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What are the main types of nuclear power reactors?

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Labeled diagram showing the process of a nuclear power plant with a pressurized-water reactor. Water circulates through the reactor core, heats to produce steam in a steam generator, which drives a turbine connected to an electric generator. Steam is then cooled in a condenser using water from a cooling tower, which releases nonradioactive water vapor. Control rods, pumps, and transmission lines are also indicated. — nuclear power Schematic diagram of a nuclear power plant using a pressurized-water reactor.

Nuclear power reactors are primarily categorized by their cooling and moderation methods, as well as their fuel utilization strategies. The main types include:

Light-Water Reactors (LWRs): These use ordinary water as both coolant and moderator. They are divided into pressurized-water reactors (PWRs), which use a secondary loop to generate steam, and boiling-water reactors (BWRs), which produce steam directly within the reactor vessel.1
CANDU Reactors: Developed by Canada, these utilize natural uranium fuel and are moderated and cooled by heavy water. Their horizontal design allows for refueling while the system is operational.2
Breeder Reactors: These are designed to produce more fissionable material than they consume. Fast breeder reactors typically use liquid metal coolants to convert uranium-238 into plutonium-239, while thermal breeder reactors use thorium-232 as fertile material.3

Reactors are also classified by generations, ranging from early prototypic designs (Generation I) and current commercial plants (Generation II) to advanced systems with passive safety features (Generation III) and future concepts (Generation IV) focused on efficiency and waste reduction.4