This study presents the determination of fuel rejuvenation times in a D-T fusion breeder reactor fuelled with a mixture of natUO2 and ThO2 for multi-reuse of nuclear fuels in CANDU-37 reactors. To determine the effect of thorium on the fuel enrichment and rejuvenation times, neutronic analyses are performed by increasing the percentage of ThO2 in the fuel mixture from 10 to 35. The time-dependent neutronic calculations are carried out in three stages. In the first stage, which is the fuel enrichment or rejuvenation process in the fusion breeder reactor, the subcritical calculations of the fusion breeder reactor fuelled with the fuel mixtures are performed by using the MCNPX 2.7/CINDER under a fusion neutron wall loading of 1 MWm-2, corresponding to neutron flux of 4.444•1013 cm-2s-1 (energy of every fusion neutron is 14.1 MeV). In the second stage, which is the thermal reactor analysis, the fuel rods enriched at the end of the first stage are placed in the CANDU-37 reactor, and the critical calculations of this reactor are performed by using MCNPX 2.7 and MONTEBURNS codes separately. The numerical results show that the neutronic values obtained from both codes are very near each other. The third stage is the two-year cooling process of CANDU spent fuels. The values obtained by numerical calculations show that this fusion breeder reactor is self-sufficient in terms of tritium and has a high performance in terms of energy multiplication as well as fuel rejuvenation and thorium utilization.