The purpose of this paper is to study the thermal-hydraulic behaviors associated with the Loss-of-Fluid Test (LOFT) Experiment of total loss-of-feedwater accident and its recovery (Test No. L9-1/L3-3), and to perform sensitivity studies to identify parameters having significant effect on the thermal-hydraulic behaviors predicted by RELAP5/MOD3.3Beta computer code. The Experiment L9-1/L3-3 was a simulation of the total loss-of-feedwater (TLOFW) accident and its recovery modes. Generally, the RELAP5/MOD3.3Beta calculation results were in good agreement with experimental data, even though some differences were also observed. Sensitivity studies showed that several parameters have significant effect on the predicted thermal-hydraulic behaviors. These parameters include the pressurizer spray system loss coefficient, nodalization of the SG secondary side, steam generator (SG) U-tube heat transfer area, heat transfer coefficient from the LOFT main components to the environment, and the power-operated relief valve (PORV) discharge coefficient. The first three parameters are significant during the short-term transient phase, while the last two are significant during the long-term transient phase. Therefore, the five parameters should be carefully modeled to obtain appropriate calculation results for transient types such as the total-loss-of feedwater accident and its recovery modes.

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