Large-scale simulations on thermal-hydraulics in fuel bundles of advanced nuclear reactors (Annual Report of the Earth Simulator Center, Sep 2007, 2006 issue)

In order to predict the water-vapor two-phase flow dynamics in a fuel bundle of an advanced light-water reactor, large-scale numerical simulations were performed using a highly parallel-vector supercomputer, the earth simulator. Although conventional analysis methods such as subchannel codes and system analysis codes need composition equations based on the experimental data, it is difficult to obtain high prediction accuracy when experimental data are nothing. Then, the present large-scale direct two-phase flow simulation method was proposed, and the void fraction distributions under the heated flow condition were analyzed. On the other hand, in order to estimate the turbulence characteristics in the fast breeder nuclear rector core, large eddy simulation and direct numerical simulation were carried out under the concentric and eccentric annular channels simulating the simplified bare fuel bundle. An objective of this work is to identify reliable and practical approaches for the simulation of unsteady flows in rod-bundles and related geometries. (author)