dbo:abstract
- Dragon was an experimental high temperature gas-cooled reactor at Winfrith in Dorset, England, operated by the United Kingdom Atomic Energy Authority. Its purpose was to test fuel and materials for the European High Temperature Reactor programme, and it was built and managed as an Organisation for Economic Co-operation and Development/Nuclear Energy Agency international project. It operated from 1965 to 1976. Dragon used helium gas as the coolant and graphite as the neutron moderator. Fuel was formed into tiny spherical pellets and then coated with ceramics. These were then mixed with the graphite and pressed together to form blocks of various shapes and sizes. Criticality is only possible when the blocks are placed together in certain configurations within a neutron reflector, allowing additional fuel to be held in a ready area and loaded on-the-fly. Helium was used due to its low nuclear cross section which led to higher neutron economy, as well as its chemical inertness allowing it to operate at higher temperatures without fear of eroding the reactor materials. Higher temperatures also allow for more efficient steam turbine operation and make it more suitable for direct use as process heat. In the case of a power failure, natural convection of the helium provided emergency cooling. Dragon was a test machine only, and did not attempt power extraction. Many designs of the 1960s and 70s were based on this general tristructural-isotropic (TRISO) fuel concept, including "prismatic" designs with fixed fuel layouts like Dragon, and the pebble-bed reactor designs being developed in Germany. As of 2019, these concepts have been used in several further research reactors, including Peach Bottom, AVR, HTTR, and HTR-10 as well as for commercial reactors Fort St. Vrain and THTR-300. The HTR-PM in China is under construction, with one unit at Shidao Bay connected to the grid as of December 2021. (en)