SMRs - High temperature reactors

The vast majority of reactors used in nuclear power plants worldwide are enriched uranium and light water reactors. In the past, other types of reactor have been studied and tested, in particular high-temperature reactors using graphite as moderator, helium as coolant and medium-enriched uranium (HALEU), in the original form of TRISO particles. This report presents the experimental reactors developed in the UK, USA and Germany, followed by the two power reactors at Fort Saint-Vrain in the USA and THTR 300 in Germany. The technology was not developed industrially and commercially, as these experiments proved unconvincing, also due to the dominance of water reactors and a general decline in interest in nuclear power generation from the 1980's onwards. However, for several years now, the field has been attracting interest from promoters of small modular reactors, SMRs, which are relatively 'small' in terms of the power of the basic 'module', but above all would be mass-produced in a dedicated plant and then transported to site, in order to ensure the profitability of the business through the number of orders for identical installations. This study presents the characteristics of these reactors, which could produce high-temperature heat to meet the needs of numerous industrial sites, as well as three candidate SMR reactors from the IAEA's selection of HTR projects: the HTR-PM reactor and its predecessor HTR-10, 'ballistic' type reactors, in China; and the HTTR reactor, 'prismatic' type, in Japan. These descriptions are accompanied by a critical analysis of the announced properties of the HTR SMR projects, in terms of safety issues, vulnerability to external aggression, radioactive waste production and management, and proliferation risks. A key question concerns the risks of coupling an HTR nuclear reactor to an industrial facility. There is a wide range of HTR proposals, and while each is lauded for its virtues, there are many questions about the industrial and economic capacities involved, which may prove to be totally prohibitive. Ultimately, each individual project will have to be subjected to meticulous scrutiny by safety organizations