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Positive Void Coefficient of Reactivity and CANDUs

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Positive void reactivity, very simply, is that if...

In the unlikely event of a loss of coolant accident,

or a big pipe break if you like, and that there is gas introduced

or water removed from the pipes, in a CANDU design,

the power will increase.

In other designs, the power will decrease.

However, this is a very known feature,

it's been known from the very beginning-and there's

engineering controls for that.

In particular, the CANDU system has two very,

very fast independent shut-down systems which will shut down the

reactor within two seconds and completely eliminate

any of those-- that problem, if you like.

So we are very confident that it's a controlled item.

Should it not function as designed,

there still would not be a serious consequence,

in the sense of public danger, because the reactor geometry

is very, very precise for this phenomena to occur.

So as soon as any kind of damage starts happening

to the reactor itself, the reactor will shut itself

down even without the control systems.

So, that aspect, if you like, as I mentioned,

is very well understood,

you have lots of engineering controls around it,

and we do not see that as a safety concern.

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