Li2TiO3 pebble beds constitutive equations of using standard three-axial tests: Implementation of the model in an FEM code

During the ITER operation, various Test Breeding Modules (TBM) will be tested in the equatorial ports of the reactor. These TBMs are currently being developed in several research centres around in the world. The Helium-Cooled Pebble Bed (HCPB) blanket is one of two breeder blanket concepts developed in Europe. HCPB uses Beryllium pebbles act as a neutron multiplier and Li4SiO4 or Li2TiO3 pebbles act as breeder materials. The structural analysis of the breeding blanket is complex in terms of its geometry and loading conditions. Advanced computer codes are needed in order to determine the reliability of the various designs. In this context the mechanical characterization of pebble beds is important in order to simulate their behaviour. This paper illustrates three-axial experimental tests performed on Li2TiO3 pebble beds. In addition, preliminary results of the numerical simulations are shown. The numerical analyses were performed using an original model, based on the elastic–plastic behaviour of a single pebble, implemented in an FEM code. The paper highlights the importance of the confining pressure on the mechanical behaviour of pebble beds and the possibility of simulating them with homogeneous materials.