When Glenn Seaborg’s team discovered in 1942 that thorium can be transmuted to uranium-233, they say that the future Nobel laureate exclaimed that they had made a 50 quadrillion dollar discovery – that is ‘5’ followed by 16 zeroes. Perhaps it was just euphoria, or maybe Seaborg thought of a world powered by thorium for a thousand years that made him utter what seems like such a hyperbole. Regardless, the scientist’s observation still stands – thorium provides an excellent option for the world to adopt a fuel that is reliable, abundant, safer, and environmentally friendlier than anything that is in use today.
For enthusiasts, progress is always slow, but all signs indicate that after decades of neglect, thorium technology is witnessing a revival. Several small private companies have started researching, designing, and promoting new reactors that are fuelled by thorium instead of uranium. Coming at just the right time with concerns of climate change reaching a peak and an ambivalence towards conventional nuclear energy in the West, thorium energy can well be the vehicle that creates tomorrow’s energy barons.
It is not that thorium has sprouted new enthusiasts overnight – the benefits were known decades ago. However, thorium reactor designs did not serve what was then seen as the primary purpose of providing for the military’s requirements of fissile material for their weapons programme. Alvin Weinberg, former director of the Oak Ridge National Laboratory, who, ironically, was one of the pioneers in light water reactor technology, was one of the early thorium enthusiasts as far back as the mid-1940s. Weinberg had criticised the light water path in a 1946 paper he had co-authored, suggesting the use of thorium to resolve several of the challenges the LWR design faced.
Thorium advocates even today emphasize some of these same strengths that Weinberg pointed out over half a century ago. One, for example, is that thorium reactors consume their fuel much more efficiently than uranium reactors. Conventional reactors burn through only about two or three percent of the fuel; a whopping 97 percent is jettisoned as nuclear waste. This waste contains not just uranium but also other long-lasting, highly radioactive, elements that makes disposal a complicated process. Furthermore, the volume of waste generated will be of concern if the world adopts nuclear power wholesale.
On the other hand, thorium reactors have been designed to burn their fuel more completely: some 98 percent of the fuel is used up and the resultant waste is a fraction of what conventional reactors generate. Such a high burnup reduces the cost of fuel as well as waste storage. Its most positive feature, however, is that few of the radioactive transuranic elements in conventional nuclear waste are present in thorium reactor waste; the thorium-uranium fuel cycle does not irradiate uranium-238 and consequently, plutonium, the key element proliferation experts fear, is also not present. Storage becomes significantly easier, safer, and trustable with thorium technology, a most useful feature when considering the possible deployment of hundreds of such reactors worldwide. In fact, thorium reactors can even be configured to burn existing nuclear waste and bypass the endless debates on geological depositories.
It is not just the waste that makes thorium technology attractive: the Liquid Fluoride Thorium Reactor as well as the Advanced Heavy Water Reactor, the two primary thorium reactor designs in vogue presently, operate at low pressures. This reduces the chance of what is called a Loss of Coolant Accident or LOCA and lowers operational and construction costs. In fact, once a short, initial learning period is over and thorium reactors become mainstream, construction costs may become competitive with thermal power plants.
Although important, cost is not the primary lure of thorium technology. Thorium reactor designs come with several passive safety features that enhance safety. These innovations have made the reactors so safe that they can run for several days without any human input. The use of inherent properties of the fuel and other materials ensures that the reactor would shut down in case of an accident and the probability of a threat to human health is minuscule. For example, the Indian AHWR is considered so safe that Shiv Abhilash Bhardwaj, chairman of the Indian Atomic Energy Regulatory Board, has declared that the reactor could be built in the middle of a city without causing any concern. Not only would this reduce transmission costs but such characteristics could go a long way in allaying public fear about nuclear energy.
Another quality thorium reactors can boast of is their proliferation resistance. With the elimination of plutonium from its fuel cycle, thorium reactors are not particularly useful in clandestine nuclear weapons programmes. Over the past decade, several countries have expressed an interest in nuclear energy. Although dampened by the accident at Fukushima, Asia and Africa remain firm in their enthusiasm. The expansion of nuclear energy will put additional strain on an already extended IAEA. However, were thorium to become the face of the nuclear renaissance, it would ease the burden on the world’s proliferation watchdogs.
However, it is true that the uranium-233 into which thorium transmutes is a fissile material and may be used for weapons manufacture. Nonetheless, this is easier said than done: the uranium-233 in a thorium reactor contains an admixture of its isotope, uranium-232. The decay chain of this latter isotope is a potent source of gamma radiation and handling it requires remote manipulators. Furthermore, radioactivity increases and peaks around ten years for uranium-233 with even a five parts per million contamination of uranium-232. This is largely because of the presence of thallium-208 in the decay chain. Since the two uranium isotopes are chemically indistinguishable, it is very difficult to separate them for a weapons project.
Still, it is possible to remove the protactinium from the reactor so that it would decay to pure uranium-233. This would, however, require a dedicated national programme and make the theft or diversion of materials for a weapons programme easier to detect. Like the Non-Proliferation Treaty, the Limited Test Ban Treaty, or the export controls of the Nuclear Suppliers Group which do not eliminate nuclear proliferation but make it more difficult, thorium reactors present several hurdles to a potential proliferation effort that makes weaponisation more difficult.
The best part about the promise of thorium is that it is already known to work. Research efforts in the United States between the 1960s and early 1980s have demonstrated that thorium reactors are feasible. Since then, related technology has only moved forward. India is ready to break ground on its AHWR design, proofing another design for the same principles.
The world stands on the cusp of a thorium renaissance. Not only has the thorium movement attracted excellent nuclear talent to itself but it has also evinced the interest of billionaire businessmen like Bill Gates, whose TerraPower has been investing in developing its own thorium molten salt reactor design. The environmental benefits of thorium reactors aside, there is an enormous economic windfall awaiting the first movers in this technology. The immediate next step, however, is for businesses to sit down with regulatory authorities to develop safety protocols for these new reactors.