The entire UK inventory of high level waste from fuel reprocessing could be discharged in seven boreholes with an average depth of 4.85 km, spread over an area of less than three football pitches.
This is the claim of Prof Fergus Gibb of Sheffield University, who co-authored a study outlining a design for a new way to permanently dispose of high-level radioactive waste deep underground in boreholes.
“These can be used alongside or separately from a much smaller, cheaper mined repository needed for the massive amount of medium-level waste,” he said.
Q&A: Handling Britain’s Nuclear Waste?
The UK has about 248,000 m. collected3 of radioactive waste of which more than 95 percent of the radioactivity comes from 1390 m3 (0.56 percent), which falls under the category of high-level waste.
The current government plan is to bury the waste at a depth of a few hundred meters in a geological repository (GDF) if and when a geologically, politically and socially appropriate site is found.
It is estimated that a GDF will cost more than £13 billion, may not be available before 2040 at the earliest, and cannot absorb high-level radioactive waste before 2080. It would then remain operational and remain open for over 150 years.
It used to be thought that dumping high-level waste into deep boreholes was not possible because British waste is packed in containers that were considered too large.
Now Prof Gibb and John Beswick of Marriott Drilling propose a combination of blind well and oilfield drilling technologies that increase reachable diameters in deep boreholes.
“The innovative combination of blind well bores – normally used for submerging mine shafts – for the top 2.5 km with conventional oilfield bores for the bottom half of the hole, allows holes to be drilled at full depth, or about 5 km, almost twice to be as wide as previously considered practical,” Gibb said. “This will allow for disposal of larger waste containers, such as those that already contain the UK’s high-level waste.”
He added that in practice, a borehole would be drilled, encapsulated to full depth, cleaned, calibrated, and then waste packages would be lowered onto coiled tubing into the borehole and deposited one at a time at the bottom of the hole.
“There is then an option to just leave them stacked or to seal them individually in the borehole,” he continued. “Once the borehole disposal zone — less than 3 km — is filled, the entire borehole will be sealed all the way to the surface.”
A generic reference design is presented in the paper published in Energy and the researchers have concluded that the disposal of the highly radioactive waste, using currently available technology, can be completed in less than ten years from the site and approval of a suitable site.
Cost estimates in the study show that a full deep borehole removal program including an idle demonstration borehole could be performed for less than £750m at current prices, equating to a net saving of over £8bn on the combined GDF and deep well removal programs.
Gibb added that the right geological conditions exist in a wider range of sites than would accommodate the much larger mine storage needed for co-disposal.
The borehole solution is also potentially safer due to the magnitude of greater isolation (depth) and strength of the natural geological barriers, which can be shown to survive for the necessary time scale.
