An engineering system to seal deep boreholes is being tested as part of Radioactive Waste Management’s (RWM) preparations for an underground disposal facility for UK radioactive waste.
RWM worked with Jacobs to research, design and build a ‘Downhole Placement System’(DPS) that will be lowered from a 25-metre rig to seal boreholes at depth. The work was carried out as part of a £5 million research project,
"Projects such as this bring to life one small part of the research and development programme that will support construction of a safe, secure Geological Disposal Facility," RWM said.
A UK Geological Disposal Facility (GDF) could be safely developed in three different rock types; higher-strength, lower-strength sedimentary and evaporite rocks; the DPS has been designed to seal boreholes in any of these geological settings.
The full-scale demonstration project is taking place at the Magnox site at Harwell in Oxfordshire.It will involve sealing an existing borehole, in lower-strength sedimentary Oxford clay, in spring 2021. Once this has been completed, the DPS will move on to demonstrate its capabilities in Cornwall’s higher-strength rock in late 2021/early 2022. Work to seal a borehole in an evaporite salt rock location will follow, RWM said.
Bentonite, which has very low permeability, will be used to seal the boreholes. Bentonite will also be used as buffer material packed around waste packages in a GDF, where it will form an additional long-term barrier to groundwater and gas movement.
“It’s been hugely exciting to see our research reach this stage, demonstrating that we are prepared for formal site investigation work in the future. We carry out extensive R&D into all aspects of a GDF to understand exactly the requirements for designing, building and operating a facility up to 1000 metres deep – it will need to be safe for many hundreds of thousands of years," said Dr Mohammed Sammur, technical director at RWM.
RWM is responsible for identifying a suitable site for a GDF in England or Wales, a process based on seeking consent from a willing community.
Once a potential UK search area for a future GDF has been identified and a Community Partnership has been formed, RWM will start geological investigations. A series of deep boreholes will be drilled, beginning a comprehensive process to establish whether the underlying rocks could be suitable. This stage is expected to be serveral years away.
Photo: One of the boreholes to be sealed at the Harwell site (Credit: RWM)