Das Projekt "Fuel behaviour under accident contitions, 1992-1994" wird vom Umweltbundesamt gefördert und von European Commission, Joint Research Centre (JRC). Institute for Transuranium Elements (ITU) durchgeführt. Objective: To contribute to the understanding of severe reactor accident mechanism by providing support to code development and application, by specifying and characterising fission products to be released from fuel in a particular accident scheme and by developing and applying specialised instrumentation for in-pile tests. General Information: Progress to end 1991. In-pile equipment for safety studies with nuclear fuels has been developed and tested (ultrasonic thermometers). An analytical solution for the transport of gaseous species in nuclear fuel pore channels under transient conditions has been proposed. A new version of the MITRA code has been applied to study transport and release of radioactive fission products from irradiated fuel. The release of volatile fission products from ThO2 with a simulated burn-up of 4 per cent has been studied. Code development work as a contribution to the establishment of a European Accident Code (in collaboration with Ispra) continued. Three articles on modelling work related to problems of reactor safety were published in 1991. Detailed description of work foreseen in 1992 (expected results). Characterisation of irridiated fuel to be subjected to in-pile fission products release tests. Application and extension of existing mathematical models to studies of fission product migration observed in transient tested UO2 under the electron microscope. Short description of evolution of work in 1993. Continuation of experimental and theoretical studies of fission product migration and release. Achievements: In pile equipment for safety studies with nuclear fuels has been developed and tested (ultrasonic thermometers). An analytical solution for the transport of gaseous species in nuclear fuel pore channels under transient conditions has been proposed. A new version of the MITRA code has been applied to study transport and release of radioactive fission products from irradiated fuel. The release of volatile fission products from thorium oxide (THO2) with a simulated burn up of 4 per cent has been studied. Code development work as a contribution to the establishment of a European accident code continued.