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Just last month, the US secretary of energy Steven Chu had announced the formation of a Blue-Ribbon Commission on America’s nuclear future to resolve what to do with the waste. Space for the nuclear wastes comes at a premium. To tackle the problem, an old idea has been dressed in new language. But this time around it may make more sense.
The idea of so-called fast-neutron reactors has been resurrected. The reactor could consume nuclear waste through nuclear fission. But the designs of such reactors have a mixed track record. Since the 1950s, roughly around $100 billion has been spent on the research and development of such reactors around the world, yet there is currently only one such reactor producing electricity, the BN-600 in Russia. In a report on such fast-neutron reactors, von Hippel reported, “The interest in these reactors is that they are more efficient at fissioning long-lived isotopes…(which) will minimise the waste problem.”
The fast-neutron reactors are so-called because the neutrons used to initiate the nuclear fission chain reaction travel faster than neutrons moderated by water in a conventional nuclear reactor. The speed of neutrons is achieved at temperatures as high as 550 degrees celsius where liquid sodium is used instead of water as a coolant. The main problem with the reactor is that sodium is a highly reactive substance and burns explosively when exposed to either air or water. This reactive property requires efficient safety controls.
The problem and other design issues associated with steam generators that transfer heat from sodium to water have kept commercial designs of the fast-neutron reactors from becoming a reality. The French Superphenix sodium-cooled fast-neutron reactor operated successfully only for sometime because an accident at the plant cost one engineer his life and injured four other people when a leftover tank with roughly 100 kg of sodium residue exploded.
Perhaps the other significant problem with the fast-neutron reactors is the need for reprocessing the spent uranium fuel to plutonium and other fissile materials that could then be reused in the fast-neutron reactors. Such a reprocessing programme was encouraged in the US until the 1970s and was revived by the second Bush administration but shelved again by the Obama administration in 2009.
Another concern with reprocessing spent fuel is that the technology could be used to produce nuclear weapons. This also imposes a security threat. According to Von Hippel, roughly 250 mt of spare plutonium have been stockpiled in the UK and France and never used as nuclear reactor fuel. That's enough to make 30,000 Nagasaki-size nuclear bombs.
At the other end of the spectrum, the production of uranium as a primary fissile fuel in nuclear reactors has been experiencing shortages in the US. Reactors consume some 25,000 tonnes of uranium annually but only about 1,800 tonnes of the nuclear fuel is produced in the country, says Amir Adnani, CEO of Uranium Energy.
India has also faced limited natural supplies of the uranium fuel and this has led the country to explore another fissile element, thorium, as an alternative. If the highly fissile plutonium is enclosed in a thorium blanket then this could produce enough nuclear fuel forever, according to the vision laid out by the architect of India’s nuclear programme, physicist Homi J Bhabha in 1954. “The Indian government is in the process of developing a prototype fast-breeder reactor, despite limited success with a precursor, said Princeton physicist M V Ramana adding that “the cost of electricity is 80 per cent higher than from heavy-water reactors.” Uranium prices would need to increase 15-fold from current levels of roughly $80 per kg to make it economically attractive.
But as the future needs of power generation turn towards greener power production technologies, nuclear power might provide the ‘carbon-free’ alternative. Nuclear reactors “produce about 20 per cent of our electricity but fully 70 per cent of our carbon-free electricity,” Chu noted at a conference call recently.
The current disposal solution for the used fuel rods by first cooling them in water pools before being moved to dry casks sitting on the site of existing reactors is likely to continue in the status quo. About 64,000 tonnes of spent fuel is stored precisely that way today. “There is no problem with that in the short-term. Dry cask storage is very safe,” von Hippel said. “But over the longer term, you don't want spent fuel at 66 reactor sites indefinitely.”
The writer is a doctoral candidate at Carnegie Mellon University, Pittsburgh, PA and also knowledge editor at Financial Chronicle
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