UK's plutonium stockpile dilemma
Britain has accumulated the biggest stockpile of civil plutonium in the world. What was once a valued asset is now viewed as a costly liability and a target for terrorists.
Previous attempts to deal with the stockpile have gone wrong and the government now faces a dilemma. Should it try to turn the stuff into nuclear fuel or write off the plutonium altogether?
Amid tight security at the Sellafield nuclear plant in Cumbria, is a store holding most of Britain's stockpile of plutonium.
The UK is currently home to 112 tonnes of what is the most toxic substance ever created - and most of it is held in a modern grey building to one side of the site.
Such is the sensitivity surrounding the building and its contents that only a handful of staff, with the necessary security clearance, are allowed inside.
Estimates suggest that the taxpayer currently spends £80m a year to store it safely and stop it from falling into the wrong hands.
Adrian Simper, Director of Strategy and Technology for the Nuclear Decommissioning Authority which now owns the site, admits the threat from terrorists is an ever-present risk.
"It is an active management constantly requiring expenditure of taxpayers' money and constantly managing the risk of having that material," he says.
Experimental nuclear reactors
So how did such a costly situation develop?
In the early years of Britain's nuclear programme it was forecast that the world's supply of uranium, the basic fuel for civilian nuclear technology, would rapidly run out.
It was a prediction that later turned out to be wrong. However, at the time Britain singled out plutonium as an alternative.
The material, extracted from reprocessed nuclear waste, was stockpiled as a source of fuel to power a new breed of experimental nuclear reactors.
But in the 1990s the reactor programme was cancelled on the grounds of cost and safety.
Only a small amount of plutonium had been used up and the stockpile grew further when Britain subsequently agreed to take in nuclear waste from abroad.
The aim was to turn it into plutonium and return it to its country of origin for a fee.
But, to date, none of the foreign owners have shown much practical interest in having it back.
Foreign owned plutonium now accounts for a quarter of Britain's entire stockpile.
Adding to the pressure is the fact that Sellafield continues to produce plutonium at its Thorp reprocessing plant.
The site, overlooking the Irish Sea, is a huge complex stretching a third of a mile long.
Each year it produces between four and six tons of plutonium, all of it adding to the stockpile.
So, while one arm of Sellafield is looking at ways of safely disposing of the plutonium, another is churning it out on a daily basis.
The question facing the government now is what to do with this most deadly of substances.
Their favoured option is to transform the plutonium into fuel that can be used in nuclear power stations.
It would involve building a factory that can turn plutonium into something called Mixed Oxide Fuel.
"The advantage for the UK is massive," says Sir David King the former science adviser to Tony Blair.
"We end up generating a large proportion of our energy needs from fuel that is available in this country," he says.
However, the cost of building the technology needed is estimated at between £5bn and £6bn.
And the plan has been tried before. On that occasion, it failed miserably.
Back in 1993 British Nuclear Fuels got approval to build a Mox fuel plant not unlike the one proposed today.
In 2006, a report by the consultants that originally recommended the idea, cited problems at the plant.
It listed 6,000 minor equipment failures in just two months.
It said the plant was "beset with difficulties" and the production line was "fragile and difficult to manage".
The Mox plant never reached a satisfactory level of production. When it closed, in March 2011 it had produced around 1% of what was expected.
The BBC has learned that the final cost to the taxpayer was £1.4bn.
So, what is the logic of trying to revive the plan?
"We believe we have learnt the lessons of the past," says Adrian Simper from the Nuclear Decommissioning Authority.
"There is no reason why a future Mox plant should not be very successful," he says.
The government will also have to be mindful of other practicalities before returning to this technology.
Of all the nuclear power stations in Britain only one, at Sizewell in Suffolk, is capable of using Mox fuel but it has not yet been licensed to do so.
Potentially valuable asset
It would therefore fall to those building new nuclear power stations to use it. But, so far, they are reluctant to do so.
Treating plutonium as waste, and disposing of it in a safe underground repository for thousands of years, is another option being considered.
The idea has gained traction with those who argue it sends out a better message to the world, including countries like Iran, about the use of nuclear materials.
Critics say burying waste is risky and, even then, the plutonium would have to be treated before it could go into the facility.
Supporters of plutonium as a fuel claim that would be throwing away a potentially valuable asset.
On top of that, we are not likely to have a repository for decades and very few local authorities have volunteered to consider having it in their back yard.
The policy took a blow when Cumbria Country Council blocked plans for a nuclear repository in January 2013.
Whatever the government decides will prove politically controversial and costly to the taxpayer.
The legacy of Britain's plutonium stockpile will be with us for years to come.