Fluid Flow and Heat Transfer Analysis of the Vhtr Lower Plenum Using the Fuego Cfd Code

There are a number of safety and heat transfer issues in the lower plenum (LP) of a prismatic core very high temperature reactor (VHTR), such as the formation of hot spots in the lower support plate and thermal stratification of the helium gas coolant. In this paper, results of key separate-effect validation and verification (V&V) calculations, as well as the calculated flow fields and heat transfer characteristics in the LP are presented and discussed. The calculations with helium gas at 1,273 K were performed with Fuego, a 3D, massively parallel, unstructured element, computational fluid dynamics (CFD) code being developed at Sandia National Laboratories. The calculations employed the dynamic Smagorinsky large eddy simulation (LES) turbulence model, participating media radiation (PMR), and 1D conjugate heat transfer (CHT). The results qualified the impact of using swirling helium gas flow into the LP to minimize the effect of the hot spots and enhance heat transfer in the bottom plate and mixing in the LP. _____________________________________________________________________ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DEAC04-94AL85000.