Abstract : In 1993, professor C. Rubbia proposed an accelerator driven sub-critical system. In 1995 the concept of an energy amplifier is developped. Besides the intrinsic sub-caitidty of the nuclear reactor, its main characteristics are the use of the thorium-232 uranium-233 cycle, and the use of lead as a spallation target, slowing-down medium and coolant. The aim of such a system is both to produce energy and to transmute long lived fission products such as technetium-99. This thesis work studies neutron transport properties in lead with the perspective of long lived fission products transmutation. The first part describes the experimental set-up of the TARC experiment. Theoretical and numerical approaches of neutron transport and slowingdown properties in lead are given. The second part deals with the experimental determination achieved by the group from 1SN Grenoble of the spatial and energy neutron flux distribution in the load block. This distribution is compared with numerical simulations and measurements made with the different detection systems used simultaneously by the collaboration. The last part of this work validates the concept of adiabatic resonance crossing for long lived fission products transmutation in lead. The results of the second and the third part are based on the relation connecting neutron energy and slowing-down time in lead.