Tritium breeding

Nuclei ( Li, Li) for Tritium Breeding. For either magnetically confined or inertially confined fusion, the near term nuclear species involved will be deuterium (0) and tritium (T). 

The use of lithium as a solid compound, a pure melt, or a molten alloy is required for tritium breeding in at least the first generation of fusion reactors. Three fusion reactor concepts are discussed with emphasis on material selection and material compatibility with lithium. Engineering details designed to safely handle molten lithium are described for one of the example concepts. Tritium recovery from the various breeding materials is reviewed. Finally, two aspects of the use of molten Li-Pb alloys are discussed the solubility of hydrogen isotopes, and the influence of the alloy vapor on heavy ion beam propagation. 

The Li nucleus can absorb a fast (above 3 MeV) neutron to produce a tritium nucleus, an alpha particle, and a slower neutron. A moderated neutron can be absorbed by a Li nucleus to produce a tritium and an alpha. Neutronic calculations indicate that a thick sphere of natural lithium could breed about 1.8 tritium atoms for each tritium atom burned in a fusion reaction (1 ). Structure and portions of the volume left open for fueling or driver beams reduce the 1.8 tritium breeding ratio. If the ratio falls below 1.0, it may be increased by addition of a neutron multiplier such as Be or Pb, and by isotopically enriching the Li in °Li. 

For lithium temperatures of 500°C, the liquid metal heat exchanger requires 3.3 to 8.0 m of area per MWj-(10,600 to 25,600 m for a 1-GWg plant). The wall thickness will be about 0.65 mm to 1.3 mm for a Cr-1 Mo heat exchanger. For a 30% tritium burn fraction and a 1.75 tritium breeding ratio, 19.5 mg/sec of tritium are added to a 1-GWg HYLIFE plant s liquid metal wall, and the same amount must diffuse out. The permeability constant for tritium diffusing through 2 1 Cr-1 Mo steel is (21)... 

Hydrogen Pressure Ranges for Liquid-Only or Vapor-Only Tritium Recovery for IMW IGF Reactors. For a 2700-MWf IGF reac-tor with a 600-m chamber, a 30% tritium bum fraction and a 1.75 tritium breeding ratio, 19.5 mg/s of tritium are added to the reaction chamber. If tritium is to be recovered from only the liquid, a maximum loss through the vacuum system of 1% (0.2 mg/s) is assumed to be acceptable. With a laser driver (26), the vacuum system might operate at a 1.3 Pa (10 2 Torr) with about 10% of the vapor being pumped per second. Then, about 3.5 mPa (2.6 x 10 Torr) of tritium, or 10 times the pressure associated with 0.2 mg tritium, is allowable. 

The irradiation of solids with fast neutrons results in the displacement of atoms from their lattice sites the resultant interstitials and vacancies can cause various radiation damage phenomena. In addition, the determination of H and He gas production as well as the neutron multiplication by 14 MeV-neutron-induced (n,p), (n,a) and (n,2n) reactions, respectively, in the construction materials of fusion reactors is very important. Studies on the tritium breeding and outgassing efficiency for different blanket materials are also important tasks. 

However, it will utilize techniques, which will not be possible on a reactor due to the continuous operation and/or higher neutron dose. From the technology point of view, one important aim is to demonstrate tritium-breeding technologies. ITER will not be self-sustaining of tritium as only a few test blanket modules (TBM) will be installed for the testing... 

The basic simplicity of the Linus concept is due to the combination in one element, the liner, of functions which in other fusion concepts require separate systems. It is the confining field coil, the plasma heater, the first wall, the tritium breeding blanket, the heat transfer medium and the main vacuum pump. Perhaps its most important function is that of providing a continuously regenerated liquid first wall whose mean power loading can greatly exceed the limits of a solid first wall. 

Thus prospects seem good for quite attractive satellites. The generator plants, however, must face, to a large degree, the same issues (except for tritium breeding) posed in D-T plants. 

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