The Liberals recently abandoned plans to build two new nuclear reactors, after spending $180 million in preparatory work, but said they would refurbish existing reactors at the Darlington power station to extend their service life until 2055.
"The procurement for it is going to take place in stages, and the final cost is not known at this particular point in time," said Energy Minister Bob Chiarelli.
The NDP released a statement from the Ministry of Energy showing "a final timeline and cost will not be known until the regulatory and technical scope is determined" and contracts are signed, sometime in 2015.
"We were shocked when the minister responded to our request by saying 'We're spending $950 million on contracts we've already signed but we can't tell you what the final cost is going to be,'" said Horwath. "That is frightening."
It's hard to believe the Liberals are prepared to waste more money on the electricity file after the auditor general reported the costs of their decisions to cancel gas plants in Oakville and Mississauga could top $1.1 billion, added Horwath.
"They haven't learned their lesson when it comes to cancelling power plants, when it comes to planning for new nuclear and now this refurbishment plan, where apparently the sky is the limit when it comes to the price," she said.
"You cannot go into a project like this, which is going to cost literally billions and billions of dollars, without having some kind of target, otherwise there's no attempt whatsoever for cost containment."
However, Chiarelli said the province was looking to negotiate contracts, as it did for the refurbishment of reactors by Bruce Power, where the developer is on the hook for any cost overruns, not taxpayers or hydro ratepayers.
"Bruce went over budget, but we weren't responsible for the costs," he said. "Bruce Power footed all the bill of the overrun, and I'm assuming we're going to have the same type of risk management (at Darlington)."
The Progressive Conservatives, meanwhile, introduced a motion calling on the Liberal Party of Ontario to pay back $950 million for the decisions to cancel the two gas plants prior to the 2011 election.
"This was a conscious decision to save five Liberal seats and it was party politics, nothing to do with the Ontario government," said Conservative Jane McKenna. "They should be the ones paying it back."
Former premier Dalton McGuinty has said the government made a mistake in deciding to locate the two plants close to homes and schools so they had to be cancelled.
McKenna said she wasn't worried about setting a dangerous precedent of holding political parties financially accountable for their actions in government.
But Premier Kathleen Wynne was lying in wait with examples of mismanagement by previous Tory administrations, including the "fire sale" of Highway 407.
"Will the party opposite find a way to pay back the billions on the 407, the hundreds of millions on the Eglinton subway and the stranded hydro debt," asked Wynne. "I would like to know what her leader would say about those debts."
Both the Tories and New Democrats have warned electricity rates in Ontario will have to rise to cover the cost of the Liberals' decisions to kill the two gas plants.
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