High-temperature gas-cooled reactor

A high-temperature gas-cooled reactor (HTGR) is a type of gas-cooled nuclear reactor which uses uranium fuel and graphite moderation to produce very high reactor core output temperatures. (700 to 950 °C) All existing HTGR reactors use helium coolant.

Source: Wikipedia — High-temperature gas-cooled reactor (CC BY-SA 4.0)