OVERVIEW OF ADVANCED TECHNIQUES FOR FABRICATION AND TESTING OF ITER MULTILAYER PLASMA-FACING WALLS

The design of the ITER primary first wall incorporates a multi-layered structure consisting of a layer of beryllium bonded to a layer of cop per alloy with embedded stainless ste:el tubes which in turn is bonded to a stainless steel structure. In this configuration, the stainless steel provides structural support, the copper alloy improved resistanc e to high heat loads, and the beryllium layer a low Z metal interface with plasma. Fabrication, testing and control of this multi-layered st ructure, and indeed the entire blanket shield module, calls for advanc ed methods. Several associations in the four home teams and their indu strial partners have been involved in various fabrication and joining tasks now grouped under L4 blanket project. In this paper, an overview of the work done so far for joining stainless steel to stainless stee l, stainless steel to copper alloy, copper alloy to copper alloy, and copper alloy to beryllium is presented. Specialised papers dealing wit h most of the topics treated here;Ire scheduled in this symposium. The fabrication and joining methods presented here, other than the conven tional welding and brazing, follow four main routes. Two of them make extensive use of hot-isostatic pressing (HIP); (a) solid to solid; (b) solid or powder to powder, with or without a prior cold or hot isosta tic pressing of one of the products. The third combines advantages of casting and HIPping for fabricating large and complex parts. The fourt h investigates the possibility of using explosive welding for joining copper alloys to stainless steel. Other methods, including friction we lding, are investigated for specific parts. After a brief recall of co nsiderations leading to selection of individual materials, specificati ons derived for wrought and powder products are presented. Optimised c onditions for bonding steel to steel, copper to copper and steel to co pper are tabulated and preliminary results obtained from tests on join ts are compared with the values obtained for parent materials. Also pr esented in the paper are the results obtained from high heat flux test ing of small scale mock-ups. Throughout the paper the collaboration wi th industry in defining specifications for reference products, fabrica tion routes, and construction of large scale mock-ups anti their testi ng are referenced. (C) 1998 Elsevier Science S.A. All rights reserved.