Experimental evidence for the significance of optical phonons in thermal transport of tin monosulfide

Wu, P.*; Murai, Naoki; Li, T.*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Kofu, Maiko; Nakajima, Kenji; Xia, K.*; Peng, K.*; Zhang, Y.*; et al.

New Journal of Physics (Internet), 25(1), p.013032_1 - 013032_11, 2023/01

https://doi.org/10.1088/1367-2630/acb3ed

Precipitation of minerals on rock kept in water with different calcium ion concentrations

Nara, Yoshitaka*; Kuwatani, Ryuta*; Kono, Masanori*; Sato, Toshinori; Kashiwaya, Koki*

Zairyo, 67(7), p.730 - 737, 2018/07

https://doi.org/10.2472/jsms.67.730

Information of confining ability of rock is important for the geological disposal of radioactive wastes. To maintain or improve the confining ability of rocks, it is important to seal pores and cracks. In this study, we investigated the precipitation of minerals on the rock surface. As rock samples, we used Berea sandstone and Toki granite in this study. It was shown that precipitation occurred on the surface of rock specimens kept in calcium hydroxide solution for 1 month if the concentration was high. Specifically, if the concentration of calcium hydroxide solution was higher than 300 mg/l, the precipitation occurred obviously. After keeping rock specimens in calcium hydroxide solution, the weight of the rock samples increased and the concentration of calcium ion decreased by the precipitation. It is considered that the calcium ion in water was used for the precipitation on rock surfaces. Since the precipitation has been recognized for rock surfaces, it is possible to seal pores and cracks in rocks. Therefore, it is also possible to keep or decrease the permeability of rocks by the precipitation of calcium compounds.

Stabilization of MOX dissolving solution at STACY

Kobayashi, Fuyumi; Sumiya, Masato; Kida, Takashi; Kokusen, Junya; Uchida, Shoji; Kaminaga, Jota; Oki, Keiichi; Fukaya, Hiroyuki; Sono, Hiroki

JAEA-Technology 2016-025, 42 Pages, 2016/11

JAEA-Technology-2016-025.pdf:17.88MB

A preliminary test on MOX fuel dissolution for the STACY critical experiments had been conducted in 2000 through 2003 at Nuclear Science Research Institute of JAEA. Accordingly, the uranyl / plutonium nitrate solution should be reconverted into oxide powder to store the fuel for a long period. For this storage, the moisture content in the oxide powder should be controlled from the viewpoint of criticality safety. The stabilization of uranium / plutonium solution was carried out under a precipitation process using ammonia or oxalic acid solution, and a calcination process using a sintering furnace. As a result of the stabilization operation, recovery rate was 95.6% for uranium and 95.0% for plutonium. Further, the recovered oxide powder was calcined again in nitrogen atmosphere and sealed immediately with a plastic bag to keep its moisture content low and to prevent from reabsorbing atmospheric moisture.

Role of van der Waals corrections in first principles simulations of alkali metal ions in aqueous solutions

Ikeda, Takashi; Boero, M.*

Journal of Chemical Physics, 143(19), p.194510_1 - 194510_7, 2015/11

https://doi.org/10.1063/1.4935932

By resorting to a novel implementation of the first-principles-based van der Waals correction based on maximally localized Wannier functions, we inspect its performance and assess its reliability for aqueous solutions of alkali metal ions. We find that van der Waals interactions, when added to the widely used revPBE gradient corrected functional, influence substantially both structural and dynamical properties of water molecules, with particular emphasis on the hydration shell of the alkali cations. These effects are more evident for strong structure-making and -breaking cationic species. Moreover, self-diffusion coefficients and reorientation correlation times of solvating water molecules change systematically, showing a trend in better agreement with experiments with respect to simulations neglecting the long-range dispersion contributions.

Possible oxygen reduction reactions for graphene edges from first principles

Ikeda, Takashi; Hou, Z.*; Chai, G.-L.*; Terakura, Kiyoyuki*

Journal of Physical Chemistry C, 118(31), p.17616 - 17625, 2014/08

https://doi.org/10.1021/jp5038365

N-doped carbon-based nanomaterials are attracting a great interest as promising Pt-free electrode catalysts for polymer electrolyte fuel cells (PEFCs). In this computational study, we demonstrate that N-doped graphene edges can exhibit enhanced catalytic activity toward oxygen reduction reactions by controlling their electron-donating and -withdrawing abilities, and basicity, resulting in higher selectivity of 4e reduction via inner and outer sphere electron transfer at edges in acidic conditions, respectively. Our simulations also show that 2e reduction occurs selectively in the presence of pyridinic N next to carbonyl O at zigzag edges. This study thus rationalizes the roles of doped N in graphenelike materials for oxygen reduction reactions.

NMR chemical shifts of N-bearing graphene

Wang, X.*; Hou, Z.*; Ikeda, Takashi; Terakura, Kiyoyuki*

Journal of Physical Chemistry C, 118(25), p.13929 - 13935, 2014/06

https://doi.org/10.1021/jp502190y

The NMR chemical shifts of possible N-containing moieties at edges and defects of graphene are investigated by using the first-principles method. Our computations show that pyridine-like and graphite-like N are rather easily identifiable using N NMR technique, in agreement with experiment. On the other hand, pyridinium-like N is hardly distinguished from pyrrole-like one because these N nuclei give nearly overlapping signals. However, our simulations suggest that H NMR is useful to discriminate between them; The NMR chemical shift of H directly bonded with pyridinium-like and pyrrole-like N is estimated as 0.8 and 10.8 ppm, respectively. The N NMR signals for various moieties at edges we considered are found to be similar to the corresponding ones at defects except for pyridine-like nitrogens. Conversely, the N NMR chemical shifts are altered sensitively by the degree of aggregation of pyridine-like N atoms both along armchair edges and at defect sites.

Extraction separation of Am(III) and Eu(III) with TPEN isomers and decanoic acid

Matsumura, Tatsuro; Takeshita, Kenji*

ACS Symposium Series, 933, p.261 - 273, 2006/07

https://doi.org/10.1021/bk-2006-0933.ch017

Three TPEN isomers with different positon of nitrogen donor in pyridyl groups, t2pen, t3pen and t4pen, were synthesized and the extraction separation of Am(III) and Eu(III) with these ligands and a fatty acid, decanoic acid, was investigated. All isomers were similar in the complexation in the aqueous phase, such as the protonation and the formation of metal complex, however, they showed different extraction behavior of Am and Eu. The synergistic extraction effect for Am was observed for t2pen and the high separation factor about 100 was measured, when 1:2. The value is comparable to that for the extraction system with a famous nitrogen-donor extractant, BTP. On the other hand, the extractability of other isomers was very low and no separation of Am and Eu was observed. Only t2pen, in which nitrogen donor in pyridyl groups is positioned in the vicinity of the skeletal structure (N-C-C-N structure) of ligand, is available for the extraction separation of Am.

Development of a simple reprocessing process using selective precipitant for uranyl ions; Engineering studies for precipitating and separating systems

Yamasaki, Kazuhiko*; Chikazawa, Takahiro*; Tamaki, Yoshihisa*; Kikuchi, Toshiaki*; Morita, Yasuji; Kawata, Yoshihisa*; Mineo, Hideaki; Koshino, Nobuyoshi*; Asanuma, Noriko*; Harada, Masayuki*; et al.

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 4 Pages, 2005/10

N-cyclohexyl-2-pyrrolidone (NCP), can selectively precipitate U(VI) ions in aqueous nitric acid solutions. Utilizing this property, we have been developing a simple reprocessing process of spent nuclear fuel based only on precipitation method. In the first precipitation step, only U is separated by precipitation in a yield of about 70%, and in the second precipitation step both U and Pu are recovered and separated from fission products (FP) and other transuranium elements (TRU). In the present study, a precipitator and a precipitate separator were designed and built up, and were tested with aspets of operationability and system performance.

Improvement of Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI), 2; Evaluation of numerical models by Cs deposition due to the Chernobyl nuclear accident

Terada, Hiroaki; Chino, Masamichi

Journal of Nuclear Science and Technology, 42(7), p.651 - 660, 2005/07

https://doi.org/10.3327/jnst.42.651

The prediction performance of WSPEEDI (Worldwide version of System for Prediction of Environmental Emergency Dose Information), which consists of the atmospheric dynamic model MM5 and the Lagrangian particle dispersion model GEARN-new, is evaluated by measurements of precipitation and surface deposition of Cs over Europe during the Chernobyl accident. It is concluded that MM5/GEARN-new can predict Cs deposition distribution with good accuracy when accurate precipitation is predicted by using a explicit scheme on cloud microphysics with ice phase processes. High-resolutional calculation is also conducted for the area surrounding Chernobyl by a nesting method. MM5/GEARN-new can predict quite a realistic distribution of Cs deposition around Chernobyl which was not calculated by the previous version.

Development of cold isostatic pressing graphite module for a heat-resistant lower hybrid current drive antenna

Maebara, Sunao; Goniche, M.*; Kazarian, F.*; Seki, Masami; Ikeda, Yoshitaka; Imai, Tsuyoshi*; Beaumont, B.*

Review of Scientific Instruments, 76(5), p.053501_1 - 053501_7, 2005/05

https://doi.org/10.1063/1.1891465

Development of a plasma facing module using Cold Isostatic Pressing Graphite (CIPG) had been done for a heat-resistant LHCD antenna. A thin stainless film (10m), molybdenum film (10m) and copper film (50m) are laid to overlap each other on the CIPG materials, the CIPG surfaces were successfully coated with copper layer by diffusion bonding method. This module has four waveguides and a water cooling channel, the length is 206 mm. High power long pulse operation was successfully achieved up to 250 kW (125 MW/m)/700s. The module has been successfully tested at a RF power density which is equivalent, in terms of RF electric field (5kV/cm), to the one proposed for the LHCD antenna of ITER-FEAT. The outgassing rate of the copper-coated CIPG is estimated to be 3.2-5.110 Pa.m/s.m at 100C, it is assessed that a pumping system is not required to evacuate the pressure in the LHCD antenna.