Thermal hydraulics of the pebble bed high temperature reactor under accident conditions

The transient temperature behavior of the pebble bed core after loss of forced cooling is determined by the natural heat transport phenomena heat conduction, convection and radiation. The 2-D-transient thermal hydraulics code THERMIX allows to quantify these effects for core heat up accidents with a pressurized and depressurized primary circuit and for the flow stability analysis for the lay-out of the auxiliary cooling system. The core internal natural convection heat transport is simulated by a convection experiment which is described by the code with high accuracy. The effective heat conductivity of the homogenized pebble bed at elevated temperatures has been gained by high temperature experiments