An advanced fusion reactor project, called APEX, with improved effectiveness has been developed using a protective flowing liquid wall for tritium breeding and energy transfer. In the modified APEX concept, the flowing molten salt wall is composed of Flibe as the main constituent with increased mole fractions of heavy metal salt (ThF4 or UF4) for both fissile and fusile breeding purposes and to increase the energy multiplication. Neutron transport calculations are conducted with the help of the SCALE4.3 SYSTEM by solving the Boltzmann transport equation with the code XSDRNPM. By preserving a self sufficient tritium breeding ratio (TBR > 1.05) for a mole fraction up to 6% of ThF4 or 12% of UF4, the modified APEX reactor can produce up to similar to2800 kg of U-231/year or similar to4950 kg of Pu-239/year, assuming the same baseline fusion power production of 4000 MWth, as in the original APEX concept. With 6% ThF4 or 12% UF4 in the coolant, the total energy output will increase to 5560 MWth or 8440 MWth, respectively. For a plant operation period of 30 full power years, the atomic displacement and helium production rates remain well below the presumable limits. The additional benefits of fissionable metal salt in the flowing liquid in a fusion reactor can be summarized as breeding of high quality fissile fuel for external reactors and increase of total plant power output. (C) 2003 Elsevier Ltd. All rights reserved.