Investigation of scale-up capability of RELAP5/MOD3 and scaling distortion in the IIST facility via natural circulation experiments

During the past years, a number of reduced-scale test facilities have been constructed to investigate the physical phenomena of transients or accidents occurring in nuclear power plants. Since the behavior of a nuclear power plant is complicated, it is quite impossible for a small-scaled facility to simulate all the physical phenomena during the transient process. But, by way of proper scaling, most of the important aspects of transient behavior can be simulated. Calculations using RELAP5/MOD3 investigate whether most of the key thermal-hydraulic phenomena observed in the Institute of Nuclear Energy Research Integral System Test (IIST) facility can be expected in a prototype plant. When compared with experimental data, the calculated results of two different scale models show reasonable agreement with the natural circulation transients. The scale-up capability of RELAP5/MOD3 is demonstrated by simulating the single-phase and two-phase natural circulation transients. Also, the scaling distortions in the heat transfer areas of the IIST facility do not strongly distort the thermal-hydraulic behavior of experimental data