[en] The design of the High Temperature Gas Cooled Reactor (HTGR) core permits considerable latitude in the choice of fuel cycles. In this report, the various fuel cycles which can be employed in the HTGR core are reviewed, discussed and ranked. A hybrid fusion-fission system is described in which a fusion reactor with a fertile material blanket is used to produce both fuel for a number of HTGRs, and electricity. The basic parameters of both the fusion machine and the HTGRs are defined and an example is given of such a system including estimated fuel cycle costs. It is concluded that the HTGR is a very flexible reactor in its ability to adapt to economic and political conditions, and that a symbiotic fusion-fission system can be defined which is economic and insensitive to the fusion reactor capital costs