Quantifying uncertainty induced by scattering angle distribution using maximum entropy method

丸山 修平; 山本 章夫*; 遠藤 知弘*

Annals of Nuclear Energy, 205, p.110591_1 - 110591_13, 2024/09

https://doi.org/10.1016/j.anucene.2024.110591

This study developed a new method for evaluating the uncertainty in reactor core/shielding characteristics attributable to the scattering angle distribution, employing a random sampling (RS) technique integrated with continuous energy Monte Carlo (CEMC) calculations. The impact of neutron scattering angle is not negligible in the analysis of fast reactor cores and shielding. Recent advancements have enabled the high-accuracy assessment of nuclear data-induced uncertainty by merging CEMC calculations and the RS technique. Nonetheless, a method to quantify uncertainty due to scattering angle distribution remains unestablished. This study introduces a new approach for uncertainty quantification related to scattering angle distribution in CEMC-RS, utilizing the maximum entropy method. The effectiveness of this method was verified through comparison with results from the classical deterministic uncertainty quantification approach based on generalized perturbation theory. Overall, this method offers a more accurate tool for nuclear engineers and researchers in evaluating and managing uncertainties in reactor design and safety analysis.

Evaluation of radiation dose caused by bremsstrahlung photons generated by high-energy beta rays using the PHITS and GEANT4 simulation codes

志風 義明

Journal of Nuclear Science and Technology, 61(7), p.894 - 910, 2024/07

https://doi.org/10.1080/00223131.2023.2285934

福島第一原子力発電所事故により原子炉建屋内で放出された放射性核種のうち、SrやY等の高エネルギー線源は、壁、床、壁や内部構造などの建屋の物質中で制動放射光子を発生させる。したがって、原子炉建屋の作業員に対する制動放射の放射線量を評価することは、放射線防護にとって極めて重要である。制動放射線量の評価計算の精度を、粒子重イオン輸送コードシステム(PHITS)とGEometry AND Tracking(GEANT4)シミュレーションコードの結果を比較することにより調査した。計算では、様々な遮蔽板(鉛、銅、アルミニウム、ガラス、ポリエチレン、厚さは1.040mm)の背後にある水円筒を評価材料として設定し、制動放射光子による吸収線量及び付与エネルギースペクトルを得て、両シミュレーションコードの特性と差異を調査した。付与エネルギースペクトルの比較結果では、スペクトル形状には矛盾しない同様の傾向がある。数十keV以下のエネルギー範囲では、鉛遮蔽物質のPHITSのスペクトルにピークが見られる。制動放射光子を発生させるための遮蔽板の様々な条件下での吸収線量を比較すると、両コードのほとんどの結果は、2.280MeV線源については約10%差以内、0.5459MeV線源については20mm厚の鉛の場合の約30%を除いて約20%差以内で相関している。場合によっては差異はあるが、2つのシミュレーションコードの評価結果は上記の精度で良く相関していると結論付けられた。

Measurement of the prompt fission -rays from slow neutron-induced fission of U with STEFF

Wright, T.*; 原田 秀郎; 木村 敦; 他121名*

European Physical Journal A, 60(3), p.70_1 - 70_11, 2024/03

https://doi.org/10.1140/epja/s10050-024-01277-8

The average energy and multiplicity of prompt -rays from slow neutron-induced fission of U have been measured using the STEFF spectrometer at the neutron time-of-flight facility n_TOF. The individual responses from 11 NaI scintillators were corrected for multiple -ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission -rays. The results give an average -ray energy of 1.71(5) MeV and multiplicity of 2.66(18) considering -rays emitted within the energy range from 0.8 to 6.8 MeV. The n_TOF data has a slightly larger and smaller than other recent measurements, however the product of the two is in agreement within the quoted uncertainties.

Understanding muon diffusion in perovskite oxides below room temperature based on harmonic transition state theory

伊藤 孝; 髭本 亘; 下村 浩一郎*

Physical Review B, 108(22), p.224301_1 - 224301_11, 2023/12

https://doi.org/10.1103/PhysRevB.108.224301

In positive muon spin rotation and relaxation (SR) spectroscopy, positive muons () implanted into solid oxides are conventionally treated as immobile spin-probes at interstitial sites below room temperature. This is because each is thought to be tightly bound to an oxygen atom in the host lattice to form a muonic analogue of the hydroxy group. On the basis of this concept, anomalies in SR spectra observed in oxides have been attributed in most cases to the intrinsic properties of host materials. On the other hand, global diffusion with an activation energy of 0.1~eV has been reported in some chemically-substituted perovskite oxides at cryogenic temperatures, although the reason for the small activation energy despite the formation of the strong O bond has not yet been quantitatively understood. In this study, we investigated interstitial diffusion in the perovskite oxide lattice using KTaO cubic perovskite as a model system. We used the SR method and density functional theory calculations along with the harmonic transition state theory to study this phenomenon both experimentally and theoretically. Experimental activation energies for global diffusion obtained below room temperature were less than a quarter of the calculated classical potential barrier height for a bottleneck transfer path. The reduction in the effective barrier height could be explained by the harmonic transition state theory with a zero-point energy correction; a significant difference in zero-point energies for at the positions in the O bonding equilibrium state and a bond-breaking transition state was the primary cause of the reduction. This suggests that the assumption of immobile in solid oxides is not always satisfied since such a significant decrease in diffusion barrier height can also occur in other oxides.

Relationship between internal stress distribution and microstructure in a suspension-sprayed thermal barrier coating with a columnar structure

山崎 泰広*; 篠宮 啓介*; 奥村 忠晴*; 鈴木 賢治*; 菖蒲 敬久; 中村 唯我*

Quantum Beam Science (Internet), 7(2), p.14_1 - 14_12, 2023/05

https://doi.org/10.3390/qubs7020014

The suspension plasma spray (SPS) technique has attracted attention because of its various microstructures, which can be achieved by mixing submicron spray particles with a solvent to form a suspension. Thermal barrier coatings (TBCs) with a columnar structure, which might achieve high strain tolerance, can be obtained using the SPS technique. In this study, the internal stress distribution of the SPS-TBC with different columnar structures was evaluated by hybrid measurement using high-energy synchrotron X-ray diffraction analysis and laboratory low-energy X-rays. The effect of microstructure on the internal stress distribution of the SPS-TBC was discussed on the basis of the experimental results. In addition, the in-plane internal stress was decreased by decreasing the column diameter. The thin columnar microstructure of the SPS-TBC has superior strain tolerance. The internal stresses in the column of the SPS-TBC are periodic decrements caused by stress relaxation in porous layers.

New material exploration to enhance neutron intensity below cold neutrons; Nanosized graphene flower aggregation

勅使河原 誠; 池田 裕二郎*; Yan, M.*; 村松 一生*; 須谷 康一*; 福住 正文*; 能田 洋平*; 小泉 智*; 猿田 晃一; 大竹 淑恵*

Nanomaterials (Internet), 13(1), p.76_1 - 76_9, 2023/01

https://doi.org/10.3390/nano13010076

冷中性子以下の中性子強度を高めるため、ナノサイズグラフェンの集合体が、ナノダイヤモンドと同様に中性子のコヒーレント散乱を促進できることを提案した。さらには、グラフェンの強いsp2結合は、高い耐放射線性を有する可能性を秘める。理研の加速器駆動型小型中性子源やJ-PARCのiMATERIAを用いて、ナノサイズグラフェンの中性子全断面積測定,中性子小角散乱測定を行った。測定結果より、ナノサイズのグラフェン集合体は、コヒーレント散乱に起因すると考えられる冷中性子エネルギー領域での全断面積と小角散乱を増大させ、ナノダイヤモンドと同様に高い中性子強度をもたらすことを世界で初めて明らかにした。

Experimental and numerical study on energy separation in vortex tube with a hollow helical fin (Joint research)

呉田 昌俊; 山形 洋司*; 宮腰 賢*; 増井 達也*; 三浦 義明*; 高橋 一憲*

JAEA-Research 2022-007, 28 Pages, 2022/09

JAEA-Research-2022-007.pdf:8.17MB

ボルテックスチューブにおけるエネルギー分離を促進するために、新たに設計した中空螺旋状フィンを管内に挿入した。本報では、3種類の管を用いて、フィンがエネルギー分離に及ぼす影響を実験的に調べ、次に、数値流体力学(CFD)シミュレーションを行い、実験結果と中空螺旋状フィン付き管内の流動構造との関係を研究した。実験データから、フィンがエネルギー分離を促進し、管長を短くできることがわかった。入口空気圧が0.5MPaのとき、入口から出口までの最大温度差は62.2Cであった。レイノルズ応力モデル(RSM)乱流モデルを組み込んだCFDコードを用いて流体解析をした結果、フィン無とフィン有の場合とで淀み点の位置が大きく変わり、流動構造が全く異なることを確認した。中空螺旋状フィンによって、低温側フィン端と淀み点との間に小さな循環渦構造を持つ強い反転渦流が形成され、乱流運動エネルギーが大きな領域が生成されることによってエネルギー分離が促進されたと考えられる。

A Theoretical investigation on the intermolecular potential curve between ruthenium tetroxide and NO (X = 1, 2)

城戸 健太朗

International Journal of Quantum Chemistry, 121(21), p.e26781_1 - e26781_15, 2021/11

https://doi.org/10.1002/qua.26781

Ruthenium tetroxide (RuO) is one of chemical species of fission products assumed to be released to the environment during a severe accident of nuclear facilities and a target compound to assess the amount produced, reactivity, mobility and release timing. In this article, the NO (X = 1, 2) adduct formation of RuO has been investigated, based on the potential energy curve (PEC) evaluated by UM06, UTPSSh, CASSCF, and CASPT2 methods. At several stationary points, CCSD and LR-CCSD(T) energies are also computed for a comparison. The PEC shows that there is an activation barrier to form the NO adduct and that the process is endothermic in terms of free energy. In the system, the electron transfer occurs from NO to RuO when the bond between the nitrogen and oxo ligand is formed. It has been discussed in detail using active orbitals, weight of electron configurations and spin population obtained by CASSCF.

Development of a membrane reactor with a closed-end silica membrane for nuclear-heated hydrogen production

Myagmarjav, O.; 田中 伸幸; 野村 幹弘*; 野口 弘喜; 今井 良行; 上地 優; 久保 真治; 竹上 弘彰

Progress in Nuclear Energy, 137, p.103772_1 - 103772_7, 2021/07

https://doi.org/10.1016/j.pnucene.2021.103772

Hydrogen production from nuclear energy has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. With respect to the large-scale and economical production of hydrogen using nuclear energy, the thermochemical water-splitting iodine-sulfur (IS) process is a promising method. The IS process uses sulfur and iodine compounds to decompose water into its elemental constituents, hydrogen and oxygen, by using three coupled chemical reactions: the Bunsen reaction; sulfuric acid decomposition; and hydrogen iodide (HI) decomposition. The decomposition of HI is the efficiency-determining step of the process. In this work, a membrane reactor with a silica membrane closed on one end was designed, and its potential for hydrogen production from HI decomposition was explored. In the reactor-module design, only one end of the membrane tube was fixed, while the closed-end of the tube was freely suspended to avoid thermal expansion effects. The closed-end silica membranes were prepared for the first time by a counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. In application, HI conversion of greater than 0.60 was achieved at a decomposition temperature of 400C. Thus, the membrane reactor with closed-end silica membrane was shown to produce a successful equilibrium shift in the production of hydrogen via HI decomposition in the thermochemical IS process.

Visualization of the boron distribution in core material melting and relocation specimen by neutron energy resolving method

阿部 雄太; 土川 雄介; 甲斐 哲也; 松本 吉弘*; Parker, J. D.*; 篠原 武尚; 大石 佑治*; 加美山 隆*; 永江 勇二; 佐藤 一憲

JPS Conference Proceedings (Internet), 33, p.011075_1 - 011075_6, 2021/03

https://doi.org/10.7566/JPSCP.33.011075

Since the hardness of fuel debris containing boride from BC pellet in control rod is estimated to be two times higher as that of oxide, such as UO and ZrO, distribution of such boride in the fuel debris formed in the Fukushima-Daiichi Nuclear Power Plants may affect the process of debris cutting and removal. The high neutron absorption of boron may affect the possibility of re-criticality during the process of debris removal. Therefore, boride distribution in fuel debris is regarded as an important issue to be addressed. However, boron tends to have difficult in quantification with conventionally applied methods like EPMA and XPS. In this study, accelerator-driven neutron-imaging system was applied. Since boron is the material for neutron absorption, its sensitivity in terms of neutron penetration through specimens is concerned. To adjust neutron attenuation of a specimen to suit a particular measurement by selecting the neutron energy range, we focused on the energy resolved neutron imaging system RADEN, which utilizes wide energy range from meV to keV. Development of a method to visualize boron distribution using energy-resolved neutrons has been started. In this presentation the authors show the status of the development of a method utilizing energy-resolved neutrons and provide some outcome from its application to the Core Material Melting and Relocation (CMMR)-0 and -2 specimens.