Commonwealth Edison, the country’s largest utility generator of nuclear energy, announced on 15 January that it will shut down the 25-year-old Zion nuclear plant. The company said the two-unit station, which has been offline for a lengthy period, would not be able to produce competitively priced power in a deregulated marketplace over the remaining years of its useful life. The utility will take a charge of approximately $515 million against net income.

James J O’Connor, chairman and CEO of Unicom, ComEd’s parent corporation, said the analysis was based on three factors: the cost of operating and supporting Zion, the amount of power the plant would likely have generated, and the projected price of electricity in a deregulated market. Illinois recently became the tenth state in the US to enact a law that will open up retail electricity markets to competition.

O’Connor said Zion’s 801 employees will remain on site for the next three to six months in order the place the plant in a safe permanent shutdown state. Within one year, the company expects the number to drop to between 150 to 200. Those employees will see the plant through its initial two-year transition period. After this, ComEd will maintain the plant in a secured mode with a smaller staff until 2014, when final decommissioning is scheduled to begin.

The Zion units were among the first of the larger 1000 MWe class of reactors.