Experimental Studies on the Thermal Hydraulics of a Fuel Column for a Gas-Cooled Micro Reactor (GMR)

A thermal-hydraulic test facility is designed to explore the thermal-hydraulic characteristics inside a fuel assembly under normal operating conditions, thereby providing data for validating computer codes for a novel gas-cooled micro reactor (GMR). The primary loop supplies helium at a prototypic temperature and pressure to the test section containing a full-size fuel assembly. The experimental procedure and the test conditions were elaborated. Pre-test simulations using the COMSOL Multiphysics 5.0 software yield detailed 3D distributions of the temperature and flow fields inside the test section, which were employed to guide the positioning of thermocouples. The maximum temperature and its locus, the pressure drop of the coolant through the test section, and the helium temperature at the outlet duct were determined. The simulation indicates that the “mixer” component can effectively enhance the mixing of helium in the rear plenum and reduce the outlet helium temperature. The measured data of preliminary tests at the facility agree well with the predicted values, which proves the accuracy and reliability of the thermocouples. An unheated section at the end of the heating rods leads to a relatively large deviation of the results on the last measuring plane.