Abstract: A high-temperature reactor with a reactor core containing fuel elements crossed by a cooling gas circuit comprises a malfunction filter for filtering metal fission products discharged from the fuel elements in the event of core overheating. The filter is mounted in the cooling gas circuit outside the reactor core and consists of a carbon which is incompletely graphitized, or is not graphitized at all.

Abstract: Removal of the graphite structure from the nuclear fuel material of fuel elements of gas-cooled high-temperature reactors is performed by heat-treatment of the fuel elements in oxygen-containing gas at temperatures below 700.degree. C. until the carbon or graphite structure is loosened up and converted into a mechanically removable material. During heat-treatment, mechanical forces are preferably applied for continually removing the outer layers that are most heavily attacked and transport of the dust into cooler temperature zones. For this purpose, the fuel elements are agitated during heat-treatment, as by an oscillating sieve or by brushes. Pre-impregnation with a material catalyzing the combustion is useful if it is important to have the heat-treatment temperature as low as possible.