Fig. 2-19 Simulated experiment of the tokamak fusion reactor blanket A doughnut shaped blanket of the tokamak fusion reactor is simulated in a linearly expanded fashion. Fourteen MeV neutrons are produced from DT reactions by firing energetic deuteron beams onto the tritium target located at the tip of the beam line through which the deuteron beam is accelerated. The beam line is shown extended from the right in the figure. The experimental system (blanket model) will be operated with this simulated point neutron source.

Fig. 2-20 Estimated reliability of tritium production rate and design margin As shown in the diagram, if we want to obtain the tritium production rate in the blanket with a 100 % reliability, the JAERI/MORSE calculation method, for example, indicates the design margin required is 1.16. Namely, to obtain a 10 % breeding of tritium in the blanket with a 100 % reliability (tritium breeding ratio of 1.1), the design calculation of the tritium production rate on the basis of the JAERI/MORSE code will give a design margin of 1.28 as 1.1 x 1.16 = 1.28.

In a DT fusion reactor a breeding blanket is an essential component to produce or breed tritium fuels by using the DT neutron-induced nuclear reactions of lithium, which is contained in the blanket as a lithium compound. The development of a highly reliable method to estimate the tritium production rate or the breeding ratio in the blanket with high precision and with reasonable margin is therefore crucially important. JAERI has promoted R&D on the physical behavior of fusion-produced neutrons in a fusion reactor and provided many pioneering results in this area by using an accelerator-type fusion neutron source called FNS. Joint experiments on the tritium production in a fusion blanket have been conducted with FNS under the Japan-US collaboration research program. In the experiments, particular emphasis was put on data acquisition and data evaluation from a basic engineering point of view. As shown in Fig. 2-19 we have investigated the behavior of neutrons and measured tritium production rates under various configurations and conditions of simulated experiments on fusion blanket models with lithium oxides as breeding materials of tritium. After detailed and careful comparison of the experimental data with theoretical calculations, we have first obtained a quantitative data base for evaluating the nuclear design of the tritium production in a fusion reactor blanket. The results are summarized in Fig. 2-20.

Reference Y. Oyama et al., JAERI/USDOE Collaborative Program on Fusion Blanket Neutronics, J. At. Energy Soc. Jpn. 36 (7), p.611-618 (1994).

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