Development and first use of an experimental device for fission-induced spectrometry applied to neutron flux monitoring

Abstract In order to provide dependable neutron flux instrumentation for Generation IV Sodium-cooled Fast Reactors (SFR), the French Atomic and Alternative Energies Commission (CEA) is investigating the feasibility of an innovative technology based on the optical signal produced within a fission chamber. In such gaseous detectors, neutrons interact with fissile material releasing heavy ions in the MeV-range, eventually leading to spontaneous photon emission in the ultraviolet-to-infrared range thanks to gas excitation and ionization. In this paper, the process of light generation is analyzed through semi-empirical models and custom-developed codes. A specific instrumentation has been defined and manufactured to emulate optical fission chambers and collect basic spectroscopic data required for model-based development approach. That testing device was named PSEG, which stands for Prototype of Scintillator Electrodes-Gas. Experimental validations have been carried out: the ionized argon gas exhibited no local thermodynamic equilibrium. Furthermore, the broadening of selected argon emission lines due to pressure change offers a promising self-diagnosis capability for future optical fission chambers.