I think Mr. MacDiarmid may be able to provide further technical details, but the problem, as the minister outlined, is that there was behaviour that was predicted by the design and safety codes that were presented to the CNSC, and there was an observed behaviour that was different. AECL to date has not been able, despite engaging experts from all over the world, to ascertain exactly why the actual behaviour observed is different from that predicted in the safety case.
On June 5th, 2008. See this statement in context.