High Voltage Instrument Cables for 650°C, in-Vessel Breeder Reactor Service

MgO insulated nuclear instrument cables have been developed for use in the Fast Flux Test Facility (FFTF) and breeder reactor in-vessel environments. Prototype cables have been successfully fabricated and tested: voltage Breakdown Pulse Noise (BPN) thresholds in excess of 800 Vdc and cable resistivities in excess of 108 Ω.ft. were achieved at temperatures to 650°C. Factors demonstrated to strongly affect breakdown phenomena and insulation resistance in bulk cable were insulation and backfill gas purity (especially as affected by fabrication processing) and high temperature annealing. Copper electrical conductors did not adversely affect cable performance if fabrication parameters were appropriately adjusted.