Nuclear Reactors: Components, Types, and Operation
Nuclear Reactor: Core Components and Function
A nuclear reactor is the most important component of a nuclear power plant, constituting its core. The reactor system allows for a sustained and controlled chain reaction, enabling the utilization of thermal energy to produce steam. This steam then drives a turbine that powers an electric generator.
Reactor Components
- Reactor Vessel: A robust container housing the neutron source and nuclear fuel.
- Moderator: Reduces the speed of neutrons emitted during fission reactions, facilitating further fission reactions and maintaining the chain reaction.
- Control Rods: Composed of neutron-absorbing materials, these rods regulate the rate of fission within the reactor.
- Coolant: Cools the reactor, prevents overheating, and transports the generated heat to the turbine-alternator group, either directly or via a secondary circuit, before returning to the reactor to repeat the cycle.
Types of Nuclear Power Plants
Pressurized Water Reactor (PWR) Plants
PWR plants utilize enriched uranium as fuel and water as both coolant and moderator. The generated heat is transferred from the reactor core through a primary cooling circuit to a secondary circuit, producing steam.
Boiling Water Reactor (BWR) Plants
BWR plants also use enriched uranium and water. However, unlike PWR reactors, they employ only one cooling circuit, as steam is generated directly inside the reactor due to the lower pressure at which the water boils. This simplifies the primary circuit.
Nuclear Equipment Buildings
- Containment Building: Encloses the reactor and primary circuit components, typically consisting of three parallel loops, each with a pump, pressurizer, and steam generator.
- Turbine Building: Houses the turbine-alternator group, steam reheaters and condensers, and feedwater preheaters.
- Fuel Building: Used for storing fresh fuel for reactor refueling and spent fuel awaiting reprocessing.
- Control Building: Contains the control room, the central hub of the plant, where performance data from all equipment and security systems is monitored, and commands are issued.
- Auxiliary Building: Houses auxiliary systems, security systems, radioactive waste treatment systems, air filtration and conditioning equipment, and the containment building’s air conditioning.
Nuclear Power Plant Operation
Energy generated in the reactor core is extracted and transported by the coolant, which operates in a closed circuit at high pressure. This heat is then transferred to a secondary circuit in the steam generators. The resulting steam drives a turbine coupled to an alternator, generating electricity. This electricity is then transmitted to the power grid after voltage elevation via transformers.
After passing through the turbine, the steam condenses back into liquid, returning to the steam generator via feedwater pumps. There, it vaporizes again, completing the cycle. The condenser cooling water operates in an open circuit, drawing water directly from a river or the sea, circulating it through the condenser, and returning it to its source. If the river flow is low, potentially causing thermal pollution, the water is pre-cooled using forced-draft cooling towers.