engineering fan:
If a leak occurs in a heavy water reactor, then the majority of the fluid leaked would be heavy water (2H2O or D2O). Any tritium molecules would most likely have combined with oxygen, so they would be in the liquid form (3H2O or T2O) -- which answers your second question. The tritiated water would be intermixed with and basically indistinguishable from the heavy water. So if there were a leak, then both the heavy water and the tritiated water would escape through the leak -- which, hopefully, answers your first question.
However, I'm not saying there was [red]zero[/red] gaseous tritium; just that the majority would be water.
Patricia Lougheed
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