Decommissioning work at Sellafield nuclear site in the UK has reached two milestones.

Work has begun to remove Sellafield’s most hazardous material, a highly radioactive ‘liquor’ that has been taken out of one of the oldest parts of the Magnox Swarf Storage Silo for the first time.

And the site’s tallest chimney is being brought down brick-by-brick using a platform that climbs up the structure itself.

The radioactive ‘liquor’ has been inside the waste store for many decades. It was created when water was used to cover the waste so it could not ignite.

New networks of heavily-shielded pipes have been built to help get take the material out of the building. Teams from Sellafield Ltd and supply chain companies recently transferred the first batch.

Chris Halliwell, of Sellafield Ltd, said: “This has been one of our biggest technical and engineering challenges to date. The first transfer worked just as planned. The team can now press on with meticulously making each transfer, reducing the hazard posed by our biggest current risk.”

The clean-up of the Magnox Swarf Storage Silo is one of the Nuclear Decommissioning Authority’s (NDA) highest priority programmes.

Duncan Thompson, head of Sellafield programme for the NDA, said: “The clean-up of the Magnox Swarf Storage Silo is one of our highest priority programmes. It is a highly complex task involving the removal of many different types of waste. I’m delighted to see the progress being made in removing radioactive liquor.

The building contains 22 vertical compartments that store waste from the UK’s first generation of nuclear power stations. It was constructed without plans for how the waste would eventually be taken out. The building is no longer suitable for long-term storage of nuclear waste.

As a result, innovative solutions are being deployed to retrieve waste from what is effectively a locked vault.

Work to ‘scoop’ solid waste out of the store, using the first of three 350-tonne mobile emptying machines, is scheduled to start next year.

They will be locked into position above each compartment and the waste pulled out through an opening. It will then be transferred to new buildings at Sellafield for treatment and interim storage, pending final disposal at the UK’s Geological Disposal Facility.

The silo will then be fully decommissioned and demolished.

Meanwhile, the demolition of the chimney marks on of the most daring projects ever undertaken at Sellafield.

Workers on top of the platform have been removing the concrete and steel structure by hand at a rate of one metre a week.

The painstaking approach is necessary because the 61m chimney sits on top of an old nuclear reprocessing plant and is surrounded by buildings containing hazardous material.

That means traditional explosive, compressed air, or water-related demolition techniques can not be used.

Simon Rowe, of Sellafield Ltd, said: “We’ve safely demolished 15 metres of the stack, taking a quarter off its height. That means it no longer poses a risk to any of the active plants around it.

 “It’s a major achievement and removes the radiological risk associated with this landmark of the Sellafield skyline. The tricky nature of the demolition job wasn’t the only complicating factor of the project.

Because the chimney provided ventilation to many other buildings around it, a new stack had to be built and those ventilation lines re-routed.

The new chimney – known as the Separation Area Ventilation project – began operating in 2016. The older chimney is due to disappear completely by 2020.

The self-climbing platform is similar to the method used to demolish chimneys at London’s iconic Battersea Power Station. It is held in place by 84 rubber pads which press against the barrel of the chimney. Only friction prevents it from falling. To move upwards, half of the pads are released, raised and tightened. The other are then raised and the platform inches up to the top of the stack.

It began its 61m ascent in November 2016 and arrived nine months later in August 2017.