9 Apr (NucNet): Workers at the Dounreay nuclear site in Scotland have completed the destruction of one of the most hazardous legacies of Britain’s earliest atomic research.
On 6 April 2012 a purpose-built chemical plant processed the last of 57,000 litres of liquid metal lifted from the primary cooling circuit of the experimental fast breeder reactor at the UK’s former centre of fast reactor research and development.
The reactor – built in the 1950s – was one of only two ever built in the UK to run on liquid metal.
In a statement Dounreay Site Restoration Limited, the company responsible for the closure programme at Dounreay,said the coolant – an alloy of sodium and potassium (NaK) – was a major chemical and radiological hazard.
An estimated 1,000 trillion becquerels of caesium-137 was removed from the coolant during the chemical process that turned the 57 tonnes of liquid metal into 20,000 tonnes of salty water and took four years to complete.
The Nuclear Decommissioning Authority, which has overall responsibility for the cleanup of the UK’s legacy sites, said it was “extremely pleased” the liquid metal no longer posed a hazard.
“This was very high on the list of hazards we wanted reduced across our whole estate,” said Nigel Lowe, head of the NDA’s Dounreay programme.
Destruction of the liquid metal was among the strategic national priorities of the Department of Energy and Climate Change, which sponsors the NDA.
The reactor had two cooling circuits that were filled with more than 161,000 litres of liquid metal.
More than 100,000 litres of NaK from the secondary circuit was destroyed when the reactor shut down in 1977.
Work on the primary circuit – a labyrinth of pipes nine kilometres in length – stopped in the early 1980s when higher levels of radioactive contamination were detected.
The primary circuit contained 57,000 litres of NaK that flowed over the fuel pins in the reactor core.
With the reactor vessel empty of liquid metal, attention now turns to cleansing the residual traces from the primary circuit pipework and destroying small pockets in other vessels.
When complete, a robotic arm will reach into the reactor vessel and begin removing the burst fuel pin and almost 1,000 breeder elements still positioned around the core.
