The entire UK inventory of high-level waste from fuel reprocessing could be disposed of in seven boreholes averaging 4.85km depth spread over an area less than three football pitches.
This is the claim of Sheffield University’s Prof Fergus Gibb who has co-authored a study that sets out a design for a new way of permanently disposing of high-level radioactive waste deep underground in boreholes.
“These could be used alongside or separate from a much smaller-cheaper mined repository which is needed for the huge volume of intermediate-level wastes,” he said.
The UK has accumulated around 248,000m3 of radioactive waste with over 95 per cent of its radioactivity arising from 1,390m3 (0.56 per cent), which is categorised as high-level waste.
The government’s current plan is to bury the waste at a depth of a few hundred metres in a geological disposal facility (GDF) if, and when, a geologically, politically and socially suitable site is found.
It is estimated that a GDF will cost over £13bn, could not be available before 2040 at the earliest and would not be able to take any high-level waste before 2080. It would then remain operational and open for over 150 years.
Disposing of high-level waste in deep boreholes was previously thought not to be possible, as the UK’s waste is packaged in containers that were considered too large.
Now, Prof Gibb and John Beswick of Marriott Drilling propose a combination of blind shaft and oilfield drilling technologies that increase the diameters achievable in deep boreholes.
“The innovative combination of blind shaft drilling – normally used for sinking mine shafts – for the top 2.5km with conventional oilfield drilling for the bottom half of the hole enables holes at full depth, or approximately 5km, to be almost twice as wide as previously considered practical,” said Gibb. “This enables disposal of larger waste containers, such as those in which the UK’s high-level waste is already packaged.”
He added that in practise a borehole would be drilled, cased to full depth, cleaned, calibrated and waste packages would then be lowered downhole on coiled tubing and deposited one at a time at the bottom of the hole.
“There is then an option of just leaving them stacked up or sealing them individually into the borehole,” he continued. “Once the disposal zone of the borehole – below 3km – is filled the whole borehole is sealed up all the way to the surface.”
A generic reference design is presented in the paper published in Energy and the researchers have concluded that disposal of the high-level waste could be completed, using currently available technology, in under ten years from the location and approval of a suitable site.
Cost estimates in the study show an entire deep borehole disposal programme, including a non-active demonstration borehole, could be undertaken for less than £750m at current prices, representing a net saving on the combined GDF and deep borehole disposal programmes of over £8bn.
Gibb added that the correct geological conditions exist at a greater number of locations than might be suitable for the much larger mined repository needed for co-disposal.
The borehole solution is also potentially safer because of the order of magnitude greater isolation (depth) and strength of the natural geological barriers, which can demonstrably survive for the necessary timescale.