Estimation of Errors Caused by Radiation and Temperature on Coaxial Signal Cables

To evaluate the combined effects of radiation-induced conductivity and radiation-induced currents cm dc readout errors as a function of radiation and temperature, an equivalent dc circuit has been used for a coaxial cable in a reactor core. Experimentally obtained data are used in this circuit to estimate readout errors as a function of source impedance and source output voltage for radiation and temperature fields of 5 × 10⁹ R/h and 650°C. Results indicate that in this radiation temperature environment there will be no significant errors from a voltage source with output >10 mV for a cable-sensor combination under these conditions:

1. source impedance <100 Ω
2. total radiation-induced current equal to −1 µA
3. 3 ft of cable in a flux zone of 5 × 10⁹ R/h and 650°C; 25 ft of cable in 10⁶ R/h and 650°C
4. stainless-steel sheath and center conductor cable, 0.250-in. o.d., 0.025-in.-diam conductor, 0.019-in. sheath thickness in MgO insulation.

It is also found that (a) radiation-induced conductivity of powdered MgO changes linearly with dose rate to at least 9 × 10¹⁰ R/h, and (b) magnitude and polarity of radiation-induced currents are independent of temperature.