After the milling process is complete, the uranium must next undergo a process of conversion, "to either uranium dioxide , which can be used as the fuel for those types of reactors that do not require enriched uranium, or into uranium hexafluoride , which can be enriched to produce fuel for the majority of types of reactors" .
Naturally-occurring uranium is made of a mixture of U and U Most nuclear reactors require enriched uranium, which is uranium with higher concentrations of U ranging between 3. There are two commercial enrichment processes: gaseous diffusion and gas centrifugation. Both enrichment processes involve the use of uranium hexafluoride and produce enriched uranium oxide. Reprocessed uranium RepU is a product of nuclear fuel cycles involving nuclear reprocessing of spent fuel.
RepU recovered from light water reactor LWR spent fuel typically contains slightly more U than natural uranium , and therefore could be used to fuel reactors that customarily use natural uranium as fuel, such as CANDU reactors. It also contains the undesirable isotope uranium , which undergoes neutron capture , wasting neutrons and requiring higher U enrichment and creating neptunium , which would be one of the more mobile and troublesome radionuclides in deep geological repository disposal of nuclear waste.
Wrapping the weapon's fissile core in a neutron reflector which is standard on all nuclear explosives can dramatically reduce the critical mass. Because the core was surrounded by a good neutron reflector, at explosion it comprised almost 2. Neutron reflectors, compressing the fissile core via implosion, fusion boosting, and "tamping", which slows the expansion of the fissioning core with inertia, allow nuclear weapon designs that use less than what would be one bare-sphere critical mass at normal density.
The presence of too much of the U isotope inhibits the runaway nuclear chain reaction that is responsible for the weapon's power. For the secondary of a large nuclear weapon, the higher critical mass of less-enriched uranium can be an advantage as it allows the core at explosion time to contain a larger amount of fuel. The U is not fissile but still fissionable by fusion neutrons.
The Fermi-1 commercial fast reactor prototype used HEU with Significant quantities of HEU are used in the production of medical isotopes , for example molybdenum for technetiumm generators. Isotope separation is difficult because two isotopes of the same element have nearly identical chemical properties, and can only be separated gradually using small mass differences. This problem is compounded by the fact that uranium is rarely separated in its atomic form, but instead as a compound UF 6 is only 0.
A cascade of identical stages produces successively higher concentrations of U. Each stage passes a slightly more concentrated product to the next stage and returns a slightly less concentrated residue to the previous stage. Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride hex through semi-permeable membranes.
This produces a slight separation between the molecules containing U and U. Thermal diffusion utilizes the transfer of heat across a thin liquid or gas to accomplish isotope separation. The process exploits the fact that the lighter U gas molecules will diffuse toward a hot surface, and the heavier U gas molecules will diffuse toward a cold surface. It was abandoned in favor of gaseous diffusion.
The gas centrifuge process uses a large number of rotating cylinders in series and parallel formations. Each cylinder's rotation creates a strong centripetal force so that the heavier gas molecules containing U move tangentially toward the outside of the cylinder and the lighter gas molecules rich in U collect closer to the center.
It requires much less energy to achieve the same separation than the older gaseous diffusion process, which it has largely replaced and so is the current method of choice and is termed second generation. It has a separation factor per stage of 1. The Zippe centrifuge is an improvement on the standard gas centrifuge, the primary difference being the use of heat.
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The bottom of the rotating cylinder is heated, producing convection currents that move the U up the cylinder, where it can be collected by scoops. This improved centrifuge design is used commercially by Urenco to produce nuclear fuel and was used by Pakistan in their nuclear weapons program. Laser processes promise lower energy inputs, lower capital costs and lower tails assays, hence significant economic advantages.
Several laser processes have been investigated or are under development.
Using building materials to monitor for high enriched uranium
Separation of isotopes by laser excitation SILEX is well advanced and licensed for commercial operation in Atomic vapor laser isotope separation employs specially tuned lasers  to separate isotopes of uranium using selective ionization of hyperfine transitions. The technique uses lasers tuned to frequencies that ionize U atoms and no others.
The positively charged U ions are then attracted to a negatively charged plate and collected. Molecular laser isotope separation uses an infrared laser directed at UF 6 , exciting molecules that contain a U atom. A second laser frees a fluorine atom, leaving uranium pentafluoride , which then precipitates out of the gas.
Separation of isotopes by laser excitation is an Australian development that also uses UF 6. After a protracted development process involving U. SILEX has been projected to be an order of magnitude more efficient than existing production techniques but again, the exact figure is classified.
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Aerodynamic enrichment processes include the Becker jet nozzle techniques developed by E. Becker and associates using the LIGA process and the vortex tube separation process. These aerodynamic separation processes depend upon diffusion driven by pressure gradients, as does the gas centrifuge. They in general have the disadvantage of requiring complex systems of cascading of individual separating elements to minimize energy consumption.
In effect, aerodynamic processes can be considered as non-rotating centrifuges. Enhancement of the centrifugal forces is achieved by dilution of UF 6 with hydrogen or helium as a carrier gas achieving a much higher flow velocity for the gas than could be obtained using pure uranium hexafluoride. The Uranium Enrichment Corporation of South Africa UCOR developed and deployed the continuous Helikon vortex separation cascade for high production rate low enrichment and the substantially different semi-batch Pelsakon low production rate high enrichment cascade both using a particular vortex tube separator design, and both embodied in industrial plant.
However all methods have high energy consumption and substantial requirements for removal of waste heat; none are currently still in use.
In the electromagnetic isotope separation process EMIS , metallic uranium is first vaporized, and then ionized to positively charged ions. The cations are then accelerated and subsequently deflected by magnetic fields onto their respective collection targets. A production-scale mass spectrometer named the Calutron was developed during World War II that provided some of the U used for the Little Boy nuclear bomb, which was dropped over Hiroshima in Properly the term 'Calutron' applies to a multistage device arranged in a large oval around a powerful electromagnet.
Electromagnetic isotope separation has been largely abandoned in favour of more effective methods. One chemical process has been demonstrated to pilot plant stage but not used for production. An ion-exchange process was developed by the Asahi Chemical Company in Japan that applies similar chemistry but effects separation on a proprietary resin ion-exchange column. Plasma separation process PSP describes a technique that makes use of superconducting magnets and plasma physics.
In this process, the principle of ion cyclotron resonance is used to selectively energize the U isotope in a plasma containing a mix of ions. Funding for RCI was drastically reduced in , and the program was suspended around , although RCI is still used for stable isotope separation. Separative work is not energy. The same amount of separative work will require different amounts of energy depending on the efficiency of the separation technology.
In addition to the separative work units provided by an enrichment facility, the other important parameter to be considered is the mass of natural uranium NU that is needed to yield a desired mass of enriched uranium. As with the number of SWUs, the amount of feed material required will also depend on the level of enrichment desired and upon the amount of U that ends up in the depleted uranium. However, unlike the number of SWUs required during enrichment, which increases with decreasing levels of U in the depleted stream, the amount of NU needed will decrease with decreasing levels of U that end up in the DU.
For example, in the enrichment of LEU for use in a light water reactor it is typical for the enriched stream to contain 3. On the other hand, if the depleted stream had only 0. Because the amount of NU required and the number of SWUs required during enrichment change in opposite directions, if NU is cheap and enrichment services are more expensive, then the operators will typically choose to allow more U to be left in the DU stream whereas if NU is more expensive and enrichment is less so, then they would choose the opposite.
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The opposite of enriching is downblending; surplus HEU can be downblended to LEU to make it suitable for use in commercial nuclear fuel. High concentrations of U are a byproduct from irradiation in a reactor and may be contained in the HEU, depending on its manufacturing history. HEU reprocessed from nuclear weapons material production reactors with an U assay of approx. So, the HEU downblending generally cannot contribute to the waste management problem posed by the existing large stockpiles of depleted uranium.
From through mid, tonnes of high-enriched uranium enough for 10, warheads was recycled into low-enriched-uranium. The goal is to recycle tonnes by The United States Enrichment Corporation has been involved in the disposition of a portion of the Through the U. They argue the availability of high-quality imported uranium from close allies, including Canada, means more taxpayer support for the industry is unnecessary.edutoursport.com/libraries/2020-01-04/3354.php
Reading : Power Plays Enriched Uranium And Homeland Security
The nuclear power industry is "trying to leverage the 'America First' moment to get more government financial support for the operating fleet," said Edwin Lyman, a nuclear expert with the Union for Concerned Scientists advocacy group. Other industry requests to a working group made up of representatives from the Pentagon and agencies including the Commerce and Energy departments include vastly expanding a U.
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The American Assured Fuel Supply Reserve established in currently has six so-called "reloads" of low enriched uranium. A nuclear plant needs reloading with processed fuel at least every two years. The U. The administration already has done plenty to ease environmental and other regulations and at this point, only tariffs and quotas would "move the needle" to help the industry, said Travis Deti, director of the Wyoming Mining Association, which represents the state's mining companies.
Most uranium in the U. The water is then pumped to the surface and ore is extracted.