Ontario's government stood behind its nuclear power plants on Tuesday, saying it has no plans to back down from a planned expansion to one of its facilities.

A spokesperson for Energy Minister Brad Duguid said the government remained committed to building two new units at the Darlington Nuclear Generating Station in Clarington, Ont., in the wake of a possible nuclear meltdown in Japan.

On Tuesday, New Democrat energy critic Peter Tabuns called for the Ontario government to halt construction on the facility amid safety concerns and cost increases.

"What's happened in Japan has illustrated once gain that it doesn't matter the technology or how advanced the country, things can go very wrong," Tabuns told CTV Toronto.

Public hearings on the new reactors are scheduled to start next week, despite the province having not yet finalized construction details.

Statistics show that five million Ontarians live within 100 kilometres of the nuclear facilities in Clarington and in Pickering.

The latest seismic assessment conducted by Ontario Power Generation (OPG) says the Pickering facility can withstand an earthquake of magnitude 6 to 7. Friday's earthquake in Japan was 9.0.

In 2000, another study concluded that the western Lake Ontario basin is an area of low seismic activity, with no evidence of a magnitude 4 earthquake in the previous 100 years.

Last year, a magnitude 5.0 quake hit parts of Ontario and Quebec, but did not cause serious damage in the GTA.

OPG's Ted Gruetzner said Ontario's plants are built to withstand a disaster of the scope expected in the province.

"We've got back ups to back ups to back ups," he told CTV Toronto.

In Japan, workers are having trouble keeping the reactors cool after they lost power in the wake of the tsunami. Ontario's plants have three back-up power supplies: diesel generators, liquid fuel generators and giant batteries. If power is cut, the three back-up systems are designed to keep cooling systems running for at least one week.

Switzerland, Lithuania and Germany have all put a halt to nuclear plans in the wake of Japan's atomic crisis.

According to the International Atomic Energy Agency, there are 442 nuclear reactors in operation worldwide, with 65 new facilities being made.

Construction last year was started on 14 new reactors -- in China, Russia, India, Japan and Brazil. In 2005, in comparison, ground was broken for only three reactors.

Japan had plans to add 14 plants to the 55 it had in operation, while China and India have also been looking at massive increased to their nuclear power systems.

Ontario has a total of 16 reactors, all located within 300 kilometres of one another.

Denise Carpenter, president of the Canadian Nuclear Federation, said it was important that Canadians understand how safe the country's nuclear power industry is, and the value it brings as a clean energy source.

"It is important to remember that the plant was damaged not as a result of the reactor design, but from the largest earthquake in their history. And then on top of that a devastating tsunami," Carpenter told CTV's Power Play on Monday.

Nuclear power provides more than 50 per cent of power in Ontario, and about 15 per cent of Canada's power on a whole.

With files from The Canadian Press and a report from CTV Toronto's Paul Bliss