This paper deals with the development of a qualified thermal-hydraulic nodalization for modeling Station
Black-Out (SBO) accident in PSB-VVER Integral Test Facility (ITF). This study has been performed in the
framework of a research project, aiming to develop an appropriate accident management support tool
for Bushehr nuclear power plant. In this regard, a nodalization has been developed for thermal-hydraulic
modeling of the PSB-VVER ITF by MELCOR integrated code. The nodalization is qualitatively and quantitatively qualified at both steady-state and transient levels. The accuracy of the MELCOR predictions
is quantified in the transient level using the Fast Fourier Transform Base Method (FFTBM). FFTBM provides an integral representation for quantification of the code accuracy in the frequency domain. It was
observed that MELCOR predictions are qualitatively and quantitatively in the acceptable range. In addition, the influence of different nodalizations on MELCOR predictions was evaluated and quantified using
FFTBM by developing 8 sensitivity cases with different numbers of control volumes and heat structures
in the core region and steam generator U-tubes. The most appropriate case, which provided results with
minimum deviations from the experimental data, was then considered as the qualified nodalization for
analysis of SBO accident in the PSB-VVER ITF. This qualified nodalization can be used for modeling of
VVER-1000 nuclear power plants when performing SBO accident analysis by MELCOR code.