To which I say BS, at least for the reason cited.

Sure, the U-232 contaminated U-233 is nasty, but as long as it doesn't make it impractical to make a nuclear warhead it's quantitatively different from the uranium cycle, where after a few months at most plutonium is impossibly contaminated with two even more undesirable isotopes (one is very hot, I've seen estimates of 100kW for a bomb sized quantity (it's used for RTGs in deep space probes), the other precludes much of a bang and required the Manhattan Project to go with an implosion design).

Despite the gamma ray emission drawbacks, it could still be the easiest way to get lots of weapons grade fissionables from civilian power plants.

These folks seem to think the problem is solvable by adding U-238 http://www.coal2nuclear.com/MSR%20-%20Denatured%20-%20CNSLeB...

Yeah, that solves it neatly.

Reduces to a protoactinium problem, it decays to U-233 with a half-life of 27 days. The article claims there's so little protoactinium in the total mass of salt and stuff that it's not practical to isolate it, at least not without detection, and failing that, not quickly. This gets into fine details beyond my level of expertise, but I agree the problem is much reduced. Although very possibly still greater than for current LEU designs.

What about the health impact following a release of materials?

Molten salt thorium reactors are "continuous reprocessing" ones, which means they burn all the (active) waste they create for more energy.

Solid thorium reactors mix Th with the existing waste piles of Plutonium sitting in cooling pools and burn that up for us[1].

There's no waste materials to release from either of these reactors.

[1] http://www.extremetech.com/extreme/160131-thorium-nuclear-re...

Waste != Materials.

These reactors by definition have a fair amount of very "hot" materials; it hardly matters if none of them are declared "waste" if they'll still kill you in a few minutes of direct exposure.

...

molten salt reactors (the kind in the comment at the top of this thread) are at atmospheric pressure, and are designed with a drain plug which isolates the (very hot) materials from the neutron source, after which they cool down happily on their own in a separate but similarly shielded compartment.

release of materials is one of the most unlikely outcomes ever.

You really can't imagine a release of materials outcome in the context of active sabotage?

(Which is relevant in the context of massive distributed ones; current nuclear power systems mitigate this by being few in number such that they can be well guarded.)

since you can't weaponise the mixture, and it's just stupidly hot and dangerous for a while and then inert, I can't see why anyone would try to sabotage one. (apart from terrorists just out to cause mayhem, but that argument also works for cars, roads, planes, train stations, etc right?)

The addition of uranium or plutonium is unnecessary for operation of a LFTR, rather it is being sold as an extra advantage that a LFTR can safely consume the waste already created at PWR's. Consuming PWR waste in a LFTR is a better option than burying it in the desert (at least it is to some).

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.

That's an answer to how almost anything can be released.

Petrol from a tanker? Shaped charge.

Cracking armored vehicle? Shaped charge.

Unlocking stuck door? Shaped charge.

It really does seem people try to downplay any potential reactor designs because global thermonuclear war may damage the reactor. Stop living in fear.