The aim of this study is to investigate the high-level waste (HLW) transmutation and fissile breeding potentials of a lead-bismuth eutectic (LBE) cooled accelerator-driven system (ADS) for the various configurations (the target radius, R-T = 10-50 cm and the radial thickness of the sub-critical core, delta(SC) = 50-80 cm) and for the various fuel compositions (the fuel volume fraction, VFF = 10%, 12%, 15% and 20% and the fissile fraction, FF = 10-24%) under sub-critical condition. The long-lived fission products (LLFPs: Tc-99, I-129 and (CS)-C-115 nuclides) and the uranium mono carbide (UC) ceramic fuel are considered as the HLW and the fissile fuel, respectively. The neutronic calculations have been performed per the incident proton (1000 MeV) with the high-energy Monte Carlo code MCNPX in coupled neutron and proton mode using the LA 150 library. The numerical results bring out that the case of R-T = 30 cm, delta(SC) = 80 cm, VFF = 10% and FF = 23% is the optimum configuration and fuel composition, from the energy gain point of view, and has a high neutronic performance for an effective LLFP transmutation and fissile breeding. (c) 2007 Elsevier Ltd. All rights reserved.