The roles of fusion-fission hybrids and fast breeders in the nuclear futures of the United States and the world as a whole (outside centrally planned economy areas) have been examined. The primary objectives have been:

  1. to determine whether hybrids can allow the projected nuclear component of the energy demand to be met within current estimates of uranium resources with and without fast breeders
  2. to identify the time window for hybrid introduction that would allow the demand to be met within the resource base and how such a window is affected by market penetration constraints and hybrid coupling scenarios with the fission industry.
Five hybrid coupling scenarios have been examined, namely, Th/U hybrids coupled to either light water denatured or heavy water denatured reactors, and U/Pu hybrids coupled to either light water reactors (LWRs), plutonium high converters, or fast breeders. In addition, two reference scenarios where LWRs are coupled to either fast breeders or plutonium high converters have been examined. The annual and cumulative uranium demand for the different scenarios examined between the present and the year 2075 have been determined for both the world and the United States alone. These uranium demand values correspond to the optimum time-dependent shares of the different reactor types in each scenario over the period of interest. A strategy optimization code has been used to determine these time-dependent shares so that the cumulative uranium consumption in 2075 is minimized. The analyses have been performed for both the world and the United States with different hybrid, breeder, and advanced reactors introduction dates and market penetration constraints. The International Nuclear Fuel Cycle Evaluation's low demand projection of world nuclear capacity has been used in these calculations to obtain a lower bound on the world uranium demand. For the United States, the calculations have been performed for two different nuclear capacity projections corresponding to “moderate” and “high” growth scenarios. Values of the minimum cumulative uranium demand for the different scenarios examined with different hybrid and breeder introduction dates and market penetration constraints have been compared with current estimates of uranium resources with recovery costs up to 130 $/kgU. Based on these comparisons, conclusions are made regarding the role of hybrids in the nuclear futures of the United States and the world.