George and I were swapping emails about liquid fuel in Molten Salt Reactors. He suggested I post this, so here goes:
As I see it, liquid fuel is the key, and not an indirect safety feature.
When solid fuel heats up, it comes together (corium) and gets even hotter. Corium quickly reaches 2800°C, hot enough to eventually melt through any reactor vessel, unless it is cooled by emergency measures.
But liquid fuel will never get that hot, because it expands and cools, or melts the freeze plug and drains and cools, or expands and bursts a pipe or a seam and spills out and cools. Any of these events would prevent the fuel from ever getting hot enough to melt the reactor. It would drain out, before the reactor vessel got anywhere close to melting.
The only way I can see liquid fuel melting an MSR is if the designers built a burst-proof, drain-proof reactor vessel without a freeze plug. And there would be no rational reason for doing so. On the contrary, MSRs would be designed to burst and drain in case of damage or sabotage. Not doing so would be like building a car without any brakes. It just wouldn’t make sense.
The problem with solid fuel is that it can’t get away from itself and cool off. That’s the fatal flaw in every solid fuel design, and that’s what all the safety features and cooling systems and redundancy is there to contend with.
Liquid fuel can get away from itself, and cool off naturally. That’s the beauty and genius of liquid fuel. In my opinion, Weinberg, Wigner, and their colleagues should have been awarded the Nobel Prize for this alone. It’s that big of a deal. It changes everything.
Because of this inherent safety feature (heat = expansion = cooling), I would contend that the liquidity of the fuel is a primary, and not a secondary, safety feature.
It’s the non-killer app of MSR.