gascooled

Gas-cooled refers to systems that transfer heat from a source using a gas as the primary heat-transfer medium. In nuclear engineering, gas-cooled reactors (GCRs) use a gas to remove heat from the reactor core. The gases most commonly used are carbon dioxide (CO2) and helium. Helium is chemically inert and has low neutron absorption, making it attractive for high-temperature, low-activation operation. CO2 has good heat transfer properties and was historically used in large-scale reactors but requires materials able to withstand corrosion and radioactivation over time.

Historical examples include the Magnox reactors in the United Kingdom (1950s–1980s), which used natural uranium metal fuel, a graphite moderator, and CO2 cooling. The Advanced Gas-Cooled Reactor (AGR) series, also in the UK, used enriched uranium oxide fuel, a graphite moderator, and CO2 cooling at higher pressure, achieving higher outlet temperatures and thermal efficiency than Magnox. Several AGR units operated for decades before decommissioning began in the 2010s and 2020s.

Beyond these, gas cooling continues in experimental and generation IV designs. The Gas-Cooled Fast Reactor (GFR) is a concept that uses a fast neutron spectrum with a gas coolant, typically helium, to achieve high thermal efficiency and a closed fuel cycle. High-temperature, gas-cooled reactors aim to provide not only electricity but also industrial process heat for hydrogen production or desalination.

Advantages of gas cooling include good neutron economy (especially with helium), the potential for high outlet temperatures, and the use of non-flammable coolants. Disadvantages include lower heat capacity and density compared with liquids, requiring larger or higher-pressure systems, and material challenges at high temperature and with gas flow. Overall, gas-cooled technologies have played a historically significant role and remain a focus of ongoing research for high-temperature applications.