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Sometimes, it is not easy to assess the importance of a discovery: JJ Thompson, the discoverer of the electron, is said to have once called his sub-atomic particle a most useless thing. Today, that same useless electron has gone on to drastically transform the world. Thorium shares an almost similar tale. Discovered in 1829 by Swedish chemist JJ Berzelius from samples of earth sent him by mineralogist Jens Esmark, the new element named after the Norse god of thunder, Thor, held only academic interest for the next half century.
In 1884, Auer von Welsbach invented the incandescent gas light mantle which used thorium oxide. However, when electricity replaced gas for lighting by the mid 1920s, thorium was again nearly forgotten. What saved the element was World War II and the quest for the atomic bomb.
It was the golden age of atomic science: in 1895, German physicist William Röntgen discovered x-rays, though their mechanism eluded him then. The following year, French physicist Henri Becquerel observed that uranium salts emitted rays similar to x-rays in their penetrating power but differing in that they seemed to arise internally in the uranium than be caused by any external excitation. Although credit for the 1898 discovery of radioactivity in thorium goes to the German chemist Gerhard Carl Schmidt, he believed that “thorium rays” were similar to “Röntgen rays”; an accurate understanding of the phenomenon had to await the work of Marie Curie and Ernest Rutherford.
Rutherford’s further experiments revealed basic atomic structure as well as a better understanding of radioactivity. Frederick Soddy, Rutherford’s colleague, saw the enormous potential of their discovery and wrote that here was a virtually inexhaustible source of energy that could, properly applied, “transform a desert continent, thaw the frozen poles, and make the whole earth one smiling Garden of Eden.”
The beginning of World War II put nuclear physics front and centre of the Allies’ agenda. Afraid that Germany might beat them to a horrendous new type of weapon – the German chemists, Otto Hahn and Fritz Strassmann, together with Austrian physicist Lise Meitner, had successfully created a small fission chain reaction in 1938, after all – the United States commenced the Manhattan Project, one of the most secretive, international, well-funded, and undemocratic technological initiative to date.
In this project, Glen Seaborg was tasked with assessing which would be the most suitable element to make a nuclear device. Due to wartime exigencies, no efforts were spared in rushing to an atomic bomb. Seaborg was allowed to experiment simultaneously on all tracks he thought worthy of yielding a working weapon – a very expensive proposition. As a result, research was conducted on uranium, plutonium, and thorium paths towards weaponisation. Thorium was found to be unsuitable for weaponisation and, again, the war came first: Seaborg spent most of the war years working with plutonium.
Seaborg’s work, however, had pointed to thorium’s eminent suitability as a fuel for peaceful purposes. Along with his research assistant John Gofman, Seaborg bombarded the thorium atom with neutrons from a cyclotron. They observed that thorium-232 transmuted to thorium-233 and then to protactinium-233. This was carefully extracted from the sample to avoid further transmutation to protactinium-234; after waiting for a couple of months, Gofman observed that the protactinium-233 had transmuted further, into uranium-233 as was later discovered. With the help of fellow researcher Raymond Stoughton, Gofman separated enough of the uranium-233 to test it for fissionability. As per his meticulous notes, it was on February 02, 1942, at 9:44 PM, that the uranium-233 first underwent fission via slow neutron absorption.
Seaborg had already noticed how abundant thorium was, far more than uranium, and when Gofman showed him the results of their labour, he is said to have exclaimed, “we have just made a $50,000,000,000,000,000 (fifty quadrillion) discovery!”
After the war, several of the scientists who worked on the Manhattan Project shifted their attention to peacetime applications of nuclear energy. Two of them, Alvin Weinberg and Forrest Murray, co-authored a paper on what would eventually evolve into the basic design for light water reactors. The authors were not remiss in noting the several drawbacks of their design, suggesting instead that a reactor operating on thorium would not face similar problems. In 1948, Weinberg became the director of the Oak Ridge National Laboratory and he kept the research on thorium reactors going. The Molten Salt Reactor Experiment was an experimental reactor that operated at ORNL from 1965 to 1969 and proved the viability of molten salt reactors.
Despite its success, the MSR programme was mothballed. The United States continued to work on the 50 quadrillion dollar discovery sporadically – such as with the experimental thorium-uranium-233 core inserted into a conventional pressurised water reactor at Shippingport in 1977 – but the results were not built upon. The reason for this, according to some such as Nobel laureate Carlo Rubbia, is that Washington was not interested in energy but in the production of plutonium to expand its nuclear arsenal and thorium reactors are particularly useless at supporting a nuclear weapons programme. It is only in the last decade that interest in thorium reactors in the United States has again risen but this time more among private entrepreneurs than the government.
Like the United States, most countries that were involved in thorium research gradually abandoned them. West Germany shut down the Lingen reactor in 1973, the Arbeitsgemeinschaft Versuchsreaktor in 1988, and the Thorium High Temperature Reactor in 1989; Britain’s Dragon reactor was switched off in 1976, and the Netherlands pulled the plug on their SUSPOP/KSTR in 1977. India was one of the handful of exceptions that continued to try and tame thorium for energy purposes. Homi Bhabha, the father of the Indian nuclear programme, had theorised along the same lines as Weinberg by 1954 that given the abundance of thorium and the scarcity of uranium in his country, they would be better served by a fleet of thorium reactors rather than what was appearing to be the conventional choice of uranium fuelled reactors. Indian scientists were keen on collaborating with as many of the advanced Western countries as possible, from the United States to France, West Germany, Poland, Hungary, and others in basic nuclear science.
The Atomic Energy Establishment Trombay started working on producing thorium nitrates and oxides in 1955; Indian Rare Earths had been extracting thorium from the beaches of southern India already since 1950, primarily for export to the United States in exchange for help setting up the nuclear programme. By the mid-1960s, India had started irradiating thorium in the Canadian-supplied CIRUS reactor and in September 1970, uranium-233 was first recovered from the process. Throughout the 1980s and 1990s, scientists at the Bhabha Atomic Research Centre conducted experiments on the properties of thorium, uranium-233, mixed oxide fuels, reprocessing, fabrication, and other aspects of the thorium fuel cycle. Progress was slow for multiple reasons: the technical requirements of handling highly radioactive substances are stringent and remote manipulation in glove boxes was time-consuming and tedious; India’s nuclear tests in 1974 resulted in technological sanctions against the country which disrupted academic networks and supply chains; as a developing country, India could not afford the lavish sums thrown at nuclear programmes in the United States, France, and elsewhere; finally, a lack of political vision and bureaucratic politics stifled the pace of development.
Nonetheless, by 1984, India had built Purnima II, the first reactor in the world that handled uranium-233, part of the thorium fuel cycle. Experiments were also conducted using thorium-based mixed oxide fuel bundles in the regular fleet of heavy water reactors. In 1996, KAMINI went critical, the only presently operating uranium-233 fuelled reactor operating in the world. India has also been working on several thorium reactor designs, each at different stages of completion: the Compact High Temperature Reactor, the Innovative High Temperature Reactor, the Indian Molten Salt Breeder Reactor, and most famously, the Advanced Heavy Water Reactor. Construction on the AHWR is supposed to break ground this year but that is a tale that has been repeated for the past 12 years.
In recent years, several private companies have also started entering the thorium reactor business. Flibe Energy has been marketing the Liquid Fluoride Thorium Reactor, while two doctoral students at the Massachusetts Institute of Technolgy started Transatomic Power on the strength of their Waste Annihilating Molten Salt Reactor.
Despite much optimism and promise, the development of thorium energy has historically been hampered by politics, bureaucracy, and economics. For a species whose hallmarks are greed and violence, it is sometimes puzzling that a 50 quadrillion dollar discovery is lying around, waiting to be tapped even 70 years after the realisation of its terraforming potential.
This post appeared on FirstPost on June 04, 2016.