Effect of Pebble Size Distribution and Wall Effect on Inner Packing Structure and Contact Force Distribution in Tritium Breeder Pebble Bed

Baoping Gong,Xiaofang Luo,Hao Cheng,Yongjin Feng,Xiaoyu Wang,Long Wang

doi:10.3390/en14020449

Abstract

In the tritium breeding blanket of nuclear fusion reactors, the heat transfer behavior and thermal-mechanical response of the tritium breeder pebble bed are affected by the inner packing structure, which is crucial for the design and optimization of a reliable pebble bed in tritium breeding blanket. Thus, the effect of pebble size distribution and fixed wall effect on packing structure and contact force in the poly-disperse pebble bed were investigated by numerical simulation. The results show that pebble size distribution has a significant influence on the inner packing structure of pebble bed. With the increase of the dispersion of pebble size, the average porosity and the average coordination number of the poly-disperse pebble bed gradually decrease. Due to the influence of the fixed wall, the porosity distribution of the pebble bed shows an obvious wall effect. For poly-disperse pebble bed, the influenced region of the wall effect gradually decreases with the increase of the dispersion of pebble size. In addition, the gravity effect and the pebble size distribution have an obvious influence on the contact force distribution inside the poly-disperse pebble bed. The majority of the contact force are weak contact force that is less than the average contact force. Only a few of pebbles have strong contact force that is greater than average contact force. This investigation can help in analyzing the pebble crushing characteristics and the thermal hydraulic analysis in the poly-disperse tritium breeder pebble bed.

Highlights

Granular matter widely exists in nature and industrial systems, especially in fixed beds or fluidized beds, which are widely used in chemical engineering systems [1,2] or the nuclear energy industry [3,4,5,6,7,8,9,10,11,12]
For nuclear reactor energy systems, the reactor core of the high temperature gas cooled nuclear reactor is formed by fuel pebbles [9,10,11,12], and the tritium breeder and the neutron multiplier in the tritium breeding blanket of nuclear fusion reactors [3,4,5,6,7,8] are used in form of pebble beds
The pebble packing structure and the contact force distribution of mono-sized pebble bed was simulated and analyzed to validate the discrete element method (DEM) simulation by comparing with the experimental and numerical results reported in literature

Summary

Introduction

Granular matter widely exists in nature and industrial systems, especially in fixed beds or fluidized beds, which are widely used in chemical engineering systems [1,2] or the nuclear energy industry [3,4,5,6,7,8,9,10,11,12]. The contact state (coordination number) and the contact force of pebbles inside the bed is another very useful and important parameter that characterizes the performance related to the heat transfer and mechanical behaviors of a pebble bed. Too strong a contact force may cause cracks and fragmentation near the contact point of a pebble, affecting the mechanical behaviors of the fixed pebble bed. From this perspective, accurately determining and predicting the pebble bed packing structure (porosity distribution and coordination number) and contact force distribution are of great significance for the analyzing the heat and mass transfer characteristics of a fixed bed, which is the key to designing a fixed pebble bed

Methods

Results

Conclusion