Specific Features of Electron-Beam Welding of ITER Blanket First Wall Components

Abstract

Specific features of fabricating welded structures of the international thermonuclear experimental reactor (ITER) blanket components are considered. The results from elaborating the technology for electron-beam welding of cooling system’s channel caps in the first wall bearing structure (FWBS) of the ITER blanket shielding module are presented. The design of welded joint samples made of Grade 316L(N) steel and the welding equipment are described. The welding techniques and butt joint design features whose use makes it possible to obtain the required strengthening of weld bead and to avoid metal droplets from appearing in the FWBS inner cavities are considered. A simplified thermal–mechanical model of the cap-welding technological process is described, and the results from experimentally evaluating the structural and mechanical state of the obtained welded structures are presented. A comparison between the modeling and experimental results is given. It is pointed out that the stressed and strain state varies in an active manner at the initial loading stage. Initially, the metal in the heat-affected zone (HAZ) experiences plastic deformation followed by elastic relief at the subsequent stages. It is pointed out that the postweld deformations are on the whole characterized by a low level and remain within the permissible limits. The distribution of mechanical properties in weld joint local zones determined using the indentation method is given. The results from tensile tests and an indenter impressing test show that the weld metal has even better mechanical characteristics than the parent metal. Data are presented from metallographic investigations, which testify that there is no growth of grains in the HAZ, which is due to high rates of cooling in the used welding method. Based on the results of elaborating the electron-beam welding technology and using the developed techniques, an FWBS mockup has been fabricated that complies with the class VQC 1A tightness requirements.