Well, I was wrong when I thought the slag couldn't get through the thick steel vault. It has cracked, which is almost the same thing. As well, I underestimated their ability to jam spent fuel so tightly into the swimming pools, that they can start the fission reaction again.
One of the problems with a light water reactor is that the light water is such a severe moderator of neutrons. Thus, the fuel has to be of a higher grade, and more tightly packed than Candu. This gives space efficiencies, and the new ACR1000 uses more light water. Whereas if we replaced the heavy water in Candu with light water (as in an emergency core injection), the reaction would be totally shut down. When they inject seawater, it makes no difference, and that is why they are using Boron, but they can't inject the required huge amounts of water and keep up the Boron levels. We actually use light water in columns to control and shut down the reaction during normal operation. There are the control rods for emergencies.
Don't panic about the existing Candu reactors. Even with my best imagination, they can't reach this stage of meltdown, there is just too much water in the reactors. When we had experts in the old company, I think we could have reached out and stopped the panic. Now, people don't believe platitudes, or government toadies, and we have what we have. I always said this was the consequence of going totally Stalinist-Soviet management in the nuclear industry.