The UK government has decided that the UK’s stockpile of some 140 tonnes of civil plutonium will be immobilised and eventually disposed of in a geological disposal facility. The inventory – currently stored at the Sellafield site in Cumbria – arose from the reprocessing of used fuel undertaken over many decades.
Michael Shanks, Parliamentary Under-Secretary of State at the Department for Energy Security & Net Zero (DESNZ), said in a written statement to the House of Commons: “Continued, indefinite, long-term storage leaves a burden of security risks and proliferation sensitivities for future generations to manage.” He added that it is the government’s objective “to put this material beyond reach, into a form which both reduces the long-term safety and security burden during storage and ensures it is suitable for disposal in a Geological Disposal Facility (GDF)”.
After a public consultation in 2011, the government adopted a preliminary policy option of reusing plutonium as mixed-oxide (MOX) fuel but remained open to alternative proposals for plutonium management. However, following the March 2011 Fukushima disaster, the UK government decided to close the Sellafield Mox Plant, effectively ending that option.
The Nuclear Decommissioning Authority (NDA) has since carried out technical, deliverability and economic analysis to identify a preferred option for a long-term disposition solution, including options for immobilisation and reuse. The outcome of this work recommended immobilisation as the preferred method.
“Following further development work, the NDA will select a preferred technology for immobilisation of the plutonium as a product suitable for long-term storage and subsequently disposal in a GDF,” Shanks said. “We expect that around the end of the decade following government approval the NDA and Sellafield will begin delivery of the major build programme of plutonium disposition infrastructure.”
The NDA welcomed the decision, saying the next phase will be to seek approval for a major programme on plutonium disposition, requiring a nuclear material processing plant and interim storage capability to be built at Sellafield, “bringing major investment to the area and supporting thousands of skilled jobs for decades”. However, in the meantime, “plutonium will continue to be stored in a suite of custom-built facilities at Sellafield that ensure its safety and security in line with regulatory requirements”.
Sellafield Ltd CEO Euan Hutton said: “We have safely and securely managed plutonium at Sellafield since the 1940s, developing world leading expertise in the process. The decision to immobilise the material places Sellafield at the centre of the effort, working with the NDA, Nuclear Waste Services and our partners including the supply chain, to create a solution that delivers maximum value for all of our stakeholders.”
A 46-page study published in 2023 by the University of Manchester’s Dalton Institute, UK plutonium stockpile: no easy choices, looked at the origins of the stockpile and management options and made recommendations.
The UK started manufacturing plutonium for military purposes in 1950, reprocessing the fuel from the Windscale air-cooled, graphite-moderated piles. After closure of the Windscale Piles in 1957, reprocessing continued with used fuel from the dual-purpose Magnox reactors at Calder Hall and Chapelcross and then from the subsequent civil Magnox reactors. The aim was to provide fuel for future fast reactors. Even after the fast reactor programme in the UK was closed reprocessing of Magnox fuel continued because it was not suitable for storage. Fuel from the second-generation Advanced Gas-cooled Reactors (AGRs), was not obliged to be reprocessed but some was for commercial reasons. Consequently, the UK accumulated a significant stockpile of plutonium which varied in its nuclide composition and physical properties.
The UK’s inventories of fissionable, fissile and fertile materials include separated plutonium and Depleted, Natural and Low-Enriched Uranium (DNLEU). The plutonium reserve corresponds to approximately 3,000 TWh and the DNLEU to around 2,200,000 TWh of energy, which could meet the UK’s energy needs for centuries. However, the obstacles to extracting this energy “may be insurmountable”, the report said. This leads to a range of management options – waste, in mox, in fast reactors and as a neutron multiplier in fusion.
Having considered these options, the report makes 10 recommendations and a final, overarching recommendation. These are:
- Before making any policy decisions, Government should ensure that national dialogue takes place allowing stakeholders from all sides to share their views.
- The current programme of repackaging and storing the plutonium inventory in optimal conditions must be carried out by the NDA and Sellafield Ltd to the currently programmed end point of 100-year design life storage to provide sufficient time for comprehensive Research, Development and Innovation (RD&I).
- Both Government and NDA should provide the commitment and resources needed to ensure continuity and development of capability over this timescale.
- Government should decide on and implement a preferred end point for the plutonium once a satisfactory assessment is available, taking into account changes in storage environment and the hazard that plutonium presents.
- Government, NDA and other stakeholders must ensure that sufficient attention and resources are devoted to long term care of these assets.
- The hazard represented by the plutonium stockpile would be greatly decreased by conversion from dispersible powder into a solid form, but the choice of form will determine which future option is to be followed. Government should ensure that a comprehensive assessment is carried out on the options.
- Government needs to develop a full understanding of the whole plutonium lifecycle for each pathway before committing to irrevocable decisions.
- Because of the major uncertainties associated with the UK’s plutonium management programme, it is unwise to rely on discounted costs to evaluate the programme and the assumption of cost decrease should not be used as a pretext to delay decision making and action.
- Government should ensure there is a sufficient supply of suitably qualified and experienced personnel to deliver the programme.
- Government should ensure that a robust, long-term RD&I programme is in place to support selection and implementation of any plutonium management option.
The Overarching Recommendation is that “Government, which is ultimately responsible for management of the UK’s plutonium stockpile, should acknowledge that this is an unavoidably complex, multi-generational undertaking, requiring ongoing stewardship prior to an irrevocable decision on the end point for the material, and should put in place suitable arrangements. There are significant major uncertainties which can only be managed through a long term, programmatic approach with continuity, flexibility, adaptability, underpinned by RD&I commensurate with the scale of the challenge.
