As the ceramic breeder material is used in the form of pebble beds, the macroscopic properties of the gran­ular material are of particular interest. Most of these properties (mechanical, thermal, etc.) cannot be deduced directly or precisely from the properties of the base material or the single pebble; therefore, dedicated experiments are required. In these experi­ments, particular attention is paid to reproduce rep­resentative conditions in terms of, for example, pebble bed typical dimensions, packing factor, reduc­ing atmosphere, and so on, as envisaged for the blan­ket component.

This section mostly follows the approach devel­oped for the European blanket program and the work Reimann and coworkers94-106,110,115 have performed from the late 1990s onwards.