Neutron irradiation effects on thermal shock resistance and fracture toughness of graphites as plasma-facing first wall components for fusion reactor devices

Abstract

The thermal shock resistance and thermal shock fracture toughness of graphites to be used as the plasma-facing first wall of fusion reactor devices are quantitatively determined by applying arc discharge heating at the central area of the disk specimens. The graphites used in the measurements included IG-11. a fine grain isotropic mold, HCB-18, a very fine grain mesophase pitch carbon, and C/C-B. a carbon fiber felt reinforced carbon composite. The results obtained showed that the C/C-B composite has an outstandingly high thermal shock resistance and fracture toughness. However, contrary to expectation, HCB-18 was found to have relatively low thermal shock resistance and fracture toughness, although it has higher mechanical strengths than IG-11. The measurements were also carried out for IG-11 and HCB-18 after irradiating them (1.1−1.5 × 10 21 n/ cm 2, > 29fJ at 750–1000°C) in a fission neutron reactor Japanese Material Testing Reactor (JMTR). The thermal shock resistances and the fracture toughnesses of these graphites were found to degrade to about 68–78% of the unirradiated values after undergoing the neutron irradiations. In this study, tile-like plates of HCB-18 and C/C-B graphites were used as the first wall materials at different positions inside a fusion reactor device together with a fine grain isotropic graphite ETP-10, which is similar to IG-11. According to a tentative surveillance following the operations, the tiles of HCB-18 were found to be considerably damaged, but no damage was found for the tiles of ETP-10 and C/C-B. The C/C-B composites, which were placed at comparatively intense positions, showed conspicuous integrity. These results agree with the values of thermal shock resistance and fracture toughness determined in this study.