> The shutdown mechanisms are specifically about the containment of heat. The problem is generally about a reaction not being shut off.

Indeed? I was of the understanding that the shutdown mechanisms were specifically for halting the chain reaction, and largely a solved problem with mature tech, and it was containing the decay heat of Gen 2 designs that was the trickier problem.

I am happy to be wrong about the latter, though perhaps not as happy to be wrong about the former.