The UK will ship 700kg of excess nuclear waste to the US in a deal expected to help fight cancer.
Prime Minister David Cameron will make the announcement at the Nuclear Security Summit in Washington later today.
The excess Highly Enriched Uranium (HEU) will be transferred from the Dounreay nuclear site on the north coast of Scotland.
In return, the US will send a different type of used uranium to the European Atomic Energy Community (Euratom) in France. That could be used in radiotherapy to diagnose and treat conditions such as thyroid cancer by weakening or destroying the cancerous cells.
Speaking ahead of the summit, Mr Cameron said: “This is a landmark deal to turn nuclear material we no longer need into a cancer-fighting treatment that could potentially save many lives. It’s a win-win, innovative solution that shows what working together with our international partners can achieve.”
He will also announce the launch of a cyber security scheme to strengthen other countries’ abilities to withstand cyber attacks at nuclear sites and power plants.