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Thorium was first discovered in Norway, and definitively established as a unique element in 1828 by Jons Jakob Berzelius. The element was named after Thor, the Norse god of thunder in Scandinavian mythology. Marie Curie first established thorium’s radioactivity in 1898. It was the observation of thorium in experiments that first lead to the conceptualization of the half-life disintegration of radioactive elements[i]. Thorium’s industrial history, outside of the realm of nuclear fuel, has been limited.
Thorium has a substantive history with respect to its prospective use as a nuclear fuel. The world’s interest in thorium began at the inception of the atomic energy industry. It was evident that thorium was an abundant and naturally-occurring fertile element, similar to natural uranium, which could be used to create fissile material, and hence fuel nuclear reactions. This section summarizes the experiments and practical applications that have taken place using a thorium-based nuclear fuel.
Thorium’s initial interest subsided when it was discovered that it was extremely difficult to separate U233 for use in weapons, as compared to U235 or Pu239, which are relatively easy to weaponize. The USA, who was driving the nuclear race prior to and leading into the Cold War (1946-1989), made the decision to merge their military and civil nuclear programs, with the implications that:
- their fuel infrastructure would be the same as their bomb material infrastructure, which necessitated that the fuel be a U238/U235 cycle rather than Th232/U233 cycle, and;
- the rest of the world followed the lead of the USA and developed similar systems in their own sovereign nuclear programs;
- Uranium resources were thought to be abundant enough to support the infrastructure, and thorium was promptly dismissed, except for academic pursuits, and the uranium fuel cycle was adopted worldwide. At present, the global fleet of 440 reactors all utilize a uranium fuel cycle. (To find out why thorium fuel cycle is not in use, please visit [hyperlink for “Why Not Thorium?” page])
Thorium fuel cycles have been demonstrated in various nuclear reactor applications, including the following: High Temperature Gas-cooled Reactors (HTGR), Light Water Reactors (LWR), Pressurized Heavy Water Reactors (PHWR), Liquid Metal-cooled Fast Breeder Reactors (LMFBR), and Molten Salt Reactors (MSR), sometimes also referred to as Liquid Fluoride Thorium Reactors (LFTR or “LiFTeR”).
The most well-known and accessible example of a thorium fuel campaign took place at the Shippingport Atomic Power Station in Pennsylvania, USA. Shippingport was in fact the very first commercial-scale nuclear power station in the world to operate; it began operations in 1957. Between August 1977 and October 1982, Shippingport conducted a fuel campaign that burned a Th232/U233 seed-and-blanket fuel cycle in the light water application. The campaign generated an aggregate 2,100 gigwatt-hours (GWh) of electricity over 29,000 power-hours. The U233 was manufactured at Los Alamos National Laboratory in New Mexico, USA. The fuel achieved maximum burn-up of 60,000 MWd/tTh without fuel failure, which is still not achieved in practice in today’s reactors. (NB. Thorium One consultants project-managed the core design for that fuel campaign from 1965 to 1971.)
Beyond Shippingport, the table below, which is reproduced from the IAEA TECDOC on Thorium Fuel Cycle[ii], summarizes the history of thorium fuel tests since the beginning of the atomic industry.
It is noteworthy that these experiments with thorium have been largely unsuccessful. Experiments have often resulted in fuel failures, such as, for example, disintegration of fuel elements, melting of cladding, or explosions. Power reactors have not proven the commercial viability of a thorium fuel, and certainly not of a thorium reactor, such as MSR or LFTR. It has not been a simple matter to create a technically or commercially viable thorium-based fuel, which is why the advent of such a design constitutes a valuable and strategic resource. It is also important to note that of all the agencies involved in this area of research and development, it is the Atomic Energy of Canada Limited (AECL) who has had the most documented success. The AECL is Canada’s government-owned nuclear agency, and designer and seller of the CANDU Heavy Water Reactors (HWR). The AECL has conducted 25 separate irradiation tests on thorium-based fuels. These facts are essential to Thorium One’s business plan. (Please visit [hyperlink for “Fuel Technology” page] for more information.)
[i] Simmons, John Galbraith, “The Scientific 100: A Ranking of the Most Influential Scientists, Past and Present”, 2000
[ii] IAEA TECDOC-1450, “Thorium Fuel Cycle – Potential benefits and challenges”, May 2005
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