23 Apparatus for fission gas release measurements from HTGR fuel elements at very high temperatures

Since 1968 p.i.e. determinations of the fission gas release from fuel samples are performed at irradiation temperatures in the range of 900 to 1250°C. The fission gas release is an indicator for the behaviour of the ceramic coated particle fuel IM. This method e.g. rendered possible the detection and consequent removal of a certain type of spherical fuel elements responsible for an increased primary circuit activity in the AVR prototyp power station /2/. Another example is a special heating program developped for the purpose of selecting within a few minutes fuel elements with defects particles /3,4/. In the course of reactor safety investigations it became necessary to heat fuel elements up to their failure limit, at least to 2500°C, calculated to be the maximum temperature in a loss of coolant accident /5/.