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What makes uranium-235 so special? How does this 'king of fission' play a key role in nuclear energy?
When discussing nuclear energy, uranium-235 (235U) often becomes the focus and is known as the "king of fission". This special isotope, with its unique physical properties, has an indispensable influence on nuclear power generation technology and weapons manufacturing. Uranium-235 is the only nuclide in nature that can be fissioned by thermal neutrons, making it a key role in various nuclear reactions.
In nuclear energy, the concentration of uranium-235 must be higher than the level found in natural uranium to support fission reactions.
Uranium in nature is mainly composed of uranium-238 (238U), accounting for more than 99%, while uranium-235 accounts for less than 1%. Although uranium-238 also has important uses, it does not have the ability to fission, which makes uranium-235 play a key role in nuclear energy and nuclear weapons development. In nuclear power generation, most nuclear reactors use enriched uranium, where the uranium-235 content is increased to between about 3.5% and 4.5%.
The roasting and enrichment process of uranium is necessary to ensure it can be used in reactors.
There are two main commercial technologies for enriching uranium: gaseous diffusion and gas centrifuge. These processes first convert uranium into uranium hexafluoride (UF6), and then extract the product with a high uranium-235 content through physical and chemical means. Globally, nearly 90% of uranium enrichment is done through gas centrifuges because of their high efficiency and low energy consumption.
In addition to uranium-235 itself, other uranium isotopes such as uranium-236 and uranium-238 also have their specific uses. Among them, uranium-236 consumes the neutrons required for fission reactions through neutron capture, which makes high-enriched uranium-235 crucial in the nuclear reaction process.
The presence of high-concentration uranium-235 not only ensures the operating efficiency of nuclear reactors, but also enhances the power of nuclear weapons.
Specific uranium products, including low-enriched uranium (LEU), highly enriched uranium (HEU) and highly enriched low-enriched uranium (HALEU), enable use in many different types of reactors. For example, many small modular reactors require HALEU to ensure their operation. In nuclear weapons manufacturing, the standard concentration of HEU is usually over 85%.
The interpretation and handling of various uranium species is not limited to economic and technical challenges, but also faces numerous environmental and safety laws and regulations. Uranium reprocessing (RepU) technology can effectively reduce nuclear waste and improve the utilization rate of uranium in the process of obtaining usable uranium.
The reuse of uranium not only optimizes resources, but is also crucial for nuclear waste management.
Specifically, among various uranium enrichment methods, lithography and laser technology have gradually shown their superiority. These emerging technologies not only reduce energy consumption and costs, but also have greater flexibility and may have a place in the nuclear energy industry in the future. In addition, addressing the risk of nuclear proliferation is also a major challenge facing scientists today.
In short, uranium-235 has played a vital role in the development of nuclear energy. Its unique fission properties and upstream enrichment technology make it the cornerstone of nuclear power generation and military use. With the advancement of technology and the challenge of renewable energy, how will the role of uranium-235 evolve in the future?
