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Kaji, Yoshiyuki; Tsuru, Tomohito; Shibutani, Yoji*
Materials Research Society Symposium Proceedings, Vol.1215, 6 Pages, 2010/10
In the present study three types of grain boundaries of coincidence site lattice (CSL), small angle (SA), and random types are considered as the representative example of grain boundaries. The grain boundary energies and atomic configurations of CSL are first evaluated by first-principle density functional theory (DFT) and the embedded atom method (EAM) calculations. SA and random grain boundaries are subsequently constructed by the same EAM and the fundamental characteristics are investigated by the discrete dislocation mechanics models and the Voronoi polyhedral computational geometric method. As the result, it is found that stress distributions of CSL and SA grain boundaries are localized around the grain boundary core. The random grain boundary shows extremely heterogeneous core structures including a lot of pentagon-shaped Voronoi polyhedral resulting from the amorphous-like structure.
Tanaka, Kosuke; Osaka, Masahiko; Kurosaki, Ken*; Muta, Hiroaki*; Uno, Masayoshi*; Yamanaka, Shinsuke*
Materials Research Society Symposium Proceedings, Vol.1215, p.95 - 100, 2010/10
In order to investigate the effect of MAs and FP addition on the oxygen potential of MOX fuels, thermogravimetric analysis (TGA) were carried out. MOX fuels with Am and 26 kinds of fission product elements (FPs), simulating low-decontamination MOX fuel and high burn-up to 250 GWd/t, were prepared by a conventional powder metallurgical route in a glove box. The oxygen potentials for simulating low-decontamination MOX fuels were higher than the fuels without FPs and increased positively with increasing simulated burn-up.
-O ( = Mo or U) ternary compoundsTokushima, Kazuyuki*; Tanaka, Kosuke; Kurosaki, Ken*; Gima, Hiromichi*; Muta, Hiroaki*; Uno, Masayoshi*; Yamanaka, Shinsuke*
Materials Research Society Symposium Proceedings, Vol.1215, p.151 - 156, 2010/10
The thermal diffusivities of Cs
MoO
and CsUO using samples fabricated by hot press and SPS techniques were measured by a laser flash method in the range from room temperature to 823 K for CsMoO and to 900 K for CsUO. The thermal conductivities of these cesium ternary oxides were quite low compared with UO and MOX fuel. This is consistent with previous findings. These results would be useful for evaluating the thermal performance of MOX fuels at the high burn-up region in the fast reactors.
Ce
)O
Osaka, Masahiko; Tanaka, Kosuke; Miwa, Shuhei; Kurosaki, Ken*; Uno, Masayoshi*; Yamanaka, Shinsuke*
Materials Research Society Symposium Proceedings, Vol.1215, p.199 - 203, 2010/10
Oxygen potentials of (ThCe)O were experimentally determined by means of thermogravimetric analysis as a function of non-stoichiometry at 1173 and 1273 K. Oxygen potentials of (ThCe)O at each temperature increased with increase of O/M ratio (= 2-x) and steep increases of the oxygen potentials toward O/M = 2 were observed. These characteristics are typical for non-stoichiometric fluorite-type actinides dioxides. The oxygen potentials of (ThCe)O were similar to those of CeOO when they were plotted as a function of average Ce valence.
Suzudo, Tomoaki; Yamaguchi, Masatake; Kaburaki, Hideo; Ebihara, Kenichi
Materials Research Society Symposium Proceedings, Vol.1215, 7 Pages, 2010/10
We applied ab initio calculation and an object kinetic Monte Carlo modeling to the study of He-vacancy cluster nucleation under irradiation in bcc and fcc Fe, which are surrogate materials for ferritic/martensitic and austenitic steels, respectively. The ab initio calculations provided parameters for the object kinetic Monte Carlo model, such as the migration energies of point defects and the dissociation energies of He and vacancy to He-vacancy clusters. We specially focused on the simulation of high He/dpa irradiation such as He-implantation into the materials and tracked the nucleation of clusters and the fate of point defects such as SIAs, vacancies, and He atoms. We found no major difference of He-vacancy cluster nucleation between bcc and fcc Fe when we ignore the intracascade clustering even if the migration energies of point defects are significantly different between the two crystals.
Yamaki, Tetsuya; Yamamoto, Shunya; Hakoda, Teruyuki; Koshikawa, Hiroshi
Materials Research Society Symposium Proceedings, Vol.1217, p.151 - 157, 2010/07
This study concerns our attempt to improve catalytic properties of nanoparticles of Pt and Pt-group metals by modification with ion beams. We expected that a completely high electronic excitation induced by high-energy ion beams could achieve new atomic arrangement and electronic states at the nanoparticle surface. Pt nanoparticles were prepared on a glassy carbon plate by a sputtering method and then irradiated with proton beams at energies of 0.38 and 10 MeV at room temperature. Cyclic voltammetry in a 0.5 M sulfonic acid aqueous solution suggested that the lower-energy beam irradiation enhanced the active surface area of the Pt nanoparticles, calculated from the coulombic charge for hydrogen adsorption. Thus, the nanoparticles will be modified by the proton-beam excitation so that they have higher surface reactivity. The mechanism determining this irradiation effect is still unclear at present, but we may discuss it in relation to a change in the interfacial crystal structure induced by the irradiation.
Suzudo, Tomoaki; Kaburaki, Hideo; Itakura, Mitsuhiro
Materials Research Society Symposium Proceedings, Vol.1225E (Internet), 7 Pages, 2010/00
We used a three-dimensional Monte Carlo method to investigate subgrain growth with different initial values for average grain-boundary misorientation, and found that abnormal grain growth emerges for relatively large average misorientation, with remaining cases revealing an exponential kinetics of subgrain growth. We also found that the growth exponent was 
4.4, and that it was virtually independent of the average misorientation. Self-similarity of the misorientation distribution was observed during growth.
Kadoyoshi, Tomoko; Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake
no journal, ,
Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Ebihara, Kenichi
no journal, ,
In this talk we study the interaction between hydrogen and grain boundaries of iron, and present simulation results of grain boundary decohesion of polycrystalline iron induced by hydrogen segregation. The model consists of two parts: (1) hydrogen diffusion and segregation on grain boundaries and (2) finite element model of bulk elasticity and coarse grained cohesive elements at grain boundaries. We have developed an extended FEM scheme which allows simulation of length scale in 10 micro meter and timescale in hours, and we could reproduce the time to failure in small hydrogen density case that is on the order of hours.
Machida, Akihiko; Saito, Hiroyuki; Katayama, Yoshinori; Aoki, Katsutoshi
no journal, ,
