核廃棄物中の微量不純物が照射ギブサイトの水素生成量を変える仕組みを解明（Understanding How Trace Impurities in Nuclear Waste Change the Hydrogen Yield of Irradiated Gibbsite）

2026-08-26 パシフィック・ノースウェスト国立研究所（PNNL）

IDREAM researchers probed the structure of gibbsite with specialized techniques to better understand the fundamental science needed for nuclear waste management. (Illustration by Nathan Johnson | Pacific Northwest National Laboratory)

＜関連情報＞

• https://www.pnnl.gov/publications/understanding-how-trace-impurities-nuclear-waste-change-hydrogen-yield-irradiated
• https://pubs.rsc.org/cc/article/62/2/470/883928/Detecting-impurity-specific-effects-on-structure
• https://pubs.rsc.org/qi/article/13/3/950/1247794/Localizing-tetrahedral-aluminum-in-nitrate-bearing

水酸化アルミニウムの構造および放射線分解による水素生成に対する不純物特異的影響の検出 Detecting impurity-specific effects on structure and radiolytic hydrogen production in aluminum hydroxide

Trent R. Graham;Khashayar Ghandi;Micah Prange;Gregory Schenter;Larry M. Anovitz;Jay A. LaVerne;Carolyn I. Pearce
ChemComm  Published:05 November 2025
DOI:https://doi.org/10.1039/d5cc05272f

While radiolytic hydrogen (H₂) generation is an intrinsic property of aqueous and mineral radiolysis in nuclear waste systems, detection of the sub-ns events leading to H₂ generation is challenging. Interfacial processes involving key mineral phases in the sludge, e.g., gibbsite (α-Al(OH)₃), have been implicated, with impurities affecting the amount of H₂ generated. To understand why gibbsite synthesized from nitrate precursors produces less H₂ than gibbsite from chloride precursors, we paired ²⁷Al multiple quantum magic angle spinning (MQMAS) NMR spectroscopy to determine structural heterogeneity with transverse-field muon spin rotation (TF-μSR) to probe electron availability. MQMAS revealed greater structural disorder in the gibbsite synthesized with nitrate (NO₃-gibbsite). Correspondingly, TF-μSR showed a larger diamagnetic fraction for NO₃-gibbsite, indicating reduced persistence of μ⁺-electron bound states (muonium or other radicals) and thus fewer electrons available for reaction on the sub-ns timescale. This establishes a correlation between impurity-induced disorder and electron loss. The diamagnetic fraction serves as a signature for these sub-ns events, as it provides a key constraint for predictive models without currently resolving whether the electron is lost to direct chemical scavenging or trapping at lattice defects.

硝酸塩含有ギブサイト中の四面体アルミニウムを局在化させて欠陥・不純物結合を抑制する Localizing tetrahedral aluminum in nitrate-bearing gibbsite to constrain defect-impurity coupling

Trent R. Graham;Micah P. Prange;Xin Zhang;J. David Bazak;Nancy M. Washton;Khashayar Ghandi;Gregory K. Schenter;Carolyn I. Pearce
Inorganic Chemistry Frontiers  Published:29 October 2025
DOI:https://doi.org/10.1039/d5qi01703c

The enhanced radiolytic stability of gibbsite (α-Al(OH)₃) containing trace nitrate (NO₃⁻) is a phenomenon in nuclear waste management, but its structural origins remain unresolved. Motivated by the detection of minority tetrahedral aluminum (T_d) defects in synthetic gibbsite, we hypothesized that these sites may participate in NO₃⁻ retention or mediate H₂ suppression. To evaluate this, we combined orthogonal techniques comprised of spatially selective solid-state ²⁷Al MAS NMR, comparative spectroscopy, and density functional theory (DFT) modeling. Paramagnetic editing and dynamic nuclear polarization (DNP) MAS NMR confirm that T_d defects are confined to the particle interior. DFT calculations reveal no energetic stabilization of NO₃⁻ near T_d sites. Comparative NMR analysis shows that T_d is also present in chloride-bearing gibbsite, which exhibits high radiolytic hydrogen yields. These three independent disqualifications rule out T_d as a structural contributor to nitrate-mediated suppression and narrow the scope of defect-driven explanations. The findings redirect mechanistic attention away from coordination defects and toward redox-active impurity pathways, providing a refined foundation for understanding radiation tolerance in Al(OH)₃.