Periez, R.*; Bezhenar, R.*; Brovchenko, I.*; Jung, K. T.*; Kamidaira, Yuki; Kim, K. O.*; Kobayashi, Takuya; Liptak, L.*; Maderich, V.*; Min, B. I.*; et al.
Journal of Environmental Radioactivity, 198, p.50 - 63, 2019/03
A number of marine radionuclide dispersion models were applied to simulate Cs releases from Fukushima Daiichi Nuclear Power Plant accident in 2011 over the northwest Pacific. Simulations extended over two years and both direct releases into the ocean and deposition of atmospheric releases on the ocean surface were considered. Dispersion models included an embedded biological uptake model (BUM). Three types of BUMs were used: equilibrium, dynamic and allometric. Model results were compared with Cs measurements in water, sediment and biota. A reasonable agreement in model/model and model/data comparisons was obtained.
Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Nunami, Masanori*
Computer Physics Communications, 235, p.9 - 15, 2019/02
We have implemented the Sugama collision operator in the gyrokinetic Vlasov simulation code, GKV, with an implicit time-integration scheme. The new method is versatile and independent of the details of the linearized collision operator, by means of an operator splitting, an implicit time integrator, and an iterative Krylov subspace solver. Numerical tests demonstrate stable computation over the time step size restricted by the collision term. An efficient implementation for parallel computation on distributed memory systems is realized by using the data transpose communication, which makes the iterative solver free from inter-node communications during iteration. Consequently, the present approach achieves enhancement of computational efficiency and reduction of computational time to solution simultaneously, and significantly accelerates the total performance of the application.
Kitamura, Yasunori*; Fukushima, Masahiro; Kitamura, Yasunori*
Annals of Nuclear Energy, 125, p.328 - 341, 2019/01
It has been taken for granted that the neutron correlation methods that employ two sets of neutron counting systems, e.g., the covariance-to-mean and the cross-correlation methods, are free from the count-loss effect for determination of the neutron decay constant. It was however found in the present study that these methods overestimate the neutron decay constant under high counting rate conditions. New formulae of these methods were hence obtained on the basis of a rigorous theoretical approach for treating the count-loss process. It is expected that the present formulae work better than conventional ones for determination of the neutron decay constant.
Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito; Matsuda, Kenji*; Toda, Hiroyuki*
Computational Materials Science, 156, p.368 - 375, 2019/01
The segregation of multiple hydrogen atoms along aluminum (Al) grain boundaries (GBs) and fracture surfaces (FSs) was investigated through first-principles calculations considering the characteristics of GBs. The results indicate that hydrogen segregation is difficult along low-energy GBs. The segregation energy of multiple hydrogen atoms along GBs and FSs and the cohesive energy was obtained for three types of high-energy Al GBs. With increasing hydrogen segregation along the GBs, the cohesive energy of the GB decreases and approaches zero with no decrease in GB segregation energy. The GB cohesive energy decreases in parallel with the volume expansion of the region of low electron density along the GB.
Manabe, Kentaro; Matsumoto, Masaki*
Journal of Nuclear Science and Technology, 56(1), p.78 - 86, 2019/01
If an insoluble cesium-bearing particle is incorporated into the human body, the radioactivity will move as a single particle. In this case, it is impossible to estimate the number of disintegrations by considering the average behavior of countless nuclei. Then, a method was developed to simulate the behavior of the particle stochastically; and a biokinetic model was constructed to consider the characteristics of insoluble particles. Combination of the method and the model enables to estimate the number of disintegrations, and consequently the internal doses considering the stochastic behavior of the single cesium particle. We evaluated a probability density function of committed equivalent and effective doses and its 99th percentile value and arithmetic mean by repeating the above described procedure, and compared them to the reference values based on the existing models. As a result, the 99th percentile value of committed effective doses was 70 times the reference value when the number of incorporated particles was one, and consequently the dose level was quite low. When the exposure level is 1 mSv in committed effective dose, the uncertainty originating in the insolubility of cesium particles was negligibly small.
Iwamoto, Hiroki; Meigo, Shinichiro
Journal of Nuclear Science and Technology, 56(2), p.160 - 171, 2019/01
We present a new model to describe the fission probability of the high-energy fission model, as deduced from the intranuclear cascade calculation with the Intra-Nuclear Cascade model of Lige (INCL) version 4.6 and Prokofiev's phenomenological systematics of the proton-induced fission cross sections. This model is implemented in the de-excitation model of the Generalized Evaporation Model (GEM), and applied to Monte Carlo spallation reaction simulation using the Particle and Heavy Ion Transport code System (PHITS). Comparing with experimental data for subactinide nuclei shows that this model can provide a unified prediction of the proton-, neutron-, and deuteron-induced fission cross sections with markedly improved accuracy. The calculated fission fragments tend to shift to higher mass numbers. To account for the isotopic distributions of fission fragments within the framework of a coupled INCL/GEM, modification of INCL is required, especially for description of the highly-excited states of residual nuclei.
Saeki, Morihisa*; Matsumura, Daiju; Yomogida, Takumi; Taguchi, Tomitsugu*; Tsuji, Takuya; Saito, Hiroyuki*; Oba, Hironori*
Journal of Physical Chemistry C, 123(1), p.817 - 824, 2019/01
Reaction kinetics of laser-induced particle formation in an aqueous solution of PdCl was investigated by transmission electron microscope (TEM) and dispersive X-ray absorption fine structure (DXAFS). The Pd particle was generated by irradiation of nanosecond pulsed 266-nm laser. The TEM observation showed dependence of the particle size on the laser fluence and promotion of the particle growth by irradiation of high-fluence laser. The DXAFS data give us the Pd concentration. Temporal changes of the Pd concentration analyzed based on Finke-Watzky two step mechanism. The analysis elucidates that the laser photon contributes to the reduction of the PdCl ion by the one-photon process and to the autocatalytic growth of the Pd particles by the multi-photon process.
JAEA-Review 2018-021, 79 Pages, 2018/12
Japan has vast marine environment. Therefore, the marine environmental assessment to grasp oceanic structure of shelf and coastal area in the vicinity is important from various viewpoints, such as marine and seafloor resources, national defense, and disaster prevention for Japan. For instance, preserving the coral coasts around the Ryukyu Islands, and assessing marine pollution due the raidionuclides released form the Fukushima Daiichi Nuclear Power Plant are urgent matters for Japan. In the present study, submesoscale-eddy-resolving numerical experiments using Regional Oceanic Modeling System (ROMS) were conducted for areas around the Ryukyu Islands and the northeast Pacific coast of Japan to investigate the applicability of the high-resolution model to the marine assessment system. In addition, we considered improving the Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) to reproduce more realistic oceanic dispersal of radionuclide by introducing multiple-nested downscaling ocean modeling system using the ROMS. Extensive model-data comparison demonstrated that the submsoscale eddy-resolving models, with a lateral grid resolution of 1km, could successfully reproduce the synoptic and mesoscale oceanic structures. According to the eddy heat flux analysis and energy conversion analysis relevant to the eddy-generation mechanisms revealed that both of shear instability and baroclinic instability enhanced the three-dimensional mixing of tracers induced by submesoscale eddy. These results suggested that the multiple-nested, high resolution, downscaling ocean modeling has important role to develop the accurate marine environmental assessment system.
Kaneko, Masashi; Watanabe, Masayuki; Miyashita, Sunao*; Nakashima, Satoru*
Hyperfine Interactions, 239(1), p.20_1 - 20_10, 2018/12
We optimized a mixing ratio of exchange energy between pure DFT and exact Hartree-Fock using TPSS exchange-correlation functional to estimate the accurate coordination bonds in f-block complexes by numerically benchmarking with the experimental data of Mssbauer isomer shifts for Eu and Np nuclides. Second-order Douglas-Kroll-Hess Hamiltonian with segmented all-electron relativistically contracted basis set was employed to calculate the electron densities at Eu and Np nuclei, i.e. contact densities, for each five complexes for Eu(III) and Np(IV) systems. We compared the root mean square deviation values of their isomer shifts between experiment and calculation by changing the mixing ratio of Hartree-Fock exchange parameter from 0 to 100 % at intervals of 10 %. As the result, it was indicated that the mixing ratio of 30 and 60 % for Eu and Np benchmark systems, respectively, gives the smallest deviation values. Mulliken's spin population analysis indicated that the covalency in the metal-ligand bonds for both Eu and Np complexes decreases with increasing the Hartree-Fock exchange admixture.
Isotope News, (760), p.2 - 5, 2018/12
Recently, we proposed a new model for estimating the biological effectiveness for Boron Neutron Capture Therapy (BNCT) based on the absorbed dose distributions in cellular scale. The model quantitatively highlighted the indispensable need to consider the synergetic effect and the dose dependence of the biological effectiveness in the estimate of the therapeutic effect of BNCT. This paper reviews the basic features of the model.
Fukumitsu, Nobuyoshi*; Yamauchi, Yusuke*; Saptiama, I.*; Ariga, Katsuhiko*; Hatano, Kentaro*; Kumada, Hiroaki*; Fujita, Yoshitaka; Tsuchiya, Kunihiko
Isotope News, (760), p.15 - 18, 2018/12
Nakamura, Shoji; Kimura, Atsushi; Hales, B. P.; Iwamoto, Osamu; Shibahara, Yuji*; Uehara, Akihiro*; Fujii, Toshiyuki*
JAEA-Conf 2018-001, p.199 - 203, 2018/12
Study on cross-section measurements has been promoted for Cs among long-lived fission products in ImPACT Project. The feasibility study on Se sample preparation also has been conducted to measure its cross sections in future. During the feasibility study, we started the neutron-capture cross-section measurements of stable Se isotopes. This paper reports research progresses on preparation of a radioactive Cs sample, neutron irradiation experiments with the Cs sample, and cross-section measurements of stable Se isotopes.
Shibahara, Yuji*; Uehara, Akihiro*; Fujii, Toshiyuki*; Nakamura, Shoji; Kimura, Atsushi; Hales, B. P.; Iwamoto, Osamu
JAEA-Conf 2018-001, p.205 - 210, 2018/12
In the ImPACT project, high-precision mass analysis was performed on a Cs standard solution for using Cs included in the standard solution as an impurity to measure the Cs cross-sections. A Cs standard solution of only 10Bq (pg order) was analyzed, and the isotope ratio of Cs and Cs was obtained with an accuracy of 0.5%.
Otosaka, Shigeyoshi; Sato, Yuhi*; Suzuki, Takashi; Kuwabara, Jun; Nakanishi, Takahiro
Journal of Environmental Radioactivity, 192, p.208 - 218, 2018/12
From August 2011 to October 2013, the concentration of iodine-129 (I) in the seabed sediment collected from 26 stations located within 160 km from the Fukushima Daiichi Nuclear Power Plant was estimated. The concentrations of I in seabed sediment off Fukushima in 2011 ranged between 0.02 and 0.45 mBq/kg. Although iodine is a biophilic element, the accident-derived radioiodine negligibly affects the benthic ecosystem. Until October 2013, a slightly increased activity of I in the surface sediment in the shelf-edge region (bottom depth: 200-400 m) was observed. The increase of the I concentrations in the shelf-edge sediments was affected by the (1) transport of I-bound particles from the land through rivers and (2) re-deposition of I desorbed from the contaminated coastal sediment to the shelf-edge sediments, which were considered to be dominant processes.
Nordlund, K.*; Zinkle, S. J.*; Sand, A. E.*; Granberg, F.*; Averback, R. S.*; Stoller, R. E.*; Suzudo, Tomoaki; Malerba, L.*; Banhart, F.*; Weber, W. J.*; et al.
Journal of Nuclear Materials, 512, p.450 - 479, 2018/12
Scientific understanding of any kind of radiation effects starts from the primary damage. We consider the extensive experimental and computer simulation studies that have been performed over the past several decades on what the nature of the primary damage is. We review both the production of crystallographic or topological defects in materials as well as radiation mixing, i.e. the process where atoms in perfect crystallographic positions exchange positions with other ones in non-defective positions. We also consider the recent effort to provide alternatives to the current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model for metals. We present in detail new complementary displacement production estimators ("athermal recombination corrected dpa": arc-dpa) and atomic mixing ("replacements per atom": rpa) functions that extend the NRT-dpa, and discuss their advantages and limitations.
Ishikawa, Tetsuo*; Matsumoto, Masaki*; Sato, Tatsuhiko; Yamaguchi, Ichiro*; Kai, Michiaki*
Journal of Radiological Protection, 38(4), p.1253 - 1268, 2018/12
The current knowledge on internal dose estimation and its health effect were reviewed in this paper. The goals were to discuss the uncertainty of current dose coefficients, to compare the effects of external and internal exposures, and to review recent epidemiological studies. Radionuclides focused on in this study were caesium-137 (Cs), caesium-134 (Cs), and iodine-131 (I), which primarily contributed to internal effective thyroid doses after the Fukushima Dai-ichi Nuclear Power Station accident. Current knowledge suggests that the risk of internal exposure could be generally the same as or less than that of external exposure, when they are compared at the same effective dose.
Kusaka, Ryoji; Watanabe, Masayuki
Physical Chemistry Chemical Physics, 20(47), p.29588 - 29590, 2018/12
Mechanistic understanding of solvent extraction of uranyl ions (UO) by tributyl phosphate (TBP) will help improve the technology for the treatment and disposal of spent nuclear fuels. So far, it has been believed that uranyl ions in the aqueous phase are adsorbed to a TBP-enriched organic/aqueous interface, form complexes with TBP at the interface, and are extracted into the organic phase. Here we show that uranyl-TBP complex formation does not take place at the interface using vibrational sum frequency generation (VSFG) spectroscopy and propose an alternative extraction mechanism that uranyl nitrate, UO(NO), passes through the interface and forms the uranyl-TBP complex, UO(NO)(TBP), in the organic phase.
Shizuma, Toshiyuki; Iwamoto, Nobuyuki; Makinaga, Ayano*; Massarczyk, R.*; Schwengner, R.*; Beyer, R.*; Bemmerer, D.*; Dietz, M.*; Junghans, A.*; Kgler, T.*; et al.
Physical Review C, 98(6), p.064317_1 - 064317_12, 2018/12
The dipole strength distribution of Pb was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The photo-absorption cross sections were extracted from the measured scattering cross sections and the branching ratios. The present (,) data combined with (,) data from the literature were used as an input to the statistical calculation code CCONE to evaluate the neutron capture cross section of the unstable Pb nucleus.
Kimura, Taiki*; Kaneko, Masashi; Watanabe, Masayuki; Miyashita, Sunao*; Nakashima, Satoru*
Dalton Transactions, 47(42), p.14924 - 14931, 2018/11
We demonstrated density functional calculations of Eu(III) and Am(III) complexes with pnictogen-donor (X) ligands, CH)X-CH-CH-X(CH) (X = N, P, As and Sb). We investigated the optimized structures of the cmoplexes and the Gibbs energy differences in the complex formation reactions. Those results indicated that the N- and P-donor ligands have Am(III) ion selectivity over Eu(III) ion, especially, the P-donor ligand showed the highest selectivity. The tendency of the Am(III)/Eu(III) selectivity by the pnictogen-dono ligands was found to be comparable to that of soft acid classification in hard and soft acids and bases rule. Mulliken's spin population analysis indicated that the bonding property between the metal ion and the pnictogen atoms correlated with the Am(III)/Eu(III) selectivity. In particular, the participation of f-orbital electrons of the metal ion in the covalency was indicated to have an important role for the selectivity.
Uchiyama, Yusuke*; Miyagawa, Tsubasa*; Odani, Sachika*; Kamidaira, Yuki; Odani, Sachika*
Doboku Gakkai Rombunshu, B2 (Kaigan Kogaku) (Internet), 74(2), p.I_1291 - I_1296, 2018/11