Britannica Sources used in this answer

How do nuclear reactors control fission chain reactions to generate electricity?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — actinoid element Modern version of the periodic table of the elements (printable).

Nuclear reactors generate electricity by harnessing the heat produced during nuclear fission, a process where actinoid elements like uranium-235 split into smaller parts, releasing energy and additional neutrons. To generate electricity safely and consistently, reactors must maintain a steady-state chain reaction where the multiplication factor, k, is kept equal to unity.12

Control is primarily achieved through the use of control rods made of materials with a high neutron-capture cross section, such as boron, cadmium, or hafnium. These rods are inserted into or withdrawn from the reactor core to absorb excess neutrons, thereby regulating the rate of fission.13

Different types of rods serve specific functions:
* Safety rods: Designed to terminate the chain reaction rapidly in emergencies.3
* Regulating rods: Used for fine-tuning the power output.3
* Shim rods: Used to compensate for long-term changes in reactivity as fuel is depleted.3

Additionally, moderators like water or graphite are used to slow down fast neutrons, increasing the probability of further fission, while coolants transport the generated heat to steam-generating equipment to drive turbines for electricity production.14