Development and qualification of a thermal-hydraulic nodalization for modeling station blackout accident in PSB-VVER facility

tThis paper deals with the development of a qualified thermal-hydraulic nodalization for modeling StationBlack-Out (SBO) accident in PSB-VVER Integral Test Facility (ITF). This study has been performed in theframework of a research project, aiming to develop an appropriate accident management support toolfor Bushehr nuclear power plant. In this regard, a nodalization has been developed for thermal-hydraulicmodeling of the PSB-VVER ITF by MELCOR integrated code. The nodalization is qualitatively and quan-titatively qualified at both steady-state and transient levels. The accuracy of the MELCOR predictionsis quantified in the transient level using the Fast Fourier Transform Base Method (FFTBM). FFTBM pro-vides an integral representation for quantification of the code accuracy in the frequency domain. It wasobserved that MELCOR predictions are qualitatively and quantitatively in the acceptable range. In addi-tion, the influence of different nodalizations on MELCOR predictions was evaluated and quantified usingFFTBM by developing 8 sensitivity cases with different numbers of control volumes and heat structuresin the core region and steam generator U-tubes. The most appropriate case, which provided results withminimum deviations from the experimental data, was then considered as the qualified nodalization foranalysis 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.