All about uranium

Before the fuel manufacturing process begins, the uranium undergoes several transformations. After extraction, the ore is crushed and subjected to chemical processes that release the uranium. This process yields a uranium concentrate in the form of a yellow powder known as ‘yellow cake’. Following a refining stage, the yellow cake is converted into a gas known as uranium hexafluoride. This conversion stage is followed by enrichment processes. The enriched uranium hexafluoride is then sent to the fuel assembly fabrication plant. Once manufactured, the fuel assemblies are transported to the nuclear power station where they are loaded into the reactor core. Generally speaking, two years elapse between the extraction of the ore and the loading of the uranium into the reactor core.

Uranium is found in ores whose deposits are located in open-cast mines or underground tunnels. Uranium ore is often extracted as a by-product, that is to say, from a mine that primarily contains another ore such as gold or copper, for example. Uranium mines are operated in around twenty countries. Half of global production comes from around ten mines in six countries: Canada, Australia, Niger, Kazakhstan, Russia and Namibia.

Charter for Uranium Mine Operators

For several years now, uranium mine operators have been taking societal concerns on board. The World Nuclear Association has laid down rules setting out the principles for managing radiation, the health and safety of miners and neighbouring communities, the management of mining waste, and the environment as a whole. These principles apply to all stages of mining operations: from exploration to mine development, from extraction through to mine decommissioning and site rehabilitation.

Find out more about the charter on the World Nuclear Association’s website.

Uranium is extracted from the ore through a series of processes that produce a highly concentrated form of uranium. This is known as ‘yellow cake’, a yellow powder containing approximately 75 per cent uranium, or 750 kg of uranium oxide per tonne. The yellow cake is then refined to produce virtually pure uranium in the form of uranium octoxide (U₃O₈). For use in a reactor, it is further ‘refined’ to achieve a purity of over 99.95 per cent.

Next comes the conversion stage, the aim of which is to transform the yellow cake into a gas known as uranium hexafluoride (UF₆). This gas is then compressed and cooled until it becomes a liquid. For transport, it is placed in a special container where it is cooled until it solidifies. It can then be transported to the enrichment plant.

Yellow cake is the form in which uranium is traded. When people talk about the market price per tonne of uranium, they are actually referring to the price per tonne of yellow cake.

The processes used to enrich nuclear fuel with uranium-235 are based on the difference in mass between the various isotopes of uranium. In natural uranium, two types of isotope are found in constant proportions: uranium-238 (heavier) and uranium-235, present at 99.3 per cent and 0.7 per cent respectively. Only uranium-235 is fissile, meaning it is capable of releasing energy through fission in nuclear reactors. For nuclear fuel to be usable in a pressurised water reactor, it must contain between 3 and 5 per cent uranium-235 (U-235).

Uranium enrichment therefore involves increasing the proportion of uranium-235 from 0.7 per cent to between 3 and 5 per cent.

Today, enrichment is carried out by centrifugation, using centrifuges arranged in series, known as cascades. This technique has completely replaced the gas diffusion method, which was far too energy-intensive. Research is also focusing on a laser enrichment process (Separation of Isotopes by Laser Excitation – SILEX), a promising new technology which has the advantage of consuming little energy and achieving isotopic enrichment in virtually a single pass. This process is currently undergoing commercial development.

Uranium’s high energy density also makes it easier to build up a large stockpile than is the case with oil, coal or gas. Belgium maintains a permanent stockpile of (enriched) uranium sufficient for approximately two years. Some EU countries even have a stockpile of uranium sufficient for five to ten years. It is impossible to build up such a large stockpile with coal, oil or, certainly, gas, due to the enormous volumes required. Consequently, uranium is far less susceptible to market disruptions caused by geopolitical tensions than coal, oil or gas.