Overview of high-temperature reactor engineering and research

In the future, it is essential that nuclear energy be used under the conditions of sustainability. Enhanced reactor safety, improved economics, suited waste management and best use of resources are very important topics in this context. The modular high-temperature reactor can contribute to fulfil these requirements because it has excellent safety characteristics and it can be applied not only to produce electricity very efficiently, but also to deliver nuclear process heat for many applications in the energy economy. Broad activities in the field of HTR are currently being undertaken in countries such as Japan and China, which commissioned test reactors, and in South Africa, the USA and Russia, which plan to build such plants. In countries having a long-term tradition of gas-cooled reactors (i.e. Great Britain, France and Germany), interest in this type of reactor persists. The safety analysis of these nuclear power plants is dedicated to a system which will avoid the problems which are connected to existing reactors. These HTR reactors cannot melt even in severe accidents of loss of coolant and fuel cannot be destroyed by other severe accidents. Therefore, the release of radioactivity to the environment is very limited. The state of technology and new developments are explained in more detail in this paper. The overall concept of inherent safety, including questions concerning self-acting decay heat removal and hypothetical impacts from outside, are discussed and analysed. Open questions and future needs for research and development in the field of HTR technology are added to better establish an impression of the state of HTR technology worldwide.