What do we mean by Uranium Enrichment?
There has been a lot of discussions recently, in the international media, regarding the uranium enrichment activities by Iran. This subject has been covered extensively by news outlets.
The international community have been asking the questions. What does it mean if a State or other entity has the capability of enriching uranium, by 20%, and what are the benefits?
That article tries to answer these questions and provide some information about uranium, its properties, its different uses, and glance at the different enrichment stages.
What is uranium?
Uranium is a naturally occurring material. It is slightly radioactive, ubiquitous, a heavy metal found in various chemical forms in soils, most rocks, many rivers, seawater, and oceans. It is also present in drinking water and food. It is about 500 times more abundant than gold and as common as tin. There are many countries around the world, where the concentration of uranium in the ground is of sufficient quantity to be economically viable for extraction. Examples of this are the energy and medical industry, research and agriculture.
Such concentrations are called uranium ore, and they exist in several countries such as Kazakhstan, Canada, Australia, Niger, Russia, Namibia, Uzbekistan, China, USA, and Ukraine.
On average, approximately 90 micrograms of uranium exist in the human body from drinking water, eating food, and the air. About 66% can be found in the skeleton, 16% in the liver, 8% in the kidneys and 10% in other tissue.
Natural uranium consists of a mixture of three radioactive isotopes of uranium: U-238, U-235, and U-234.
The percentage of uranium ore in U-238 is 99.272%. U-235 has a concentration of 0.712%, and U-234 has 0.0054% (all identified by the mass numbers).
Only isotope U-235 is a fissile isotope, which means that it undergoes fission if bombarded by a neutron.
All three isotopes are chemically identical; however, their physical properties are different, but most notably, their mass. For example, the nucleus of the U-235 atom contains 92 protons and 143 neutrons. The nucleus of the U-238 atom also contains 92 protons but contains 146 neutrons. This means three more neutrons than U-235, and therefore has a mass of 238 (92+146).
This small difference in mass is very important because it allows the isotopes to be separated and makes it possible to increase or Enrich the percentage of U-235.
Many research reactors are still using Highly Enriched Uranium (HEU) to produce medical radioisotopes etc. The enrichment percentage needed for such activities is between 3-5% (after several Nuclear Security summits, many nuclear facilities have replaced their HEU by a Low Enriched Uranium (LEU) for security reasons). In other words, the uranium enrichment needed for civil activities is usually between 3-5%, not more.
Let us focus on uranium enrichment
1). Uranium mining: There are two techniques used in uranium ore mining. The first process is known as the ‘excavation technique’, which takes uranium from the underground and open pit. The second process is known as the ‘The insitu technique’. Here groundwater with additives, such as oxygen, is pumped through the porous ore-body to dissolve the uranium and bring it to the surface. The uranium is finally extracted from the solution.
2). Uranium milling: After being transported to the milling facility, the uranium is crushed, ground and leached. The uranium is extracted from the solution and then precipitated and dried. Scientists have called this product ‘Yellowcake’, a concentrated form of uranium oxide (U3O8).
3). Conversion: The enrichment process requires uranium to be in a gaseous form. Fluorine gas is added to the ‘Yellowcake’ to convert it into uranium hexafluoride (UF6) gas.
4). Enrichment: Two enrichment processes are in large scale commercial use: gaseous diffusion and gas centrifuge enrichment. Both of these processes use UF6 as a feed and produce two different streams. One of the streams is enriched to the required level of U-235, and the other is called ‘Tails’ or ‘Depleted Uranium (DU). If the enrichment is below 20% the U-235 is considered a LEU. However, by the time enrichment reaches 20%, U-235 is considered a HEU and therefore a highly sensitive material. This enrichment has been chosen by the International Atomic Energy Agency (IAEA) as the line above which enriched uranium is treated in the same category as plutonium, the other nuclear explosive material.
NB: If we want to enrich uranium for power generation only, the level of enrichment needed is between 3-5%, not more.
When the uranium enrichment exceeds 20%, up to 90% and above, it can also be used for civil purposes, for example, in small research reactors, reactors used for ship propulsion, satellites, and nuclear submarines. The reason for this is because of the high power densities achievable with such enrichments. Small reactors generally require only a few kilograms of fuel to achieve criticality (i.e., a self-sustained nuclear reaction).
Since the HEU of 90% and above is used for military purposes (nuclear warheads fabrication) the IAEA and the international community try to stop states from reaching a level of uranium enrichment due to regional and global security concerns. Consequently, The Non-Proliferation Treaty (NPT) and other legally binding instruments, in addition to the IAEA safeguards, are instruments used by the international community to stop the proliferation of nuclear weapons, and therefore preventing new States from joining the list of international countries with a military nuclear capability club which includes, the US, Russia, France, UK, China, India, Pakistan, Israel, and North Korea.
- World Institute for Nuclear Security (WINS Academy), (2016). Nuclear Security Management Certification Program
- World Health Organization (WHO). Department of Protection of the Human Environment (2001). Depleted Uranium, Sources, Exposure and Health Effects
- Krass, et al. (1983). Uranium Enrichment and Nuclear Weapon Proliferation