Image caption Thorium could prove to be safer in reactors than uranium

Nuclear scientists are being urged by the former UN weapons inspector Hans Blix to develop thorium as a new fuel.

Mr Blix says that the radioactive element may prove much safer in reactors than uranium.

It is also more difficult to use thorium for the production of nuclear weapons.

His comments will add to growing levels of interest in thorium, but critics warn that developing new reactors could waste public funds.

Mr Blix, the former Swedish foreign minister, told BBC News: "I’m a lawyer not a scientist but in my opinion we should be trying our best to develop the use of thorium. I realise there are many obstacles to be overcome but the benefits would be great.

"I am told that thorium will be safer in reactors - and it is almost impossible to make a bomb out of thorium. These are very major factors as the world looks for future energy supplies."

Image caption Hans Blix says the world should try its best to develop thorium

His enthusiasm is shared by some in the British nuclear establishment. Scientists at the UK’s National Nuclear Laboratory (NNL) have been encouraged by the government to help research on an Indian thorium-based reactor, and on a test programme in Norway.

The Norway tests at the OECD’s nuclear trials facility in Halden are conducted in a Bond-style underground bunker.

A couple of charming Nordic homes perch on top of a hill at the edge of the town. Below them a garage door in a cliff face leads into a tunnel deep into the hill where the reactor hall lies.

In theory, at least, the mountain protects the town from an accident.

The thorium tests are being carried out by a private firm, Thor Energy (the element itself was discovered in Norway in 1828 and named after the Norse god of thunder).

The company hopes to get thorium licensed alongside uranium in current water-cooled reactor plants.

The British government says it would be useful to increase the fuel options for nuclear operators, as thorium is believed to be three times more plentiful than uranium. It is also currently being produced as a by-product from mining rare earths.

Staff from NNL have been advising Thor on the use of mixed oxide fuels (MOX). NNL has also been helping the Indian authorities develop a thorium reactor, as India sits on top of the world’s biggest thorium reserves.

Media playback is unsupported on your device Media caption Inside Norway's experimental nuclear power plant

The Thor project represents an evolutionary approach, using thorium in existing reactors together with uranium or plutonium.

Oystein Asphjell, chief executive of Thor Energy told BBC News: "There is lots of thorium in the world, very well distributed all over the globe. In operations, in a reactor, it has some chemical and physical properties that make it really superior to uranium as well. On the waste side, we don’t generate long lived waste."

China is going for a revolutionary approach, devising a next-generation reactor which its supporters say will enable thorium to be used much more safely than uranium.

Media playback is unsupported on your device Media caption Inside a mine rich in thorium

When a uranium reactor overheats and the fuel rods can’t contain the chain reaction, as happened at Fukushima, the crisis continues. If something happened to a thorium reactor, technicians could simply switch off the stimulus which comes from uranium or plutonium in a small feeder plant and the thorium reaction would halt itself.

Prof Carlo Rubbia from Cern previously told BBC News: "Thorium will be able to shut itself off without any human intervention... You just switch off the beam.”

"There are also no long-lived waste products... We estimate that after something like 400-500 years all the radioactivity will be dissipated away."

These advantages, if they were realised, would be huge. But thorium still has many technical problems to overcome. What is more, countless billions have been ploughed into uranium-based research and development, and in the words of Mr Blix, uranium has a very deep furrow, backed by vested interests.

Canada, China, Germany, India, the Netherlands, the UK and the US have experimented with thorium as a substitute fuel in the past.

Image caption The nuclear trials at Halden are conducted underground

Questions are being raised, though, about the advisability of pinning the world’s energy ambitions on another nuclear dream. Environmentalists often allege that if renewable power had commanded a fraction as much research funding as nuclear it would already be much cheaper and more common.

Dr Nils Bohmer, a nuclear physicist working for a Norwegian environmental NGO, Bellona, said developing thorium was a costly distraction from the need to cut emissions immediately to stave off the prospect of dangerous climate change.

"The advantages of thorium are purely theoretical," he told BBC News.

"The technology development is decades in the future. Instead I think we should focus on developing renewable technology - for example offshore wind technology - which I think has a huge potential to develop.”

If thorium ever makes it as a commercial nuclear fuel, uranium may be seen as a massive and costly diversion. Some supporters of thorium believe that it was bypassed in the past because governments wanted the plutonium from certain conventional reactors to make atomic bombs.

They believe thorium was rejected because it was simply too safe.

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