Answer :
Final answer:
U-235 is used in nuclear reactors more than U-238 because it is fissile and can sustain a nuclear chain reaction effectively. U-235 releases more energy per fission event compared to U-238 and is essential in both energy generation and military contexts. While U-238 is abundant, it does not easily undergo fission with thermal neutrons.
Explanation:
Why U-235 is Preferred in Nuclear Reactors
Uranium-235 (U-235) is used more in nuclear reactors than Uranium-238 (U-238)) due to its unique nuclear properties. While U-238 makes up about 99.27% of natural uranium, U-235 is only 0.72% and is the only isotope in natural uranium that can sustain a reaction with thermal neutrons effectively.
One major reason U-235 is favored is that it is a fissile material, meaning it can readily undergo fission when it captures a neutron. The fission of U-235 releases a significant amount of energy and more neutrons, which can then induce further fission reactions, leading to a stable chain reaction. In contrast, U-238, while more abundant, does not easily undergo fission with thermal neutrons and instead often requires fast neutrons or can be converted to plutonium-239 (Pu-239) in breeder reactors.
Moreover, the energy release from U-235 is about 2 MeV greater per fission event compared to U-238. This makes workflows more efficient in reactors. Because of its properties, U-235 not only fuels most commercial nuclear reactors but is also the material from which nuclear weapons are derived, emphasizing its importance in both energy generation and military applications.
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