tough going, page-70

@HappyCats - yeah. Basically, the thorium reactor turns the thorium into U-233, which is then fissioned without ever leaving the reactor. So you turn off the neutron generation, the thorium stops being turned into uranium, the reaction inevitably has to stop. The fission products will still give off heat as they decay naturally, but it's not a case of the fission process being able to continue unchecked.

Better U reactor designs can also provide for passive safety of that sort, but it's much more inherent in the design of a thorium reactor; you'd have to work pretty hard at it (as I understand it) to design a thorium reactor that could cause problems in the way that happened at Fukushima and Chernobyl. (Chernobyl, by the way, was a really bad design - the RBMK-1000 is a liquid cooled design with a positive void coefficient, meaning - handwave, handwave - that the core power has a tendency to increase if not kept under control. Doesn't mean that a negative void coefficient is necessarily good, though; it all depends on the overall design.)

All of which is somewhat beside the point - interesting, but somewhat off-topic. Right now, the politics of nuclear energy mean that high thorium and/or uranium content makes mining the material more problematic in complying with all the regulations; this makes Peak's low-thorium, low-uranium ore more valuable (everything else being equal) than most others'. That's all that really matters to us.