VVER TRANSIENT SIMULATION RESULTS ANALYSIS FOR MAIN STEAM LINE BREAK ACCIDENT USING FUEL ASSEMBLY PIN-BY-PIN MODEL BY KORSAR/GP CODE
29th Symposium of AER on VVER Reactor Physics and Reactor Safety (2019, Energoland, Mochovce NPP, Slovakia)
reactor dynamics and safety analysis
Abstract
One of the determining accidents in the safety analysis of VVER NPP is a main steam line break accident. For this accident the several typical stages of transient can be picked-out. At the first, initial stage, as a result of the initial event the secondary steam-water mixture outflowing into the «leak» begins, that results in the quick secondary pressure decrease and increase in the heat flux removed from the primary circuit. As a result, the coolant temperature of the core inlet decreases and causes an power increase due to the action of feedbacks. At this stage of the accident the maximum values are reached for the fuel temperature and specific enthalpy. The scram brings the reactor into subcritical state.
In this work the first stage of the accident was simulated. The maximum values of fuel temperature and enthalpy were estimated using the pin-by-pin model of fuel assembly. The results were compared with the results obtained using of the «hot channel» model. The calculations were performed for different initial state of the power plant. The realistic and conservative initial state of RP is considered. Recommendations of the using fuel assembly pin-by-pin model for this accident were developed.