Numerical Investigation on Gas and Powder Flow Characteristics of Pebble Bed of Fusion Blanket

Abstract

The breeding blanket, which is core component for fusion device, plays an important role in tritium breeding and energy conversion. Ceramic particles are usually used as tritium breeders (e.g., Li₄SiO₄, Li₂TiO₃ particle) and neutron multipliers (e.g., Be/Be₁₂ particle) inside the blanket, and pebble bed structure is utilized to hold ceramic particles. The helium pressure drop inside the ceramic pebble bed is closely related to the design of the tritium purge structure of the blanket, the flow characteristics of helium and powder directly affect the tritium breeding and extraction efficiency. Hence, there is a great need to promote research in the flow behavior of purge gas and dynamic behavior of the crushed particles. Based on the two-way coupled Computational Fluid Dynamics and Discrete Element Method, the velocity distribution, pressure distribution and inlet and outlet pressure drop of helium in pebble bed structure under different inlet flow rates were obtained. The velocity and quantity distribution of lithium powder at different moments and inlet flow rates were numerically investigated. The results indicated that helium flow velocity distribution along the z-axis fluctuates in the opposite direction to the axial voidage distribution, the helium dimensionless flow velocity keeps nearly the same in the whole pebble bed. The magnitude and distribution trend of the dimensionless helium velocity is independent of the magnitude of v0. The average absolute velocity of powder increased with the increase of the inlet gas flow rate, while the average dimensionless velocity decreased with the increase of the helium inlet flow rate. The results in the paper can provide technical recommendations for fusion ceramic blanket design.