Enriching uranium is the most difficult part of building a nuclear bomb. If you can get hold of 15 pounds of highly-enriched uranium, which is a lump about the size of a grapefruit, and have a reasonably sophisticated engineering industry, you can build a nuclear bomb.
Uranium, one of the heaviest metals, has the atomic number 92, which means that a uranium atom has 92 protons at its core. Most naturally-occurring uranium also has 238 neutrons (u-238), but a tiny part of it, 0.7 percent, has 235 neutrons at its core and is lighter. This is u-235.
Increase that 0.7 percent to 3 percent and you have fuel for a nuclear power plant. Increase it to 90 percent and you have the core of an atomic bomb. (A nuclear bomb can also be made with plutonium, but to make plutonium you first have to have a nuclear reactor).
Discussion of the spread of nuclear weapons often focuses on dual-purpose technology, meaning technology that can produce either nuclear power or nuclear bombs. Uranium enrichment is the ultimate dual-purpose technology. The same machinery that can enrich the uranium to 3 percent for a power plants, with a little tweaking in its connections, can enrich it to 90 percent for a bomb.
Enriching uranium is difficult and expensive. During World War Two, when the first atomic bombs were being built in America in secret, the uranium enrichment plant at Oak Ridge, Tennessee was using five percent of the electricity supply of the entire country.
There are several ways to enrich uranium. The favoured one today is the centrifuge method. Uranium is turned into a gas, fed into a centrifuge machine, and then whirled around at a speed of 70,000 revolutions a minute, so that a little more of the heavier u-238 collects on the outside. Then it is passed to another centrifuge, and so on in a cascade. Because the difference in weight is so slight – around 0.3% – this takes a long time.
This places great stress on the machinery, and it involves special design and special equipment. The blueprints for that are what the Pakistani A.Q. Kahn was hawking around in the 1970s, to Libya, Iran and North Korea. He learned the trade and stole the blueprints while working at a contractor for Urenco, the British-Dutch-German enrichment consortium.
The framework for efforts to halt the spread of nuclear weapons is the 1968 Non-Proliferation Treaty, which was designed to prevent the spread of nuclear weapons while allowing the spread of peaceful nuclear power. Under the NPT, a country must allow inspectors from the International Atomic Energy Agency to monitor its nuclear programme to ensure that it is not diverting civil nuclear material. Iran has complied with this. IAEA inspectors visit the Iranian enrichment plant regularly.
The principal fear of the Western powers negotiating with Iran is not that Iran is about to produce a nuclear arsenal. It is that Iran – and this applies to other countries – wants to get itself into a position of nuclear break-out, that is, a situation in which some future government, if it decided to, could throw out the IAEA inspectors and create nuclear bombs in short order, while other countries were still meeting to discuss sanction. For the fuel for atomic bombs, it would simply keep those centrifuges whirling a little longer.
In fact the situation is worse than it seems. I use the word “enrich” because that is the term in general use, but it is misleading, and in a serious way. Look up the word in the dictionary. It defines it as “adding something to a substance to increase its value.” However, when we enrich uranium, meaning that we increase the proportion of u-235, we are not doing so by adding u-235 but by winnowing out the u-238. The difference is critical.
If we were adding u-235, then a country that has enriched uranium to three percent would have a long way to go to having 90 percent enriched uranium. It would have to do thirty times as much work. But because it is taking away u-238, it has gone two-thirds of the way. As for Iran’s 20 percent enriched uranium, a few more weeks or months in the cascade, and they could have the material for an atomic bomb.
Iran has never given a satisfactory explanation of why it needs to enrich uranium. It is not to fuel its own nuclear power program. This consists of one nuclear plant supplied by Russia. Russia has tied the Iranians’ hands. This power plant requires complex fuel rods produced in Russia to specific secret specifications. Iran will be dependent on a continuing fuel supply from Russia.
Every measure designed to stop the spread of nuclear weapons involves enrichment. This includes the very first proposal for nuclear arms control proposal, the Acheson-Lilienthal proposal, put forward by America in 1946 when America still had a nuclear monopoly. This proposed international control of enrichment.
International control of enrichment facilities is not a radical proposal. 72 countries have nuclear power plants working or under construction, but only 15 have their own enrichment plants, and some of these are controlled by international consortiums. The rest are content to import their enriched uranium.
We can aim for a situation in which no country has the ability to enrich uranium on its own, without safeguards. This continues to be central to controlling the spread of nuclear weapons.
These are the views of the author.