US-based Deep Isolation EMEA Ltd has published a study, commissioned by the UK Nuclear Decommissioning Authority (NDA), which assessed the role directional borehole technology might play in supporting the UK Government’s strategic commitment to deep geological disposal of nuclear waste.

Borehole disposal cannot replace the UK’s need for a Geological Disposal Facility (GDF), the 22-page study concludes, because it is not suited to the full diversity of the UK’s waste inventory. However, some waste is potentially compatible with deep borehole disposal.

Deep Isolation's solution involves emplacing used fuel and high -level waste in corrosion-resistant canisters placed in deep horizontal drillholes. The technology uses existing directional drilling technology. The waste can be retrieved during a specified period or permanently secured. In 2019, Deep Isolation demonstrated the concept when it placed and retrieved a prototype nuclear waste canister hundreds of metres underground through a borehole.

The study found that 63% by volume of the UK's Inventory for Geological Disposal (IGD) is intrinsically not compatible with borehole disposal. A further 26% can in principle be transferred to Deep Isolation disposal canisters for borehole disposal, but the existing plans for disposal in a mined repository are likely to be more cost-effective. This means 11% of the IGD may be operationally and commercially suitable for disposal in a deep borehole repository. This comprises all the UK's high heat generating waste (HHGW) – accounting for 96% of NDA's forecast for radioactivity levels of the IGD in 2200.

Publication of this study followed an announcement by the UK’s Department for Energy Security & Net Zero in February that it is providing grant support to Deep Isolation EMEA Ltd to develop in the UK a corrosion-resistant canister capable of safely encapsulating used fuel assemblies for disposal within deep borehole repositories 1-3 kilometres underground. Funding for this project comes from the Energy Entrepreneurs Fund, part of the Net Zero Innovation Portfolio. The canister will be tested at the Deep Borehole Demonstration Center, a new non-profit initiative being launched with multinational support from government and industry bodies.

Deep Isolation developed 15 scenarios. Noting that costs vary across geological environments, and between single site and multi-site approaches. The scenarios for disposing 100% of HHGW estimated costs between £2.98bn ($3.64bn) and £4.45bn. Other scenarios indicated that all the UK's legacy used fuel could be disposed of for £1.0-1.4bn and all high-level waste for £256-288m. However, the study concluded that further work would be needed to evaluate the impact of such an approach on the overall costs, benefits and risks.

Deep Isolation’s recommendations to NDA include:

  • Undertaking more detailed business case work to assess the possible role for the technology as part of the NDA’s integrated waste management strategy; and
  • Engagement in international collaboration on demonstration of deep borehole technology.

Nuclear Waste Services (NWS – part of NDA), which is responsible for the delivery of the UK's GDF noted the insight afforded by the study and said it “will continue to engage with such developments”. However, it said “a GDF will still be required for the majority of the UK higher activity waste inventory, even when Deep Isolation's directional borehole technology is developed to sufficient maturity for potential implementation".

Image: Cross-section of Deep Isolation's concept for the disposal of nuclear fuel and high-level waste (courtesy of Deep Isolation)