High Quality Content by WIKIPEDIA articles! The Very High Temperature Reactor (VHTR), or High Temperature Gas-cooled Reactor (HTGR), is a Generation IV reactor concept that uses a graphite-moderated nuclear reactor with a once-through uranium fuel cycle. The VHTR is a type of High Temperature Reactor (HTR) that can conceptually have an outlet temperature of 1000°C. The reactor core can be either a “prismatic block” or a “pebble-bed” core. The high temperatures enable applications such as process heat or hydrogen production via the thermochemical sulfur-iodine cycle.