Status of Qualification of High-Temperature Reactor Fuel Element Spheres

To cover a large number of possible high-temperature reactor applications in the Federal Republic of Germany, the fuel element is designed to be uniform and acceptable for conditions set by different approaches for various plants following the thorium high-temperature reactor (THTR). To minimize fission product release, silicon carbide coated fuel (Triso) is required for all types of fuel cycles, and limits are specified for both fabrication and in-service coating defects. Fabrication processes using precise classification of coated and overcoated particles by tabling techniques ensure satisfaction of specified limits on fabrication-induced coating defects. A comprehensive irradiation test program was performed for both high-enriched uranium/thorium fuel elements used in the THTR and Arbeitsgemeinschaft Versuchs-Reaktor cycle and the low-enriched uranium fuel elements to be used for follow-up projects. The results demonstrate good performance of all types of fuel.