Irradiation tests in BR2 of miniature fission chambers in pulse, Campbelling and current mode

The FNDS system ("Fast Neutron Detection System") for the on-line in-pile detection of the fast neutron flux in the presence of a significant thermal neutron flux and a high gamma dose rate is being developed in the framework of the SCK·CEN-CEA Laboratoire Commun. The system has been patented in 2008. The system consists of a miniature Pu-242 fission chamber as main detector, complemented by a U-235 fission chamber or a rhodium Self-Powered Neutron Detector (SPND) for thermal neutron flux monitoring and a dedicated acquisition system that also takes care of the processing of the signals from both detectors to extract fast neutron flux data. This paper describes a FNDS qualification experiment in the SCK·CEN BR2 reactor, with experimental results on a large set of fission chambers in current and Campbelling mode.