Research on purge gas flow characteristics in different pebble bed structures for fusion blanket

Abstract

Lithium ceramics are equipped as pebble beds in the solid-type breeding blanket, with the tritium purge gas flowing through it at a low velocity and pressure to achieve tritium transport. This paper investigated the effects of friction coefficient on the packing and purge gas flow characteristics of the pebble bed. Furthermore, this research assessed the purge gas flow characteristics in the pebble bed and verified the dependency of the flow characteristics on the configuration of pebble beds. The discrete element method (DEM) was selected to analyze the packing characteristics of pebble beds with different friction coefficients. The simulation component was benchmarked. The computational fluid dynamics method was used to construct and simulate various pebble bed models. A series of numerical analyses revealed that particles with a lower friction coefficient are more beneficial in the pebble beds which could benefit the tritium exaction. The pressure drop is related to both the purge gas flow velocity and the structure of the pebble beds. The pressure drop increases with the decrease in the friction coefficient, whereas the proportion of mass flow in the internal region increases with the increase in the friction coefficient. Although a denser structure of pebble beds is preferable for high tritium breeding rates, it could generate considerable flow resistance inside the pebble beds, causing tritium retention. This research can serve as a foundation for resolving the practical challenges such as purge gas flow, fragmentation and cracks, pebbles resettlement, among others, in the design of the blanket system.