ML20062N808

From kanterella
Jump to navigation Jump to search
Forwards Suppl Info Revising Section D.4 in TS Amend for Class 1E 125 Volt Battery Replacement Mod for Units 1 & 2
ML20062N808
Person / Time
Site: Byron, Braidwood  Constellation icon.png
Issue date: 01/07/1994
From: Saccomando D
COMMONWEALTH EDISON CO.
To: Murley T
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
Shared Package
ML20062N810 List:
References
NUDOCS 9401240073
Download: ML20062N808 (6)


Text

7 .

/ s ' Commonwealth Edison f 14 1400 Opus Plice f ,\ Downers Grove, tiiinois 60515 January 7,1994 Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission -

Washington, D. C. 20555 Document Contml Desk

Subject:

Supplemental Infomiation Regarding the September 2,1993, Technical Specification Amendment Pertaining to the Electrical Power System, D. C. Sources Byron Station Units I and 2 NPF-37/66; NRC Docket Nos. 50-454/455 Braidwood Station Units 1 and 2 -

NPF-73/77; NRC Docket Nos. 50-456/457  ;

References:

1) D. Saccomando letter to Dr. Murley dated September 2,1993, transmitting pmposed revision to Braidwood and Bymn Stations Technical Specifications Pertaining to the Electrical Power System, D.C. Sources t
2) Teleconference between Commonwealth Edison Company (CECO) and the Nuclear Regulatory Commission (NRC) on December 22,1993, regarding the proposed Technical Specification pertaining to the Electrical Power System, D.C. Sources Commonwealth Edison Company (CECO) is providing this supplemental information to NRR to n vise portions of Section D,4,(Impact of Changes), of Attachment "A",(Description and Safety Analysis of Proposed Changes), in CECO's Technical Specification amendrnent submittal for the Class IE 125 volt Battery Replacement Modifications at Byron and Braidwood Stations. This supplement is .

intended to correct and clarify the discussion associated with our submittal and does not alter the proposed changes to the Technical Specification or Technical Specification Bases.

Section D.4 of the reference Technical Specification Amendment submittal discusses battery sizing. The submittal presently states, in part:

" . The AT&T battery sizing was then selected based on having sufficient capacity to energize the design basis DC loads for an operating unit with the IEEE-485 design margin of -

15% while maintaining the desired limited DC load of 100 amps for a shutdown unit. The sizing of the AT&T battery is conservative compared to the sizing of the Gould battery  ;

because the cmsstie load limit of 63 amps for the Gould battery utilizes a portion of the IEEE-48515% design margin."

k:\nla\brdwd\bbbat2d.wpf\1 f

^

\td l 9401240073 DR 94did7 .

ADOCK 05000454 PDR y

. y e

, . -r i

. Dr. T.E. Murley - January 7,1994-  :!

i CECO would like to replxe this paragraph with the following: ,

. The AT&T battery sizing was then selected based on having sufficient capacity to energize f the design basis DC loads for an operating unit while carrying the desimd limited DC load of 1 100 amps for a shutdown unit and still maintaining sufficient design margin for future load l growth. The remaining design margin in the AT&T battery is higher than that currently; available for the Gould battery, even though the 63 amp crosstie load has been increased to ,

100 amps "  !

This revision is necessary because the actual design margin of 15% as referenced in Section  :

D.4 has been revised to range from 4.7% to 10.8% depending on the station and electrical division l being considered.

CECO believes that the AT&T batteries have been conservatively sized and pmdently .j designed. Attxhment 1 provides additional infonnation conceming battery sizing. As requested '

during the reference teleconference call, we are also providing a discussion of the events leading up .;

to this supplemental response and portions of the appropriate calculations which support the design of l the new batteries at minimum allowable tenninal voltages of 105 V and 107.88 V. (See Attachments i 2,3 and 4 respectively)

.t Once again, this supplement is intended to correct and clarify the discussion associated with -  !

our submittal and does not alter the proposed changes to the Technical Specification, its bases or the associated significant hazards discussion. Commonwealth Edison arologizes for any inconvenience  :

that was caused by amending Attachment "A" CECO has reviewec the submitted amendment, the j battery design related to this modification and the calculations and considers them to be complete and j finalized. We are confident at this time that there are no outstanding isses. We are currently .i ieviewing the events involved in the preparation of this amendment to identify any actions which j would pmelude a similar recurrence.

i Please address any further comments or questions regarding this matter to this office.

Sin rely, M~h pcwwk Denise M. Sace ando Nuclear Licensing Administrator l Attachments l t

cc: R.' Assa, Braidwood Pmject Manager - NRR .l H. Peterson, Senior Resident Inspector - Byron l 4

S.. Dupont, Senior Resident Inspector - Braidwood l

. J. Martin, Regional Administrator - Region 111  !

Office of Nuclear Facility Safety - IDNS l i

k:\nla\brdwd\bbbat2d.wpf\2 .j i

F t=

.i Attachment 1 The reduction of the design margin will not have a detrimental effect on the design of the plant. The design margin, also known as capacity margin, of 10%-15% is recommended by IEEE Std. 485 as a prudent design practice when sizing a new battery. It is intended to allow for unforeseen additions to the DC system and less than optimum operating conditions of the battery due to imptuper mainte-nance, recent discharge, or ambient temperatures lower than anticipated, or both. IEEE Std. 485 is  !

applicable to generating stations and substations in both the nuclear and non-nuclear industries. While i these variables are present in the electric industry as a whole, the administrative and design controls present at Byron and Braidwood Nuclear Stations preclude their occurrence.  ;

The aging factor used in the Byrun and Braidwood List ISH cell battery design is very conservative  !

and could have been used to pmvide additional inargin. The Byron and Braidwood Technical ,

Specifications require the battery is capable of delivering 80% of mted capacity when subjected to a - 'l performance discharge test every 60 months. In addition. IEEE Std. 450,(Recommended Practice for  :

Maintenance, Testing, and Replacement of Large Lead Storage Batteries for Generating Stations and Substations), recommends that a battery be mplaced when its actual capacity drops to 80% of its >

nominal rating. Therefore, the battesy's rated caprity should be at least 125% of the load expected at the end of its service life. This increase is nonnally referred to as the 1.25 aging factor in battesy  ;

sizing calculations. Since receiving the discharge data to an end voltage of 1.86 VPC from AT&T,  ;

CECO has perfonned battery sizing calculations that demonstrate that the List ISH cells will meet the ,

design requircraents of the DC systems with a minimum allowable batteiy tenninal voltage of 107.88 VDC (See Attachment 3). An aging factor of 1.25 was maintained as well as the minimum electm-  ;

lyte temperature of 60 degrees F. Maintaining an aging factor of 1.25 for the List ISH cells is  ;

considered very conservative. This aging fxtor is intended to account for the loss of capacity experi-  ;

enced by typical lead acid (lead calcium and lead antimony) storage cells over time. Based on the  :

results of AT&T accelerated life testing, the capacity of AT&T Round cells has been demonstrated to l inemase with age. This is a result of the design of the round cell (plate configuration, stacking of the' plates horizontally, and pure lead plates versus plates constmeted of lead calcium or lead antimony i alloys). The 1.25 aging factor for the List ISil cell was included in the sizing calculations to maintain i compliance with the Byron and Braidwood Technical Specifications which state that the battery is  ;

capable of delivering 80% of rated capacity when subjected to a perfonnance discharge test every 60  !

months and the battery replacement recommendations of IEEE Std. 450. By incorporating an aging  ;

fxtor of 1.25 into the Bymn and Braidwood Class IE 125 volt List ISH cell battery sizing calcula- >

tions, the batteries will have 25% additional capacity fmm what is mquired to meet the DBA loads. -

IEEE P485 Draft, presently at the IEEE Standards Boani for approval, addresses the issue of aging i factors in sizing different types of lead acid storage batteries. This revision to IEEE Std. 485 states that them are exceptions conceming the use of an aging factor of 1.25 when sizing a lead acid battery. ,

Depending on the cell design (e.g. Plante cells) an aging factor of L0 may be used pmvided the cell capacity is capable of remaining at or above 100% of the manufacturer's rating throughout the service  :

life of the battery and that the battery be replaced when its capacity drops below 100% of the manufacturer's rating.

i

.r nla\lardwd\bbbat2d.wpf\3 l

Attxhment 1 (Continued)

In conclusion, a decrease in the design margin to lesr than 15% is the result of increasing the minimum allowable battery tenninal voltage. The use of the 10%-15% design margin in sizing a new battery installation is not a Technical Specification requirement rather it is a recommended practice based on IEEE Std. 485. CECO administrative controls preclude the variables that require the use of a design margin from occurring. Thus, maintaining a 15% design margin throughout the life of the battery is not required. CECO believes that the remaining design margin is sufficient for future load additions and that the proposed increase in minimum allowable battery tenninal voltage can be considered a load addition that utilized pan of the original 15% design margin that was available when the minimum allowable battery temiinal voltage was at 105 VDC. In addition CECO has maintained an aging factor of 1.25 as opposed to an aging factor of 1.0 thereby pruviding additional capacity margin. By raising the minimum allowable battery temiinal voltage from 105 volts to 107.88 volts, CECO has been pruactive in resolving the voltage drop conce-m of the instmment power inveners and at the same time has increased the operating reliability of the inveners during a DBA.

By utilizing the excess capacity of the new Class lE 125 volt batteries, CECO will have provided both a technically and economically acceptable solution to this concem. CECO has fully demonstrated that the List ISil cell is properly sized with ample capacity margin for the Class IE 125 VDC applications at Byron and Braidwood Stations and meets the intent of IEEE Std. 485.

Y k:\nla\brdwd\bbbat2d.wpf\4

. i i

1 Attachment 2 f i

The Byron and Braidwood Class IE 125 volt batteries are presently scheduled to be replaced with AT&T List IS11 Round Cell batteries,(referred to as the List ISH cell in this response). Each battery  !'

will consist of 58 cells and have a guaranteed minimum rating of 1760 ampere-hours at the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> discharge rate to an end voltage of 1.75 volts per cell, (VPC). The nominal specific gravity of the cells is 1300. The List ISH cell is the largest ampere-hour capacity mund cell available. ,

During the conceptual design stage of the battery replacement project, the design basis for the new l batteries was detennined to be the ability to supply the design basis accident (DBA) loads of the DC i system plus 100 amps of cmsstie load to the other unit without load shedding while maintaining a minimum battery tenninal voltage of 105 V,(1.81 VPC). Initial battery sizing calculations were - i peifonned following the recommendations of IEEE Std. 485 using a minimum electmlyte temperature l of 60 degrees F, a design margin of 15% and an aging factor of 1.25. This would assure that battery j capacity would be 15% greater than that required to supply the DBA and crosstie loads while main-taining the battery voltage above 105 VDC assuming the battery capacity has dropped to an end-of-life value of 80% of the manufacturers guaranteed minimum rating, and the average electrolyte .

temperatum of the battery was at the 60 degrees F Technical Specification Limit.  :

'l Concurrent with the design pmcess of the battery mplacement project, CECO identified i. voltage dmp concem regarding the 7.5 KVA instmment power inverters during pmparation for the Bymn and .

j Braidwood EDSFIs. The inveners are specified to operate at a minimum input voltage of 105 VDC.  ;

During full load operation, a 2.6 volt drop exists between the battery and the DC input of the invener, i Therefore,107.6 volts is required at the battery in order to ensure proper operation of the inveners  :

during a DBA. A voltage dmp calculation completed in May of 1993 demonstrated the voltage of the .

existing batteries would not drop below this 107.6 VDC limit. .'l i

Because this concem did not surface until after completion of initial battery sizing calculations and award of the contract for the replacement batteries, the CECO specification for the replacement batteries required ampere-hour capacity to meet the design requirements of the DC system with a ~!

minimum battery tenninal voltage of 105 VDC. Once the voltage dmp concem was identified, CECO (

considered several altematives to resolve this issue. These included, testing of the inverters to deter- _;

mine if the inveners would maintain pmper output voltage mgulation at DC input voltages less than J

105 VDC; increasing the size of the feeder cable from the distribution bus to the invener to reduce the voltage dmp; and reviewing the DC system loads to eliminate conservatism in the pmsent design.  :

Recognizing these altematives may not yield results in the time frame required to support the  ;

installation of new batteries, CECO also pursued obtaining the data needed to complete the design l calculations with a 107.6 VDC minimum voltage. ..

l

-j 1

i k:\nla\brdwd\bbbat2d.wpf\5

, = - .

L

l. .

Attxhment 2 (Continued)

In order to accomplish this, cell discharge currents to an end voltage of 1.86 VPC (107.6 volts + 58 '

cells) was required. This data would be used to detennine if the List ISH cells had the required L

capacity to meet the design requirements of the DC systems with an end voltage of 107.88 VDC, (1.86 VPC X 58 cells). It was discovered that AT&T did not have published discharge data to an end .

voltage of 1.86 VPC but agreed to perfonn discharge tests on the List ISH cell in order to detennine cell discharge characteristics to an end voltage of 1.86 VPC. The approved data was provided to CECO in November of 1993. Subsequently, this data was incorporated into design calculations to determine the effect of raising the minimum allowable battery tenninal voltage At this time it was

,. discovered that by raising the minimum allowable battery tenninal voltage to 107.88 VPC, part of the l design margin was sacrificed.

l l

l l

l l

l l

l-1, l

i k:\nla\brdwd\bbbat2d.hpf\6