After the Fukushima Daiichi nuclear disaster where 3 reactors that were first commissioned over 40 years ago went into full meltdown the future of nuclear power has been lifted from obscurity to the forefront of many news cycles. The world is reacting quickly and decisively for fear of a Fukushima type disaster. Germany has decided to close all nuclear power facilities by 2022 . Switzerland has followed suit with Germany by issuing a nuclear power end date of 2034 . Even China is taking a closer look at the safety of its variety of aging nuclear reactors . The entire history of nuclear power has been plagued by concerns over nuclear waste, catastrophic meltdown, nuclear weapon proliferation, and high costs of new plants. But what if nuclear power plants could use a “magic” fuel that had essentially no chance of melting down, produced an order of magnitude less radioactive waste with a shorter half-life, did not produce national security sensitive plutonium as a by-product, and served as an incinerator for the pesky nuclear waste from older reactors? Thorium may be this “magic” fuel of choice.
Over the near 60 year history of splitting the atom uranium has been used as the primary fuel stock for nuclear fission (typically uranium-235). However, thorium may be posed to assume this throne from Uranium (and incinerate the old king at the same time). Thorium is found naturally in the earth with the United States retaining a significant portion as shown in the table below. There is approximately 550 times more thorium in the earth’s crust than uranium.
The fission material is not fissile in that it does not react on its own; rather, thorium needs a “catalyst”. There are two main methods of thorium fission that have been proposed thus far. One method uses a uranium core, surrounded by a plutonium blanked, and then an outer shell of thorium. This method still relies on the “bad stuff” to get the atoms to split. The second method involves bombarding lead with high-energy protons using a particle accelerator which subsequently releases neutrons that cause the thorium begin its fission process . The advantage of this method is that the process is sub-critical, in other words it won’t continue on its own like a uranium or plutonium reaction.
When Thorium (Th-232) absorbs a neutron it transmutes into unstable Th-233 and then protactinium (PA-233) and then into Uranium (U-233). This eventual U-233 is fissile like U-235 but it is lighter and fission using this element results in waste that is less radioactive than products from U-235 . One of the most notable absences in the process is the lack of plutonium production such as in the U-235 process. The waste from a thorium reactor would be just as manageable as coal ash after 500 years . This is in stark contrast to the 10,000 years of U-235 process waste. The thorium process will also incinerate plutonium if it is added to the mixture providing a disposal avenue for the controversial material.
Norway is currently in the planning stages for a four year test of thorium in a heavy water reactor which simply means that the coolant for the reaction is deuterium oxide. Molten salt or pebble bed reactors would be a better match for the thorium reaction but the heavy water reactor serves as a start of potentially revolutionary operational research . It is also worth noting that the first method of thorium fission using a uranium core and plutonium blanket could be retrofitted into currently existing nuclear power plants while the second method using a particle accelerator and lead would require new construction which is often cost prohibitive .
Thorium is nowhere near prime time as a replacement for uranium reactors but it holds great promise for more stable, secure, and prolific energy in the future. There is simply not enough in the way of practical research using thorium as a fuel yet . It’s possible that one day Lewis Strauss, the first chairman of the Atomic Energy Commission, will have his prediction come to fruition of electricity being “too cheap to meter” due to thorium.
<Insert stereotypical space race to the moon analogy>