Störfällsimulation an bestrahlten Kugelbrennelementen bei Temperaturen von 1400 bis 2500 ° C

To simulate accident conditions in a HTGR of the pebble bed type 72 spherical fuel elements with 7 different fuel particle kinds were heated to 1400 to 2500 ° C. Fission product release and changes on fuel elements were investigated. Cesium release from all fuel elements started within 100 hours between 1400 and 1600 ° C. Krypton 85 on the other hand will released in significant amounts (> 1 %) only above 2000°C as a result of particle defects. A relatively good fission product retention was observed with 41 fuel elements with (U,Th)O$_{2}$ -BISO particles (THTR type). Particle defects and krypton release amounted to less than 1 %, whereas the cesium release at 1600 °C increased with higher burn up, exceeding 10 % after 50 hours. A lower cesium release of 3 to 5 % after 100 hours at 1600 °C was only measured from two fuel elements with TRISO particles