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Why are control rods important in a nuclear reactor?
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nuclear fission
Italian-born physicist Enrico Fermi explaining a problem in physics, c. 1950. He was awarded the 1938 Nobel Prize for Physics.
Control rods are essential components in a nuclear reactor because they regulate the rate of the nuclear fission chain reaction by absorbing neutrons. By inserting or withdrawing these rodsāwhich are made of materials with a high neutron-capture cross section, such as boron, cadmium, or hafniumāoperators can control the multiplication factor, k, to maintain a steady-state reaction or shut the system down entirely.12
Reactors typically utilize three types of rods to manage reactivity:
- Safety rods: Designed to terminate the chain reaction rapidly during scheduled shutdowns or emergencies by dropping into the core.1
- Regulating rods: Used for routine adjustments to the reactor's power rate by adding or removing small amounts of reactivity.1
- Shim rods: Employed to compensate for long-term reactivity changes caused by fuel depletion (burnup) over time.1
By precisely managing the neutron population, control rods ensure the reactor operates safely and within designed power limits.12