TORONTO - Ontario Power Generation's nuclear plants are safe and robustly designed, the utility said Friday following a review in the wake of Japan's nuclear crisis.

The Canadian Nuclear Safety Commission asked OPG to review its nuclear reactors after a massive earthquake and tsunami knocked out power to the cooling system at the Fukushima Daiichi plant on March 11, leading to a situation officials still describe as very serious.

In its preliminary report, OPG said it has made significant progress in evaluating the lessons learned from Japan.

"What we're looking at, is there something that we can learn from Japan that we should be enhancing our safety," said OPG's chief nuclear officer Wayne Robbins. "We're safe now, that's not the question, but how do we get even more safety, what lessons should we put in there?"

OPG did a review of external hazards such as earthquakes, flooding, fire and extreme weather and found an "acceptably low risk" to power supplies for reactor cooling systems.

Canada's reactors are designed differently, and have many redundant backup systems, added Robbins, who said OPG would continue to look into possible disasters and how they could impact the nuclear plants.

"It may have us looking at even further accident-type scenarios that are really, really beyond design basis," he said. "What we have right now are designs, what we meet are beyond design basis events, but what if we go even further? That's what we're looking at now."

One of the biggest advantages Ontario has over Japan when it comes to locating nuclear reactors is the relatively modest amount of seismic activity in the Great Lakes region.

"To experience a magnitude-nine earthquake and then a 15-metre tsunami, that's not our environment," said Robbins. "So very first, right off the bat, our environment is a lot different. With our design being safe, and where we live, it really does add that extra layer of confidence to us."

OPG's report to the federal nuclear regulators said so far, "no significant issues requiring immediate corrective measures have been identified," but the utility said it would continue a rigorous review looking for more safety improvements.

However, Greenpeace Canada says government-owned OPG is refusing to release data on the potential health and environmental impacts of a radiation release from a Fukushima-like accident.

"It is unacceptable for OPG to withhold information on the potential environmental and human health impacts of accidental radiation releases from its reactors while publicly claiming those reactors are safe," said Greenpeace's Shawn-Patrick Stensil. "In light of the ongoing radiation releases at Fukushima and the continued impacts at Chornobyl 25 years after that disaster, Canadians have the right to know the risks they face from OPG's reactors."

Other countries, including China, paused approvals of new nuclear reactors in the wake of Fukushima, said Stensil, but Canada merely asked nuclear plant operators to assess their own operations without any public input.

"OPG is acting like the fox in charge of the henhouse," he said.

OPG said it will provide another update on its post-Fukushima review to the Canadian Nuclear Safety Commission by May 28. The utility owns and operates nuclear reactors at Pickering and Darlington in southern Ontario and leases another nuclear generating facility to Bruce Power near Kincardine on Lake Huron.