THTR300

THTR-300 was a prototype high-temperature gas-cooled reactor (HTGR) built in Germany to demonstrate pebble-bed technology and the potential use of the thorium fuel cycle. Located in Hamm-Uentrop, North Rhine-Westphalia, it was a graphite-moderated, helium-cooled reactor with an electrical output on the order of 300 megawatts. The core used spherical fuel elements ("pebbles") containing coated fuel particles designed for high-temperature operation and robust fission product retention.

Designed in the 1970s and brought into service in the 1980s, THTR-300 was intended to explore higher thermal efficiencies and process heat applications compared with conventional light-water reactors. Although the concept emphasized thorium as an alternative fertile material, the plant operated primarily with uranium-based fuel during its commercial life. The reactor incorporated features typical of HTGR designs, including high outlet temperatures and strong negative temperature coefficients that contributed to inherent safety characteristics.

THTR-300 faced technical, economic and political challenges: construction and operating costs grew, public opposition increased after a small release of radioactive dust in 1986, and operational interruptions reduced availability. These factors contributed to its permanent shutdown in 1989. Decommissioning and waste management have been lengthy and costly processes, reflecting the complexities of dismantling graphite-moderated reactors and handling irradiated fuel. THTR-300 remains an important case study in the development of high-temperature reactor technology and the practical challenges of deploying novel nuclear concepts.