Work is well underway at the Janetstown off-site test facility near Thurso to remove clean sodium from an assortment of vessels that were stored on the Dounreay site.
Sodium removal requires the operators to enter the vessel and break the sodium into blocks using electric breakers fitted with chisels. The sodium is then packed in steel drums for destruction in a national high-temperature incinerator. The remaining steel is sold as scrap. Eight vessels containing approximately three tonnes of sodium were destroyed last summer.
To complete the project, the final two vessels, each approximately three tonnes and containing two tonnes of sodium, must be processed in an oxygen-free atmosphere. Special equipment has been designed and constructed so the vessels can be opened and reduced in size without exposing the sodium to atmospheric oxygen. The sodium will then be destroyed at Janetstown using the water vapour nitrogen process developed there.
Each vessel will be cut open in a specially-designed containment glove box. The glove box has been designed so the vessel can be cut apart in an inert nitrogen atmosphere with operators using power tools standing outside. Oval glove ports allow arm movement and counterbalanced tools reduce fatigue. Once cut, the exposed sodium will be covered with nitrogen-filled bags and the glove box opened to allow each section to be moved into a special argon-filled vessel for the water vapour nitrogen process to destroy the sodium.
The glove box and equipment was designed by BNS Nuclear Services and built by JGC Engineering at Harpsdale and Janetstown. The containment will be relocared to Dounreay after use to support the sodium inventory disposal facility at the prototype fast reactor.
The project icost s in the region of £1.1million, with 10 staff deployed by BNS Nuclear Services and JGC Engineering. The Janetstown facility is run by the alkali metal residue removal alliance of companies BNS, JGC Engineering, Jacobs and DSRL.
Following this project, work will continue at Janetstown to develop water vapour nitrogen techniques for the destruction of sodium at high temperatures.