Experience with the irradiation of 550 deg C ionisation chambers

Tests on pulse fission chambers and wide range gamma compensated chambers in the Windscale Advanced Gas-cooled reactor are reported. Four pulse fission chambers were irradiated for approximately 3 years; one pair at a flux of 2 x 106 cm2sec1 and the other at 6 x 1011 cm2sec1. The high flux pair were calculated to have received a total dose exceeding 6 x 1019 cm1 plus an estimated 2 x 1010 rad of gamma radiation. Irradiation and time at temperature were found to have little effect on the fission chambers. Two wide range d.c. chambers were loaded into fluxes of 3 x 109 cm2sec1 and 4 x 109 cm2sec1 respectively. One detector failed after 5 years while the second, having survived for nearly 6 years, remains operational. The insulation performance of both detectors was found to deteriorate slowly with time. The neutron polarization electrode in the failed chamber suffered breakdown at 100 V after 15 months, but analogous failures were not observed on the corresponding gamma polarizing electrode or collector in the ensuing 4 years. (O.T.)