High-temperature oxidation failure in reactivity-initiated accidents; An Evaluation of failure criteria based on oxygen concentration from the previous NSRR experiments

Luu, V. N.; 谷口 良徳; 宇田川 豊; 勝山 仁哉

Nuclear Engineering and Design, 442, p.114222_1 - 114222_15, 2025/10

https://doi.org/10.1016/j.nucengdes.2025.114222

For near-term application, coated-Zr alloy claddings show potential for enhancing safety by providing better oxidation resistance and minimizing hydrogen absorption under design-basis accidents (DBA). This benefit could extend the burnup and operational cycles of fuel rods. In assessing safety, reactivity-initiated accidents (RIA) are considered as one of the DBA conditions. The current safety criteria for high-temperature oxidation failure, one of the failure modes linked to RIA, are defined by peak fuel enthalpy values that range from 205 to 270 cal/g. This wide variability presents challenges when attempting to generalize criteria for modified-Zr alloy claddings with superior oxidation resistance. Therefore, it may be more relevant to apply failure criteria based on embrittlement mechanisms, such as oxygen concentration in the -Zr phase. This study aimed to assess the failure based on both peak fuel enthalpy and cladding embrittlement by analyzing previous NSRR experiments conducted with conventional materials using the RANNS fuel performance code. The findings suggest that the failure criteria associated with cladding embrittlement can provide a rational evaluation of failure behavior compared to the existing criterion based on peak fuel enthalpy. The local failure criterion leading to the formation of through-wall cracks during quenching is consistent with Chung's proposal (NUREG/CR-1344): -Zr thickness of 0.9 wt% oxygen is less than 0.1 mm, and this corresponds to approximately 35% BJ-ECR.

セメント固化におけるペーストの流動性に影響する化学物質についての調査

谷口 拓海; 松本 早織; 平木 義久; 佐藤 淳也; 藤田 英樹*; 金田 由久*; 黒木 亮一郎; 大杉 武史

JAEA-Review 2024-059, 20 Pages, 2025/03

JAEA-Review-2024-059.pdf:1.0MB

廃棄物のセメント固化で求められる基本的な性能である硬化前の流動性および硬化後の強度特性は、廃棄物に含まれる物質や成分などの化学的作用の影響を受けることが予想される。硬化前の流動性および硬化後の強度特性はセメントの硬化速度に大きく影響されることから、セメントの硬化速度に影響を与える化学物質を対象に着目して既往の知見を調査し、取りまとめを行った。本報告書ではセメントの流動性に影響を及ぼす化学物質を大きく分類し、無機物質として(1)陰イオン種、(2)重金属等金属元素、(3)セメント混和剤として用いられる無機物質および(4)セメント混和剤として用いられる有機物質の4つに整理した。調査の結果、化学物質によって硬化を促進する効果と遅延する効果に大きく分類されることが分かったが、一部の化学物質ではその添加量によって硬化に与える影響が逆転するものも見られたことから、実際に化学物質を添加し、凝結時間測定を実施した。その結果、硬化促進に寄与するメカニズムが複数あることが分かった。セメントの硬化反応を阻害する化学物質を調査し、セメント固化における混入禁忌成分を検討するための情報を整理することができた。

Internal strain measurement by neutron diffraction under transverse compressive stress for NbSn wires with and without Cu-Nb reinforcement

中本 美緒*; 菅野 未知央*; 荻津 透*; 杉本 昌弘*; 谷口 諒*; 廣瀬 清慈*; 川崎 卓郎; Gong, W.; Harjo, S.; 淡路 智*; et al.

IEEE Transactions on Applied Superconductivity, 34(5), p.8400806_1 - 8400806_6, 2024/08

https://doi.org/10.1109/TASC.2024.3379124

For an accelerator magnet, a certain mechanical strength is required to sustain against a transverse compression stress due to Lorentz force. A bronze-route NbSn wire with Cu-Nb reinforcement was developed by Tohoku University and Furukawa Electric to enhance the strength against axial tension. The Cu-Nb reinforcement wire also exhibited some indication of strength improvement against transverse compression; however, the details of a reinforcement mechanism for the transverse compression stress have not been clarified. In this study, the internal strains of NbSn bronze-route wires with and without the Cu-Nb reinforcement under transverse compression stress were evaluated by neutron diffraction at BL19 (TAKUMI) in J-PARC. The samples were attached to jig with solder only at the ends and compression was applied at the center of the samples with 30-mm anvil with 5-mm wide and 8- to 15-mm high beam. Since a critical current, Ic of a superconducting wire depends on the three-dimensional strain, internal strain of NbSn along the axial and two orthogonal radial directions were evaluated at room temperature (RT). In the different setup, Ic measurements of the wires under transverse compression stresses were also performed at 4.2 K and 14.5 T. Using 3-mm wide anvil, the transverse compression was applied at 4.2 K or RT. The neutron diffraction results indicated no significant differences in the internal strains of NbSn under transverse compression between the samples with and without Cu-Nb reinforcement, while the Ic measurements showed potential increase in the irreversible stress () for Cu-Nb reinforced wires. The reason for this discrepancy was discussed based on the difference in the experimental setups for each measurement.

Synthesis of heat-resistant living polymer particles by one-step reversible addition-fragmentation chain transfer precipitation polymerization of styrene and -phenylmaleimide

山崎 駿*; 金子 直矢*; 加藤 敦也*; 渡邉 航平*; 青木 大輔*; 谷口 竜王*; 唐津 孝*; 上田 祐生; 元川 竜平; 大倉 滉生*; et al.

Polymer, 298, p.126846_1 - 126846_11, 2024/04

https://doi.org/10.1016/j.polymer.2024.126846

Synthesis of heat-resistant, living polymer particles via one-step reversible addition-fragmentation chain transfer precipitation polymerization (RAFTPP) of styrene and -phenylmaleimide is reported. Gel permeation chromatography and nuclear magnetic resonance spectroscopy confirmed that the polymerization proceeded in a living manner. The scanning electron microscopy results showed that the monodisperse P(St-PhMI) RAFTPP particles with a diameter of 1.88 micrometer were successfully synthesized. The P(St-PhMI) RAFTPP showed excellent thermal stability with a high glass transition temperature and a 5 percent weight loss temperature. The surface concentration of the RAFT groups was determined to be 0.181 groups/square-nanometer due to fragmentation of the RAFT groups exposed on the particles. The small-angle neutron scattering measurements showed the particle formation mechanism, in which the swollen, growing polymer chains were consumed for particle formation. The introduction of grafted chains by surface-initiated RAFT polymerization demonstrated the possibility of further functionalization of P(St-PhMI) RAFTPP particles by exploiting their living nature.

High-temperature rupture failure of high-burnup LWR-MOX fuel under a reactivity-initiated accident condition

谷口 良徳; 三原 武; 垣内 一雄; 宇田川 豊

Annals of Nuclear Energy, 195, p.110144_1 - 110144_11, 2024/01

https://doi.org/10.1016/j.anucene.2023.110144

A reactivity-initiated accident (RIA)-simulated test CN-1 on a high-burnup 64 GWd/t mixed-oxide fuel rod sheathed with M5 cladding was conducted at the Nuclear Safety Research Reactor, resulting in fuel failure. A small opening with slight ballooning deformation characterized the post-test visual appearance of the test fuel rod. Simulation using fuel performance codes FEMAXI-8/RANNS predicted rod survival under early phase loading induced by pellet-cladding mechanical interaction and subsequent boiling transition, and the cladding surface temperature measured online confirmed the occurrence of boiling transition. The experimental observation and simulation indicate that the failure was caused by a high-temperature rupture following increased rod-internal pressure. The RANNS sensitivity analysis revealed that a mechanical state parameter dedicated to predicting plastic instability might be an effective index for evaluating the risk of rupture failure during RIAs.

気候変動予測結果を用いた河川における放射性セシウム将来流出量予測の検討

入澤 歩*; 佐久間 一幸; 竹内 幸生*; 谷口 圭輔*; 恩田 裕一*

KEK Proceedings 2023-2, p.29 - 33, 2023/11

昨今の地球温暖化に伴う気象災害の激甚化など、河川を取り巻く環境が変化すると考えられるが、それが放射性セシウム流出量に与える影響の有無については必ずしも自明ではない。そこで、IPCC第5次報告書に基づく複数のシナリオを用いた降水量を入力条件として、河川から海洋に流出するセシウムを迅速に算出できる計算モデルMERCURYを用いた流出量予測計算を行った。対象流域は福島県阿武隈川二本松地点とした。気候変動シナリオは、RCP2.6、RCP4.5、RCP8.5の3つとし、近未来(2031年7月31日から2049年8月1日まで)と未来(2081年7月31日から2099年8月1日まで)のそれぞれのシナリオにおける日降水量と日平均気温を用いた。年間平均土砂流出量は近未来と未来あるいはシナリオごとに大きな差は見られなかった。放射性セシウム流出量(Bq)は、最新データ以降の河川水中放射性セシウム濃度変化を物理学的半減期のみの減衰として計算したところ、2031-2049年および2081-2099年の期間の年間平均流出量は、それぞれ初期沈着量に対し0.05%、0.02%程度となった。

Measurement of mechanical behavior of B-enriched MgB wire using a pulsed neutron source

町屋 修太郎*; 長村 光造*; 菱沼 良光*; 谷口 博康*; Harjo, S.; 川崎 卓郎

Quantum Beam Science (Internet), 7(4), p.34_1 - 34_17, 2023/10

https://doi.org/10.3390/qubs7040034

Measuring the actual strain on the MgB filaments are of paramount importance, since tensile stress and strain diminish the critical current. In this study, the strain measurement using neutron diffraction during tensile loading was established. We fabricated a MgB wire enriched with boron-11, an isotope having a smaller neutron absorption cross- section than natural boron, and succeeded in obtaining changes in the lattice constant under tensile loading through Rietveld analysis.

Development of hydrogen oxidation reaction catalysts to overcome CO poisoning and elucidation of reaction mechanism

稲川 康平*; 松村 大樹; 谷口 昌司*; 上垣 伸弥*; 中山 智仁*; 浦野 純乃介*; 青谷 拓朗*; 田中 裕久*

Journal of Physical Chemistry C, 127(24), p.11542 - 11549, 2023/06

https://doi.org/10.1021/acs.jpcc.3c02237

Passive autocatalytic recombiner (PAR) represents a potential technology for ensuring process safety in the hydrogen society. PARs function through the catalytic oxidation of generated or leaked hydrogen, facilitating its conversion into water and effectively mitigating the risk of hydrogen explosions. CO is recognized as a catalyst poison that hampers surface catalytic reactions. To investigate the negative effects of CO on the local structure of platinum metal nanoparticle catalysts during water formation, in situ and time-resolved X-ray absorption spectroscopy analyses were conducted. The results revealed that the Pt-Fe/CZY catalyst exhibited notable hydrogen oxidation activity even in the presence of CO. The enhanced performance can be attributed to the combined effects of Pt-Fe alloy composition and CZY support materials.

Behavior of high-burnup BWR UO fuel with additives under reactivity-initiated accident conditions

三原 武; 垣内 一雄; 谷口 良徳; 宇田川 豊

Journal of Nuclear Science and Technology, 60(5), p.512 - 525, 2023/05

https://doi.org/10.1080/00223131.2022.2122616

Fuels with additives are expected to provide enhanced fuel performance in fission gas retention owing to their large grain size, which elongates fission gas migration path. To investigate behavior of the fuels during a reactivity-initiated accident (RIA), RIA-simulated experiments OS-1 and LS-4 were performed on ADOPT (chromia- and alumina-doped UO) fuel of 64 GWd/t and chromia-doped UO fuel of 48 GWd/t, respectively. The OS-1 rod failed at a fuel enthalpy increase of 160 J/g due to pellet-cladding mechanical interaction failure, which was the lowest failure limit among the test results ever obtained at the NSRR on high-burnup fuels from 40 to 65 GWd/tU. Comparison of the hydride morphologies in the cladding metallic layer between the rods subjected to the past NSRR tests suggests the contribution of radially oriented hydrides during base irradiation to the low failure limit. The LS-4 rod survived for a peak fuel enthalpy increase of 549 J/g, which resulted in cladding deformation of 2.4% in the residual hoop strain and FGR of 1.4%-6.1%. Whereas the low fission gas release exhibits the effect of additives, the cladding deformation is within the range explained by the deformation mechanism essentially identical to those recognized for high-burnup undoped fuels.

Laser-fluence dependence of resonance-enhanced multiphoton reduction of trivalent europium

松田 晶平; 中島 信昭*; 横山 啓一; 谷口 誠治*; Chosrowjan, H.*; 染川 智弘*; 八ッ橋 知幸*

Chemical Physics Letters, 802, p.139759_1 - 139759_6, 2022/09

https://doi.org/10.1016/j.cplett.2022.139759

ブロック元素の-遷移波長での共鳴多光子励起によって標的元素の酸化数のみを選択的に制御する技術は、希少金属の高純度な精製方法への応用が期待できる。この共鳴多光子過程を経る酸化還元の効率については、一光子目と二光子目それぞれの量子収率と吸収断面積が重要な因子である。そこで本研究では三価ユウロピウム(Eu)から二価ユウロピウム(Eu)への還元効率のレーザーフルエンス依存性を精密に調べることでそれらを評価した。その結果、励起波長394nmでのEuの二光子吸収過程における一光子目の量子収率の値、二光子目の量子収率と吸収断面積の積の値を見積もることができた。また、従来よりも広いフルエンス領域を調べたことで飽和が観測され、必要なレーザー出力の上限が推定できた。