Mechanical characterization of Li 2TiO 3 and Li 4SiO 4 pebble beds: Experimental determination of the material properties and of the pebble bed effective values

Abstract

This paper deals with a research activity performed in the frame of the breeding blankets design for nuclear fusion reactors, connected with the ITER experiment. In fact during the ITER operation, Test Blanket Modules (TBM) will be tested in the equatorial ports in order to determine their performances. The breeding blankets are presently developed for the DEMO reactor. One of the breeding blanket under study, called Helium Cooled Pebble Bed (HCPB), uses a solid breeder and a solid neutron multiplier in form of pebble beds. Lithium metatitanate (Li 2TiO 3) and lithium orthosilicate (Li 4SiO 4) are considered as the best candidate materials for solid breeder. The analysis of the breeding blanket is complex for the geometry as well as for the loading conditions. Advanced computer codes are needed in order to determine the reliability of the different designs. In this context, the mechanical characterization of pebble beds is important in order to simulate their behaviour. The objective of this research activity is to determine the effective properties of the pebble beds in order to develop a complete constitutive model of the granular material. In particular, with a resonant column device the effective shear modulus and the damping ratio have been determined. Moreover compression tests on single spheres have permitted to obtain the mechanical properties of the materials.