A review of the US joining technologies for plasma facing components in the ITER fusion reactor

Abstract

This paper is a review of the current joining technologies for plasma facing components in the US for the International Thermonuclear Experimental Reactor (ITER) project. Many facilities are involved in this project. All of those facilities are not represented in the authors list but all contributions will be noted throughout the report and in the acknowledgements. Many unique and innovative joining techniques are being considered in the quest to join two candidate armor plate materials (beryllium and tungsten) to a copper base alloy heat sink (CuNiBe, OD copper, CuCrZr). These techniques include brazing and diffusion bonding, compliant layers at the bond interface, and the use of diffusion barrier coatings and diffusion enhancing coatings at the bond interfaces. The development and status of these joining techniques will be detailed in this report. Ultimately, these assemblies will be considered for possible use in selected regions of a full-scale, tokamakdesigned fusion reactor.Because beryllium reacts with all but a few elements to form intermetallics and is a strong oxide former, this study considered several different surface coatings as a means of both inhibiting these reactions and promoting a good diffusion bond between the two substrates. All bonded assemblies used aluminum and/or an aluminum-beryllium composite (AlBeMet 150) as the interfacial material in contact with beryllium. In all cases, a hot iso-static pressing (HIP) furnace was used to reduce oxidation and apply sufficient pressure to the bond area to produce metal-metal contact and subsequent bonding. Several different processing schedules were evaluated during the course of this study. Tensile testing followed by postmortem examination of the fractures and cross-sections showed that several of the trial assemblies produced excellent strength (100-200 MPa) and ductility. Two of these assemblies including one brazed assembly and one diffusion bonded assembly were tested in the electron beam test system (EBTS facility) at SNL-NM. These actively-cooled mock-ups were subjected to heat loads of up to 2000 cycles at 5 MW/m2 and 1000 cycles at 10 MW/m2 without bond failure or damage to any tiles. Several tiles were subjected to short term heat loads as high as 250 MJ/m2 (0.5s) to simulate vertical disruption events which caused surface melting of the beryllium tiles.Several different techniques and geometries are being evaluated in joining a tungsten armor rod bundle (tungsten brush) to a CuCrZr heat sink. Methods being used to coat the tungsten rod bundles with copper include plasma spraying, electroplating, and ion sputtering. Also, in collaboration with the Efremov Institute in Saint Petersburg, Russia, research is underway to coat tungsten rod bundles using a copper casting technique. Following the coating process, these bundles are bonded to the copper substrate using a low temperature diffusion bonding technique which employs a HIP process at 400-500°C. Thin coatings (100-200 nm) of nickel are used at the bond line to enhance diffusion ...

Recent developments toward the use of tungsten as armour material in plasma facing components

“…Missiaen (2) , P. Brustolin (3) , O. Ozer (2) , A. Durocher (1) , C. Ruset (4) , C.P. Lungu (4) , X. Courtois (1) , C. Dominicy (5) , H. Maier (6) , C. Grisolia (1) , G. Piazza (7) , P Chappuis (1) (1) Euratom -CEA, Direction des sciences de matière, département de recherches sur la fusion contrôlée, CEA Cadarache, Saint Paul les Durances, France (2) LTPCM, UMR CNRS 5614, Université Joseph Fourier, Grenoble, France (3) Institut de Soudure, YUTZ, France (4) NILPRP, Magurele-Bucharest, Romania (5) CP2M, Université d'Aix Marseille III, Marseille, France (6) Max-Planck-Institut für Plasmaphysik, Euratom Association, Garching, Germany (7) EFDA JET , Close Support Unit, Culham Science Centre, UK…”

“…Additionally it is difficult to manufacture by processes based on milling and welding. The current reference concepts for tungsten armoured plasma facing components all rely on contacts bonds (hot isostatic pressing, active metal casting, brazing), with typical cross -bond dimensions of less than 0.1 mm [2][3][4]. Test mock-ups have undergone successfully cycled high heat flux tests [5], however such bonds are still considered unfavourable regarding high temperature deformation, cycle fatigue, creep or thermal shocks [6,7].…”

W–steel and W–WC–steel composites and FGMs produced by hot pressing

“…These include the dissimilarity in thermal and mechanical properties, leading to stress concentration at the interface, physicochemical compatibility, such as lack of wetting or high mutual reactivity, neutronics problems with certain brazes, etc. [5][6][7]. Some of these issues can be solved by the use of interlayers or graded transitions between the two materials.…”

Study on the structural evolution of modified phenol–formaldehyde resin adhesive for the high-temperature bonding of graphite

“…Welding, brazing and other methods need costly metals to activate the inert surface of the carbon materials [7][8][9]. The joining of carbon materials is still a research focus [10,11].…”