Electrical properties of mineral-insulated cable under fusion neutron irradiation

Degradation of electrical insulation property of mineral-insulated (MI) cables under fusion neutron irradiation was examined by use of Fusion Neutronics Source at Japan Atomic Energy Research Institute. Observed increase of leakage current in an MI cable (diameter; 4.8 mm, length; 2.0 m) was ∼5.0 pA for the DT neutron flux of 2.9×107 n/cm2/s and bias voltage of 200 V between the central wire and sheath. The bias voltage and neutron flux dependence of the leakage current indicates that the degradation of insulation property of the cable is dominated by the production rate and drift of electric charge in the insulator. Furthermore, the appearance of large transient leakage currents immediately after the start and stop of the irradiation and the growth of leakage current even for the bias voltage of 0 V imply that electrical properties of MI cables under irradiation are considerably affected by the distribution of electric charge trapped in the insulator.