Breeder element removal tool installed in fast reactor

24th December 2008

A versatile remotely-operated machine that will cut the heart out of Dounreay's fast reactor has been installed in the sphere.

The retrieval cell is a highly engineered tool that will reach down inside the reactor vessel and remove the remaining breeder elements in a delicate and precise operation.

The retrieval cell mast towers 27ft above the floor of the sphere. It is bolted onto the top of the retrieval cell, which in turn is bolted onto the rotating shields covering the reactor. The cell houses a series of specialist tools purpose built for the removal job.

The tools will be used to remove each 8ft element from the reactor core. It is an extremely hostile environment - the highly active elements are coated with volatile liquid metal at temperatures of fifty degrees centigrade.

Many of the elements are expected to be warped and distorted or swollen, and will have to be cut out of the reactor core before they can be removed.

Once free of the core they will be lifted into a flask and transported via a transfer tube to a process cell in the adjoining containment building, where they will be dismantled, washed, and packaged for safe storage. All of these operations are conducted under a nitrogen environment to prevent NaK fires.

The retrieval cell and mast were built in Toulon, France by French nuclear experts Areva, and tested with DSRL engineers in attendance, before being shipped over to Caithness and installed in the sphere.

It is a completely bespoke tool, which project manager Peter Poulton believes is unique.

"The distortion of the breeder elements was caused during the irradiation process, and has posed a problem to their removal," he explained.

"With our input, Areva have produced a machine that is versatile enough to be able to cut away every stuck element and remove it from the core."

Retrieving the breeder elements is expected to begin in 2012, once the bulk liquid metal coolant has been destroyed, and will take an estimated two to three years to complete.