Numerical study of the effects of loading method on mixing of two kinds of pebbles in HTGR: A GPU-DEM simulation

Abstract

The flow, stacking, and mixing of pebbles in the High-Temperature Gas-cooled Reactor (HTGR) will affect the power distribution of the core and thus affect the economy and safety of the nuclear reactor. Simulations of pebble loading and mixing in HTR-PM based on GPU-DEM have been studied with particle numbers ranging from 230,000 to 420,000. The effects of four loading methods on pebble mixing are compared and analyzed. Mean position, segregation index (SI), Lacey’s mixing index (PSMI), mixing entropy (ME), and porosity are used for quantitative analysis. In addition, an alternative approximate method is proposed to calculate the particle number fraction, which can help solve the problem that the particle number fraction is related to the mesh size. The final result shows that different physical parameters, such as mass and Young’s modulus, will induce slight stratification during pebble mixing. At the same time, the simulation results with different loading methods have different mixing degrees. The reduced model mixes better than the single-pebble-loading method, but the latter is closer to engineering practice.