Large-scale numerical predictions on heat transfer and fluid flow characteristics in a fuel bundle of the reduced-moderation light water reactor (RMWR) were performed in order to contribute the thermal design in the RMWR core. Since an analytical geometry is complicated and analysis results become huge, it takes lots of time for quantitative evaluations. Then, to make easy quantitative evaluations on the predicted results such as velocity, temperature, void fraction, etc., the flow visualization program using the software AVS/Express and the coordinates transformation processing was developed. It can reproduce thermal-hydraulic phenomena on a computer visually. By the present study, the numerical observation procedure with the AVS/Express was attained.
