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Fusion reactors have, in a first stage, to burn an equal mixture of deuterium and tritium. The supply of the first of these hydrogen isotope is not a concern but the second one, that doesn't exist in large quantities on the earth, has to be produced by the Li (n,alpha) reaction inside the reactor itself in the breeding blanket. It is generally agreed that a commercial fusion reactor, with a net electrical power of 1000 MW will burn 450 g of tritium per day. To produce such a large tritium quantity in the toroidal geometry of a reactor, accounting for all the penetrations, impurity control systems, etc ... is a real challenge. In addition to that, to maintain in the plant a minimum tritium inventory, tritium has to be kept inside the blanket at the p.p.m. level. An important factor is the doubling time, i.e. the time required to produce, in addition to the tritium burned, enough tritium to be able to supply the initial tritium inventory. This impacts directly on the tritium system, in the way that one of the most important criteria to select among possible processes for this system is to account for the tritium inventory. As much as possible, continuous processes have to be preferred to batch processes that always add to the inventory in the way that they require, at least, additional tanks and piping. Another important aspect that has to be controlled, is the tritium permeation. In all heated parts of the reactor and in the tritium system, tritium permeation through walls takes place. In a commercial reactor, with hot first wall and blanket a large tritium permeation is unavoidable. Depending on the surface cleanliness condition, tritium permeation rate as large as 10 to 100 g/d have been calculated. The immediate implication is that the coolant has to be reprocessed to recover this permeation flow. In this area again the process selection for the coolant detritiation has to be made in such a way that the tritium inventory in the detritiation process is kept at a minimum.

Additional information

Bibliographic Reference: 14TH SOFT CONFERENCE, AVIGNON (FRANCE), SEPT. 8-12, 1986 VOL. 1, PP. 189-199 1895 P., 1986, VOL. 1 AND VOL. 2, ISBN 0 08 034935 8 WRITE TO PERGAMON PRESS, HEADINGTON HILL HALL, OXFORD, OX3 0BW (UK), PRICE: UKL 220 (FOR BOTH VOLS.)
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