Investigation of the impurities and fission products in the AVR coolant gas at an average hot-gas temperature of 9500C

Since 27 February, 1974, the AVR pebble bed reactor has been producing gas at an average temperature of 9500C. Therefore it is possible for the first time to gain experience in high temperature reactor operations and in experiments with such a high temperature level. This is of particular interest with regard to efforts using high temperature reactors for production of nuclear process heat. This paper reports briefly on the preparations for a temperature increase and on the first experimental results obtained with a hot-gas temperature of 9500C. Measured data are given on the behaviour of inactive gaseous impurities, on the increase of fission gas activities, and on the increase of concentrations of solid fission products in the helium coolant gas. While the activities of the fission gases showed an insignificant increase in the coolant gas, considerable increase of activity was measured for solid fission products, especially for Ag isotopes. However, activities released from fuel elements are low so that there are no operational or safety problems. (Auth.)