ZION, Ill.  Twelve years ago, Commonwealth Edison found itself in a bind.

The Zion Station, its twin-unit nuclear reactor here, was no longer profitable. But the company could not afford to tear it down: the cost of dismantling the vast steel and concrete building, with multiple areas of radioactive contamination, would exceed $1 billion, double what it had cost to build the reactors in the 1970s. Nor could Commonwealth Edison walk away from the plant, because of the contamination.

The result was that Zion Station sat in limbo for more than a decade, and Commonwealth Edison, now part of Exelon, paid about $10 million a year to baby-sit the defunct reactor.

Now, though, the company is trying out a radical new approach to decommissioning the plant that promises to make the process faster, simpler and 25 percent less expensive  instead of hiring a contractor, it has turned the job and the reactors over to a nuclear demolition company that owns a nuclear dump site. The cost will be covered by the $900 million that Exelon accumulated in a decommissioning fund.

If the approach is successful, it could have implications for 10 other nuclear plants around the country that are waiting to be decommissioned, and for the 104 reactors that are still in operation but will eventually be torn down. It will also save money for electricity customers, who often end up paying for the cleanup of nuclear plants through their utility bills.