STATUS OF EC SOLID BREEDER-BLANKET DESIGNS AND RESEARCH-AND-DEVELOPMENT FOR DEMO FUSION-REACTORS

Within the European Community Fusion Technology Programme, two solid b reeder-blankets for a DEMO reactor are being developed. The two blanke ts have various features in common: helium as coolant and as tritium-p urge gas; the martensitic steel MANET as a structural material; and be ryllium as the neutron multiplier. The configurations of the two blank ets, however, are different: in the breeder inside tube concept, the b reeder materials are LiAlO, or Li2ZrO3 in the form of annular pellets contained in tubes surrounded by beryllium blocks, with the coolant he lium being outside the tubes; in contrast, in the breeder out of tube concept, the breeder and multiplier materials are Li4SiO4 and berylliu m pebbles, forming a mixed bed placed outside the tubes containing the coolant helium. The main critical issues for both blankets are the be haviour of the breeder ceramics, and of beryllium under irradiation an d the tritium control. Other issues are the low temperature irradiatio n-induced embrittlement of the MANET; the mechanical effects caused by major plasma disruptions; and safety and reliability. The R&D work co ncentrates on these issues. The development of martensitic steels, inc luding MANET, is part of a separate programme. Breeder ceramics and be ryllium irradiations have been performed so far under conditions which do not cover the peak values projected for the DEMO blankets. Further irradiations in thermal reactors and in fast reactors, especially for beryllium, are required. Effective tritium control requires the devel opment of permeation barriers and/or of methods of oxidation of the tr itium in the main helium cooling system. First promising results have been obtained also in the field of mechanical effects from plasma disr uptions and safety and reliability. However, further work is required in the reliability field and to validate the codes for the calculation s of the plasma disruption effects.