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Journal Articles

Molecular dynamics simulations of physical properties of water and cations in montmorillonite interlayer; Application to diffusion model

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.

Journal Articles

Stability of montmorillonite edge faces studied using first-principles calculations

Sakuma, Hiroshi*; Tachi, Yukio; Yotsuji, Kenji; Suehara, Shigeru*; Arima, Tatsumi*; Fujii, Naoki*; Kawamura, Katsuyuki*; Honda, Akira

Clays and Clay Minerals, 65(4), p.252 - 272, 2017/08

 Percentile:100(Chemistry, Physical)

Structure and stability of montmorillonite edge faces (110), (010), (100), and (130) of the layer charges y = 0.5 and 0.33 are investigated by the first-principles electronic calculations based on the density functional theory. Stacking and single layer models are tested for understanding the effect of stacking on the stability of montmorillonite edge faces. Most stacking layers stabilize the edge faces by making hydrogen bonds between the layers; therefore, the surface energy of stacking layers is reduced rather than the single layer model. This indicates that the surface energy of edge faces should be estimated depending on the swelling conditions. Lowest surface energies of (010) and (130) edge faces were realized by the presence of Mg ions on the edge faces. These edge faces have a strong adsorption site for cations due to local negative charge of the edges.

Journal Articles

Diffusion and adsorption of uranyl ion in clays; Molecular dynamics study

Arima, Tatsumi*; Idemitsu, Kazuya*; Inagaki, Yaohiro*; Kawamura, Katsuyuki*; Tachi, Yukio; Yotsuji, Kenji

Progress in Nuclear Energy, 92, p.286 - 297, 2016/09

 Times Cited Count:4 Percentile:31.55(Nuclear Science & Technology)

Diffusion and adsorption behavior of uranyl (UO$$_2^{2+}$$) species is important for the performance assessment of radioactive waste disposal. The diffusion behaviors of UO$$_2^{2+}$$, K$$^{+}$$, CO$$_3^{2-}$$ and Cl$$^{-}$$ and H$$_{2}$$O in the aqueous solutions were evaluated by molecular dynamics (MD) calculations. The diffusion coefficient (De) of UO$$_2^{2+}$$ is the smallest and is 26% less than the self-diffusion coefficient of H$$_{2}$$O. For the aqueous solution with high concentration of carbonate ions, uranyl carbonate complexes: UO$$_{2}$$CO$$_{3}$$ and UO$$_{2}$$(CO$$_{3}$$)$$^{2-}$$ can be observed. For the clay (montmorillonite or illite)-aqueous solution systems, the adsorption and diffusion behaviors of UO$$_2^{2+}$$ and K$$^{+}$$ were evaluated by MD calculations. The distribution coefficients (Kd) increase with the layer charge of clay, and Kd of UO$$_2^{2+}$$ might be smaller than that of K$$^{+}$$. Further, their two-dimensional diffusion coefficients were relatively small in the adsorption layer and were extremely small for illite with higher layer charge.

Journal Articles

Oxygen potential of a prototypic Mo-cermet fuel containing plutonium oxide

Miwa, Shuhei; Osaka, Masahiko; Nozaki, Takahiro*; Arima, Tatsumi*; Idemitsu, Kazuya*

Journal of Nuclear Materials, 465, p.840 - 842, 2015/10

 Times Cited Count:1 Percentile:81.41(Materials Science, Multidisciplinary)

Oxygen potential of a prototypic Mo-cermet fuel containing PuO$$_{2-x}$$ was experimentally determined. It was shown that the oxygen potentials of Mo-cermet fuel containing PuO$$_{2-x}$$ were the same as those of pure PuO$$_{2-x}$$. It was also confirmed that the gradual oxidation of the Mo matrix occurred only above the oxygen potential of Mo/MoO$$_{2}$$. It is concluded that the oxidation-reduction behavior of the Mo-cermet fuel can be evaluated individually for each phase of actinides oxide and Mo matrix. Better phase structures of the Mo-cermet fuel for taking full advantage of the oxidation-reduction controllability were suggested by the confinement of the actinides oxide phase with Mo.

Journal Articles

Oxygen potential measurement of (Pu$$_{0.928}$$Am$$_{0.072}$$)O$$_{2-x}$$ at high temperatures

Matsumoto, Taku; Arima, Tatsumi*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Kato, Masato; Morimoto, Kyoichi; Sunaoshi, Takeo*

Journal of Nuclear Science and Technology, 52(10), p.1296 - 1302, 2015/10

 Percentile:100(Nuclear Science & Technology)

The oxygen potentials of (Pu$$_{0.928}$$Am$$_{0.072}$$)O$$_{2-x}$$ were measured at 1873K, 1773K and 1473K by gas equilibrium method. It was shown that following the reduction of Am at the O/M ratio above 1.96, Pu was reduced at the O/M ratio below 1.96.

JAEA Reports

Research on diffusion behavior in oxide fuels (Joint research)

Sato, Isamu; Arima, Tatsumi*; Nishina, Masahiro*; Tanaka, Kosuke; Onose, Shoji; Idemitsu, Kazuya*

JAEA-Research 2012-006, 66 Pages, 2012/05

JAEA-Research-2012-006.pdf:13.55MB

As one of the important properties for fuel manufacturability and burning behavior, the diffusion behavior of actinides in oxide fuels was investigated by both the experimental and the molecular dynamics simulation (MD). Using diffusion couples consisted of an Am containing mixed oxide fuel and a UO$$_{2}$$ fuel, the diffusion tests were performed. The diffusion coefficients were estimated to be 10$$^{-12}$$m$$^{2}$$/s $$sim$$ 10$$^{-14}$$m$$^{2}$$/s. In addition, the difference between Pu and Am diffusion coefficients was vanishingly small. The temperature dependence of bulk diffusion coefficients of actinides in mixed oxide fuels could be evaluated by MD. An evaluation technique for the grain boundary diffusion could be established based on the coincidence site lattice theory. The practical diffusion coefficients were obtained by combining data from the experiments with those predicted from MD. The practical diffusion coefficients obtained was discussed for use of a fuel behavior analysis code.

Journal Articles

Initial dissolution rate of a Japanese simulated high-level waste glass P0798 as a function of pH and temperature measured by using micro-channel flow-through test method

Inagaki, Yaohiro*; Makigaki, Hikaru; Idemitsu, Kazuya*; Arima, Tatsumi*; Mitsui, Seiichiro; Noshita, Kenji*

Journal of Nuclear Science and Technology, 49(4), p.438 - 449, 2012/04

 Times Cited Count:13 Percentile:18.43(Nuclear Science & Technology)

Dissolution tests were performed for a simulated HLW glass by using a Micro-Channel Flow-Through (MCFT) test to evaluate the initial dissolution rate, $$r$$$$_{0}$$, as a function of pH and temperature. The results indicated that the $$r$$$$_{0}$$ shows a "V-shaped" pH dependence at 25$$^{circ}$$C, which is almost consistent with the previous results measured by using other test methods including Single Pass Flow-Through (SPFT) test. At elevated temperatures, however, the $$r$$$$_{0}$$ shows a "U-shaped" pH dependence with a flat bottom at neutral pH, which differs from the previous results. The results also indicated that the MCFT provided a higher value of the $$r$$$$_{0}$$with a steep slope of pH dependence than the SPFT results at basic pH from 8 to 11 at 90$$^{circ}$$C. With respect to the temperature dependence, the $$r$$$$_{0}$$ increases with temperature according to an Arrhenius law at any pH, and the apparent activation energy increases with pH, which suggests that the dissolution mechanism can change depending on pH.

Journal Articles

COMPASS code development; Validation of multi-physics analysis using particle method for core disruptive accidents in sodium-cooled fast reactors

Koshizuka, Seiichi*; Morita, Koji*; Arima, Tatsumi*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Naito, Masanori*; Shirakawa, Noriyuki*; Okada, Hidetoshi*; Uehara, Yasushi*; et al.

Proceedings of 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8) (CD-ROM), 11 Pages, 2010/10

In this paper, FY2009 results of the COMPASS code development are reported. Validation calculations for melt freezing and blockage formation, eutectic reaction of metal fuel, duct wall failure (thermal-hydraulic analysis), fuel pin failure and disruption and duct wall failure (structural analysis) are shown. Phase diagram calculations, classical and first-principles molecular dynamics were used to investigate physical properties of eutectic reactions: metallic fuel/steel and control rod material/steel. Basic studies for the particle method and SIMMER code calculations supported the COMPASS code development. COMPASS is expected to clarify the basis of experimentally-obtained correlations used in SIMMER. Combination of SIMMER and COMPASS will be useful for safety assessment of CDAs as well as optimization of the core design.

Journal Articles

Diffusion behaviors of plutonium and americium in polycrystalline urania

Sato, Isamu; Tanaka, Kosuke; Arima, Tatsumi*

IOP Conference Series; Materials Science and Engineering, 9, p.012005_1 - 012005_8, 2010/05

 Percentile:100

UO$$_{2}$$ discs and Am containing MOX discs were prepared to be diffusion couples. They were annealed for 4.5 h at 1600$$^{circ}$$C in a furnace under the constant oxygen partial pressures, and then concentrations of Pu and Am across the interfaces of them were measured with EPMA. The average diffusion coefficients of Pu and Am were obtained from the concentration profiles and were between 10$$^{-15}$$ and 10$$^{-13}$$m/s$$^{2}$$, in which the difference between Pu and Am was undetermined. This indicates that the difference between redistributions of Pu and Am found in a PIE may not be caused by the diffusion but by the other transport phenomenon. Moreover, the diffusion behavior was affected by existence of grain boundaries and the oxygen partial pressure in the furnace during annealing. From the affection of the grain boundary to the diffusion, the "practical" diffusion estimation may need grain boundary modeling.

Journal Articles

Detailed analyses of specific phenomena in core disruptive accidents of sodium-cooled fast reactors by the COMPASS code

Morita, Koji*; Zhang, S.*; Arima, Tatsumi*; Koshizuka, Seiichi*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Shirakawa, Noriyuki*; Inoue, Fusao*; Yugo, Hiroaki*; et al.

Proceedings of 18th International Conference on Nuclear Engineering (ICONE-18) (CD-ROM), 9 Pages, 2010/05

A five-year research project has been initiated in 2005 to develop a code based on the MPS (Moving Particle Semi-implicit) method for detailed analysis of specific phenomena in core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). The code is named COMPASS (Computer Code with Moving Particle Semi-implicit for Reactor Safety Analysis). The specific phenomena include (1) fuel pin failure and disruption, (2) molten pool boiling, (3) melt freezing and blockage formation, (4) duct wall failure, (5) low-energy disruptive core motion, (6) debris-bed coolability, and (7) metal-fuel pin failure. Validation study of COMPASS is progressing for these key phenomena. In this paper, recent COMPASS results of detailed analyses for the several specific phenomena are summarized.

Journal Articles

Validation for multi-physics simulation of core disruptive accidents in sodium-cooled fast reactors by COMPASS code

Koshizuka, Seiichi*; Morita, Koji*; Arima, Tatsumi*; Zhang, S.*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Naito, Masanori*; Shirakawa, Noriyuki*; Okada, Hidetoshi*; et al.

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) (CD-ROM), 11 Pages, 2009/09

Dispersion and freezing of molten core material was calculated by the COMPASS code to compare with the experimental data of GEYSER. Molten core material flowed up with freezing on the pipe inner surface. As a molten pool behavior, CABRI-TPA2 experiment was analyzed, where a sphere of solid steel was surrounded by solid fuel. Power was injected to cause melting and boiling of the steel sphere. SCARABEE-BE+3 test was analyzed by COMPASS as a validation of failure of duct walls.

Journal Articles

Measurement of HLW glass dissolution/alteration kinetics by using micro-reactor flow-through test method

Inagaki, Yaohiro*; Mitsui, Seiichiro; Makigaki, Hikaru*; Idemitsu, Kazuya*; Arima, Tatsumi*; Bamba, Tsunetaka; Noshita, Kenji*

Materials Research Society Symposium Proceedings, Vol.1193, p.219 - 228, 2009/05

We developed a new flow-through test method using micro-reactor, and applied it to measurement of the dissolution/alteration kinetics for a simulated HLW glass (P0798). In this method, a glass coupon is placed just on a Teflon plate having a micro-channel, and a solution is injected into the inlet of micro-channel by micro-syringe pump at a constant flow rate. The injected solution flows through the micro-channel reacting with the glass to the outlet, and the outlet solution is retrieved at certain intervals to be analyzed for determination of the dissolution/alteration rate. This method has some major features, i.e., simple test apparatus with compact size, high S/V ratio, sensitive/precise measurement of the glass dissolution/alteration rate, adequate glass shape for analysis of reacted glass surface, and so on. By use of this method the dissolution/alteration rate for P0798 was measured as a function of pH, temperature, flow rate, and time, and some available results were obtained to evaluate the dissolution/alteration kinetics.

Journal Articles

Measurement of initial dissolution rate of P0798 simulated HLW glass by using micro-reactor flow-through test method

Makigaki, Hikaru*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Arima, Tatsumi*; Mitsui, Seiichiro; Bamba, Tsunetaka; Noshita, Kenji*

Materials Research Society Symposium Proceedings, Vol.1193, p.307 - 314, 2009/05

By using micro-reactor flow-through test method we measured the initial dissolution rate of P0798 glass at 25$$^{circ}$$C as a function of pH between 5.6 and 12. The results showed that the initial dissolution rate determined by dissolution rate of Si has "V-shaped" pH dependency similar to R7T7 glass reported by CEA, France. We also measured the initial dissolution rate at pH 5.6 as a function of temperature between 25 and 90$$^{circ}$$C, and the activation energy was evaluated to be 51 kJ/mol, which value is slightly smaller than that of R7T7 glass at pH 9 reported by CEA. On the basis of these results and comparison, we discussed the dissolution kinetics of P0798 glass.

Journal Articles

COMPASS code development and validation; A Multi-physics analysis of core disruptive accidents in sodium-cooled fast reactors using particle method

Koshizuka, Seiichi*; Liu, J.*; Morita, Koji*; Arima, Tatsumi*; Zhang, S.*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Naito, Masanori*; Shirakawa, Noriyuki*; et al.

Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), 1 Pages, 2009/05

A computer code, named COMPASS, is developed for multi-physics analysis of core disruptive accidents of sodium-cooled fast reactors (SFRs). A meshless method, called MPS method, is employed since complex thermal-hydraulics and structural problems with various phase change processes have to be analyzed. Verification for separeted basic processes and validation for practical phenomena are carried out. COMPASS is also expected to investigate molten fuel discharge to avoid re-criticality in large size SFR cores. Both MOX and metal fuels are considered. Eutectic reactions between the metal fuel and the cladding material are investigated by phase diagram calculation, classical and first-principles molecular dynamics. Basic studies relevant to the numerical methods support the code development of COMPASS. Parallel processing is implemented by OpenMP to treat large-scale problems. A visualization tool is also prepared by using AVS.

Journal Articles

Code development for multi-physics and multi-scale analysis of core disruptive accidents in fast reactors using particle methods

Koshizuka, Seiichi*; Morita, Koji*; Arima, Tatsumi*; Zhang, S.*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Shirakawa, Noriyuki*; Naito, Masanori*; Okada, Hidetoshi*; et al.

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

A computer code, named COMPASS, is being developed for various complex phenomena of core disruptive accidents (CDAs) in sodium-cooled fast reactors (SFRs). The COMPASS is designed to analyze multi-physics problems involving thermal hydraulics, structure and phase change, in a unified framework of the MPS (Moving Particle Semi-implicit) method. The project has been carried out by six organizations for five years from FY2005 to FY2009. In this paper, the outcomes of the project in FY2007 are presented. Three validation calculations were completed by following the validation plan: melt freezing and blockage formation, molten pool boiling, and duct wall failure. The COMPASS code development was supported by basic studies of the numerical method, material science for eutectic reaction of the metal fuel, and SIMMER-III analyses.

Journal Articles

Building an application-specific grid computing environment using ITBL for nuclear material engineering

Tsujita, Yuichi*; Arima, Tatsumi*; Idemitsu, Kazuya*; Suzuki, Yoshio; Kimura, Hideo

Proceedings of 16th International Conference on Nuclear Engineering (ICONE-16) (CD-ROM), 9 Pages, 2008/05

Journal Articles

Building a computing environment for nuclear material engineering using ITBL

Tsujita, Yuichi*; Arima, Tatsumi*; Idemitsu, Kazuya*; Suzuki, Yoshio; Kimura, Hideo

Joho Shori Gakkai Kenkyu Hokoku 2008-ARC-177, 2008-HPC-114, p.103 - 108, 2008/03

Recently, many research works for Pu-recycle have been done. We proposed a molecular dynamics method to have deep understandings in nuclear materials. We adopted a parallel computing technique by using an ITBL's computing environment in our simulation program because a huge amount of computations and time steps is required. We received a request from application users to incorporate a user friendly interface in a computing environment for specifying parameters in a simulation program and successive operations of parallel computation and visualization on a user's terminal. So, we have built a GUI computing environment to realize such the functionalities by using an ITBL's client API. In this paper, we report objectives of this development, implementation method of this application, and examples of the computing environment. Finally, we mention its future plan.

Journal Articles

Development of a computer simulation environment for nuclear material engineering using ITBL

Tsujita, Yuichi*; Arima, Tatsumi*; Idemitsu, Kazuya*; Nakajima, Norihiro; Suzuki, Yoshio; Kimura, Hideo

Kinki Daigaku Kogakubu Kenkyu Hokoku, (41), p.87 - 92, 2007/12

no abstracts in English

Journal Articles

Code development for core disruptive accidents in sodium-cooled fast reactors

Koshizuka, Seiichi*; Liu, J.*; Morita, Koji*; Arima, Tatsumi*; Zhang, S.*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Naito, Masanori*; Shirakawa, Noriyuki*; et al.

Proceedings of IAEA Topical Meeting on Advanced Safety Assessment Methods for Nuclear Reactors (CD-ROM), 9 Pages, 2007/10

A computer code, named COMPASS (Computer Code with Moving Particle Semi-implicit for Reactor Safety Analysis), is being developed for various complex phenomena of core disruptive accidents (CDAs) in sodium-cooled fast reactors (SFRs). Theoretical studies are performed about a unified algorithm for compressible and incompressible flows, fluid flow with solid debris, and algorithm improvement for free surface flows. Code verification and validation procedures are established by exploiting the past experiences in those of SIMMER-III code. COMPASS will be used for separated phenomena in CDAs, while the whole core will be analyzed by SIMMER-III. COMPASS is expected to clarify the detailed process in duct wall failure and fuel discharge to avoid re-criticality during CDAs in large size SFRs.

Journal Articles

Multi-physics and multi-scale simulation for core disruptive accidents in fast breeder reactors

Koshizuka, Seiichi*; Liu, J.*; Morita, Koji*; Arima, Tatsumi*; Tobita, Yoshiharu; Yamano, Hidemasa; Ito, Takahiro*; Shirakawa, Noriyuki*; Hosoda, Seigo*; Araki, Kazuhiro*; et al.

Proceedings of 5th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-5), p.472 - 479, 2006/11

A 5-year research project started in FY2005 in the framework of Innovative Nuclear Research and Development Program funded by the Ministry of Education, Culture, Sports, Science and Technology in Japan. A computer code, named COMPASS (Computer Code with Moving Particle Semi-implicit for Reactor Safety Analysis), is being developed using the Moving Particle Semi-implicit (MPS) method for various complex phenomena of severe accidents in fast breeder reactors. Both MOX and metal fuels are considered. Eutectic reactions between the metal fuel and the cladding material are being investigated by molecular dynamics and molecular orbital methods. The molten metal flow with solidification was analyzed by MPS. The elastic analysis of a hexagonal wrapper tube was analyzed by the MPS method as well. The results were compared with an experiment and an calculation using an commercial code. Eutectic reactions were calculated by molecular dynamics and compared with the references. We found that the combination of the above numerical methods was useful for multi-physics and multi-scale phenomena of core disruptive accidents in fast breeder reactors.

52 (Records 1-20 displayed on this page)