Abstract
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 (HTFC). The relation between the shape of the PD signal and various parameters (nature and pressure of the chamber filling gas, electrode gap distance, and fission chamber geometry) are first described. Next, experiments designed to identify the location within the chambers where the PD are being generated are presented. After verification and refinement of the results of these localization studies, it should be possible to propose changes to the fission chamber in order to reduce or eliminate the PD signal.
Highlights
THE purpose of high temperature fission chamber (HTFC) is to detect neutrons inside the core of sodium-cooled fast reactors [1]
To perform the discharges localization, we used two different methods: the first involves the use of a Phase Resolved Pattern Diagrams (PRPD), and the second is based on the comparison between the partial electrical discharge (PD) observed in real neutron detectors (HTFC 1B) as opposed to the PD observed in the HTFC 3 and 4, which were constructed to test for electrical discharges outside of the active zone of the real fission chambers
In the PRPD, partial discharge events are displayed as points with a total charge value represented in the ordinate and the timing with respect to applied voltage in abscissa
Summary
THE purpose of high temperature fission chamber (HTFC) is to detect neutrons inside the core of sodium-cooled fast reactors [1]. To operate in–core, the HTFC will have to withstand the high operating temperatures, up to 650°C, of the sodium-cooled fast reactors and to operate under high irradiation, up to 1010 n/cm2.s. After years of study [2,3,4,5], it is known that an electrical signal, more or less similar to the signal resulting from neutron. Electrical discharge occurs when a seed electron is accelerated by an imposed electric field, acquiring energy superior to the ionization energy of the gas atoms/molecules, leading to an electron avalanche. Sources of seed electrons include cosmic rays, photo-ionization, etc
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