The UK, US, and EU have agreed to turn the UK’s excess stockpile of highly enriched uranium (HEU) into medical isotopes to be used in cancer treatment, according to a 31 March statement by the UK Prime Minister’s Office. The agreement was concluded in the framework of the 2016 Nuclear Security Summit in Washington.

The transaction will see the US receive a transfer of 700kg of excess HEU from the UK, after which it then send a "different type" of HEU to Euratom in a form suitable for manufacturing into fuel and targets for use at a European research reactor that produces medical isotopes. The manufacturing will take place in France. The Prime Minister’s Office said the isotopes could be exported to the UK and other European countries to help cancer treatment and diagnosis. The excess HEU, which is to be sent to the US, is currently stored at the Dounreay nuclear site on the north coast of Scotland.

In 2013, the UK Nuclear Decommissioning Authority (NDA) published papers on the options it was considering to manage the approximately 1000 kg of HEU stored at Dounreay, along with other experimental nuclear fuels collectively termed ‘exotics’. "None of the exotics held at Dounreay are considered to be waste," it stated, explaining the HEU was in various forms – oxide powders, pellets and metal – and at various levels of enrichment. The HEU is unirradiated, which means it has a relatively low level of radioactivity.

At that time, the option to "Send material overseas for reprocessing and utilise products" was seen as low probability but useful to maintain as a contingency because there were no specialised facilities to store HEU at Sellafield, where the NDA would have preferred to consolidate similar materials. Removing the fuels from Dounreay is a step towards lowering the site’s security classification and cost savings.

The Department of Energy and Climate Change said, "This movement is the largest ever consolidation of such material and represents a significant milestone in achieving our goals of consolidating all our holdings in one secure location, while reducing our overall nuclear material stocks".