THEORETICAL AND EXPERIMENTAL INVESTIGATIONS INTO THE SAFETY BEHAVIOR OF SMALL HTRS UNDER NATURAL-CONVECTION CONDITIONS

Results are described as they were obtained in the experimental facility LUNA-HTR for the study of natural convection/circulation characteristics of different HTR primary circuits. In consideration of thermodynamic similarity principles, transients have been simulated with heat removal from a pebble-bed into the primary circuit via natural convection. The mass flow and the temperatures in the loop were measured for different geodetic heights of the heat exchanger position and starting temperature conditions, as well as calculated with the code THERMIX-CRAY-2D. Both upward and downward mass flow, as well as flow reversal, have been studied in detail in a set of experiments to determine their dependence upon key physical conditions.