Recent Developments on Micrometric Fission Chambers Dedicated for High Neutron Fluxes

With the development of innovative nuclear systems and new generation neutron sources, the nuclear instrumentation should be adapted. Since several years, we developed microscopic fission chambers to study the transmutation of minor actinides in high thermal-neutron fluxes. The recent developments done to fulfill the drastic conditions of irradiations are described in this paper together with the feedback from the measurements. Two installations were used: the HFR of the ILL for its high thermal neutron flux and the MEGAPIE target which was the first liquid Pb-Bi spallation target in the MW range.