The Thorium “Dream Factory” (Updated 15.10.20)
When nuclear power was sold to a reluctant public in the 1950s, it was “safe, clean, cheap, dependable and virtually inexhaustible”. It took a few decades or longer for people to realize that these were lies. It is amazing that otherwise reasonable people are now falling for the same claim being made for another generation of nuclear reactors. Fact is, if it sounds too good to be true, it isn't true.
Some of us are old enough to remember when Atomic Energy of Canada pursued thorium technology aggressively in the 1970's only to abandon it when the risk of nuclear weapons became evident. One very small thorium reactor operated for five years in the 1960's at Oak Ridge, Tennessee. There is media buzz about thorium reactors in India and China but none have yet been built. The technology to bump energy production from the 15 KW of Oak Ridge to something suitable for commercial use is just not there; theory did not translate into action. Even the industry admits that developing the technology would be 30 to 40 years before scaled-up energy production would happen.
The Theory: Thorium, Th-232, is lighter than uranium and about four times more widespread in nature. Its decay is rapid with less high-level waste (defined as waste with lots of short-acting gamma emitters). A thorium reactor could act as a waste disposal unit for plutonium and produce uranium-233 for its own use. If such a reactor used a particle accelerator, it could be shut down quickly simply by turning off the neutron beam.
Safety? Referring to thorium-232 as a fuel is misleading. Thorium-232 has to be turned into uranium-233 by absorbing a neutron either fired at it by a linear accelerator or from the plutonium or uranium-235. The plutonium or uranium used to get the thorium started needs to be weapons grade. In the formation of uranium-233, U-232 also gets formed. Both U-233 and U-232 are extremely unstable.
A thorium reactor would use a molten salt in place of solid fuel. A meltdown accident is impossible. Molten salt in continuous flow is extremely corrosive; no one knows how well it can be sufficiently contained.
Clean? This cycle is not clean. It needs neutrons from another source to produce the fission cycle to get the process started. Then it is run by using protons from the uranium-233. To keep it running, the uranium-233 needs to be continually stripped of U-232 or the process clogs up. If reprocessing is done, it requires acids and alkalis producing large volumes of high-level liquid nuclear waste.
Recycle nuclear waste? Conventional reactors have created over 200,000 tonnes of waste so it would be a dream come true if a reactor could truly recycle that waste. There are a few radioisotopes that can be recycled; they are the ones that produce neutrons. Thus the only wastes that can be “recycled” would be U-238 (Depleted Uranium), U-235 (conventional fuel still present in waste), Pu-239 and other “actinides”.
Terrorist free? If the reactor is “recycling” plutonium, it has to be transported to the reactor. This step by itself would require extensive security measures. The uranium-233 produced in the reactor is itself weapons-grade material. In 1955, U-233 was used in a bomb that was part of the USA Operation Teapot.
Waste free? This is the most bizarre claim. Of course, thorium reactors would produce waste. Uranium-232 has a highly toxic decay chain. It must be continually removed from the molten salt in order for the energy-producing reaction to continue; otherwise, the reactor just winds down. Would a fission reactor be waste-free? While the waste would probably be more short-lived, it's production would be uncontrollable.
Cost? The biggest argument against following this line of research is that it is still theoretical and would cost unbelievable sums of money to develop. None of the main companies within the nuclear industry are particularly interested without huge government subsidies – something the nuclear industry has relied upon for the last seventy years.
Conclusion: Thorium is not a source of sustainable or renewable energy. Besides generating a list of false claims, a thorium reactor, if it existed, would be, like conventional nuclear power plants, unable to connect to the “smart grid” of the future.
“With uranium-based nuclear power continuing its decades-long economic collapse, its awfully late to be thinking of developing a whole new fuel cycle whose problems differ only in detail from current versions.” Amory Lovins, March 2009.
