Theoretical and experimental investigations into the safety behavior of small HTRs under natural convection conditions

This paper describes further results obtained with 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 with heat removal via natural convection from a pebble bed into the primary circuit were simulated. The mass flow and the temperatures in the loop were simulated. 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. Depending on these various conditions, an upward or downward mass flow, or a flow reversal, have been studied in detail in new experiments.