Thorium

Thanks to my Friday morning pal Joe Gilad for introducing me to the subject of Thorium. What's interesting about Thorium, symbol Th, atomic number 90, is that it is a naturally occuring element found abundantly around the world, it is radioactive and can be used in nuclear energy production. It has two great advantages over uranium, first it does not need to be isotopically purified, as uranium does to enrich U235, which is the fissionable isotope of uranium, so it is much cheaper to use, and second that it cannot be used for the production of weapons and cannot go into "melt down." Given the recent events at the Fukushima nuclear energy plant in Japan these are significant advantages.

Why haven't we all heard about Thorium, when in fact it has been used in the US to produce energy in an experimental facility for 5 years, and there are major programs under way to exploit it in India, Russia, China and S. Africa. These are all countries that have large deposits of Thorium ores from which the necessary metal compounds can be isolated with relative ease. The isotope with 100% abundance of Thorium is Th232. When it is bombarded with neutrons from a small uranium or plutonium source it produces the unstable isotope U233 that fissions into smaller products similar to U235 and produces heat energy. But, if the activating source is removed the Thorium pile immediately cools and loses its fission capability.

It has been used in various designs, most notably as a molten salt that is circulated through a network of pipes, thus heating water to produce steam and electriciy, the so-called molten salt reactor (MSR). This was run successfully in Oak Ridge National Laboratory under physicist Alvin Weinberg, and a similar project was undertaken at Tel Aviv University by Alvin Radkovsky in collaboration with the IAEA. Among the further research and development projects of Thorium based energy production, Ben Gurion University has a joint project with the Bookhaven National Labororatory. Since India and China have active programs developing Thorium based energy plants, we cannot say that this is an unknown and obscure subject. Perhaps the most important fact about Thorium is that it does not produce neutrons itself and so cannot develop a self-sustaining nuclear chain reaction, in other words neither a bomb nor a melt-down.