ELI5- Why does heat decrease reactivity in a nuclear reactor?
In: Physics
It doesn’t always; depends on the design. For most water-based reactors (so, most reactors), it’s because the hotter the water is, the less dense it is. There’s literally fewer hydrogen atoms per unit volume. That means it’s worse at moderating (slowing down) the fast neutrons that come from fission. Since most reactors rely on moderated (slow) neutrons to sustain a chain reaction, less moderation means a decrease in reactivity.
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