The Combined Influence of Gadolinium Doping and Non-stoichiometry on the Structural and Electrochemical Properties of Uranium Dioxide

Kim, Jandee; Lee, Jeongmook; Youn, Young-Sang; Liu, Nazhen; Kim, Jong-Goo; Ha, Yeong-Keong; Bae, Sang-Eun; Shoesmith, David W.; Kim, Jong-Yun

doi:10.1016/j.electacta.2017.07.023

Cited by 14 publications

(16 citation statements)

References 28 publications

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“…The similarity of stabilizing effects due to the doping observed in electrochemical oxidation (He et al, 2007;Razdan and Shoesmith, 2013;Kim et al, 2017;Liu et al, 2017), in oxidative dissolution (Trummer et al, 2010;Casella et al, 2016;Barreiro Fidalgo and Jonsson, 2019) and in air oxidation experiments (Kim et al, 2001) suggests that all these phenomena might be linked to a common thermodynamic factor.…”

Section: Introductionmentioning

confidence: 90%

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

et al. 2021

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Available data on the dependence of the equilibrium chemical potential of oxygen on degrees of doping, z, and non-stoichiometry, x, y, in U1-zLnzO2+0.5(x-y) fluorite solid solutions and data on the dependence of the lattice parameter, a, on the same variables are combined within a unified structural-thermodynamic model. The thermodynamic model fits experimental isotherms of the oxygen potential under the assumptions of a non-ideal mixing of the endmembers, UO2, UO2.5, UO1.5, LnO1.5, and Ln0.5U0.5O2, and of a significant reduction in the configurational entropy arising from short-range ordering (SRO) within cation-anion distributions. The structural model further investigates the SRO in terms of constraints on admissible values of cation coordination numbers and, building on these constraints, fits the lattice parameter as a function of z, y, and x. Linking together the thermodynamic and structural models allows predicting the lattice parameter as a function of z, T and the oxygen partial pressure. The model elucidates contrasting structural and thermodynamic changes due to the doping with LaO1.5, on the one hand, and with NdO1.5 and GdO1.5, on the other hand. An increased oxidation resistance in the case of Gd and Nd is attributed to strain effects caused by the lattice contraction due to the doping and to an increased thermodynamic cost of a further contraction required by the oxidation.

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Section: Introductionmentioning

confidence: 90%

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

et al. 2021

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“…2. The lattice parameter of Gd doped UO 2 has been discussed previously with two possible charge compensation mechanisms as the Gd content increases: the creation of the smaller U 5+ cation and the formation of oxygen vacancies [29,34,35]. The smaller U 5+ cation results in a contraction of the lattice, while the oxygen vacancies were reported to be larger than the O 2− ion [34].…”

Section: Details Of the Simulationmentioning

confidence: 94%

“…For hypo-stoichiometric et al [34] explained that this increase in the lattice parameter was due to the size of the oxygen vacancy, which is 10% larger than that of the O 2− ion. Kim et al [35] observed a contraction of the lattice for the hypo-stoichiometric sample, but the contraction factor (the slope of the relationship between the lattice parameter and the Gd content) is smaller than those of the hyper-stoichiometric and stoichiometric samples. The authors also explained this observation with the larger size of the oxygen vacancies.…”

Section: Details Of the Simulationmentioning

confidence: 96%

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Thermal conductivity variation in uranium dioxide with gadolinia additions

Qin

Middleburgh

Cooper

et al. 2020

Journal of Nuclear Materials

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By combining experimental observations on Gd doped fuel with a theoretical understanding, the variation in thermal conductivity with Gd concentration and accommodation mechanism has been modelled. Four types of Gd accommodation mechanisms have been studied. In UO 2−x , isolated substitutional Gd 3+ ions are compensated by oxygen vacancies and {2Gd U : V •• O } × defect clusters. In UO 2 , isolated substitutional Gd 3+ ions are compensated by U 5+ ions and {Gd U : U • U } × defect clusters. The results indicate that defect clusters can be considered as less effective phonon scatterers and therefore result in less thermal conductivity degradation. The thermal conductivity predicted for UO 2 with {Gd U : U • U } × defect clusters is in good agreement with experimental data for UO 2 with 5 wt% Gd 2 O 3 . This supports the previous theoretical results that Gd is accommodated through defect clusters {Gd U : U • U } × in UO 2 in the presence of excess oxygen.

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“…In electrochemical studies by Liu et al and Kim et al, it was shown that the oxidation of UO 2 , as well as Gd‐doped UO 2 proceeds in two stages, where the first stage is the formation of a thin oxidized surface layer (U 1‐2 x IV U 2 x V O 2+ x ) and the second stage is the oxidation of this surface layer to U VI which dissolves as UO 2 (CO 3 ) 2 2– in carbonate media. In addition, it was shown that Gd‐doping in stoichiometric specimens only influences the second stage, while the first stage was found insensitive to doping.…”

Section: Introductionmentioning

confidence: 99%

Impact of H₂ and Consecutive H₂O₂ Exposures on the Oxidative Dissolution of (U_1–xGd_x)O₂ Pellets Under Deep Repository Conditions for Spent Nuclear Fuel

2020

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The reactivity of H 2 O 2 towards (U 1-x Gd x )O 2 (x = 0.03, 0.045, 0.08) in the presence of H 2 was studied experimentally to assess the effect of H 2 on oxidative dissolution of Gd-doped UO 2 under deep repository conditions for spent nuclear fuel. Gd-doped UO 2 was chosen as a model substance for spent nuclear fuel due to its chemical similarity but low radiotoxicity. While H 2 O 2 is a radiolysis product capable of driving fuel matrix dissolution, H 2 , which is expected to evolve mainly through the corrosion of cast iron canisters encapsulating the fuel, might 157 Gd have high neutron cross-sections and can be introduced into the reactor core as burnable absorbers by doping standard UO 2 fuel. In addition, Gd builds up as a fission product in minor quantities in nuclear fuel during in-reactor irradiation. Therefore, Gd-doped UO 2 is part of the nuclear fuel cycle and after being discarded from the nuclear reactor it will eventually be stored in a deep geological repository according to the current plans in many countries. [3] After being discarded from a nuclear reactor, used fuel still consists mainly of UO 2 with small fractions (approx. 5 %) of highly radioactive fission products and heavier actinides that are present in different forms within the fuel matrix. [4,5] Among [a] Dr.

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The Combined Influence of Gadolinium Doping and Non-stoichiometry on the Structural and Electrochemical Properties of Uranium Dioxide

Cited by 14 publications

References 28 publications

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

Thermal conductivity variation in uranium dioxide with gadolinia additions

Impact of H₂ and Consecutive H₂O₂ Exposures on the Oxidative Dissolution of (U_1–xGd_x)O₂ Pellets Under Deep Repository Conditions for Spent Nuclear Fuel

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The Combined Influence of Gadolinium Doping and Non-stoichiometry on the Structural and Electrochemical Properties of Uranium Dioxide

Cited by 14 publications

References 28 publications

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

Thermal conductivity variation in uranium dioxide with gadolinia additions

Impact of H2 and Consecutive H2O2 Exposures on the Oxidative Dissolution of (U1–xGdx)O2 Pellets Under Deep Repository Conditions for Spent Nuclear Fuel

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Impact of H₂ and Consecutive H₂O₂ Exposures on the Oxidative Dissolution of (U_1–xGd_x)O₂ Pellets Under Deep Repository Conditions for Spent Nuclear Fuel