This study presents the spent fuel rejuvenation potential of the PROMETHEUS-H fusion reactor. For this purpose, three different spent fuels were selected, i.e., (1) CANDU, (2) PWR-UO2 and (3) PWR-MOX spent fuels. The spent fuel (volume fraction of 60%), spherically prepared and cladded with SiC (volume fraction of 10%), was located in the fuel zone (FZ) in the blanket of the modified PROMETHEUS-H fusion reactor. The FZ was cooled with high pressure helium gas (volume fraction of 30%) for the nuclear heat transfer. The neutronic calculations were performed by solving the Boltzmann transport equation with the help of the neutron transport code XSDRNPM-S/SCALE4.3. The calculations of the time dependent atomic densities of the isotopes were performed for an operation period (OP) of up to 4 years with a 75% plant factor (eta) under a first wall neutron load (P) of 4.7 MW/m(2). The temporal variations of the atomic densities of the isotopes in the spent fuel composition and other physical parameters were calculated for a discrete time interval (Delta t) of 1/12 year (one month) by using the interface program (code). In all investigated spent fuel cases, the tritium self sufficiency is maintained for the DT fusion driver along the OP. The CANDU spent fuel becomes usable in a conventional CANDU reactor after a regeneration time of similar to 5.5 months. The CFFE value approaches 3.5% in the blanket fuelled with the PWR-UO2 and PWRMOX spent fuels after 41 and 35 months, respectively. The plutonium component can never reach a nuclear weapon grade quality during the spent fuel rejuvenation. Consequently, the modified PROMETHEUS-H fusion reactor has high neutronic performance for the rejuvenation of the spent fuels. (c) 2005 Elsevier Ltd. All rights reserved.