Speaker
Description
Dario Passafiume1, Marc Kamlah1
1Karlsruhe Institute of Technology, Institute for Applied Materials, Karlsruhe, Germany
The European solid breeder blanket concept Helium Cooled Pebble Bed (HCPB) uses advanced lithium ceramic breeder (ACB) material in the form of pebbles. During the HCPB breeder blanket operation, a fragmentation of the pebbles due to thermomechanical loads can occur, as well as the formation of dust. This dust represents a safety issue, as it can block purge gas paths inside the HCPB or it can be transported with the purge gas from the pebble bed into the tritium extraction system (TES) and accumulate there, especially in filters. Therefore, it is crucial to understand the ACB pebbles’ fragmentation mechanism and dust formation, as well as to estimate the amount of breakage and dust that could be transported out of the bed. For this purpose, a coupling between the open-source DEM (Discrete Element Method) code LIGGGHTS and the open-source CFD (Computational fluid dynamics) code OpenFOAM is being used in this work. First, dust transport investigations are discussed, focusing on the transport of a group of particles as a function of their size. Here, large particles show the tendency to spread more in the pebble bed and seem to be subject to a non-negligible drag to gravitational force ratio. Particles with diameters below 20 microns exhibit a higher clogging probability, which then remains relatively constant until the particle’s size gets close to the average pore size of the pebble bed. When particles reach about 110 microns in diameter, the clogging probability sharply increases to nearly 100% within a travel distance of 40 mm.
Afterwards, the plausibility of previously carried out thermo-mechanical FEM analyses on the HCPB concept of DEMO will be discussed. This will be done by comparison to DEM simulations where a sensitivity DEM study on a portion of the pebble bed will be presented. In particular, stresses rising from the thermal expansion of the ACB pebbles and related fracture probability when varying parameters such as initial PF, pebble size distribution, and temperature amplitude will be discussed.
