This paper presents a numerical study of the stationary and dynamic pebbles in a pebble bed reactor (PBR) by means of discrete element method (DEM). At first, the packing structure of stationary pebbles is simulated by filling process until the settling of pebbles into PBR. The packing structural properties are obtained and analyzed. Subsequently, when the outlet of PBR is open during the operational maintenance of PBR, the stationary pebbles start to flow downward and are removed at the bottom of PBR. The dynamic behavior of pebbles is predicted and discussed. Our results indicate the DEM can offer both macroscopic and microscopic information for PBR design calculations and safety assessment.

This paper presents discrete element simulations of granular flow in a rectangular hopper model of the pebble bed reactor (PBR). Two flow conditions with/without granular materials recycled back are considered in this work. For both flows, the simulations have been conducted under comparable conditions so that the similarity and difference between them can be examined. The distributions of the physical properties including flow patterns, velocity and flow structure are also investigated. Moreover, the mean velocity, diffusion and particle mixing, the effects of wall friction have been analyzed based on the simulation results. The implications for the reactor design and fundamental research on granular flow physics are discussed as well.

The nuclear thermal rocket is one of the candidate propulsion systems for future space exploration including traveling to Mars and other planets of the solar system. Nuclear thermal propulsion can provide a much higher specific impulse than the best chemical propulsion available today. A basic nuclear propulsion system consists of one or several nuclear reactors that heat hydrogen propellant to high temperatures and then allow the heated hydrogen and its reacting product to flow through a nozzle to produce thrust. This paper presents computational study on a single flow element in a nuclear thermal rocket. The computational results provide both detailed and global thermo-fluid environments of a single flow element for thermal stress estimation and insight for possible occurrence of mid-section corrosion.

In this paper, computational fluid dynamics (CFD) gas flow simulations are carried out for the pebble bed reactor. In CFD calculations, geometry modeling and physical modeling are crucial to CFD results. The effects of the treatments of the interpebble contacts on gas flow fields and heat transfer are examined. A sensitivity analysis for the gap size is conducted with two spherical pebbles, in which the interpebble region is modeled by means of two types of interpebble gap and two kinds of direct contact. Both large eddy simulation and Reynolds-averaged Navier–Stokes models are employed to investigate the turbulent effects. It is found that the flow fields and relevant heat transfer are significantly dependent on the modeling of the interpebble region. The calculations indicate the complex flow structures present within the voids between the fuel pebbles.

This paper presents a review on the research activities conducted at AAMU (Alabama A&M University) in the last five years. The researchers in College of Engineering, Technology and Physical Sciences of AAMU have been receiving financial support from the U.S. Department of Energy under Massie Chair Excellence Program in Nuclear Engineering from 2008. The main objectives of this project were to improve the capability of understanding the static, dynamic behavior of pebbles and gas flows/heat transfer in a pebble bed reactor (PBR), which is the key to the design, optimization and safe operation of the reactors.