Experimental and numerical analysis on pebble beds used in an ITER Test Module Blanket

This paper deals with a research activity on the breeding blankets of nuclear fusion reactors. In particular, an experimental set up for the determination of the granular material conductivity in the presence of an interstitial pressurized gas is described. This activity is performed in the frame of test Blanket Module (TBM) development in fact the neutron multiplier and the breeder of the Breeding Blanket Modules, which will be tested in ITER, could be realized as a pebble bed. Preliminarily the tested material was Al2O3 and a pebble bed with a packing factor of 0.63 and with interstitial air at atmospheric pressure was considered. The so called ‘guarded hot plate’ method was used to determine the conductivity. The tests were performed with a simultaneous compression of the bed (uniaxial oedometric deformation), which allowed us to obtain the effective conductivity of the bed versus the axial deformation at different temperatures. Moreover, we are also developing a theoretical model to simulate the thermal–mechanical behaviour of the ceramic pebble bed. The results obtained with this theoretical model were compared with those of the experimental tests. The comparison shows a good agreement between the theoretical and experimental results in terms of bed conductivity and stiffness.