How does nuclear fission work?

02 Tem 04:19

In nuclear fission, when a thermal neutron strikes a uranium-235 (U-235) atom nucleus, the nucleus splits into two, releasing a large amount of energy along with 2-3 new neutrons. These neutrons then collide with other U-235 nuclei, causing them to split as well, thus sustaining the chain reaction. When I simulated this process in a previous project, I observed the neutrons' kinetics and how they are slowed down using a moderator (usually water)—because fast neutrons are less likely to be absorbed by U-235 compared to U-238, so slowing them down is crucial for maintaining an efficient reaction. From a control perspective, control rods in reactors (typically made of cadmium or boron) regulate the reaction rate by absorbing neutrons. Pushing the rods deeper increases neutron absorption, slowing the reaction; pulling them out allows more neutrons to propagate, speeding up the chain reaction. Regarding uranium enrichment, while natural uranium contains only 0.7% U-235, power plants typically use fuel enriched to 3-5%. This process involves separating uranium isotopes using methods like gas diffusion or centrifuges—I witnessed this during an internship and took notes on the chemical behavior of uranium hexafluoride (UF6).

02 Tem 05:40

In order for Uranium-235 atoms to undergo fission, a neutron must first collide with the atom's nucleus. This causes the atom to split into two, releasing additional neutrons that initiate a chain reaction. Control rods absorb neutrons in the core, and graphite rods are used to absorb excess heat from these neutrons. Enriching U-235 involves using centrifuges to concentrate the lighter U-235 isotopes, increasing their natural abundance from 0.7% to a range of 3-5%.