For uranium to work in a nuclear reactor it must be enriched to contain 2-3% uranium-235 while weapons-grade uranium must contain 90% or more uranium-235.
The idea was for Iran to ship 1, 200kg of its low-enriched uranium overseas to produce fuel for a research reactor, thus leaving the country for a while with too small a stockpile with which to make a bomb.
U.S. and United Nations officials have documented what they describe as serious limitations in Iran's ability to quickly and efficiently produce the enricheduranium required to either fuel a nuclear power reactor or to build an atomic weapon.
The United States and other leading nations have been negotiating with Iran to send low-enriched uranium abroad to be turned into material for use in medical research and treatment at a reactor in Tehran.