Characterization of aged Li4SiO4 pebbles performance

Many studies and research have been carried out in the recent years to identify which breeder material and (in which) form, solid or liquid, are most suitable to be used in the Breeder Blanket (BB) modules. Nonetheless, the choice of a stable material, with high thermal conductivity and melting point remains unsolved and becomes even more complex when durability is considered. The breeder material must guarantee that the thermo-mechanical properties change as little as possible under environmental and operating conditions. The aim of this study is to investigate the ageing effects on the mechanical behaviour of lithium orthosilicate (Li4SiO4) in form of pebbles. The pebbles had been produced at the University of Pisa at room temperature by a hydrolytic sol-gel supported drip casting method and subsequently stored for 4 years in an environment simulating normal storage (i.e., standard condition). These pebbles of about 1.2–1.4 mm diameter have been subjected to uniaxial compression tests, without radial constraints, and SEM analysis. The results obtained were compared to those of non-aged pebbles to highlight the degradation caused by the ageing. SEM examination of aged pebbles showed increased porosity and a pebble surface that was not entirely homogeneous and uniform. This affected the crack shapes on the contact surface and the crushing load.