XANES characterization of UO 2 /Mo(Pd) thin films as models for ϵ-particles in spent nuclear fuel - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Physics: Conference Series Année : 2013

XANES characterization of UO 2 /Mo(Pd) thin films as models for ϵ-particles in spent nuclear fuel

Résumé

X-ray absorption near edge structure (XANES) is recorded for nano-and micro-particles formed in Mo doped UO 2 thin films (TFs) prepared by in situ sputter co-deposition and 1000°C tempering. These UO 2 /Mo TFs are intended to serve as synthetic models for ε-particles in spent nuclear fuel. We find that when Si is used as substrate, nano-sized zero-valent Mo particles form as desired. However, these are embedded in USi 3 , which forms at the high temper temperatures. Micron-sized Mo-particles are formed when SiO 2 is used as substrate. Using focussed X-ray beams of varying size (500µm, 25µm and 5µm), these particles are characterized to be predominantly hexavalent Mo oxides, potentially with tetrahedral coordinated [Mo(VI)O 4 ] 2-at the surface and a MoO 3-like phase in the bulk. These TFs are poor synthetic models for spent fuel ε-particles but do offer the opportunity to study changes in surface structures in response to stress/charge as a function of particle size. 1. Introduction Spent nuclear fuel (SNF) consists of 95% UO 2 and 5% mixture of radionuclides (RNs) and fission products, heterogeneously distributed throughout the fuel matrix in different phases, e.g., gases (Xe, Kr, I), oxides (including transuranic elements Pu, Np, etc.) and metallic precipitates or so-called ε-particles (Pd, Mo, Rh, Ru, etc.)[1,2]. Systematic investigations of SNF matrix corrosion as an important source term for the mobilization of RNs are essential for evaluating SNF disposal safety [3,4]. We prepare UO 2 /Mo thin films (TFs) for potential use as models to study the influence of ε-particles on the surface corrosion of SNF. The TFs provide a less complex system and lower radiation fields than actual SNF samples, which allow systematic mechanistic investigations even in non-radioactive laboratories. We determine how well these TF models mimic the SNF surface by thoroughly characterizing their composition, structure and morphology using numerous methods. Studies of UO 2 /Mo TFs having varying Mo content prepared via in situ sputter co-deposition on different substrates (Si, SiO 2 or LaAlO 3) by means of 2-dimensional (2D) and 3-dimensional synchrotron-based imaging methods (scanning nano-/micro-XRF, scanning nano-XRD and XRF, holographic and ptychographic tomography) reveal that nano-and micro-sized Mo-particles form in TFs prepared on Si and SiO 2

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Chimie
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Dates et versions

hal-01904360 , version 1 (24-10-2018)

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M A Denecke, T Petersmann, Remi Marsac, K Dardenne, T. Vitova, et al.. XANES characterization of UO 2 /Mo(Pd) thin films as models for ϵ-particles in spent nuclear fuel. Journal of Physics: Conference Series, 2013, 430, ⟨10.1088/1742-6596/430/1/012113⟩. ⟨hal-01904360⟩

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