This is just molten salt reactors all over again. They have disastrous security problems. Basically the salt eats away metal parts of the reactor, the graphite moderators are flammable and large parts of the reactor become radioactive because they catch neutrons which makes repair, maintenance and deconstruction almost impossible.

(edit:) I forgot about loss of fuel solubility events and the unsolved problem of tritium retention.

(edit:) It's interesting how the english wikipedia pages miss all the details on the failed projects in this field.