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The existing nano-indentation method and developmental micro-tensile testing method are more attractive in accurately defining the irradiation effect on the mechanical behavior and adopted in this study to identify the detailed irradiation behavior of pure tungsten. The pure tungsten (A.L.M.T. Corp., Japan) produced by the powder metallurgy and hot-rolling process has a purity of 99.99 wt%. The irradiation was conducted to a maximum of 18.0 dpa by the TIARA (Takasaki Ion Accelerators for Advanced Radiation Application) at 500 and 800 ℃. The micro-tensile specimens with the gauge section of about 0.8 µm (width) × 0.8 µm (thickness) × 10 µm (length) were machined by a focused ion beam device. The nano-indentation results showed the saturation of irradiation hardening and its irradiation temperature dependence. In the case of 500℃, the indentation hardness of pure tungsten irradiated in TIARA increased with increasing dose, and it reached 6.5 GPa after irradiation to 1.0 dpa. Beyond 1.0 dpa, indentation hardness approached a constant. In the case of 800℃, indentation hardness reached 8.1 GPa by irradiation to 3.0 dpa with an irradiation hardening saturation.

In Japan Demonstration fusion reactor, the divertor plays a critical role for it helps sustaining plasma shape and hence demanding high requirements on its structural materials for the cooling system. CuCrZr alloy is considered as one of candidates and would be used in one independent cooling system. Proposals of operating conditions would be similar with fission light water reactor, where experiences have shown that water chemistry significantly influences corrosion behavior. Available references on the corrosion of CuCrZr also address the importance of water chemistries. Because the design proposal could be one of proposals towards reactor, it is worthwhile an investigation to understand the corrosion behavior of CuCrZr alloy under high temperature water environments. This work aims at the effect of dissolved oxygen, and dissolved hydrogen on corrosion behavior. Tests were conducted in an autoclave with relatively static water flow. Three different water chemistries: water with dissolved oxygen 100ppb, water with dissolved hydrogen 1600ppb and degassed water were chosen. The exposure time of CuCrZr coupons was 100 hr. Results showed that specimens in water with oxygen 100ppb had highest weight loss with light-reflecting, grain-oriented surface while in water with hydrogen 1600ppb had lowest weight loss with tarnished surface and nanoscale pure copper precipitates attached. It is believed that hydrogen reduced dissolved copper ions back to copper atoms; atoms returned to surface in precipitate forms hence reducing weight loss.

Nondestructive analysis of tritium (T) distribution was performed by means of imaging plate technique on specimens cut from the Be limiters, W-coated carbon tiles and bulk W lamellae retrieved from the JET tokamak after the first and third experimental campaigns with the ITER-like wall. Afterwards, analyses were continued using X-ray photoelectron spectroscopy, microscopy techniques and thermal desorption spectroscopy. Co-deposits formed on the W-coated tiles in the 1st campaign showed large T retention because of high carbon content reaching up to 50 atomic %, while the carbon fraction in co-deposits after the 3rd campaign was distinctly lower. The T retention of the plasma-facing surface of the bulk W tile was smaller than that of the W-coated tiles by a factor of 20, while deposition of small amount of T was found at the side surfaces facing to the gaps in a lamella structure. The correlation of T distributions with surface morphology and the discharge conditions is discussed.

The interface bonding strength of thinly coated materials is difficult to be measured accurately owing to the size limitations of the coating layer. In this study, the interfaces bonding strength of an underwater explosive welded tungsten foil on ferritic steel was investigated by deep-notch-type micro-tensile tests and microscopic double-notch shear (DNS) compression tests. The micro-tensile tests were carried out using a focused ion beam (FIB) tensile system. The results showed that the tensile strength of the interface region near the ferritic steel was larger than that of the ferritic steel but weaker than that of the tungsten foil. The micro-DNS compression tests were conducted in both the tungsten and interface regions. The obtained shear strength of tungsten exhibited a strong size dependence as follows: the smaller the size, the higher the strength. Although interface specimens with a large gauge section area showed a shear strength similar to that of tungsten DNS specimens, an interface region specimen with an area of the gauge section of approximately 1 ² showed larger shear strengths (∼4.8 GPa) than the tungsten region (3.2 GPa). Observations of the bonding microstructure and fracture surface indicated that the obtained shear strength with 1 ² specimens corresponded to the interface bonding shear strength between tungsten and ferritic steel obtained by underwater explosive welding.