It is a very corrosive and dangerous chemical, and needs to be handled with care.
Step 4: Steal some parts
Now its time to find a centrifuge. This will separate uranium-235 from uranium-238 in much the same way a salad spinner separates dense water droplets from lightweight lettuce leaves. But a salad spinner won't come close. To separate tiny atomic masses requires something that can spin at tens of thousands of rotations per minute.
Centrifuges are a tough technology to master, and a rogue nation shouldn’t expect a lot of help from established nuclear powers. Through a trade organization known as the Nuclear Suppliers Group, they carefully regulate the export of centrifuge parts and designs.
Nevertheless, there are ways around the restrictions, according to Joshua Pollack, a consultant to the US government on deterrence and nuclear proliferation. In 2004, the father of Pakistan's nuclear bomb, Abdul Qadeer Khan, admitted that he had been at the centre of a vast smuggling network that supplied centrifuge designs, parts and expertise to Iran, North Korea, and Libya, among others.
Khan's network has since been shut down, but even when running, Pollack says he's not sure it was the best way to get a centrifuge. Khan often supplied cheap, faulty parts and misleading designs to his customers. “He was taking Iran and Libya to the cleaners,” Pollack says.
Given the unreliability of the black market, some countries have established other dubious ways to get their hands on the necessary machinery, such as setting up shell companies in other countries. “The North Koreans are just masters of this,” Pollack says. For example, according to a report by the Institute for Science and International Security (Isis). the North Koreans set up a firm in China with the name “Shenyang Aircraft Group Dandong Import and Export Co. Ltd.”. The lengthy title was nearly identical to that of a legitimate Chinese firm known as the “Shenyang Aircraft Industry Group Import & Export Co., Dandong Branch”. The confusion allowed North Korea to import centrifuge parts undetected.
Step 5: Enrich
Regardless of how they do it, a country will need several thousand centrifuges. These must be strung together into “cascades” that can enrich the uranium hexafluoride gas made earlier. By passing the uranium hexafluoride from cascade to cascade, uranium-235 begins to slowly accumulate. Iran has been working on enrichment since the early 2000s and in February 2010 said it had begun processing uranium to 20% enrichment. This has civilian uses but is also a significant step towards producing weapons-grade uranium.
It's a tedious process that will take months to complete, and may be slowed by accidents and sabotage. A powerful computer virus called Stuxnet, for example, caused hundreds of Iran's centrifuges to spin themselves apart. However, if a state uses its centrifuges wisely, it can have enough uranium-235 for a bomb in under a year, and the 150 kg (330lb) needed for two or three in less than two years.
Step 6: Get a design
While a country is waiting for its uranium to enrich, it needs to start thinking about bomb design. First , it needs to work out what this nuclear weapon is for. If it wants an object of stealthy terror, or a device that will prop up a shaky regime's domestic reputation, then a gun-type weapon is the most likely way to go. A gun device can be easily fashioned out of an old artillery barrel that will literally shoot two, near-critical masses of uranium together. It requires more than twice as much material as your standard nuclear weapon, and it can't fit easily onto a missile. But the gun-type weapon is guaranteed to work on first try.