What Is Nuclear Power Generation?

Nuclear power generation is the production of electricity through the controlled fission of heavy atomic nuclei, primarily uranium-235, inside a nuclear reactor. Fission releases approximately 200 MeV per event in the form of kinetic energy of fission fragments, which heats a coolant, which drives a steam turbine connected to a generator. The process is fundamentally a heat engine: the nuclear reaction supplies the thermal energy, and conventional turbomachinery converts that thermal energy to electricity. Globally, nuclear power plants supply roughly 10 percent of world electricity and about 20 percent of electricity in the United States, where 93 commercial reactors operated as of 2023 with an average annual capacity factor of 92.7 percent.

Nuclear power generation draws on nuclear physics for reactor core design, on thermal engineering for heat transfer and thermodynamic efficiency, and on electrical engineering for generator, transformer, and grid interconnection design. The long operational lifetimes of reactor plants (typically 40 to 80 years with license renewals) and their high upfront capital costs distinguish nuclear from most other generation technologies.

Reactor Types and Operation

The majority of the world's reactors are light-water reactors (LWRs), which use ordinary (light) water as both the coolant that transfers heat from the core and the moderator that slows neutrons to the thermal energies at which fission cross sections are highest. Within the LWR category, pressurized water reactors (PWRs) keep the primary coolant under high pressure to prevent boiling, transferring heat to a secondary steam loop, while boiling water reactors (BWRs) allow the primary coolant to boil directly, with the steam going to the turbine. Canada's CANDU design uses heavy water as moderator and coolant, which permits operation on unenriched natural uranium. High-temperature gas-cooled reactors and fast neutron reactors form smaller but growing fractions of the global fleet.

A nuclear fuel assembly typically remains in the core for three to five years before the U-235 concentration falls too low to sustain criticality. Refueling occurs every 18 to 24 months during planned outages. The U.S. Energy Information Administration's nuclear industry overview provides current data on fleet composition, capacity, and generation for U.S. reactors.

Safety Systems and Regulation

Nuclear reactor safety relies on a layered approach called defense-in-depth: multiple independent barriers, including the fuel cladding, reactor pressure vessel, and reinforced containment building, separate radioactive material from the environment. Safety systems include emergency core cooling systems that flood the reactor with water to prevent overheating, passive safety features in newer designs (such as the Westinghouse AP1000) that rely on gravity and natural convection rather than active pumps, and automatic scram systems that insert neutron-absorbing control rods to halt the chain reaction within seconds of an abnormal signal.

The U.S. Nuclear Regulatory Commission licenses and oversees commercial reactors, while the International Atomic Energy Agency (IAEA) sets international safety standards and conducts peer reviews of national programs. According to the Department of Energy's information on enhanced safety in advanced reactors, advanced designs currently under development pursue passive safety features that can cool a shutdown reactor indefinitely without operator intervention or external power.

Advanced reactor designs in development include small modular reactors (SMRs) with factory-fabricated units of 50 to 300 MWe output, molten salt reactors, and sodium-cooled fast reactors. The U.S. Nuclear Regulatory Commission's regulatory framework governs both existing LWRs and the licensing pathways for these novel designs.

Applications

Nuclear power generation has applications in a range of fields, including:

• Baseload electricity supply on national and regional grids
• Naval propulsion in submarines and aircraft carriers
• District heating and desalination in several countries
• Industrial process heat for hydrogen production and chemical manufacturing
• Remote or off-grid power generation using small modular reactors