Major milestones of HTR development in Germany and still open research issues

For more than 50 years the pebble-bed High Temperature Reactor (HTR) has been under development in Germany. Forschungszentrum Jülich (FZJ), Aachen University (RWTH), industrial companies and other organizations were involved in this task, which was for about two decades something like a national showcase. For more than ten years before the German decision to shut down all nuclear power plants in Germany, there was a strong decrease in the interest of HTR-related activities. Reasons include the lack of competitiveness of HTRs for electricity production only in a well-developed grid, the poor performance of the German demonstration plant THTR and the rise in the general 'German Angst'. The remaining HTR activities, including experimental study of dust behavior and the development of the HTR Code Package (HCP), will come to an end in the near future. In this paper, we summarize the German experience in fuel fabrication and qualification, the performance of AVR and THTR, the HTR-Modul concept, economic aspects of HTR, competition and/or complementarities to LWR, the statement of “inherent HTR safety” and the development of large components for turbine, steam generator, blower, and bearings. Lessons learned and remaining challenges will be addressed.