ML20085K156
| ML20085K156 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/25/1991 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| 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 9110300174 | |
| Download: ML20085K156 (11) | |
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-1 Orcober 23, 1991 U.S. Nuclear Regulatory Cammissien ATINt Document Control Desk Washira ton , D.C. '0555 2
Cen t l emen :
In tt;e Matter of Docket Nos. S 'l- 32 7 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT (SQN) - CENERIC LF.TTLi' (GL) 91-05, RESOLUTION OF GENERIC ISSUE A-30, "ALEQUACY OF SAFETY-RELAILD DC POWER SUPPLIES "
PURSUMIT 10 10 CFR 50. 54(f )
This letter provides SQN's response to the subject GL. The attached enclosure provides a de'alled res.ponse to each question in the CL. if you have any questions concerning this !ssue, please contact W. C. Ludwig at (615) 843-7660.
Sincerely,
/
.5 W J L. Wilson J
i ed before me Sworn this, to ga d of d day subs < h k y 1391
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No ary Public My Commission Expires M Enclosure ec: See page 2
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9110300174 911023 PDR ADOCK 03000327 F.
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. U.S. Nuclear Regulatory Commission ,
0ct:ber 25, 1991-L cc (EnclosureJ' Mr. D. E.-LaBarge, Project Y.ana ge r ,
p U.S. Nuclear' Regulatory Commissitt, One White' Flint, Narth 11555 Rockvil~1e ?ike.
L Rockville; Maryland 20B52 y XRC Resident 7nspec:c ,
L Sequoyah Nuclear Plant 2600 Igou Ferry Boad
-Soddy-Daisy, Ienr.essee 37379 ;
.; Mr.;B. A. Wilaan, Project Chief-U.S. Nuclear Regulatory-Cenmission Region II 101 Marietta street, IAJ, sutte 2900 At!.anta, Georgia 303:3 i
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. ENCLOSURE l SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 RESPONSE TO NRC GENERIC LETTERS 91-06, RESOLUTION OF' GENERIC ISSUE A 40. " ADEQUACY OF SAFETY-RELATED DC POWER SUPPLIES." ,
PURSUANT TO 10 CFR 50.54(f) 4 s
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ENCLOSURE The.following is a direct response to each question contained in Enclosure 1 2 to Generic Letter (GL) 91-06. Because of the design of SQN, the unit 4
responses have been combined. Also, an additional explanation or ,
justification has been included with each response to supplement the response required by Questions 5 and 9. Additionally, Section 8.3 of the SQN Updated r Fin-1 Safety. Analysis Report (UFSAR) contains information describing the direct-current (de) pswer system at SQN. '
- 1. . Unit: 1 and 2
- 2. a. The number of independent redundant' divisions of Class IE or safety-related, de power for this plant is 8 .
4 Sequoyah has four diesel generator (D/G) batteries and four vital batteries. A fifth (spare) vital battery is not included in the above count,
- b. The number of functional safety-related divisions of de power necessary to attain safe shutdown for this unit 18 7 .
The GL requires the D/G batteries to be included in the response and for that reason SQN considers that for the worst-case considerations, seven out of eight batteries are required. Under worst-case conditions, the failure of two de power divisions could prevent the safe shutdown of~one unit. . For example, a vital battery f ailure associated with Train A and a Train B D/G battery failure for a single unit would cause the loss of both shutdown boards for that unit. This is the basis of responding that seven of eight batteries are .
required. However, under less conservative scenarios a single unit can be shut down with only two vital batteries and two D/G batteries.
- 3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division on de power?
- a. Alarms
- 1. Battery disconnect or circuit breaker open?
The circuit breakers in the discharge path for each o' the primary vital batteries have contacts that alert the control room of a tripped breaker. T1.ere is a-nonalarmed circuit breaker located in each of the vital hattery boards that is associated with the fifth vital battery. Although this breaker is not ala'rmed, there is an alarm in the. control room that notifies the operators that the tifth vital battery is replacing a primary battery. Since the breaker is not alarmed, this installation does not conform to 1 SQN's design criteria. A Problem Evaluation Report (SQP910273)
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has been written and this issue will be addressed by the Corrective Action Program. There are two additional alarms to provide supplementel information, one for Vital Battery I or III being replaced and one for Vital Battery II or IV being replaced.
-The circuit braakers are verified by inspection once every seven l l
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days and are only-aligned to the discharge path when the fifth vital bat tery is substituting f or a primary battery. UFSAR Figure 8.1.2-2 provides -a schenutic of the de power system r installed at SQN. ,
The D/G battery disconnect circuit breakers do not have annunciation (refer to Question 5).
- 2. Battery charger disconnect or circuit breaker open (botn. input alternating current [ac] and output de)?
The vital-battery chargers.have an ac failure card to monitor the input 480-volt, ac supply. This card will annunciate the loss of ,
the supply voltage for any reason, including an open input charger circuit breaker. The output de breaker for these battary chargers has an alerm contact for position annunciation. These alarms are 4 annunciated in the main centrol room. Additionally, charger failure is annunciated in the main control room. i
. The fif th vital battery charger is removed- f rom service when the fifth vital battery is substituted for one of the other four vital batteries. The fif th vital battery is naintained by.one of the safety-related chargers when it is replacing one of the four primary batteries, t
The D/G batteries do not have an alarm for the charger input.and output circuit breakers (refer to Question 5). >
- 3. de system ground?
All four of. the vit battery boards have local ground indicators with an alarm contact.that annunciates in the main control room.
When the fif th vital battery is substituted for one of the other four, it is connected to the respective battery board and that board's existingEground ledication and alarm.
The D/G batteries have local ground-indicators but they are not annunciated in the main control room.
- 4. de bus undervolrage?
Each vital battery-board has an undervoltaga relay-that annunc:ates-in-the main control room. Wher. the fifth vital batterf is substituted'for any of the other four, it is connected to the respective battery board and uses that board's existing undervoltage annunciation. 'The fifth vital battery board has its own undervoltage relay that- is used to indicate . problems when it is not connected as the-primary source.
The D/G batteries do not have annunciation for bus undervoltage.
The principal load on the D/G battery is the D/G control' panel.
This panel contains a loss-of-voltage alarm that is annunciated in the main control room as a diesel generator common alarm.
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. 5. de bus overvoltage?
Each vital battery board has an overvoltage relay that annunciates in the main control room. When the fifth vital battery is subs.tituted f or any of the other four, it is connected to the respec;ive battery board and uses that board's existing overvoltage annunciation.
The d/G batteries do not have annunciation for bus overvoltage.
- 6. Battery charger failure?
The 125-volt, Vital Battery Chargerr I, II, III, and IV and Spare Chargers 1-S and 2-S have charger failure annunciation in the main control rcom.
The fifth vital battrry charger is removed from service when the fif th vital battery is replacing a primary battery. The fifth vital battery has in underva;tage relay that is annunciated in the main control room. The fif tn vital battery cbstrger, which only charges the fifth vital battery when diaconnected from vital battery boards, has nc, other alartu because it has no safety functions.
The D/G battery chargers use loss of ac input or low de output to provide a " battery trouble" annunciation in the main control room for charger failure.
- 7. Battery discharge?
Each of the four vital battery boards has annunciation for battery discharge in the main control room. When the fifth vital battery is substituted for any of the other four, it is connected to the 4 respective battety board and uses that board's existing battery discharge annunciation.
The D/G batteries do not have annunciation in the nain control rocm for battery discharge other than the " battery trouble" initiated by Item 6 above,
- b. Indications
- 1. Battery float charg rrent?
The main control rooni panel has an ammeter for each vital bettery with an indicating scale of ~200 amperes to +600 amperes. These are sized to allow adequate monitoring of the battery discharge current and subsequent recharge :arrents. Float charging current is less than 2 amperes when the battery is fully charged. Battery board bus voltage and correct breaker alignments provide indication that the battery is on the float charge. '4 hen the fifth vital battery is substituted for any of the other four, it is connected to the respective battery board and uses that board's existing battery current indication.
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f 1.ie D/G batteries do not have battery current indication in the !
main control room (refer to Question 5). (
- 2. Battery circuit output current? f The main control room panal has an ammeter for each vital battery with an indicSting scale of -200 amperes to +600 amperes. There is no tuain control room indication for any of the battery charger i currents (only local-indication). When the fifth vital battery is l Substituted for any of the other four, it is connected to the respective battery board and uses that board's existing battery ,
current indication. ;
The D/G batteries do not have battery current.or battery charger [
current indication in the main control room (refer to Question 5). :
J 3. Battery discharge?
5 The main control room panel does' have an arnmeter for each vital "
battery board with an indicating scate of ~200 amperes to ;
+600 amperes. Additionally, there is a battery discharge alarm in the main control room. Thus, these ammeters would indicate if the !
battery was discharging (positive entrent_ flow). When the fifth l vital battery _is Substituted for any of the other four, it is }
connected to the respective battery boord s.1d uses that board's !'
existing battery current !ndication.
The D/G batteries do not have battery charge or current indication i in the main control room (refer to Question 5). l 4 Bus voltage?
The main contrci room panel has a voltmeter, which has a scale of 75-150 volts. A selector switch is used for selecting the status ,
of each of the primary vital battery boards. _Therefora. SQN_has. _.
i bus voltage indication in the main control room, but it is not ,
separate or independent.- When the fifth vital battery is i
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substituted for any of the other four, it is connected to the respective battery bcard and uses that board's existing bottery l voltage indication, t The D/G batteries do ent have battery vol tage indication-in the-main control room.
- c. Does the 1 nit have-written pre.cedure" for response to the above alarrrs and indications?
The alarms that exist'in the main control room have operating _i procedures that assist the operator in determining what possible problems exist and the. probable cause. .The serator must then investigate the alarits and make corrections in the plant. -. Written procedures do not exist for control room indications, and there are no preplanned operator actions that are required for battery indications.
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- 4. Does thin unit have ludication of bypassed and inoperable status ai [
circuit 1reakers or other devices that can be nwed to disconnect the i battery aad charger f rom its de bus and the battery charger f rom its ac l power source during maintenance or testing? !
t Major eminte ance or testing on the vital batteries is performed with the fifth vital tattery in service replacing the affected primary battery. As
- previously discussed, when the fifth vital battery board is aligned to the primary boards. the alarms and indications of the primary board are used. l
' The division of de power remains fully operable durir.g the testing since j tLe battery in test or maintenance is removed f rem service. !
Major maintenance or testing for the b/G batteries la performed under the '
limiting condition of operation of technical specifications (TS) for the appropriate unit. Maintenance and testing affecting TS hattery parameters and alignments are not performed on a battery while it 14 in service, j
- i. If the answer to any part of Question 3 or 4 14 no. then provide information justif ying the existing design f eatur es of the f acility's '
safety-related de system. '
EQN vital and D/G batteries have adequate alarms and indication to alert the operators of pending problems. SQN does not have the exact alarms and !
Indications that are listed in the GL. A description and justification !
for_each difference have been provided_as part of the response to i Questions 3 and 4 Tbc fallowing additional information is provided to r support the adequacy of the SQN design. :
1 The Gb indicates . that - the alarms should be for a single entity. SQN's [
alarm system is designed for grouping common problems in a single i annunciator window. They are independent for the four safety channels.
For_ example, "125V DC Vital Charger i Failure or Vital Battery I Discharge" is a single annunciation with multiple inputs. Additionally, '
there are instru tions in place that provide the operator with a list of. l these inputs.
The D/G batteries only have annunciation in the main control room for loss of control voltage to the control panel and for battery charger failure. [
llowever, the charger volts are recorded daily. Additionally, the D/G
-batisries are surveyed in accordance with TS Surveillance Requirement (SR) 4.8.1.1. 3.L which ensures aheir cont inued-operat ions. These requirements are not-included in tne present Revirolon 4 of_the Westinghouse Standard Technical Specification (WSTS) and represent an additional level of< conservatism that SQN has' implemented to ensure D/G battery operability.
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(1) Have you conducted a review of maintenanme and testing _ activities to -
-minimite the potential for human error causing more than one de division to be unavailable, and (2) do plant procedures prohibit maintenance or testing on redundant.dc divisions at the game time?
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6-(1) Administrative controls allow equipment to be worked only in the associated trtin week.- Maintenance is performed on "A" train equipment one week then on "B" train equipment the next week. In addition, a review of procedures controlling naintenance and testing activities was performed in the 1986 and 1487 timeframe, which considered various technical and administrative adequacy attributes including evaluation of common mode failure criteria and availability of redundant equipment. Procedure enhancement efforts are contiauing, which consider various human factor attributes.
(2) The plant ISs prohibit maintenance from being performed on more than one battery at a time, if the bnttery must be taken out of service for maintenance. For minor maintenance, procedures include precautions to warn personnel not ta work on more than one battery at a time.
- 7. Are maintenance, surveillance and test procedures regarding station batteries conducted' routinely at this plant? Specifically:
- a. At least once every 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 _vnitage? _Yes_ (For pilot cell)
(4) Total bus voltage on float charge? _Yee (5) Physical condition of all cells? No The physical condition of all cells is-not verified weekly on the vital batteries or DIG batteries. Presently, there is a preventive maintenance procedure in place to perform a visual inspection on the batteries on a monthly basis,
- b. At least once every 92. days, or within 7 days after a battery discharge or 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, except for D/G batteries for discharge / overcharge conditions.
(2) The average specific gravity of all cells? Yes, except for the D/G batteries for discharge / overcharge conditions.
(3) The specific gravity of_each call? Yes, except for the D/G batteries far discharge / overcharge conditions.
(4) The avecage electrolyte temperature of a representative number of cells? Yes, except for the D/G hatteries for discharge /overcharga conditions.
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_7 (5) -The float voltage of each cell? Yes,. except for the D/G l batteries for discharge / overcharge conditions.
i (6) Visually inspect or measure resistance of terminals and ,
- connectors (including the connectors at the de bus)? No (see r further explanation)
For Question 7(b.), battery parameters are verified to be within
, acceptable limits except for the following instancest
- The de bus connection (the battery bohrd bus) is not identified to !
be included in the terminal and connections of the battery bank. i Because of .he battery interface to the board being through a breaker, this resistance is not meaningful in relation to normal !
battery connections.
- The vital and D/G battery discharge procedures presently allow a battery to be returned to service without verifying connection -
resistances. This is inconsistent with TS requirements for the .
vital batteries. This issue has been reported in Licensee Event Report 50-327/91021 and associated precedures are scheduled for revision.
- The D/G batteries do not have TS requirements to perform a full battery parameter surveillance for an overcharge incident (refer to SQN TS D/G batteries SR 4.8.1.1.3). The D/G batteries are considered inoperable immediately upon a battery discharge, based en battery terminal voltage being below the required TS value.
- c. At least 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'its design duty cycle to the '
de bus? -Yes ,
4 The capability of the battery to deliver its design duty cycle to the de bus? Yes_
5.- Each individual cell voltage is within acceptable limita during the service test? No While performing the service test. TVA monitors and records at specific intervals each individual cell's voltage. However, there is no acceptance criteria.for individual cell voltage (only for overall battery. voltage),
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- d. At least every 60 months, is the capacity of~each hattery verified by performance of a discharge test? _Yes_
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- e. At least annually, is the battery capacity verified by performance discharge test. if the battery shows signs of degradation or has reached 85 percent of the expected service life? Yes
- 3. Does this plant have operational features such that following loss of one safety-related, de power supply or bust
- a. Capebility is maintained for ensuring continued and adequate reactor cooling?
! oar of one safety-related, de power supply or bus (vital batteries or D/G batteries) will affect only one train of safety-related equipment. Therefore. the capability in maintained for ensuring continued and adequate react d cooling,
- b. I(eactor coolant system integrity and isolation capability are maintained?
Loss of one safety-related. de power supply or bus fvital batteries or D/G batteries) will affect only one train of critical systems, structures, and components. Therefore, the reactor coolont system integrity and isolation capability are maintained.
- c. Operatlng procedures, instrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to maintain adequate core cooling?
The 125-volt, de vital battery failure is covered by abnormal l
operating instructions (A0!si Each individual board has its own !
A01, which indicates all por slo annunciations that would be i generated. The A01s then di.ect the operator to take corrective action to compensate for the equipment lost wher, this board has failed. The A01 also. lists the safety-related equipment that .,
i would be inoperable because of this board failure.
Instrumentation is fed from the--120-volt. ac vital system and would not be affected unless a total loss of ac occurred.
The 125-volt, de D/G batteries do not have procedures to address i loss of dc. If the battery were lost. the D/G would be declared '
4noperable and appropriate lirniting condition of operattun actions i
entered. Immediate action work requests would be initiated to correct the problerr,
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- 9. If the answer to any part of Questions 6. 7, or 8 is no. theri provide ,
-your basis for not performing the maintenance, surveillance, and test j procedures described and/or the bases for not including the l' operational features cited.
Nege.tive responses to Questions 6, 7, or 8 have been supplemented with '
add.tional inforn:ation to support the basis for the variance of the cperational feature. In addition, it should be noted that the SQN TS :
is very similar to the WSTS (Revision 4). Since there are some minor l differences, TVA has provided a complete response. The major i difference is the D/C SR that has been added to the SQN TS. SQN bas. ,
also based its SR on the manuf acturer's recommendation and the guid3nce of IEEE Standard 450 "IEEE Recommended Practice for :
Maintenanca. Testing and Replacement of Large Lead Storage Batteries for Generating Stations and Sub-Stations."
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