I think it's important to point out that once this reactor has started... it still will require cooling. The decay heat won't stop instantly just because the ma

I think it's important to point out that once this reactor has started... it still will require cooling. The decay heat won't stop instantly just because the mass is no longer in criticality. There will be daughter products producing 1% of the heat for quite some time if it's Thorium based, or 10% of the heat for Uranium based salts. Also note that molten salts, while they won't burn, are still capable of quite explosive reactions with water. It's not as simple as a chip, which you can just turn off.