Overview of the Mechanical Properties of Tungsten/Steel Brazed Joints for the DEMO Fusion Reactor

Abstract

A Demonstration (DEMO) thermonuclear reactor is the next step after the International Thermonuclear Experimental Reactor (ITER). Designs for a DEMO divertor and the First Wall require the joining of tungsten to steel; this is a difficult task, however, because of the metals’ physical properties and necessary operating conditions. Brazing is a prospective technology that could be used to solve this problem. This work examines a state-of-the-art solution to the problem of joining tungsten to steel by brazing, in order to summarize best practices, identify shortcomings, and clarify mechanical property requirements. Here, we outline the ways in which brazing technology can be developed to join tungsten to steel for use in a DEMO application.

Brazing Tungsten/Tantalum/RAFM Steel Joint for DEMO by Fully Reduced Activation Brazing Alloy 48Ti-48Zr-4Be

“…The test scheme should be improved, because the relative error of 15% is believed to be high. We calculated earlier that a minimum required shear strength for W/steel joint in Water Cooled Lithium Lead blanket is 180 MPa [21], though some attempts can be made to improve the strength of the joint. Figure 10b shows the SEM image in secondary electrons of Rusfer/TiZr4Be/Ta seam after the shear test.…”

“…Brazing 2 of 15 is considered to be the most reliable technology, because it does not cause creep of the materials which are to be joined, and the cost is lower compared with hot isostatic pressing et al According to ITER experience, it is also important to use a technology which allows local repair of damaged components during production [20]. However, until now no fully reduced activation brazing alloy has been used, or the strength of the joint was low [21]. Instead, scientists use nickel [17,22,23] or copper [11,[24][25][26] brazing alloys, although these materials do not fully satisfy the requirement of reduced activation.…”

Microstructure, Residual Stresses, and Strain-Rate-Dependent Deformation and Fracture Behavior of AISI 304L Joints Brazed with NiCrSiB Filler Metals

“…The mechanical properties are generally determined by interdependencies between the geometry of the brazed joint [9] and the microstructure [10], but also residual stress distributions arising from the brazing process or following post-processing [11]. The microstructure can be adjusted by the filler metal alloy compositions and the manufacturing parameters used.…”

Monte Carlo simulations of pure tungsten and advanced “smart” tungsten alloys under helium bombardment for future fusion power plants

“…DEMO represents an important step between ITER and a power plant 1 ; the containment needs to hold the plasma in place, while maintaining its density at even higher temperatures than in ITER. 2 Future fusion power plants require the development of a first wall armor material standing extreme particle and radiation loads. 3,4 Considering safety, the formation of long-lived radioactive isotopes when irradiated with neutrons and a tritium inventory has to be prevented.…”