How would the materials be released? The reactors operate near 1 Atmosphere. If they are switched off, the molten salt cools and solidifies.
There could be a risk of contamination from the cooling loop, but such contamination might even be less than the normal radioactive fallout from the flues of coal plants.
I've been trying to imagine how blowing one of these things up with shaped charges, or anything else, is worse than blowing up other things like industrial plants, gas stations, etc.
The radioactive fuel is a molten salt, so it will cool and solidify soon after dispersal. It is certainly not good, but is it really worse than say, a chemical plant?
The radioactive stuff won't remain airborne after the initial blast, so that means a predictable and small area to remediate.
The fuel dispersed in an explosion can be collected, since it will solidify, so it won't poison the water table.
While not perfectly safe (nothing is), the disaster contingencies seem fundamentally different and better than those from a PWR + solid nuke waste disposal site.
There would be many more of them, which is both good and bad for various cases.
There could be a risk of contamination from the cooling loop, but such contamination might even be less than the normal radioactive fallout from the flues of coal plants.