With the construction of the cold finger apparatus, a new method has been developed to determine fission product release profiles during heating tests of irradiated spherical fuel elements. It is shown that this equipment works with high sensitivity and great precision for all important fission product nuclides up to 1800 °C.Together with the existing equipment, a total of 22 fuel elements with modern TRISO particles has been tested in the temperature range of 1500 - 2500 °C. In addition, experiments were done on seven UO2 samples at 1400 to 1800 °C. For heating times up to 100 hours at the maximum temperature, the followingresults were obtained: silver is the only fission product to be released at 1200 - 1600 °C by diffusion through intact SiC, but is of low significance in accident scenarios; caesium, iodine, strontium and noble gas releases up to 1600 °C are solely due to various forms of contamination. At 1700 - 1800 °C, corrosion-induced SiC defects cause the release of Cs, Sr, I/Xe/Kr. Above 2000 °C, thermal decomposition of the silicon carbide layer sets in, while pyrocarbons still remain intact. Around 1600 °C, the accident specific contribution of caesium, strontium, iodine and noble gas release is negligible. This report is a translation of Jül-2091 published October 1986 in German
