First in situ measurement of electrical resistivity of ceramic insulator during irradiation with neutrons of energy 14 MeV

Substantial degradation of the electrical resistivity of ceramic insulators may occur during the operation of fusion reactors. This is caused by radiation-induced conductivity (RIC) resulting from high energy neutrons with energies up to 14 MeV. Although data on the RIC resulting from neutrons of energy 14 MeV are required, no measurements have been performed so far. The first in situ measurements of the electrical resistivity during irradiation with neutrons of energy 14 MeV was carried out for Al2O3 in the present study using the Fusion Neutronics Source (FNS) at the Japan Atomic Energy Research Institute. An irradiation chamber was developed which could realize appropriate measurements of RIC for the specimens in the neutron field of the FNS. Using the irradiation chamber, the RIC of Al2O3 resulting from irradiation by neutrons of energy 14 MeV was measured at room temperature in the neutron flux range 1012−1015 n m −2 s−1. If the obtained relationship between the RIC and the neutron dose rate can be extrapolated to fusion-reactor-relevant neutron dose rates, then the electrical conductivity of Al2O3 increases to a level of 10−7−10−6 Ω−1 m−1. Such a level of degradation of the electrical resistivity may be accommodated with appropriate fusion reactor design.