In this paper, accuracy sensitivity of MELCOR code in prediction of Thermal-Hydraulic (TH) behavior of test facilities of Nuclear Power Plants (NPP) is quantitatively analyzed. MELCOR is a fast-running code with integrated structure, and it is extensively employed for modeling of severe accidents in NPPs. Fast Fourier Transform Based Method (FFTBM) is a tool to determine differences between code predictions and measurements in frequencies. Cut frequency plays an important role in quantitative evaluation of TH calculations by FFTBM. In the current research, a sensitivity study has been carried out by different cut frequencies. Suitable cut frequency removes incorrect influence of higher noise frequencies of investigated signals, while avoiding loss of information in accuracy indices of FFTBM. Determined cut frequencies for both original FFTBM and improved FFTBM by signal mirroring, have a good agreement. Accuracy indices calculated with the determined cut frequency, provide more consistent understanding of calculation accuracy variations during the modeled transients.
