LONDON – Britain's plutonium stockpile, the biggest in the world, has just grown by another three tonnes as the German and Dutch governments have handed over their stores, apparently glad to be rid of it.

This manmade metal was once thought to be the most valuable substance in the world. 10 kg could make a nuclear bomb, or generate 100 million kilowatt hours of electricity. But plutonium is now widely seen as a major liability, particularly if you have 118 tonnes of it, as the UK now does.

The British government, however, believing it may still find a peaceful use for the plutonium, still regards it as an asset. It keeps its stockpile under 24-hour armed guard at the Sellafield nuclear plant in Cumbria in northwest England.

It argues that the energy the plutonium contains should be harnessed to produce low carbon electricity as part of the battle against climate change.

Anyone who comes up with a scheme to do this would make billions of pounds from British taxpayers. But experience has shown that exploiting plutonium is not for the faint-hearted.

Unworkable, uneconomic, or both

Despite previous setbacks there are companies who believe they can provide a solution using techniques similar to past failures. Several nuclear states – Russian, Japan and France – have tried to develop fast breeder reactors using plutonium, but all have abandoned them as unworkable, uneconomic or both.

The British government ran a successful prototype in the 1980s but concluded a scaled-up version, even if it could be made to work, would be hopelessly uneconomic.

The second option, of burning plutonium in normal reactors by mixing it with uranium to create a fuel called MOX, or mixed oxide, is complex. It is always expensive and in Britain has been an economic disaster.

Sellafield's MOX plant was designed to use up the plutonium stockpiles and produce 120 tonnes of fuel a year, but repeated technical difficulties proved insuperable. After five years the plant had produced only five tonnes of usable fuel.

Treat as waste?

To fulfill the few contracts it had, the plant's operator, British Nuclear Fuels, paid the French to produce the fuel in their own much older MOX plant. The Sellafield plant's closure was announced in August 2011 after Japan, its major customer, no longer wanted fuel following the Fukushima disaster. Over its short lifetime it lost £1.4 billion.

The alternative to using plutonium as a fuel is to treat it as waste, an approach favored by many governments and most environmental groups. This, too, would involve investing billions of pounds in finding some way of destroying or diluting the plutonium so it could never be used for weapons.

Britain, aware that this process would also render its expensively produced plutonium useless for energy production, has repeatedly rejected this course of action. This is partly because thousands of people are still employed in Cumbria creating yet more plutonium.

Thirty years ago the Government erroneously thought uranium for nuclear reactors would become scarce and plutonium could be substituted. As an insurance against scarcity it sanctioned new reprocessing works to recover plutonium and spent uranium from used fuel for peaceful purposes (previous works had been developed to feed plutonium to the nuclear weapons program).

World's largest stockpile

To make money out of the new plant, contracts were signed to reprocess spent fuel from Japan, Germany and six other countries, recovering their plutonium as well. The result is the world's largest stock of plutonium, some of it owned by these customer governments which now, finding they have no use for it, have handed it over to Britain.

Although there is no obvious market for all this plutonium, spent fuel from existing reactors is still being reprocessed to extract yet more plutonium, adding to the stockpile.

Meanwhile owning 118 tonnes of plutonium is an ever-more-expensive problem. It is a volatile substance constantly in a state of radioactive decay that can be stored only in small separated amounts to keep it from reacting with itself, a process called "going critical."

A specially built new store has just been commissioned at Sellafield. The annual costs of looking after this much plutonium are currently estimated at £80 million a year.

The government is convinced that one day it will be an asset despite all the evidence to the contrary. It is waiting for the Nuclear Decommissioning Authority, a quasi-autonomous watchdog charged with dealing with waste and "end products" of the nuclear industry, to come up with a solution.

Three options

Three options under consideration are new versions of failed technologies. Two involve building a new MOX plant to create a new sort of fuel to burn plutonium and uranium in either Canadian reactors or yet-to-be-built British ones. Both require large investments by British taxpayers, about £6 billion.

The third option is a new fast-breeder reactor, different from the old failed type, or so its proposers claim. The GE Hitachi Prism reactor, to be developed by the Japanese, would burn plutonium and also produce new fuel for other reactors. Not yet built, in theory it will work, and its proposers say they will bear the cost of construction.

The Decommissioning Authority says it will come up with a preferred option on what to do with the plutonium soon, burning it as fuel or disposing of it as waste, and then the government will have to decide.

Campaigners against the UK nuclear industry believe none of the schemes to use plutonium as fuel will work, and that by taking ownership of other countries' stockpiles Britain is making a bad situation worse.

Abandoning plutonium

Martin Forwood, of Cumbrians Opposed to a Radioactive Environment, said successive governments had pledged to ensure that plutonium belonging to foreign governments would be returned to them. Now, as these governments had abandoned using their plutonium as fuel, the UK had agreed to take it.

"Britain is being used as a plutonium dumping ground," he said. "All those promises and the contracts saying the waste and plutonium would be returned to the country of origin have been put on one side. It is a disgrace."

As for using plutonium as a fuel, he said: "Lessons have clearly not been learned from the UK's past MOX mistakes, which have already cost the taxpayer a fortune. Common sense dictates the government and the NDA should treat plutonium as waste and put it out of harm's way once and for all."

Adrian Simper, the NDA's strategy and technology director, seemed pleased at what he called the "market tension" of alternative ways of using the plutonium. He told the London Financial Times the intention was to tell the government whether there were "three, two, one – or even no ways forward." At some point it would have to decide the fate of the plutonium.

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.