The resurgence of nuclear power keeps popping in and out of news, with some media outlets decrying nuclear power as deadly and pointing to Three Mile Island (where no one died or was injured), Chernobyl (caused by a combination of bureaucratic incompetence and extremely poor reactor design), and Fukishima (reactors of Generation 1 design that were not adequately protected from the possibility of a tsunami, but where no one died from the reactor failures) as examples of how bad nuclear power is.
But one of the new nuclear technologies (which isn't new by any means) that is garnering more interest is nuclear reactors using the thorium power cycle rather than the uranium power cycle. Why thorium? Because it is a much better fuel for generating power than uranium.
First, thorium is quite common compared to uranium. There are thousand of tons of the stuff being stored in buried storage containers. This is not to keep it away from the environment like nuclear waste but because it takes less effort and money to store it in this fashion.
Second, it doesn't require enrichment in order to be used as nuclear fuel. Uranium in its natural state is mostly U238, a non-radioactive isotope, along with a very small percentage of U235, the isotope needed for nuclear fission to take place. Uranium must be enriched to approximately 5 percent U235 in order to be used in a reactor. Enrichment is an expensive and dangerous process.
Third, it can't melt down like a uranium fueled reactor because it requires an external neutron source in order to start and maintain a nuclear fission chain reaction. Shut off the neutron source and the fission reactions stops. Uranium reactors are self-sustaining meaning that unless some external device disrupts the chain reaction it will keep running. (This is usually achieved by control rods that absorb or block neutrons from the chain reaction when they are inserted in between the fuel rods in the reactor.)
Fourth, the fission products have short half-lives, unlike the plutonium byproduct of uranium fission which has a half-life of 25,000 years. This makes storing any waste products easier because they don't need to be stored very long before they are safe. Thorium reactors also produces less nuclear waste than uranium-fueled reactors. Plutonium is also dangerous in a chemical sense because it is a toxic material even without it being radioactive.
Fifth, it cannot be used to make nuclear fission bombs or so-called 'dirty' bombs that spread radioactive material over a wide area.
Sixth, and most important, one ton of thorium can produce as much energy as 200 tons of uranium or 3.5 million tons of coal. That's a lot of carbon-free energy. And we have a lot of thorium already in storage and there is a lot more readily available to be mined here in the US.
That brings us to a question I've heard again and again over the years: If thorium is so great, then why haven't we been using it? The answer is quite simple: nuclear weapons.
Since uranium fission produces plutonium, an essential ingredient in any nuclear weapon, it made sense to the Department of Defense to have commercial reactors use uranium in order to generate both power and the plutonium needed for nuclear weapons production. (The first atomic bomb detonated at the Trinity site used plutonium and was an implosion device. Little Boy, used on Hiroshima, used uranium and was a gun-type of device. Fat Man was another plutonium implosion device like the Trinity bomb.) Thorium reactors don't create the plutonium needed for nuclear weapons. Since having reactors that used two entirely different fuel cycles didn't make sense, the uranium fuel cycle was chosen. Of course that was back in the days when atomic bombs were seen as the weapon to end all wars. We have more plutonium on hand than we know what to do with so switching to the thorium fuel cycle makes more sense on a number of levels.
Now all that's need is convincing the rabid anti-nuclear folks that this is a viable means of producing vast amounts of clean energy without the downsides of four generations of uranium-fueled reactors.
