Long-term behavior of the AVR-core

Considered is the numerical treatment of the reactorphysical long-term behaviour of the AVR-reactor, which is operated since 1967. At present time the AVR is run at an average hot-gas temperature of 950$sup 0$C, while originally laid out for 850$sup 0$C. The pebble-bed core consists of 7 different spherical fuel-element types. This mode of operation requires in connection with the rather poor shutdown system and with regard to the statistical fuelling as well as the lack of in-core instrumentation extensive reactor-following calculations. (orig.)