Plutonium disposal

A scientist from Sheffield University has developed a pioneering method of disposing safely of plutonium, the highly-dangerous, radioactive waste element used in most modern nuclear weapons.

There is currently no method for the safe disposal of unwanted plutonium that is generated during the production of nuclear energy. Until now, the world´s 1800 tonnes of unwanted plutonium, which exists largely in the form of spent fuel, has been kept in interim storage, with no way of disposing of it completely. This has caused a long-term waste management problem, as well as creating a potential security threat. Only a few kilograms of plutonium are needed to make a nuclear bomb.

But now, Prof Fergus Gibb and a team of researchers from the university´s Department of Engineering Materials, have successfully demonstrated that plutonium can be incorporated in a stable waste form and mixed with crushed granite, which is then partially melted and completely recrystallised under slow cooling conditions. This recrystallised rock can then be safely disposed of.

It had been widely believed that such recrystallisation could only be achieved through extremely slow natural cooling over hundreds, if not many thousands, of years. However, Prof Gibb says that his tests have successfully melted and completely recrystallised the granite within a few months.

The method uses deep borehole technology to dispose of the plutonium-bearing granite. In conventional systems for nuclear waste disposal, the waste is buried in tunnels between 300 and 800 metres below the surface. In deep borehole technology, one of Prof Gibb´s major research topics, the granite containing the waste is deposited into vertical shafts three to five kilometres down, deep into the Earth´s crust where it is in equilibrium with the enclosing rock, thus rendering it safe to bury forever.

'Our method of plutonium disposal is surprisingly simple. Recent advancements in drilling technology have meant that we can now go much deeper into the Earth´s crust to dispose of nuclear waste. Using these deep boreholes we at the university have created a method of safely encapsulating plutonium before burying it and disposing of it completely,' said Prof Gibb.