Preliminary investigation of Li4SiO4 pebbles structural performance

One of the main purposes of a breeder blanket is to remove the heat produced in the blanket by the fusion reaction neutrons, and to breed the tritium required to sustain it. To achieve these requirements, several breeder materials (solid or liquid lithium-bearing ones) have been investigated in the past decades. To date it has not yet been possible to identify a stable material, with high thermal conductivity and melting point. This paper deals with the mechanical characterization of the lithium orthosilicate (Li4SiO4) in form of pebbles, produced at the University of Pisa at room temperature by a drip casting forming technique, starting from an aqueous suspension of Li4SiO4 precursor prepared by a sol-gel synthesis method. To investigate also numerically, by means of FE code, the breeder blanket behaviour, it is of meaningful importance the mechanical characterization of such pebbles. To the purpose, either static or cyclic uniaxial compression tests, without radial constraints, have been performed on several produced pebbles of about 1.5 mm diameter in order to determine the collapse and crushing loads and the stiffness. Moreover, the carried-out post-test SEM examination allowed to evaluate the failure mode and the crack shapes on the contact surface. Results show the influence of the elastic properties and matrix flaw population on the crushing load. The pebbles produced by the sol-gel method showed also a high strength, the value of which is comparable to that of the pebbles obtained by melting process