Experimental & numerical study of ceramic breeder pebble bed thermal deformation behavior

Experiments on thermomechanics interactions between clad and pebble beds have been performed with overstoichiometric lithium orthosilicate pebbles (pebble diameters between 0.25 and 0.63 mm) at temperatures of 700-800 degrees C. The experimental results show that the thermal deformation of our pebble bed system is nonlinear and when the operating temperature is higher than 600 degrees C, thermal creep deformation is generated In this paper, constitutive equations of the elastic and creep deformation are derived from the experimental results. Incorporating the effective constitutive equations infinite element method (FEM), numerical investigations presenting the elastic and plastic deformation characteristics of pebble bed system are comparable to the experimental behaviors. In addition, discrete element method (DEM) is underdevelopment to derive constitutive equations for different pebble beds. The preliminary results of DEM show the stress distribution inside the pebble beds at steady or transient states, which helps us to identify the destructive region in a pebble bed system.