Challenges for plasma-facing components in nuclear fusion

Abstract

The interaction processes between the burning plasma and the first wall in a fusion reactor are diverse: the first wall will be exposed to extreme thermal loads of up to several tens of megawatts per square meter during quasistationary operation, combined with repeated intense thermal shocks (with energy densities of up to several megajoules per square meter and pulse durations on a millisecond time scale). In addition to these thermal loads, the wall will be subjected to bombardment by plasma ions and neutral particles (D, T, and He) and by energetic neutrons with energies up to 14 MeV. Hopefully, ITER will not only demonstrate that thermonuclear fusion of deuterium and tritium is feasible in magnetic confinement regimes; it will also act as a first test device for plasma-facing materials (PFMs) and plasma-facing components (PFCs) under realistic synergistic loading scenarios that cover all the above-mentioned load types. In the absence of an integrated test device, material tests are being performed primarily in specialized facilities that concentrate only on the most essential material properties. New multipurpose test facilities are now available that can also focus on more complex loading scenarios and thus help to minimize the risk of an unexpected material or component failure. Thermonuclear fusion—both with magnetic and with inertial confinement—is making great progress, and the goal of scientific break-even will be reached soon. However, to achieve that end, significant technical problems, particularly in the field of high-temperature and radiation-resistant materials, must be solved. With ITER, the first nuclear reactor that burns a deuterium–tritium plasma with a fusion power gain Q ≥ 10 will start operation in the next decade. To guarantee safe operation of this rather sophisticated fusion device, new PFMs and PFCs that are qualified to withstand the harsh environments in such a tokamak reactor have been developed and are now entering the manufacturing stage.

Fusion Materials Development at Forschungszentrum Jülich

“…Here, the focus will be the applicability in the medium-to-long term for a European Demo to be constructed in the 2040s. Material testing of those components will then be performed analogous to the activities described by Linke et al [184] that successfully lead to the use and qualification of bulk baseline tungsten materials in ITER.…”

Flat-Top Cylinder Indenter for Mechanical Characterization: A Report of Industrial Applications

“…As mentioned in the previous section, W is the first-choice material to protect structural components, divertor and cooling systems in future nuclear fusion reactors because of its excellent thermo-mechanical proprieties, high melting point, high thermal conductivity, low physical sputtering, tritium retention, and activation under neutron irradiation [ 46 , 47 , 48 ].…”

Plasma Facing Material by Self-Interstitial Solid Solution Strengthening – Problem, Proposition, and a Solution

“…In physical chemistry sense, He atoms have strong repulsion to W atoms [80,92]. This ultra-low solubility forces He atoms to self-precipitate into small He bubbles [83] that become nucleation sites [90] for further void growth [93] under radiation induced vacancy supersaturations [94], resulting in material swelling [69,86,95] and high temperature He embrittlement [71,96,97], as well as surface blistering [75][76][77][78] under low energy and high flux He bombardment [54,98] at elevated temperatures [99]. This may be mitigated by engineering structures in material which help in outgassing of He.…”

“…Other designs include, 5.5 cm thick divertor consists of ~40% W-1.1TiC alloy, ~12% ODS ferritic steel, and 18% He coolant, by volume [194]. The 14 MeV source neutrons will activate the armor and generate radioactive materials at the end of the divertor service lifetime [97,195]. Ni ( [100,196] Above modified phase diagram of stainless steel is used to identify chemical composition, temperatures, and phases to be formed in alloy.…”