Experimental evaluation of the bypass flow in the VHTR core

In the core of Very High Temperature Gas-Cooled Reactor for the hydrogen production, there is the bypass flow that does not pass through coolant holes within the graphite blocks. The main bypass flow path is the gap channel between the core blocks. The amount of effective coolant and the temperature of the outlet coolant decrease as the bypass flow rate increases. Since the bypass flow affects the success of hydrogen production, it is important to evaluate the amount and the distribution of the bypass flow. In this study, the experimental facility to measure the amount of the bypass flow was designed and set up. The experiments and CFD analysis to evaluate the bypass were carried out with several gap sizes and the combinations of the blocks. As the results, the bypass flow ratio increases as gap size, it is independent of the inlet mass flow rate but decreases as the number of fuel block in the unit cell increase.