Salt of the Earth: the promise of thorium nuclear reactors

The bottom of the Periodic Table is a murky place. It’s the home of elements with long, unfamiliar names; the domain of radioactivity and radiation. There are things down there which not even the furious furnaces of a supernova can make; things that only exist if you bombard other elements with subatomic particles. If the table were a medieval map, the bottom edge would be the bit marked ‘Here Be Dragons’.

Yet one of the elements from this lesser-known atomic landscape has been attracting increasing attention from engineers, who believe it might be important to helping to solve one of our greatest problems — how to generate plentiful, clean, safe electricity. Thorium, element 90, is one of the most energy-dense materials known, but it currently has almost no industrial applications.

Thorium is an alternative to uranium, which either fuels directly or is the basis for the fuel in every current nuclear reactor. Its proponents claim many advantages for thorium over uranium: greater safety margins, better safeguards against proliferation of nuclear weapons, shorter-lived waste products. But to get the best out of it would require a type of nuclear reactor which has never been built, and whose development was halted four decades ago.