Britain is to accept a small quantity of highly enriched uranium fuel from a nuclear reactor outside Tbilisi in Georgia.
The presence of the material in such a volatile region had caused considerable unease in Washington, where there were fears that it could fall into the wrong hands. The United States had hoped that Russia would accept the fuel but when Moscow failed to act, it sought to enlist Britain's help.
This report from our Defence Correspondent Jonathan Marcus.
The highly enriched uranium is in the form of both fresh and spent nuclear fuel and has been stored for several years at the research reactor outside Tbilisi.
Although the quantities involved are said to be less than would be needed for a nuclear weapon, the presence of the materials in such a volatile region had prompted serious concerns in Washington - concerns shared by the Georgian authorities themselves.
The United States has established a variety of programmes to dismantle the vast nuclear legacy of the former Soviet Union.
Many of these involve schemes to help the Russians build safer and more secure storage depots for disused warheads and nuclear materials.
But the Russians raised legal objections to taking back the fuel. In the past the Americans stepped in to buy up nuclear materials from Kazakhstan in 1994.
It is unclear why waste will not go to the US
The deal with Georgia is similar, though this time the highly-enriched uranium will not go to the United States, but to the atomic plant at Dounreay in Scotland. British official say that the arrangement demonstrates Britain's concern to do its bit to prevent the proliferation of nuclear materials.
Much of it will be used to manufacture medical isotopes for the treatment of cancer. The highly-enriched uranium may well be flown to Britain in a US air force transport plane later this week.
But British officials would not be drawn as to why the materials were going to Scotland - clearly the United States would have more than adequate facilities of its own that could handle such a project.