The planned shutdowns of two of Ontario's biggest nuclear plants during normally high peak times could mean soaring prices for consumers next year.

The Bruce Power and Darlington Nuclear Generating Stations will be shut down at the same time next spring and summer for 16 weeks for planned repairs.

The closure means that Ontario will not have enough electricity to meet its mandatory reserve during those weeks, when power demands normally soar.

Last year, Ontario's top-10 record days for electricity demand fell during those weeks. And Toronto also declared six extreme heat alerts during the same time.

The massive shutdowns combined with the possible added demand for power could mean the province may import electricity from the U.S. to avoid an outage.

"We always have the option if we see extreme weather coming to import power from our neighbours," Alexandra Campbell, a spokesperson for the Independent Electricity System Operator, told CTV Toronto.

But Ontario's NDP energy critic Peter Tabuns is warning that could mean higher prices for consumers.

"Let's all pray for a cool, rainy May and a cloudy June and July because very high prices comes with those very high temperatures," Tabus said.

Ontario Energy Minister Bob Chiarelli says, however, that gas plants will be used to make up for the 6,800 megawatts of power that will be coming offline during the temporary shutdowns.

"They’re usually operating between 30 and 40 per cent capacity so there’s a lot of room to … take care of outages at the nuclear facilities," he said.

With a report from CTV Toronto's Paul Bliss