Reactor types refer to the various designs used in nuclear reactors to facilitate nuclear fission. The most common types include Pressurized Water Reactors (PWR), which use water under high pressure to cool the reactor, and Boiling Water Reactors (BWR), where water boils to produce steam directly in the reactor core. Each type has its own safety features and operational methods. Another category is Fast Breeder Reactors, which generate more fissile material than they consume, and Molten Salt Reactors, which use liquid salt as a coolant. These reactors aim to improve efficiency and sustainability in nuclear energy production.