Uranium is used as an energy source for nuclear reactors and was used to build the first atomic bomb, dropped on Hiroshima in 1945. Uranium is extracted with a mineral called uraninite, made up of various isotopes with different atomic weight and level. of radioactivity. To be used in fission reactors, the amount of the isotope 235U must be raised to a level that allows fission in a reactor or explosive device. This process is called uranium enrichment, and there are several ways to accomplish it.
Steps
Method 1 of 7: The Basic Enrichment Process
Step 1. Determine what uranium will be used for
Most of the uranium extracted contains only 0.7% isotope 235U, and the rest contains mostly the stable isotope 238U. The type of fission the mineral will be used for determines at what level the isotope 235U must be brought in in order to make the best use of the mineral.
- The uranium used in nuclear power plants needs to be enriched in a percentage between 3 and 5% 235U. Some nuclear reactors, such as the Candu reactor in Canada and the Magnox reactor in the UK, are designed to use unenriched uranium.)
- Uranium used for atomic bombs and nuclear warheads, on the other hand, must be enriched up to 90 percent. 235U.
Step 2. Turn uranium ore into a gas
Most of the methods currently in existence for enriching uranium require that the ore be transformed into a gas at a low temperature. Fluorine gas is usually pumped into the ore conversion plant; uranium oxide gas reacts on contact with fluorine, producing uranium hexafloride (UF6). The gas is then processed to separate and collect the isotope 235U.
Step 3. Enrich uranium
The subsequent parts of this article describe the various possible procedures for enriching uranium. Of these, gaseous diffusion and gas centrifuge are the most common, but the isotope separation process with the laser is intended to replace them.
Step 4. Convert the UF gas6 in uranium dioxide (UO2).
Once enriched, uranium must be converted into a solid and stable material to be used.
Uranium dioxide used as a fuel in nuclear reactors is transformed using synthetic ceramic balls enclosed in 4-meter-long metal tubes
Method 2 of 7: Gas Diffusion Process
Step 1. Pump the UF gas6 in the pipes.
Step 2. Pass the gas through a porous filter or membrane
Since the isotope 235U is lighter than the isotope 238U, the UF gas6 containing the lighter isotope will pass through the membrane faster than the heavier isotope.
Step 3. Repeat the diffusion process until enough isotope is collected 235U.
The repetition of the diffusion process is called "cascade". It could take up to 1,400 passes through the porous membrane to get enough 235U and enrich uranium sufficiently.
Step 4. Condensate the UF gas6 in liquid form.
Once the gas is sufficiently enriched, it is condensed into liquid form and stored in containers, where it cools and solidifies to be transported and transformed into nuclear fuel in the form of pellets.
Due to the number of steps required, this process requires a great deal of energy and is being eliminated. In the United States, only one gaseous diffusion enrichment plant remains in Paducah, Kentucky
Method 3 of 7: Gas Centrifuge Process
Step 1. Assemble some high speed rotating cylinders
These cylinders are the centrifuges. The centrifuges are assembled both in series and in parallel.
Step 2. Pipes the UF gas6 in centrifuges.
Centrifuges use centripetal acceleration to send gas with the isotope 238U heavier towards the cylinder walls, and the gas with the isotope 235U lighter towards the center.
Step 3. Extract the separated gases
Step 4. Reprocess the gases in separate centrifuges
The gases rich in 235U are sent to centrifuges where a further quantity of 235U is extracted, while the gas depleted of 235U goes to another centrifuge to extract the remainder 235U. This process makes it possible for the centrifuge to extract a greater quantity of 235U with respect to the gaseous diffusion process.
The gas centrifuge process was first developed in the 1940s, but began to be used in a significant way starting in the 1960s, when its low energy consumption for the production of enriched uranium became significant. At present, there is a gas centrifuge plant in the United States in Eunice, New Mexico. Instead, there are currently four such plants in Russia, two in Japan and two in China, one in the UK, the Netherlands and Germany
Method 4 of 7: Aerodynamic Separation Process
Step 1. Build a series of narrow, static cylinders
Step 2. Inject the UF gas6 in high-speed cylinders.
The gas is pumped into the cylinders in such a way as to give them a cyclonic rotation, producing the same type of separation between 235U and 238U which is obtained with a rotating centrifuge.
One method being developed in South Africa is to inject gas into the cylinder on the tangent line. It is currently being tested using very light isotopes, such as those of silicon
Method 5 of 7: Thermal Diffusion Process in the Liquid State
Step 1. Bring the UF gas to a liquid state6 using pressure.
Step 2. Build a pair of concentric tubes
The pipes must be long enough; the longer they are, the more isotopes can be separated 235U and 238U.
Step 3. Immerse them in water
This will cool the outer surface of the pipes.
Step 4. Pump the liquid gas UF6 between the pipes.
Step 5. Heat the inner tube with steam
The heat will create a convective current in the UF gas6 which will make the isotope go 235U lighter towards the inner tube and will push the isotope 238U heavier to the outside.
This process was experimented in 1940 as part of the Manhattan Project, but was abandoned in the early stages of experimentation, when the gaseous diffusion process, believed to be more effective, was developed
Method 6 of 7: Electromagnetic Separation Process of Isotopes
Step 1. Ionize the UF gas6.
Step 2. Pass the gas through a powerful magnetic field
Step 3. Separate the isotopes of ionized uranium using the trails they leave as they pass through the magnetic field
The ions of the isotope 235U leave trails with different curvature than those of the isotope 238U. These ions can be isolated and used to enrich uranium.
This method was used to enrich the uranium from the bomb dropped on Hiroshima in 1945 and is also the method used by Iraq in its nuclear weapons development program in 1992. It requires 10 times more energy than the gaseous diffusion process. making it impractical for large-scale enrichment programs
Method 7 of 7: Laser Isotope Separation Process
Step 1. Adjust the laser to a specific color
The laser light must be adjusted entirely to a specific wavelength (monochromatic). This wavelength will only affect the atoms of the isotope 235U, leaving those of the isotope 238U unaffected.
Step 2. Apply the uranium laser light
Unlike other uranium enrichment processes, you do not need to use uranium hexafloride gas, even though it is used in most processes with laser. You can also use an alloy of uranium and iron as a source of uranium, as is the case in the Laser Vaporization of Isotope Separation (AVLIS) process.
Step 3. Extract the uranium atoms with the excited electrons
These are the isotope atoms 235U.
Advice
In some countries, nuclear fuel is reprocessed after use to recover spent plutonium and uranium that are created as a result of the fission process. The isotopes must be removed from the reprocessed uranium 232U and 236U that are formed during fission and, if subjected to the enrichment process, must be enriched to a higher level than normal uranium since the isotope 236U absorbs neutrons and inhibits the fission process. For this reason, reprocessed uranium must be kept separate from that being enriched for the first time.
Warnings
- Uranium is only slightly radioactive; in any case, when it is transformed into UF gas6, becomes a toxic chemical substance which in contact with water transforms into corrosive hydrochloride acid. This type of acid is commonly referred to as "etching acid" as it is used to etch glass. Uranium enrichment plants need the same safety measures as chemical plants that process fluoride, such as holding UF gas6 at a low pressure level most of the time and using special containers in areas where it must be subjected to higher pressure.
- Reprocessed uranium must be kept in highly shielded containers, as the isotope 232U can decay into elements that emit a large amount of gamma rays.
- Enriched uranium can only be reprocessed once.
