Experimental and Numerical Studies of Pressure and Oscillatory Flow Effects on the Two-Phase Flow and Heat Transfer in a Rod Bundle

An experimental and numerical study was performed to investigate the effects of pressure and constant vs oscillatory flooding rates on the two-phase flow and heat transfer behavior of a rod bundle under reflood transient conditions. Experimental results were obtained from the NRC/PSU Rod Bundle Heat Transfer (RBHT) test facility from various test cases covering a range of system pressures with light water as the working coolant. For each pressure case, two experiments were performed, one for a constant flow rate, and one for an oscillating flow rate about the constant flow rate. The RBHT test facility, which contains 49 vertical, 3.66 m (12 ft) long test rods (four unheated corner rods and 45 heated rods) with Inconel 600 cladding in a 7 × 7 geometry, having the rod diameters, rod pitches and spacer grids comparable to those in commercial PWRs, was specifically designed to obtain fundamental flow and heat transfer data during reflood transients. The thermal–hydraulic code TRAC/RELAP Advanced Computational Engine (TRACE) was used in this study by performing simulations with the same geometry and operating conditions as the RBHT facility for each experiment. Results of the TRACE simulations were compared to the experimental data obtained in the RBHT tests. It was found that the trends on the pressure effects for constant and oscilatory flows on the thermal–hydraulic behavior of the rod bundle (i.e., the two-phase flow and heat transfer behavior of the rod bundle during reflood transients) predicted by the TRACE model agree well with the RBHT data. This comparison of results has also assisted in other studies to investigate numerical discrepancies currently underway.