Agence France-Presse,
PARIS: The process for enriching uranium to generate energy in a nuclear reactor or for building a nuclear bomb is essentially the same.
What differs — and it is a critical difference — is the degree of enrichment.
Iran's claim to now be able to produce nuclear fuel on an industrial scale could be applied to either purpose, though Tehran says it intends to use uranium for energy only.
Uranium ore mined from the earth contains in excess of 99 percent of the more stable U-238 isotope, and just 0.7 percent of the U-235 isotope useful to nuclear engineers.
Uranium used in a nuclear reactor must contain three to five percent U-235, whereas the proportion must reach or exceed 90 percent for weapons-grade material.
There are two ways to enrich uranium, and for both the first step is to mill the ore into a concentrate called yellowcake, which is then converted into uranium hexafluoride gas (UF6).
During gas centrifuge enrichment — the method used by Iran — the UF6 is piped in a cylinder which is then spun at very high speed. The rotation pushes the heavier U-238 isotopes to the far end of the cylinder, while the lighter U-235 isotopes stay toward the center.
Some of the U-238 is extracted, and the process is repeated many times over until the sought-after level of enrichment is obtained.
Iran has said it has not enriched uranium beyond 4.8 percent.
This basic technique is half a century old, but it requires thousands of centrifuges connected in cascades to produce weapons-grade uranium, as well as highly sophisticated and precise equipment.
Tehran announced in February that it had successfully set up two cascades containing 164 centrifuges each at its nuclear facility in Natanz, and that two other cascades were in the final phase of installation.
Iran has remained vague as to exactly how many centrifuges are currently in operation, though it said earlier that it planned to have 3,000 by the end of last month.
A facility with 3,000 centrifuges could produce enough enriched uranium to produce one atomic bomb in about a year, according to experts.
Enrichment is only one of several hurdles to overcome before a country is considered nuclear-weapons capable.
Another is the electronic trigger, whose split-second timing is essential for unleashing the chain reaction necessary for a military device.
There is “weaponisation” — putting the device into a missile or bomb that can be delivered to a target.
Little Boy, the Hiroshima bomb, used 64.1 kilos (141 pounds) of enriched uranium, although a device can also be built from between 15 and 25 kilos (33 and 55 pounds) of material, according to experts.
A bomb can also be made from as little as six kilos (13.2 pounds) of plutonium, a by-product of nuclear reactors.
The other method used for enrichment is called gas diffusion
