Then there's the safety side of thorium reactions. That's a heck of a lot better than the 3% to 5% of uranium that comes in the form we need. Thorium's advantages start from the moment it is mined and purified, in that all but a trace of naturally occurring thorium is Th232, the isotope useful in nuclear reactors. As such, the waste has to be housed for up to 10,000 years, cloistered from the environment and from anyone who might want to get at the plutonium for nefarious reasons. This waste fuel is highly radioactive and the culprits – these high-mass isotopes – have half-lives of many thousands of years. When the U235 content burns down to 0.3%, the fuel is spent, but it contains some very radioactive isotopes of americium, technetium, and iodine, as well as plutonium. When an atom of U238 absorbs a neutron, it transmutes into short-lived U239, which rapidly decays into neptunium-239 and then into plutonium-239, that lovely, weaponizable byproduct. The U238 does not just sit idly by, however it transmutes into other fissile elements. Once in the reactor, U235 starts splitting and releasing high-energy neutrons. As such, to make reactor fuel we have to expend considerable energy enriching yellowcake, to boost its proportion of U235. By contrast, the less-prevalent U235 is fissile. ![]() Most naturally occurring uranium is U238, but this common isotope does not undergo fission – which is the process whereby the nucleus splits and releases tremendous amounts of energy. The typical nuclear-fuel cycle starts with refined uranium ore, which is mostly U238 but contains 3% to 5% U235. In the post-Cold War world, is there any hope for thorium? Perhaps, but don't run to your broker just yet. The fact that thorium reactors could not produce fuel for nuclear weapons meant the better reactor fuel got short shrift, yet today we would love to be able to clearly differentiate a country's nuclear reactors from its weapons program. And here we come to it: Thorium reactors do not produce plutonium, which is what you need to make a nuke. The $2 billion Manhattan Project that produced the atomic bomb sparked a worldwide surge in nuclear research, most of it funded by governments embroiled in the Cold War. So why on earth are we using uranium? As you may recall, research into the mechanization of nuclear reactions was initially driven not by the desire to make energy, but by the desire to make bombs. ![]() ![]() And as proponents of the underdog fuel will happily tell you, thorium is more abundant in nature than uranium, is not fissile on its own (which means reactions can be stopped when necessary), produces waste products that are less radioactive, and generates more energy per ton. That means thorium could be used to fuel nuclear reactors, just like uranium.
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