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Ontario Nuclear Safety: Reflecting On Events In Japan

by Tom Mitchell President and CEO of Ontario Power Generation

As we in Ontario have watched the images in Japan from the earthquake and tsunami, the damage to some of its nuclear power plants has been a major cause for concern. For many of us, among the first questions asked were: “Could similar events happen here? In Ontario? In the Greater Toronto Area?” The short answer is, “No.”

[Canadian Nuclear Safety Commission (CNSC) posted a number of Q & A’s that explains the robustness of Canada’s nuclear technology and seismic qualification, please visit their website which will be frequently updated.]

Let me give you the reasons. When I say that similar nuclear emergencies could not happen here, I am not writing with a sense of complacency. Safe operations and emergency preparedness are a priority at Ontario Power Generation. Along with other nuclear operators in the world, we will closely examine the Japanese experience to learn how we can make our operations even safer.

It is important to note some basic differences between the conditions in Japan and those of Ontario’s 16 operating nuclear reactors.

Background Material:
Observations on OPG’s Nuclear Operations after the Japan Earthquake and Tsunami [PDF]
Ontario Nuclear Safety: Reflecting On Events In Japan [PDF]

Japan is in a region where severe earthquakes and tsunamis are not uncommon. Ontario is not such a region. Ontario’s reactors are at two sites on Lake Ontario and one site on Lake Huron where major earthquakes are not expected.

Similarly, the Great Lakes are highly unlikely to produce a tsunami that would damage the operations of our nuclear units. They are in a geologically-stable region with a geologically-stable shoreline.

Despite this, the reactors have been built to resist earthquakes stronger than those that seismic studies say are likely to occur in Ontario once in 1,000 years. Ontario nuclear facility equipment and structures are built to meet Canadian Standards Association nuclear seismic standards.

The containment structures in which the nuclear reactions take place consist of thick reinforced concrete. In addition, the containment has a steel lining.

The containment for every reactor is linked to a vacuum building, the large circular structure that is the most visible feature of each of the Ontario Candu stations. This building is kept at a near vacuum. If steam builds up in a reactor’s containment, it flows to the vacuum building. A massive pool of water at the top of the building is then sprayed onto the steam to cool it.

Each reactor has two shutdown systems that can be operated manually or that are triggered automatically if there is a problem. In one of the shutdown systems, the unit has rods made of cadmium that, in an emergency, would drop rapidly into the reactor core and shut off the reaction by absorbing neutrons. Each of the stations also has a secondary means of stopping the fission reaction.