As Dounreay’s decommissioning progresses, tiny amounts of fissile material caught up in nooks and crannies of inaccessible pipework and equipment are being identified.
This material had previously been given up as lost and described as “Material Unaccounted For” in Dounreay’s inventory of its nuclear material balance, published annually.
With the clean out and demolition of reprocessing plants progressing, the site is showing an apparent ‘gain’ in material, counterbalancing past years where it had shown an apparent ‘loss’.
A five-year drum repacking project in the Billet Production Plant has detected some of this ‘lost’ nuclear material.
Over two hundred waste drums full of material produced during historic operations were inspected, assayed and repacked for safe long-term storage.
During the work, operators opened up the old packaging and confirmed that there was more uranium trapped in the waste than had previously been measured.
Decommissioning engineer Bob McKiddie takes up the story.
“The equipment that we are using to assay the waste is far more accurate than that available when the drums were originally packed,” he explained.
“We had suspected that the historical results had under-estimated the uranium content in a number of waste items. The repackaging work has resulted in an overall gain in the amount of uranium declared.
“The figures from the repackaging work show that material previously considered ‘lost’ was in fact safely packaged as waste."
The figure for the previous year showed that the site had recovered approximately 1.5kg of uranium-235. The nuclear materials balance figures for 2008/09 will be published at the end of the year.