I studied physics at university and they never told me about thorium.
Apparently it is “a naturally occurring radioactive chemical element, found in abundance throughout the world.” Including Wales and Cornwall.
According to this piece in the Daily Telegraph recently, US physicists explored the idea of using thorium for power in the late 1940s. “It has a higher neutron yield than uranium, a better fission rating, longer fuel cycles, and does not require the extra cost of isotope separation” (which sounds to me like it means it would work better). But “the plans were shelved because thorium does not produce plutonium for bombs.”
As a happy bonus, apparently, thorium can also burn up our existing plutonium and toxic waste from old reactors, reducing radio-toxicity and acting as an eco-cleaner.
The Chinese are pioneering a design whereby, if it overheats slightly, the liquid fuel simply drains automatically into a separate container and the reactor turns itself off. No power supplies needed to pump water in or out. No high pressure containers that explode if the pressure rises too high.
Why would we have done it any other way?
(Oh, and apparently, although the earth’s crust holds about 80 years of uranium at expected usage rates (I have also read 60 years or less) thorium is as common as lead — there is enough to power civilization for “thousands of years”.)