Creep behavior of pebble bed for solid breeder blanket under multiple perturbations

Abstract

Tritium breeding plays a crucial role in achieving the commercialization of fusion reactors. Solid breeding and multiplication pebble beds are considered promising solutions for tritium breeding. The pebble bed is exposed to a complex service environment, leading to structural instability. This can cause the structure to reorganize, resulting in creep behavior. Such creep may deteriorate heat transfer and reduce the efficiency of tritium extraction. In this study, a beryllium-based pebble bed is adopted, and the Discrete Element Method (DEM) is employed to investigate its structural evolution under multiple perturbations. First, the theoretical framework for structural evolution under external loads is presented. Subsequently, the effects of cycle loading, electromagnetic (EM) load perturbations, and vibration with various frequencies and amplitudes on the pebble bed are examined. The creep behavior of the pebble bed under various disturbances, with varying particle surface friction coefficients, is analyzed. Finally, based on the results, a solution to mitigate significant creep is proposed. The findings reveal that creep behavior is an inherent characteristic of pebble beds. The direction of creep is primarily governed by the dominant external forces. The particle surface friction coefficient exerts a significant influence on creep behavior, suggesting that it can be adjusted to influence the structural stability. This study provides valuable insights for the design of solid breeding blankets and the optimization of pebble bed configurations in fusion reactors.