An advanced engineering system has passed its first major test, sealing a deep borehole in one of the rocks that could house a future geological disposal facility (GDF) for the UK’s nuclear waste material.
An existing borehole at the Magnox Harwell site in Oxfordshire was the center of one of Radioactive Waste Management’s (RWM) largest research projects, with RWM conducting the first ever large-scale fieldwork demonstration over three months earlier this year.
RWM is the government’s “nominated implementer” for providing a geological repository (GDF) for the UK’s higher active radioactive waste.
The borehole sealing project involved the development of a unique system for permanently sealing deep boreholes, which could be up to 2000 meters deep.
As the UK’s geological disposal program progresses, boreholes will need to be drilled as part of site surveys.
It allows detailed analyzes of the extracted rock samples, one of the key steps needed to determine if the geology could be right for the underground facility.
Before the site survey can start, RWM is obliged to seal off any boreholes to supervisors of the Environmental Service (EA).
The borehole sealing project is part of the RWM research and development program that will support the construction of a safe, secure GDF deep subsurface.
On the £5 million project, scientists, engineers and geologists worked with contractors Jacobs, Marriott Drilling and NeoProducts to develop and test approaches to borehole sealing.
This included an extensive program of work that began in 2013, including the design and construction of a state-of-the-art ‘Downhole Placement System’ (DPS) for the placement of sealing material at the correct depth.
Bentonite clay was used as a sealant due to its low permeability and swelling properties. Commonly found worldwide, bentonite will also be wrapped around some GDF waste packaging as part of the engineered barrier system that will isolate and contain removed radioactive waste.
At the Harwell site, a 25m rig was used to lower the DPS filled with dry bentonite pellets into the borehole.
When the correct depth was reached, the DPS was hydraulically activated, deploying the bentonite into the water column.
In total, about a ton of bentonite was deployed at depth and formed a seal as it swelled. In addition, three other redundant boreholes at the site were also sealed as part of the collaboration between RWM and Magnox.
EA representatives have observed Harwell’s ongoing work and will review the project and any future work and provide feedback prior to any environmental permit application, which is required before drilling holes at a potential GDF site.dr. Simon Norris, principal research manager at RWM and technical project leader, said:
“The demonstration was invaluable in enabling us to thoroughly test our research and engineering works and has brought out a number of technical insights that we will take into account as we undertaking further field trials as part of this important project.
” The practical lessons include a better understanding of the behavior of the stability of clay rocks when drilling at depth, which will lead to changes in the planned geological surveys that will guide any GDF site program in the future.
The RWM said it is making its findings internationally will share, particularly with its French and Swiss “sister” organizations looking at sites in similar rock formations.
After the Harwell demonstration, the DPS will then demonstrate its capabilities in very deep boreholes in higher strength rock. borehole in an evaporated salt rock site will follow.
The RWM is responsible for identifying a suitable site for a GDF in England or Wales, a process based on seeking permission from a willing community.As a potential search area in England or Wales.
the UK is identified and a Community partnership has been formed, would the RWM be a initiate a formal on-site investigation.