A thermal-neutron reactor is a type of nuclear reactor that uses slow or thermal neutrons, which are neutrons in thermal equilibrium with the reactor's materials and have much lower energy than the original fast neutrons. Most nuclear power plants use these reactors, employing a neutron moderator to slow down neutrons to improve the likelihood of fission in uranium-235, which has a much higher nuclear cross section for thermal neutrons. Thermal reactors include components such as the neutron moderator, nuclear fuel, reactor vessel, radiation shielding, and containment buildings to ensure safe operation and radiation protection.
Types of thermal-neutron reactor
Light-Water Reactor, LWR
Main article: Light-water reactor
Light-Water Reactors, are the most widespread globally and include:
- Pressurised Water Reactors (PWRs) – used in the U.S., France, China, and many others.
- Boiling Water Reactors (BWRs) - common in Japan and parts of the U.S.
Both use ordinary water as coolant and moderator.
Heavy Water Reactor, HWR
Main article: Heavy-water reactor
- CANDU reactors (Canada) use heavy water (D₂O) moderator and coolant, allowing them to run on natural uranium.
Gas-Cooled Reactor, GCR
Main article: Gas-cooled reactor
- Advanced Gas-cooled Reactors (AGRs) in the UK use graphite as moderator and carbon dioxide as coolant.
Examples by generation
Generation I (1950s–1960s)
These were early prototypes and demonstration reactors.
- Shippingport Atomic Power Station (USA): The world’s first full-scale PWR.
- Magnox reactors (UK): Used natural uranium and graphite moderation.
- Obninsk Nuclear Power Plant AM-1 (USSR): The first grid-connected nuclear power plant.
Generation II (1970s–1990s)
Commercial reactors with standardized designs and improved safety.
- Pressurized Water Reactor (PWR) – e.g., Westinghouse and Framatome designs.
- Boiling Water Reactor (BWR) – e.g., GE BWR series.
- CANDU reactor – Canadian heavy water reactors using natural uranium.
- Advanced Gas-cooled Reactor (AGR) – UK graphite-moderated, CO₂-cooled.
All of these are thermal reactors using moderators like water or graphite.
Generation III / III+ (1990s–present)
Enhanced safety, longer lifespans, and passive safety systems.
- AP1000 (USA): A Gen III+ PWR with passive cooling.
- EPR (European Pressurized Reactor): High-output PWR used in France and Finland.
- VVER-1200 (Russia): Modernized version of Soviet PWRs.
- CANDU 6 Enhanced: Updated heavy water reactor with improved safety.
See also
- Thermal breeder reactor
- Enriched uranium
- Fast-neutron reactor
- Liquid fluoride thorium reactor
- India's three-stage nuclear power programme
References
Squires, G. L. (2012-03-29). Introduction to the Theory of Thermal Neutron Scattering. Cambridge University Press. ISBN 978-1-107-64406-9. 978-1-107-64406-9 ↩
"Some Physics of Uranium". Archived from the original on March 3, 2008. Retrieved 2009-01-18. https://web.archive.org/web/20080303234940/http://www.uic.com.au/uicphys.htm ↩