It will cost between $6 billion and $10 billion to refurbish the Darlington nuclear power station to extend its life by another 30 to 40 years.

Energy Minister Brad Duguid released today what he calls the "best possible preliminary cost estimate," one day after Ontario Power Generation confirmed it would refurbish the plant.

Duguid says that works out to about 8 cents per kilowatt-hour over the lifespan of the project, and defends the cost as an investment in the future stability of Ontario's electricity system.

New Democrat critic Peter Tabuns says $6 billion to $10 billion is a huge price range, especially when nuclear projects always come in over budget.

Tabuns wants the government to make sure Ontario taxpayers are not on the hook for cost overruns for Darlington, which is some 70 kilometres east of Toronto.

OPG also announced Tuesday it would spend $300 million to keep the Pickering nuclear station going for another 10 years before it is mothballed.