Predicted two-phase flow structure in fuel a bundle of an advanced light-water reactor

In order to predict the water-vapor two-phase flow structure in a fuel bundle of an advanced light-water reactor, large-scale numerical simulations were carried out using a newly developed two-phase flow analysis method and a highly parallel-vector supercomputer. Conventional analysis methods such as subchannel codes need composition equations based on the experimental data. In case that there are no experimental data regarding the thermal-hydraulics in the tight-lattice core, therefore, it is difficult to obtain high prediction accuracy on the thermal design of the advanced light-water reactor. Then, a new analysis method using the large-scale direct numerical simulation of water-vapor two-phase flow was proposed. The axial velocity distribution in a fuel bundle changed sharply around a spacer. The bridge formation occurred at the position of adjacent fuel rods where an interval is the narrowest, and vapor mainly flows downstream the triangular part where the interval of adjacent fuel rods is large. (author)