Study on the mechanical properties and thermal conductivity of silicon carbide-, zirconia- and magnesia aluminate-based simulated inert matrix nuclear fuel materials after cyclic thermal shock

Abstract Modification of thermo-mechanical properties of simulated (SiC) silicon carbide-, (ZrO 2 ) zirconia- and (MgAl 2 O 4 ) spinel-based inert matrix nuclear fuels after cyclic thermal shock was analyzed in terms of Vickers hardness ( H V ), fracture toughness ( K IC ) and thermal conductivity. Three different simulated specimens were used for the experiment; a solid solution of yttria-stabilized zirconia and ceria (composition: Er 0.07 Y 0.10 Ce 0.15 Zr 0.68 O 1.915 , 92.0% TD, specimen hereafter called Ce–ZrO 2 ), a CeO 2 -dispersed Mg-spinel (composition: 15wt%CeO 2 –MgAl 2 O 4 , 93.7% TD, specimen hereafter called Ce-spinel) and a CeO 2 -dispersed silicon carbide (composition: 80.8 wt% SiC, 6.9 wt% Al 2 O 3 , 5.1 wt% Y 2 O 3 and 5.0 wt% CeO 2 , specimen hereafter called Ce–SiC), CeO 2 being surrogate materials for PuO 2 . Cyclic thermal shock experiment and thermal conductivity measurements were simultaneously carried out by heating disc-shaped specimens up to maximum temperature ranging from 1073 to 1673 K and then cooling down to 343 K with Ar gas during 20–25 min. The Vickers hardness of the three different thermally shocked specimens showed nearly constant values with increasing number of cycles, except for the specimen heated at 1673 K. The K IC values of the corresponding specimens increased with the increasing number of cyclic thermal shock at 1673 K. For Ce–ZrO 2 heated at 1673 K, however, it decreases considerably due to the combined effects of formation of second phase and modification of the matrix composition thereby. The calculated thermal conductivity of Ce-spinel decreases as the number of cycles in thermal shock increases in the temperature range between 1073 and 1673 K, and Ce–SiC slightly decreased with the number of cycles in cyclic thermal shock and the variations in thermal conductivity are almost the same for the temperature increases of 1073 and 1373 K, whereas, in Ce–ZrO 2 , it remains nearly constant.