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New, Clear And Safe?

BW Online Bureau Nov 08, 2014

<?xml version="1.0" encoding="UTF-8"?><root available-locales="en_US," default-locale="en_US"><static-content language-id="en_US"><![CDATA[If you are an apologist of nuclear energy, pause for a moment to consider these statistics. The world has 442 nuclear power plants that together produce 374 gigawatts (GW). Under construction are another 65, which will produce 62 GW. A typical plant also produces about 20 tonne radioactive waste in a year. This needs to be stored safely for near-eternity, if we think in practical terms. It does not need too much ingenuity to realise we would run out of space to store the waste if the industry expands rapidly. Look at India's nuclear ambitions. India gets 4 per cent of its electricity from nuclear energy. This will rise to 10 per cent by 2022 and 25 per cent by 2050, a plan that needs a consistent growth of 9.5 per cent a year for the next four decades. By then, India will be producing 470 GW of nuclear-based electricity, probably making it the largest user of nuclear power in the world. While many analysts consider this plan a piped ream, even partial success of it will generate huge waste. Given India's high population density, where will it store the waste? Fortunately, next- generation nuclear technologies can reduce the waste to manageable levels. For example, at the University of Texas in Austin, the Institute of Fusion Studies has been researching the problem. But instead of developing methods for safe burial of the waste, it looks at using it as a fuel in another reactor. It has designed a system that can burn 90 per cent of this nuclear waste, while also reducing the time the waste remains radio-active from centuries to decades. This techno-logy has attracted interest from all over the world, especially from India and China. In fact, the Department of Atomic Energy is planning to send a team to work in this lab.The institute has developed a hybrid nuclear reactor that combines nuclear fission and fusion to produce energy. Fusion is the way the Sun gets its energy; it happens when two atomic nuclei combine. In nuclear fission, an atomic nucleus splits into two or more. Both processes release enormous amounts of energy, but fusion is relatively safe as it produces far less radioactive waste than fission. But it is also more difficult to achieve controlled fusion. At the Institute of Fusion Studies and the University of Texas department of physics, scientists use fusion not as an energy source, but as a method to produce neutrons. It is the neutrons that split the nuclei, and lack of sufficient neutrons is the reason why we end up with the waste in the first place. As the byproducts of fission accumulate, they start absorbing neutrons without splitting. If we have a powerful external neutron source, the by-products of fission — which are highly radioactive — can be burned further. "We will never reach a situation where we have no waste, but we can reduce it to manageable levels," says Swadesh Mahajan, senior research scientist at the Institute of Fusion Research. The hybrid reactor, which combines fission and fusion in one device, has been a concept from the 1950s, but technology had not advanced enough then. Now hybrid reactor concepts have advanced to design and engineering stage. Three major groups work on this: Nuclear engineer Weston Stacey's group at Georgia Tech University, the Institute of Fusion Research in Texas University and the Institute of Plasma Physics at Hefei in China. All three have made major advances, but the Texas group has recently made a breakthrough that could lead to a real hybrid system soon. The group has designed Super X Divertor, a fusion device that is small enough to be lifted by a crane and put inside a blanket of fissile material. You can test this idea in two years, instead of the usual 10 years. There are, of course, several hurdles to cross before reaching a working hybrid, but experts do not consider any of them insurmountable. In fact, hybrid may become a necessity if we accumulate unprocessed waste the way the light-water reactors do at the moment. The beauty of the hybrid approach is that you need only one such reactor for every 15 conventional reactors to cut waste significantly. But the conventional reactor technology is itself going through a large shift. Almost all reactors are of second generation, which use Uranium 235 as fuel and krypton and barium as byproducts. They also produce elements such as plutonium that remain radioactive for hundreds of thousands of years. These are dangerous, and need enormous safety precautions. Most reactors have the spent but unprocessed fuel stored nearby. The Japanese Fukushima reactors would not have been so affected had they stored the waste as dry pellets elsewhere. Many such problems are taken care of in the fourth generation of reactors that will be tried over the next two decades. Three basic kinds of fourth-generation reactors are being developed: the gas cooled, water cooled and the fast reactors; all notable for their simplicity and safety features. For example, ‘pebble-bed' (gas-cooled) reactors have only two subsystems compared to 200 in light-water reactors.Fast reactors allow us to move away from using only uranium as the fuel source. "Physics does not tell us that only uranium can be used as a fissile material," says P.K. Iyengar, former chairman of India's Atomic Energy Commission. India is developing a fast reactor that will use thorium as a fuel. Thorium is not fissile, but can be converted into the fissile uranium 233 inside the reactor.  Fast reactors can handle an accident like the loss of coolant much better. It generates negligible amounts of plutonium and very little long-lived waste. Fourth-generation reactors could be the future of nuclear energy. Says Robert Grimes, professor of materials physics at Imperial College in London: "We may need to enter a phase of reactor building in two decades. And for this to happen, we need to excite young people to take up nuclear engineering as a career now."