Abstract
A Steady-state three-dimensional (3-D) non-compressible CFD model is developed in this paper to investigate the thermal-hydraulic characteristics within the core of a Pebble Bed reactor (PBR). This steady-state model essentially includes the continuity equation, momentum equation, energy equation, standard k-ε turbulence model and the RSM turbulence model. The variables of thermal properties with temperature are considered and the gas coolant is assumed to be the ideal gas. In this study, Fluent 12.0 is used as simulation software. A high temperature gas cooled reactor (HTGR) with a pebble bed core (PBR) can be considered as one of the possible energy generation sources in the incoming future due to its inherently safety performance, lower power density, and higher conversion efficiency, etc. It is important to study thermal-hydraulic characteristics in a PBR for optimum design and safe operation of a HTGR. In this paper, two kinds of contact modeling between adjacent pebbles are adopted, including area and point contact treatments, respectively. The former contact treatment is a geometric approximation modeling. Based on the comparisons of thermal-hydraulic characteristics in the pebbles predicted by both contact treatments, no significant difference is revealed except for the near-wall secondary flow pattern. In addition, compared with the calculated results from the well-known correlations, the present predicted dependences of Nu number and friction factor on the particle Reynolds number show good agreement qualitatively and quantitatively.Follow by the real geometric design, the single-point contact with the pebble bed of fuel accumulation. Two pebble arrangements are selected, which are Body-Centered Cubic (BCC), and Face-Centered Cubic (FCC). Results showed that the FCC arrangement having the lowest porosity gives the low fuel temperature. Comparison of the CFD results with an empirical correlation was made for the Nusselt number and friction factor but there were large differences between them.