ML20151S247

Proposed Tech Spec Pages 4.6-4 & 4.6-8,allowing Up to 5 Consecutive Days to Perform Equalizing Charge W/Station Battery

ML20151S247
Person / Time
Site:	Fort Saint Vrain
Issue date:	04/20/1988
From:	PUBLIC SERVICE CO. OF COLORADO
To:
Shared Package
ML20151S197	List: ML20151S193 ML20151S241 ML20151S247
References
P-88116, TAC-67933, NUDOCS 8804280259
Download: ML20151S247 (8)

Text

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. s . Fort St. Vrain #1 ~

Technical Specifications

, ' Amendment No.

Page 4.6-4 charger or battery may be inoperable for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, l unless disconnected to perform an equalizing . charge,'

provided conditions l'through'4 below are satisfied.

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1) The other station battery and- its associated; battery charger and both D'.C. buses are operabl . ,

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1 2) D.C. bus independence is maintained and the I disconnect switch for the PPS battery is open,

3) Both diesel generators and their, associated essential 480v buses-are operable.

4) The PPS battery and battery charger / inverter are operable.

A battery and battery charger disconnected from a D.C.

l bus to perform an equalizing charge is considered-l inoperable, but may be disconnected for up to 5 l consecutive days provided conditions 1) 'through 4) 1 above are met, j 1

One D.C. bus may be inoperable for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> provided l l

the following conditions are satisfied:

1) The station battery and the associated battery charger of the operable D.C. bus are operable.

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2) Instrument power inverter suoplied from the 3

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operable D.C. bus is operable.  ;

< 3) Both diesel generators and their associated 480v essential buses are operable.

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s Fort St. Vrain 01 Technical Specifications Amendmentdo',

Page 4,6-8

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The station batteries supply power for the instrument power inverters, protective devices and equipment  ;

j operational control. During normal operation,.D.C. power i l is supplied by A.C. to 0.C. rectifiers, that is, battery I chargers, which also keep the' batteries fully charged.

- (FSAR Section 8.2.2.4.)

l Tne backup sources of electric pow'e r for th'e non-l interruptible A.C. Instrument Power Buses are provided ,

I from Instrument Power Transformers fed from the 480 VAC l essential buses through the Inverter / Static Transfer ,

l Switches. Interruptible Instrument Bus No. 3 receives its.

power from redundant instrument transformers which are supplied from the essential 480 volt switchgear. (FSAR Section 8.2.2.3.) 1 i.

l A redundant source of electric power for the D.C.

l instrument loads is available from bus tie breakers l between the two D.C. buses which allows the backup battery l charger to supply either one of the two buses while l maintaining D.C. bus independence. [

These backups and redundancies permit the temporary  !

removal from service of an instrument power inverter, a

• l , battery, a D.C. bus or a battery charger.

A diesel fuel storage capacity of 50,000 gallons is  !

orovided. A supply of 20,000 gallons of ciesel fuel is ,

i adequate to provice for operation of the standby.

i generators for at least seven days under required loading

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i ATTACHMENT 3 SIGNIFICANT HAZARDS CONSIDERATION i

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SIGNIFICANT HAZARDS CONSIDERATION Description of the Amendment Request The proposed amendment request would modify Fort St.' Vrain Technical Specification 4.6.1,(e) regarding the D.C. buses, the station and PPS batteries and the battery chargers. The purpose of the proposed il amendment is to allow a station battery and associated batte ry d charger to be disconnected from its D.C. bus for up to 5 consecutive f days to perform an equalizing charge. During this period, the station ba ttery and associated battery charger would be declared inoperable. In addition, the purpose of this proposed amendment is to require that the D.C. bus tie breakers be configured such that D.C. bus independence is maintained and the disconnect switch for the PPS battery is open when a station battery or battery charger is e inoperable.

System Description I The Fort St. Vrain D.C. power systeri consists of two D.C. buses, three 125 VDC batteries, and four battery chargers. The two station batteries supply power for the two separate and normally independent D.C. buses which feed two of the three instrument power inverters, protective devices, and equipment operational control. The PPS 4

battery supplies power for the third instrument power inverter which feeds the third channel of the PPS. .Three of the four battery chargers are powered directly from the 480 VAC essential buses and j maintain the proper charges on each of the three 125 VDC batteries and supply D.C. power during normal operation. An electrical single-line diagram of the instrument power and the D.C. power system is attached.

A bus tie circuit is provided for maintenance and service purposes.

A disconnect feature permits the performance of an equalizing charge during plant operation, while the associated 0.C. bus is energized by the backup battery charger. Independence is maintained by ensuring the D.C. bus tie breakers associated with the operable station battery are open, as is the disconnect switch for the PPS battery.

3 Reasons for the Change i

Per IEEE 450-1980 proper maintenance of a battery will prolong the life of a battery and will aid in assuring that it is capable of performing its design function. As part of this maintenance, action l

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s P-88116 Attachment 3 Page 2 of 5 may be required in the form of an equalizing charge to prevent conditions which can reduce the battery life, but do not necessarily indicate a loss of capacity. An equalizing charge normally . requires that an eqcalizing voltage be applied continuously for 35 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br /> to 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br /> or longer based on manufacturer's instructions.

At Fort St. Vrain, it is necessary to disconnect a station battery and associated battery charger from its D.C. bus during the performance of an equalizing charge to preclude damage to the loads on the D.C. bus. However, the existing Technical Specifications allow only 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for this condition. Based on manufacturer's instructions, up to 5 consecutive days may be required to perform an adequate equalizing charge. Therefore, the battery can not receive an adequate equalizing charge while the plant is operating under the existing Technical Specifications.

The proposed change would allow a station battery and associated battery charger to be disconnected from its D.C. bus to perform an equalizing charge. This would allow appropriate corrective action to be taken to properly maintain the batteries and prevent damage to the loads on the D.C. bus. As stated above, the performance of an equalizing charge is to prevent the life of the battery frcm being reduced and to prevent a loss of capacity. Therefore, in the event of an accident, such as the loss of all A.C. power, the equal ir.ng charge could be terminated and the battery could be reccnnected to the D.C. bus to perform its intended function.

The practice of electrically connecting the D.C. buses together when a battery or battery charger is inoperable as required in the existing Technical S;,ecifications is not in accordance with the 2 0 guidance provided in Safety Guide 6. The slightly improved defense against random failures achieved by the bus tie is more than offset by the additional vulnerability to common mode failures which the existing Technical Specification requirement creates. The bus tie allows a station battery and associated battery charger to be ,

disconnected from the D.C. system and to align the backup battery I charger to supply power to the D.C. bus while niai ntaini ng D.C. bus independence.

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• l P-88116 Attachment 3 Page 3 of 5 Evaluation PSC has analyzed the proposed amendment request for significant hazards consideration using the standards in Title 10, Code of Federal Regulation, Part 50.92. The proposed amendment request involves no significant hazards consideration, since the proposed amendment would not:

1. involve a significant increase in the probability or consequences of an accident previously evaluated.

Either one of the two station batteries is adequate to supply the required shutdown D.C. loads for four hours following the loss of all A.C. power. (FSAR 8.2.3.4). In the event all A.C. power is lost, the inoperable battery being charged can readily be  !

reconnected to the system to perform its design function. For other possible accidents that could occur, the associated D.C.

bus is supplied by the backup battery charger while maintaining D.C. bus independence such that both D.C. buses are available.

Therefore, this charge cannot increase the probability or i consequences of an accident. )

2. create the possibility of a new or different kind of accident e from any previously evaluated, y  ;

This change extends the period of time that a stapion battery and  !

associated battery charger can be disconnected from its D.C. bus by allowing up to 5 consecutive days to perform an equalizing charge. This is required for proper maintenance of the batteries.

Ensuring D.C. bus independence is maintained and the disconnect switch for the PPS battery is open when a station battery and/or associated battery charger is inoperable eliminates the possibility of a common mode failure. Therefore, it does not create the possibility of a new or different kind of accident.

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3. involve a significant reduction in a margin of safety.  !

The D.C. loads normally supplied by the station battery and associated battery charger are being supplied by the backup battery charger during the performance of an equalizing charge  !

while maintaining D.C. bus independence. The allowance of up to 5 consecutive days to perform an equalizing charge will assure ,

the station battery i s capable of sati sfying its design l requirements. The disconnecting of a station battery and battery '

charger for up to 5 consecutive days does not reduce the margin of safety of the Auxiliary Electric Power System to provide e e- -- *- ,-,e nm. , --

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/~ adequate electric power since the required power- source still

f exists. The. station battery can be reconnected to supply the required electrical loads to effect a safe shutdown of the plant.

Ensuring D.C. bus independence eliminates the possibility of a common mode. failure. Therefore, continued operation -under this configuration will not reduce significantly a margin of safety.

Conclusion Based on' the above evaluation, it is concluded that operation of Fort. St.' Vrain in accordance with the proposed changes will- involve '

no significant hazards consideration. PSC considers the changes to be an improvement in the overall plant reliability as the allowance .

for up to 5 consecutive days for the station batteries to be disconnected from its D.C. bus to perform an equalizing charge will provide the means to properly maintain the station batteries and prevent damage to any of the loads on the D.C. bus. In addition, ,

deleting the requirement that the D.C. bus tie breaker is closed and '

replacing it with the requirement that D.C. bus independence is maintained and the disconnect swi'tch for the;PPS battery is open ensures D.C. bus independence is not compromised. ,

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