Joint estimation of the fast and thermal components of a high neutron flux with a two on-line detector system

A fission chamber with a Pu242 deposit is the best suited detector for on-line measurements of the fast component of a high neutron flux (∼1014ncm-2s-1 or more) with a significant thermal component. To get the fast flux, it is, however, necessary to subtract the contribution of the thermal neutrons, which increases with fluence because of the evolution of the isotopic content of the deposit.This paper presents an algorithm that permits, thanks to measurements provided by a Pu242 fission chamber and a detector for thermal neutrons, to estimate the thermal and the fast flux at any time. An implementation allows to test it with simulated data.