A Light Water Reactor (LWR) is a type of nuclear reactor that uses ordinary water as both a coolant and a neutron moderator. This means that the water helps to slow down neutrons, making it easier for them to cause fission in the reactor's fuel, typically enriched uranium. LWRs are the most common type of nuclear power plants in operation today. In an LWR, the heat generated from nuclear fission is used to produce steam, which drives turbines to generate electricity. There are two main designs of LWRs: Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs). Both designs are crucial for providing a significant portion of the world's electricity.