Pulse-reactor core monitoring with an innovative optical neutron detector

Abstract To minimise uncertainty and strengthen estimation of energy deposited during power transients, we set up an online passive neutron flux measurement of a pulse reactor. Optical fission chambers, are being developed in the framework of dependable neutron flux instrumentation for Sodium-cooled Fast Reactor (SFR) and Molten-Salt Reactor (MSR) of Generation IV by the French Atomic Energy and Alternative Energies Commission (CEA). Neutron interactions with a fissile layer coating release heavy-ions in the MeV-range, eventually leading to spontaneous photon emission in the ultraviolet to infrared range of the surrounding noble gas. Prototypes have previously been tested in an ideal pure neutron field. In this paper, linearity of optical signal versus reactor power is assessed during startups and high power transients up to 21.6 GW. Excellent linearity results are obtained over 5 reactor power decades and detection remain possible over 7 decades. Detection range is only restrained by photodetector properties. Such detector may be routinely employed for high-dynamic transients monitoring by the core caisson of pulse reactors.