Experts get ready to open liquid metal vaults

Experts are getting to look inside a concrete vault used to store liquid metal from the cooling system of the Dounreay Fast Reactor.

It’s the latest phase of a major programme of work to dismantle one of the country’s biggest environmental hazards – Britain’s experimental fast breeder.

The tanks contained primary and secondary sodium-potassium liquid metal coolant, known as NaK. Now empty, they still contain residual matter.

The primary coolant is radioactive, so their decommissioning will be strictly monitored to maintain a safe working environment.

The investigation work will be done from a purpose-built steel-framed structure. A specialised camera will be lowered into the tanks through a stainless steel tube. This will penetrate the 250mm thick vault roof allowing, all drilling and camera operations to be performed outwith the vault itself, where an inert atmosphere must be maintained due to the nature of the liquid metal.

The drilling rig and purging system was designed in-house by DSRL design engineers. The drilling technique was developed at Gow’s of Lybster in an off-site replica trial rig to safely mimic the physical conditions on site.

The rig will be located on the vault roof and mounted within a nitrogen-charged glovebag. The drill will be lowered down the stainless steel tube and a hole cut in the top of the tank. The drill is then withdrawn and the penetration sealed at the vault roof. The specially-adapted camera descend into the tanks via the tube.

The camera footage will give the team a better understanding of the amount and disposition of NaK residues within the tanks and assist their strategy for the dismantling work. Initial inspections are due to be complete by June 2011.

Mike Brown, reactors decommissioning manager, explained: “The DFR NaK is one of the highest hazards for the NDA estate and the safe removal of this highly dangerous material and dismantling of associated facilities is crucial to the site’s decommissioning programme.

“Decommissioning DFR is one of the most significant challenges in the UK today and has presented DSRL with many unique challenges over many years. The staff and contractors involved have been totally committed and worked extremely hard to ensure the safe and successful progress that has been made to date.”