Spherical fuel elements for small and medium sized HTR

The German high temperature gas-cooled reactors (HTR) are distinguished by spherical graphitic fuel elements with 60 mm diameter, which are loosely packed to form the reactor core. To cover a large number of possible HTR applications the fuel element in Germany is designed so as to be uniform and acceptable for conditions set by different approaches of small and medium sized HTR subsequent to the THTR. Since 1980, the fuel cycle is based on the use of low enriched UO2. Fabrication processes using precise classification of kernels coated and overcoated particles by tabeling techniques ensure satisfaction of specified limits on fabrication induced coating defects. A comprehensive irradiation test programme was performed for the low enriched uranium fuel elements used in the current fuel cycle. The results demonstrate excellent performance of the reference fuel element design. (orig.)