Immobilisation mechanisms of simulated radioactive colloidal wastes in alkali-activated metakaolin-based geopolymers

Shi, D.*; Niu, X.*; Elakneswaran, Y.*; Li, A.*; 菊池 亮佑*; 平木 義久; 佐藤 淳也; 大杉 武史; Walkley, B.*

Journal of Nuclear Materials, 633, p.156997_1 - 156997_12, 2026/11

https://doi.org/10.1016/j.jnucmat.2026.156997

During the retrieval of fuel debris and the treatment of contaminated water at the Fukushima Daiichi Nuclear Power Station, the generation of radioactive colloidal slurries containing iron and zirconium oxides is inevitable. This study investigates the solidification of these secondary wastes using a metakaolin geopolymer, exploring the reaction behaviour and immobilisation mechanisms of colloids with differing chemical activities within an alkali-activated system. While the introduction of metal colloids improved paste fluidity via the "ball-bearing effect", compressive strength was compromised due to interfacial defects. The 28-day leaching experiments revealed distinct immobilisation mechanisms for the two colloids. For chemically active FeO colloids, a synergy of inner-sphere surface complexation and physical agglomeration was observed.

Fundamental study on design margin for fast reactor plant with seismic isolation system

岡村 茂樹; 中島 理紗子*; 平山 智之*; 湯川 正貴*; 渡部 翔太郎*; 藤田 聡*; 山口 彰*

Journal of Nuclear Science and Technology, 63(10), p.1209 - 1217, 2026/10

https://doi.org/10.1080/00223131.2026.2680222

A sodium-cooled fast reactor plant uses liquid metal sodium as a coolant. Sodium has a high boiling point and excellent heat transfer capabilities. These properties allow the reactor to operate at low pressure. However, thermal fatigue occurs due to repeated thermal expansion and contraction within the creep temperature range. Accordingly, the fast reactor's components and piping are designed with thin walls. Seismic isolation systems are used to reduce the seismic loads acting on components. Seismic isolation systems are used to reduce the seismic loads acting on components. Research and development of seismic design methods is progressing. Applying seismic isolation to nuclear power plants requires clarifying the design margin approach for equipment in fast reactor plants and seismic isolation devices. Here, the design margin refers to the margin relative to the design criteria for components or seismic isolation systems, i.e. the ratio of seismic response to the design criteria for the design basis ground motion, The design margin should be set to a value equal to or greater than the safety margin. Here, the safety margin is defined as the minimum margin specified in regulatory requirements and standards. This report proposes an approach for determining design margins for fast reactor plants with the horizontal seismic isolation system. We conducted the seismic response analysis of the reactor building and created the fragility curve with buckling evaluation of the reactor vessel. Based on these results, an approach for determining design margins of the components and the horizontal seismic isolation system was investigated.

データ駆動型オンサイト診断技術: 長期的健全性を確保するための微生物腐食リスク予測(委託研究); 令和6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; 海洋研究開発機構*

JAEA-Review 2026-013, 86 Pages, 2026/07

JAEA-Review-2026-013.pdf:5.3MB

日本原子力研究開発機構(JAEA)廃炉環境国際共同研究センター(CLADS)では、令和元年度から英知を結集した原子力科学技術・人材育成推進事業(以下、「本事業」という。)を実施している。本事業は、東京電力ホールディングス株式会社福島第一原子力発電所(1F)の廃炉等をはじめとした原子力分野の課題解決に貢献するため、国内外の英知を結集し、さまざまな分野の知見や経験を従前の機関や分野の壁を越えて緊密に融合・連携させた基礎的・基盤的研究および人材育成を推進することを目的としている。平成30年度の新規採択課題から実施主体を文部科学省からJAEAに移行することで、JAEAとアカデミアとの連携を強化し、廃炉に資する中長期的な研究開発・人材育成をより安定的かつ継続的に実施する体制を構築した。本研究は、令和6年度に採択された研究課題のうち、「データ駆動型オンサイト診断技術:長期的健全性を確保するための微生物腐食リスク予測」の令和6年度分の研究成果について取りまとめたものである。本研究は、ハイスループットな解析手法の開発や現場環境を模擬した試験、事故炉環境を想定した試験を通して、データ駆動型の統計解析を駆使し、高精度に微生物腐食リスクを予測することが可能な革新的オンサイト診断技術のプロトコルを確立・提供することを目的としている。そのために、ハイスループット解析手法、現場環境を模擬した試験、事故炉環境を想定した試験を組み合わせ、データ駆動型の統計解析を導入した。福島県内から環境試料を採取し、微生物群集構造を解析するとともに、オンサイト遺伝子診断に必要な要素技術の開発を進めた。これらの試料を用いて、さまざまな培養条件下で鉄腐食能を評価し、1F施設環境を模擬した試験系の設計を行った。さらに、実際の鉄腐食を測定できるハイスループット試験系を検証し、腐食バイオマーカーデータベースの基盤を整備した。また、微生物群集構造データと過去のMIC活性データを統合し、統計解析手法の適用性と課題を明らかにした。加えて、福島県内で先導的に環境試料採取を行い、腐食試料中の微生物観察に有効な固定条件を特定した。以上により、環境微生物群集情報、腐食関連微生物の培養、統計解析の適用性に関する有益な知見を得た。本成果は、1F周辺を含む多様な環境に適用可能なバイオマーカーに基づくユビキタスMIC診断技術の基盤を提供するものである。

高転換軽水炉を模擬したFCA XV炉心系における臨界実験の特性試験と臨界性評価

櫻井 健; 福島 昌宏

JAEA-Data/Code 2026-001, 235 Pages, 2026/06

JAEA-Data-Code-2026-001.pdf:16.46MB

高速炉臨界実験装置FCAを用いて高転換軽水炉の核特性を模擬するために実施した臨界実験のうち、プルトニウム燃料を主として用いた第2フェーズ実験のXV炉心系の臨界性の評価を行い、核データライブラリーJENDL-4.0とJENDL-5及び連続エネルギー法による中性子輸送計算モンテカルロコードMVP3による解析を行った。臨界性の評価では、FCAのウランとプルトニウムの燃料板や減速材等の模擬物質板の重量や組成の不確かさの影響を取り入れた詳細な不確かさ評価を実施した。解析では、FCAの燃料や格子管の構造を詳細に模擬して計算を行った。JENDL-4.0とJENDL-5のいずれを用いても、実効増倍率の計算結果は実験結果を0.4%から0.8%過大評価した。

Development of a fiber laser-based method to generate Cs-bearing microparticles from glass fiber filters

萩原 大樹; 小菅 淳; 斉藤 淳一; 浪江 将成; 木曽原 直之; 峰原 英介*; 坪井 昭彦; 石森 有

Next Research (Internet), 8, p.101581_1 - 101581_9, 2026/06

https://doi.org/10.1016/j.nexres.2026.101581

To understand how Type-A Cs-bearing microparticles were generated at the Fukushima Daiichi nuclear power plant, identifying the materials from which these particles originated is important. In this study, we focus on a methodological approach for generating Cs-bearing microparticles by laser irradiation of glass-fibers-based filter materials, with the aim of producing surrogate particles under controlled laboratory conditions. To evaluate this approach, a series of experiments was conducted, including vapor-phase exposure and aqueous loading of Cs, Fe, and Zn onto filter substrates, followed by laser irradiation to induce rapid, localized high-temperature effects. Morphology and size distributions of the Cs-containing surrogate particles were found to be comparable to those reported for Type-A particles, within the scope of the applied analytical methods. Overall, a reproducible laboratory framework was established for producing Cs-bearing surrogate microparticles suitable for systematic characterization, while not aiming to fully reproduce specific accident conditions.

Measurement of uranium and fission products in a spent fuel sample using fiber-optic laser-induced breakdown spectroscopy

Batsaikhan, M.; 大場 弘則*; 狩野 貴宏; 赤岡 克昭; 若井田 育夫*; 岩田 圭弘; 坂本 寛*

Journal of Analytical Atomic Spectrometry, 41(4), p.1324 - 1335, 2026/04

https://doi.org/10.1039/D5JA00451A

This study presents the development and application of a fiber optic laser-induced breakdown spectroscopy system designed for remote, in situ analysis of nuclear fuel debris at Fukushima Daiichi Nuclear Power Station (FDNPS). The system was deployed for the first time in a hot cell under high radiation to analyse an actual Boiling Water Reactors spent fuel sample as an exemplar of FDNPS fuel debris. The system successfully identified the main fuel components along with several long lived fission products and related markers such as Sr, Cs, Mo, Ba, and Rb. The emission intensity of the Ba, Rb, and Cs near the periphery region was slightly higher than at the center of the fuel. This indicates a higher concentration of these elements in that area.

In situ study of growth mechanism of germanene segregated through Ag(111) thin films by Raman and X-ray photoelectron spectroscopy

寺澤 知潮; 勝部 大樹*; 矢野 雅大; 小澤 孝拓*; 津田 泰孝; 吉越 章隆; 朝岡 秀人; 鈴木 誠也

Chemistry of Materials, 38(6), p.2933 - 2945, 2026/03

AA2025-0822.pdf:1.33MB

https://doi.org/10.1021/acs.chemmater.5c03462

Germanene, a honeycomb lattice of Ge atoms, has attracted attention for next-generation electronics and as a topological material. Among reported synthesis routes, the segregation method enables reproducible monolayer germanene formation on Ag(111) through simply annealing an Ag(111) thin film on a Ge(111) substrate. Despite this success, the physical origins of its monolayer selectivity and the mechanism for suppressing competing Ge phases remain unclear. Here, we investigate germanene formation via Ge segregation using in situ Raman spectroscopy and X-ray photoelectron spectroscopy to directly track Ge behavior during annealing and cooling. In situ observations revealed that annealing at 500C yielded no Ge-related byproducts, and the system reached a high-temperature surface equilibrium state, independent of the initial Ge amount. Cooling from this state produced a Ge-enriched surface that stabilizes the formation of monolayer germanene. In contrast, heating only to 300C produced three-dimensional Ge islands without Ge-enrichment, followed by Ge-Ag alloy formation upon subsequent cooling. By integrating the temperature-dependent diffusion length and the process-dependent diffusion direction, we established a unified description of Ge behavior on Ag/Ge(111) substrates, in which cooling-induced Ge-enrichment at the surface reproducibly stabilizes the selective formation of monolayer germanene.

TiC nanoparticles tune phase stability and deformation mechanisms in directed energy deposition processed Fe60Co15Ni15Cr10 medium-entropy alloy composites

Ahn, S. Y.*; Kim, E. S.*; Jeong, S. G.*; Harjo, S.; 川崎 卓郎; Gong, W.; Kim, H.-J.*; Hong, S.-J.*; Hong, S. I.*; Kwon, H.*; et al.

Materials Science & Engineering A, 955, p.149839_1 - 149839_18, 2026/03

https://doi.org/10.1016/j.msea.2026.149839

Additive manufacturing (AM) of particle-reinforced metal matrix composites (MMCs) enables control of both strength and deformation behavior. In this study, TiC (2 wt%) nanoparticles were added to FeCoNiCr medium-entropy alloy (MEA) using directed energy deposition (DED). Although part of the TiC decomposed during processing, the released C and Ti stabilized the -austenite phase and suppressed deformation-induced martensitic transformation (DIMT), shifting deformation toward slip-dominated behavior. Microstructural observations revealed dispersed TiC particles and modified grain boundary morphology that promoted distributed plastic flow. In-situ neutron diffraction during tensile testing confirmed enhanced early-stage dislocation activity. These findings demonstrate that nanoparticle-induced phase stability changes strongly influence deformation mechanisms in AM-processed MMCs.

Effect of nanoscale cellular structure on the mechanical properties of Inconel 718 with unique hierarchical structure fabricated by laser powder bed fusion

Cho, K.*; 山下 葵平*; 角谷 心之輔*; 齊藤 拓馬*; 佐々木 泰祐*; 澤泉 克彦*; 奥川 将行*; 小泉 雄一郎*; 眞山 剛*; 菊川 泰地*; et al.

Acta Materialia, 303, p.121696_1 - 121696_18, 2026/01

https://doi.org/10.1016/j.actamat.2025.121696

The deformation behavior and strengthening mechanism of Inconel 718 with a hierarchical structure composed of microscale crystallographic lamellar microstructure (CLM) and nanoscale cellular structure, fabricated by laser powder bed fusion, were clarified via nanoscale microstructural and in-situ neutron diffraction analyses. The CLM is a layered structure parallel to the building direction (BD) and consists of relatively wide main and narrow sub-layers with 110 and 100 orientations, respectively, with respect to BD. This is the first study to demonstrate that the yield stress of the alloys depends strongly on deformation stresses of the sub-layers, even though Schmid factors of the primary slip system for both layers are the same. The sub-layer continues to deform elastically even beyond the micro-yield point of the main layer, which results in the macroscopic strengthening at an early stage of deformation. On the other hand, the cellular structure is formed in both layers, associated with a dendritic cell growth along 100 direction, Nb segregation between the cells and an accumulation of dislocations to decrease a residual stress. The cell boundaries with numerous dislocations and Nb segregation act as a strong barrier to dislocation motion resulting in a stress increase through the Hall-Petch law, even though they are low-angle grain boundaries. The spacing and morphology of the cell boundary depend strongly on fabrication conditions. The optimized cellular structure provides significant strengthening comparable to or greater than that caused by large-angle grain boundaries, thereby increasing the macroscopic strength of the alloys through hardening of the sub-layer.

Developing a Monte Carlo-based fault tree quantification module for SAPHIRE targeting seismic probabilistic risk assessments

久保 光太郎; 藤原 啓太*; 村松 健

Nuclear Technology, 21 Pages, 2026/00

https://doi.org/10.1080/00295450.2026.2672881

During the probabilistic risk assessments (PRAs) of nuclear power plants for external events, such as earthquakes and tsunamis, accurately evaluating system, structure, and component damage correlations is crucial for analyzing risk profiles. This study develops a module called Module Using Random Monte Carlo Sampling (MURAMASA), which integrates the direct quantification of fault trees using Monte Carlo simulation (DQFM) method into System Analysis Programs for Hands-on Integrated Reliability Evaluations. MURAMASA is designed to enhance the treatment of correlated failures and to improve integration with internal event PRAs, thereby providing a practical tool for seismic PRA analysts. The DQFM method enables accurate consideration of correlations of failures in seismic PRA by introducing correlation coefficients into the random sampling of seismic responses and capacities. In conventional DQFM, many trials are required to estimate low-probability outcomes, such as in cases with low seismic acceleration levels. To address this issue, we propose partial DQFM method, which combines DQFM with the minimal cut set upper bound approximation to improve conditional core damage probability accuracy in such cases. A case study involving two integrated fault trees confirmed that MURAMASA can accurately and efficiently obtain fragility curves. MURAMASA demonstrated usability and computational efficiency in seismic PRA analyses.