Iran is still disassembling centrifuges, which enrich uranium, and disabling a plutonium reactor, among other steps that are required under the nuclear agreement struck in July.
For face-saving purposes, Iran is calling the uranium shipment part of a "fuel swap." But the fuel it is receiving, partly from Kazakhstan, is natural uranium, which would require substantial processing to be used for either a nuclear reactor or a weapon.
Mr. Kerry's statement said that with the removal of the fuel, Iran's "breakout time" — the time needed to produce a weapon — had already moved from two to three months to six to nine months. Before the deal goes into effect, that time is supposed to extend to a full year.
Iran is permitted to hold 300 kilograms, or about 660 pounds, of low-enriched uranium under the deal. But that is not enough to produce a single weapon.
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In a telephone interview, the Rosatom spokesman, Sergei Novikov, said the shipment fulfilled the requirement between Iran, the United States and five other world powers, including Russia, to remove Iran's stockpile of uranium enriched to this level.
The other fuel that can be used to make a bomb, plutonium, is made by irradiating uranium in a nuclear reactor. The process transforms some of the uranium into plutonium. The agreement requires Iran to disable its reactor at Arak and redesign it to minimize its plutonium output. The Obama administration has said these two requirements close for Iran both paths to becoming a nuclear power.
Despite the progress toward carrying out the nuclear agreement, hostility and mistrust between Iran and the United States have not abated. The Iranians have expressed anger over a new American law that curtails visa-free travel, saying it amounts to a sanction that violates the nuclear agreement, and they are threatening unspecified retaliation.