Very-high-temperature reactor. Diagram of the workings of a very-high-temperature reactor (VHTR), or high-temperature gas-cooled reactor (HTGR). This type of experimental nuclear reactor uses a graphite-moderated nuclear reactor (left) with a once-through uranium fuel cycle. It is a type of high-temperature reactor (HTR) that can in theory have an outlet temperature of 1000 C. Heat from the core is passed via helium coolant through heat exchanger systems (centre). The high outlet temperatures allow for applications such as hydrogen production. On the right is a hydrogen production plant, with hydrogen outlet indicated by a red arrow.