Thermodynamics of chromium in UO2 fuel: A solubility model

Riglet-Martial, C.; Martin, Philippe; Testemale, Denis; Sabathier-Devals, C.; Carlot, G.; Matheron, P.; Iltis, X.; Pasquet, U.; Valot, C.; Delafoy, C.; Largenton, Rodrigue

doi:10.1016/j.jnucmat.2013.12.021

Cited by 44 publications

(60 citation statements)

References 23 publications

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“…2 and are marked as 1Cr and 2Cr + 1Ov, respectively. Following the interpretation of XANES measurements by Riglet-Martial et al 4 , in both cases we initially assumed formation of Cr 3+ species. In the case (1) we assumed the charge balance through formation of one U 5+ per one Cr atom.…”

Section: Resultsmentioning

confidence: 99%

“…The previous experimental studies of Cr-doped UO 2 show evidence of bulk Cr incorporation as Cr 3+ 4 . At the same time, only small amounts of Cr could be incorporated into UO 2 , with maximum solubility at high temperature (T~2300 K) of up to 0.1 wt%∕UO 2 [3][4][5]9 . The formed diluted solid solution shows a linear decrease in the matrix lattice parameter with content of Cr 1,9 , which however, is significantly smaller than the predictions by most theoretical models 1 .…”

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confidence: 99%

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The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

2020

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Doping by Cr is used to improve the performance of uranium dioxide (UO 2)-based nuclear fuel. However, the mechanism of structural incorporation of Cr remains unclear. Here, in order to understand this process on the atomic scale and the redox state of Cr in UO 2-based nuclear fuel, we performed intensive ab initio atomistic simulations of the Cr doped UO 2 matrix. We unexpectedly found that Cr in UO 2 exists as Cr 2+ species and not as the widely claimed Cr 3+. We re-evaluated previously published x-ray absorption near edge structure spectroscopy data and confirmed the computed redox state of Cr. Thermodynamic consideration shows that the favorable structural arrangement of Cr in UO 2 is given by a pair of associated Cr 2+ and oxygen vacancy. The realism of this doping mechanism is further demonstrated by a match to the measured maximum Cr solubility and small lattice contraction.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

2020

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“…As mentioned above, the spectra have been decomposed into two lifetimes t 1 and t 2 . Two lifetime components are generally reported for UO 2 [5,9,10]. Such decomposition enables to calculate the lattice lifetime t bulk .…”

Section: Resultsmentioning

confidence: 99%

“…This component could be a signature of the defects created by the incorporation of additives in the UO 2 lattice. Indeed, Riglet-Martial et al [2] have shown by X-ray absorption near edge structure (XANES) that the oxidation state of soluble Cr is 3+ only in UO 2 , creating obvious charge defects. According to the experimental and calculation work of Cardinaels et al [16], the most favorable site for Cr satisfying the observed variation of lattice parameter of doped UO 2 is the substitution of uranium combined with a bonding with a [9], are formally expected to be positively charged, and should therefore in principle be invisible to PAS.…”

Section: Pas Componentsmentioning

confidence: 99%

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Positron annihilation spectroscopy study of lattice defects in non-irradiated doped and un-doped fuels

Chollet

Kršjak

Cozzo

et al. 2017

EPJ Nuclear Sci. Technol.

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Abstract. Fission gas behavior within the fuel structure plays a major role for the safety of nuclear fuels during operation in the nuclear power plant. Fission gas distribution and retention is determined by both, micro-and lattice-structure of the fuel matrix. The ADOPT (Advanced Doped Pellet Technology) fuel, containing chromium and aluminum additives, shows larger grain sizes than standard (undoped) UO 2 fuel, enhancing the fission gas retention properties of the matrix. However, the additions of such trivalent cations shall also induce defects in the lattice. In this study, we investigated the microstructure of such doped fuels as well as a reference standard UO 2 by positron annihilation spectroscopy (PAS). Although this technique is particularly sensitive to lattice point defects in materials, a wider application in the UO 2 research is still missing. The PAS-lifetime components were measured in the hotlab facility of PSI using a 22 Na source sandwiched between two 500-mmthin sample discs. The values of lifetime at the center and the rim of both samples, examined to check at the radial homogeneity of the pellets, are not significantly different. The mean lifetimes were found to be longer in the ADOPT material, 220 ps, than in standard UO 2 , 190 ps, which indicates a larger presence of additional defects, presumably generated by the dopants. While two-component decomposition (bulk + one defect component) could be performed for the standard material, only one lifetime component was found in the doped material. The absence of the bulk component in the ADOPT sample refers to a saturated positron trapping (i.e., all positrons are trapped at defects). In order to associate a type of lattice defect to each PAS component, interpretation of the PAS experimental observations was conducted with respect to existing experimental and modeling studies. This work has shown the efficiency of PAS to detect lattice point defects in UO 2 produced by Cr and Al oxides. These additives create lattice irregularities, which are acting as sinks for fission products on one hand and trapping positrons on the other hand. Fitting of the obtained experimental data with a suitable theoretical model can provide a valuable qualitative assessment of these defects. At this stage of the research, some of the existing models were used for this purpose.

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Characterisation of 3000 ppm Cr₂O₃ doped UO₂ and its precipitates

Devillaire

Desgranges

Tarisien

et al. 2023

J Raman Spectroscopy

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The thermochemical state of UO 2 -based nuclear fuel is a key parameter for which experimental data are difficult to obtain. A new experimental procedure using in situ oxido-reduction indicators was applied to irradiated fuel, and we aim to use it with chromium-doped unirradiated UO 2 . Nevertheless, we had first to characterise the chemical state of the chromium precipitates in our sample before. Here, we present the method we used for statistical characterisation of these precipitates using several methods, amongst which Raman spectroscopy plays a major role. Moreover, the Raman spectra of the precipitates were interpreted as evidence of a uranium stabilised Cr 3 O 4 phase.

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Thermodynamics of chromium in UO2 fuel: A solubility model

Cited by 44 publications

References 23 publications

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

Positron annihilation spectroscopy study of lattice defects in non-irradiated doped and un-doped fuels

Characterisation of 3000 ppm Cr₂O₃ doped UO₂ and its precipitates

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Thermodynamics of chromium in UO2 fuel: A solubility model

Cited by 44 publications

References 23 publications

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

The +2 oxidation state of Cr incorporated into the crystal lattice of UO2

Positron annihilation spectroscopy study of lattice defects in non-irradiated doped and un-doped fuels

Characterisation of 3000 ppm Cr2O3 doped UO2 and its precipitates

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Characterisation of 3000 ppm Cr₂O₃ doped UO₂ and its precipitates