Construction starts on Dounreay vaults

25 November 2011

Work to construct a series of underground concrete vaults to hold solid low-level waste (LLW) from the decommissioned experimental fast reactors at Dounreay started today.


LLW typically consists of debris such as metal, plastics and rags that have been contaminated during the clean-out and demolition of facilities where radioactive materials were handled. Dounreay site owner, the Nuclear Decommissioning Authority (NDA), is investing £100 million ($155 million) in a project to dispose of this waste from the site. Up to six sub-surface vaults are to be built adjacent to the Dounreay site to receive some 240,000 tonnes of LLW from the site's demolition.



Dounreay LLW vaults (DSRL)
An artist's impression of how the first two vaults will look
(Image: DSRL)



DSRL selected the firm Graham Construction in January 2011 after a competitive tendering exercise from a short-list of five companies to design and construct the first two of the six vaults. Graham is expected to take two years to develop the first phase of the site under a contract valued at £13 million ($20 million). Subject to regulatory clearance, waste disposal is due to begin in 2014.


When the UK's experimental fast reactors have been cleared away in 2025 the vaults will be sealed and the surface restored. The facility will be used for the disposal of up to a maximum of 175,000 cubic metres of solid LLW which is expected to be generated during the decommissioning of the site, in addition to waste that will be retrieved from a series of historical LLW pits at the site.


By volume, low level waste represents more than 80% of all the radioactive waste generated by Dounreay's demolition. However, by radiological hazard, it represents less than 0.01%, according to DSRL.


The decommissioning waste is collected in 200-litre drums that are processed on-site. Each drum is currently supercompacted to one-fifth of its original volume and placed inside half-height shipping containers. These containers will be filled with grout to make them ready for disposal.


Each vault will cover an area about 1.8 hectares and will be 20 metres deep. An agricultural-style building will be built over each vault to provide cover during its operation, before each is finally backfilled with grout and capped.


Subject to regulatory consent, the first boxes of waste will be moved into the vaults in 2014 and grouted in place. The last disposals are expected to occur sometime in the next decade. After capping, it will be monitored for 300 years, by when 95% of the radioactivity will have decayed.


"Dounreay was at the forefront of the country's reactor program when it was first built," said Nigel Lowe, NDA's director for Dounreay. He added, "Today, as the site opens a new chapter in its history, it is again at the forefront as exemplified by this low level waste construction project. This facility will ensure the material is safely and securely looked after well into the future, utilizing modern standards and technologies."


Audrey Cooper, senior project manager at DSRL, said: "Cleaning out and knocking down a redundant site like Dounreay generates significant quantities of radioactive waste. This facility provides us with a safe disposal route for much of that waste."


Researched and written

by World Nuclear News