Characterization and Localization of Partial-Discharge-Induced Pulses in Fission Chambers Designed for Sodium-Cooled Fast Reactors

During the operation of the superphenix and phenix reactors, an aberrant electrical signal was detected from the fission chambers used for neutron flux monitoring. This signal, thought to be due to partial electrical discharge (PD) is similar to the signal resulting from neutron interactions, and is generated in fission chambers at temperatures above 400 °C. This paper reports work on the characterization and localization of the source of this electrical signal in a high-temperature fission chamber. The dependence of the shape of the PD or neutron signal on the various experimental parameters (nature and pressure of the chamber filling gas, electrode gap distance, and fission chamber geometry) are described. Next, experiments designed to identify the location within the chambers where the PD are being generated are presented in way to propose changes to the fission chamber in order to reduce or eliminate the PD signal.