Performance of thermal mixing structure of HTR-PM regarding bypass flow and power effect

The temperature of bypass flow not flowing through the reactor core is obviously lower than that of the main coolant helium in a High Temperature Gas-cooled Reactor (HTGR). In addition, change and deviation of reactor power will introduce higher radial temperature difference of main coolant helium. In order to investigate the effects of bypass flow and power change and deviation on radial temperature difference of the helium flow, model experiments and simulation calculations are proposed to evaluate the temperature profiles and Thermal Mixing Performance (TMP) of the thermal mixing structure at Pebble-bed Module High Temperature gas-cooled Reactor (HTR-PM) core outlet. We gave three definitions of TMP by describing the thermal nonuniformity of the inlet flow of the mixing structure in different ways. The TMP defined by the temperature difference between main flow and bypass flow is within the range of 97.5 ± 1.1% under all considered conditions which is suitable for evaluating the experiment and simulation results. The new definition of TMP integrating specific heat, flow rate and inlet position needs further improvement. In addition, the maximum radial temperature difference at the outlet of the mixing structure fulfils the requirement of steam generator, less than 30 °C (±15 °C). Furthermore, future works are discussed.