<human>:  What happens inside a nuclear reactor?
<bot>: A nuclear reactor is a device used to initiate, control, and maintain a sustained nuclear chain reaction. Inside a nuclear reactor, a controlled sequence of nuclear fission reactions takes place, releasing energy in the form of heat and radiation. The heat produced inside the reactor is used to turn water into steam, which is then used to generate electricity. To maintain the chain reaction, nuclear fuel must be continuously replenished, and the reactor components must be securely cooled to prevent overheating. The safety and efficiency of a nuclear reactor are managed by a system of automation and containment that limits any release of radiation.