Thermal expansion of neptunium-uranium mixed oxides

Yamashita, Toshiyuki; Nitani, Noriko; Tsuji, Takeshi; Kato, Tetsuya

doi:10.1016/s0022-3115(97)00031-7

Cited by 54 publications

(36 citation statements)

References 10 publications

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“…This larger cell was used in order to better treat the more extended Xe clusters and keep interactions among their periodic images controlled. The supercell volumes were kept fixed at the corresponding calculated volume of UO 2 , for which we predict a = 5.45 A within the current DFT scheme 52 compared to 5.47 A observed in experiments 57 . A 2×2×1 Monkhorst-Pack k-point mesh 58 with a Gaussian smearing of 0.05 eV was used for all defect calculations within the 2 × 2 × 3 supercell.…”

Section: Approachmentioning

confidence: 90%

U and Xe transport in UO2±x: Density functional theory calculations

et al. 2011

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The detrimental effects of the fission gas Xe on the performance of oxide nuclear fuels are well known. However, less well known are the mechanisms that govern fission gas evolution. Here, in order to better understand bulk Xe behavior (diffusion mechanisms) in UO2±x we calculate the relevant activation energies using density functional theory (DFT) techniques. By analyzing a combination of Xe solution thermodynamics, migration barriers and the interaction of dissolved Xe atoms with U, we demonstrate that Xe diffusion predominantly occurs via a vacancy-mediated mechanism. Since Xe transport is closely related to diffusion of U vacancies, we have also studied the activation energy for this process. In order to best reproduce experimental data for the Xe and U activation energies, it is critical to consider the active charge-compensation mechanism for intrinsic defects in UO2±x. Due to the high thermodynamic cost of reducing U 4+ ions, any defect formation occurring at a fixed composition, i.e. no change in UO2±x stoichiometry, always avoids such reactions, which, for example, implies that the ground-state configuration of an O Frenkel pair in UO2 does not involve any explicit local reduction (oxidation) of U ions at the O vacancy (interstitial).

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Section: Approachmentioning

confidence: 90%

U and Xe transport in UO2±x: Density functional theory calculations

et al. 2011

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“…On the other hand, little information is available for NpO 2 . (4)(5)(6)18) Westrum et al (6) measured C p,m for NpO 2 from T = 10 K to T = 315 K using an adiabatic calorimeter; their value of C p,m at T = 298 K was 66.22 J · K −1 · mol −1 . However, Arkhipov et al (5) measured high-temperature C p,m using a drop calorimeter in the temperature range of T = 350 K to T = 1100 K and reported the C p,m value at T = 298 K was 80.07…”

Section: Thermal Expansion Of Npomentioning

confidence: 99%

“…Comparing C p,m for other actinide dioxides, the value reported by Arkhipov et al is apparently high. (4) They ascribed the difference to the purity of the substance. (5) Yamashita et al (4) presented an estimated C p,m that was calculated from the thermal and mechanical data.…”

Section: Thermal Expansion Of Npomentioning

confidence: 99%

“…(3) They also studied the thermal expansion of mixed oxides of neptunium and uranium. (4) Thus far, no results have been reported at temperatures higher than T = 1300 K. Arkhipov et al (5) measured the high temperature molar heat capacity for NpO 2 C p,m by a drop calorimetric experiment. The C p,m in the low temperature region from T = 10 K to T = 315 K was examined by Westrum et al (6) using an adiabatic calorimeter.…”

Section: Introductionmentioning

confidence: 99%

“…The C p,m in the low temperature region from T = 10 K to T = 315 K was examined by Westrum et al (6) using an adiabatic calorimeter. Yamashita et al (4) estimated C p,m from the coefficient of linear thermal expansion (l.t.e.) from the thermodynamic relation C p,m = β · V m /κ T · γ , where β is the coefficient of isobaric volumetric expansion, V m is the molar volume, κ T is the adiabatic compressibility and γ is the Grüneisen constant, respectively.…”

Section: Introductionmentioning

confidence: 99%

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