Numerical Simulation of the Loss of Offsite Power to the VVER-1200 Nuclear Power Unit Auxiliaries

Justification of the cyclic strength of equipment and pipelines is an integral part of the VVER-based reactor plant basic design. The results of thermal-hydraulic calculations of variations in the primary and secondary coolant circuit parameters in various emergency modes serve as input data for this justification. Loss of offsite power to plant auxiliaries is one of the considered plant operation conditions. In view of loss of power supply to the plant auxiliaries, all electrically driven feed pumps are disconnected under these conditions, thus resulting in the loss of feedwater flowrate. As a consequence, the water level in all steam generators starts to decrease until the setpoint for switching on the electrically driven emergency feedwater pumps is reached. In the course of supplying emergency feedwater to the steam generators, steam condensation occurs. This entails a drop of pressure in the steam generators, which, in turn, can cause disconnection of the emergency feedwater pumps on reaching the relevant tripping setpoint. The results of a numerical simulation of the “Loss off site power for plant auxiliaries” mode for a VVER-1200 nuclear power unit carried out using the KORSAR\GP thermal-hydraulic code are presented.