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Clean power

Only a decade ago, the future of nuclear energy seemed uncertain. Countries such as France relied heavily on this source of energy, but environmentalists in most parts of the world opposed the technology. In the US, no new nuclear power plant had been built since 1978. Europe — with exceptions like France — was dead against nuclear power plants. Nuclear energy seemed at best a fringe option, until it stopped completely when we developed clean energy sources like wind and solar power. People had not reckoned with climate change.

Now as the world heats up, and no good alternative to fossil fuels is in sight, nuclear energy has come back to centre-stage. In the US, a few months ago, energy secretary Steven Chu awarded contracts to two sets of firms to design next generation nuclear reactors. If successful, these reactors could be approved by 2013, started by 2017 and be operational by 2021. In Sweden, always a staunch opponent of nuclear power, Parliament voted to overturn a 30-year ban on building new nuclear power plants. Other European countries like the UK, Finland and Italy are also working on plans to build new nuclear power plants.

However, this time there is a twist to the story: the new generation plants are considered safer. There is no uniform approach, but many countries are pursuing technologies that would result in considerably less radioactive waste. In fact, some of the new designs propose to use existing nuclear waste to run safer and more efficient reactors. Such reactors would still produce waste, but it would last a few hundred years instead of tens of thousands of years.

Current reactors use nuclear fission, in which a uranium nucleus is bombarded with neutrons. This splits the uranium nucleus, generating energy in the form of gamma rays and more neutrons that go and split other uranium atoms. If there are enough neutrons to split enough uranium atoms, the process sustains itself. However, it needs to be contained with the so-called moderators for the material to not explode like in a bomb. In all current reactors, the process exhausts itself after a while, resulting in waste that needs to be removed and stored.

Almost all reactors currently use decades-old technology called the pressurised water reactor. The waste that is removed from these reactors contains almost all the uranium that was originally there, apart from some plutonium that is a byproduct of the fission. Both are dangerously radioactive, apart from being useful materials to make bombs. Disposing of this is a problem, but the new breed of reactors would reduce the problem.

The Generation IV International Forum, a joint venture of sorts between the developed nuclear powers and Brazil, has shortlisted some designs to serve as the fourth generation of nuclear reactors. They include concepts like gas-cooled reactors, molten lead reactors, and those that dissolve the fuel in molten salt. The US programme will try out some of these designs, as will some of the European countries. All of them have their strengths and weaknesses. For example, the so-called sodium-cooled fast reactor uses spent fuel, and is thus useful to get rid of the waste, but can also be used to produce weapons-grade plutonium.

Two other processes, currently under development, would reduce the waste problem considerably. One is the travelling wave reactor (TWR), which is being developed by a private company called Terrapower. This firm, based near Seattle, has received investments from Bill Gates and has thus become one of the most keenly watched start-ups in the US. However, the concept has several technical challenges to overcome, and could become a reality only after a decade.

A TWR is actually an old concept, but has never been tested. On paper, it is a very useful concept. It eliminates the need for enrichment (and thus the chances of proliferation) and reprocessing the waste. It can use natural or even depleted uranium as fuel. Its champions say it can even be competitive with coal, the cheapest form of energy available. The TWR is named so because the reactor gradually creates the enriched fuel it needs from non-fissile material. Such a reactor could run for 200 years before it needs to be stopped.

The new concepts reduce the amount of waste produced. Yet another method is considered even safer: nuclear fusion. In nuclear fusion, two atomic nuclei fuse with the release of energy. Pure fusion still does not figure in the realm of possibility, but scientists have come up with hybrid methods that are safer than fission. Fusion is not used now to produce energy but it can produce neutrons. These neutrons can be used to sustain a fission reaction. Fission reactors end with a lot of waste because there are not enough neutrons to burn all the fuel.

Scientists at the University of Texas at Austin have designed a hybrid reactor that would work with modern light water reactors. It can use up 99 per cent of sludge, the most dangerous waste. It can also work in a small room. So the concept is ideal for producing energy as well as reducing nuclear waste. Of course, it takes a long time for a concept to become a reality.

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