プルトニウム廃棄物処理開発施設 第2難燃物焼却工程設備の更新

山下 健仁; 牧 翔太; 横須賀 一裕; 福井 雅裕; 家村 圭輔

JAEA-Technology 2023-023, 97 Pages, 2024/03

JAEA-Technology-2023-023.pdf:8.21MB

プルトニウム廃棄物処理開発施設第2難燃物焼却室に設置されている第2難燃物焼却工程設備は、混合酸化物燃料製造等に伴い発生する放射性固体廃棄物のうち塩化ビニル(主にビニルバッグ)、RI用ゴム手袋等の難燃性廃棄物の減容処理技術開発を目的に2002年から焼却処理実証運転を行ってきた。しかし、難燃性廃棄物を処理する際に発生する塩化水素等による設備内部の腐食が進むとともに、焼却炉内壁の耐火物に亀裂の発生、進展が確認されたため、2018年から2022年に運転停止期間を設け、焼却炉等の更新を行った。本設備は廃棄物供給工程、焼却工程、廃ガス処理工程、灰取出工程により構成されており、このうち2020年3月から2021年3月にかけて廃ガス処理工程のスプレー塔の更新を、2021年1月から2022年2月にかけて焼却工程の焼却炉の更新を実施した。また、更新機器の腐食・劣化状況調査のため既設機器の撤去・解体作業中に焼却炉、スプレー塔から試料採取を行い、走査型電子顕微鏡/X線マイクロアナライザーによる観察とX線回折による分析を行った。本報告書ではスプレー塔・焼却炉の撤去・解体に係るグリーンハウスの設営方法、更新手順、更新対象機器の腐食・劣化状況の分析結果について報告する。

Automatic object recognition using deep learning for legacy waste treatment

吉田 幸彦

IL Nuovo Cimento, 46(2), p.33_1 - 33_8, 2023/03

https://doi.org/10.1393/ncc/i2023-23033-x

JAEA is addressing the back-end issues with the steadfast promotion of sustainable measures. The R&D plans are being rationally pursued by considering priorities based on indicators such as bottleneck issues in waste streams, relevance to WAC settings, and effectiveness of cost reduction. In addition, the future vision (JAEA 2050+) has been formulated to promote cross-disciplinary R&D through a new approach that cannot be reached by conventional methods, and active incorporation of information technologies, such as AI technologies. Currently, we are developing intelligent sensing that combines sensing and information processing technologies to realize automatic sorting technology, and non-destructive evaluation technology using high-energy X-ray CT, for legacy wastes. The core technology common to these technologies is image evaluation technology using deep learning models, which was confirmed to perform very well in the evaluation of waste object recognition.

Insights into machine-learning modeling for Cr(VI) removal from contaminated water using nano-nickel hydroxide

Maamoun, I.; Rushdi, M.*; Falyouna, O.*; Eljamal, R.*; Eljamal, O.*

Separation and Purification Technology, 308, p.122863_1 - 122863_16, 2023/03

https://doi.org/10.1016/j.seppur.2022.122863

The aim of this study is to employ machine learning (ML) in providing high-accuracy prediction of Cr(VI) removal efficiency by nickel hydroxide (-Ni(OH)) unconventional sorbent, towards the new era of artificial intelligence (AI) applications in (waste) water treatment. Hence, a reliable ML modeling was conducted based on the experimental investigation, considering different reaction parameters, including -Ni(OH) dosage, initial pH, reaction temperature, and initial Cr(VI) concentration. Linear regression model was selected as the suitable regression model with respect to the obtained reasonable correlation and the less training time and evaluation time, comparing to other considered regression techniques. The adopted linear regression model, for the time corresponding Cr(VI) removal efficiencies, exhibited satisfactory prediction accuracy. Furthermore, the importance of models coefficients was determined and implied the high importance of the dosage feature. The contributive effect of the investigated features was mainly concentrated at the early stage of the reaction (5 to 10 min), with an average range of 50 to 80 %, which was in agreement with the experimental findings of the rapid and full removal of Cr(VI) by -Ni(OH). The elucidated insights into the effects of different factors that influence Cr(VI) removal process by -Ni(OH) revealed the underlying interactions and removal pathways, which shall benefit other researchers in the preliminary design of pilot-scale applications and anticipating the predicted performance.

Arsenic removal from contaminated water utilizing novel green composite and nano zero-valent iron

Islam, M. S.*; Maamoun, I.; Falyouna, O.*; Eljamal, O.*; Saha, B. B.*

Journal of Molecular Liquids, 370, p.121005_1 - 121005_11, 2023/01

https://doi.org/10.1016/j.molliq.2022.121005

Arsenic waste must be carefully managed because of the adverse effects of arsenic in wastewater on the ecosystem. In the present study, an environmentally friendly novel composite of microalgae and nano-zero valent iron (NZVI) was employed as an adsorbent to eliminate arsenic from the aqueous environment. Fourier Transform Infrared spectroscopy, X-ray diffraction, and scanning electron microscope images were used to characterize and analyze the CV/NZVI composites. Batch tests using initial arsenic concentrations ranging from 5 to 100 mg/L were conducted to evaluate removal efficiencies. According to kinetic analysis, the best model for fitting the experimental data was the pseudo first-order model, which had the lowest Akaike information criterion (AIC), and Bayesian information criterion (BIC) values of -23.878 and -7.902, respectively. Results alluded that physisorption is the primary mechanism influenced by As-removal by CV/NZVI composite. Due to the negative sign of the enthalpy and Gibbs free energy, the thermodynamic investigation revealed that the adsorption reaction was exothermic and spontaneous. The thermodynamic analysis also affirmed that the arsenic removal process involved primarily physisorption and slight chemisorption phenomena. Meanwhile, 1.5 g/L CV/NZVI dosage achieved 99% As(V) removal efficiency in synthetic groundwater systems, confirming the high potential of the composite in complex aqueous systems.

塩素含有TRU廃棄物の焼却試験

山下 健仁; 横山 文*; 高貝 慶隆*; 牧 翔太; 横須賀 一裕; 福井 雅裕; 家村 圭輔

JAEA-Technology 2022-020, 106 Pages, 2022/10

JAEA-Technology-2022-020.pdf:4.77MB

福島第一原子力発電所事故に伴い発生した放射性固体廃棄物は、津波や海水の放水によって塩分を多く含んでいる可能性があるとともに、今後の廃止措置に係る作業や放射性廃棄物を処理する際の閉じ込めにはポリ塩化ビニル(PVC)製品を使用することも想定される。固体廃棄物の処理方法のうち、廃棄物の減容・安定化の効果が優れている焼却法は、検討を進めるべき手法の一つではあるが、塩素成分を含む超ウラン元素(TRU)固体廃棄物の処理には、放射性核種及び塩素成分の廃ガス処理系への移行挙動や塩素成分による機器の腐食の程度等を把握した上で、設置する処理施設の構造、使用材料などを決めていく高度な技術が求められる。そこで、国内で唯一、塩素成分を含むTRU固体廃棄物を焼却可能な設備である、核燃料サイクル工学研究所プルトニウム廃棄物処理開発施設(PWTF)の第2難燃物焼却設備を用い、廃棄物中塩素成分の廃ガス処理系移行挙動試験、焼却設備の金属材料選定に資する腐食試験及び廃棄物中プルトニウムの廃ガス処理系への分布調査を実施することとし、処理設備の設計検討に必要な種々のデータを蓄積することとした。本報告書は第2難燃物焼却設備を用いたこれらの試験により得られた焼却設備廃ガス処理系への塩素成分の移行挙動、適した耐食材料選定のための金属材料の評価、プルトニウムの分布調査の結果をまとめたものである。

ゼオライト粒子と接触したステンレス鋼の線による腐食影響

加藤 千明; 山岸 功; 佐藤 智徳; 山本 正弘*

材料と環境, 70(12), p.441 - 447, 2021/12

https://doi.org/10.3323/jcorr.70.441

ゼオライト粒子は福島第一原子力発電所(1F)の汚染水の浄化のためのセシウム吸着塔内で用いられている。使用後のセシウム吸着塔は敷地内で保管されているが、ステンレス鋼製胴部の局部腐食が懸念された。この腐食リスクに対し、線による影響データを照射下電気化学試験装置で取得した。また、内溶液の変化状態を実規模サイズのモックアップ試験装置で検討した。それらの結果から、過酸化水素による電位の上昇がゼオライト粒子の存在で防ぐことができ、塩化物イオンの濃化もそれほど生じないことを明らかにし、局部腐食が相当に小さく抑えられることを示した。

Temperature effects on local structure, phase transformation, and mechanical properties of calcium silicate hydrates

Im, S.*; Jee, H.*; Suh, H.*; 兼松 学*; 諸岡 聡; 小山 拓*; 西尾 悠平*; 町田 晃彦*; Kim, J.*; Bae, S.*

Journal of the American Ceramic Society, 104(9), p.4803 - 4818, 2021/09

https://doi.org/10.1111/jace.17881

This study aims to elucidate the effect of heating on the local atomic arrangements, structure, phase transformation, and mechanical properties of synthesized calcium-silicate-hydrate (C-S-H). The alteration in the atomic arrangement of the synthesized C-S-H (Ca/Si = 0.8) and the formation of crystalline phases that occurred in three distinct transformation stages of dehydration (105-200 C), decomposition (300-600 C), and recrystallization (700-1000 C) were investigated via powder X-ray diffraction, Si nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. Further, the deformation of the local atomic bonding environment and variations in mechanical properties during the three stages were assessed via pair distribution function analysis based on in-situ total X-ray scattering. The results revealed that the C-S-H paste before heating exhibited a lower elastic modulus in real space than that in the reciprocal space in the initial loading stage because water molecules acted as a lubricant in the interlayer. At the dehydration stage, the strain as a function of external loading exhibited irregular deformation owing to the formation of additional pores induced by the evaporation of free moisture. At the decomposition stage, the structural deformation of the main d-spacing (d 3.0 ) was similar to that of the real space before the propagation of microcracks. At the recrystallization stage, the elastic modulus increased to 48 GPa owing to the thermal phase transformation of C-S-H to crystalline -wollastonite. The results provide direct experimental evidence of the micro- and nanostructural deformation behavior of C-S-H pastes after exposure to high temperature under external loading.

パルス中性子応力測定法による超音波衝撃処理した十字溶接継手の残留応力評価

鈴木 環輝*; 大川 鉄平*; Harjo, S.; 佐々木 敏彦*

日本機械学会論文集(インターネット), 87(894), p.20-00377_1 - 20-00377_15, 2021/02

https://doi.org/10.1299/transjsme.20-00377

The residual stress state inside the cruciform welded joints were measured using the pulsed neutron stress measurement method. The points of interest in this study are the weld toe and its interior. We also compared the cases with and without ultrasonic impact treatment (UIT), which is expected as a fatigue strength improvement technology. Furthermore, the case where tensile stress or compressive stress was applied after UIT treatment was also examined. The applied stresses at this time were 75% or 85% of the yield point, respectively. From the above, we considered the cause of the change in the residual stress on the surface after UIT treatment, which was clarified in the preliminary experiment, in the early stage of fatigue. As a result, the load after the UIT treatment caused plastic deformation in a part of the inside, which caused the redistribution of residual stress.

Waste management in a Hot Laboratory of Japan Atomic Energy Agency, 1; Overview and activities in chemical processing facility

野村 和則; 小木 浩通*; 中原 将海; 渡部 創; 柴田 淳広

International Journal of Nuclear and Quantum Engineering (Internet), 13(5), p.209 - 212, 2019/00

Chemical Processing Facility of Japan Atomic Energy Agency is a basic research field for advanced back-end technology developments with using actual high-level radioactive materials. Most of them were treated properly and stored in the liquid waste vessel, but some were not treated and remained at the experimental space as a kind of legacy nuclear waste, which we must treat in safety and dispose if we continue research activities in the facility. Under this circumstance, we launched a collaborative research project called the STRAD project, which stands for Systematic Treatment of Radioactive liquid waste for Decommissioning, in order to develop the treatment processes for wastes of the nuclear research facility. In this project, decomposition methods of certain chemicals, which have been directly solidified without safety pretreatment but may cause a troublesome phenomenon, is developing and a prospect that it will be able to decompose in the facility by simple method. And solidification of aqueous or organic liquid wastes after the decomposition has been studied by adding cement or coagulants. Furthermore, we treated experimental tools of various materials with making an effort to stabilize and to compact them before the package into the waste container. It is expected to decrease the number of transportation of the solid waste and widen the operation space. The project is expected to contribute beneficial waste management outcome that can be shared world widely.

Heat treatment of phosphate-modified cementitious matrices for safe storage of secondary radioactive aqueous wastes in Fukushima Daiichi Nuclear Power Plant

入澤 啓太; 谷口 拓海; 並木 仁宏; Garca-Lodeiro, I.*; 大杉 武史; 榊原 哲朗; 中澤 修; 目黒 義弘; 木下 肇*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04

東京電力福島第一原子力発電所から発生する汚染水二次廃棄物の安全な貯蔵のために、リン酸セメントを用いて低含水固化技術を開発している。従来のセメントシステムは水和反応を経由して固化し、一定量の水の要求と含有を必要とする。しかしながら、リン酸セメントは酸塩基反応を経由して固化する。それゆえ、水は作業性の観点から必要とされているだけである。水分量が低減されたリン酸セメントシステムは放射性廃棄物による水の放射線分解で発生する水素ガスを低減できるため、安全な貯蔵に貢献できる。本研究は、異なる温度(60, 90, 120C)の開放系及びリファレンスとして20Cの閉鎖系で養生したカルシウムアルミネートセメント(CAC)とリン酸添加CAC(CAP)の含水率と特性を調査した。CACとCAP中の水分量は時間経過に伴い減少した。 90Cにおいて、CAPはCACよりも低い含水率を得た。CAC中の自由水は、加熱処理により構造水に転換したが、CAPでは生じなかった。ハイドロキシアパタイトの前駆相である正リン酸塩が20, 60CのCAP中で発見され、90Cでは正リン酸塩とハイドロキシアパタイトの混合物が発見された。120CのCAP中のリン酸生成物は、20, 60, 90CのCAPと比較して異なるリン酸塩からなるようにみえる。