No no no no.. you don't want to do subcritical particle accelerator reactors. Well, you don't want solid fuel reactors, solid fuel has the same cooling issues as standard uranium, since it's the fission product breakdown that caused the Fukushima accidents (not an initial nuclear excursion, like Chernobyl).

Molten salt can be passively cooled (much better thermal conductivity) and can be moved from core to containment by gravity. Also it expands when its hot, which slows the reaction, and it's chemically stable and doesn't crack like uranium fuel pellets.