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JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018) (Translated document)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2020-007, 249 Pages, 2020/10

JAEA-Research-2020-007.pdf:15.83MB

The accident of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, Japan Atomic Energy Agency (JAEA) has been conducting "Long-term Assessment of Transport of Radioactive Contaminants in the Environment of Fukushima" concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Journal Articles

Seven-year temporal variation of caesium-137 discharge inventory from the port of Fukushima Daiichi Nuclear Power Plant; Continuous monthly estimation of caesium-137 discharge in the period from April 2011 to June 2018

Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*

Journal of Nuclear Science and Technology, 57(8), p.939 - 950, 2020/08

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

After direct discharges of highly contaminated water of the Fukushima Daiichi Nuclear Power Plant (1F) from April to May 2011, Kanda suggested that relatively small amounts of run-off of radionuclides from the 1F port into the Fukushima coastal region subsequently continued by his estimation method. However, the estimation period was limited to up to September 2012. Therefore, this paper estimates the discharge inventory up to June 2018. In the missing period, the Japanese government and Tokyo Electric Power Company Holdings have continued efforts to stop the discharge, and consequently, the radionuclide concentration in seawater inside the 1F port has gradually diminished. We show the monthly discharge inventory of $$^{137}$$Cs up to June 2018 by two methods, i.e., Kanda method partially improved by the authors and a more sophisticated method using Voronoi tessellation reflecting the increase in the number of monitoring points inside the 1 F port. The results show that the former always yields overestimated results compared with the latter, but the ratio of the former to the latter is less than one order of magnitude. Using these results, we evaluate the impact of the discharge inventory from the 1F port into the coastal area and radiation dose upon fish ingestion.

Journal Articles

Kinetic inductance neutron detector operated at near critical temperature

Vu, TheDang; Nishimura, Kazuma*; Shishido, Hiroaki*; Harada, Masahide; Oikawa, Kenichi; Miyajima, Shigeyuki*; Hidaka, Mutsuo*; Oku, Takayuki; Soyama, Kazuhiko; Aizawa, Kazuya; et al.

Journal of Physics; Conference Series, 1590, p.012036_1 - 012036_9, 2020/07

Journal Articles

Monte Carlo radiation transport modelling of the current-biased kinetic inductance detector

Malins, A.; Machida, Masahiko; Vu, TheDang; Aizawa, Kazuya; Ishida, Takekazu*

Nuclear Instruments and Methods in Physics Research A, 953, p.163130_1 - 163130_7, 2020/02

 Times Cited Count:2 Percentile:6.04(Instruments & Instrumentation)

Journal Articles

High performance eigenvalue solver for Hubbard model; Tuning strategies for LOBPCG method on CUDA GPU

Yamada, Susumu; Machida, Masahiko; Imamura, Toshiyuki*

Parallel Computing; Technology Trends, p.105 - 113, 2020/00

no abstracts in English

Journal Articles

Simulation study of the effects of buildings, trees and paved surfaces on ambient dose equivalent rates outdoors at three suburban sites near Fukushima Dai-ichi

Kim, M.; Malins, A.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Journal of Environmental Radioactivity, 210, p.105803_1 - 105803_10, 2019/12

 Times Cited Count:0 Percentile:100(Environmental Sciences)

To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of $$gamma$$ rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Seven-year temporal variation of cesium-137 discharge inventory from the port of Fukushima Dai-ichi Nuclear Power Plant; Continuous monthly estimation of cesium-137 discharge in the period from April 2011 to June 2018

Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 18(4), p.226 - 236, 2019/12

After direct discharges of highly-contaminated water from Unit 2 and 3 in Fukushima Daiichi Nuclear Power Plant (1F) in April to May 2011, Kanda suggested that relatively small run-off of radionuclides from 1F port into Fukushima coastal region has subsequently continued by using his estimation scheme. However, the estimation period was limited until September 2012, and there has been no report on the issue since the work. Therefore, this paper focuses on discharge inventory from 1F port until June 2018. In the missing period, the central government and Tokyo Electric Power Company Holdings have done continuous efforts to stop the discharge, and consequently sea water concentration inside 1F port has diminished gradually. We show monthly discharge inventory of Cs-137 until June 2018 by two schemes, i.e., Kanda's scheme partially improved by authors and more sophisticated one using Voronoi tessellation reflecting the increment of the number of monitoring points inside 1F port. The results show that the former always presents overestimated results compared to the latter but the ratio of former to latter is less than one order. Based on these results, we evaluate impact of discharge inventory from 1F port into the coastal area and radiation does via fish digestion.

Journal Articles

Research and development behind a computation system for 3D distributions of air dose rates in the environment; Estimating environmental radiation doses using PHITS together with remote sensing data

Kim, M.; Malins, A.; Sakuma, Kazuyuki; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Isotope News, (765), p.30 - 33, 2019/10

Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The $$^{134}$$Cs and $$^{137}$$Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, individual conifer and broadleaf trees, and the topography of the land surface. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Journal Articles

Recent status and future issues of molecular modeling studies for clay and fungi adsorbing cesium

Suno, Hiroya; Okumura, Masahiko; Machida, Masahiko

Jiban Kogakkai-Shi, 67(10), p.34 - 35, 2019/10

no abstracts in English

Journal Articles

Quantum chemical calculations for the norbadione A complexes with Cs$$^+$$, K$$^+$$, and Na$$^+$$ in gas and aqueous phases

Suno, Hiroya; Machida, Masahiko

Chemical Physics Letters, 730, p.26 - 31, 2019/09

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

We perform quantum chemical calculations for the Cs$$^+$$, K$$^+$$, and Na$$^+$$ complexes of norbadione A (NBA), a pigment molecule in mushrooms known to accumulate Cs$$^+$$. A numerical two-step approach, by Ota $textit{et al.}$, is employed to examine its alkali-metal-cation complexation selectivity in aqueous solutions. Applying it to the neutral, di- and tetra-deprotonated NBAs, we confirm that the complexation selectivity on Cs$$^+$$ emerges only in high pHs, in which the di-protonated NBA dominates, in agreement with experimental results. This is the first demonstration of the approach for a biological molecule whose selectivity is known to be anomalous.

Journal Articles

First-principles calculation of mechanical properties of simulated debris Zr$$_x$$U$$_{1-x}$$O$$_2$$

Itakura, Mitsuhiro; Nakamura, Hiroki; Kitagaki, Toru; Hoshino, Takanori; Machida, Masahiko

Journal of Nuclear Science and Technology, 56(9-10), p.915 - 921, 2019/09

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

To elucidate the mechanical properties of fuel debris inside the Fukushima Daiichi Nuclear Power Plant, we use first-principles calculations to evaluate mechanical properties of cubic Zr$$_{x}$$U$$_{1-x}$$O$$_{2}$$, which is a main component of the fuel debris. We focus on the dependence of mechanical properties on the fraction x of zirconium, compare our results with recent experiment of simulated debris, in which dependences of elastic moduli and fracture toughness on the ZrO$$_{2}$$ content showed deviation from a simple linear relation. We show that elastic moduli drop at around x=0.25 and increase again for larger values of x, as has been observed in experiments. The reason of the drop is a softening owing to disordered atomistic structures induced by the solute zirconium atoms. We also find that stress-strain curves for the x=0.125 case show marked hysteresis owing to the existence of many meta-stable states. We show that this hysteresis leads to slightly increased fracture toughness, but it is not enough to account for the significant increase of fracture toughness observed in experiments.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2019-002, 235 Pages, 2019/08

JAEA-Research-2019-002.pdf:21.04MB

The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Journal Articles

Research and development on membrane IS process for hydrogen production using solar heat

Myagmarjav, O.; Iwatsuki, Jin; Tanaka, Nobuyuki; Noguchi, Hiroki; Kamiji, Yu; Ioka, Ikuo; Kubo, Shinji; Nomura, Mikihiro*; Yamaki, Tetsuya*; Sawada, Shinichi*; et al.

International Journal of Hydrogen Energy, 44(35), p.19141 - 19152, 2019/07

 Times Cited Count:6 Percentile:26.46(Chemistry, Physical)

Journal Articles

Long-term simulations of radiocesium discharge in watershed with improved radiocesium wash-off model; Applying the model to Abukuma River basin of Fukushima

Liu, X.; Machida, Masahiko; Kurikami, Hiroshi; Kitamura, Akihiro

Journal of Environmental Radioactivity, 203, p.135 - 146, 2019/07

 Times Cited Count:1 Percentile:71.43(Environmental Sciences)

In order to simulate the long-term migration and distribution of radiocesium after the Fukushima accident, a numerical model, Soil and Cesium Transport (SACT) based on universal soil loss equation (USLE), has been developed in previous studies. Although the SACT model's results on radiocesium discharge in 2011 are in reasonable agreement with field measurements, it fails to capture the sharp decrease of radiocesium flux in subsequent years, especially in the case of Abukuma River. We therefore have improved SACT by implementing the vertical migration and fixation of radiocesium in soil. For validation purpose, the annual average radiocesium concentration in sediments discharged from Abukuma River has been evaluated from measurement data. New model achieved much better agreement with the measurement results without parameter tuning.

Journal Articles

First-principles calculation study on phonon thermal conductivity of thorium and plutonium dioxides; Intrinsic anharmonic phonon-phonon and extrinsic grain-boundary-phonon scattering effects

Nakamura, Hiroki; Machida, Masahiko

Journal of Nuclear Materials, 519, p.45 - 51, 2019/06

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Thermal conductivity of nuclear fuel materials is one of the most essential thermophysical data in analyzing nuclear reactor safety and fuel performance. To establish a reliable technique of computation of their thermal conductivity, we apply a scheme based on first-principles electronic calculations and calculate phonon thermal conductivity of both plutonium and thorium dioxides. In the employed scheme, all phonon properties are calculated from harmonic and third-order anharmonic force constants obtained through first-principles calculations. Using these phonon properties, phonon thermal conductivity are computed with a standard phonon transport theory. The calculation results show a good agreement with experiments. Moreover, we evaluate grain-boundary effects on phonon thermal conduction. These results prove that the present first-principles scheme is reliably applicable to accurate computation of phonon thermal conductivity of fuel materials in the considered temperature range.

Journal Articles

Development of the ReaxFF methodology for electrolyte-water systems

Fedkin, M. V.*; Shin, Y. K.*; Dasgupta, N.*; Yeon, J.*; Zhang, W.*; van Duin, D.*; Van Duin, A. C. T.*; Mori, Kento*; Fujiwara, Atsushi*; Machida, Masahiko; et al.

Journal of Physical Chemistry A, 123(10), p.2125 - 2141, 2019/03

 Times Cited Count:6 Percentile:12.48(Chemistry, Physical)

no abstracts in English

Journal Articles

Understanding competition of polyalcohol dehydration reactions in hot water

Chang, Y. L.*; Sasaki, Takehiko*; Ribas-Ari$~n$o, J.*; Machida, Masahiko; Shiga, Motoyuki

Journal of Physical Chemistry B, 123(7), p.1662 - 1671, 2019/02

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

Dehydration of biomass-derived polyalcohols has recently drawn attention in green chemistry as a prototype of selective reactions controllable in hot water or hot carbonated water, without any use of organic solvents or metal catalysts. Here, we report a free-energy analysis based on first-principles metadynamics and blue-moon ensemble simulations to understand the mechanism of competing intramolecular dehydration reactions of 1,2,5-pentanetriol in hot acidic water. The simulations consistently predict that the most dominant mechanism is the proton-assisted S$$_{rm N}$$2 process, where the protonation of the hydroxyl group by water and the C-O bond breaking and formation occur in a single step. The detailed mechanism found from the simulations shows how the reaction paths are selective in hot water and why the reaction rates are accelerated in acidic environments, thus giving a clear explanation of experimental findings for a broad class of competing dehydration processes of polyalcohols.

Journal Articles

Modelling the effect of mechanical remediation on dose rates above radiocesium contaminated land

Malins, A.; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko

Remediation Measures for Radioactively Contaminated Areas, p.259 - 272, 2019/00

Journal Articles

Radiocesium interaction with clay minerals; Theory and simulation advances Post-Fukushima

Okumura, Masahiko; Kerisit, S.*; Bourg, I. C.*; Lammers, L. N.*; Ikeda, Takashi*; Sassi, M.*; Rosso, K. M.*; Machida, Masahiko

Journal of Environmental Radioactivity, 189, p.135 - 145, 2018/09

 Times Cited Count:20 Percentile:9.76(Environmental Sciences)

no abstracts in English

Journal Articles

Development of the evaluation tool for air dose rate in forest using a Monte Carlo radiation transport code (PHITS)

Sakuma, Kazuyuki; Niizato, Tadafumi; Kim, M.; Malins, A.; Machida, Masahiko; Yoshimura, Kazuya; Kurikami, Hiroshi; Kitamura, Akihiro; Hosomi, Masaaki*

Kankyo Hoshano Josen Gakkai-Shi, 6(3), p.145 - 152, 2018/09

We simulated air dose rates using PHITS to consider how the partitioning of radiocesium between the forest canopy, litter layer and soil layer affected air dose rates by perturbing the radiocesium source distribution between different simulations. Transferring radiocesium from the canopy to the litter layer did not affect air dose rates at 1 m above the ground when setting up the simulation with a radiocesium distribution measured in October 2015. This is because there was almost no radiocesium in the canopy at that time. However air dose rates tended to be high near the canopy, and above the canopy up to 200 m altitude, when the simulations were initiated using source distribution data applicable for August-September 2011, due to the larger amount of radiocesium in the canopy at that time. Transferring the radiocesium from the canopy to the litter layer in this case was associated with a three times increase in the air dose rate at 1 m, as the average distance between radiocesium in the forest and 1 m above the ground was shortened. In both cases radiocesium transfer from the litter layer to the underlying soil was associated with a one third to 50% reduction in air dose rates at 1 m, due to the self-shielding effect of soil.

642 (Records 1-20 displayed on this page)