Yotsuji, Kenji*; Tachi, Yukio; Sakuma, Hiroshi*; Kawamura, Katsuyuki*
Applied Clay Science, 204, p.106034_1 - 106034_13, 2021/04
Okubo, Takahiro*; Yamazaki, Akio*; Fukatsu, Yuta; Tachi, Yukio
Microporous and Mesoporous Materials, 313, p.110841_1 - 110841_11, 2021/01
Pore distributions in water-saturated Ca-montmorillonite were investigated using H NMR measurements under various dry densities (0.8 - 1.6 g/cm) and porewater salinity conditions (deionized water, 0.1 and 1 M CaCl), at the temperature range of 233 - 303 K. The volume fractions of the interlayer pore including two and three hydrated layers and the non-interlayer pore in compacted Ca-montmorillonite were quantified by NMR relaxometry including and distribution analysis, and were compared with NMR cryoporometry and X-ray diffractometry. These analysis provided consistent pictures on the pore distributions in compacted Ca-montmorillonite, in contrast to Na-montmorillonite. The main factor affecting the pore distribution in compacted Ca- and Na-montmorillonite is the density, whereas the effect of porewater salinity is relatively smaller. The effect of interlayer cations is also relatively smaller at higher density, although the differences in the pore structures are significant at low density.
Udagawa, Yutaka; Mihara, Takeshi; Taniguchi, Yoshinori; Kakiuchi, Kazuo; Amaya, Masaki
Annals of Nuclear Energy, 139, p.107268_1 - 107268_9, 2020/05
Takahashi, Hiroaki*; Tachi, Yukio
Applied Clay Science, 168, p.211 - 222, 2019/02
Microstructural and mass transport properties of compacted Na- and Cs-montmorillonites with different swelling properties were investigated by combining 3D microstructure analysis using nanofocus X-ray CT and diffusion measurement of HDO. The X-ray CT observations indicated that macropores in the dry state of compacted Na-montmorillonite are filled with gel phases, and the grain sizes of clay particles shifted toward smaller values through the saturation and swelling processes. By contrast, no gel phase and no decrease in the grain and pore volumes were observed for saturated Cs-montmorillonite. The geometrical factors of the macropores including tortuosity and geometric constrictivity of saturated Cs-montmorillonite determined by the X-ray CT was consistent with the corresponding values derived in the HDO diffusion test. In the case of Na-montmorillonite, the larger differences between the geometric factors evaluated by the X-ray CT and the diffusion tests can be explained by the electrostatic constrictivity factor and the additional geometrical factors in gel phase and interlayer that are smaller than the detection limit of the X-ray CT.
Yotsuji, Kenji*; Tachi, Yukio; Kawamura, Katsuyuki*; Arima, Tatsumi*; Sakuma, Hiroshi*
Nendo Kagaku, 58(1), p.8 - 25, 2019/00
Molecular dynamics (MD) simulations were conducted to investigate physical properties of water and cations in montmorillonite interlayer nanopores. The swelling behaviors and hydration states were firstly evaluated as functions of interlayer cations and layer charge. The diffusion coefficients of water and cations in interlayer nanopores were decreased in comparison with those in bulk water and came closer to those in bulk water when basal spacing increased. The viscosity coefficients of interlayer water estimated indicated a significant effect of viscoelectricity at 1- and 2-layer hydration states and higher layer charge of montmorillonite. These trends from MD calculations were confirmed to be consistent with existing measured data and previous MD simulation. In addition, model and parameter related to viscoelectric effect used in the diffusion model was refined based on comparative discussion between MD simulations and measurements. The series of MD calculations could provide atomic level understanding for the developments and improvements of the diffusion model for compacted montmorillonite.
Irisawa, Keita; Meguro, Yoshihiro
Journal of Nuclear Science and Technology, 54(3), p.365 - 372, 2017/03
Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito
Journal of Asian Ceramic Societies (Internet), 3(4), p.402 - 406, 2015/12
Hegeman, J. B. J.*; Van der Laan, J. G.*; Kawamura, Hiroshi; Mslang, A.*; Kupriyanov, I.*; Uchida, Munenori*; Hayashi, Kimio
Fusion Engineering and Design, 75-79, p.769 - 773, 2005/11
no abstracts in English
Onozawa, Atsushi; Kushida, Teruo; Kanazawa, Hiroyuki
JAERI-Tech 2004-061, 39 Pages, 2004/11
The swelling observed on irradiated fuels is caused by the accumulation of fission products and irradiation defects. The swelling ratio is changed along with radius region in the pellet due to burn up difference caused by that of neutron flux. To investigate the swelling behavior at the small area of the pellet, it is needed to measure the density of fuel fragments picked from an irradiated pellet. In this circumstance, once-through type densitometer was developed to measure the density of the small irradiated specimen precisely and to handle the samples easily with remote control systems. Several kinds of metallic and ceramic standard specimens are prepared to investigate the dependence of the sample weight, density and porosity on the accuracy. The results of characteristic examination using these specimens indicate that this densitometer has enough accuracy. In addition, some parts of this apparatus are controlled by motor drive units, which made it possible to measure the density full-automatically.
Tanaka, Kosuke*; Maeda, Koji*; Katsuyama, Kozo*; Inoue, Masaki*; Iwai, Takashi; Arai, Yasuo
Journal of Nuclear Materials, 327(2-3), p.77 - 87, 2004/05
no abstracts in English
Suzuki, Motoe; Uetsuka, Hiroshi; Saito, Hiroaki*
Nuclear Engineering and Design, 229(1), p.1 - 14, 2004/04
Mechanical load on cladding induced by fuel swelling in a high burn-up BWR type rod has been analyzed by a fuel performance code FEMAXI-6. The code has been developed for the analysis of LWR fuel rod behaviors in normal operation and transient conditions using FEM. During a power ramp for the high burn-up rod, instantaneous pellet swelling can significantly exceed the level that is predicted by a "steady-rate" swelling model, causing a large circumferential strain in cladding. This phenomenon has been simulated by a new swelling model to take into account the fission gas bubble growth, and as a result it has been found that the new model can give reasonable predictions on cladding diameter expansion in comparison with post-irradiation data. In addition, a pellet-clad bonding model which has been incorporated in the code to assume firm mechanical coupling between pellet outer surface and cladding inner surface has predicted the generation of bi-axial stress state in the cladding during ramp.
Lee, C. G.; Omura, Takahito*; Takeda, Yoshihiko*; Matsuoka, Saburo*; Kishimoto, Naoki*
Journal of Nuclear Materials, 326(2-3), p.211 - 216, 2004/03
Magnesium aluminate spinel of single crystal was irradiated with 60 keV Cu at a dose rate up to 100 A/cm, to a total dose of 310 ions/cm, in order to study changes in hardness and step-height swelling by high-flux implantation. Hardness determined by nano-indentation measurements steeply decreased with implantation. There is a strong negative correlation between dose-rate dependences of the hardness and the step-height swelling: the former decreases as the latter increases. The Rutherford Backscattering Spectrometry (RBS)/channeling measurements showed that the spinel is not completely amorphized over the dose-rate range in this study, and the radiation-induced softening observed is not due to amorphization. Results of optical absorbance suggested that radiation-induced point defects and their clusters on the anion sublattices of the spinel played an important role in the radiation-induced swelling under high-flux ion implantation.
Suzuki, Motoe; Saito, Hiroaki*; Iwamura, Takamichi
Nuclear Engineering and Design, 227(1), p.19 - 27, 2004/01
To assess the feasibility of the 31percentPu-MOX fuel rod design of reduced-moderation boiling water reactor in terms of thermal and mechanical behaviors, a single rod which is assumed to be irradiated in the core of RMWR up to 106 GWd/tHM has been analyzed by a fuel performance code FEMAXI-RM which is an extended version of FEMAXI-6 code. In the analysis, design specifications of fuel rod and irradiation conditions have been input, and available models of both MOX fuel and UO fuel have been used complementally. The results are: FGR is several tens of percent, rod internal pressure does not exceed the coolant pressure, and the highest fuel center temperature is 2400K, while cladding diameter increase caused by pellet swelling is within 1percent strain. These predictions suggest that the MOX fuel rod integrity will be held during irradiation in RMWR, though actual behavior of MOX pellet swelling requires to be investigated in detail.
Inoue, Masaki*; Iwai, Takashi; Arai, Yasuo; Asaga, Takeo*
Proceedings of GLOBAL2003 Atoms for Prosperity; Updating Eisenhower's Global Vision for Nuclear Energy (CD-ROM), p.1694 - 1703, 2003/11
no abstracts in English
Yamashita, Toshiyuki; Kuramoto, Kenichi; Shirasu, Noriko; Nakano, Yoshihiro; Akie, Hiroshi; Nagashima, Hisao; Kimura, Yasuhiko; Omichi, Toshihiko*
Journal of Nuclear Materials, 320(1-2), p.126 - 132, 2003/07
Two irradiation tests on the rock-like oxide (ROX) fuels, small disk-shape fuel targets and pellet-type fuels, were performed in order to clarify in-pile irradiation stabilities. Swelling, fractional fission gas release (FGR) and phase change were examined by puncture test, profilometry and ceramography. YSZ single-phase fuel showed an excellent irradiation behavior, ie. low fission gas release (less than 3%), negligible swelling and no appreciable restructuring. The particle dispersed fuels showed lower swelling and higher fission gas release than those of mechanically blended fuels. Spinel decomposition and subsequence restructuring in the spinel matrix fuels was observed for the first time in the present investigation. It would be possible to reduce the FGR of the spinel matrix fuels, if the maximum fuels temperature is limited below 1700 K where neither spinel decomposition nor restructuring was observed. Damaged area of spinel matrix due to fission fragment irradiation seemed to be confined to thin layers around the surface of YSZ particles.
Nakayama, Shinichi; Iida, Yoshihisa; Nagano, Tetsushi; Akimoto, Toshiyuki
Journal of Nuclear Science and Technology, 40(4), p.227 - 237, 2003/04
Leaching behavior of synthetic bituminized waste form was studied to inquire data for performance assessment of the geologic disposal. Laboratory-scale leaching tests were performed. The bituminized samples were contacted with an alkaline solution representing cement-contacting groundwater, with a saline solution simulating seawater for a possible repository construction at the coastal area, and with deionized water as reference. The release of soluble components, Na and Cs, was enhanced by the swelling, and considered to be diffusion controlled in the swelled layers of the specimens. The release of insoluble components such as Ba and Np was solubility-limited in addition to control by the progression of leaching. Neptunium, a redox-sensitive element, showed a distinct difference in release reflecting the difference between the anoxic and atmospheric conditions. The concentrations of Pu were below the detection limit ( mol/L) under all of the leaching conditions in this study.
Suzuki, Motoe; Uetsuka, Hiroshi
IAEA-TECDOC-CD-1345 (CD-ROM), p.217 - 238, 2003/03
A fuel performance code FEMAXI-6 has been developed for the analysis of LWR fuel rod behaviors. The code uses FEM analysis, and has incorporated thermal and mechanical models of phenomena anticipated in high burn-up fuel rods. In the present study, PCMI induced by swelling in a high burn-up BWR type fuel rod has been analyzed. During a power ramp for the high burn-up fuel, instantaneous pellet swelling been simulated by a new swelling model which has been installed in the code to take into account the FP gas bubble growth, and the new model can give satisfactory predictions on cladding diametral expansion. In addition, a pellet-clad bonding model in the code, which assumes firm mechanical coupling between pellet outer surface and cladding inner surface, predicts an increased tensile stress in the axial direction of cladding during the power ramp, indicating the generation of bi-axial stress state in the cladding.
Arai, Yasuo; Iwai, Takashi; Nakajima, Kunihisa; Nagashima, Hisao; Nihei, Yasuo; Katsuyama, Kozo*; Inoue, Masaki*
Proceedings of GLOBAL2003 Atoms for Prosperity; Updating Eisenhower's Global Vision for Nuclear Energy (CD-ROM), p.1686 - 1693, 2003/00
no abstracts in English
Ishihara, Masahiro; Baba, Shinichi; Hoshiya, Taiji; Shikama, Tatsuo*
Journal of Nuclear Materials, 307-311(Part2), p.1168 - 1172, 2002/12
no abstracts in English
Wakai, Eiichi; Sawai, Tomotsugu; Furuya, Kazuyuki; Naito, Akira; Aruga, Takeo; Kikuchi, Kenji; Yamashita, Shinichiro*; Onuki, Somei*; Yamamoto, Shunya; Naramoto, Hiroshi; et al.
Journal of Nuclear Materials, 307-311(Part.1), p.278 - 282, 2002/12
no abstracts in English