ML20203B194

Supplemental SE Accepting Proposed Changes Which Are Consistent W/Recognized Battery Stds & Station Blackout Rule

ML20203B194
Person / Time
Site:	LaSalle
Issue date:	12/04/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20203B167	List: ML20203B163 ML20203B194
References
NUDOCS 9712120368
Download: ML20203B194 (3)

Text

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SUPPLEMENTAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO STATION BLACKOUT RULE (10 CFR 50.S3)

COMMONWEALTH EDISON COMPANY LASALLE COUNTY STATION. UNITS 1 AND 2 DOCKET NOS. 50-373 AND 50-374 1.0 INTRODUCTIOP The NRC stairs Safety Evaluation (SE) pertaining to Commonwealth Edison Company's (the licensee) original responses to tne Station Blackout (SBO) rule was transmitted to the licensee by letter dated March 6,1992. In a letter dated May 28,1997, the licensee requested clarification of the March 6,1992 SE. Specifical'y, the clarification rcquested is related to the Class 1E battety capacity discussed in Section 2.3.2 of the original SBO SE. The SE discussion reflects what the licensee believed to be an unintended constraint in the battery capacity design basis. The SE, in addition to stating that the battery capacity calculations used an electrolyte temperature of 60 F, a design margin of 1.0, and an aging factor of 1.25, also states that the batte'y calculation provido a minimum margin of 8.3% for all Class 1E batteries except the Division-3 batteries. The licensee his determined that the original margin of 8.3% was overstated and the margin is actually 3.7%.

2.0 BACKGROUND

The existing Class 1E batteries at LaSalle were sized in accordance with Institute of Electrical and Electronics Engineers (IEEE) 485, "lEEE Recommended Practice for Sizing Large Lead Storage Batteries for Generating Stations and Substations,' using the loss of offsite power (LOOP)/

loss-of-coolant accident (LOCA) duty cycle. In response to the SBO rule, additional battery sizing calculations (for the existing batteries) were performed for the SBO duty cycle to demonstrate adequate capacity to service the SBO loads. These calculations were consistent with the methods prescribed in IEEE 485 and were based on a desir (capacity) margin of 1.0, an electrolyte temperature correction of 60'F (65'F for the 2504 uatteries), and an aging factor of 1.25. Based on the calculation, the minimum remaining margin prior to recovery from an SBO event wrs 8.3% and 6.3% after racwery. The recovery is the required load to close breakers to reestablish ac power to the battery chargers and should occur immediately after the 4-hour SBO event, in 1992, the battery manufacturer advised LaSalle County Station that the published 1-minute rating for the NCX batteries af LaSalle was overstated and provided a revised 1-minute battery Iating (this was reported by the manufacturer in accordance with 10 CFR Part 21). The revision was incorporated into the SBO battery sizing calculations and resulted in a reduction of the remaining margin. Specifically, the minimum umaining battery margin of any Class 1E batteries after an SBO event was now 3.7% after recovery. The licensee considers a margin of 5% or greator to be acceptable and sufficient to adaress any uncertainty related to battery capacity. The licensee is 9712120368 971:t04 PDR ADOCK 05000373  ;

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proposing to reduce the aging factor as required to maintain the 5% remaining margin. In view of this, LaSalle County Station would like to remove the specific reference of the aging factor (i.e.,1.25) from the original SBO SE.

3.0 EVALUATION e

IEEE 450, *lEEE Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead Acid Batteries for Stationary Applications," states that the recommended practice is to replace the station battery if its capacdy is below 80% of the manufacturers rating when the battery is sized using a 1.25 aging factor, if a lesser aging factor is used, battery replacement is required before the 5 80% capacity is reached to ensure that the required loads can be served up to the predicted end of useful life.

The licensee is proposing to remove the reference to the aging factor of 1.25 in order to have flexibility in maintaining a minimum 5% margin per SBO guidance. The dont is to maintain flexibility in addressing battery capacity _ issues by adjusting the aging factor if necessary. However, the decrease in the aging factor will require that the battery be replaced before 80% of the manufacturers rating per IEEE 450.

In response to the following questions from the staff, the licensee provided tUs additional information in a letter dated October 3,1997.

1. How will the requirement to replace the Class 1E batteries at 84% be implemented?

Answer: The requirement to replace the 125V de Division 1 and 2 class 1E batteries when the capacity reaches the value corresponding to the aging factor used in the SBO battery Sizing Calculation will be implemented by revising the applicable procs. dure (s). Specifically, the revised procedure (s) will reflect a minimum battery capacity that corresponds to the aging factor used in the calculation and a reference to the calculation as a basis for the minimum capacity. The pattery perfomunce test procedu.e will include words similar to 'varify the battery capacity is at least (e.g.,84%) of the manufacturers rating when subjected to a performance discharge test. If the battery capacity is determined to be less than (e.g.,84%)

of the manufsicturers rating, then the performance test is unsatisfactory.' The specide battery capacity value reflected in the procedure (s) will be based on the aging factor used in the SBO battery sizing calculation. The procedure (s) will also reference the appropriate licensing correspondence / documents Please note that a specific aging factor, as implied in the above question, was not identified in the referenced letter. The intent is to maintain flexibility in addressing capacity issues while maintaining a minimum remaining margin of 5% by adjusting (e.g., reducing) if necessary, the aging factor at the expense of earlier battery replacement.

2. What plant documents will be changed, !! any, to reflect the abange to the aging factor for the

% Class 1E batteries?

Answer: In addition to revising the applicable procedure (s), as discussed in the response to the firtt question, the UFSAR (updated final safety analysis report) will be revised to reflect (1) a minimum remaining margin of 5% regarding the SBO battery capacity, (2) that the aging factor may be adjusted (i.e., may be less than 1.25) to maintain the minimum 5% remaining margin, and (3) that the appropriats procedure (s) will require verification that the batteries

i have a minimum capacity consistent with the aging fador used in the SBO battery sizing calculations. As in the current revision of the UFSAR, the design margin used in the SBO battery sizing will remain unchanged at 1.0.

4.0 CONCLUSION

lEEE 450 states that the recommended practice is to replace the station battery if its capacity is below 80% of the manufacturer's rating when the battery is sized using a 1.25 aging fador. if a lesser aging factor is used, battery replacement will be required before the 80% capacity is reached to ensure that the required loads can be served. The licensee is proposing to reduce the aging i factor to maintain the 5% margin required by the SBO rule. The reduction in the aging factor will result in an increaseu economic expense in terms of replacing the battery at an eariier tirw, consistent with the aging factor. The licensee has recognized this economic expense sad will revise plant procedures / documents to be consistent with the change to the acing factor and 5% remaining battery margin. These changes will be implemented prior to restart of either unit.

Based on the above, the staff concludes that the proposed changes are consistent vnth recogn; zed battery standards and the SBO rule. Therefore, the changes are found to be, acceptable by the staff.

Principal Contributor: M. Pratt ,

Date: December 4,1997

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