I'm curious, how does the nuclear fission process work? For example, how does the atomic nucleus split and how does the chain reaction start? What are the critical factors in this process, such as the role of neutron count or the moderator? Can you explain it simply?
What are the basic principles of nuclear fission?
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Wow, I actually took an "Introduction to Nuclear Engineering" course in university for a semester, and my professor's explanations kind of confused me, you know? Back then, we did a small lab experiment—a simple model of a nuclear reactor working with a uranium-235 sample. You know how it is; when a slow neutron hits a uranium nucleus, it splits into two, releasing energy. This split also shoots out an average of 2-3 new neutrons, which then go on to hit other uranium atoms, kickstarting a chain reaction.
When they talk about the critical factor, like the speed of the neutrons is super important. If they're too fast, they just zip past the uranium without hitting anything, but if you slow them down (say, with graphite or water), you get a much more efficient reaction. These materials, called moderators, help slow the neutrons down. Then there's how much uranium the reactor contains and its geometry—if there isn't enough uranium or the setup isn't right, the chain reaction just stops on its own. In my lab experiment, I was trying to manually adjust these factors, and the machines kept beeping—good thing there wasn’t an explosion at least 😅.
When a neutron strikes a heavy atomic nucleus like Uranium-235, the nucleus splits apart, releasing a tremendous amount of energy while forming lighter elements. The newly created neutrons then go on to split other nuclei, triggering a chain reaction.