RADIATION-INDUCED ELECTRICAL DEGRADATION EXPERIMENTS IN THE JAPAN MATERIALS TESTING REACTOR

An experiment to measure radiation-induced electrical degradation (RIE D) in a sapphire sample and in three MgO-insulated cables was conducte d at the JMTR light water reactor. The materials were irradiated at ab out 260 degrees C to a fluence of 3 x 10(24) n/m(2) (E > 1 MeV) with a n applied DC electric field between 100 kV/m and 500 kV/m. Even though the results for the sapphire sample are somewhat ambiguous because of an unexplained offset current of about 0.6 mu A, substantial degradat ion was not observed in the sapphire: instead, radiation-induced condu ctivity (RIC) seemed to decrease slightly during the experiment. Subst antial increase in leakage current, that increased with applied electr ic field, occurred in the MgO-insulated cables. This increased conduct ivity disappeared when the reactor was shut down and sample temperatur e returned to ambient. However, the physical degradation apparently re mained in the material while the reactor was off because restarting th e irradiation brought the conductivity back to its previous, degraded, reactor-on value. This effect is different from the RIED effect repor ted by Hodgson but is similar to previous results reported by Shikama et al. Considerable data were taken to determine the sample temperatur e and leakage currents during the irradiation.