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09/10/11
 

Thor forges safer nuclear power

Thorium could replace uranium to provide a reliable source of energy. Even environmentalists are backing it, reports David Derbyshire

It has 200 times the energy content of uranium yet creates 1,000 times less radioactive waste. It is as common as lead, as cheap as chips and can be carried in your pocket. And, appropriately for a metal named after a god, thorium is being touted as the metal that could save the world.

A growing number of scientists, engineers and politicians believe that the needs of Britain and the world will not be met by fossil fuels, wind farms or uranium. They believe the future lies in thorium nuclear power.

Tomorrow an international conference of thorium advocates will meet in New York to raise the profile of the "forgotten element".

Supporters of the International Thorium Energy Organisation include some unlikely figures. Along with the usual collection of bearded engineers and grey-haired civil servants are green activists who have finally conceded that nuclear power has a place in a zero carbon world.

Chief among them is Baroness Worthington, the 39-year-old Labour peer, former Friends of the Earth activist and force behind the last government's climate change act. She is also patron of the Weinberg Foundation, a body set up to campaign for thorium reactors.

The foundation is named after Alvin Weinberg, who developed a power station using the radioactive metal in America in the 1960s. His "molten salt reactor" was shut down in the 1970s.

Worthington believes the metal was sidelined because it did not produce the plutonium wanted for the cold war weapons programme.

"We need renewables such as wind, solar and marine power, but we also need a safe and sustainable form of nuclear power," she said. "If there is a form of energy that's zero carbon and can be deployed safely, why wouldn't you use it? "It has numerous potential advantages over uranium. The design of molten salt reactors can be made inherently safer and more fuel efficient, creating far less waste. The waste it does produce is less dangerous and not as long-lasting. As a fuel it's more abundant but also more dense, so you need less of it."

Uranium has been used for so long in the nuclear industry that few people are aware there is an alternative.

Thorium, however, was once a serious contender.

Discovered in 1828, named after the Norse god Thor and used for decades in gas mantles and toothpaste, it is four times more common than uranium but far more efficient as a fuel source. Unlike uranium, it does not have to be enriched before it can be used in nuclear reactors.

More than 30,000 tonnes are mined every year, and geologists estimate there are 3m tonnes in the earth's crust. Thorium is so energy dense that a ball the size of a marble can generate enough electricity for one person's entire life.

In the 1960s a prototype reactor using liquid thorium fluoride salt was created at the Oak Ridge National Laboratories, Tennessee, by Weinberg. Despite being fairly successful, it was dropped in the mid-1970s in favour of uranium plants. Now the mantle has been picked up again in America by Kirk Sorensen, a former Nasa rocket engineer who came across Weinberg's old notebooks. He is lobbying for money to create an experimental liquid fluoride thorium reactor.

Like the Weinberg model, his fuel rods would be made from thorium dissolved in fluoride salts. The fuel would be surrounded by a tank of liquid thorium salt that would absorb radiation and form new fuel that could be progressively fed back into the core. Heat from the salt would be used to turn water into steam to drive turbines.

"Thorium in itself is only a minor improvement over uranium in terms of economics, since in both cases fuel costs are a minor aspect of the operating costs of a nuclear reactor," said Sorensen.

"Far greater economic improvements can be realised by the use of liquid fluoride salts as the fuel carrier and coolant, since they can operate at high temperatures yet at low pressures.

It removes the basic accident conditions that can follow from the use of very high pressure water as a reactor coolant and solid enriched uranium oxide as a fuel."

Thorium needs help to get going and scientists estimate that a 1 gigawatt reactor would need a tonne of uranium-233 before a nuclear reaction got under way.

That would be all the uranium you need, however. Once the nuclear reaction begins, the thorium in the core turns into uranium-233. That releases neutrons, which turn more thorium into uranium-233. When a reaction has started, it can be kept going indefinitely simply by pouring in more thorium.

Supporters of thorium claim a liquid fluoride thorium reactor (LFTR) would be much safer than a conventional nuclear plant. If the reactor goes wrong, an emergency plug underneath the core can be pulled, allowing the radioactive liquid to drain into a storage tank where it will cool.

The cores are cooled by air, so they do not need the high pressure domes and containment tanks used in conventional reactors. And without the mechanical cooling systems to go wrong, there is far less risk of a Fukushima-style accident and less risk of gas leaking.

Unlike conventional power plants, thorium reactors do not produce plutonium — the crucial ingredient for nuclear bombs. That means they are less likely to lead to nuclear weapons proliferation.

Sorensen said an LFTR would produce 1,000 to 10,000 times less radioactive waste than a traditional reactor. About 83% of waste products would be safe within a decade — while the rest would be safe within 300 years. Waste from a conventional uranium reactor can be deadly for 10,000 years. The reactors can also be used to process waste from current nuclear plants.

The Sorensen model isn't the only plan in the pipeline. Bob Cywinski, a physicist at the University of Huddersfield, wants to create a thorium plant where the fission reaction is initiated by a particle accelerator bombarding the core.

"We could get a prototype up and running by 2025," he said. "The problem is that we need the investment in the accelerator technology." Worthington reckons that Britain has just a few years to take thorium seriously or risk being left behind. The next generation of British nuclear reactors — planned for the end of this decade and the 2020s, will be based on conventional uranium.

China, however, has announced plans to fund a thorium molten salt reactor. India is looking at using thorium in solid fuel nuclear reactors. And the Czech Republic is waking up to the potential.

Worthington said: "The UK is woefully under-investing in nuclear development. If we are serious about this technology then this has to be reversed and funding for thorium should be made a priority."


Copyright David Derbyshire 2011