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Soil dust and bioaerosols as potential sources for resuspended $$^{137}$$Cs occurring near the Fukushima Dai-ichi Nuclear Power Plant

太田 雅和; 高原 省五; 吉村 和也; 長久保 梓; 廣内 淳; 林 奈穂; 阿部 智久; 舟木 泰智; 永井 晴康

Journal of Environmental Radioactivity, 264, p.107198_1 - 107198_15, 2023/08

 被引用回数:0 パーセンタイル:0(Environmental Sciences)



Occurrence of radioactive cesium-rich micro-particles (CsMPs) in a school building located 2.8 km south-west of the Fukushima Daiichi Nuclear Power Plant

笛田 和希*; 小宮 樹*; 蓑毛 健太*; 堀江 憲路*; 竹原 真美*; 山崎 信哉*; 塩津 弘之; 大貫 敏彦*; Grambow, B.*; Law, G. T. W.*; et al.

Chemosphere, 328, p.138566_1 - 138566_12, 2023/07

 被引用回数:0 パーセンタイル:0(Environmental Sciences)

Fukushima Daiichi Nuclear Power Plant (FDNPP) derived radioactive Cs-rich microparticles (CsMPs) present a potential health risk through inhalation. Despite their occurrence in indoor environments impacted by the FDNPP accident, little is known about their prevalence. In this study, we quantitatively analyse the distribution and number of CsMPs in indoor dust samples collected from an elementary school located 2.8 km to the southwest of FDNPP. The school had remained untouched until 2016. Then, using a modified version of the autoradiography based "quantifying CsMPs (mQCP) method," we collected samples and determined the number of CsMPs and Cs radioactive fraction (RF) values of the microparticles (defined as total Cs activity from CsMPs / bulk Cs activity of entire sample). The numbers of CsMPs were determined to be 653 - 2570 particles/g and 296 - 1273 particles/g on the first and second floors of the school, respectively. The corresponding RFs ranged between 6.85 - 38.9 % and 4.48 - 6.61 %, respectively. The number of CsMPs and RF values in additional outdoor samples near the school building were and 23 - 63 particles/g and 1.14 - 1.61 %, respectively. The CsMPs were most abundant on the School's first floor near to the entrance, and the relative abundance was high near to the stairs on the second floor, indicating a likely CsMP dispersion path through the building. Additional wetting of the indoor samples combined with autoradiography revealed that indoor dusts had a distinct absence of intrinsic, soluble Cs species like CsOH. Combined, the results indicate that a significant amount of poorly soluble CsMPs were likely contained in initial radioactive airmass plumes from the FDNPP and that the microparticles could penetrate buildings. Clean-up plans for buildings / residential areas impacted by CsMP containing plumes, and monitoring of areas re-opened to the public, should take account of CsMPs in dusts.


Establishing an evaluation method for the aging phenomenon by physical force in fuel debris

鈴木 誠矢; 荒井 陽一; 岡村 信生; 渡部 雅之

Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07

 被引用回数:0 パーセンタイル:0.02(Nuclear Science & Technology)



Aging of fuel-containing materials (fuel debris) in the Chornobyl (Chernobyl) Nuclear Power Plant and its implication for the decommissioning of the Fukushima Daiichi Nuclear Power Station

北垣 徹; Krasnov, V.*; 池田 篤史

Journal of Nuclear Materials, 576, p.154224_1 - 154224_14, 2023/04

 被引用回数:0 パーセンタイル:0.85(Materials Science, Multidisciplinary)

Nuclear fuel debris is a complex material containing a wide range of elements, compounds, and radiation. This complexity renders all the stages of the treatment of nuclear fuel debris extremely difficult and troublesome in the technical context. The whole treatment of nuclear fuel debris is also an extremely long-term process for tens of thousands of years, during which the aging of nuclear fuel debris is an unavoidable but critical issue. This applies to the decommissioning of the damaged reactors of the Fukushima Daiichi Nuclear Power Station (1F). This review article aims at collecting and summarizing the knowledge and information about the aging of materials containing nuclear fuels (fuel-containing materials) formed as a result of the accident at ChNPP-4 in the light of the decommissioning of 1F and assessing the potential effects of aging on the nuclear fuel debris remaining in the damaged 1F reactors.


Applicability of differential die-away self-interrogation technique for quantification of spontaneous fission nuclides for fuel debris at Fukushima Daiichi Nuclear Power Plants

長谷 竹晃; 相樂 洋*; 小菅 義広*; 能見 貴佳; 奥村 啓介

Journal of Nuclear Science and Technology, 60(4), p.460 - 472, 2023/04

 被引用回数:0 パーセンタイル:0.01(Nuclear Science & Technology)

This paper provides an overview of the applicability of the Differential Die-Away Self-Interrogation (DDSI) technique for quantification of spontaneous fissile nuclides in fuel debris at the Fukushima Daiichi Nuclear Power Plants. In this research, massive fuel debris stored in a canister was evaluated, and the void space of the canister was assumed to be filled with water for wet storage and air for dry storage. The composition of fuel debris was estimated based on elements such as the inventory in the reactor core and operation history. The simulation results show that for wet storage, the DDSI technique can properly evaluate the neutron leakage multiplication and quantify spontaneous fissile nuclides with a total measurement uncertainty (TMU) of approximately 8%. For dry storage, the known-alpha technique, which was previously established, can be applied to quantify spontaneous fissile nuclides with a TMU of approximately 4%. In both cases, the largest uncertainty factor is the variation in water content in the canister. In the case of wet storage, the uncertainty could be significantly increased in cases where the fuel debris is extremely unevenly distributed in the canister.


Origin of Cs-bearing silicate glass microparticles observed during Fukushima accident and recommendations on nuclear safety

日高 昭秀

Journal of Radioanalytical and Nuclear Chemistry, 332, p.1607 - 1623, 2023/03

 被引用回数:0 パーセンタイル:0.02(Chemistry, Analytical)

福島第一原子力発電所事故時に初めて放出されたタイプA Cs含有微粒子(以下、タイプA)の生成機構について、これまで様々な生成機構説が議論されてきた。筆者は、3号機の非常用ガス処理系(SGTS)のHEPAフィルタが水素爆発時に溶融して微粒化したことにより生成したと考えた。しかし、その仮説は、熱水力と大気拡散及びその学際領域にも及んで複雑であり、まだ推論が多く含まれている。このため、今後は様々な専門家による検証や、タイプA生成に関する再現試験が必要と考えた。さらに、もし仮説が正しいとした場合、HEPAフィルタは安全上重要な機器であり、水素爆発防止対策やHEPAフィルタの設計等にも影響するかもしれないと考え始めていた。そこで、これらの検討を進めるため、タイプAの生成機構に関して、総合的に解説したレビューが必要との結論に至った。本稿では、筆者がこれまでに執筆した論文等に基づき、仮説の根拠、検証及びその仮説が正しいとした時に実際に何が起こったと考えられるか、今後の課題、原子力安全性の更なる向上の観点からの提言について述べる。



友常 祐介; 矢嶋 まゆみ; 奥野 浩; 山本 一也

労働安全衛生研究, 16(1), p.29 - 43, 2023/02



The Formation mechanism of radiocesium-bearing microparticles derived from the Fukushima Daiichi Nuclear Power Plant using electron microscopy

萩原 大樹; 近藤 啓悦; 日高 昭秀

Journal of Radioanalytical and Nuclear Chemistry, 331(12), p.5905 - 5914, 2022/12

 被引用回数:2 パーセンタイル:72.55(Chemistry, Analytical)

Radiocesium-bearing microparticles (CsMPs) were released from the Fukushima Daiichi Nuclear Power Plant during the 2011 accident. We examined the CsMP formation process by analyzing Type-A particles and conducting in situ glass fiber experiments. The results demonstrated that heating glass fibers to 450$$^{circ}$$C - 800$$^{circ}$$C formed spherical particles, their morphologies and elemental compositions were similar to those of actual CsMPs. The mock-up particles size was strongly dependent on the glass-fiber thickness. Our findings reveal that glass fibers can form microparticles after being exposed to high temperatures.


High-temperature gaseous reaction of cesium with siliceous thermal insulation; The Potential implication to the provenance of enigmatic Fukushima cesium-bearing material

Rizaal, M.; 中島 邦久; 斉藤 拓巳*; 逢坂 正彦; 岡本 孝司*

ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08

 被引用回数:0 パーセンタイル:0(Chemistry, Multidisciplinary)

Here we report an investigation of the gas-solid reaction between cesium hydroxide (CsOH) and siliceous (calcium silicate) thermal insulation at high temperature, which was postulated as the origin for the formation mechanism of cesium-bearing material emitted from the Fukushima Daiichi Nuclear Power Plant. A developed reaction furnace consisting of two heating compartments was used to study the reaction at temperatures of 873, 973, and 1073 K. Under the influence of hydrogen-steam atmospheric conditions (H$$_{2}$$/H$$_{2}$$O = 0.2), the reaction between cesium hydroxide vapor and solid thermal insulation was confirmed to occur at temperatures of 973 and 1073 K with the formation of dicalcium silicate (Ca$$_{2}$$SiO$$_{4}$$) and cesium aluminum silicate (CsAlSiO$$_{4}$$). Water-dissolution analyses of the reaction products have demonstrated their stability, in particular, the CsAlSiO$$_{4}$$. Constituents similarity of the field-observed cesium-bearing materials near the Fukushima Daiichi Nuclear Power Plants with CsAlSiO$$_{4}$$ suggests for the first time that gaseous reaction between CsOH with calcium silicate thermal insulation could be one of the original formation mechanisms of the cesium-bearing materials.


Validation of a model for estimating individual external dose based on ambient dose equivalent and life patterns

佐藤 里奈; 吉村 和也; 眞田 幸尚; 佐藤 哲朗*

Journal of Radiation Protection and Research, 47(2), p.77 - 85, 2022/06



Contamination processes of tree components in Japanese forest ecosystems affected by the Fukushima Daiichi Nuclear Power Plant accident $$^{137}$$Cs fallout

太田 雅和; 小嵐 淳

Science of the Total Environment, 816, p.151587_1 - 151587_21, 2022/04

 被引用回数:4 パーセンタイル:74.58(Environmental Sciences)




安藤 真樹; 斎藤 公明

JAEA-Technology 2021-032, 66 Pages, 2022/03




Characterization of radiocesium-bearing microparticles with different morphologies in soil around the Fukushima Daiichi Nuclear Power Plant

萩原 大樹; 舟木 泰智; 尻引 夏*; 菅野 麻里奈*; 眞田 幸尚

Journal of Radioanalytical and Nuclear Chemistry, 331(1), p.415 - 426, 2022/01

 被引用回数:5 パーセンタイル:74.78(Chemistry, Analytical)

Radiocesium-bearing microparticles (CsMPs) from Fukushima Daiichi Nuclear Power Plant (FDNPP) are observed in Eastern Japan. To examine their source and formation, multiple particles were isolated from soils from three sites around the FDNPP and their radioactivity, morphology, and elemental composition were analyzed. Cesium-137 radioactivity ranged from 0.23 to 8.57 Bq and particles were primarily composed of Si, Fe, Zn, C, and Cs at each site. Uranium-rich parts in certain CsMPs show their origin in the vicinity of the nuclear reactor. Our results will help characterize CsMPs and evaluate the internal dose exposure of personnel employed at the FDNPP


Comparison of dose rates from four surveys around the Fukushima Daiichi Nuclear Power Plant for location factor evaluation

眞田 幸尚; 石田 睦司*; 吉村 和也; 三上 智

Journal of Radiation Protection and Research, 46(4), p.184 - 193, 2021/12

[背景] 9年前の福島第一原子力発電所事故により放出された放射性核種は、現在も様々な研究チームや日本政府によりモニタリングが行われている。異なる調査結果を比較することで、被ばく量や当該地域の都市環境における放射性セシウムの挙動メカニズムを評価することができる。そこで、本研究ではビッグデータを用いて、土地利用と周辺線量率(空間線量率)の時間変化との関係を明らかにした。[材料と方法] FDNPPの80km圏内に1$$times$$1km$$^{2}$$のメッシュを連続して設定し、異なる調査結果を比較検討した。そして、すべての調査メッシュから解析データセットを作成し、空間線量率の時間変化を解析した。選択したメッシュには、歴代の調査キャンペーンで得られたすべての調査タイプ(空中,定点,バックパック,車載)のデータが含まれている。[結果と考察] 次に、このデータセットを用いて測定対象に依存する各調査結果の特徴を評価した。データセット解析の結果、例えば、カーボーン調査の視野は舗装道路に限定されるため、カーボーン調査の結果は他の調査結果よりも小さくなることがわかった。また、4つの調査方法の特徴を考慮し土地利用の違いによる立地要因の評価も行った。FDNPP事故後9年経過した時点で立地係数は0.26から0.49の範囲にあり、空間線量率の半減期は0.5秒であった。


Analysis of Fukushima-Daiichi Nuclear Power Plant Unit 3 pressure data and obtained insights on accident progression behavior

佐藤 一憲

Nuclear Engineering and Design, 383, p.111426_1 - 111426_19, 2021/11

 被引用回数:2 パーセンタイル:41.01(Nuclear Science & Technology)

The D/W (Drywell) and S/C (Suppression Chamber) pressure data of Fukushima-Daiichi Nuclear Power Plant Unit 3 was analyzed in depth. This analysis provided valuable information related to the accident progression behavior on one hand, and gave a hint for understanding of the debris-to-coolant heat transfer when fuel debris relocated to the pedestal on the other hand. In this unit, the D/W and S/C pressure increased and decreased cyclically with a relationship, which seems to have been dependent on the composition of vapor and non-condensable gases in the S/C cover gas region. Based on this characteristic, the vapor pressure in the S/C cover gas region was evaluated for two pressure decrease cycles during and after the expected debris relocation to the pedestal respectively. This evaluation allowed an understanding that the S/C vapor pressure increased due to the heat transfer from the debris relocated to the pedestal.



堀田 拓摩; 山岸 功; 永石 隆二; 柏谷 龍之介*

JAEA-Technology 2021-012, 34 Pages, 2021/07


東京電力ホールディングス(株)福島第一原子力発電所における多核種除去設備(Advanced Liquid Processing System; 以下「ALPS」という。)および増設多核種除去設備(Improved ALPS)の前処理設備から発生する炭酸塩沈殿物を主とする廃棄物(以下「炭酸塩スラリー」という。)は高性能容器(High Integrity Container; 以下「HIC」という。)に格納されている。このHIC内において、水の放射線分解により発生した水素ガスの炭酸塩スラリー内での保持および、それに伴う容積増加が原因と推定される上澄み水のHIC外部への漏えい事象(溢水)が発生した。この溢水の発生が確認された当時に保管されていた大部分のHICにおいて、外部への溢水は観察されていない。このことはHIC内炭酸塩スラリー自体の性状や気泡の保持特性の理解が溢水発生条件を明らかにする上で重要であることを示唆している。そこで本研究では、溢水したHIC内炭酸塩スラリーの組成を模擬した炭酸塩スラリーを作製し、その炭酸塩スラリーの非放射性条件下での性状および気泡の保持特性を明らかにすることを目的とした。まず、溢水が発生した炭酸塩スラリーの組成を模擬するために、溢水した炭酸塩スラリーが調製された当時のALPS運転条件を調査し、炭酸塩スラリーの主要元素であるマグネシウムとカルシウムの比率を変えた5つの原水を調製した。これら原水から炭酸塩等を沈殿させ、実機ALPSと同じクロスフローフィルタ方式を用いて模擬炭酸塩スラリーを作製した。次に、作製した炭酸塩スラリーの化学分析を実施した。また、沈降試験を実施して沈降層の密度(以下「沈降密度」という。)、降伏応力を測定した。最後に、沈降層への気泡注入試験を実施し、炭酸塩スラリー内部での気泡保持/放出特性について検討した。模擬炭酸塩スラリーは原水組成のカルシウム含有率が高いほど沈降密度が高くなることが分かった。そして、沈降密度が高い模擬炭酸塩スラリーでは沈降層の降伏応力が高く、注入した気泡を保持しやすい傾向が観察された。これらのことから、溢水したHIC内炭酸塩スラリーを模擬するためには原水組成に関する情報が重要であり、また、スラリー内での気泡の保持状況には炭酸塩スラリーの密度が影響を及ぼすことを明らかにした。


Temporal change in atmospheric radiocesium during the first seven years after the Fukushima Dai-ich Nuclear Power Plant accident

阿部 智久; 吉村 和也; 眞田 幸尚

Aerosol and Air Quality Research, 21(7), p.200636_1 -  200636_11, 2021/07

 被引用回数:4 パーセンタイル:37.75(Environmental Sciences)

After the Fukushima Dai-ichi Nuclear Power Plant accident, atmospheric radiocesium concentration has been monitored by the Nuclear Regulation Authority (NRA) as a national project to assess its temporal change from August 2011 to November 2017. During the first two years, the atmospheric radiocesium concentration ranged between 10$$^{-1}$$ - 100 Bq m$$^{-3}$$, while concentrations of 10$$^{-5}$$ - 10$$^{-1}$$ Bq m$$^{-3}$$ were detected about seven years after the accident. Moreover, two years after the accident, the resuspension factor (RF) ranged between 10$$^{-7}$$ - 10$$^{-6}$$ m$$^{-1}$$ and gradually decreased to 10$$^{-11}$$ - 10$$^{-7}$$ m$$^{-1}$$ over time. Thus, the time dependence of RF can be divided into two phases, including a rapid decrease for the first two years, followed by a slow decreasing phase. The annual average RF values were also reduced by about half due to decontamination. Furthermore, to investigate the impact of anthropogenic activities on the RF temporal change, the monitoring data were classified into two groups, namely inside and outside the Fukushima evacuation zone. The RF decreased faster in the second than in the first group, which was consistent with the reported data on the time dependence of the air dose rate, suggesting that anthropogenic activities can promote environmental remediation and thereby reduce atmospheric radiocesium content. In addition, the currently observed RF reduction was faster than that reported for the Chernobyl Nuclear Power Plant accident for the same period, consisting with faster environmental remediation at catchment scale in Fukushima compared to Europe.


Microparticles with diverse sizes and morphologies from mechanical and laser cutting of fuel debris simulants and geopolymer as a covering material

Zhou, Q.*; 斉藤 拓巳*; 鈴木 誠矢; 矢野 公彦; 鈴木 俊一*

Journal of Nuclear Science and Technology, 58(4), p.461 - 472, 2021/04

 被引用回数:4 パーセンタイル:56.29(Nuclear Science & Technology)

During the decommissioning of Fukushima Daiichi Nuclear Power Plant, the dismantling of massive fuel debris is important for the defueling process. The production and dispersion of radioactive microparticles highly depends on the cutting technique implemented. Previous studies have been conducted on the development of cutting techniques and the treatment of radioactive particles generation during the cutting process. Besides, adequate understanding of the microparticle products during the cuttings of fuel debris is of vital necessity. Nowadays, geopolymer application is proposed as a covering material during the fuel debris retrieval in order to keep the structural integrity of damaged components. In this study, the microparticle products during mechanical and laser cutting of fuel debris simulants (Hafnium oxide and Tungsten(IV) oxide pellets) and geopolymer material were investigated. The cuttings have been carried out for samples of the simulants, geopolymer, and simulants with geopolymer covering. The generated particles were collected and investigated by laser diffraction particle size analyzer and Scanning Electron Microscope with X-ray spectrometry. Particles with diverse sizes and morphologies were observed from the products of each sample. It also appears that particles with unique sizes and morphologies can generate from the laser cuttings due to the thermal effect of laser cutting.



安藤 真樹; 松田 規宏; 斎藤 公明

日本原子力学会和文論文誌, 20(1), p.34 - 39, 2021/03



低線量・低線量率放射線被ばくによる臓器別酸化ストレス状態の検討(委託研究); 令和元年度英知を結集した原子力科学技術・人材育成推進事業

廃炉環境国際共同研究センター; 東北大学*

JAEA-Review 2020-048, 49 Pages, 2021/01



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