question 5. 1 declare that the statements set forth herein are true and ccrrect to the

                                  .best of my know! edge, information, and belief.                                                       ;
                                  .If you have.any questions, please call.at your convenience.

Very truly yours, John L. Skolds-DCH:JLS: led i

Attachment:

c: 0. W..Dixon Jr. NkC R iident Inspector

                                         .R. R. Mahan-                                   J . t,   inotts Jr.                             :

R. J. White NSRC S. D. Ebneter RTS LTR890006)- G; F. Wunder.- ' File-((815.14)

                                         ' General; Managers-b
                                                                                                                                ,gO cu        i  .

h;RD7 $ - . NUCLEAR EXCELLENCE:- A SumER T B DITION! h . 9110290419 911022-p o JDR,1ADOCKL0500 g 5-'

     ,                                                                          ENCLOSURE 1 10 CFR 50.54(f) REQUEST - GENERIC ISSUE (Gl) A-30 " ADEQUACY OF SAFETY-RELATED DC POWER SUPPLIES" Backgrou_nd 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             l power plants, particularly with regard to multiple and common cause failures.             !

Risk analysis and past plant experience support conclusions that failure of the l 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 ' several previously issued regulatory notices (IENs), bulletins (IEBs) and letters (GLs) submitted to licensees include recomendations 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", lEB 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 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 facility. Question The following information is to be~ provided for each unit at each site:

1. Unit Virgil C. Summer Nuclear Station

2. a. The number of independent redundant divisions of Class IE or safety-related de power for this plant is _ _ _

two . (Include any separate Class 1E or safety-related de, such as any de 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, independently annunciated alarms and indications for each division of de power?

a. alarms

1. Battery disconnect or circuit breaker open? Yes

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)? __ Yes

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

3. de system groundt __Yes t

4. de bus underveltage? _ Yes

5. de but overvoltage? Yes

6. Battery charger failure? Yes

7. Battery discharge? _ Yes __

b. Indications

1. Battery float charge current? No-

2. Battery circuit output current? -_ No

 ~

3. Battery discharge? _ _ Yes

4. Bus voltage? Yes

c. - Does the unit have written procedures for response to the above alarms and_ indications? _ Yes

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 bettery charger from                 I 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 information justifying de systems.the existing design featcres of the facility's safety-related

                                      *See note below.

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

                                                             ~

Y e s '*

• and(2)doplantproceduresprohibit maintenance or testing on redundant 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 surveillance, then question 7 may be skipned and a statement to that effect may be inserted here. JySNSTechnicalSpcciffcationisequivaientto v,e m ngovu>e manuo,u. -

7. Are maintenance, surveillance and test procedures regarding station batteries conducted routineiy 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? __ N/A

a - h

                                                                                                                    'c .                   Spectiic gravity or charging current?                                                                                 N/A

3. Float voltage? N/A l

4 Total bus voltage on float charge? N/A

5. Physical condition of all cells? N/A

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 7-day surveillance requirements cre the following verified to be within acceptohle limits:

1. - trolyte level of each cell? N/A _

2- .ie s.verage specific 9 avity of all cells? N/A

3. The specific gravity of each cell? N/A 4 The average electrolyte temp 6rature of a representative number of cells? N/A

5. The float voltage of each cell? _ N/A

6. Visually inspect or measure resistenr:e of terminals and connectors (including the connectors at the de bus)?

N/A _

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

1. Low resistance of each connection (by test)? N/A

2. Physical condition of the battery? II/A

3. Battery charger capability to deliver rated ampere output to the de bus? -M/A

4. The capability of the battery to deliver its design duty cycle to the de bus? N/A

5. Each individual cell voltage is within acceptable limits during the service test? II/A

d. At least every 60 renths, is capacity of each battery verified by performance of a discharge test? il/A

e. is the battery capacity verified by performance At discharge least annually, test, 11 the battery shows signs of degradation or has reached 85% of the expected service life? N/A

,.,' 8. Does this plant have operational features such tMt following n.. nf 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 (ir.cluding indicators and 4

annunciators), and control functions are adequate to initiate systems as required to maintain adequate core cooling? Ye5 9. If the answer to any part of question 6, 7 or 8 is no, then provide vour 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 infomation (question nun;bers 6 and 9) instead of developing and supplying the information in response to this letter, you may consit to further evaluate the need for such provisions during the perfomance of your individac) plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required to:

            *(1) So stata in response to these questions, and (2) Comit to explicitly address questicns 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."
       # Question 3.b.3: VCSNS is currently in an outage in which a modification is being installed to add a DC system ground alarm in the control room. This modification is expected to be couplete prior to startup from Refuel-6.
       ** Question 6: There is no explicitly documented review of the potential for human error to cause more than one DC division to be unavailable dea to maintenance and testing. However, the entire process of planning, scheduling, required reviews and final approval of maintenance and testing of all plant equipment is based on working on one train of plant equipment at a time. Therefore, the development of this process and the associated procedures that apply to this process, as well as any changes that impact this process, are reviewed with an emphasis on minimi:'ing human error and any other error from performing maintenance or testing on more than one train at a time.

It should be noted that an individual maintenance procedure does not explicitly

      " prohibit" maintenance on more than one DC division but the process for initiating or. approving the maintenance does. The only exception to this would De in outage or other situations where the operating license would allow both trains to be inoperable and plant management concurren e was obtained.

(Justification for Question 5 on next page)

Justificatien for Question 5 Question 3.b.1: VCSNS, in accordance with manufacturer's instructions, .. monitors the float charge on the battery by monitoring float voltage. The ) float voltage is indicated and monitored in the control room. In addition, the setpoint for the DC sye'em undervoltage alarm is such that loss of float voltage will cause the annur. elation of the alarm. These factors coupled witn the requirements of Technical Specifications assure the adequacy and awareness of float charge status. Question 3.b.2: As stated above, battery operability is monitored by using voltage as an indicator. The design of the DC system is such that each battery train is sized to provide adequate power for the 4 hour duration assumed under "St,'. ion Bla:kout" conditions without requiring any operator actions to shed DC loads. Therefore, battery circuit output current is not needed to monitor battery status. Additionally the battery circuit current (both input and output) is indicated on a local indicator.}}