The Waste Encapsulation Treatment Plant (WETP) at Winfrith has been demolished, marking the final stage of decommissioning of the plant, following successful completion of a five year sludge retrieval and processing programme by site licence company RSRL, parent body organisation Babcock reports.
The WETP was designed and built to receive and process sludge from the Steam Generating Heavy Water Reactor (SGHWR). Operations began in mid 2005 to empty the External Active Sludge Tanks (EAST) storing the radioactive sludge (mostly ion exchange resins) and stabilise it in cement in 500 litre stainless steel drums in the WETP. The drums were then transferred to the site’s Treated Radwaste Store (TRS), pending final disposal off site.
A total of 1,068 encapsulated sludge drums were produced, the last of which was transferred to the TRS in mid 2010. The successful completion of the recovery and encapsulation of SGHWR sludges marked a major milestone in the restoration of the Winfrith site.
The project ran smoothly until the final stages of recovery when discovery of a ‘sandy material’ (mostly silica) was discovered in the bottom of the tanks and required development of an innovative solution to enable recovery. This was achieved with the use of an industrial vacuum pumping system (known as ‘Big Brute’) to recover the material in 20kg batches, which was then encapsulated in 40 litre containers within prepared 200 litre waste drums. A total of 178 drums were filled using this process.
Since transfer of the last drum to the TRS following removal and encapsulation of the sludge, work has been underway to decontaminate and dismantle the empty sludge tanks. First man access for forty years was achieved in November 2010 to undertake a radiological survey. After post operational clean out and decontamination, this has been followed by work to remove the tank roofs and walls, using innovative diamond wire cutting techniques which minimise secondary wastes, provide excellent control during the precise size-reduction operations required, and achieve maximum exempt waste disposal volumes. A weir box found to contain a small amount of sludge has also been emptied and removed ready for consignment as waste. The majority (90%) of the concrete blocks from the tank dismantling will be disposed of as very low level waste (VLLW) or exempt material. The remainder, mainly construction joints, is low level waste (LLW).
Having completed its role to encapsulate the sludge, the demolition of WETP is the final piece in the decommissioning jigsaw. Following extensive post operational clean out and decontamination of the cells (exceptionally the WETP was designed to facilitate final decontamination and decommissioning), one end of the building was taken down to allow access to remove the embedded stainless steel storage tanks for decontamination and size reduction. This was followed by full demolition. This work commenced in October 2011, and was successfully completed in December. After extensive radiological monitoring it is anticipated that all demolition wastes will be consigned as exempt waste.
RSRL Managing Director Alan Neal said: “We are delighted to have achieved another successful milestone in the decommissioning programme at Winfrith. As is to be expected when decommissioning legacy plant, a number of challenges have been encountered in the course of this project which have been addressed with ingenuity and innovation.”