Structural change by phosphorus addition to borosilicate glass containing simulated waste components

Okamoto, Yoshihiro; Shiwaku, Hideaki; Shimamura, Keisuke*; Kobayashi, Hidekazu; Nagai, Takayuki; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*

Journal of Nuclear Materials, 570, p.153962_1 - 153962_13, 2022/11

https://doi.org/10.1016/j.jnucmat.2022.153962

Simulated nuclear waste glass samples containing phosphorus, which increase the solubility of molybdenum, were prepared and analyzed using synchrotron X-ray Absorption Fine Structure (XAFS) analysis for some constituent elements and Raman spectroscopic analysis of their complex structure. Changes in local structure and chemical state due to different phosphorus additions and waste loading rates were systematically studied. Consequently, no crystalline phase due to the molybdate compound was observed even at a maximum waste content of 30 wt% (corresponding to 1.87 mol% MoO). Oxidation proceeded when the waste-loading rate was increased, whereas the reduction proceeded when phosphorus was added. In some cases, the effects of oxidation and reduction were offset. The local structure around specific elements can be classified as follows; Zn that is affected mainly by the waste-loading rate, Ce that is affected by both the waste-loading rate and phosphorus addition, and Zr element that is not affected by either of them. From the comparison between the analytical results of Mo and other elements, it was considered that the added phosphorus exists as a free PO structural unit and may deprive the alkali metal coordinated to the molybdate ion.

Radiocesium-bearing microparticles cause a large variation in Cs activity concentration in the aquatic insect (Tricoptera: Stenopsychidae) in the Ota River, Fukushima, Japan

Ishii, Yumiko*; Miura, Hikaru*; Jo, J.*; Tsuji, Hideki*; Saito, Rie; Koarai, Kazuma; Hagiwara, Hiroki; Urushidate, Tadayuki*; Nishikiori, Tatsuhiro*; Wada, Toshihiro*; et al.

PLOS ONE (Internet), 17(5), p.e0268629_1 - e0268629_17, 2022/05

https://doi.org/10.1371/journal.pone.0268629

We investigated the variability in Cs activity concentration in individual aquatic insects in detritivorous caddisfly () and carnivorous dobsonfly () larvae from the Ota River, Fukushima. Caddisfly larvae showed sporadically higher radioactivity, whereas no such outliers were observed in dobsonfly larvae. Autoradiography and scanning electron microscopy analyses confirmed that these caddisfly larvae samples contained radiocesium-bearing microparticles (CsMPs), which are insoluble Cs-bearing silicate glass particles. CsMPs were also found in potential food sources of caddisfly larvae, such as periphyton and drifting particulate organic matter, indicating that larvae may ingest CsMPs along with food particles of similar size. Although CsMPs distribution and uptake by organisms in freshwater ecosystems is relatively unknown, our study demonstrates that CsMPs can be taken up by aquatic insects.

Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan

Funaki, Hironori; Tsuji, Hideki*; Nakanishi, Takahiro; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*

Science of the Total Environment, 812, p.152534_1 - 152534_10, 2022/03

https://doi.org/10.1016/j.scitotenv.2021.152534

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediment to water columns, which may contribute to a long-term contamination in aquatic products. This study systematically investigated the Cs activities between sediment and pore water, which is a direct evidence of the remobilisation of bioavailable Cs from sediments, in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Our results strongly indicate a competitive ion exchange process between Cs and NH via a highly selective interaction with the frayed edges sites of phyllosilicate minerals to be the major reason for the variability of the Kd values between sediment and pore water, even in the Fukushima case.

Dynamics of radiocaesium within forests in Fukushima; Results and analysis of a model inter-comparison

Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.

Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11

https://doi.org/10.1016/j.jenvrad.2021.106721

This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.

Dynamics of Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi Nuclear Power Plant Accident

Tsuji, Hideki*; Nakagawa, Megumi*; Iijima, Kazuki; Funaki, Hironori; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*

Global Environmental Research (Internet), 24(2), p.115 - 127, 2021/06

Lake water, phytoplankton and zooplankton were sampled by a total of 12 quarterly surveys from August 2014 to May 2017 at a dam lake in the Fukushima nuclear disaster area, and variations of dissolved form of Cs and planktonic Cs were observed. Seasonal variations in dissolved Cs concentration with high in summer and low in winter were observed in the upstream, midstream and downstream areas of the lake, but no seasonal or site specific differences in planktonic Cs concentrations and dominant species were found. The amount of planktonic form of Cs in the water was less than 1.4% of the total Cs in the lake water, therefore the effect of plankton on the dynamics of Cs in the lake was minimal.

The Effects of steam addition on the unstable behavior of hydrogen-air lean premixed flames under the adiabatic and non-adiabatic conditions

Furuyama, Taisei*; Thwe Thwe, A.; Katsumi, Toshiyuki; Kobayashi, Hideaki*; Kadowaki, Satoshi

Nihon Kikai Gakkai Rombunshu (Internet), 87(898), p.21-00107_1 - 21-00107_12, 2021/06

https://doi.org/10.1299/transjsme.21-00107

The effects of steam addition on the unstable behavior of hydrogen-air lean premixed flames under adiabatic and non-adiabatic conditions were investigated by numerical calculations. Adopting a detailed chemical reaction mechanism of hydrogen-oxyfuel combustion modeled by 17 reversible reactions of 8 active species and diluents, a two-dimensional unsteady reaction flow was treated based on the compressible Navier-Stokes equation. As the steam addition and heat loss increased, the burning velocity of a planar flame decreased and the normalized burning velocity increased. The addition of water vapor promotes the unstable behavior of the hydrogen-air lean premixed flame. This is because the thermal diffusivity of the gas decreases and the diffusion-thermal instability increases. The effect of adding water vapor on the instability of hydrogen premixed flames is a new finding, and it is expected to connect with hydrogen explosion-prevention measures as in NPP.

Position dependency of the scattered intensity in the time-of-flight backscattering spectrometer DNA

Matsuura, Masato*; Yamada, Takeshi*; Tominaga, Taiki*; Kobayashi, Makoto*; Nakagawa, Hiroshi; Kawakita, Yukinobu

JPS Conference Proceedings (Internet), 33, p.011068_1 - 011068_6, 2021/03

https://doi.org/10.7566/JPSCP.33.011068

The position dependence of the scattered intensity in the time-of-flight backscattering spectrometer DNA was investigated. A periodic structure for both vertical (pixel) and horizontal (PSD) directions was observed. The solar slit and over-bending of an analyzer crystal is discussed as a possible origin of the modulation in the intensity. We have developed software program for the systematic correction of the position-dependent intensity and offset energy for the elastic peak. This corrects the deviation from the true scattering intensity and improve the quality of the data, which includes the energy resolution.

Evaluation of bioavailable radiocesium in the sediment in forest river and dam reservoir

Takechi, Seiichi*; Tsuji, Hideki*; Koshikawa, Masami*; Ito, Shoko*; Funaki, Hironori; Hayashi, Seiji*

Rikusuigaku Zasshi, 82(1), p.1 - 16, 2021/02

Since the Fukushima Daiichi Nuclear Power Plant accident in 2011, soil minerals and organic matter including radiocesium have been deposited in the dam lakes near the nuclear power plant. There is concern that radiocesium will gradually leach from the lake bottom into the lake water, resulting in prolonged radioactive contamination of the freshwater ecosystems especially in downstream of the dams. In this study, we collected undisturbed sediment core samples at the center of the Yokokawa Dam lake in Fukushima Prefecture and suspended sediment in the inflowing river of the dam for 4 years and evaluated the amount of bioavailable form of radiocesium (exchanged, oxidized, and organic forms) in these samples by sequential extraction tests using the BCR method focusing on the temporal change.

Factors controlling dissolved Cs concentrations in east Japanese rivers

Tsuji, Hideki*; Ishii, Yumiko*; Shin, M.*; Taniguchi, Keisuke*; Arai, Hirotsugu*; Kurihara, Momo*; Yasutaka, Tetsuo*; Kuramoto, Takayuki*; Nakanishi, Takahiro; Lee, S*; et al.

Science of the Total Environment, 697, p.134093_1 - 134093_11, 2019/12

https://doi.org/10.1016/j.scitotenv.2019.134093

To investigate the main factors that control the dissolved radiocesium concentration in river water in the area affected by the Fukushima Daiichi Nuclear Power Plant accident, the correlations between the dissolved Cs concentrations at 66 sites normalized to the average Cs inventories for the watersheds with the land use, soil components, topography, and water quality factors were assessed. We found that the topographic wetness index is significantly and positively correlated with the normalized dissolved Cs concentration. Similar positive correlations have been found for European rivers because wetland areas with boggy organic soils that weakly retain Cs are mainly found on plains. However, for small Japanese river watersheds, the building area ratio in the watershed strongly affected the dissolved Cs concentration.

Investigation of simulated waste glass samples prepared from borosilicate glass frit including vanadium

Nagai, Takayuki; Okamoto, Yoshihiro; Shiwaku, Hideaki; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*; Hirono, Kazuya*; Homma, Masanobu*; Kobayashi, Hiromi*; Takahashi, Tomoe*; et al.

JAEA-Research 2018-007, 87 Pages, 2018/11

JAEA-Research-2018-007.pdf:61.21MB

To select the chemical composition of a glass frit which can increase the waste content, the simulated waste glass samples prepared from a borosilicate glass frit including vanadium (V) were investigated by using Laser Ablation (LA) ICP-AES analysis, Raman spectrometry, and synchrotron XAFS measurement in this study on foundation business of the Agency for Natural Resources and Energy.