Experimental characterization of ceramic pebble beds

Several materials have been developed in Europe and Japan for the DEMO reactor that will be tested in ITER. The paper describes a solid breeder for nuclear fusion reactor exploiting ceramic pebbles made of Lithium Orthosilicate (Li4SiO4) and Lithium metatinate (Li2TiO3), with a diameter ranging between 0.5 mm and 1 mm. The main advantages of the pebbles are resistance to thermal stresses and the possibility to easily fill the complex geometries of the blanket. The results of experimental tests are presented, which enable the determination of the behaviour of single pebbles under compression and the parameters of the pebble beds needed to define their constitutive equations. Several standard tests on samples of pebble beds were performed: triaxial, direct shear and compression. The parameters of the Cam–Clay model were obtained from these tests. This model is normally used to describe soil materials (clay, sand) but in our case was used to simulate the triaxial tests with a finite elements computer code. The numerical results show a good agreement with the theoretical ones. Therefore this model could be used to determine the mechanical behaviour of the solid breeding blanket under normal and accidental conditions.