An assessment of the open-source CFD software package OpenFOAM has been performed considering buoyancy-driven mixing flow inside a KONVOI type Reactor Pressure Vessel (RPV). The intrinsic complexity of the geometry and the physics of the flow are beyond the reach of one-dimensional thermal- hydraulic system codes, and thus the need to use properly verified and validated CFD simulation tools and models originates.
The chosen test represents a typical configuration that occurs during a Main Steam Line Break (MSLB) with Loss-Of-Offsite-Power (LOOP) scenario. The experiment Test 1.1 of the ROssendorf COolant Mixing (ROCOM) facility has been selected from the OECD-NEA PKL-2 project database. Previous analysis showed that Unsteady Reynolds Averaged Navier-Stokes (URANS) solutions are strongly affected by the physical and turbulent transport properties. A hexahedral mesh was employed to discretize all the geometrical details important for the mixing process in the RPV. To evaluate the accuracy of the code, a modified transient, incompressible solver was developed to include a variable turbulent Prandtl number formulation to resemble as closely as possible to the best performing numerical model previously identified using the commercial code STAR-CCM+.
The paper presents the first attempt to model the mixing in a RPV during a MSLB LOOP scenario with the open-source code OpenFOAM. Results indicate that the modified solver is usable for gravity driven flows but the current model needs improvements, in particular the mesh generation. It was also confirmed that a large integration time-step leads to a wrong estimation of the mixing, especially in the downcomer region.