ML18155A270

Submits Results of Evaluation of Upgrades to Offsite Power Sys to Improve Reliability

ML18155A270
Person / Time
Site:	Palisades
Issue date:	09/24/1987
From:	Buckman F CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Crutchfield D Office of Nuclear Reactor Regulation
References
NUDOCS 8709290486
Download: ML18155A270 (4)

Text

consumers Power Frederick W Buckman

-company Vice President Nuclear Operations General Offices: 1945 West Parnall Road, Jackson, Ml 49201 * (517) 788-1217 September 24, 1987 D M Crutchfield Director, Division of Reactor Projects-III/IV}V and Special Projects Nuclear Regulatory Commission DOCKET 50-255 - LICENSE DPR PALISADES PLANT-*

PLANT MODIFICATIONS TO IMPROVE.OFFSITE POWER RELIABILITY LER-87-024 reported a loss of offsite 'power event which occurred at Palisades on July 14, 1987. Included in the LER was a commitment to evaluateupgrades

.to the offsite power system toimprove reliability. The purp~se of this letter is to present the results of that evaluation.

Prior to the loss of offsite power event of July 14, 1987, various alter-natives for improving the electrical interconn.ection between the plant and the Palisades switchyard were being studied. Following the July 14, 1987 event, efforts on this study were intensified. Several alternative methods for increasing the reliability of power to the plant were studied. The probability of losing power to** the 2400. volt safeguard buses for each

• alternative a~d also estimated costs associated with.each alternative were evaluated. Based on. the results, Consumers Power Company will install the follow1ng modifications to improve the reliability of the offsite power supply. Appropriate 10CFR50.59 review will be completed and, *if required, a Technical Specification change request will be initiated before the modifications.are completed. The existing and planned offsite power arrangements are shown in Figures 1 and 2.

1. A new transformer will be located at the Palisades Switchyard to provide power to the plant 2400 volt buses including the safeguard buses.

Connections between this transformer and the plant buses will be made via underground cable to provide for physical separation from the existing overhead lines connecting the switchyard to the plant. The new transformer will be connected to the F" bus in the switchyard via a motor operated di.sconnect. The existing 2400 volt startup transformer will .

remain connected to the "R" bus. This provides for immediate access to the.

alternate switchyard bus in the event one of the switchyard buses is lost.

Finally, the new transformer will be the normal source of power to the safeguards buses during normal operations eliminating the need to fast transfer the safeguard loads following a reactor trip *

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2. The bolted link disconnects located in the main generator isophase bus will be replaced with a motor-operated disconnect to decrease the time required to backfeed power through the main transformer to the station power transformers. Currently, disconnecting the bolted links to backfeed power requires approximately 4-6 hours to accomplish. Incorporation of the motor operated disconnect will reduce this time to minutes - thus reducing the time required to restore power to the primary coolant pumps and allow forced circulation cooldown. This backfeed capability also potentially provides for a third source of power to the safeguards buses in the unlikely event that both the "F" and "R" buses are lost in the switchyard. Backfeed capability can be provided from incoming line Cl to the switchyard independent of the "F" and "R" buses. The Cl line is a Consumers Power Company tie to the Indiana and Michigan Power Company.

3. An existing spare transformer will be installed as station power trans-former 1-3 to power the cooling towers during normal operation.

Currently, the cooling towers are powered from the "R" bus through Startup Transformer 1-3 for all modes of operation. This results in the potential for a single, failure of the "R" bus resulting in a reactor trip due to the loss of condenser cooling and a concurrent loss of offsite power.

Operating the cooling towers from a station power transformer eliminates dependence on the "R" bus as the only source of cooling tower power and thus eliminates the single failure which results in a concurrent reactor trip and loss of offsite power.

Due to lead times associated with obtaining the new transformer and motor operated disconnect switch, the modifications planned in Items 1 and 2 above will require approximately 18 months to complete. The long lead times coupled with an outage requirement for installation of the equipment will necessitate scheduling the installation of the modification identified in Items 1 and 2 during the first scheduled outage of sufficient duration following the next refueling outage. Item 3, installation of the existing spare transformer as a station power transformer, does not require equipment having long lead times and thus we intend to perform this portion of the modification during the next refueling outage.

Frederick W Buckman Vice President Nuclear Operations CC Nuclear Regulatory Commission-Document Control Desk Administrator, Region III, NRC NRC Resident Inspector - Palisades Attachment OC0987-0166-NL02

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