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Journal Articles

Temporal change of radiocesium loss in a decontaminated deciduous broad-leaved forest

Watanabe, Takayoshi; Sasaki, Yoshito; Niizato, Tadafumi; Mitachi, Katsuaki*; Ito, Satomi

KEK Proceedings 2019-2, p.114 - 119, 2019/11

no abstracts in English

Journal Articles

Amount of radioactive cesium sedimentation in a soil saving dam with 3D laser scanner

Watanabe, Takayoshi; Oyama, Takuya; Ishii, Yasuo; Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito

KEK Proceedings 2017-6, p.122 - 126, 2017/11

no abstracts in English

Journal Articles

Translocation of radiocesium released by the Fukushima Daiichi Nuclear Power Plant accident in Japanese chestnut and chestnut weevil larvae

Sasaki, Yoshito; Ishii, Yasuo; Abe, Hironobu; Mitachi, Katsuaki; Watanabe, Takayoshi; Niizato, Tadafumi

Horticulture Journal, 86(2), p.139 - 144, 2017/04

To examine the translocation of radiocesium (Cs) scattered by the Fukushima Daiichi Nuclear Power Plant accident that occurred in March 2011 to the Japanese chestnut, we investigated the autoradiography and radiocesium concentration in each part of the Japanese chestnut. The Japanese chestnut fruit has a thin skin between the kernel (cotyledons) and shell; the kernel of the fruit is edible. $$^{137}$$Cs concentration in each part of the fruit was found to be almost the same at about 1.0$$times$$10$$^{4}$$ Bq$$cdot$$kg$$^{-1}$$. Radiocesium concentration in chestnut weevil larvae found on the fruit was approximately one-seventh of that in the kernel.

Journal Articles

The Transfer of radiocesium from the bark to the stemflow of chestnut trees (${it Castanea crenata}$) contaminated by radionuclides from the Fukushima Dai-ichi Nuclear Power Plant accident

Sasaki, Yoshito; Abe, Hironobu; Mitachi, Katsuaki; Watanabe, Takayoshi; Ishii, Yasuo; Niizato, Tadafumi

Journal of Environmental Radioactivity, 161, p.58 - 65, 2016/09

AA2015-0311.pdf:1.93MB

 Times Cited Count:6 Percentile:65.02(Environmental Sciences)

We report the behavior of radiocesium on the tree bark and its transfer into the stemflow of chestnut in a forest in Fukushima. The radiocesium concentration is greatest in $$phi$$2-cm stem, less in $$<$$$$phi$$5-mm stem, and least in the leaves. In the $$phi$$2-cm stem, the radiocesium concentration of the bark was approximately 10 times that of wood. The average Cs-137 concentration of the dissolved fraction of stem flow was about 10 Bq/L; the pH was nearly constant at 5.8. A strong positive correlation was observed between the radiocesium concentration and the electrical conductivity of the dissolved fraction of stemflow; this result suggests that radiocesium and electrolytes have the same elution mechanism from the tree. Some of the particles in the particulate fraction of the stem flow was strongly adsorbed radiocesium.

Journal Articles

Input and output budgets of radiocesium concerning the forest floor in the mountain forest of Fukushima released from the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident

Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito; Ishii, Yasuo; Watanabe, Takayoshi

Journal of Environmental Radioactivity, 161, p.11 - 21, 2016/09

 Times Cited Count:19 Percentile:24.87(Environmental Sciences)

Estimations of radiocesium input and output budgets concerning the forest floor in a mountain forest region have been conducted in the north and central part of the Abukuma Mountains of Fukushima, after 2 to 3 year period following the TEPCO Fukushima Dai-ichi Nuclear Power Plant accident. The radiocesium input and output associated with surface washoff, throughfall, stemflow, and litterfall processes at the experimental plots have been monitored on a forest floor of evergreen Japanese cedar and deciduous Konara oak forests. The results at both monitoring locations show the radiocesium input to be 4-50 times higher than the output during the rainy season in Fukushima. These results indicate that the radiocesium tend to be preserved in the forest ecosystem due to extremely low output ratios. Thus, the associated fluxes throughout the circulation process are key issues for the projecting the environmental fate of the radiocesium levels.

Oral presentation

The Relation between imaging of soil structure with GPR and depth profile of radioactive cesium

Watanabe, Takayoshi; Mitachi, Katsuaki; Abe, Hironobu; Niizato, Tadafumi

no journal, , 

Radionuclides such as radioactive cesium, now the main radiological contributor, were released in the environment by the Fukushima Dai-ichi Nuclear Power Plant accident. Japan Atomic Energy Agency initiated a project entitled "Long-Term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima" (F-TRACE project) in November 2012. To understand radioactive cesium transport in forest, we have conducted forest investigation at Ogi district, Kawauchi Village and Yamakiya district, Kawamata Town, Fukushima Prefecture since December 2012. As a part of the investigation, we carried out geophysical exploration of soil structure with ground penetrating radar (GPR) with 100 MHz and 500 MHz radio wave. In this presentation, we report correlation between imaging of soil structure obtained by GPR survey and depth profile of radioactive cesium in soil.

Oral presentation

Forest investigation; Monitoring of surface runoff and downward movement of soil (soil loss), 2

Abe, Hironobu; Ishii, Yasuo; Niizato, Tadafumi; Mitachi, Katsuaki; Watanabe, Takayoshi; Sasaki, Yoshito

no journal, , 

no abstracts in English

Oral presentation

Environmental dynamics of radiocaesium and its outflow flux in the mountain forest; Abukuma Mountains, Fukushima

Niizato, Tadafumi; Abe, Hironobu; Ishii, Yasuo; Watanabe, Takayoshi; Mitachi, Katsuaki

no journal, , 

Environmental dynamics of radiocaesium and its outflow flux are crusial issues for the remediation of the Fukushima environment affected by contamination of the fall out of Fukushima Daiichi Nuclear Power Plant Accident. This paper presents the current status of field investigation and monitoring related to the dynamics and outflow flux of radiocaesium in the mountation forest, Abukuma Mountains, Fukushima, Japan.

Oral presentation

Estimates of a sediment yield sedimentation rate and a outflow variation of radioactive Cs in an erosion control dam with 3D laser scanner

Watanabe, Takayoshi; Oyama, Takuya; Ishii, Yasuo; Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito; Kitamura, Akihiro

no journal, , 

For an estimate of movement from forest to living spheres, it is important to understand value of movement of soil and radioactive Cs from forest. We measured volumes of deposit with 3D laser scanner in an erosion control dam in Namie town, Fukushima prefecture on August 29, 2013 and December 3, 2014. As a result of measurement, an amount of increase of sediment for 15 months is 0.5 m$$^{3}$$. A denudation rate is 0.02 mm/year. This value is on the same level with denudation rates in meadows and forest, 10$$^{-2}$$ $$sim$$ 10$$^{-1}$$ mm/year (Fujiwara et al, 1999). And it is estimated that a variation of radioactive Cs is Cs-137: 200 MBq, Cs-134: 80 MBq.

Oral presentation

Long-term assessment of transport of radioactive contaminant in the environment of Fukushima (F-TRACE Project), 8; Analysis of surface run-off substances

Ishii, Yasuo; Mitachi, Katsuaki; Abe, Hironobu; Niizato, Tadafumi

no journal, , 

As part of "Long-Term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima" (F-TRACE project), JAEA have researched to expect the transportation of radioactive caesium from contaminated mountain forests based on survey data in Fukushima prefecture, and to implement technical information and remedial measures to prevent contamination of decontaminated areas and domestic water supply. In this study, we report characterization and radio assay of the surface run-off substances at forest research plots in Ogi district of Kawauchi-mura and Yamakiya district of Kawamata-machi in 2013-2014, Fukushima.

Oral presentation

Temporal change in depth profile of radiocaesium released by the Fukushima Daiichi Nuclear Power Plant accident in the Fukushima forest

Niizato, Tadafumi; Abe, Hironobu; Ishii, Yasuo; Sasaki, Yoshito; Mitachi, Katsuaki; Kitamura, Akihiro; Yamaguchi, Masaaki

no journal, , 

The depth profile of radiocaesium at the mountain forest of Abukuma Mountains, Fukushima Prefecture, shows the decreasing tendency of the radiocaesium inventory in the most upper part of the soil layer at ridge and valley bottom. A very slightly downward infiltration of the radiocaesium was found with decreasing of the inventory near the ground surface but most of the radiocaesium still exist in the upper part of the soil layer. Outflow of the radiocaesium from the mountain forest get to decrease due to the downward infiltration of the radiocaesium in the soil horizon by the application of the SACT model developed in JAEA.

Oral presentation

Temporal changes of radiocesium outflow in mountainous forest of the Abukuma Mountains, Fukushima

Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Ishii, Yasuo; Sasaki, Yoshito; Watanabe, Takayoshi; Kitamura, Akihiro; Yamaguchi, Masaaki

no journal, , 

This paper presents outflow characteristics of Cs-137 in mountainous forest of the Abukuma Mountains, Fukushima, during 2013-2014. Cs-137 deposition via throughfall, stemflow, and litterfall processes was estimated to be on the order of 10$$^{3}$$ Bq m$$^{-2}$$, and the outflow of Cs-137 via surface washoff was estimated to be on the order of 10$$^{2}$$ Bq m$$^{-2}$$ from April 2013 to December 2014 in the experimental plots installed in deciduous broad-leaved and cedar forests in the Abukuma Mountains. Cs-137 inventories of forest soil down to a level of 1 cm were decreasing in ridge and valley-bottom soil during the period from December 2012 to October 2014. The inventories in mountain slope showed both decreasing and increasing tendencies because of the heterogeneous transportation of Cs-137 via surface washoff on the slope. The results of outflow rate simulations using the SACT model developed in the Japan Atomic Energy Agency indicate decreasing tendency accompanied with a deeper penetration of Cs-137 into soil profile. Thus, the forest floor in the mountainous forest seems to be a sink of radiocesium contamination rather than a source for the contamination of the other ecosystems.

Oral presentation

Changes in the concentrations of radioactive cesium outflowed from the steep mountainous forest of Abukuma Mountains, released by Fukushima Daiichi Nuclear Power Plant accident

Ishii, Yasuo; Watanabe, Takayoshi; Oyama, Takuya; Sasaki, Yoshito; Abe, Hironobu; Mitachi, Katsuaki; Niizato, Tadafumi

no journal, , 

Mountainous forest is currently one of the most important sources of radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant accident in Fukushima prefecture, which was covered approximately 70% of the land area by the forest. This study reports the changes in concentrations of radioactive cesium in sediments outflowed from the steep mountainous forest of the Abukuma Mountains, Fukushima, during September - December 2015.

Oral presentation

Changes of surface run-off substances and air dose rate in Fukushima mountainous forest

Ishii, Yasuo; Mitachi, Katsuaki; Abe, Hironobu; Niizato, Tadafumi

no journal, , 

Mountainous forest is currently one of the most important sources of radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant Accident in Fukushima. This study reports the changes in amounts and concentrations of radioactive cesium of the surface run-off substances and dose rate at forest observation plots in Ogi district of Kawauchi-mura and Yamakiya district of Kawamata-machi, and Ogaki soil saving dam, Fukushima during 2013 - 2015.

Oral presentation

Radiocesium outflow related to the forest floor conditions in mountainous forest of the Abukuma Mountains, Fukushima

Niizato, Tadafumi; Sasaki, Yoshito; Mitachi, Katsuaki*

no journal, , 

The outflow of $$^{137}$$Cs from the mountainous forest floor was estimated in the Abukuma Mountains, Fukushima. The outflow rates are decreased with a cover rate of the forest floor by a litter layer. The result shows the important role of the litter layer and undergrowth on a migration control of the radiocesium outflow from the forest floor.

Oral presentation

Installation of observation device for soil loss in a decontaminated forest

Watanabe, Takayoshi; Ishii, Yasuo; Niizato, Tadafumi; Sasaki, Yoshito; Mitachi, Katsuaki*

no journal, , 

no abstracts in English

Oral presentation

Estimate of variation of radioactive cesium sedimentation in a soil saving dam with the 3D laser scanner

Watanabe, Takayoshi; Oyama, Takuya; Ishii, Yasuo; Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito

no journal, , 

no abstracts in English

Oral presentation

Effects on environmental dynamics of radiocesium related to the wildfire in mountainous forest of the Abukuma Mountains, Fukushima

Niizato, Tadafumi; Sasaki, Yoshito; Watanabe, Takayoshi; Mitachi, Katsuaki*; Ito, Satomi; Kuramoto, Takayuki*; Arai, Hirotsugu*; Nomura, Naoki*; Hayashi, Seiji*; Tamaoki, Masanori*

no journal, , 

$$^{137}$$Cs released from the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident has a long half-life of about 30 years, it is necessary to monitor the distribution and its radioecological impact over the long term. Mountainous forests, which accounts for about 70% of Fukushima prefecture, tend to be a sink of radiocesium contamination rather than a source for the contamination of other ecosystems. An understanding of the environmental dynamics of radiocesium in the forest floor of various conditions is important issue, while progressing to the resident return. In this paper, we report on the results of the field investigation into the $$^{137}$$Cs distribution and the $$^{137}$$Cs outflow in the mountainous forest of Fukushima, where the wildfire broke out in the spring of 2017.

Oral presentation

Transfer of radiocesium in the tree of Japanese cedar (Cryptomeria japonica)

Sasaki, Yoshito; Niizato, Tadafumi; Mitachi, Katsuaki*

no journal, , 

We collected the tree sap in the Japanese cedar, and clarified the concentration of the dissolved radiocesium contained in the sap. It was shown that the amount of dissolved radiocesium in sap in each part was about 30 to 50% of the total amount of radiocesium at each part.

Oral presentation

5 years monitoring results for the environmental dynamics of radiocesium in mountainous forest of the Abukuma Mountains, Fukushima

Niizato, Tadafumi; Watanabe, Takayoshi; Mitachi, Katsuaki*; Sasaki, Yoshito; Ito, Satomi; Abe, Hironobu

no journal, , 

An understanding of long-term environmental dynamics of radiocesium, which is released by the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident, is a key issue for predicting the future radiocesium distribution and forest products radioactivity in a forested environment, especially $$^{137}$$Cs with half-life of 30 years. We compiled the five-years monitoring results of radiocesium input-output budgets in broad-leaved deciduous forests and Japanese cedar evergreen forests of the Abukuma Mountains, Fukushima, Japan. The input-output rates were a few percent of the radiocesium inventory of the monitoring site. In addition, both rates have been decreasing with time. Belowground radiocesium occupied 90% of the total inventory in the Japanese cedar forest on October 2015. The belowground radiocesium was distributed mainly in the topsoil of 0-6 cm depth, approximately 70-80% of the underground inventory on August 2016. These results indicate that the distribution of radiocesium in the forest is similar to the distribution of tree rootlet responsible for absorption of inorganic elements, nutrients, and water. This means long residence time of radiocesium in rooting zone. In the condition of the limited amount of radiocesium input-output rates in the forest, estimation of the migration flux of radiocesium from forest floor to the forest products are considered to be most important issues in the present.

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