Outer breeder

There are 977 elements still positioned vertically around the reactor core.

Each element is approximately 2.4m in length, 33mm in diameter and is made up of 14 metal “pucks” laid end to end inside a steel tube.

They remained inside the reactor after its shutdown in 1977 because the site did not have enough storage space.

Before they can be removed, the reactor system needs to drained of its coolant - a liquid metal alloy known as NaK.

Once the bulk of this liquid metal has been removed, each element can be lifted out the reactor vessel and transferred to a new facility where it will be checked, dismantled, cleaned and packaged up.

The last two elements remaining in the inner breeder zone will also be removed.

About 10 per cent of these elements are thought to have been distorted by radiation when the reactor was running.

Construction of the facilities needed to remove the last of the breeder from the reactor started in 2004.

A retrieval and processing cell has been constructed inside the sphere in the reactor hall.

The cell towers 27ft above the floor and contains a robotic arm that will reach down through the rotating shields that made up the roof of the reactor vessel.

There are 16 different tool heads on the robotic arm and these will be used to grip, cut and lift each element from the rack of the breeder zone.

This highly specialist tool was manufactured and tested by Areva at Toulon, France.

Animation showing how the breeder material will be removed

Each element will be lifted into a sealed container inside the sphere.

The container will leave the sphere through a transfer tube that exits inside an adjoining facility built to process this material.

Here, each element will be dismantled inside a cell and the “pucks” lifted out and cleansed of any residues of liquid metal.

In the next compartment, the pucks will be “recanned” inside a new tube that meets the specification for fuel going into the chemical works at Sellafield.

Once recanned, the material will be moved into a robust transport container, known as a flask. At this stage it will be ready to be exported from the site.

The whole process line is sealed, with its own ventilation system, behind reinforced concrete walls. Viewing windows made from lead glass will allow staff to work on the breeder using remotely-operated tools.

This includes long extension arms known as master/slave manipulators that can reach every area of the workspace.

All this work is undertaken in a nitrogen atmosphere to reduce the risk of air ingress and a reaction with any residues of liquid metal.

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Image: The 24ft high retrieval mast towers above the process cell on top of the reactor

The 24ft high retrieval mast towers above the process cell on top of the reactor

Image: The top of the reactor where the process cell and retrieval equipment is being installed

The top of the reactor where the process cell and retrieval equipment is being installed

Image: A mock breeder element sits in the process line where the material will be dismantled

A mock breeder element sits in the process line where the material will be dismantled

Image: Work begins on the new facility where the outer breeder will be processed

Work begins on the new facility where the outer breeder will be processed

Image: The exterior cladding of the building nears completion

The exterior cladding of the building nears completion

Image: These are the remotely operated manipulators that workers will use to handle the breeder inside the process cell

These are the remotely operated manipulators that workers will use to handle the breeder inside the process cell