2.13 Perspective of a Mass Production Method of Lithium Ceramics for Nuclear Fusion Fuel

Fig. 2-23 Flow chart production process for Li2TiO3 pebble by wet type grain production method This indicates a summary of the process in which lithium titanate (Li2TiO3), sodium alginic acid and 4-H furfuryl alcohol solutions are sintered after heating up, being dried and baked to produce micro spheres of Li2TiO3.

Fig. 2-24 Results of the investigation to establish the production conditions for suitable gel-spheres It was found that nearly true spheres were obtained in region B, where the PVA content is 3-5 wt%. This shows an example of the conditions.

Fig. 2-25 Test results of grain size control It is considered to be beneficial for the production of nuclear fusion reactor fuel that the grain size of Li2TiO3 is small. In the case of target sintering density of 85%, the figure shows that it is better for the grain size of the starting powder to be small, from 10 µm to 0.6 µm. The grain size of the pebble becomes 100 µm to 20 µm and the figure indicates that it becomes less than 10 µm when titanium oxide is added (5%) at 0.6 µm.

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Tritium, which is a fusion reactor fuel, is produced by a reaction of lithium with neutrons that are generated by deuterium-tritium nuclear fusion reactions. Lithium is to be used in the shape of a ceramic microsphere which contains lithium like Li2TiO3. Ceramic microspheres of total weight one hundred tons are loaded in a blanket. In the case of ITER ceramic microspheres of one ton are needed as a test of a breeding blanket. The production of the ceramic microspheres that are the tritium breeding blanket materials has been conducted only on a laboratory scale, in the world. At that time there was no prospect of mass production. We have devised a "wet type grain production method" (Fig. 2-23) in cooperation with a company that has production experience of micro-coated fuel particles for high temperature gas-cooled reactors (patent taken). A study of using an automatic dropping device has been performed to produce gel spheres that lead to a nucleus of microspheres. A method for getting an adequate particle size has been found (Fig. 2-24). The production technique had a better yield rate as compared to the usual production method. By this technique the production of microspheres that have the desirable small particle size was not only probable but also presented the possibility of easily making a large scale production facility. The ability to supply one ton of ceramic microspheres for breeding tritium has been acquired. The ceramic microspheres are needed for "an irradiation test of a test breeding module," that is one of the purposes of the construction of ITER. Furthermore, the recycling of lithium that is a rare resource is probable by dissolving the microspheres used in fusion reactors with acid to produce the starting material for microsphere production.

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Reference K. Tsuchiya et al., Development of Wet Process with Substitution Reaction for the Mass Production of Li2TiO3 Pebbles, J. Nucl. Mater., ICFRM-9, 283-287, 1380 (2000).

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