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論文

Sintering behavior analysis of compacted dry recycled U $_{0.7}$ Pu $_{0.3}$ O $_{2}$ powder using master sintering curve theory

中道晋哉; 砂押剛雄*; 廣岡瞬; Vauchy, R.; 村上龍敏

Journal of Nuclear Materials, 595, p.155072_1 - 155072_11, 2024/07

https://doi.org/10.1016/j.jnucmat.2024.155072

Using dry recycled powders for uranium and plutonium mixed oxide (MOX) fuel production can reduce unnecessary storage and accountability of nuclear material in facilities. The shrinkage behavior of green compacts of dry recycled powders differs from that of conventional raw powders because the dry recycled MOX powder is obtained from the fabrication scrap of sintered pellets. The shrinkage behavior of dry recycled MOX powder has been investigated by dilatometry. Based on the shrinkage curves, sintering apparent activation energies were evaluated using the master sintering curve (MSC) and the constant rate of heating methods. The obtained values were higher than the energy evaluated for raw powder experiments. The sigmoid sintering prediction equation using the MSC function was constructed. The accumulation of data on the activation energy for various sintering conditions will lead to the wide application of this prediction formula in the future.

論文

A Science-based mixed oxide property model for developing advanced oxide nuclear fuels

加藤正人; 沖拓海; 渡部雅; 廣岡瞬; Vauchy, R.; 小澤隆之; 上羽智之; 生澤佳久; 中村博樹; 町田昌彦

Journal of the American Ceramic Society, 107(5), p.2998 - 3011, 2024/05

https://doi.org/10.1111/jace.19609

被引用回数：0 パーセンタイル：0.01(Materials Science, Ceramics)

Herein, a science-based uranium and plutonium mixed oxide (MOX) property model (Sci-M Pro) is derived for determining properties of MOX fuel and analyzing their performance as functions of Pu content, minor-actinide content, oxygen-to-metal ratio, and temperature. The property model is constructed by evaluating the effect of phonons and electronic defects on heat capacity and thermal conductivity of MOX fuels. The effect of phonons was evaluated based on experimental datasets related to lattice parameter, thermal expansion, and sound speeds. Moreover, the effect of electronic defects was determined by analyzing oxygen-potential data based on defect chemistry. Furthermore, the model evaluated the effect of the Bredig transition on the thermal properties of MOX fuel by analyzing the irradiation test results. The derived property model is applied to the performance code to analyze fast reactor fuel pins.

論文

Uranium-plutonium-americium cation interdiffusion in polycrystalline (U,Pu,Am)O $_{2 pm x}$ mixed oxides

Vauchy, R.; 松本卓; 廣岡瞬; 宇野弘樹*; 田村哲也*; 有馬立身*; 稲垣八穂広*; 出光一哉*; 中村博樹; 町田昌彦; et al.

Journal of Nuclear Materials, 588, p.154786_1 - 154786_13, 2024/01

https://doi.org/10.1016/j.jnucmat.2023.154786

被引用回数：1 パーセンタイル：72.91(Materials Science, Multidisciplinary)

Diffusion couples made of dense polycrystalline (U,Pu,Am)O $_{2 pm x}$ oxides were annealed in various thermodynamic conditions (temperature, oxygen partial pressure), and for different durations. The associated actinide redistribution was quantified using Electron Probe Micro-Analysis (EPMA). Average diffusion profiles were obtained from elemental U, Pu, and Am X-ray maps and the resulting interdiffusion coefficients were calculated, then analyzed at the light of our model of point defect chemistry.

論文

Ionic radii in fluorites

Vauchy, R.; 廣岡瞬; 村上龍敏

Materialia, 32, p.101934_1 - 101934_12, 2023/12

https://doi.org/10.1016/j.mtla.2023.101934

The construction of the fluorite unit-cell from the ionic radii of the constitutive species is proposed with the use of our hybrid model, considering flexible anion and cation radii. 27 binary and stoichiometric compounds crystallizing in this structure were investigated to find a correlation between the anion's radius as a function of the cation's size.

論文

Ionic radii in halites

Vauchy, R.; 廣岡瞬; 村上龍敏

Materialia, 32, p.101943_1 - 101943_8, 2023/12

https://doi.org/10.1016/j.mtla.2023.101943

The construction of the halite unit-cell from the ionic radii of the constitutive species is proposed with the use of our hybrid model, considering flexible anion and cation radii. 312 binary halite-structured stoichiometric compounds were analyzed. This systematic study focuses first on the revision of the ionic radii of the considered species then on the proposition of relations between the anionic radius as a function of the cation's size.

論文

Sintering and microstructural behaviors of mechanically blended Nd/Sm-doped MOX

廣岡瞬; 堀井雄太; 砂押剛雄*; 宇野弘樹*; 山田忠久*; Vauchy, R.; 林崎康平; 中道晋哉; 村上龍敏; 加藤正人

Journal of Nuclear Science and Technology, 60(11), p.1313 - 1323, 2023/11

https://doi.org/10.1080/00223131.2023.2192725

被引用回数：3 パーセンタイル：95.99(Nuclear Science & Technology)

収率が高く燃料に固溶するFP(模擬FP)としてNd $_{2}$ O $_{3}$ 及びSm $_{2}$ O $_{3}$ を添加したMOXの焼結試験を行い、焼結後の微細組織を評価した。熱膨張計を用いて取得した焼結中の収縮曲線から、模擬FP含有MOXは通常のMOXよりも高温で焼結が進むことが分かった。焼結後の密度評価及び金相組織の観察から、模擬FP含有MOXは通常のMOXよりも粒成長と高密度化が進むことが分かった。これは、添加元素の影響を受けて一部のUが4価から5価に変化し、拡散速度が大きくなったことが原因と考えられる。また、XRDの結果から焼結後の試料は均質に固溶した結晶構造が示されたが、EPMAによる元素マッピングの結果からは模擬FPの濃度が一様でなく、完全には均質に分布していない微細組織が示された。不均質に分布したNd $_{2}$ O $_{3}$ 含有MOXを微粉砕し、再焼結を行う過程を繰り返すことで、均質性が向上し、密度も十分に高い模擬FP含有MOXペレットを作製することができた。

論文

Lattice parameters of fluorite-structured uranium-americium mixed oxides

Vauchy, R.; 廣岡瞬; 渡部雅; 横山佳祐; 村上龍敏

Journal of Nuclear Materials, 584, p.154576_1 - 154576_11, 2023/10

https://doi.org/10.1016/j.jnucmat.2023.154576

被引用回数：2 パーセンタイル：90.12(Materials Science, Multidisciplinary)

The room temperature lattice parameters of stoichiometric U1-yAmyO $_{2}$ uranium-americium mixed oxides were re-evaluated at the light of our hybrid crystallographic model. The complex charge compensation mechanisms that take place in this solid solution were also considered to shed light on the available experimental unit-cell values.

論文

Oxygen potential of neodymium-doped U $_{0.817}$ Pu $_{0.180}$ Am $_{0.003}$ O $_{2 pm x}$ uranium-plutonium-americium mixed oxides at 1573, 1773, and 1873 K

Vauchy, R.; 砂押剛雄*; 廣岡瞬; 中道晋哉; 村上龍敏; 加藤正人

Journal of Nuclear Materials, 580, p.154416_1 - 154416_11, 2023/07

https://doi.org/10.1016/j.jnucmat.2023.154416

被引用回数：4 パーセンタイル：98.08(Materials Science, Multidisciplinary)

Oxygen potentials of U $_{0.817}$ Pu $_{0.180}$ Am $_{0.003}$ O $_{2 pm x}$ incorporating 10 and 20 mol% of neodymium (Nd/Metal) were investigated by thermogravimetry at 1573, 1773, and 1873 K. The presence of neodymium induced an increase in the oxygen potential of the U-Pu mixed oxide. The correlation between oxygen partial pressure pO $_{2}$ and deviation from stoichiometry x was analyzed, and a model of defect chemistry was proposed. Finally, the crystal structure of these mixed oxides was discussed at the light of the mechanisms of possible Nd(III)/U(V) charge compensation, and deviation from stoichiometry.

論文

Breaking the hard-sphere model with fluorite and antifluorite solid solutions

Vauchy, R.; 廣岡瞬; 渡部雅; 加藤正人

Scientific Reports (Internet), 13, p.2217_1 - 2217_8, 2023/02

https://doi.org/10.1038/s41598-023-29326-0

被引用回数：6 パーセンタイル：93.59(Multidisciplinary Sciences)

Using the hard-sphere model with the existing tabulated values of ionic radii to calculate the lattice parameters of minerals does not always match experimental data. An adaptation of this crystallographic model is proposed by considering the cations and anions as hard and soft spheres, respectively. We demonstrate the relevance of this hybrid model with fluorite and antifluorite-structured systems.

論文

Liquid phase sintering of alumina-silica co-doped cerium dioxide CeO $_{2}$ ceramics

Vauchy, R.; 廣岡瞬; 渡部雅; 横山佳祐; 砂押剛雄*; 山田忠久*; 中道晋哉; 村上龍敏

Ceramics International, 49(2), p.3058 - 3065, 2023/01

https://doi.org/10.1016/j.ceramint.2022.09.295

被引用回数：8 パーセンタイル：75.06(Materials Science, Ceramics)

Pure and low -Al $_{2}$ O $_{3}$ -SiO $_{2}$ co-doped ceria specimens were prepared by conventional ceramic processing using powder metallurgy. The effect of co-doping on the microstructural and structural properties of cerium dioxide was investigated by means of optical microscopy, scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The co-addition of alumina and silica promoted liquid phase sintering (LPS) and significantly contributed to grain growth, even in the small concentrations of the present study (1 wt% and 2 wt%). A glassy-look phase precipitated at the grain boundaries, characteristic of liquid phase sintering. The addition of dopants to the formulation greatly enhanced the grain growth process without disturbing the CeO $_{2}$ structure.

論文

Oxygen diffusion in the fluorite-type oxides CeO $_{2}$ , ThO $_{2}$ , UO $_{2}$ , PuO $_{2}$ , and (U, Pu)O $_{2}$

加藤正人; 渡部雅; 廣岡瞬; Vauchy, R.

Frontiers in Nuclear Engineering (Internet), 1, p.1081473_1 - 1081473_10, 2023/01

https://doi.org/10.3389/fnuen.2022.1081473

This study evaluates oxygen self-diffusion and chemical diffusion coefficients of fluorite-type oxides CeO $_{2}$ , ThO $_{2}$ , UO $_{2}$ , PuO $_{2}$ , and (U, Pu) O $_{2}$ using point defect concentration, oxygen vacancies, and interstitial oxygen. The self-diffusion coefficient changed in proportion to the 1/n power of oxygen partial pressure, which is similar to the oxygen partial pressure dependence of the defect concentration. All parameters used to represent the diffusion coefficients were determined, and the experimental data were accurately stated. The chemical diffusion coefficient was much higher at O/M = 2.00 than in low O/M oxides. In the reduction process, the chemical diffusion control rate was dominant, and a new phase with O/M = 2.00 was formed, and it expanded from the surface in the oxidation process from a low O/M ratio to O/M = 2.00.

論文

Cation interdiffusion in uranium-plutonium mixed oxide fuels; Where are we now?

Vauchy, R.; 廣岡瞬; 松本卓; 加藤正人

Frontiers in Nuclear Engineering (Internet), 1, p.1060218_1 - 1060218_18, 2022/12

https://doi.org/10.3389/fnuen.2022.1060218

Diffusion phenomena in uranium-plutonium mixed oxides U $_{1-y}$ PuyO $_{2}$ dictate the physicochemical properties of MOX nuclear fuel throughout manufacturing, irradiation and storage. More precisely, estimating the cation interdiffusion is paramount insofar as it dovetails with the actinide redistribution during sintering and under irradiation. In this paper, we propose a critical review of the existing experimental data of U and Pu interdiffusion coefficients in MOX fuel.

口頭

Experimental measurements of oxygen potential of neodymium doped MOX fuel

Vauchy, R.; 廣岡瞬; 砂押剛雄*; 加藤正人

no journal, ,

Uranium plutonium mixed oxides (MOX) are used worldwide as fuel elements for different nuclear reactor technologies. The Oxygen to Metal ratio of these materials is a first order parameter influencing most of their thermal properties (from cation interdiffusion to melting point). By definition, the relative partial free energy of oxygen, abusively designated as oxygen potential, of U Pu mixed oxides corresponds to the relation between the activity of oxygen in the solid (hence the Oxygen to Metal ratio) and the oxygen partial pressure of the surrounding gas phase. This fundamental thermodynamical property is of prime importance as it can be used for tailoring the Oxygen to Metal ratio of fuels during their manufacturing and, or, to be implemented in performance codes. Studying the influence of some of the main fission products on the oxygen potential of MOX is needed to better understand its in pile behavior but also within the frame of developing a low decontamination reprocessing of spent nuclear fuels. Most of the elements (and their isotope declinations) of the Mendeleev s periodic table are produced when nuclear fuels are irradiated. Neodymium is one of the more abundant solid fission products (FPs) and is also known to be soluble within the fluorite structure. Due to its high fission yield, evaluating the effect of Nd incorporation on the thermal properties of MOX fuels is necessary. Up to now, no oxygen potential data of Nd doped uranium plutonium americium mixed oxides are published.

口頭

次世代革新炉のためのMOX燃料技術,1; 比熱と熱伝導率における電子的欠陥の寄与

加藤正人; 廣岡瞬; 渡部雅; Vauchy, R.; 沖拓海

no journal, ,

酸素ポテンシャル,拡散係数及び電気伝導率の実験結果について欠陥化学により評価し、得られた電子欠陥濃度から比熱と熱伝導率の寄与を評価した。MOXの比熱及び熱伝導率は、UO $_{2}$ 及びPuO $_{2}$ に比べて低温側から上昇することを示した。また、照射燃料温度を解析するための熱伝導率式を検討した。

口頭

Oxygen potential measurements of Nd doped (U,Pu,Am)O $_{2}$ mixed oxides

Vauchy, R.; 廣岡瞬; 砂押剛雄*; 中道晋哉; 村上龍敏; 加藤正人

no journal, ,

Relative oxygen potentials of U $_{0.817}$ Pu $_{0.180}$ Am $_{0.003}$ O $_{2}$ incorporating 10 and 20 mol% of neodymium (Nd/Metal) were investigated by thermogravimetry at 1573, 1773, and 1873 K.

口頭

Ionic radii in fluorite structured actinide dioxides

Vauchy, R.; 廣岡瞬; 村上龍敏

no journal, ,

蛍石構造の二酸化アクチニドの構成種のイオン半径を、結晶学的ハイブリッドモデルを使用して再評価した。

口頭

Manufacturing and property measurements of homogeneous simulated FP (Nd/Sm/Gd/Zr)-doped MOX

堀井雄太; 廣岡瞬; Vauchy, R.; 林崎康平; 宇野弘樹*; 田村哲也*; 砂押剛雄*; 大和田英明*; 山田忠久*; 村上龍敏

no journal, ,

核分裂生成物(FP: Fission Product)は、照射された燃料中に生成・蓄積し、燃料の熱物性に影響を与える。照射挙動のシミュレーションの精度を高めるため、FPを含む燃料の物性に関する研究が必要である。しかし、照射燃料の取り扱いの困難さから、照射燃料特性、特にMOX燃料に関する報告は世界的に少ない。また、照射済燃料には数多くのFPが含まれているため、個々のFPの影響を評価することができない。そのため、燃料特性に及ぼすFPの影響を簡便に評価できる手法を提案する必要がある。本研究では、模擬燃焼燃料として模擬FPを添加した試料を作製し、その燃料物性を測定した。評価に当たっては、ウランやプルトニウムと同様に試料中のFPの均質性が重要である。均質な試料を得るために焼結ペレットの粉砕と再焼結の工程を繰り返し、焼結するごとにEPMAとXRDにより均質性を確認した。一連の工程を3回繰り返すことで、測定に適した均質性の高い試料を作製した。模擬FPとしては、照射後のMOX燃料中で主要な固溶性FPであるSm $_{2}$ O $_{3}$ 、Gd $_{2}$ O $_{3}$ 、ZrO $_{2}$ を使用し、個々のFPが熱伝導率や熱膨張率などの物性に及ぼす影響を評価した。また、複数のランタノイドを含有する際の影響も評価し、比較するため、Nd $_{2}$ O $_{3}$ 、Sm $_{2}$ O $_{3}$ 、Gd $_{2}$ O $_{3}$ を含むMOXも作製した。

口頭

MOX燃料物性試験に供する均質な模擬FP(Nd $_{2}$ O $_{3}$ /Sm $_{2}$ O $_{3}$ /Gd $_{2}$ O $_{3}$ /ZrO $_{2}$ )含有MOXの作製

堀井雄太; 廣岡瞬; Vauchy, R.; 林崎康平; 宇野弘樹*; 田村哲也*; 砂押剛雄*; 大和田英明*; 山田忠久*; 村上龍敏

no journal, ,

MOX燃料の照射により燃料中に生成・蓄積する核分裂生成物(FP: Fission Product)は、MOXの燃料物性に影響を与える。これまで、未照射のMOX燃料物性については数多く報告されているが、FPが蓄積した燃焼燃料に関する報告例は少ない。燃焼燃料の物性評価において、実際に原子炉で照射した燃料は取り扱いが困難であることから、FPとして含まれる元素をMOXに添加した模擬燃焼燃料を研究することが有効な手段である。模擬FPの影響評価にあたっては、模擬FPが均質であることが重要である。本研究では、乾式での試料作製方法として考案した溶融法と粉砕混合法の2つの手法について、模擬FPを含む試料の作製方法としての適性を評価した。

口頭

Phase separation and recombinaison in U1-yPuyO $_{2}$ -x with y = 0.30, 0.45, and 1.00

Vauchy, R.; 小笠原誠洋*; 山田忠久*; 砂押剛雄*; 田村哲也*; 堀井雄太; 廣岡瞬; 加藤正人; 村上龍敏

no journal, ,

The locus of MOX and plutonia fluorite phase separation and recombination into two structures was investigated using a combination of differential scanning calorimetry (DSC) and differential thermal analysis (DTA) at the Plutonium Fuel Development Center of JAEA, Tokai-mura, Japan. The systematic cross-experiment procedure allowed refining the limits of the solvus existing in hypostoichiometric dioxides, MOX and plutonia. This allows to better understand the crystallographic behavior, and associated redox properties, of MOX fuel for fast reactors during manufacturing, and its subsequent storage.

口頭

MOX燃料の熱伝導率における燃焼度の影響評価,1; 模擬FP添加MOXの熱伝導率評価

堀井雄太; 廣岡瞬; Vauchy, R.; 宇野弘樹*; 小笠原誠洋*; 山田忠久*; 村上龍敏

no journal, ,

MOX燃料中に生成・蓄積する固溶性のFPは、燃料マトリクスに均質に固溶することで、MOXの熱伝導率を大きく低下させる。本研究では、主要な固溶性FPであるNdO、SmO、GdOを模擬FPとして添加したMOXペレットを作製し、レーザーフラッシュ法を用いて、熱拡散率を測定した。それらの結果から、個々のFPがMOX燃料の熱伝導率に与える影響を系統的に評価し、FPの影響を考慮した熱伝導率の評価式を導出した。