Analysis of the LOFT L2-5 Experiment Using the 3D Module of the MARS-KS Code

The Loss-of-fluid-test (LOFT) L2-5 experiment is one of the LBLOCA experiments. The LOFT facility is a 50 MWt pressurized water reactor with instrumentation to measure and provide data on the thermal-hydraulic and nuclear conditions throughout the system. The LOFT L2-5 experiment simulated a 200% break in the cold leg piping with simultaneous loss of offsite power. In this study, three-dimensional thermal-hydraulic phenomena are analyzed using cladding surface temperature data from the L2-5 experiment using postprocessing program, TECPLOT 360. Also, the L2-5 experiment is simulated with both a 1D and a 3D RPV modeling using the system thermal-hydraulic code MARS-KS. The 3D RPV modeling was performed with the "multi-d" component of MARS-KS. Thermal responses in the core of L2-5 experiment were observed by visualizing measured cladding temperature using TECPLOT 360. Quenching occurs at the upper region in the core, and at the bottom and middle in order. The cladding surface temperature near the broken loop cold leg falls earlier than near the broken loop hot leg during reflood process. The L2-5 experiment was simulated using the MARSKS code. Discharge flow rate, primary system pressure, cladding temperature calculated with the 3D RPV modeling were compared with the experiment and the 1D calculation. There was no significant difference in discharge flow rate, pressure and accumulator level between 1D and 3D simulation results. From these results, it can be said that the "multi-d" component of the MARS-KS code has the capability to analyze the thermal response in the core under the LBLOCA well.