Three-Dimensional Simulation of a VVER-1000 Reactor’s Pressure Chamber in the Modes with Asymmetrical Loop Operation Using a KORSAR/CFD Computation Code

The KORSAR/CFD code results from the development of the KORSAR/GP system code certified in 2009 by the Rostekhnadzor (Federal Service for Ecological, Technological, and Nuclear Supervision) as applied to the calculated justification of the safety for VVER reactors. One of the important aspects of development consists in the introduction of the CFD-module code into functional content for the simulation of spatial turbulent flows in the mixing chambers of reactors using a nested boundary method in the RANS-approximation. The CFD module is combined with a one-dimensional model according to a semi-implicit scheme as a standard code element. Calculation results using the KORSAR/CFD code are presented for the following three modes with the asymmetrical operation of a VVER-1000 reactor’s flow-circuit loops. They consist in breaking the steam pipeline in the steam generator, in connecting the main circulation pump while initially operating three pumps at the reactor power of 71% with respect to the nominal one, and in connecting a pump while initially operating two opposite pumps at the reactor power of 52% with respect to the nominal one. The calculations have been carried out based on the input data file for the NPP power unit with a VVER-1000 developed by the specialists in VVER design at OKB Gidropress, the Chief Designer in the field of VVER reactor units. A three-dimensional simulation of coupled neutron-physical and thermohydraulic processes in the reactor core has been performed. A thermohydraulic model of the reactor core has been used in a channel-by-channel approximation and a program block for the calculation of three-dimensional neutron kinetics. In the problems under consideration, the three-dimensional simulation domain for the CFD module includes four inlet manifolds and a part of the reactor pressure chamber before entering the holes in the elliptical bottom of the shaft. The holes in the elliptical bottom and the area beyond the shaft up to the outlet manifolds have been represented by the elements of a one-dimensional model. Based on the results of the calculations, the heat-carrier flow pattern in the reactor pressure chamber has been analyzed. A flow pattern effect exerted on the dynamics of the liquid temperature distribution at the entry into the fuel assemblies of the core and on the energy release power of the fuel assemblies in the simulated modes has been demonstrated.