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Computational simulation of natural convection in a pool representative of a molten core in lower head of a PWR pressure vessel
Camila B. Vieira and Jian Su
This paper presents computational simulation of natural convection of a molten core in the lower head of a typical PWR pressure vessel during a severe accident, performed by a pool representative in two-dimensional semicircular geometry with isothermal walls. We simulated transient turbulent natural convection heat transfer of a fluid with uniformly distributed volumetric heat generation rate using a commercial computational fluid dynamics (CFD) software ANSYS CFX 12.0. We used the two-equation κ – ω based Shear Stress Transport (SST) turbulence model to model the turbulent stresses in the Reynolds-Average Navier-Stokes equations (RANS). The Boussinesq model was used for the buoyancy effect generated by the internal heat source in the flow field. Two Prandtl numbers, 6.13 and 7.0, were considered. Five Rayleigh numbers (109 – 1013) were simulated for each Prandtl number. The average Nusselt numbers on the bottom surface of the semicircular cavity were in good agreement with those obtained by Mayinger et al. . The average Nusselt numbers on the top flat surface were in agreement with both the outcomes calculated by Mayinger et al.  and Tzanos  up to Ra = 1010.
Keywords: Heat transfer, turbulence models, Shear Stress Transport, severe accident, natural convection.