[en] The AMMON experimental program in the Cadarache EOLE zero power reactor is devoted to the experimental validation of the HORUS-3D neutron and photon calculation scheme for the future Jules Horowitz Material Testing Reactor. Several experimental core configurations have been investigated, based on the same lattice global geometry: a central hexagonal aluminum box, with 7 JHR fuel elements, surrounded by a driver zone composed of standard PWR- fuel pins. For experimental purposes, one assembly can be fully disassembled to enable precise measurements of local fission rates in the plates. Within this framework, a dedicated -spectrometry device has been designed to precisely measure axial and azimuthal fission rate distributions on these special fuel elements. The present paper details design studies on this bench; experimental results are given for three studied configurations: - 'Reference' configuration; - 'Beryllium periphery' configuration, where a beryllium cylinder is placed on the outer ring of the central experimental zone; - '1/2 hafnium' configuration, with a hafnium rod partially inserted in the central assembly. Fission rates in the 'Reference' and perturbed configurations are finely described and in good agreement with the preliminary calculations. Measurements show good repeatability, with overall uncertainties around 1%. (authors)