THE NACOK EXPERIMENTAL FACILITY FOR INVESTIGATING AN AIR INGRESS INTOTHE CORE OF A HIGH-TEMPERATURE REACTOR

For investigating an air ingress into the core of the Siemens designed HTR-module, Forschungszentrum Juelich GmbH has set up an experimental facility designed to represent the reactor construction as realistica lly as possible. The accident scenario is based on the assumption of a complete break in the coaxial duct between the reactor pressure vesse l and the steam generator vessel, which makes possible a continuous fl ow of air through the core driven by natural convection. The aim of th e experiments is the validation of the computer codes, which are used to calculate the air mass flow, and the associated corrosion of the fu el elements and of the graphitic core structures. The experimental fac ility is presented, and the results of the experiments concerning aero dynamic aspects are described, including temperature dependence of the air mass flow, pressure drop and mass transfer on the sphere surface within the fuel ball packing under the relevant conditions, and delay time for the onset of natural convection.