Discrete Element Analysis of Heat Transfer in the Breeder Beds of the European Solid Breeder Blanket Concept

In this work, an in-house thermal–Discrete Element Method (DEM) code, recently developed at Karlsruhe Institute of Technology to evaluate the heat transfer in ceramic packed pebble beds, was applied to study the thermal behavior of the breeder beds of the European solid breeder blanket concept. The breeder zone of the helium-cooled pebble bed (HCPB) blanket for the Demonstration (DEMO) reactor was considered as the reference model implementing the same materials, applying the related neutronic heating, and simulating the relevant bed thicknesses. The code was used to evaluate the temperature profile generated by the neutronic heating in the thickness of the breeder bed. A column cutout of packed pebbles bounded by upper and bottom walls, representing the cooling plates of the HCPB, was considered as a representative geometry to carry out the work. The implemented three-dimensional network model evaluates the heat transfer inside packed beds through chains of thermal resistances describing the thermal contacts (particle-particle and particle-wall) occurring in the assembly. Besides thermal transport through the mechanical contact area, thermal transport through the surrounding gas phase is accounted for including the Smoluchowski effect. Sensitivity studies revealed the influence of the operational conditions and the parameters that mainly affect the temperature profile in the bed.