Federal regulators next year will decide how the cost for decommissioning Maine Yankee nuclear power plant will be covered. It is a difficult decision involving hundreds of millions of dollars. The key for regulators is to separate the unavoidable costs of operating a nuclear plant from business practices that could have led to higher operating expenses.

To make the case that the plant has been a financial boon to Maine, Yankee officials recently have issued statements that describe the savings customers have enjoyed over the years and will continue to enjoy now that the nuclear-power plant has closed. This may sound contradictory, but they view the cost question along the following lines.

New England consumers of Maine Yankee have saved approximately $4 billion over the past 25 years by having Yankee operating, plant officials assert, compared with the operation of a similar oil-fired plant. Consumers in Maine, by the way, account for approximately half of Yankee’s customer base. During the next 11 years — to what would have been the end of Yankee’s expected operating life in 2008 — Yankee says it expects to bill wholesale customers $2.1 billion less than what it would have had the plant continued to operate.

Maine Yankee has a quarter-century history of providing low-cost power to Maine, and certainly if the state had been forced to rely solely on oil power customers would have paid more. But there is another way for the Federal Energy Regulatory Commission to consider Yankee’s figures. The first number — the $4 billion over the last 25 years — ignores recent history, at best. To understand why, go back to just before the plant was built and listen to the promises made at the time. Take a chance with nuclear power, Yankee proponents pledged, and electricity coming from the plant will be too cheap to meter. Some of the acknowledged tradeoffs for this inexpensive power was the risk, however tiny, of a nuclear accident, the uncertainty of government regulation that could close the plant prematurely and the possibility that after the plant closed, for whatever reason, the state could be stuck long-term with a high-level nuclear waste site. Mainers paid for the inexpensive power by accepting these risks, so in this sense, there are no savings.

The number projected forward raises similar questions. The $2.1 billion savings makes a number of assumptions about the cost of operating Maine Yankee, figuring largely among these are the cost of maintaining the plant and the likely intensity of oversight from the Nuclear Regulatory Commission. There is no reason to doubt that Yankee officials are accurate in their assessment. But the question for the public and FERC is whether these costs were in part generated by Yankee’s performance. An internal study at the plant, for instance, found that workers were reluctant to report nonsafety maintenance problems because they believed management was more interested in keeping costs down than addressing these problems. How have these maintenance problems contributed to the added cost and, perhaps more importantly, contributed to the increased oversight of Yankee?

It is unfair to expect any company to operate perfectly for 25 years. Maine Yankee has had both an admirable performance record during much of its life and it has had shortcomings. It is in reviewing these — and not by discussions of theoretical savings — that FERC must decide how ratepayers and shareholders divide the cost of decommissioning.