Ceramic breeder for fusion nuclear reactors

This paper is aimed at the evaluation of the thermal conductivity of ceramic pebble beds which are one of the candidates in the design of breeder blankets for fusion power technology. In particular the characterization of the thermo-mechanics of pebble beds has been done by means of an experimental test campaign considering different temperatures, different interstitial gas (air, helium or in vacuum conditions) and at varying of the compression forces (up to 100 kN). To the purpose a suitable experimental device, set up at the DIMNP-University of Pisa, based on the principles of the steady state and axial heat flow methods, allowed to measure the thermal conductivity of the pebble beds in order to simulate the conditions foreseen for the breeding blanket. The effective thermal conductivity of pebble beds was evaluated as a function of the thermal conductivity of an alumina disc experimentally determined through furnace test (in the 20-200°C range) with the hot wire method. Furthermore numerical simulation of the thermo-mechanical tests were performed by means of FEM approach in order to optimize the operating conditions and determine the uncertainty of the obtained results. The experimental results may also contribute to the creation of a database of the thermal conductivity of pebble beds which can be used for the design and analysis of fusion breeder blankets