At the end of 2021, the UK closed the curtain on one part of its nuclear waste legacy and took a few more steps towards a longer-lasting legacy. A reprocessing plant, built at the cost of £9bn in the 1990s to repackage waste plutonium from pressurized water reactors in the UK and around the world for use in new fuel, finally converted the last remaining liquid residue from Germany, Italy and Japan into glass and packed it into steel containers. It will take another six years to ship it and all the other waste that belongs to the reactor owners, who are contractually obliged to take it back. Even when the foreign-owned waste has headed back home, the UK will still play host to one of the largest hoards of plutonium in the world, standing at more than 110 tonnes. It amounts to a fifth of the world’s total and a third of the global civilian stockpile of 316 tonnes. Despite operating a smaller nuclear fleet than France’s, the UK has 1.5 times more plutonium. It was never meant to end this way. The long-term dream was for fission-capable fuel to keep going round in a circle, only topped up with virgin uranium when necessary. The plutonium produced during fission could itself sustain further fission in the right conditions. However, fast-breeder reactors that would be needed to close the cycle remain largely experimental, even in countries such as Russia where their development continues. Driven by both safety concerns and worries about nuclear proliferation that might result from easier access to separated and refined plutonium-239, the West abandoned its fast-breeder program decades ago. It is possible to reprocess spent fuel into so-called mixed-oxide fuel, but it is only good for one use in a conventional reactor. Other actinides build up and begin to poison the fission process. The only prospects for change lie in so-called Generation IV reactors, but these designs have yet to be tested and may continue to fall foul of proliferation concerns.
While operators around the world have mulled over the practicality of fuel reuse, containers of both processed and reprocessed fuel have lingered in storage tanks cooled by water despite, in some countries, being earmarked for deep burial for decades. In the late 1980s, the US Department of Energy (DOE) settled on Yucca Mountain in Nevada as the single destination for the country’s spent nuclear fuel, and scheduled it for opening a decade later. By 2005, the earliest possible opening date had slipped by 20 years. It remains unopened and will probably never open. In the interim, much of the fuel has lingered in water-filled cooling tanks while politicians consider more localized deep-storage sites.
Fukushima provided a wake-up call to the industry, not just about the problems of controlling reactors but their spent fuel. After the tsunami, engineers were concerned that without replenishment pumps, the water in the storage tanks for the spent fuel would evaporate. If the fuel then caught fire, it would likely release radioactive tritium and cesium into the atmosphere. In a stroke of luck, water leaked into the damaged ponds. Now, the issue for operators of some older reactors is that the fuel canisters are just corroding into the water instead.
Experts such as Frank Hipped, professor of public and international affairs at Princeton University, recommend storage pools should only be used until the fuel is cool enough to be transformed into glass, immersed in concrete or both, and transferred to dry storage, preferably in a deep geological disposal facility (GDF).
At a conference last November organized by the International Atomic Energy Agency (IAEA), Laurie Swami, president and CEO of Canada’s Nuclear Waste Management Organization, claimed “there is scientific consensus on the effectiveness of deep geologic repositories” for highly radioactive waste. The UK similarly settled 15 years ago on a plan to build its own GDF for high-level waste in tandem with the establishment of a single government-owned body responsible for organizing where the waste goes, in the shape of the Nuclear Decommissioning Authority (NDA). The GDF took a small step forward at the end of 2021 when two candidate sites were announced, both close to the Cambrian coast. The local communities have agreed in principle that the NDA can investigate where they are suitable for a set of tunnels that may extend under the Irish Sea. With the project at such an early stage, the country remains years away from opening a GDF. Finland, in contrast, has pressed ahead and expects its GDF to open in 2025, while Sweden is likely to have the second one in the world.
At the same time, there is an enormous volume of other irradiated material that cannot economically be put into deep storage. In a keynote speech at the IAEA’s conference, James McKinney, head of integrated waste management at the NDA, explained that a lot of radioactive waste is contaminated building material. The Low-Level Waste Repository at Drigg in Cambria was designed for this kind of waste, but McKinney stressed that capacity is “precious” and in danger of running out if all the material is taken there. Over the past decade, the NDA and its subcontractors have been working to divert as much waste as possible from the Drigg site by reprocessing and repackaging it.
By bringing waste management under one umbrella instead of dividing it among power-station operators, the NDA has been able to change procurement strategies to favor the use of much more R&D for waste handling. “The destination of radioactive waste can be changed through interventions,” McKinney adds. " At this moment, we estimate some 95 per cent of potential low-level waste is being diverted away [from Drigg]. Twelve years ago, the opposite would be true ". The digital twin is becoming an important element of nuclear waste disposal, both or finding where to put it and to move it around. The UK’s Nuclear Decommissioning Authority (NDA) has adopted the concept to help build a more comprehensive picture of what is stored where and why.
Corhyn Parr, CEO designate for waste at the NDA, explained at a conference organized by the International Atomic Energy Agency in November that the agency has “more detailed lifetime planning now. It helps us to have real-time live data and have it open, to enable us to be really clear with the public how we are delivering”.
One way in which digital twins can be used is to show that the condition of the waste is not changing unexpectedly. For example, the NDA is looking at the use of sensors with a 30-year lifetime that could be powered partially by energy produced by the waste itself to indicate corrosion and other problems in dry storage. Those readings can be compared in real time with simulations and, in principle, make it easier to deal with one big problem with long-term waste management: having to guess at whether any of it is escaping or becoming dangerously hot.
Similarly, digital-twin techniques are being tried in a new generation of robotic controllers to make it easier for human operators to visualize what is happening to the robot and the surrounding environment. One example of this approach will be the Long Ops project, the result of a £12m deal between the UK and Japan to develop better long-range manipulators that can be used for decommissioning. For longer-range remote control, the digital-twin approach may make it possible to implement more intuitive control over robots using virtual or augmented reality.
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