D. Kato

H. Iwakiri

J. Yoshimatsu

K. "Morishita

N. Yoshida

N." Sakaguchi

Q. Xu

T. Muroga

T. Yoshiie

Y. Chen

Y. Kaneta

Y. Watanabe

Y. Yamamoto

National Institute for Fusion Science (NIFS-Repository)

Multiscale Modeling of Radiation Damage Processes in Fusion Materials   Morishita, K, Watanabe, Y., Yoshimatsu, J., Yamamoto, Y., Qiu Xu, Yoshiie, T. (Kyoto Univ.),  Kato, D., Muroga, T. (NIFS),  Iwakiri, H. (Univ. of the Ryukyu) Yoshida, N. (Kyushu Univ.) Kaneta, Y., Chen, Y. (Univ. of Tokyo) Sakaguchi, N. (Hokkaido Univ.)   Continuous efforts are being made towards the development of new methodology that predicts the behavior of fusion materials during irradiation, which is one of the important technologies for development of new radiation-resistant materials and for reliable assessment of reactor lifetime. Radiation damage processes leading to the degradation of materials due to irradiation are essentially multiscale phenomena that have a wide variety of time-, length- and energy-scales. Therefore, to understand the processes well, a wide variety of researchers are needed and the NIFS collaboration programs have been playing an important role. This collaboration activity recently proceeds with the different collaboration program between Kyoto University and JAEA for the DEMO-BA projects.  One of our research actions in this year is to have several meetings to exchange information to each other about multiscale modeling of radiation damage processes, which are reported in [1] and [2]. Participants whose major are the plasma-surface interaction study newly join this year.  Another action in this year is to carry out the research of theoretical modeling on defect interactions in SiC, where SiC/SiC composites are one of promising candidates for the blanket structural material, because of high stability at high temperature. As a first step towards constructing a model for simulating microstructural evolution in β-SiC during irradiation, molecular dynamics and molecular static calculations have been performed to obtain the formation and binding energies of relaxed configuration of defect clusters in β-SiC, which are necessary when the nucleation and growth process of clusters is investigated. The calculated lowest formation energies of isolated silicon- and carbon-interstitials are 3.17 eV and 3.24 eV, respectively. The most stable configuration of isolated silicon interstitial is the TC configuration where a silicon atom is located at the tetrahedral position surrounded by four regular carbon lattice atoms. On the other hand, the energetically favorable configuration for isolated carbon interstitial is the C-C dumbbell configuration in which two carbon atoms share a regular carbon lattice site along <100> direction. These stable configurations are consistent with those obtained by our previous ab-initio calculation. The calculated lowest formation energy of SIA-clusters with the cluster size n=nISi+nIC are also calculated. The formation energy strongly depends on the size and chemical composition of clusters. As to the most stable configuration of the clusters, surprisingly, each silicon interstitial in the clusters also maintains the TC configuration, while each carbon interstitial in the clusters maintains the C-C dumbbell configuration, as well.  Also, preliminary calculations were conducted to obtain the formation energy of relatively large SIA-clusters. Fig. 1(a) shows the configuration of SIA(91, 91) which was relaxed at 300K. As shown in the figure, the SIA(91,91) is a disc-shaped defect containing stacking fault on the closed-packed (111) plane, with the estimated diameter of 2.1 nm. When the relaxation was done at a higher temperature, the stacking fault was eliminated and the SIA-cluster was unfaulted to be a perfect loop, as indicated in Fig. 2(b). In order to clarify the mechanism of the unfaulted process, further investigation is underway.    Reference 1) Report of multiscale modelng of radiation damage in materials, Vol. 4, Febuary 2010, in Japanese. 2) Report of multiscale modelng of radiation damage in materials, Vol. 5, Febuary 2010, in Japanese. 3) Y. Watanabe, et al., MMM-4 conference proceedings, Tallahassee, Florida, USA.  (a)??(b)?? Figure 1  The configuration of SIA(91, 91) relaxed at (a) 300K and (b) 600K obtained by the MD and MS calculations. Some preliminary calculations show that a metastable SIA(91, 91) is a disc-shaped defect containing stacking fault on the closed-packed (111) plane, as shown in (a). When the relaxation is done at a higher temperature, the stacking fault is eliminated and the SIA-cluster is unfaulted to be a perfect loop, as indicated in (b).This work will be published in ref. [3].  Measurement of mechanical strength of the first wall coating by means of laser-shock method   Satou, M.(Tohoku Univ., (Hachinohe Inst. Tech.)),  Nagasaka, T.  It has been demonstrated that controlling of interstitial impurity levels by means of modification of melting process or addition of scavenging elements like yttrium improved the material performance through evaluation of baseline properties and irradiation behaviors for V-4Cr-4Ti alloy. As for an important issue to reduce MHD (Magneto Hydro Dynamic) pressure drop, a laser shock method have been utilized for the evaluation of bonding strength between vanadium alloys and yttrium oxide coating as electrical insulator. In order to improve the methodology, metal/metal bonds like nickel-titanium and copper-nickel, and ceramics/metal coating like magnetite-steel were also evaluated. The first wall coating of tungsten on structure materials for fusion reactor is of interest from the view point of the bonding strength. In this study, mechanical properties of the first wall coating and the insulator coating on vanadium alloys were examined by means of the laser shock method to understand the bonding strength between dissimilar materials in the fusion reactor components.   The laser shock apparatus to measure the bonding strength have been installed. A Nd:YAG laser with wave length of 1064 nm and maximum 1.6 J power at single-pulse mode (pulse width was 7 ns of full width at half maximum)  to apply tensile stress at the interface and a displacement laser interferometer using a single mode diode-pumped solid-state (DPSS) laser with wave length of 532 nm. The procedure consisted of three steps. (1) Irradiation. The Nd:YAG laser shots created shock wave that caused tensile stress after reflection at free surface. (2) Measure surface velocity. The stress depended on laser power and was estimated by the surface velocity profile measured by laser interferometer. (3) Estimation of the strength. The bonding strength was determined by the critical laser power that caused exfoliation of the bonding interface.   The target first wall coating of tungsten was under preparation. Yttrium oxide coating on vanadium alloys were measured by the laser shock method to reveal the applicability to the first wall coating. The critical laser power of the yttrium oxide coating was able to estimate as shown in fig.1. Clear exfoliation was observed after laser shots of 112 and 197mJ. The brighter area in the circles showed the exfoliation. It was hardly observed exfoliation after 89mJ-shot or less power-shots. The corresponding exfoliation was clearly observed from cross sectional view of the coating after laser shots as in fig.2. The evaluated strength in this case was less than 390MPa. Several issues to improve in the precision of the measurement were found, such as exfoliation in the coating, effects of laser profile and thickness.   The results of the evaluation of the bonding strength between yttrium oxide and V-Cr-Ti-Y type alloys indicated that the laser shock method can be powerful tool for the research and development of the first wall coating. Further improvement of the precision and application to the tungsten coating on the structure materials such as vanadium alloys and reduced activation ferrous materials are going to be conducted.    Fig. 1 Surface morphology after several laser shots on V-4Cr-4Ti-0.2Y alloy to determine the critical energy. Dotted circles indicate irradiation area and the numbers are laser energy in mJ. The brighter area indicates exfoliation of yttria coating, irradiated with 112 and 197 mJ.  Fig. 2 Scanning electron microscopy of the cross-section of interface between yttria and vanadium alloys. 261§16. Multiscale Modeling of Radiation Dam ge Processes in Fusion MaterialsMorishita, K., Watanabe, Y., Yoshimatsu, J.,  Yamamoto, Y., Xu, Q., Yoshiie, T. (Kyoto Univ.),  Kato, D., Muroga, T.,  Iwakiri, H. (Univ. Ryukyu),  Yoshida, N. (Kyushu Univ.),  Kaneta, Y., Chen, Y. (Univ. Tokyo),  Sakaguchi, N. (Hokkaido Univ.)

Multiscale Modeling of Radiation Damage Processes in Fusion Materials

Multiscale Modeling of Radiation Damage Processes in Fusion Materials

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