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論文

Analysis of particles containing alpha emitters in stagnant water in Fukushima Daiichi Nuclear Power Station's Unit 3 reactor building

蓬田 匠; 大内 和希; 森井 志織; 岡 壽崇; 北辻 章浩; 駒 義和; 今野 勝弘*

Scientific Reports (Internet), 14, p.14945_1 - 14945_11, 2024/06

 被引用回数:1 パーセンタイル:31.14(Multidisciplinary Sciences)

福島第一原子力発電所3号機建屋滞留水中の固形分の多数の粒子状物質の中から、$$alpha$$核種を含有する微粒子の検出を試みた。$$alpha$$核種濃度の異なる、トーラス室と主蒸気隔離弁室の2か所から採取した試料について分析を行った。大部分の$$alpha$$核種は10$$mu$$m以上の固形分に存在していた。SEM-EDXを用いる元素分析により、$$mu$$mサイズのUを主成分とする微粒子を検出した。また、アルファトラック法により検出した粒子では、粒径100$$mu$$m程度までの鉄粒子上に$$alpha$$核種が分布する様子を観測できた。3号機滞留水中におけるUやその他の$$alpha$$核種の存在形態が明らかになった。

論文

Microbiome analysis of the restricted bacteria in radioactive element-containing water at the Fukushima Daiichi Nuclear Power Station

藁科 友朗*; 佐藤 朝子*; 比内 浩; Shaikhutdinov, N.*; Shagimardanova, E.*; 森 宙史*; 玉木 聡志*; 斎藤 元文*; 眞田 幸尚; 佐々木 祥人; et al.

Applied and Environmental Microbiology, 90(4), p.e02113-23_1 - e02113-23_23, 2024/04

 被引用回数:0 パーセンタイル:0.00(Biotechnology & Applied Microbiology)

A major incident occurred at the Fukushima Daiichi Nuclear Power Station following the tsunami triggered by the Tohoku-Pacific Ocean Earthquake in March 2011, whereby seawater entered the torus room in the basement of the reactor building. Here, we identify and analyze the bacterial communities in the torus room water and several environmental samples. Samples of the torus room water (1 $$times$$ 10$$^{9}$$ Bq$$^{137}$$Cs/L) were collected by the Tokyo Electric Power Company Holdings from two sampling points between 30 cm and 1 m from the bottom of the room (TW1) and the bottom layer (TW2). A structural analysis of the bacterial communities based on 16S rRNA amplicon sequencing revealed that the predominant bacterial genera in TW1 and TW2 were similar. TW1 primarily contained the genus Limnobacter, a thiosulfate-oxidizing bacterium. $$gamma$$-Irradiation tests on Limnobacter thiooxidans, the most closely related phylogenetically found in TW1, indicated that its radiation resistance was similar to ordinary bacteria. TW2 predominantly contained the genus Brevirhabdus, a manganese- oxidizing bacterium. Although bacterial diversity in the torus room water was lower than seawater near Fukushima, $$sim$$70% of identified genera were associated with metal corrosion. Latent environment allocation - an analytical technique that estimates habitat distributions and co-detection analyses - revealed that the microbial communities in the torus room water originated from a distinct blend of natural marine microbial and artificial bacterial communities typical of biofilms, sludge, and wastewater. Understanding the specific bacteria linked to metal corrosion in damaged plants is important for advancing decommissioning efforts.

論文

Attempts to estimate the amount of contamination by Cs and Sr in cracked concrete considering realistic contamination conditions

山田 一夫*; 洞 秀幸*; 丸山 一平*; 粟飯原 はるか; 富田 さゆり*; 東條 安匡*; 渋谷 和俊*; 細川 佳史*; 五十嵐 豪*; 駒 義和

Proceedings of Waste Management Symposia 2024 (WM2024) (Internet), 7 Pages, 2024/03

Estimation of Cs and Sr contamination of concrete below the turbine pits after the Fukushima Daiichi NPP accident was carried out. Considerations were based on the type of cement and aggregate used, drying, carbonation and cracking of the concrete, and the contamination history, i.e. contact with contaminated water after a one-day immersion in seawater from the tsunami. The relationship between crack density and the amount of contaminated concrete was determined from the reproduction of crack density and the acquisition of apparent diffusion coefficients for cracked and uncracked areas from the immersion experiment with contamination history.

論文

福島第一原子力発電所廃炉作業効率化とソースターム予測精度向上への貢献に向けたFP挙動に関する技術調査; 本専門委員会の2年間の活動報告

勝村 庸介*; 高木 純一*; 細見 憲治*; 宮原 直哉*; 駒 義和; 井元 純平; 唐澤 英年; 三輪 周平; 塩津 弘之; 日高 昭秀*; et al.

日本原子力学会誌ATOMO$$Sigma$$, 65(11), p.674 - 679, 2023/11

本委員会では、東京電力ホールディングス株式会社(東電)福島第一原子力発電所(1F)事故後の 核分裂生成物(FP)挙動を予測可能な技術に高めて廃炉作業に貢献することと、1F事故進展事象の把握で得られた情報をソースターム(ST)の予測技術の向上に反映させ、原子炉安全の一層の向上に繋げることを目標とした活動を実施している。この2年間では、これまでの12年間の1F実機調査や1F関連研究で得られた情報を調査し、1F廃炉における燃料デブリやFP挙動の予測、及びST予測精度向上に必要な課題として「FPの量・物質収支と化学形態」「サンプリング目的とデータ活用」「環境への移行経路」を摘出した。今後、これらの課題の解決に向けた道筋の議論を進める。

論文

Penetration of Cs and Sr into cracked dry carbonated mortar considering the contamination history of Fukushima Daiichi NPP

山田 一夫*; 東條 安匡*; 粟飯原 はるか; 富田 さゆり*; 洞 秀幸*; 渋谷 和俊*; 駒 義和; 五十嵐 豪*; 細川 佳史*; 丸山 一平*

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 12 Pages, 2023/02

Experiments were conducted on mortar made from aggregates used in the Fukushima Daiichi NPP, which were dry carbonated and further cracks were introduced to reproduce the contamination history of the lower part of the turbine pit. The concrete was exposed to contaminated water after being in contact with seawater for one day due to the post-earthquake tsunami; Cs and Sr interacted differently with the constituent materials of the concrete and competitively adsorbed with ions in the seawater. The effects of various factors were quantitatively evaluated by experiment. Dry carbonation conditions enhanced infiltration but had a limited effect on cracking.

論文

Methodological developments and practice in characterisation of unconventional and legacy waste

Strand, P.*; Jefferies, N.*; 駒 義和; Plyer, J.*

Journal of Radiological Protection, 42(2), p.020501_1 - 020501_16, 2022/06

 被引用回数:2 パーセンタイル:28.39(Environmental Sciences)

Radioactive waste management requires the characterisation process to underpin the decisions that need to be taken to manage the waste safely. This paper reviews experience of characterisation of waste generated from past nuclear activities that were not conducted in compliance consistent with current criteria, or from unexpected situations that were not planned for. The development of a reliable and efficient characterisation and categorisation methodology is a common challenge for unconventional and legacy waste. Through the activities of the Nuclear Energy Agency Expert Group on the Characterisation of Unconventional and Legacy Waste (EGCUL), consideration has been given to widely used waste stream characterisation procedures and methods that were originally developed primarily for application in conventional decommissioning work. By analysing the challenges and lessons learned, it has been possible to identify opportunities for adaptations and enhancements to these characterisation methodologies, and these are set out and explained.

論文

Analysis of particles containing alpha-emitters in stagnant water at torus room of Fukushima Dai-ichi Nuclear Power Station's Unit 2 reactor

蓬田 匠; 大内 和希; 岡 壽崇; 北辻 章浩; 駒 義和; 今野 勝弘*

Scientific Reports (Internet), 12(1), p.7191_1 - 7191_10, 2022/05

AA2021-0706.pdf:2.48MB

 被引用回数:9 パーセンタイル:55.41(Multidisciplinary Sciences)

福島第一原子力発電所2号機トーラス室滞留水に含まれる$$alpha$$線放出核種の存在形態を、走査型電子顕微鏡X線検出(SEM-EDX)やアルファトラック法により分析した。SEM-EDXによる観察の結果、Uを主成分とするサブ$$mu$$m$$sim$$$$mu$$mサイズの粒子を複数同定できた。これらの粒子はZrなどの燃料被覆管や構造材を構成する元素を含んでいる。また、同じ粒径フラクションの固形分に含まれるU同位体比(235/238)は、原子炉燃料のそれと一致した。このことから、U粒子は原子炉に由来し、これが微細化したものであることを示している。アルファトラック分析により同定した$$alpha$$核種含有粒子は、粒径数10$$mu$$m$$sim$$~数100$$mu$$mのサイズであり、SEM-EDXの元素分析の結果、鉄を主成分としていた。$$alpha$$核種の物質量は極わずかであることから、Pu, Am, Cm等が鉄粒子上に付着する形態であると考えられる。分析した滞留水中の固形分試料では、Uと他の$$alpha$$核種の存在形態が異なる場合があることが明らかになった。

論文

Ten years after the NPP accident at Fukushima; Review on fuel debris behavior in contact with water

Grambow, B.; 二田 郁子; 柴田 淳広; 駒 義和; 宇都宮 聡*; 高見 龍*; 笛田 和希*; 大貫 敏彦*; Jegou, C.*; Laffolley, H.*; et al.

Journal of Nuclear Science and Technology, 59(1), p.1 - 24, 2022/01

 被引用回数:32 パーセンタイル:76.55(Nuclear Science & Technology)

Following the NPP accident, some hundred tons of nuclear fuel elements of 3 damaged nuclear reactor units were partly molten with even larger masses of steel and concrete structures, creating a big mass of corium and fuels debris. Since ten years, this heat generating mass has been cooled permanently by millions of m$$^{3}$$ of water flowing over them. Knowledge on the interaction of this solid mass with water is crucial for any decommissioning planning. Starting from analyses of the evolutions of the accident in the 3 reactor cores and associated fuel debris formations and some additional isotopic and physiochemical information of debris fragments collected in soils of Fukushima, we review the temporal evolution of the chemistry and leached radionuclide contents of the cooling water. Measured concentration ratios of the actinides and fission products in the water where compared to reported results of laboratory leaching studies with either spent nuclear fuel or simulated fuel debris under a variety of simulated environmental conditions.

論文

Radioactive waste sampling for characterisation; A Bayesian upgrade

Pyke, C. K.*; Hiller, P. J.*; 駒 義和; 大木 恵一

Nuclear Engineering and Technology, 54(1), p.414 - 422, 2022/01

 被引用回数:3 パーセンタイル:41.50(Nuclear Science & Technology)

Presented in this paper is a methodology for combining a Bayesian statistical approach with the Data Quality Objectives structured decision-making methodology to provide increased levels of confidence in analytical data when approaching a waste boundary. Development of sampling and analysis plans for the characterisation of radioactive waste often use a simple, one pass statistical approach as underpinning for the sampling schedule. Using a Bayesian statistical approach introduces the concept of Prior information giving an adaptive sample strategy based on previous knowledge. This aligns more closely with the iterative approach demanded of the most commonly used structured decision-making tool in this area (Data Quality Objectives) and the potential to provide a more fully underpinned justification than the more traditional statistical approach. The approach described has been developed in a UK regulatory context but is translated to a waste stream from the Fukushima Daiichi nuclear power station to demonstrate how the methodology can be applied in this context to support decision making regarding the ultimate disposal option for radioactive waste in a more global context.

論文

General overview of the research project investigating the radionuclide solution behavior in mock mortar matrix modeled after conditions at the Fukushima-Daiichi Nuclear Power Station

五十嵐 豪*; 芳賀 和子*; 山田 一夫*; 粟飯原 はるか; 柴田 淳広; 駒 義和; 丸山 一平*

Journal of Advanced Concrete Technology, 19(9), p.950 - 976, 2021/09

 被引用回数:5 パーセンタイル:24.97(Construction & Building Technology)

Decommissioning of the Fukushima Daiichi Nuclear Power Station (F1NPS) in a proper manner requires assessment of the contamination levels and mechanisms for contamination in the concrete structures. Between January 2018 and March 2020, Japan's Ministry of Education Ministry of Education, Culture, Sports, Science and Technology (MEXT) conducted a project called "The Analysis of Radionuclide Contamination Mechanisms of Concrete and the Estimation of Contamination Distribution at the Fukushima Daiichi Nuclear Power Station". In this review, we outline the results of this study. The experimental results from the first project indicate that concrete carbonation, Ca leaching, and drying conditions affected the adsorption behaviors of Cs and Sr and therefore, their penetration depths. Additionally, the studies showed that $$alpha$$-nuclides precipitated on the surface of the samples because concrete causes a high pH. A reaction transport model was developed to assess further the adsorption characteristics of Cs and Sr in carbonated cement paste and on concrete aggregates. The model used real concrete characteristics from the materials used at F1NPS and historical boundary conditions at the site, including radionuclide concentrations and penetration profiles within the turbine pit wall. Capillary water suction resulting from dried concrete was evaluated by considering structural changes in cement hydrates using X-ray CR and $$^{1}$$H-NMR relaxometry.

論文

Stochastic estimation of radionuclide composition in wastes generated at Fukushima Daiichi Nuclear Power Station using Bayesian inference

杉山 大輔*; 中林 亮*; 田中 真悟*; 駒 義和; 高畠 容子

Journal of Nuclear Science and Technology, 58(4), p.493 - 506, 2021/04

 被引用回数:2 パーセンタイル:20.20(Nuclear Science & Technology)

A modeling calculation methodology for estimating the radionuclide composition in the wastes generated at the Fukushima Daiichi nuclear power station has been upgraded by introducing an approach using Bayesian inference. The developed stochastic method describes the credible interval of the regression curve for the log-normal distribution of the measured transport ratio, which is used to calibrate the radionuclide transport parameters included in the modeling calculation. Consequently, the method can predict the robability distribution of the radionuclide composition in the Fukushima Daiichi wastes. The notable feature of the developed method is that it can explicitly investigate the improvement in the accuracy and confidence (degree of belief) of the estimation of the waste inventory using Bayesian inference. Specifically, the developed method can update and improve the degree of belief of the estimation of the radionuclide composition by visualizing the reduction in the width of uncertainty in the radionuclide transport parameters in the modeling calculation in accordance with the accumulation of analytically measured data. Further investigation is expected to improve the credibility of waste inventory estimation through iteration between modeling calculations and analytical measurements and to reduce excessive conservativeness in the estimated waste inventory dataset.

論文

A Project focusing on the contamination mechanism of concrete after the accident at Fukushima Daiichi Nuclear Power Plant

山田 一夫*; 丸山 一平*; 芳賀 和子*; 五十嵐 豪*; 粟飯原 はるか; 富田 さゆり*; Kiran, R.*; 大澤 紀久*; 柴田 淳広; 渋谷 和俊*; et al.

Proceedings of International Waste Management Symposia 2021 (WM2021) (CD-ROM), 10 Pages, 2021/03

To properly decommission the Fukushima Daiichi Nuclear Power Plant, the contamination levels and mechanisms for the concrete structures must be assessed. In this review, we outline the results of this study and present the objectives of a future study called "Quantitative Evaluation of Contamination in Reinforced Concrete Members of Fukushima Daiichi NPP Buildings Considering the Actual Environment Histories for Legitimate Treatments", which will run from October 2020 to March 2023. The experimental results from the first project indicate that concrete carbonation, Ca leaching, and drying conditions affected the adsorption of Cs and Sr and their penetration depths. Additionally, the studies showed that $$alpha$$-nuclides precipitated on the surface of the samples because of the high pH of concrete. A reaction transfer model was developed to further assess the adsorption characteristics of Cs and Sr in carbonated cement paste and concrete aggregates. The model used real concrete characteristics from the FDNPP materials and historical boundary conditions at the site, including radionuclide concentrations and penetration profiles within the turbine pit wall. The water suction by dried concrete was evaluated with the consideration of the structure change of cement hydrates by X-ray CR and $$^{1}$$H-NMR relaxometry. In the new project, the studies will also include concrete cracks for more realistic contamination estimations.

論文

Hydrothermal-treatment desorption of cesium from clay minerals; The Roles of organic acids and implications for soil decontamination

Yin, X.; Zhang, L.*; 針貝 美樹*; Wang, X.*; Ning, S.*; 中瀬 正彦*; 駒 義和; 稲葉 優介*; 竹下 健二*

Water Research, 177, p.115804_1 - 115804_10, 2020/06

 被引用回数:21 パーセンタイル:69.03(Engineering, Environmental)

The adsorption and desorption of cesium (Cs) on clays of contaminated soil in a rhizosphere zone can be greatly affected by various biogeochemical processes, the timespans of which are usually months to years. Herein, we present several representative scenarios of the binding of Cs on diverse sites of vermiculitized biotite by controlled Cs adsorption to particles of different sizes. We investigated whether and how the fixed Cs in the different scenarios is desorbed by ambient and hydrothermal treatments with several low-molecular-weight organic acids (LMWOAs).

論文

Selective removal of radiocesium from micaceous clay for post-accident soil decontamination by temperature-controlled Mg-leaching in a column

Yin, X.; Zhang, L.*; Meng, C.*; 稲葉 優介*; Wang, X.*; 二田 郁子; 駒 義和; 竹下 健二*

Journal of Hazardous Materials, 387, p.121677_1 - 121677_10, 2020/04

 被引用回数:13 パーセンタイル:45.03(Engineering, Environmental)

The effective and efficient removal of radioactive Cs from contaminated soil is highly urgent for the nuclear post-accident remediation. In present study, we achieved rapid Cs desorption from both a typical micaceous clay (i.e., vermiculitized biotite, VB) and actually contaminated soil by high-speed ion exchange through temperature-controlled continuous leaching with Mg-solutions in a column reactor. Cs-sorbed VB was firstly employed as a soil surrogate to explore the macro-Cs desorption process and micro-mechanism in detail.

論文

福島第一原子力発電所廃棄物分析の現況

駒 義和

原子力バックエンド研究(CD-ROM), 26(2), p.133 - 136, 2019/12

福島第一原子力発電所では廃炉工程の進展に伴い廃棄物が発生している。廃棄物管理技術の研究開発のために実施している分析の概要を報告する。

論文

質,量ともに未知なる廃棄物への取り組み

駒 義和; 新堀 雄一*

日本機械学会誌, 122(1211), p.21 - 23, 2019/10

2019年5月に日本機械学会と日本原子力学会が国際会議International Topical Workshop on Fukushima Decommissioning Researchを共催した。会議は5つのトラックから構成され、うち廃棄物管理技術に関する概要を報告する。

論文

Development of calculation methodology for estimation of radionuclide composition in wastes generated at Fukushima Daiichi Nuclear Power Station

杉山 大輔*; 中林 亮*; 駒 義和; 高畠 容子; 塚本 政樹*

Journal of Nuclear Science and Technology, 56(9-10), p.881 - 890, 2019/09

 被引用回数:4 パーセンタイル:33.76(Nuclear Science & Technology)

A calculation methodology for estimating the radionuclide composition in the wastes generated at the F1NPS has been developed by constructing a skeleton overview of the distribution of radionuclides considering the material balance in the system and calculation flowcharts of the transportation of radionuclides into the wastes. The wastes have a distinctive feature that their level of contamination includes considerable uncertainties. The developed method can explicitly specify the intrinsic uncertainties as a band to be included in the estimated radionuclide composition and can quantitatively describe the uncertainties by calibration using data on actual waste samples. Further studies to improve the quality of the calculation method, and acquiring a quantitative understanding of the spatial distribution of radionuclides inside the reactor building are suggested to be important steps toward reasonable and sustainable waste management as an integral part of the decommissioning.

論文

Contamination of Fukushima Daiichi Nuclear Power Station with actinide elements

駒 義和; 村上 絵理奈

Radiochimica Acta, 107(9-11), p.965 - 977, 2019/09

 被引用回数:1 パーセンタイル:8.72(Chemistry, Inorganic & Nuclear)

東京電力福島第一原子力発電所は、2011年3月11日に発生した地震と津波に被災し、放射性物質による重大な汚染を引き起こした。将来、廃棄物の処理や処分を行うために汚染した物質が分析されており、それにより得られたアクチニド核種の分析データを概観した。汚染水からアクチニド核種が検出されている。汚染水は化学的に除染されているが、アクチニド核種の濃度は時間とともには低下しておらず、損傷した燃料から冷却水へゆっくりと溶出しているとみられる。土壌に検出されるPu, Am, Cmは損傷した燃料に由来するが、Uは天然が支配的である。TRU核種は深部へのゆっくりとした移行が示唆される。瓦礫類の汚染は不均一であり、核分裂生成物とともにアクチニド核種も検出される。植物は、原子炉建屋に近い場所の落葉からTRU核種が検出された。

論文

Investigation of the contamination on the operation floor of unit 2 based on the radiochemical analysis data

高畠 容子; 駒 義和

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 4 Pages, 2019/05

Radioactive nuclides contaminated F1NPS on the severe accident. It is necessary to discuss about radioactive waste processing and disposal. To investigate contamination process for the waste is important to establish methodologies for their management. Operation floor of unit 2 reactor building was highly contaminated, and boring cores of floor and ceiling were radiochemicaly analyzed. Comparing with distribution of $$^{137}$$Cs and dose rate indicated the difference of degree of contamination between the floor and ceiling. Contamination with $$^{238}$$Pu, $$^{241}$$Am and $$^{244}$$Cm was higher at the floor above the reactor shield plug, where is considered that the contaminated gas leaked. Degree of contamination of $$^{3}$$H, $$^{60}$$Co, $$^{99}$$Tc, $$^{241}$$Am and $$^{244}$$Cm were highest at the point of the opposite side of the blow out panel among several sampling point of the ceiling. From the activity ratio of $$^{235}$$U to $$^{238}$$U with samples, the origin of uranium was the damaged fuel.

論文

New project on the analysis of contamination mechanisms of concrete at the Fukushima Daiichi Nuclear Power Station

山田 一夫*; 丸山 一平*; 駒 義和; 芳賀 和子*; 五十嵐 豪*; 渋谷 和俊*; 粟飯原 はるか

Proceedings of International Waste Management Symposia 2019 (WM2019) (CD-ROM), 6 Pages, 2019/03

For the decommissioning of a Nuclear Power Station (NPS) after a severe accident, estimation of contamination depth and radioactivity level in concrete is essential. This paper outlines a recently begun project on the analysis of the contamination mechanisms of concrete in the Fukushima Daiichi NPS. For this analysis, data on various parameters are required, such as the materials used in the NPS, the environmental conditions of the exposed concrete, the conditions of exposure during the accident and until decommissioning, and the fundamental transport characteristics of nuclides in concrete. These aspects of this project are illustrated with some examples.

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