11 January 2021

Testing starts on bentonite system to seal deep boreholes

In preparation for an underground disposal facility for UK radioactive waste, a borehole sealing system is being lab tested.

A deep borehole at Harwell

One of the boreholes to be sealed at the Harwell site

© RWE

The Downhole Placement System (DPS) being trialled in laboratory conditions. Where bentonite is lowered into a Perspex ‘borehole’, to test bentonite deployment and seal evolution as part of Radioactive Waste Management’s (RWM) project.

Scientists, engineers and geologists from RWM have worked with Jacobs to research, design and build the DPS that will be lowered from a 25-metre rig to seal boreholes at depth The intention is to support construction of a safe, secure Geological Disposal Facility (GDF).

A 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 firstly taking place in Harwell, Oxfordshire, at an NDA-owned site managed by Magnox, where there are existing boreholes up to 400 metres deep, originally drilled in the 1980s. When the Harwell borehole, in lower-strength sedimentary Oxford clay, is sealed in spring 2021, 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.

Bentonite, used to seal the holes, has very low permeability. 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.

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. No site has yet been selected for a GDF.

The UK is dotted with thousands of boreholes, drilled for a wide variety of purposes ranging from pure research to locating water and investigating coal, oil, gas or mineral resources.

Once a potential UK search area for a future GDF has been identified and a Community Partnership has been formed, RWM will begin geological investigations. A series of deep boreholes will be drilled, starting a comprehensive process to establish whether the underlying rocks could be suitable. It is anticipated that this stage is several years away.

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Radioactive waste disposal

RWM university partnership on geological disposal