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The mass production of CuCrZr alloy - ITER Grade tubes for the ITER divertor outer vertical target (OVT) prototype and series production is now in progress as well as other material. It is required to manufacture the CuCrZr tube with the mechanical properties required by the design and with the grain growth suppressed in terms of prevention of water leakage and durability of electromagnetic load even after the completion of the OVT. Therefore, the mechanical properties are tested prior to a use for the OVT to confirm the mechanical properties and the quality during mass production of the CuCrZr tube. This paper reports the tensile properties, which are one of important mechanical properties required for the CuCrZr tubes used in the prototype and series production of the OVT. As the results of sampling inspection during the mass production, the CuCrZr tube was capable of meeting required values of the tensile properties even after the heat treatment simulated the solution annealing and aging in the PFU manufacturing.

For the series production of the divertor outer vertical target (OVT) of the ITER, approximately 200,000 tungsten (W) monoblocks as plasma-facing material are planned to be manufactured. However, thus far, the variation in the properties of the W monoblocks has not been investigated. In this study, the chemical impurity level, material properties, and response to cyclic heat loading (i.e., durability and surface deformation) of W monoblocks manufactured using W plates supplied by A.L.M.T. Corp., Japan (ALMT) and Nidec Sankyo CMI Corp., Japan (NSCM) were investigated. On examining the manufactured lots (four from ALMT and two from NSCM), it was concluded that the variation in the material properties might have been caused by variations in the impurity level of the raw powder, contamination during manufacturing, and changes in the processing parameters. The results of the high heat flux test indicated that all the examined lots met the acceptance criteria. Hence, the variations observed in the chemical impurity level and material properties (e.g., density, Vickers hardness, and grain size) of the W plates supplied by ALMT and NSCM were acceptable. Therefore, W from the two suppliers will be employed in the full-scale plasma-facing unit prototype, which will be used for the final qualification of the material and OVT manufacturing technology.

To understand the microstructural stability of candidate plasma-facing materials under fusion-relevant environments, neutron irradiation of W and W-3%Re alloys with and without K and La dopants was per formed in the mixed-spectrum High Flux Isotope Reactor at nominal temperatures of ~850 °C and ~1100 °C to calculated doses between 0.42 and 0.47 dpa. To the best of our knowledge, this study presents the first experimental evidence of radiation-enhanced recrystallization in W and undoped W–Re alloys at ~850 °C, conditions where thermal annealing does not cause any grain growth in a similar timescale. Potassium- or lanthanum-doped tungsten alloys showed more resistance to radiation-enhanced grain growth. We explain the acceleration of grain growth by analyzing the self-diffusion constant under atomic displacement environments. The microstructural observations of the studied W variants suggest that La doping is more effective than K doping for mitigating recrystallization. This study also found that radiation-enhanced crystallization is an important consideration when designing and applying W to plasma-facing components in future nuclear fusion reactors.

The plasma facing unit (PFU) of ITER divertor is repeatedly exposed to high heat flux, and a reliable heat removal capability is crucial for its adequate performance. The cyclic high heat flux test (HHFT) that has been conducted to evaluate the reliability of PFU reveals that the surface modification and macro-crack formation in W monoblock, which is the plasma facing material, may hinder the operation of fusion reactors. Therefore, optimization of both manufacturing technology and material development is necessary for reliable operation. In this study, we investigate the dependence of material properties on the surface modification and macro-crack formation in W monoblocks. W monoblocks manufactured by two different suppliers were examined, and the results of cyclic HHFT revealed that the heat removal capability was not degraded in all the examined W monoblocks. Further, it was observed that the W monoblock exhibiting characteristic grain structure and tensile property suffered less surface modification without macro-crack formation due to cyclic heat loading.