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Journal Articles

On the hydrogen production of geopolymer wasteforms under irradiation

Cantarel, V.; Arisaka, Makoto; Yamagishi, Isao

Journal of the American Ceramic Society, 102(12), p.7553 - 7563, 2019/12

The hydrogen gas (H$$_{2}$$) production of wasteforms is a major safety concern for encapsulating nuclear wastes. For geopolymers, the H$$_{2}$$ produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the hydrogen production was measured under $$^{60}$$Co gamma irradiation. The effect of water saturation and sample size were studied for pure geopolymers, or using zeolites as an example waste. When geopolymer monolithic samples were large and saturated by water, the hydrogen released was measured up to two orders of magnitude lower with a 40 cm long cylinder samples (1.9$$times$$10$$^{-10}$$ mol.J$$^{-1}$$) than a sample in powder form (2.2$$times$$10$$^{-8}$$ mol.J$$^{-1}$$). To interpret results, a simple model was used, considering only hydrogen production, a potential recombination and its diffusion in the geopolymer matrix. Knowing the diffusion constant of the matrix, the model was able to reproduce the evolution of the hydrogen release as a function of the water saturation level and predict the evolution when sample size is increased up to 40 cm.

Journal Articles

Numerical study of transport pathways of $$^{137}$$Cs from forests to freshwater fish living in mountain streams in Fukushima, Japan

Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Sasaki, Yoshito; Niizato, Tadafumi

Journal of Environmental Radioactivity, 208-209, p.106005_1 - 106005_11, 2019/11

To assess the uptake of Cs-137 ($$^{137}$$Cs) by freshwater fish, we developed a compartment model for the migration of $$^{137}$$Cs on the catchment scale from forests to river water. We modelled a generic forest catchment with Fukushima-like parameters to ascertain the importance of export pathways of $$^{137}$$Cs from forests to river water for the uptake of $$^{137}$$Cs by freshwater fish. The results suggest that the decreasing trend of $$^{137}$$Cs in river water and freshwater fish was due to combination of the decreasing trend in the forest leaves/needles and litter compartments, and the increasing trend in soil. The $$^{137}$$Cs concentrations within these forest compartments plateau at around ten years after the fallout due to $$^{137}$$Cs circulation in forests reaching an equilibrium state.

Journal Articles

Characterizing vertical migration of $$^{137}$$Cs in organic layer and mineral soil in Japanese forests; Four-year observation and model analysis

Muto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun

Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11

Vertical distributions of $$^{137}$$Cs in the soil profile were observed at five forest sites with different vegetation types for 4.4 years after the Fukushima Dai-ichi Nuclear Power Plant accident, and $$^{137}$$Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of $$^{137}$$Cs could be suppressed rapidly in Japanese forests. The diffusion coefficients of $$^{137}$$Cs in the mineral soil were estimated to be 0.042-0.55 cm$$^2$$y$$^{-1}$$, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions indicated $$^{137}$$Cs mainly distributed in the surface mineral soil at 10 years after the accident. It suggest that the $$^{137}$$Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.

Journal Articles

A Modeling approach to estimate the $$^{137}$$Cs discharge in rivers from immediately after the Fukushima accident until 2017

Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Kurikami, Hiroshi; Namba, Kenji*; Zheleznyak, M.*

Journal of Environmental Radioactivity, 208-209, p.106041_1 - 106041_12, 2019/11

We developed a simple model to evaluate and predict $$^{137}$$Cs discharge from catchment using tank model and L-Q equation. Using this model, $$^{137}$$Cs discharge and discharge ratio from Abukuma River and 13 other rivers in Fukushima coastal region were estimated from immediately after Fukushima accident to 2017. Cesium-137 discharge ratio to the deposition amount in catchment through Abukuma River and 13 other rivers in Fukushima coastal region during about initial six months were estimated to be 18 TBq (3.1%) and 11 TBq (0.8%), respectively. These values were 1-2 orders of magnitude larger than the previous study observed after June 2011, indicating that initial $$^{137}$$Cs discharge from catchment through rivers was a significant. However it was founded that an impact on the ocean derived from initial $$^{137}$$Cs discharge through river can be limited because $$^{137}$$Cs discharge from Abukuma River and 13 other rivers in Fukushima coastal region (29 TBq) was two orders of magnitude smaller than the direct release from FDNPP into the ocean (3.5 PBq) and from atmospheric deposition into the ocean (7.6 PBq).

Journal Articles

Temporal change in concentration of radiocesium in Fukushima river water

Nakanishi, Takahiro

Isotope News, (765), p.22 - 25, 2019/10

Temporal change in concentration of radiocesium in Fukushima river water are outlined. Radiocesium concentration in river water keeps decreasing after several years, however, the declining trend for the dissolved radiocesium concentration is gradually decreasing with time.

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

Track3; Robot technology, remote control system

Kawabata, Kuniaki; Osumi, Hisashi*; Onishi, Ken*

Nippon Kikai Gakkai-Shi, 122(1211), p.16 - 17, 2019/10

no abstracts in English

JAEA Reports

Inverse analysis of steam and hydrogen generation history of Fukushima Daiichi Nuclear Power Station unit 3

Yoshikawa, Shinji

JAEA-Research 2019-004, 32 Pages, 2019/09

JAEA-Research-2019-004.pdf:2.77MB

Steam and hydrogen generation history and gas leakage area are inversely evaluated by a thermal hydraulic analysis code GOTHIC. The analyzed period in the accident progression is from the arrival of reactor liquid level at the top of active fuel (TAF) until start of depressurization of reactor pressure vessel(RPV) by activation of automatic depressurization system(ADS). Based on the measured behaviors of the RPV and PCV pressures from 6:30 of March 13th until the ADS activation, some leakage from RPV to PCV is supposed during this period. The leakage path and area are inversely derived on plural possible accident scenarios. The leakage area are estimated to be no greater than 1 cm$$^{2}$$. This result suggests that the gas flow at the time of the main slumping would have been through S/C, where vapor condensation was effective, thus certain contribution of non-condensable gases like hydrogen seems necessary to explain the observed D/W pressure increase.

Journal Articles

Proposal of laser-induced ultrasonic guided wave for corrosion detection of reinforced concrete structures in Fukushima Daiichi Nuclear Power Plant decommissioning site

Furusawa, Akinori; Takenaka, Yusuke; Nishimura, Akihiko

Applied Sciences (Internet), 9(17), p.3544_1 - 3544_12, 2019/09

Remote-controlled, non-destructive testing is necessary to detect corrosion of the reinforced concrete structures at the Fukushima Daiichi Nuclear Power Plant (NPP) de-commissioning site. This work aims to demonstrate that laser-induced ultrasonic guided wave technology can be applied to achieve this task. Hence, accelerated electrolytic corrosion is performed on a reinforced concrete specimen fabricated by embedding a steel rod into mortar. Waveforms of the laser-induced ultrasonic guided wave on the rod are measured with a previously employed piezoelectric transducer (PZT) probe, for each fixed corrosion time. Based on the results of Fourier and wavelet transforms of the waveforms, issues concerning the detection and extent of rebar corrosion are discussed. It is exhibited that the changes in bonding strength due to corrosion are distinguishable in the frequency domain of the ultrasonic signal.

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

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

A Review of Cs-bearing microparticles in the environment emitted by the Fukushima Dai-ichi Nuclear Power Plant accident

Igarashi, Yasuhito*; Kogure, Toshihiro*; Kuribara, Yuichi; Miura, Hikaru*; Okumura, Taiga*; Satou, Yukihiko; Takahashi, Yoshio*; Yamaguchi, Noriko*

Journal of Environmental Radioactivity, 205-206, p.101 - 118, 2019/09

Scientists face challenge in identifying the radioactive materials which are found as dotted images on various imaging plate (IP) autoradiographic photos of radioactively contaminated materials by the Fukushima Dai-ichi Nuclear Power Plant (F1NPP, or FDNPP) accident, such as air filter, fugitive dust, surface soil, agricultural materials, and water-shed samples. It has been revealed that they are minute particles with distinct morphology and elemental composition with high specific radioactivity, and different from those of the so-called Chernobyl hot particles. Basically, they are glassy particles once molten, composed of Si, O, Fe, Zn etc. with highly concentrated radiocaesium, which can be called as radiocaesium-bearing microparticles (CsMP). At present, CsMP can be classified into two types, Types-A and -B, which are characterized by different specific radioactivity, $$^{134}$$Cs/$$^{137}$$Cs ratio, size and morphology, and geographic distribution around F1NPP. Such studies on the CsMP from various aspects have provided valuable information about what happened in the nuclear reactors during the F1NPP accident and fates of the CsMP in the environment. This review first provides a retrospective view on the research history of the CsMP, which is helpful to understand the unique character of the CsMP. Subsequently, more details about the current understanding of the natures of these hot particles, such as origin, morphology, chemical compositions, thermal properties, water-solubility, and secondary migration of CsMP in river and ocean systems are described with future prospects.

Journal Articles

Formation mechanisms of insoluble Cs particles observed in Kanto district four days after Fukushima Daiichi NPP accident

Hidaka, Akihide

Journal of Nuclear Science and Technology, 56(9-10), p.831 - 841, 2019/09

The insoluble Cs particles (Type A) were firstly observed in Tsukuba-city on the morning of March 15. The particles have been considered to be generated in RPV of Unit 2 by evaporation/condensation based on the measured $$^{134}$$Cs/$$^{137}$$Cs ratio and the core temperatures of each unit. However, the Type A particles with smaller diameter than the Type B particles of Unit 1 origin, are covered by almost pure silicate glass and have a trace of the quenching. This indicates that the particles could have been generated due to the melting of the HEPA filter in SGTS by the fire of H$$_{2}$$ detonation at Unit 3, and atomization followed by quenching of the molten materials by air blast of the explosion. Although the particles were mostly dispersed to the sea because of the wind direction, some of them deposited onto the lower elevation of R/B at Unit 3, could have been subsequently re-suspended and released into the environment, by the steam flow in the R/B caused by restart of the Unit 3 core cooling water injection at 2:30 of March 15.

Journal Articles

Radiation imaging using a compact Compton camera mounted on a crawler robot inside reactor buildings of Fukushima Daiichi Nuclear Power Station

Sato, Yuki; Terasaka, Yuta; Utsugi, Wataru*; Kikuchi, Hiroyuki*; Kiyooka, Hideo*; Torii, Tatsuo

Journal of Nuclear Science and Technology, 56(9-10), p.801 - 808, 2019/09

Journal Articles

Effect of quenching on molten core-concrete interaction product

Kitagaki, Toru; Ikeuchi, Hirotomo; Yano, Kimihiko; Brissonneau, L.*; Tormos, B.*; Domenger, R.*; Roger, J.*; Washiya, Tadahiro

Journal of Nuclear Science and Technology, 56(9-10), p.902 - 914, 2019/09

Journal Articles

Application of InGaP space solar cells for a radiation dosimetry at high dose rates environment of Fukushima Daiichi Nuclear Power Plant

Okuno, Yasuki; Okubo, Nariaki; Imaizumi, Mitsuru*

Journal of Nuclear Science and Technology, 56(9-10), p.851 - 858, 2019/09

Decommissioning the Fukushima Daiichi Nuclear Power Plant (1F) after the accident caused by a tsunami in 2011 requires characterization of the fuel debris by dose distribution measurement. This paper describes the experimental and theoretical behavior of a radiation detector applied with InGaP solar cells is investigated and allow the localization and characterization of the fuel debris. In the irradiation test, it was observed that the radiation-induced current output of the InGaP solar cells increases linearly with increasing dose rates of $$^{60}$$Co $$gamma$$-ray. For measurements at low dose rates, it becomes clear that the minimum detectable dose rate and resolution can be determined by analyzing the noise characterization. The maximum detection limit of radiation dosimetry for the InGaP solar cell was found to be higher than the highest $$gamma$$-ray dose rate observable at the reactor core for 1F plants. Additionally, as an analysis of the radiation-induced current, it is attempted to express a relational expression between the absorbed dose rate and the creation of radiation-induced current pairs in the solar cells. The experimental and simulation results suggest that solar cells can be powerful tools for radiation dosimetry in high dose rate environments near the debris of the 1F plant.

Journal Articles

Calculation of gamma and neutron emission characteristics emitted from fuel debris of Fukushima Daiichi Nuclear Power Station

Riyana, E. S.; Okumura, Keisuke; Terashima, Kenichi

Journal of Nuclear Science and Technology, 56(9-10), p.922 - 931, 2019/09

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

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.

Journal Articles

Formation of radioactive cesium microparticles originating from the Fukushima Daiichi Nuclear Power Plant accident; Characteristics and perspectives

Onuki, Toshihiko*; Satou, Yukihiko; Utsunomiya, Satoshi*

Journal of Nuclear Science and Technology, 56(9-10), p.790 - 800, 2019/09

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

Dispersion modelling of radioactive materials

Nagai, Haruyasu; Yamazawa, Hiromi*

Environmental Contamination from the Fukushima Nuclear Disaster; Dispersion, Monitoring, Mitigation and Lessons Learned, p.230 - 242, 2019/08

An overview of SPEEDI is provided in the context of it development, functions, and role in the framework of nuclear emergency management. Thereafter, we examine how it was used and how it should be used for the Fukushima Daiichi Nuclear Power Station accident from a system developer perspective. We believe that our review can provide lessons or tasks for improving the prediction system and for considering better utilization of the system; it is also beneficial to consider reconstructing the framework of nuclear emergency management. Furthermore, we hope this review will prove useful in understanding and effectively using the atmospheric dispersion predictions from the system in the case of a similar accident in the future.

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