Preface status of metallic materials development for application in advanced high-temperature gas-cooled reactors

The first gas-cooled reactor power station was built at Calder Hall in the United Kingdom and began operation in 1956. In this Magnox reactor type, CO2 was used as the coolant and natural metallic uranium as the fuel. Magnox power plants with a combined electrical rating in excess of 8000 MW are now running and have achieved over 500 reactor-yr of operation. The advanced gas-cooled reactor (AGR) was developed in the United Kingdom as an extension of the Magnox line, retaining CO2 as the primary coolant, using enriched UO2 fuel to allow an increase in coolant temperatures from 360 to 6500C. At the present time, AGR systems with a combined electrical rating of almost 9000 MW are in operation or under construction. The high-temperature gas-cooled reactor (HTGR) represents a further development to increase coolant temperatures. The higher operating temperatures (<7500C) require changes in the fuel/core design and the substitution of helium for CO2 as the primary coolant. This leads to a more economical plant with a higher power density core and a low radioactive environment within the primary loop. The technological development of the system has proceeded steadily with regard to: 1. development of fuel particles, which are coated with layers of ceramics to retain fission products 2. use of an all-graphite core construction 3. use of helium gas as a coolant