We don’t really know what the dangers are of Molten Salt reactors; there have only been two built that anyone’s heard of; the Aircraft Reactor Experiment ARE, and the Molten Salt Reactor Experiment MSRE in the late ’60s early ’70s, both at Oak Ridge National Laboratory in the US. Things like AMSTER are conceptual; designs and computer simulations.
MSRs look safer in theory; no pressurisation and can’t melt down for a start. The bad news is they need graphite moderator, and that’s what caught fire at Windscale (and Chernobyl, but that was an effect of the accident rather than a cause). Weinberg designed both the MSRs and the PWR, but he wanted only the MSR licensed for civilian use, considering the PWR suitable for smaller scale military propulsion only. So they just sacked him.
The MSRE was under ten megawatt. I’d like to see a 100 megawatt MSR prototype. It’s a very versatile design because the nuclear fuel is liquid (molten at about 650 centigrade). Suitably prepared, U233, U235, plutonium and “spent” fuel can all be fed into the reaction and, in theory, burned almost completely down to reaction products; isotopes in the middle of the table of elements, many of which have industrial uses and most having much shorter half-life than the spent fuel that went in.
It looks good in principle. Maybe one day a better way to dispose of “spent fuel” AKA “transuranic waste” might be found, but the little MSRE looked remarkably tame, as nuclear power reactors go, so I think it’s time to try the next size up. They’ve been making the “waste” for seventy years and not one disposal reactor has yet been prototyped.