研究者データベース

小崎 完(コザキ タモツ)
工学研究院 応用量子科学部門 量子エネルギー工学
教授

基本情報

所属

  • 工学研究院 応用量子科学部門 量子エネルギー工学

職名

  • 教授

学位

  • 博士(工学)(北海道大学)
  • 工学修士(北海道大学)

ホームページURL

J-Global ID

研究キーワード

  • 地層処分   拡散   ベントナイト   放射性廃棄物   高レベル放射性廃棄物   活性化エネルギー   収着   セメント   鉄腐食生成物   電解研磨除染   周波数スペクトル   腐食   廃炉   ナトリウムイオン   電流変動スペクトル   廃止措置   オーバーパック   塩化物イオン   Ca^<2+>イオン   メゾスコピック構造   Np   モンモリロナイト   原子間力顕微鏡   原子炉材料学   原子炉廃止措置   放射性廃棄物管理   Nuclear reactor materials   Decommission and decontamination   Radioactive waste management   

研究分野

  • エネルギー / 原子力工学

職歴

  • 2019年04月 - 現在 北海道大学大学院工学研究院応用量子科学部門 教授、工学院・副学院長
  • 2013年01月 - 2019年03月 北海道大学大学院工学研究院エネルギー環境システム部門 教授
  • 2010年 - 2012年12月 - 工学研究院エネルギー環境システム部門 准教授
  • 2008年 - 2012年 北海道大学 工学(系)研究科(研究院) 准教授
  • 2005年 - 2010年 工学研究科エネルギー環境システム専攻 助教授
  • 2005年 - 2010年 Associate Professor
  • 2001年 - 2005年 工学研究科量子エネルギー工学専攻 助教授
  • 2001年 - 2005年 Associate Professor
  • 1991年 - 2001年 北海道大学助手(工学部原子炉材料学講座) 助手
  • 1991年 - 2001年 Research Associate
  • 1988年 - 1991年 日本原子力研究所東海研究所動力試験炉部研究員 研究員
  • 1988年 - 1991年 Researcher,Researcher, Department of JPDR (Japan Power Demonstration Reactor), Japan Atomic Energy Research Institute

学歴

  •         - 1988年   北海道大学   工学研究科
  •         - 1988年   北海道大学
  •         - 1986年   北海道大学   工学部   原子工学科
  •         - 1986年   北海道大学

所属学協会

  • 日本原子力学会   日本分析化学会   日本粘土学会   日本放射化学会   腐食防食協会   

研究活動情報

論文

  • Carlos Ordonez, Naoko Watanabe, Tamotsu Kozaki
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 57 7 813 - 824 2020年07月 [査読有り]
     
    Introduction: Studies on migration behaviors of colloidal materials through engineered and natural barriers are highly important for the safety assessment of radioactive waste repositories since the fate and transport of radionuclides may be significantly affected by interactions with colloids.Methods: Poly (ethylene glycol) coated gold nanoparticles (AuNPs) were used as a model colloid and the effects of the properties of AuNPs on their migration behaviors were investigated in batch and column experiments with silica sand.Results: Deposition of AuNPs on silica sand and aggregation of AuNPs were observed more for larger AuNPs despite the unfavorable conditions of both AuNPs and silica sand having overall negative surface charges. Sloping plateaus were observed in the breakthrough curves, suggesting that a limited number of sites arising from charge heterogeneities on silica sand may be responsible for attractive forces between AuNPs and silica sand. However, stronger affinity toward silica sand and with each other was observed for larger AuNPs which have more significant negative surface charges.Conclusions: The results suggest that interactions other than electrostatic and van der Waals (vdW) are controlling the migration behavior of AuNPs, including steric effects arising from the surface coating, thus need to be considered when assessing fate and transport of nanoparticles.
  • 重田 勝介, 小林 和也, 小崎 完, 渡邊 直子
    工学教育研究講演会講演論文集 2020 0 62 - 63 公益社団法人 日本工学教育協会 2020年
  • 小崎 完, 渡邊 直子, 小林 和也, 重田 勝介
    工学教育研究講演会講演論文集 2020 0 60 - 61 公益社団法人 日本工学教育協会 2020年
  • Jaka Rachmadetin, Masaya Mizuto, Shingo Tanaka, Tamotsu Kozaki, Naoko Watanabe
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 56 11 959 - 970 2019年11月 [査読有り][通常論文]
     
    In the safety assessment of radioactive waste disposal, it is critical to understand the porewater chemistry in compacted bentonite in order to predict long-term migration behavior of radionuclides in the engineered barrier. This study estimates the activity coefficients of dissolved ions in the porewater of compacted bentonite from the concentrations of ions at which CaCO3 precipitation occurred. Solutions containing CaCl2 and NaHCO3 were introduced under electrical potential gradient from the opposite sides of the compacted Na-bentonite packed at the dry density of 1.0kg/dm(3). After the electromigration, the spatial distribution of ions along the compacted bentonite sample was determined. Sequential extraction method was developed to distinctly determine the concentrations of free ions in the porewater and in solid phase in bentonite. The results show that the exchangeable Na+ ions were progressively replaced by the incoming Ca2+ ions, and the compacted bentonite sample can be divided into three zones: Ca-, Ca-/Na-, and Na-bentonite zones. Precipitates of CaCO3 were observed both in Ca- and Ca/Na-bentonite zones. The experimentally determined activity coefficients were at least smaller by a factor of 3 compared to the theoretical approximation calculated using PHREEQC code assuming dilute-solution conditions with no electrostatic interactions between ions and bentonite surface.
  • Toshihiko Ohnuki, Fuminori Sakamoto, Naofumi Kozai, Kenji Nanba, Hitoshi Neda, Yoshito Sasaki, Tadafumi Niizato, Naoko Watanabe, Tamotsu Kozaki
    ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS 21 7 1164 - 1173 2019年07月 [査読有り][通常論文]
     
    The fate of radioactive Cs deposited after the Fukushima nuclear power plant accident and its associated radiological impacts are largely dependent on its mobility from surface soils to forest ecosystems. We measured the accumulation of radioactive Cs in the fruit bodies of wild fungi in a forest at Iitate, Fukushima, Japan. The transfer factors (TFs) of radioactive Cs from soil to the fruit bodies of wild fungi were between 10(-2) and 10(2), a range similar to that reported for the fruit bodies collected in Europe after the Chernobyl accident and in parts of Japan contaminated by the nuclear bomb test fallout. Comparison of the TFs of wild mushroom and those of fungal hyphae of 704 stock strains grown on agar medium containing nutrients and Cs-137 showed that the TFs of wild mushroom were lower. The TF was less than 0.1 after the addition of the minerals zeolite, vermiculite, phlogopite, smectite, or illite of 1.0% weight to the agar medium. These results indicate that the presence of minerals decreases Cs uptake by fungi grown on the agar medium, and filamentous fungi still accumulate radioactive Cs even when minerals are present in the medium.
  • Naoko Watanabe, Ryohei Miyoshi, Tamotsu Kozaki, Shingo Tanaka, Satoshi Yanagihara
    PROCEEDINGS OF THE 26TH INTERNATIONAL CONFERENCE ON NUCLEAR ENGINEERING, 2018, VOL 7 2018年 [査読有り][通常論文]
     
    Decommissioning cost including radioactive waste management for 1100 MWe nuclear power plant (BWR) was analyzed comparing multiple scenarios. The total cost of decommissioning nuclear power plant was first estimated including the radioactive waste management cost for the standard Japanese decommissioning case with 30 years of the project duration including approximately 20 years in safe storage. It showed that the cost relating to waste management accounts for more than half of the total cost. Focusing on the radioactive waste management cost, the duration of safe storage was varied as a parameter. The timing of waste disposal was a key parameter determining the waste management cost due to the decay of radioactive nuclides resulting in the decrease in the total volume of the radioactive waste, and the change in the ratio of the waste volume in the three radioactive waste categories (intermediate-level, low-level, and extremely low-level). The total cost showed the minimum value at around 60 years of the project duration balancing the waste management cost and period dependent cost for safe storage.
  • Keiko Yamaji, Satoshi Nagata, Toshikatsu Haruma, Toshihiko Ohnuki, Tamotsu Kozaki, Naoko Watanabe, Kenji Nanba
    JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 153 112 - 119 2016年03月 [査読有り][通常論文]
     
    We found that root endophytes of Cs-137 accumulator plant produce siderophores, resulting in the desorption of Cs-137 from the contaminated soil collected at Fukushima, Japan. We selected an endemic Japanese deciduous tree, Eleutherococcus sciadophylloides (Franch. et Say), that accumulates high concentrations of Cs-137 and Mn. Root endophytic bacteria were isolated from E. sciadophylloides and microbial siderophore production was evaluated via chrome azurol S (CAS) Fe and CAS Al assays. Of the 463 strains that we isolated, 107 (23.1%) produced the siderophores. Using eight strains that showed high siderophore production in our assays, we examined desorption of Cs-137, Mn, Fe and Al by the bacterial culture filtrates from Cs-137-contaminated soil after decomposing the soil organic matter using hydrogen peroxide. We found Cs-137 and Mn desorption concomitant with Al and Fe desorption, as well as a decrease of pH. We also detected succinic acid, a well-known siderophore, in the bacterial culture filtrates of our two root endophytic bacteria. Our results strongly suggest that the root endophytic bacteria of E. sciadophylloides produce the siderophores that enhance Cs-137 and Mn desorption in the rhizosphere, making the resulting Cs-137 and Mn ions easier for E. sciadophylloides to absorb from the rhizosphere. (C) 2015 Elsevier Ltd. All rights reserved.
  • Toshihiko Ohnuki, Fuminori Sakamoto, Shinya Yamasaki, Naofumi Kozai, Hiroyuki Shiotsu, Satoshi Utsunomiya, Naoko Watanabe, Tamotsu Kozaki
    JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 144 127 - 133 2015年06月 [査読有り][通常論文]
     
    The accumulation of Cs by unicellular fungus of Saccharomyces cerevisiae in the presence of minerals has been studied to elucidate the role of microorganisms in the migration of radioactive Cs in the environment. Two different types of experiments were employed: experiments using stable Cs to examine the effect of a carbon source on the accumulation of Cs, and accumulation experiments of radioactive Cs from agar medium containing Cs-137 and zeolite, vermiculite, phlogopite, smectite, mica, or illite as mineral supplements. In the former type of experiments, the Cs-accumulated cells were analyzed by scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDS). In the latter type, the radioactivity in the yeast cells was measured by an autoradiography technique.When a carbon source was present, higher amounts of Cs accumulated in the cells than in the resting condition without a carbon source. Analyses with SEM-EDS showed that no mineral formed on the cell surface. These results indicate that the yeast cells accumulate Cs by adsorption on the cell surface and intracellular accumulation. In the presence of minerals in the agar medium, the radioactivity in the yeast cells was in the order of mica > smectite, illite >> vermiculite, phlogopite, zeolite. This order is inversely correlated to the ratio of the concentration of radioactive Cs between the minerals and the medium solution. These results strongly suggest that the yeast accumulates radioactive Cs competitively with minerals. (C) 2015 Elsevier Ltd. All rights reserved.
  • Hiroaki Takiya, Naoko Watanabe, Tamotsu Kozaki, Seichi Sato
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 52 5 728 - 738 2015年05月 [査読有り][通常論文]
     
    Apparent diffusion coefficients (D-a) of water and activation energies (E-a) of diffusion in hardened cement pastes (HCPs) were determined as a function of water-to-cement (w/c) ratio (0.36-0.60) and temperature (293-323K) using HTO and (H2O)-O-18 as tracers. The values of D-a and E-a ranged from 1.1x10(-11) to 1.7x10(-10) m(2) s(-1) and from 21.5 to 31.3 kJ mol(-1), respectively. No significant difference between the D-a values of HTO and (H2O)-O-18 suggests that water predominantly diffuses as H2O molecule and dissociation of water is not significant even at high pH range in HCP. The values of E-a at low w/c ratio were higher than in bulk liquid water, suggesting a contribution of a different water regime, such as supercooled bulk water. Two simple models consisting of capillary and gel pores were considered to estimate the volume ratio of gel pores to total pores by optimizing the model to fit with the experimental data. The result suggests that HCP has a pore network mostly consisting of capillary pores with some very narrow pores plugged with hydrates, where HTO must diffuse through gel pores. This view of the HCP pore network was made available through analysis of E-a values.
  • Aric G. Newton, Kideok Kwon, Naoko Watanabe, Tamotsu Kozaki, Garrison Sposito
    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 248 2014年08月 [査読有り][通常論文]
  • Eun Jin Seo, Chan Woo Jeong, Seichi Sato, Tamotsu Kozaki
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 50 5 534 - 545 2013年05月 [査読有り][通常論文]
     
    The concept of the representative person recommended by the International Commission on Radiological Protection (ICRP) is difficult to apply to dose assessment to the public because the representative habit data could not be determined in advance for general radiation exposure situations. So, a stylized method for constructing habit data of the representative person is needed to ensure consistency and validity of the dose estimation. This paper presents a generalized model of the representative habit data based on optimization by a linear programming technique to handle complex environmental exposure situations such as radioactive waste disposal. The model is devised in such a way that it can fully embody the ICRP's criteria for the representative person by ensuring the upper 5% exposure in the population and it is applicable to general exposure systems. The model was illustrated for Korea's low- and intermediate-level radioactive waste disposal system to show its applicability to complex exposure systems with multiple scenarios and pathways.
  • Fumio Hirano, Seichi Sato, Tamotsu Kozaki, Yaohiro Inagaki, Tomohiko Iwasaki, Toshiaki Ohe, Kazuyuki Kato, Kazumi Kitayama, Shinya Nagasaki, Yuichi Niibori
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 49 3 310 - 319 2012年03月 [査読有り][通常論文]
     
    The thermal impacts of hull and end piece wastes from the reprocessing of MOX spent fuels burned in LWRs on repository performance were investigated. The heat generation rates in MOX spent fuels and the resulting heat generation rates in hull and end piece wastes change depending on the history of MOX fuels. This history includes the burn-up of UO2 spent fuels from which the Pu is obtained, the cooling period before reprocessing, the storage period of fresh MOX fuels before being loaded into an LWR, as well as the burn-up of the MOX fuels. The heat generation rates in hull and end piece wastes from the reprocessing of MOX spent fuels with any of those histories are significantly larger than those from UO2 spent fuels with burn-ups of 45 GWd/THM. If a temperature below 80 degrees C is specified for cement-based materials used in waste packages after disposal, the allowable number of canisters containing compacted hull and end pieces in a package for 45 and 70 GWd-MOX needs to be limited to a value of 0.4-1.6, which is significantly lower than 4.0 for 45 GWd-UO2.
  • Shingo Tanaka, Natsuko Noda, Seichi Sato, Tamotsu Kozaki, Haruo Sato, Koichiro Hatanaka
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 48 3 454 - 462 2011年03月 [査読有り][通常論文]
     
    Electromigration studies of Cl-36(-) ions and Na-22(+) ions, and electro-osmosis of water traced with HTO and (H2O)-O-18 were conducted with water-saturated compacted sodium montmorillonite having dry densities from 0.8 to 1.6 Mg/m(3). The mobilities and dispersivities for each species were obtained from the apparent electromigration velocities and hydrodynamic dispersion coefficients, respectively. When corrected by water flow, the apparent diffusion coefficients of Cl- ions obtained from the Einstein relation are in good agreement with the coefficients obtained from an earlier conventional diffusion experiment in the high dry densities (above 1.3 Mg/m(3)). This result suggests that the migration pathways of Cl- ions are nearly identical to those of water above 1.3 Mg/m(3). The former diffusion coefficient is smaller than the latter in the low dry densities (below 1.3 Mg/m(3)), suggesting that Cl- ions migrate in the region distant from the montmorillonite sheets. In contrast, for Na+ ions, the obtained D-a values without water flow correction are in good agreement with conventional values at all dry densities. This suggests that Na+ ions migrate mainly in the interlayer and the vicinity of montmorillonite sheets. The dispersivities increase with increasing dry densities for all species. This corresponds to a geometrical complexity that increases with increasing dry density.
  • Hiroshi Ito, Naoyuki Miyasaka, Tamotsu Kozaki, Seichi Sato
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 47 11 1005 - 1010 2010年11月 [査読有り][通常論文]
     
    Hydraulic conductivities were determined for compacted Fe(III)-montmorillonite sample. The Fe(III)montmorillonite sample used in this study, which was prepared by the ion-exchange treatment of Na-montmorillonite in FeCl3 solution, contains less than 20% of Na+ ions as exchangeable cations and negligibly small amounts of iron precipitates. The measured hydraulic conductivities of compacted Fe(III)-montmorillonite were determined to be the order of 10(-9), 10(-11), and 10(-13) ms(-1) at dry densities of 0.80, 1.01, and 1.20 Mg m(-3), respectively. These values were found to be kept constant during the experimental period, suggesting no significant change in the physicochemical properties of Fe(III)-montmorillonite during the experiment. When compared with Na-montmorillonite, remarkably high values of hydraulic conductivities were found for Fe(III)-montmorillonite at the dry densities of 0.8 and 1.0 Mg m(-3). On the other hand, almost the same value of hydraulic conductivity was obtained at the dry density around 1.2 Mg m(-3). This different effect of exchangeable cations on the hydraulic conductivity of montmorillonite could be attributed to the different sizes of macropores in compacted montmorillonite and/or the different thicknesses of electrical double layers formed over montmorillonite sheets.
  • Satoshi Tomioka, Tamotsu Kozaki, Hidenori Takamatsu, Natsuko Noda, Shusuke Nisiyama, Naofumi Kozai, Satoru Suzuki, Seichi Sato
    APPLIED CLAY SCIENCE 47 1-2 65 - 71 2010年01月 [査読有り][通常論文]
     
    Compacted bentonite, of which the major clay mineral is montmorillonite, is a candidate buffer material for geological disposal of high-level radioactive waste. In this study, a microfocus X-ray computed tomography (micro-CT, X-ray microscope), which enables non-destructive, three-dimensional observation of the interior microstructure of a sample with high resolution (several microns), examined compacted montmorillonite samples under dry and water-saturated states. The images thus obtained were analyzed by a computer code developed for this study to obtain the information on the size and shape of montmorillonite grains in the samples before and after the water saturation. From the results of the image analysis, it can be supposed that the outer montmorillonite sheets of grains swelled and formed a gel, whereas the inner montmorillonite sheets did not change significantly in the water-saturation process. (C) 2008 Elsevier B.V. All rights reserved.
  • T. Kozaki, T. Sawaguchi, A. Fujishima, S. Sato
    PHYSICS AND CHEMISTRY OF THE EARTH 35 6-8 254 - 258 2010年 [査読無し][通常論文]
     
    Compacted Na-bentonite, of which the major mineral is montmorillonite, is a candidate buffer material for the geological disposal of high-level radioactive waste. A potential alteration of the bentonite in a repository is the partial replacement of the exchangeable cations of Na+ with Ca2+. The Ca2+ cations could be released from cementitious materials and diffuse into the buffer material in the repository. In this study, to evaluate the alteration that could reduce the performance of the bentonite buffer, the apparent diffusion coefficients of HTO and Ca2+ ions were determined from non-steady, one-dimensional diffusion experiments using Na- and Ca-montmorillonite mixtures with different ionic equivalent fractions of Ca2+ ions. The apparent diffusion coefficient of HTO at a dry density of 1.0 Mg m(-3) slightly increased with an increase in the ionic equivalent fraction of Ca2+ ions. However, the apparent diffusion coefficient of Ca2+ and the activation energy for diffusion at the same dry density were independent of the ionic equivalent fraction of Ca2+ ions. These findings suggest that unlike HTO, which can be postulated to diffuse mainly in pore water, Ca2+ ion diffusion could occur predominantly in interlayer spaces, of which the basal spacing was determined to be constant by the XRD technique. (C) 2010 Elsevier Ltd. All rights reserved.
  • T. Kamiyama, N. Miyamoto, S. Tomioka, T. Kozaki
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 605 1-2 91 - 94 2009年06月 [査読無し][通常論文]
     
    Neutron resonance absorption spectroscopy (N-RAS) with a pulsed neutron source can distinguish the dynamics of individual nuclides having resonance peaks on epithermal neutron region. The analyzed internal information of nuclide presence and its effective temperature can be reconstructed as distributions over the object cross-section using computed tomography (CT). Because some of the resonance absorption cross-sections have very large values, N-RAS could match the small neutron pulsed source by its high sensitivity. In this study, we have constructed a new instrument of N-RAS on a compact electron linac neutron source. Resonance absorption measurements and CT imaging with the instrument have succeeded for some kinds of nuclide. (C) 2009 Elsevier B.V. All rights reserved.
  • Fumio Hirano, Seichi Sato, Tamotsu Kozaki, Yaohiro Inagaki, Tomohiko Iwasaki, Toshiaki Ohe, Kazuyuki Kato, Kazumi Kitayama, Seishi Torikai, Yuichi Niibori, Shinya Nagasaki
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 46 5 443 - 452 2009年05月 [査読有り][通常論文]
     
    The thermal impacts of hull and end piece wastes from high-burn-up UO2 and MOX fuels on a conventional disposal system were investigated. The heat generation rates in the canister containing these wastes were obtained using burn-up calculations of PWR fuels. For wastes from spent MOX fuel, the heat generation rates increase to 3.2-4.5 times that from present-day burn-up spent UO2 fuel when these canisters are disposed of. The temperature distributions in the area around the disposal galleries for these wastes were obtained using two-dimensional thermal analyses by assuming a maximum 80 degrees C temperature exposure of the cement mortar. For wastes from spent MOX fuel, the temperature of the surrounding rock remains at about 60-70 degrees C after disposal, even after 1,000 years. In this case, the number of canisters loaded in a waste package must be decreased from four to around one. This increases the number of waste packages to contain the required number of canisters. It will be important to apply alternative approaches to increase the amount of wastes in a waste package by reducing the amounts of FPs and actinides adhering to hulls and to optimize the layout design of galleries, which may be done by significantly increasing the distance separating neighboring galleries.
  • Jayappa Manjanna, Tamotsu Kozaki, Seichi Sato
    APPLIED CLAY SCIENCE 43 2 208 - 217 2009年02月 [査読有り][通常論文]
     
    In the deep geological repository of high-level nuclear waste (HLW), the interaction of carbon steel (Fe) overpack container and the back-fill clay mineral, montmorillonite (mont), is an important issue to be clarified in view of the long-term performance of clay mineral as an engineered barrier. To arrive at some understanding of the altered clay at the Fe/clay interface, Fe(III)-mont is used here for preliminary investigation to see if there is any considerable difference in the basic properties, mainly diffusion of tracers with respect to Na-mont, although Fe(III)-mont is not a realistic analogue of altered clay in the reducing chemistry conditions anticipated in the subsurface of HLW, unlike Fe(II)-mont which is difficult to prepare and handle in the ambient atmosphere due to its gradual oxidation. Fe(III)-mont was prepared by the conventional cation exchange method with 0.4 M FeCl(3) solution. The total Fe(III) ions adsorbed was about 1.42 meq/g, while the CEC of parent clay was 1.2 meq/g. Thus similar to 18% excess Fe (III) ions were present presumably as iron oxy hydroxide, i.e., about 2 wt.% with respect to FeOOH or Fe(OH)(3) in the bulk sample. The sample was further characterized by X-ray diffraction (XRD), infrared (IR), thermogravimetry, magnetization, and the methylene blue (MB) adsorption. From these conventional techniques, the minor Fe-oxide phase associated with the Fe(III)-mont could not be detected, although we cannot rule out its existence. The paramagnetic behavior of Fe(III)-mont was evident from the Curie-Weiss plot (300 K down to 5 K). Some basic properties like osmotic swelling, diffusion of tracers and thermal stability are evaluated here. The osmotic swelling of Fe(III)-mont was very low, similar to 5 ml/g, while that of Na-mont was >40 ml/g. Apparent diffusion coefficient (D(a)) of tracers ViZ., (22)Na(-), HTO and (36)Cl(-) was determined using compacted (dry density, rho(d) = 1.0, 1.6 Mg m(-3)), water-saturated Fe(III)-mont. There was no considerable change in D(a) of these tracers in Fe(III)-mont when compared to that in Na-mont, in spite of higher pore water availability in Fe(III)-mont due to reduced swelling. For instance at rho(d) = 1.6 and 25 degrees C, D(a)(x10(-11) m(2)/s) of (22)Na(+)(2.6) was same as that in Na-mont whereas D(a) of HTO (11.4) and (36)Cl(-) (1.0) have varied marginally. For comparison, the corresponding D(a)(x10(-11) m(2)/s) values in Na-mont were 2.7, 7.2 and 3.4, respectively. Also, at rho(d) = 1.6, the diffusion activation energy (E(A.) kJ mol(-1)) of HTO (17.5) in Fe (III)-mont was comparable to that in free water, however, EA of (36)Cl(-) (13.1) was remarkably low, which may be ascribed to the so-called 'anion exclusion' effect. Furthermore, thermal stability of Fe(III)-mont indicated the existence of interlayer Fe(III) in the ionic state up to similar to 190 degrees C, based on the XRD and MB adsorption test. On heating to > 200 degrees C, irreversible dehydration of interlayer cations occurred, and the chemisorption of NH(3) indicated two distinct acid sites at about 300 degrees C and 600 degrees C. (C) 2008 Elsevier B.V. All rights reserved.
  • T. Kamiyama, N. Miyamoto, S. Tomioka, T. Kozaki
    2009 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC) 1266 - 1270 2009年 [査読無し][通常論文]
  • Akihiro Hara, Tamotsu Kozaki, Seichi Sato, Toshiyuki Nakazawa, Hiroyasu Kato
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 12 A352 - A352 2008年07月 [査読有り][通常論文]
  • Tomohiro Higashihara, Kumiko Kinoshita, Yorimasa Akagi, Seichi Sato, Tamotsu Kozaki
    PHYSICS AND CHEMISTRY OF THE EARTH 33 S142 - S148 2008年 [査読有り][通常論文]
     
    Diffusion of radionuclides in bentonite buffer material has been studied by many researchers. The nuclides in a form of ion diffuse in the bentonite satisfying electro-neutrality. It is important to examine major charge carriers as a possible counter ion for understanding the diffusion behavior in the bentonite. In this study, transport numbers of Na(+) ions, which are the major exchangeable cations in the sodium montmorillonite, which is the major mineral of bentonite, were experimentally determined as a function of dry density by a moving boundary method, using electromigration and electro-osmosis in the montmorillonite. The transport numbers were determined based on the electromigration of the Na(+) ions, because the contribution of the electro-osmosis to the migration of the cations is considered to be negligible. The effect of pore water ionic strength in the montmorillonite on the transport number was also examined. It was found that the transport numbers did not depend on the dry density and were nearly equal to 1. Therefore, the Na(+) ions behave as the predominant charge carrier in the montmorillonite. When salinity was increased up to 0.5 M, the transport numbers decreased down to 0.8. This suggests that the major part of the charge was carried by the Na(+) ions but the contribution of other ions to the charge carrier increased gradually with increase of the ionic strength. (C) 2008 Elsevier Ltd. All rights reserved.
  • Shingo Tanaka, Natsuko Noda, Tomohiro Higashihara, Seichi Sato, Tamotsu Kozaki, Haruo Sato, Koichiro Hatanaka
    PHYSICS AND CHEMISTRY OF THE EARTH 33 S163 - S168 2008年 [査読有り][通常論文]
     
    As migration media for radionuclides in water-saturated compacted sodium montmorillonite (Kunipia-F) at dry densities from 0.8 to 1.6 Mg/m(3), water migration under electric potential gradient was investigated as well as water diffusion, using (H2O)-O-18 as a tracer. The concentration of (H2O)-O-18 was measured in terms of delta O-18, which corresponds to a relative difference of (O-18/O-16) between a specimen and a standard, by a mass spectrometric method coupled with isotope exchange. The concentration profiles from the diffusion experiments were well described by the Fick's second law. By least-squares fits of the profile, diffusion coefficients, D-a, were obtained. The profiles from the migration experiments under the potential gradient were well reproduced by an advection-dispersion equation, and hydraulic dispersion coefficients, D-h, and migration velocities, V, were obtained. From the quantities, D-a, D-h, and V, mechanical dispersion coefficients, D-m, and dispersivities, alpha, were also obtained. The dispersivity is considered as a geometrical property of medium for chemical species. They were used to discuss migration pathways in water-saturated compacted montmorillonite, compared to available data of a for helium, 22Na(+), 85Sr(2)*, and Cl-36(-). It is found that the species are classified into three regions by the value of a; the positively charged ions in the smallest region of alpha, (H2O)-O-18 in intermediate region, and electrically neutral helium in the largest region. Based on these results, migration behavior under electric potential gradient was interpreted for water and the species. (C) 2008 Elsevier Ltd. All rights reserved.
  • Tamotsu Kozaki, Jinhong Liu, Seichi Sato
    PHYSICS AND CHEMISTRY OF THE EARTH 33 14-16 957 - 961 2008年 [査読有り][通常論文]
     
    Compacted bentonite, the major mineral being montmorillonite, is a candidate buffer material for geological disposal of high-level radioactive waste. The diffusion behavior of radionuclides in the compacted montmorillonite is an important issue to be clarified for the safety assessment of geological disposal. In this study, one-dimensional, non-steady diffusion experiments using Na-22 at different diffusion temperatures and the measurement of the basal spacings by XRD were conducted for Na-montmorillonite saturated with NaCl solutions of different concentrations. Some basal spacings of the montmorillonite were found to decrease from 1.88 to 1.56 nm as the NaCl concentration increased from 0 to 0.1 M. The apparent self-diffusion coefficients at 298 K obtained in this study slightly increased as the NaCl concentration increased from 0 to 0.5 M, while the activation energies, calculated from the temperature dependences of the diffusion coefficients, were found to be 14, 22, and 17 kJ mol(-1) at NaCl concentrations of 0, 0.1, and 0.5 M, respectively. These NaCl concentration dependences of the diffusion coefficients and their activation energies can be explained by assuming three independent diffusion processes (diffusion in pore water, on external surface of montmorillonite, and in interlayer of montmorillonite). (c) 2008 Elsevier Ltd. All rights reserved.
  • Naofumi Kozai, Koichi Inada, Yoshifusa Adachi, Sachi Kawamura, Yusuke Kashimoto, Tamotsu Kozaki, Seichi Sato, Toshihiko Ohnuki, Takuro Sakai, Takahiro Sato, Masakazu Oikawa, Fumitaka Esaka, Hisayoshi Mitamura
    JOURNAL OF SOLID STATE CHEMISTRY 180 8 2279 - 2289 2007年08月 [査読有り][通常論文]
     
    Fe2+ -montmorillonite with Fe2+ ions occupying cation exchange sites is an ideal transformation product in bentonite buffer material. In our previous study on preparation and characterization of Fe 21 -montmorillonite, the montmorillonite sample that adsorbed Fe2+ ions on almost all of the cation exchange sites was prepared using a FeCl2 solution under an inert gas condition [N. Kozai, Y. Adachi, S. Kawamura, K. Inada, T. Kozaki, S. Sato, H. Ohashi, T. Ohnuki, T. Banba, J. Nucl. Sci. Technol. 38 (2001) 1141]. In view of the unstable nature of iron(H) chemical species, this study attempted to determine the potential contaminant iron chemical species in the sample. Nondestructive elemental analysis revealed that a small amount of chloride ions remained dispersed throughout the clay particles. The chloride ion retention may be due to the adsorption of FeCl+ ion pairs in the initial FeCl2 solution and the subsequent containment of the Cl- ions that are dissociated from the FeCl+ ion pairs during excess salt removal treatment. Two explanations are advanced for the second process: the slow release of the remaining Cl- ions from the collapsed interlayer of the montmorillonite, and the transformation of a minor fraction of the remaining FeCl+ ion pairs to iron(III) hydroxide chloride complexes having low solubility. (C) 2007 Elsevier Inc. All rights reserved.
  • Jayappa Manjanna, Tamotsu Kozaki, Naofumi Koza, Seichi Sato
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 44 7 929 - 932 2007年07月 [査読有り][通常論文]
  • Masahide Takano, Susumu Tagami, Kazuo Minato, Tamotsu Kozaki, Seichi Sato
    JOURNAL OF ALLOYS AND COMPOUNDS 439 1-2 215 - 220 2007年07月 [査読有り][通常論文]
     
    ZrN is a possible candidate for the diluent material for the nitride fuels containing transuranium elements. In the present study, ZrN, DyN and their solid solutions (DyxZr1-x)N (x = 0.2, 0.5 and 0.8) as the analogous fuel material, were prepared by powder metallurgical method through the hydrides. Lattice thermal expansions of these nitrides were measured by a high-temperature X-ray diffraction method from room temperature to 1414 K. The average linear thermal expansion coefficients from 293 to 1300 K for these nitrides increased with Dy fraction x from 7.86 x 10(-6) K-1 (ZrN) to 9.54 x 10(-6) K-1 (DyN). The effects of the impurities and hypostoichiometry on the lattice parameters and thermal expansions are discussed. On the analogy with the results on the composition dependence of the thermal expansion coefficients, the preferable effect of ZrN as the diluent material is suggested. (c) 2006 Elsevier B.V. All rights reserved.
  • Ken-ichi Shiramine, Shunichi Muto, Tamaki Shibayama, Norihito Sakaguchi, Hideki Ichinose, Tamotsu Kozaki, Seichi Sato, Yoshiaki Nakata, Naoki Yokoyama, Masafumi Taniwaki
    JOURNAL OF APPLIED PHYSICS 101 3 033527  2007年02月 [査読有り][通常論文]
     
    The tip artifact in atomic force microscopy (AFM) observations of InAs islands was evaluated quantitatively. The islands were grown in the Stranski-Krastanow mode of molecular beam epitaxy. The width and height of the islands were determined using transmission electron microscopy (TEM) and AFM. The average [(1) over bar 10] in-plane width and height determined using TEM excluding native oxide were 22 and 7 nm, respectively; those determined using AFM including the oxide were 35 and 8 nm, respectively. The difference in width was due to the oxide and the tip artifact. The sizes including the oxide were deduced from TEM observations to be a width of 27 nm and a height of 6 nm with correction for the thickness of the oxide. The residual difference of 8 nm between the width determined using AFM and that determined using TEM including the oxide was ascribed to the tip artifact. The results enable us to determine the actual size of the islands from their AFM images. (c) 2007 American Institute of Physics.
  • T Kozaki, A Fujishima, N Saito, S Sato, H Ohashi
    ENGINEERING GEOLOGY 81 3 246 - 254 2005年11月 [査読無し][通常論文]
     
    As a part of the safety assessment of the geological disposal of high-level radioactive waste, the effects of dry density and exchangeable cations on the diffusion process of Na+ ions in compacted bentonite were studied from the viewpoint of the activation energy for diffusion. The apparent self-diffusion coefficients of Na+ ions in compacted Na-montmorillonite and in a Na- and Ca-montmorillonite mixture were determined by one-dimensional, non-steady diffusion experiments at different temperatures and dry densities. A unique change in activation energy as a function of dry density was found for the Na+ ions in compacted Na-montmorillonite. The activation energy suddenly decreased from 18.1 to 14.1 kJ mol(-1) as the dry density increased from 0.9 to 1.0 Mg m(-3), whereas it increased to 24.7 kJ mol(-1) as the dry density increased to 1.8 Mg m(-3). Examination of the effect of exchangeable cations on the activation energies determined that the activation energies were almost constant, approximately 25 kJ mol(-1), for the montmorillonite specimens at a dry density of 1.8 Mg m(-3). However, three different activation energy values were obtained at a dry density of 1.0 Mg m(-3). These findings cannot be explained by the conventional diffusion model (the pore water diffusion model), which suggests that the predominant diffusion process alternates among pore water diffusion, interlayer diffusion, and external surface diffusion. (c) 2005 Elsevier B.V. All rights reserved.
  • T Higashihara, H Shibuya, S Sato, T Kozaki
    ENGINEERING GEOLOGY 81 3 365 - 370 2005年11月 [査読無し][通常論文]
     
    It is important to clarify the migration behavior of hydrogen gas dissolved in water-saturated, compacted bentonite, which is a promising material for geologic disposal of high-level waste and TRU waste disposal. The diffusion coefficients of helium, which can be detected under extremely low background conditions, in water-saturated, compacted Na-montmorillonite were determined as a function of temperature by a transient diffusion method. The activation energies for diffusion of helium were then obtained. The activation energies were from 6.9 +/- 4.8 to 19 +/- 2.8 kJ mol(-1) and were regarded to be independent of dry density. The activation energies of helium in water-saturated Na-montmorillonite were roughly equal to those in bulk water, 14.9 kJ mol(-1), and in ice, from 11 to 13 kJ mol(-1). It is possible that helium diffuses not only in pore water but also in interlayer water. (c) 2005 Elsevier B.V. All rights reserved.
  • T Sakuragi, S Sawa, S Sato, T Kozaki, T Mitsugashira, M Hara, Y Suzuki
    JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY 265 3 349 - 353 2005年08月 [査読有り][通常論文]
     
    In the wide pH range of 4 to 10, distribution ratios of Am(III)-humate species to free Am(III) ions (D-AmHA = [Am(III)HA]/[Am(III)](free)) were determined at 10 ppm (4.7 center dot 10(-5) eq/dm(3)) of humic acid and 0.1M NaClO4 by a cation-exchange equilibrium method under N-2 atmosphere. The D-AmHA was insensitive to an increase in pH (logD(AmHA) approximate to 2.6-2.8), which indicates the formation of mixed hydroxo-humate complexes. The present D-AmHA value is larger than the estimated value from available stability constants for ternary complexations by spectroscopic analysis (1.4-2.1) and is markedly smaller than that of Eu(III) obtained by the dialysis method (3.7-8.0) reported in the literatures. The D-AmHA obtained in the present study is widely applicable to estimate the actinide(III) and lanthanide(III) sorption on minerals in the presence of humic and fulvic acids.
  • T Higashihara, K Kinoshita, S Sato, T Kozaki
    APPLIED CLAY SCIENCE 26 1-4 91 - 98 2004年08月 [査読無し][通常論文]
     
    Sodium ions spiked with Na-22 as a tracer were migrated by electromigration and electro-osmosis in the water-saturated, compacted Na-montmorillonite at dry densities 1.0 X 10(3) kg m(-3), under an electric potential gradient. Dissolved helium was also migrated by electro-osmosis in the montmorillonite. After migration, concentration profiles of the sodium ions and helium were obtained by gamma-spectrometry and mass-spectrometric methods, respectively. From the profiles of both chemical species, not only migration due to electrokinetic phenomena but also mechanical dispersion was observed in the montmorillonite. The dispersion coefficients, D-i, and apparent migration rates, U-i(a), of Na-22 and helium were found in the compacted Na-montmorillonite at 1.0 X 10(3) kg m(-3). The migration of helium in the montmorillonite under an electric potential gradient reflects that of water because helium migrates as an electrically neutral species. The parameters D-Hc(m), U-He(a), and alpha(He), correspond to those of water. The mechanical dispersion coefficients, D-Na(m), of Na-22(+) ions are much smaller than those of water obtained by helium. The dispersivity parameters, alpha(Na), for Na-22(+) obtained from these D-Na and U-Na(a) values are 10(-5) in and those for water (alpha(He)) are 10(-3) m. This indicates that Na-22(+) ions migrate in different spaces than water in the compacted montmorillonite under a potential gradient. This finding suggests that the migration of Na+ ions occurs in the interlayer and/or on the outer surfaces of the montmorillonite; whereas dissolved helium migrates in the pore water. (C) 2004 Elsevier B.V. All rights reserved.
  • T Sakuragi, S Sato, T Kozaki, T Mitsugashira, P Hara, Y Suzuki
    RADIOCHIMICA ACTA 92 9-11 697 - 702 2004年 [査読無し][通常論文]
     
    The uptake of Am(III) and Eu(III) on hematite (1.0 g/L) in the presence of humic acid (HA: 4.7 x 10(-5) M) was investigated at ionic strengths of 0.05 to 0.5 M (NaClO4) in the pH range of 4 to 10. The sorption behavior of Am(III) was similar to that of Eu(III). The Am(III) and Eu(III) exhibited 100% retention oil the solid in the entire pH region studied at hi-h ionic strength (0.5 M). As the ionic strength was decreased below 0.1 M, Am(III) and Eu(III) sorption which was complete at low pH values decreased stepwise with increasing pH from 5 to 7. In order to test the additivity and to understand the solid-water interface reactions for Am(III) sorption in ternary systems. binary interactions between Am(III), HA, and hematite were also examined under identical conditions. The additive results reproduced the stepwise decreases of sorption up to a pH of about 6 for lower ionic strengths, which can be ascribed to HA adsorption behavior. However. inconsistencies in additivity from experimental results were found in the pH regions above 7 at low ionic strengths and in the entire pH region at an ionic strength of 0.5 M. Some non-additive effects are discussed in this paper.
  • T Sakuragi, S Sawa, S Sato, T Kozaki, T Mitsugashira, M Hara, Y Suzuki
    JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY 261 2 309 - 314 2004年 [査読無し][通常論文]
     
    Complexation of Am(III) with humic acid was studied at various pHs in 0.1 M NaClO4. The stability constants of the Am(III)humate complexes were determined by a cation-exchange method. The values of logbeta(1) and logbeta(2) increased slightly with increases of pH from 4 to 6 and were found to be 6.9 and 11.6, respectively, at a pH of 5. Markedly larger values than these were obtained by a solvent extraction method. This discrepancy was also revealed by summarizing data from several literature sources. It is very likely that this can be ascribed to decreases in either humic acid and/or the extractant from the extraction system due to humate interactions at the aqueous-organic interface.
  • K Shiramine, S Muto, T Shibayama, H Takahashi, T Kozaki, S Sato, Y Nakata, N Yokoyama
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 21 5 2054 - 2059 2003年09月 [査読無し][通常論文]
     
    Closely stacked multilayer structures of InAs islands with intermediate-layer thicknesses d of 3, 6, 10, and 20 nm were grown by the Stranski-Krastanow mode of molecular beam epitaxy and were observed using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The multilayers consisted of five InAs layers' each of a thickness of 1.8 monolayers and four GaAs layers each of a thickness d. Columns of coherent islands were observed by cross-sectional TEM. Changes in the size and density of the islands with d, determined by AFM, could be explained in terms of (i) change in the vertical pairing probability of islands, (ii) detachment of In from the top of the island, and (iii) surface segregation of In. The observed AFM images of the islands were elliptical. Their major axis was in the [ 110] direction, and the length of the minor axis was 80% of that of the major axis. (C) 2003 American Vacuum Society.
  • J Liu, T Kozaki, Y Horiuchi, S Sato
    APPLIED CLAY SCIENCE 23 1-4 89 - 95 2003年08月 [査読無し][通常論文]
     
    A mixture of bentonite and silica sand is expected to be an important engineered barrier in a high-level radioactive waste repository. Therefore, the diffusion behavior of radionuclides in this mixture is a key issue for the safety assessment of geological disposal. This study determined the apparent diffusion coefficients of strontium ions in montmorillonite and silica sand mixtures under different temperatures at a total dry density of 1.8 Mg m(-3), while the mixing ratios of montmorillonite and silica sand were adjusted to obtain partial dry densities of Na-montmorillonite from 1.0 to 1.7 Mg m-3. When the total dry density of the pure montmorillonite sample was identical to the partial dry density of the montmorillonite in the mixture samples, the apparent diffusion coefficients in the mixture samples at 298 K were almost the same as those in pure montmorillonite. However, the activation energy in the mixture sample was found to be higher than that in the pure sample having a partial dry density of 1.2 Mg m-3, whereas it was lower in the sample having a partial dry density of 1.7 Mg m(-3). This suggests that the diffusion behaviour of strontium ions was affected by the addition of silica sand at these partial dry densities, although there was no significant effect of the silica sand on the apparent diffusion coefficient. The microstructures of the compacted montmorillonite samples were observed with microfocus X-ray computerized tomograph (micro-CT). Three-dimensional images of the microstructures were obtained for the pure and the mixture samples under the dry and wet states. The micro-CT observations suggest the addition of silica sand to the montmorillonite samples could affect the degree of water-saturation and/or swelling of montmorillonite particles. This agrees with the results of the XRD measurements that determined the effects of silica sand on the basal spacing of montmorillonite. (C) 2003 Elsevier Science B.V. All rights reserved.
  • JH Liu, H Yamada, T Kozaki, S Sato, H Ohashi
    JOURNAL OF CONTAMINANT HYDROLOGY 61 1-4 85 - 93 2003年03月 [査読無し][通常論文]
     
    The effect of silica sand on the diffusion of sodium ions in mixtures of montmorillonite and silica sand was studied by measuring the apparent diffusion coefficients, activation energies for diffusion, and the basal spacing of the mixed samples. These diffusion experiments suggest that the apparent diffusion coefficients of sodium ions in the mixed samples were almost the same as those of pure montmorillonite samples having the same partial dry densities of montmorillonite. The activation energy dependence for diffusion of sodium ions on the partial dry density was different between the mixed samples and the pure montmorillonite samples. The activation energy increased by adding silica sand at the partial dry density of 1.0 Mg m(-3), and decreased by adding silica sand at the partial dry densities higher than 1.2 Mg m(-3). A change in the XRD profile was observed after adding silica sand at the partial dry density of 1.6 Mg m(-3). Here, a three-water-layer hydrate state of montmorillonite was found in the mixed sample whereas only a two-water-layer hydrate state was observed in the pure montmorillonite sample. These experimental results suggest that silica sand changed the montmorillonite microstructure in the mixed samples, which then altered the sodium-ion diffusion process. (C) 2002 Elsevier Science B.V. All rights reserved.
  • K Shiramine, T Itoh, S Muto, T Kozaki, S Sato
    JOURNAL OF CRYSTAL GROWTH 242 3-4 332 - 338 2002年07月 [査読無し][通常論文]
     
    Islands of InAs were fabricated at various temperatures by Stranski-Krastanow growth of the molecular beam epitaxy and were observed by the atomic force microscopy. The island size increased and the island density decreased with an increase in temperature. The change was caused by an increase in the migration length of In adatoms with increasing temperature. An Arrhenius plot of the island density showed a linear tendency and agreed with the results Of other works. For understanding the results, an expression for island density was obtained on the assumption that the density is saturated under constant In flux and In atoms do not detach themselves from the islands. Using the expression, the activation energy for migration of an In adatom was estimated to be 4.0 eV from the Arrhenius plot. The activation energy was discussed based on another theoretical expression also. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Sakuragi, S Sato, T Kozaki
    CHEMISTRY LETTERS 7 656 - 657 2002年07月 [査読無し][通常論文]
     
    The effects of ionic strength on the sorption of Eu(III) on kaolinite in the presence of humic acid (HA) were examined using a batch method. Eu(III) sorption increased with increased ionic strengths in the pH range of 6 to 10, but was insensitive to ionic strength in the pH range below 5. Adsorption of HA onto kaolinite also increased in the pH range of 6 to 10, indicating that the increase in adsorption of Eu(III)-humate complexes is a predominant process for the increase in Eu(III) sorption.
  • T Sakuragi, S Sato, T Kozaki
    CHEMISTRY LETTERS 7 656 - 657 2002年07月 [査読無し][通常論文]
     
    The effects of ionic strength on the sorption of Eu(III) on kaolinite in the presence of humic acid (HA) were examined using a batch method. Eu(III) sorption increased with increased ionic strengths in the pH range of 6 to 10, but was insensitive to ionic strength in the pH range below 5. Adsorption of HA onto kaolinite also increased in the pH range of 6 to 10, indicating that the increase in adsorption of Eu(III)-humate complexes is a predominant process for the increase in Eu(III) sorption.
  • Tomofiimi Sakuragi, Aki Tokuyama, Seichi Sato, Tamotsu Kozaki, Toshiaki Mitsugashira, Mitsuo Hara, Yoshimitsu Suzuki
    Journal of Nuclear Science and Technology 39 520 - 523 2002年 [査読無し][通常論文]
     
    The sorption of actinides onto minerals depending on groundwater chemistry plays an important role in the safety aspects of geological disposal of high-level waste. The effects of Ca(II) on the sorption of Am(III) and Eu(III) onto kaolinite in the presence of humic acid (HA) were examined in this study. Distribution coefficients (Kd) of Am(III) and Eu(III), and the fractional adsorption (fHA) of HA on kaolinite were determined by a batch method under initial Ca(II) concentrations of 0 to 1.0 × 10-3 M at a constant ionic strength of 0.1 M (NaClO4) and pH region from 3.5 to 10 in an N2 atmosphere at 298 K. The Kd increased with increasing Ca(II) concentrations in regions higher than 1.0 X10-4 M and in the range of pH 7 to 10. In this pH region, fHA was also enhanced by introducing Ca(II). Concentrations higher than 1.0 X10-4 M Ca(II) can be regarded as a bridge between kaolinite and HA. It is very likely that the increase in the adsorbed HA on kaolinite, where the HA includes very stable Am(III) and Eu(M) humates, results in an increase in the Am(III) and Eu(IH) distribution coefficients. © 2002 Atomic Energy Society of Japan.
  • N Kozai, Y Adachi, S Kawamura, K Inada, T Kozaki, S Sato, H Ohashi, T Ohnuki, T Banba
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 38 12 1141 - 1143 2001年12月 [査読無し][通常論文]
  • N Kozai, Y Adachi, S Kawamura, K Inada, T Kozaki, S Sato, H Ohashi, T Ohnuki, T Banba
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 38 12 1141 - 1143 2001年12月 [査読無し][通常論文]
  • T Kozaki, S Suzuki, N Kozai, S Sato, H Ohashi
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 38 8 697 - 699 2001年08月 [査読無し][通常論文]
  • N Kozai, K Inada, T Kozaki, S Sato, H Ohashi, T Banba
    JOURNAL OF CONTAMINANT HYDROLOGY 47 2-4 149 - 158 2001年02月 [査読無し][通常論文]
     
    Diffusion of neptunium (V) in compacted Na-montmorillonite was studied through the non-steady state diffusion method. In this study, two experimental attempts were carried out to understand the diffusion mechanism of neptunium. One was to establish the diffusion activation energy, which was then used to determine the diffusion process in the montmorillonite. The other was the measurement of the distribution of neptunium in the montmorillonite by a sequential batch extraction. The apparent diffusion coefficients of neptunium in the montmorillonite at a dry density of 1.0 Mg m(-3) were from 3.7 x 10(-1)2 m(2) s(-1) at 288 K to 9.2 X 10(-12) m(2) s(-1) at 323 K. At a dry density of 1.6 Mg m(-3), the apparent diffusion coefficients ranged between 1.5 X 10(-13) m(2) s(-1) at 288 K and 8.7 X 10(-13) m(2) s(-1) at 323 K. The activation energy for the diffusion of neptunium at a dry density of 1.0 Mg m(-3) was 17.5 +/- 1.9 kJ mol(-1). This value is similar to those reported for diffusion of other ions in free water. e.g., 18.4 and 17.4 kJ mol(-1) for Na+ and Cl-, respectively. At a dry density of 1.6 Mg m(-3), the activation energy was 39.8 +/- 1.9 kJ mol(-1). The change in the activation energy suggests that the diffusion process changes depending on the dry density of the compacted montmorillonite. A characteristic distribution profile was obtained by the sequential extraction procedure for neptunium diffused in compacted montmorillonite. The estimated fraction of neptunium in the pore water was between 3% and 11% at a dry density of 1.6 Mg m(-3) and at a temperature of 313 K. The major fraction of the neptunium in the montmorillonite was identified as neptunyl ions sorbed on the outer surface of the montmorillonite. These findings suggested that the activation energy for diffusion and the distribution profile of the involved nuclides could become powerful parameters in understanding the diffusion mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.
  • T Kozaki, K Inada, S Sato, H Ohashi
    JOURNAL OF CONTAMINANT HYDROLOGY 47 2-4 159 - 170 2001年02月 [査読無し][通常論文]
     
    For safety assessment of geological disposal of HLW, it is necessary to understand the diffusion mechanism of radionuclides in compacted bentonite. In this study, the diffusion behavior of chloride ions in compacted montmorillonite was studied from the viewpoints of the activation energy for apparent diffusion and the basal spacing of the compacted montmorillonite. A unique change in the activation energy as a function of the dry density of the montmorillonite was found. The activation energy decreased from 17.4 to 13.5 kJ mol(-1) as the dry density increased from 0.7 The basal to 1.0 Mg m(-3) and increased to 25.1 kJ mol(-1) at dry densities above 1.0 Mg m spacing of 1.88 nm, corresponding to the three-water layer hydrate state, was not observed by X-ray diffraction (XRD) until the dry density increased to 1.0 Mg m(-3). where the minimum activation energy was obtained. On the other hand, a basal spacing of 1.56 nm, corresponding to the two-water layer hydrate state, was observed at the dry densities of 1.4 Mg m(-3) and above, where the activation energies were more than 22 kT mol(-1). These experimental results suggest that there are at least two additional diffusion processes that can raise or reduce the activation energy and are affected by water in the region adjacent to the montmorillonite surfaces. If the "Grahame model" can be introduced to describe the electrical double layer, surface diffusion will be considered the possible predominant diffusion process, even for anions like chloride ions. (C) 2001 Elsevier Science B.V. All rights reserved.
  • Diffusion Behavior of Ca2+ Ions in Compacted Na-Montmorillonite
    Scientific Basis for Nuclear Waste Management 663 629 - 635 2001年 [査読無し][通常論文]
  • T Kozaki, H Sato, S Sato, H Ohashi
    ENGINEERING GEOLOGY 54 1-2 223 - 230 1999年09月 [査読無し][通常論文]
     
    For the safety assessment of geological disposal of high-level radioactive waste, the diffusion behavior of Cs+ ions in compacted Na- and Ca-montmorillonite mixtures was studied. The apparent diffusion coefficients of Cs+ ions were determined as functions of the diffusion temperature and the ionic equivalent fraction of Ca2+ ions. The apparent diffusion coefficients were almost constant at higher temperatures, 323 and 313 K, while they decreased with increasing ionic equivalent fraction at lower temperatures, 298 and 288 K. The activation energies for diffusion of Cs+ ions were also determined from the temperature dependence of the apparent diffusion coefficients at each ionic equivalent fraction. The activation energy increased from 34 kJ mol(-1) to 38 kJ mol(-1) as the ionic equivalent fraction increased from zero to 0.75, after which it increased steeply and reached 49 kJ mol(-1) at the ionic equivalent fractions of .94 and 1.0. These findings cannot be explained by the pore water or surface diffusion models. Interlayer diffusion is suggested as the most probable explanation for the diffusion of Cs+ ions. (C) 1999 Elsevier Science B.V. All rights reserved.
  • T Kozaki, Y Sato, M Nakajima, H Kato, S Sato, H Ohashi
    JOURNAL OF NUCLEAR MATERIALS 270 1-2 265 - 272 1999年04月 [査読無し][通常論文]
     
    For performance assessment of bentonite buffer material in geological disposal of high-level radioactive waste, the particle size of bentonite and its effect on the diffusion behavior of radionuclides in compacted bentonite were studied. Bentonite samples with different particle sizes were prepared, and characterized by the BET and EGME methods for specific surface areas, by the laser diffraction/scattering particle size analysis for particle size distribution, and by SEM observations. Apparent and effective diffusion coefficients of tritiated water (HTO), Cl- ions and Cs+ ions in compacted bentonite were also determined using bentonite samples with different particle sizes. With HTO and Cl- ions, there were higher diffusion coefficients in fine grained samples, but opposite particle size effects were observed with Cs+ ions. These findings cannot be explained by the conventional pore water diffusion model, and suggest a different diffusion process for Cs+ ions and also at higher dry density region. (C) 1999 Elsevier Science B.V. All rights reserved.
  • T Kozaki, N Saito, A Fujishima, S Sato, H Ohashi
    JOURNAL OF CONTAMINANT HYDROLOGY 35 1-3 67 - 75 1998年12月 [査読無し][通常論文]
     
    Diffusion of chloride ions in compacted montmorillonite was studied for a performance assessment as buffer material in geological disposal of high-level radioactive waste. The apparent diffusion coefficients were from 6.8 x 10(-12) to 2.2 x 10(-10) m(2) s(-1) for sodium montmorillonite at dry densities from 1.0 to 1.8 Mg m(-3) at diffusion temperatures from 278 to 323 K. The activation energy increased from 14 kJ mol(-1) (lower than that in free water, 17.4 W mol(-1)) to 25 kJ mol(-1) (higher than that in free water), as the dry density increased from 1.0 to 1.8 Mg m(-3) These facts can be attributed to changes in the predominant diffusion process as dry density increases. The dry density dependence of the activation energy cannot be explained by conventional diffusion models, such as the pore water diffusion model. (C) 1998 Elsevier Science B.V. All rights reserved.
  • M Nakajima, T Kozaki, H Kato, S Sato, H Ohashi
    SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXI 506 947 - 948 1998年 [査読無し][通常論文]
  • T Kozaki, A Fujishima, S Sato, H Ohashi
    NUCLEAR TECHNOLOGY 121 1 63 - 69 1998年01月 [査読無し][通常論文]
     
    Diffusion of sodium ions through compacted sodium montmorillonite in a water-saturated state was studied to obtain fundamental information for performance assessments of geological disposal of high-level radioactive waste. Basal spacings obtained from X-ray diffraction measurements indicated a decrease in the interlamellar spacing with increasing dry density of the montmorillonite; the three-water-layer hydrate was observed at low dry density (less than or equal to 1.3 Mg/m(3)), and the two-water-layer hydrate was observed at high dry density (greater than or equal to 1.6 Mg/m(3)), whereas both were observed at dry densities between 1.4 and 1.5 Mg/m(3). Activation energies from 14.1 to 24.7 kJ/mol were obtained from the temperature dependence of the self-diffusion coefficients of sodium ions. Activation energies lower than that for the diffusion of sodium ions in free water were found for montmorillonite specimens with dry densities of less than or equal to 1.2 Mg/m(3), while higher activation energies were observed at dry densities greater than or equal to 1.4 Mg/m(3). The pore water diffusion model, the general model used for migration of nuclides, is based an geometric parameters; however findings cannot be explained by only the changes in the geometric parameters. Possible explanations for the dry density dependence of the activation energy are changes in the temperature dependence of the distribution coefficients of sodium ions on the montmorillonite, changes in the diffusion process with an increase in dry density, or both.
  • T Kozaki, H Sato, A Fujishima, N Saito, S Sato, H Ohashi
    SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XX 465 893 - 900 1997年 [査読無し][通常論文]
     
    For performance assessments of geological disposal of high-level radioactive waste, activation energies for the diffusion of strontium ions and the basal spacings of compacted sodium montmorillonite in the water-saturated state were determined. Basal spacings determined by XRD indicated changes in the interlamellar space from a three-water layer hydrate state to a two-water layer hydrate state as the dry density of the montmorillonite increased from 1.0 to 1.8 Mg m(-3)). Activation energies from 17.3 to 30.8 kJ mol(-1) for the apparent diffusion coefficients of strontium ions were obtained. The lower activation energies than for diffusion of strontium ions in free water were determined for montmorillonite specimens of lower dry density (1.2 Mg m(-3) and below), while the higher activation energies were at higher dry densities (1.4 Mg m(-3) and above). These findings cannot be explained by changes in only the geometric parameters, which the pore water diffusion model is based upon. Possible explanations for the dry density dependence of the activation energy are the changes of the temperature dependence of the distribution coefficients and/or of the diffusion process with increasing dry density.
  • T Kozaki, H Sato, A Fujishima, S Sato, H Ohashi
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 33 6 522 - 524 1996年06月 [査読無し][通常論文]
  • 小崎 完, 佐藤 大樹, 藤島 敦
    『放射性廃棄物研究』 3 1 25 - 31 日本原子力学会 1996年 [査読無し][通常論文]
  • 小崎 完, 河辺 英樹, 玉井 秀明
    『放射性廃棄物研究』 3 1 33 - 40 日本原子力学会 1996年 [査読無し][通常論文]
  • T KOZAKI, Y IMAMURA, J TAKADA, S SATO, H OHASHI
    SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XVIII, PTS 1 AND 2 353 329 - 336 1995年 [査読無し][通常論文]
  • Activation Energy for Diffusion of Cesium in Compacted Sodium Montmorillonite
    T. Kozaki, H. Tamai, A. Fujishima, H. Kawabe, S. Sato, H. Ohashi, J. Takada, H. Moriyama
    KURRI Prog. Rep. 224 - 224 1995年 [査読無し][通常論文]

書籍

  • 福島第一原子力発電所事故から10年-廃炉への化学のかかわり 最前線研究 Part3 放射性廃棄物の処理はどうなるのか?廃炉で生じる放射性廃棄物と燃料デブリの処分
    出光一哉, 小崎完 (担当:分担執筆)
    化学 2021年03月
  • 粘土ハンドブック第3版
    技報堂出版 2009年
  • Handbook of Clays and Clay minerals
    2009年
  • 原子炉解体
    講談社 1993年
  • Decommission of nuclear reactor
    1993年

その他活動・業績

共同研究・競争的資金等の研究課題

  • 機関連携強化による未来社会に向けた新たな原子力教育拠点の構築
    文部科学省:国際原子力人材育成イニシアティブ事業 (原子力人材育成等推進事業費補助金)
    研究期間 : 2020年10月 -2027年03月 
    代表者 : 小崎完
  • 溶脱による変質を考慮した汚染コンクリート廃棄物の合理的処理・処分の検討
    文部科学省:国家課題対応型研究開発推進事業(英知を結集した原子力科学技術・人材育成推進事業)
    研究期間 : 2020年10月 -2023年03月 
    代表者 : 小崎完、杉山隆文、渡辺直子、植松慎一郎、川崎大介、柳原敏、香西直文、駒義和、湊大輔、長岡亨
  • 多機能化金ナノ粒子を用いた地層処分バリア材性能評価手法の創成
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 小崎 完, 渡辺 直子
     
    高レベル放射性廃棄物の地層処分において、圧縮ベントナイトや母岩は、処分場から生物圏への放射性核種の移行を遅延させるバリア機能を有することが期待されている。従って、それら材料のバリア性能を評価することが重要な研究課題の一つである。 本研究では、このバリア性能を、金ナノ粒子を用いて評価する新たな手法の確立を目標として、3年の研究期間に、課題(1) 天然・人工バリア中の多機能化金ナノ粒子の移行挙動研究、課題(2) 多機能化金ナノ粒子を用いたバリア材中の化学的雰囲気の原位置測定に関する実験及び考察、を行う計画である。 研究2年目となる令和元年度は、前年度に引き続き、比表面積の大きな金微粒子の表面を特定の配位子(ポリエチレングリコール)で覆い、任意の粒子サイズで可溶化、安定化を図った多機能化金ナノ粒子を用い、天然バリア模擬材料であるケイ砂を充填したカラム中の移行挙動試験を実施した。この結果、昨年度見出した、ケイ砂を充填したカラム中での金ナノ粒子の移行が、サイズの大きな金ナノ粒子ほど遅延する現象、またカラム透過後の金ナノ粒子の粒径分布が粒子サイズが大きなものほど顕著に変化する現象の再現性を確認した。さらに、これらの現象はケイ砂と金ナノ粒子間に、静電的な相互作用やvan der Waals力とは別の相互作用が働いており、それがケイ砂表面の電荷の不均一性に起因する可能性を明らかにし、その成果を学術論文に纏めて発表した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 太田 朋子, 小崎 完
     
    2011年の福島第一原子力災害により放出された放射性核種は広域の環境中で検出されている。材の中の核種の濃度は我が国の農林水産業の分野でも関心が高く、材の原料となる樹木中の核種の未来予測は重要な課題である。3年間の試験結果を統合し、水の鉛直移動速度、土壌中のCsの移動速度、根からの吸収率、根の水の有効吸収深度等を加味したところ、直根性のスギは放射性セシウムが増えないと考えらえた
  • オープン教材の活用による原子力教育の受講機会拡大と質的向上
    文部科学省:国際原子力人材育成イニシアティブ事業 (原子力人材育成等推進事業費補助金)
    研究期間 : 2017年10月 -2020年03月 
    代表者 : 小崎 完
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 渡辺 直子, 小崎 完, 田中 真悟, 柳原 敏
     
    原子力発電所の廃止措置で大量に発生する放射性コンクリート廃棄物の合理的な処理・処分のため、セメントペースト中の放射性核種の拡散係数を決定し、移行機構を検討した。熱による変質により見かけの拡散係数は増加するが、これは脱水・脱水和による細孔分布の増大による可能性が示唆された。また、廃止措置費用のうち、作業依存費用は安全貯蔵期間の影響をあまり受けないが期間依存費用は期間に比例して増大すること、放射性廃棄物量は減衰により顕著に減少する時が存在することから、即時解体した後に将来の処分を見越して分別して廃棄体化し、廃棄物量が減少する時点まで貯蔵するというシナリオも検討に値する可能性が考えられた。
  • 汚染コンクリートの解体およびそこから生じる廃棄物の合理的処理・処分の検討
    文部科学省:国家課題対応型研究開発推進事業・英知を結集した原子力科学技術・人材育成推進事業・原子力システム研究開発事業
    研究期間 : 2016年12月 -2019年03月 
    代表者 : 小崎 完
  • オープン教材の作成・活用による実践的原子力バックエンド教育
    文部科学省:国際原子力人材育成イニシアティブ事業 (原子力人材育成等推進事業費補助金)
    研究期間 : 2014年10月 -2017年03月 
    代表者 : 小崎 完
  • 日本学術振興会:科学研究費助成事業 基盤研究(S)
    研究期間 : 2012年05月 -2016年03月 
    代表者 : 池田 泰久, 三村 均, 佐藤 修彰, 新堀 雄一, 小崎 完, 佐藤 努, 佐々木 隆之, 桐島 陽, 出光 一哉, 稲垣 八穂広, 鈴木 達也, 竹下 健二
     
    福島原発事故で発生した汚染物の合理的な処理・処分システム構築に向け、従来とは異なる固体・液体汚染物の性状研究、固体・液体汚染物の処理研究、発生廃棄物の処分研究の3分野に分け、基盤データの取得を行ってきた。 その結果、燃料デブリの性状、核種の溶出挙動、汚染物の除染法、汚染水の処理法、高塩濃度環境下での核種の移行挙動等、燃料デブリをはじめとした従来知見の少ない海水を含む水溶液に接する条件下で発生した放射性廃棄物の処理・処分技術の開発に資する多くのデータを取得し、福島原発事故廃棄物の処理・処分方策に貢献しうるとともに、放射性廃棄物の処理・処分分野の進展に寄与しうる成果を出している。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 渡辺 直子, 小崎 完
     
    放射性Csを含む土壌廃棄物の中間貯蔵・最終処分の長期的な安定性に関する基礎的な知見を得るため、粘土鉱物とCsの相互作用に与える土壌有機物の影響を与えるメカニズムを検討した。粘土鉱物表面に外表面、層間、端面等、性質の異なるCs収着サイトを想定してモデル化して収着実験結果と比較すると、モンモリロナイト層間サイトでの収着容量はフミン酸存在下で減少、非常に選択性の高いイライトのFESではフルボ酸存在下で選択性が増加する等、サイトごとにまた、有機物の種類により影響は異なることがわかった。また、MD計算により、K型マイカ端面で非常に強い内圏錯体が形成される場合の構造を明らかにした。
  • 多様なセシウム汚染廃棄物の中間・最終処分安全評価のための機関連携による多角的研究
    文部科学省:原子力基礎基盤戦略研究イニシアティブ
    研究期間 : 2012年10月 -2015年03月 
    代表者 : 小崎 完
  • 多様な環境放射能問題に対応可能な国際的人材の機関連携による育成
    文部科学省:国際原子力人材育成イニシアティブ事業 (原子力人材育成等推進事業費補助金)
    研究期間 : 2011年10月 -2014年03月 
    代表者 : 小崎 完
  • 文部科学省:科学研究費補助金(基盤研究(B))
    研究期間 : 2011年 -2012年 
    代表者 : 小崎 完
  • 文部科学省:科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2011年 -2011年 
    代表者 : 小崎 完
  • 文部科学省:科学研究費補助金(基盤研究(B))
    研究期間 : 2008年 -2010年 
    代表者 : 小崎 完, 富岡 智, 西山 修輔, 加美山 隆, 佐々木 隆之, 香西 直文
     
    本研究は、放射性廃棄物地層処分におけるバリア材料である粘土および堆積岩試料の内部微細構造に関する情報を種々の分析手法によって得ると同時に、それらの試料に対して放射性核種の拡散および収着実験を実施し、拡散や収着挙動を、試料のメゾスコピック構造の観点から検討し、それぞれの現象の基本的なメカニズムについて議論することを目的としている。研究2年目となる平成21年度は、透水試験前後の堆積岩試料のX線マイクロCT観察を行い、透水係数の経時変化と岩試料内部の亀裂構造変化との関連を明らかにした。また、Fe型に変質した粘土試料に対してμ-PIXE分析などによる特性評価を行うとともに、透水試験およびCl^-の拡散実験を行い、低圧縮の粘土試料の透水係数はFe型に変質することで大きく増加すること、これに対してCl^-の見かけの拡散係数は減少することを明らかにした。中性子分光法に関しては、中性子共鳴吸収イメージング法による核種の拡散の観察手法について、基礎的な実験を引き続き行った。収着挙動に関しては、バリア材中の有機酸を含む間隙水でのTh錯体種の見かけの溶解度ならびに溶解度制限固相を調査し、溶存錯体の安定性について熱力学的に考察し、Thイオンと有機酸の錯生成は、加水分解との競争反応であり、溶存種や固相の化学組成は両者のバランスに支配されること、また錯生成によって加水分解によるコロイド種の生成が抑制され...
  • 文部科学省:科学研究費補助金(基盤研究(B))
    研究期間 : 2004年 -2006年 
    代表者 : 小崎 完, 佐藤 正知, 香西 直文
     
    高レベル放射性廃棄物の地層処分では、粘土緩衝材(Na型ベントナイト)中でオーバーパック(炭素鋼)が徐々に腐食し、鉄腐食生成物(主としてFe^<2+>イオン)が粘土緩衝材中に放出される。このため、Fe^<2+>イオンが、Na^+やCa^<2+>イオンのようなベントナイトの元々の交換性陽イオンと置換されることで、Fe(II)型ベントナイトが生成し、その結果粘土緩衝材の性能が変わる可能性がある。ベントナイトの変質による膨潤能の低下は、緩衝材の性能を劣化させる負の効果の一つである。一方、ベントナイトの変質は、緩衝材の性能を向上させる、正の効果をもたらす可能性がある。例えば、Fe(II)型ベントナイトを含有する変質ベントナイトは、ある種の放射性核種を収着・固定化し、その結果それら核種を遅延させ得る。そこで、本研究では、Fe型化したベントナイトの調製およびその特性評価を行った。Fe型試料は、不活性ガス雰囲気のグローブボックス内でNa型ベントナイトをFeCl_2溶液に接触させる、従来型のイオン交換法によって調製した。一方、本研究では、ニトリロ三酢酸の鉄(II)錯体(Fe^<2+>-NTA)溶液を用いる新しい調製方法を開発した。調製した試料および同試料を大気中で酸化させた試料に対し、SEM-EDX観察、FT-IR分析、メスバウアー分光、マイクロPIXE分析、湿式化学分析等による特性評価を行っ...
  • 文部科学省:科学研究費補助金(基盤研究(C))
    研究期間 : 2001年 -2003年 
    代表者 : 小崎 完, 佐藤 正知, 佐藤 正知, 小崎 完
     
    高レベル放射性廃棄物の地層処分におけるベントナイト緩衝材の長期健全性を評価するための基礎的研究として、処分後長期経過後に緩衝材であるNa型ベントナイトに起こると考えられる変質反応に関する基礎的研究を行った。このうち、炭素鋼製オーバーパックの腐食に伴いベントナイトが鉄型化する反応については、無酸素雰囲気下のグローブボックス内でベントナイトをFe^<2+>イオンを含む溶液と接触させ、交換性陽イオンをFe^<2+>イオンに置換した「Fe型試料」およびこのFe型試料を大気中で酸化させた「酸化Fe型試料」を調製し、両試料の特性評価を選択的逐次抽出法、メスバウアー分光、X線回折などによって行った。その結果、Fe型試料では層間のイオンがFe^<2+>イオンに置換していること、酸化Fe型試料ではそれらの層間のFe^<2+>イオンが徐々に酸化して非晶質遊離鉄として析出していることなどが示された。さらに、両試料へのSeの収着実験においては、Na型試料のFe型化、Fe型試料の酸化によって、Se(IV)ならびにSe(VI)の収着率が増加することが明らかになった。一方、セメント溶解反応に伴うベントナイト変質反応に関する研究として、Na型とCa型が混在したベントナイト中でのNa^+およびCa^<2+>イオンの見かけの拡散係数、ならびに塩濃度の異なるNa型試料中のNa^+イオンの見かけの拡散係数を実験から...
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1999年 -2000年 
    代表者 : 小崎 完
     
    放射性廃棄物の地層処分において、地下水等からもたらされるCa^<2+>イオンによるベントナイト緩衝材の性能劣化に関する検討を行うため、ベントナイトの主たる構成鉱物であるNa型モンモリロナイト中のCa^<2+>イオンの拡散係数を測定した。乾燥密度1.0〜1.8Mgm^<-3>に圧密したNa型モンモリロナイト中で得られた見かけの拡散係数は、拡散温度298Kにおいて1.7×10^<-11>〜6.0×10^<-12>m^2s^<-1>であった。Ca^<2+>イオンの拡散係数は、それぞれの乾燥密度において、Na^+イオンの拡散係数の約4分の1であり、このことからNa型モンモリロナイトのCa型化への変質にはCa^<2+>イオンの拡散が律速となることが示唆された。一方、見かけの拡散係数の温度依存性から求めた活性化エネルギーは、乾燥密度1.0〜1.6Mgm^<-3>において自由水中の値(17.3kJmol^<-1>)とほぼ等しいほぼ一定の値(18.3〜19.7kJmol^<-1>)となったのに対し、乾燥密度1.8Mgm^<-3>では、活性化エネルギーは25.1kJmol^<-1>に急激に増加した。このようなCa^<2+>イオンの拡散の活性化エネルギーの乾燥密度依存性は、他の陽イオン(Na^+、Sr^<2+>イオン)のものと異なっており、特に乾燥密度1.8Mgm^<-3>における急激な増加は、...
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 1999年 -2000年 
    代表者 : 大橋 弘士, 香西 直文, 小崎 完, 佐藤 正知, 加藤 博康
     
    放射性廃棄物の地層処分の安全評価を行う上で、緩衝材として用いられる圧密したベントナイト中の放射性核種の収着や拡散現象に関する理解が求められている。そこで本研究では、それらの現象に影響を及ぼす因子の一つと考えられる粘土の微細構造に着目した検討を行った。まず、モンモリロナイト試料(ベントナイトの主たる構成鉱物)の微細構造を、種々の分析方法によって詳細に調べるとともに、圧密・含水したモンモリロナイト中のHTO、Np(V)、Cs^+、Cl^-およびCa^<2+>イオンならびにHeガスの拡散係数を測定した。この結果、モンモリロナイト粒子を形成しているモンモリロナイトのシートは、粒子サイズが異なっていてもほぼ同じであること、拡散係数は粘土粒径の影響を受けていることを明らかにした。また、Cs^+イオンの拡散係数に及ぼす粒子形状の影響は、HTOおよびCl^-イオンのそれと逆転しているなど、イオンはモンモリロナイト粒子間の細孔中の水を拡散するとした従来のモデル(「細孔拡散モデル」)では説明できない現象を見出した。さらに、Np(V)、Cl^-およびCa^<2+>イオンに対して拡散の活性化エネルギーを求めた結果、活性化エネルギーがモンモリロナイトの層間距離と密接に関連していることを明らかにした。これもまた、従来の拡散モデルでは説明できない現象であった。同様に、Na型モンモリロナイトに珪砂を添加した...
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1997年 -1998年 
    代表者 : 小崎 完
     
    高レベル放射性廃棄物の地層処分の安全評価のための基礎研究として、ベントナイト緩衝材の主たる構成粘土鉱物であるモンモリロナイト中のCl^-イオンの見かけの拡散係数を測定した。乾燥密度0.7〜1.8Mgm^<-3>に圧密したNa型モンモリロナイト中で得られた見かけの拡散係数は、拡散温度278〜323Kにおいて、7.3×10^<-12>〜5.3×10^<-10>m^2s^<-1>であった。また、その温度依存性から求めた活性化エネルギーは、乾燥密度0.7〜1.8Mgm^<-3>において14〜25kJ mol^<-1>であり、乾燥密度1.0kJ mol^<-1>を境に、低乾燥密度側では乾燥密度の増加とともに減少する傾向を、また高乾燥密度側では乾燥密度の増加とともに増加する傾向を示した。こうした現象は、従来から広く用いられている細孔拡散モデルでは説明できないものであり、CI^-のモンモリロナイト試料への収着が極めて小さいことを含めて考えると、乾燥密度の増加に伴ってcl^-の拡散機構が変化していることを示唆している。特に、こうした現象がNa^+イオンの拡散の活性化エネルギーにも認められることから、Na^+イオンとCl^-イオンが電荷バランスを取るために同時に移行している可能性が考えられる。特に、その際、モンモリロナイト粒子表面の拡散が拡散挙動全体に大きな影響を及ぼしている可能性が示唆された。
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1996年 -1996年 
    代表者 : 小崎 完
     
    高レベル放射性廃棄物の地層処分の安全評価のための基礎研究として、ベントナイト緩衝材の主たる構成粘土鉱物であるモンモリロナイト中のCs^+およびSr^<2+>イオンの見かけの拡散係数を測定した。乾燥密度1.0〜1.8×10^3 kg m^<-3>に圧密したNa型モンモリロナイト中での見かけの拡散係数は、拡散温度278〜323kにおいて、Cs^+イオンで1.9×10^<-13>〜2.1×10^<-11>m^2 s^<-1>、Sr^<2+>イオンで1.6×10^<-12>〜2.1×10^<-11> m^2 s^<-1>であった。一方、見かけの拡散係数の温度依存性から求めた拡散の活性化エネルギーは、Cs^+イオンで32.1〜52.8 kJ mol^<-1>、Sr^<2+>イオンで17.3〜30.1 kJ mol^<-1>となり、一部の点を除いて、自由水中のイオンの拡散の活性化エネルギーと異なった。また、両イオンとも、活性化エネルギーに明らかな乾燥密度依存性が認められた。こうした現象は、従来の細孔拡散モデルでは説明できないものであり、乾燥密度の増加に伴う拡散機構の変化あるいは収着挙動の変化を示唆するものと考え、検討を加えた。
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1995年 -1995年 
    代表者 : 小崎 完
     
    高レベル放射性廃棄物の地層処分の安全評価のための基礎研究として、研究例の限られている、ベントナイト緩衝材の主たる構成粘土鉱物であるモンモリロナイト中のNa^+イオンの見かけの自己拡散係数を測定した。乾燥密度1.0〜1.8×10^3kg m^<-3>に圧密したNa型モンモリロナイト中でのNa^+イオンの見かけの自己拡散係数は、拡散温度278〜323Kにおいて、1.2×10^<-11>〜1.2×10^<-10>m^2S^<-1>であった。見かけの自己拡散係数の温度依存性から求めた拡散の活性化エネルギーは16.8〜25.0kJ mol^<-1>であり、乾燥密度の増加とともに増加する傾向にあることを見出した。また、得られた拡散の活性化エネルギーは、低乾燥密度試料においては自由水中のNa^+イオンの拡散の活性化エネルギーである18.4kJ mol^<-1>より低く、高乾燥密度試料においては逆に高い値であった。これらは、モンモリロナイト中のイオンは自由水に近い状態にある空隙水中を移行するとした従来からの空隙拡散モデルでは説明できない。一方、モンモリロナイト試料の飽和含水率およびX線回折により求めたモンモリロナイト試料の層間距離は、乾燥密度の増加とともに減少し、拡散の活性化エネルギーとの間に相関が認められた。従って、本研究では、圧密したモンモリロナイト中のNa^+イオンは自由水中の拡散とは...
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1994年 -1994年 
    代表者 : 小崎 完, 山崎 完
     
    高レベル放射性廃棄物の地層処分の安全評価を進める上で重要な鉄オーバーパック材の腐食挙動を検討するため、粘土中の鉄の腐食挙動の研究を行った。実験は、粘土試料としてベントナイトを、オーバーパック模擬材として放射化鉄箔試料を用い、放射性同位元素の移行量より鉄箔試料の平均腐食速度とその腐食生成物の見かけの拡散係数を同時に観察することにより行った。本研究補助金の交付により、今年度は従来より行ってきた大気雰囲気下で調製した粘土試料を用いた実験に加え、窒素雰囲気下で調製した粘土試料を用いた実験を行い、酸化還元雰囲気の腐食ならびに腐食生成物の移行挙動に与える影響について検討を加えた。実験の結果、大気雰囲気及び窒素雰囲気下で調製した粘土中の鉄箔の平均腐食速度はいずれも10^<-6>m/yのオーダーとなり、粘土調製時の雰囲気の違いによる差は認められなかった。一方、あらかじめ黄鉄鉱を酸化させておいた粘土試料を用いた実験では、大気雰囲気下で鉄箔の平均腐食速度が1桁程度大きな値となることを確認した。このことは、大気雰囲気下で調製した試料においては、ベントナイト中に含まれる黄鉄鉱が、調製時に混入した酸素を消費し、結果として十分な還元雰囲気が達成されていたことによるものと考えた。腐食生成物の移行挙動は、ほとんどの試料で見かけの拡散係数が10^<-14>m^2/s以下となった。しかし、黄鉄鉱の酸化した試料で...
  • 文部科学省:科学研究費補助金(一般研究(C))
    研究期間 : 1992年 -1992年 
    代表者 : 小崎 完, 水野 忠彦, 大橋 弘士
     
    申請書の研究計画・方法に従い、購入機器のセットを行い、あわせてそれらを一括制御するためのコンピュータプログラムを作成し、電解研磨中の電流あるいは電位変動の連続的な測定記録を可能するシステムの構築を行った。つぎに、このシステムを用いて、放射性腐食生成物を模擬した酸化皮膜を形成した304ステンレス鋼を燐酸溶液中で定電位電解研磨した際の電流変動の観察を行った。この場合、燐酸濃度は28vol%とし、ステンレス鋼はあらかじめ電気炉において600℃で一定時間酸化させたものを用いた。電解研磨の際に観察された電流変動スペクトルを、最大エントロピー法(MEM)によって解析した結果、0.01Hz〜10Hzの周波数範囲で、比較的再現性のある周波数スペクトルが認められた。特に、0.1Hz〜10Hzの周波数範囲においては、両対数グラフ上で直線関係を示し、その傾きが-1から-4となった。この傾きは電解研磨開始直後には比較的高い値を示すが、研磨が進行するにつれて徐々に-3以下の低い値に落ち着く傾向のあることを見い出した。それらの傾きと測定電流値の平均あるいは分散値との相関については今後の課題である。以上の観点から、電解研磨除染時の電流変動を観察しその周波数スペクトルの傾きに着目することにより、除染進行状態をモニターできる可能性が認められた。ただし、現段階においては、ステンレス鋼試料上の酸化皮膜の厚さ、撹拌...
  • 高レベル放射性廃棄物の地層処分における工学障壁材の性能評価
  • Performance assessment of engineered barriers for geological disposal of high-level radioactive waste

教育活動情報

主要な担当授業

  • 医理工放射線物理学
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 医理工学院
    キーワード : 放射線物理学、放射線の種類と生成、荷電粒子と物質の相互作用、光子と物質の相互作用、中性子と物質の相互作用
  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 放射線物理学、放射線の種類と生成、放射線と物質の相互作用
  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 荷電粒子と物質の相互作用、光子と物質の相互作用、中性子と物質の相互作用
  • 放射線物理学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 放射線物理学、放射線の種類と生成、荷電粒子と物質の相互作用、光子と物質の相互作用、中性子と物質の相互作用
  • 原子力・エネルギー材料特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : ウラン資源、原子力材料、核燃料サイクル
  • 原子力・エネルギー材料特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
  • 原子力・エネルギーシステム特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : Nuclear waste, waste conditioning, high level waste conditioning, spent fuel reprocessing, nuclear glass, geological disposal, multi-barrier system
  • 放射線物理学特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 放射線物理学、放射線の種類と生成、荷電粒子と物質の相互作用、光子と物質の相互作用、中性子と物質の相互作用
  • 原子力・エネルギー材料特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : ウラン資源、原子力材料、核燃料サイクル
  • 原子力・エネルギー材料特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • 原子力・エネルギーシステム特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 放射線、放射能、放射線被ばく、放射線医療、原子炉、環境放射能、放射性廃棄物処理・処分、廃炉工学、オープン教材
  • 材料科学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 原子構造、結晶構造、エネルギーバンド、欠陥、拡散、状態図、材料と環境
  • 工業英語演習
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 工業英語、英文読解、英作文、英会話、プレゼンテーション、討論
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 地球環境のための科学技術(エンジン、風力,水力) 原子力の役割(システム、安全、放射性廃棄物)
  • 科学・技術の世界
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 原子力技術、原子力発電、放射線、医療応用、宇宙探査、材料開発
  • エネルギー工学概論
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 地球環境、火力発電、原子力発電、再生可能エネルギー、省エネルギー

大学運営

学内役職歴

  • 2019年4月1日 - 2021年3月31日 大学院工学院副学院長
  • 2021年4月1日 - 2023年3月31日 大学院工学院副学院長

委員歴

  • 2018年01月 - 現在   日本原子力研究開発機構 地層処分研究開発・評価委員会   委員
  • 2016年02月 - 現在   北海道原子力専門有識者会合   委員
  • 2015年04月 - 現在   原子力発電環境整備機構 技術アドバイザリー国内委員会   委員
  • 2014年08月 - 現在   日本原子力研究開発機構 廃止措置研究開発・評価委員会   委員
  • 2013年07月 - 現在   北海道原子力防災対策部会有識者専門委員会   委員
  • 2008年01月 - 現在   Journal of Hydrology (ELSEVIER)   編集委員
  • 2019年04月 - 2020年03月   日本原子力学会   バックエンド部会・部会長
  • 2014年08月 - 2020年03月   日本原子力研究開発機構 福島廃止措置研究開発・評価委員会   委員
  • 2014年04月 - 2020年03月   日本アイソトープ協会   放射線安全取扱部会 企画専門委員会委員
  • 2008年 - 2011年   日本原子力学会   プログラム編成委員   日本原子力学会
  • 2008年 - 2009年   日本原子力学会   バックエンド部会運営委員会委員   日本原子力学会
  • 2005年 - 2007年   腐食防食協会   評議員   腐食防食協会
  • 2000年 - 2003年   日本原子力学会   編集委員   日本原子力学会
  • 2001年 - 2002年   日本原子力学会   北海道支部幹事   日本原子力学会
  • 1996年 - 1997年   腐食防食協会   北海道支部幹事   腐食防食協会
  • 1995年 - 1996年   日本分析化学会   北海道支部会計幹事   日本分析化学会


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