UKAEA has applied for planning permission to hydraulically isolate the 65m-deep waste shaft at the Dounreay site in Scotland ahead of emptying the 750m3 contents resulting from around 20 years of haphazard disposal of solid intermediate-level radioactive waste.
The application to the Highland Council seeks consent to isolate the contents of the shaft from the surrounding environment by physically restricting water movement to and from the shaft by means of a grout curtain. This will require building a raised working platform, drilling approximately 350 to 400 boreholes to a depth of 80m in an oval ring around the shaft and injecting grout to create a 10m wide curtain.
Once solidified, the grout will form a barrier reducing the volume of groundwater currently flowing into the shaft which will result in less groundwater having to be dealt with as contaminated waste. The grout curtain will also provide reassurance against leakage, eliminate any lingering doubts about the shaft being a source of particles in the marine environment, and create a stable environment for waste retrieval in the future.
In addition, the proposed development involves the reinforcement of the existing shaft plug and infilling of a section of the adjacent liquid effluent discharge tunnel.
Simon Middlemas, Dounreay deputy director, said: “Hydraulic isolation of the shaft is the first phase of one of the major nuclear decommissioning challenges in the world.”
UKAEA announced the award of the contract to isolate the shaft at a cost in the region of £16 million ($28 million) to Ritchies, the specialist geotechnical division of Edmund Nuttall, last year.
Subject to consents, building the raised working platform is expected to commence in April 2006 with work on the existing shaft plug and liquid effluent discharge tunnel following. Borehole drilling and grouting is expected to commence in summer 2006 and will take between two to four years to complete.
The 15-year project to clean out the site's waste shaft at a cost of nearly £180 million ($316 million) is considered a major decommissioning challenge facing the nuclear industry and is a significant part of the £2.6 billion ($4.5 billion) programme to return the site to a near greenfield by 2036.
In other news from Dounreay, concerns have been raised that workers may have inhaled plutonium during decommissioning work at the plant.
One of the site's three reprocessing plants has been closed off after eight workers showed traces of radioactivity during routine nose blow tests following work on a four-storey pulsed column laboratory.
Full test results for the workers are not expected for several weeks.
Related ArticlesUzbek nuclear fuel returned to Russia