THERMALHYDRAULICS ANALYSIS OF FIXED BED NUCLEAR REACTOR IN SOME DIFFERENT CONFIGURATIONS

The Fixed Bed Nuclear Reactor (FBNR) is a small module reactor using the spherical fuel elements. It has a simple design, inherent safety features, passive cooling for some situations, and reduced environmental impacts. The key to the safety characteristic of FBNR is simply that the core will be become empty of fuel elements, and nuclear criticality situation will be stopped when any undesired situation occurs. Any signal from any of the numerous detectors, due to any accident event, will cut-off power to the pump, causing the fuel elements to fall back into the fuel chamber where they remain in a highly subcritical and passively cooled conditions. This mechanism helps the reactor has a very high passive safety. Therefore, FBNR is one kind of IV generation according to the International Atomic Energy Agency (IAEA) defines. However, it also makes difficulties for analytical methods to understand clearly about thermal hydraulics processes in the active core. In the paper, the authors used the Computational Fluid Dynamics (CFD) method to analyze the basic thermal hydraulics parameters of FBNR such as temperature distribution of spherical fuels, and temperature, pressure and velocity of the coolant in some different configurations. The results are highly accurate and visual, helping us to evaluate more exactly about the processes of heat generation, thermal conductivity and heat exchange between fuel elements and coolant water. Finally, we can choose the best configuration of FBNR.