Comparative gamma radiation and temperature effects on SiO2, MgO and Al2O3 insulated nuclear instrument cable

The relative merits of SiO2, MgO and Al2O3 as insulation for nuclear instrument cables are investigated. Insulation resistance, voltage breakdown phenomena, capacitance, dissipation factors, and spurious voltage and current signals have been investigated on nuclear instrument cables under the combined effects of gamma irradiation (105 R/h) and temperature (to 4500C). The SiO2, MgO and Al2O3 cables tested were all fabricated to procedures that controlled insulation and backfill gas impurities. The SiO2 cables possessed insulation resistances greater than 1010 Ω.ft at 4500C and 105 R/h - nearly two decades higher than MgO or Al2O3 cables. Spontaneously generated currents as high as 250 nA dc were observed on some cables during thermal cycling tests