Analysis of Granular Flow in a Pebble-Bed Nuclear Reactor

Abstract

Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel of diameter 3.5m and height 10m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.

arXiv comment18 pages, 21 figures

References in corpus (10)

• Is Random Close Packing of Spheres Well Defined?
• Granular flow down an inclined plane: Bagnold scaling and rheology
• Random Packings of Frictionless Particles
• Signatures of granular microstructure in dense shear flows
• Confined granular packings: structure, stress, and forces
• Diffusion and mixing in gravity-driven dense granular flows
• Size Segregation of Granular Matter in Silo Discharges
• Velocity profile of granular flows inside silos and hoppers
• Subdiffusive axial transport of granular materials in a long drum mixer
• Dynamics of Random Packings in Granular Flow

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