The hydraulic and thermal testing of two different irradiation rig models A and B, differing in the inlet nozzle design, bottom reflector length and steps inside a mock-up container is part of the HFTM validation activities which support the engineering design of the High Flux Test Module.The pressure drops for all models in the test section are measured for overall mass flow rates of 1–12g/s and different absolute pressures of 1500hPa and 2500hPa at the pressure port at the inlet section. The pressure drops in different sections of the experiment and in the single rig minichannels are also measured with additional pressure ports on the surfaces of the rig models.Predictability and reproducibility of the cooling effects of the main cooling channels in the HFTM irradiation zone can be shown. Rig model B with a backward facing step is for high mass flow rates >∼7.5g/s (this is the operation regime of the HFTM) superior to rig model A. Uniform perfusion of the multiple parallel minichannels of the irradiation rigs by helium gas is of importance to obtain uniform and predictable temperatures. Temperature fields under different heater and flow conditions have been measured.