Sensitivity Analysis for Design Extension Conditions of a VVER-1200 Power Unit

According to the latest requirements of the Russian and international regulatory bodies, the modeling of design extension conditions (DEC) shall be accompanied by a sensitivity analysis of the results to the possible variations in the parameters studied. The sensitivity analysis should yield at its output the extent to which each of the uncertainties influences the parameters studied. The subject of the study, which was carried out using a commonly adopted approach, is to perform a sensitivity analysis of the DEC “Loss off-site normal operation AC power supply to plant auxiliary equipment (commonly known as NPP LOOP conditions) with a common-cause failure of programmable I&C systems” to check the possibility of applying this approach in analyzing design extension conditions, because previously, analyses of DECs were not accompanied by a sensitivity analysis. The accomplished sensitivity analysis has yielded the following information: - values characterizing the spread of the criterion parameters (maximum fuel rod cladding temperature and maximum primary and secondary circuit pressures); - Spearman’s rank correlation coefficients; - graphs of density distribution functions and distributions of the calculation results. A methodology of performing sensitivity analyses for DECs without fuel melting and the tight primary circuit is presented, which makes it possible to fully take into account the requirements of international and Russian regulatory bodies. The methodology can be extended to all designs of VVER reactor plants.