Experimental studies on the thermal and hydraulic performance of the fuel stack of the VHTR: Part II. HENDEL multi-channel test rig with twelve fuel rods

Tests on heat transfer and fluid-dynamics of the mock-up fuel stack of the Very High Temperature Gas Cooled Reactor (VHTR) were performed by the multi-channel test rig (T 1 - M) of the Helium Engineering Demonstration Loop (HENDEL). The T 1 - M simulated one column of the fuel stack in the VHTR core and contained twelve simulated fuel rods. The heat generation rate of each fuel rod was varied to simulate the power distribution of the VHTR core in the horizontal plane. In parallel with this experiment, a three-dimensional thermal analysis code was developed in order to check the experimental temperature distribution of the fuel stack. Experimental results showed that the distribution of the helium gas flow rate was influenced by the temperature distortion in the mock-up fuel stack. The maximum deviation of the helium gas flow rate from the mean value was 10% in the case of an asymmetric power distribution test at a low Reynolds number. The variation of the calculated temperature distribution in the fuel stack was about 17-35°C in each case, indicating that the temperature distortion in the fuel stack was flattened by thermal conduction in the graphite block.