A comprehensive numerical modelling of a fission chamber to be operated over a wide dynamics in the vessel of a sodium-cooled reactor

ISBN: 978-0-89448-726-2International audienceFission chambers are the detector of choice for online, in-vessel neutron flux measurements. One of their interesting features is their ability to be operated in different modes, depending on their counting rate. This open the possibility, provided that the acquisition chain is accordingly designed and that the chamber specifications are wisely chosen, to monitor the neutron flux over a wide dynamics of reactor power with the same detector.This paper studies the case of a fission chamber alongside with a preliminary design of the foreseen ASTRID demonstrator. The quantities of interest, namely the fission rate, saturation curve, mean current, pulse shape, spectral density, are computed with a combined usage of the various modelling tools our team has developed within a decade. It is shown that the fission chamber can deliver a signal that is easy to interpret over seven decades of reactor power