A reactor is a device used to initiate and control a nuclear reaction. In nuclear power plants, reactors convert nuclear energy into heat, which is then used to produce steam that drives turbines for electricity generation. The most common type of reactor is the pressurized water reactor, which uses water as both a coolant and a neutron moderator. In addition to power generation, reactors are also used in research and medical applications. For example, research reactors are utilized for scientific experiments, while medical reactors produce isotopes for diagnostic imaging and cancer treatment. These reactors play a crucial role in various fields, including energy, medicine, and scientific research.