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The difference between uranium-235 and uranium-238: How are the two related?
In the world of nuclear energy, various isotopes of uranium play an important role, especially uranium-235 (235U) and uranium-238 (238U). Uranium in nature is mainly composed of three isotopes: uranium-238, uranium-235 and uranium-234. These isotopes have some differences in structure, and these differences have far-reaching implications for the application of nuclear power and nuclear weapons. This article will take a closer look at the properties of uranium-235 and uranium-238, and how they are related.
Uranium-235 is the only naturally occurring nuclide that can undergo fission using thermal neutrons.
Uranium-238 makes up more than 99% of natural uranium, while uranium-235 accounts for only about 0.7%. This makes uranium-235 relatively scarce, yet it is precisely because of its fissile properties that it is a key component of nuclear fuel. When uranium-235 absorbs a thermal neutron, it undergoes fission, releasing energy and additional neutrons, a property that makes it an ideal fuel for nuclear reactors.
Uranium mining and processing
After uranium is mined, it undergoes a series of processing steps to extract uranium that can be used in nuclear reactions. The uranium ore is first ground to produce "yellowcake," a concentrated product containing uranium oxide. The output of this process is the raw material required for further processing of uranium.
The "yellowcake" extracted from uranium ore after grinding contains about 80% uranium, compared to the uranium content of the original ore, which is about 0.1%.
Meanwhile, subsequent processing of uranium varies depending on its intended use. Uranium can be converted into uranium dioxide for use in reactors that do not require enriched uranium, or into uranium fluoride for enrichment to produce highly enriched uranium fuel. However, enrichment of uranium-238, despite its lack of fissionability, is still present in most commercial enrichment processes.
Uranium enrichment and uses
Most of today's nuclear reactors require enriched uranium, which usually contains uranium-235 at a concentration between 3.5% and 4.5%. The main methods of producing enriched uranium are gas diffusion and gas centrifugation. Both technologies are designed to increase the concentration of uranium-235 to meet the fuel conditions required for different reactors.
Gaseous diffusion technology was once the main method for uranium enrichment, but with the development of new technologies, gas centrifugation is now mainly used.
Specialized highly enriched uranium (HEU), typically with more than 20% uranium-235, is used for military purposes and in special reactors. This high concentration of uranium is not only vital for nuclear power generation, but is also an important component of nuclear weapons. It is worth noting that although uranium-238 is not fissile, it can still be split by fast neutrons in certain nuclear reactions, which further enriches the application of uranium.
Progress in reprocessing uranium and enrichment technology
Reprocessed uranium (RepU) comes from used nuclear fuel that has undergone a series of chemical and physical treatments to extract usable uranium again. This type of uranium has a higher concentration than natural uranium. Nevertheless, in today's nuclear power industry, the presence of uranium-236 and the challenges it brings must be handled with caution because it may consume neutrons and affect the efficiency of nuclear reactions.
Application of low-enriched and highly enriched uranium
Low-enriched uranium (LEU) is used primarily in most commercial nuclear reactors, with the concentration of uranium-235 typically between 3% and 5%, while the application of highly enriched uranium (HEU) is mainly concentrated in the military and specific research needs. The use of highly enriched uranium enables the design to meet the requirements of high thermal neutron flux and strict control of reactor dynamics.
The medical industry's demand for highly enriched uranium, especially for the production of nuclear medicine isotopes such as molybdenum-99, is particularly important.
Future Development and Security Considerations
As uranium enrichment technology advances, more cost-effective methods, such as laser separation technology, are expected to be introduced in the future, which will have the potential to reduce energy requirements and reduce environmental risks. However, the potential safety of these new technologies and the risk of nuclear proliferation require more regulation and measures to address.
The importance of uranium-235 and uranium-238 in the field of nuclear energy cannot be ignored, and their interrelated characteristics make us think about a question: in the sustainable development of nuclear energy, how should we balance its safety and energy needs?
