The high-temperature test reactor (HTTR) is a graphite-moderated gas-cooled research reactor in Oarai, Ibaraki, Japan operated by the Japan Atomic Energy Agency. It uses long hexagonal fuel assemblies, unlike the competing pebble bed reactor designs.
HTTR first reached its full design power of 30 MW (thermal) in 1999. Other tests have shown that the core can reach temperatures sufficient for hydrogen production(see more sulfur-iodine cycle).
The primary coolant is helium gas at a pressure of about 4 MPa, the inlet temperature of 395 °C, and the outlet temperature of 850–950 °C. The fuel is uranium oxide (enriched to an average of about 6%).
Coordinates: 36°15′58.8″N 140°32′50.8″E / 36.266333°N 140.547444°E / 36.266333; 140.547444