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6. Fission Fusion Thorium Hybrid - FISSION FUSION THORIUM...

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FISSION FUSION THORIUM HYBRID ©M. Ragheb 12/8/2009 INTRODUCTION The thorium fission fusion hybrid is discussed as a sustainable longer term and larger resource base to the fast breeder fission reactor concept and as an early introduction of fusion energy. In addition, it offers a manageable waste disposal process, burning of the produced actinides and serious nonproliferation characteristics. A first generation thorium hybrid would use the DT fusion reaction as a neutron source instead of the fissile isotopes U 235 and/or Pu 239 as external seed material feeds, breeding tritium from lithium. A second generation would use the catalyzed DD fusion reaction eliminating the need for tritium breeding and providing a practically unlimited supply of the deuterium at 150 ppm in water from the world oceans. Either system could use the U 233 bred from Th 232 for power generation on-site or for export to satellite smaller-size fission reactors. The nuclear performance of a fusion-fission hybrid reactor having a molten salt composed of Na-Th-F-Be as the blanket fertile material and operating with a catalyzed Deuterium-Deuterium (DD) plasma is compared to a system with a Li-Th-F-Be salt operating with a Deuterium-Tritium (DT) plasma. In a reactor with a 42-cm thick salt blanket followed by a 40-cm thick graphite reflector, the catalyzed DD system exhibits a fissile nuclide production rate of 0.88 Th(n, γ) reactions per fusion source neutron. The DT system, in addition to breeding tritium from lithium for the DT reacti on yields 0.74 Th(n, γ) breeding reactions per fusion source neutron. Both approaches provide substantial energy amplification through the fusion-fission coupling process. The catalyzed DD fusion approach to U 233 breeding from Th 232 offers distinct advantages. It eliminates the need for breeding tritium from lithium in the blanket. The requirement of tritium storage and its environmental leakage hazard are eliminated. Any tritium produced in the plasma of the catalyzed DD cycle can be directly injected into the plasma, so the active tritium inventory in the plasma loop is reduced by a factor of 3 compared with the DT fusion cycle. In addition, the competition for the available neutrons to compete for fusile and fissile breeding as occurs in the DT system is eliminated, leading to higher fissile breeding in the catalyzed DD cycle. Continuous extraction of the bred U 233 and its Pa 233 precursor from a molten salt would lead to a blanket relatively clean from fission products contamination, neutron poisoning and power swings caused by fissioning of the produced U 233 as would occur in a solid blanket.
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Fig. 1: Material flows in the DT (top) and Catalyzed DD fusion-fission hybrid (bottom) alternatives with U 233 breeding from Th 232 .
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