In-core measurement of dc electrical conductivity of ceramics

An in-situ dc conductivity capsule has been constructed and tested at the high flux beam reactor (HFBR) at Brookhaven National Laboratory. The prototype capsule contained two alumina and one silicon nitride polycrystalline samples. In-situ measurement of the DC conductivity was made utilizing custom-made mineral insulated triaxial cables with a guard ring configuration for the samples and the sample holders. Sample and capsule temperatures were also measured in situ. This prototype capsule was designed to operate at ITER relevant temperatures of 80°C (alumina) and 300°C (alumina and silicon nitride) with an applied electric field of 133 V/mm. It is significant that a large prompt increase in conductivity occurred but that no permanent radiation-induced electrical degradation was observed in alumina after irradiation at 80°C to a neutron dose of > 0.1 dpa.