Manufacturing challenges and required R&D on fusion pebbles bed material

The thermal stress on breeding blanket structure is one of the main design driver; consequently, an open issue for fusion power reactor is the choice of breeding blanket material. The mostly promising and worldwide-investigated solution refers to the ceramic material, e.g. Li4SiO4, in form of pebble beds instead of a bulk form such as a block or a disk. This would introduce some advantages, especially for what concerns the heat transfer phenomena, low activation characteristics, low thermal expansion coefficient, high thermal conductivity, etc. In this paper, particularly the reliability/availability of a methodology capable to produce stable and well-sized ceramic pebbles is a major challenge as well as the evaluation of the thermal conductivity, that is a necessary input data for the understanding of blanket behavior (support the thermal-structural and thermo-hydraulic analyses). As for this latter, moreover, a sample holder considering the heat transfer mechanism through the pebble-bed was duly designed such to determine the pebble-bed thermal conductivity by means of a hot rig with guard resistance method. This paper introduces (and analyses) preliminary results of the effective thermal conductivity on the pebble-bed as well as a description of the adopted methodology. This research activity was developed in the framework of PRA2016 project.