A simulation of VVER1000/320 operational transients was performed with the CATHARE2 V1.3L computer program. These transients consisted of consecutive shutdowns of two primary side pumps, prior to which, the reactor was under nominal operational condition with 72 and 52% power levels, respectively. The comparison between calculated and measured data indicated that the program was able to qualitatively predict the main phenomena taking place in both the primary and the secondary sides of the plant. The role of pump inertia was studied. It was found that implementation of inertial pump shutdown led to a better agreement with experiment. There was a lack of detailed information on the secondary-side geometry. Thus, it was difficult to conclude whether the quantitative discrepancy between experiment and calculation was due to the physical model or the geometric uncertainty.