Thermal conductivities of ThO2, NpO2 and their related oxides: Molecular dynamics study

Arima, Takahiro; Yoshida, Keita; Matsumoto, T.; Inagaki, Yoshiyuki; Idemitsu, Kazuya

doi:10.1016/j.jnucmat.2013.11.006

Cited by 17 publications

(6 citation statements)

References 33 publications

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“…Hence, the MD simulation techniques provide a useful means to simulate such extreme conditions. As far as we know, the thermophysical properties of UO 2 [35][36][37][38][39], ThO 2 [30][31][32][33][34], and (U, Pu)O 2 [40][41][42][43] have been predicted by MD method over a wide temperature, and the evaluated results are almost in good agreement with the experimental values.…”

Section: Introductionsupporting

confidence: 60%

“…A poor thermal conductivity will leads to a large temperature gradient across the fuel pellet. However, to the best of our knowledge, the available literature data shows that the lattice parameter [10][11][12][13][14][15], thermal expansion [16][17][18][19], enthalpy increments data [20][21][22][23][24], specific heat capacity [22][23][24][25][26] and thermal conductivity [14,18,22,23,[27][28][29][30][31][32] of U 1-y Th y O 2 solid solution exist over a limited composition and temperature ranges.…”

Section: Introductionmentioning

confidence: 95%

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Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

et al. 2016

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Section: Introductionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 95%

Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

et al. 2016

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“…The same independent simulations were also used in the inset to obtain the thermal conductivity from the Einstein formalism (see Supporting Information, Discussion II). In agreement with previous work, 59 the thermal conductivity of the solid phase is found to be primarily driven by the virial contribution as the solid atoms only vibrate around their crystalline position (so that the kinetic contribution only amounts to ∼1%). In other words, the low mobility of the atoms in the crystalline structure, which are trapped within potential energy wells, leads to a negligible convective contribution to heat flow J.…”

Section: ■ Results and Discussionsupporting

confidence: 91%

Thermal Conductivity of a Fluid-Filled Nanoporous Material: Underlying Molecular Mechanisms and the Rattle Effect

Ferreira de Souza,

Picard,

Franco

et al. 2024

J. Phys. Chem. B

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Nanoporous materials are central to the energy and environmental crisis, with key applications in adsorption, separation, and catalysis. While confinement and surface effects on fluids severely confined in their porosity are well documented, the thermal behavior of nanoporous solids subjected to fluid adsorption remains puzzling in many aspects. With striking phenomena such as the so-called rattle effect, through which fluid/solid collisions decrease the overall thermal conductivity, the solid thermal conductivity and, more generally, heat transfer and dispersion in these complex systems challenge classical approaches (e.g., mixing rules including effective medium approaches fail to capture such effects as shown here). In particular, a robust molecular framework to describe the crossover between the decrease in thermal conductivity through the rattle effect in very narrow pores and the increase in thermal conductivity when replacing vacuum with a fluid phase in larger pores is still missing. Here, using a prototypical model of fluid-filled nanoporous materials (a Lennard-Jones phase confined in an all-silica zeolite), we perform a molecular simulation study to shed light on the parameters that govern the rattle effect in nanoporous solids. First, by varying the fluid/fluid, fluid/solid, and solid/solid interaction strengths as well as the fluid number density and mass density, we unravel the ingredients that lead to the essential coupling between fluid adsorption and phonon transport. Second, despite this complex interplay, inspired by pioneering molecular approaches on the rattle effect, we show that all data obey a simple statistical physics model that relies on the change in the speed of sound due to the fluid adsorbed density and the decrease in phonon lifetime due to scattering by fluid molecules. This framework, which provides a simple formalism to rationalize the thermal behavior of this class of solid/fluid composites, points to a decrease in thermal conductivity upon fluid confinement (up to 30% in some cases). Such an effect paves the way for the design of novel applications involving fluids in interaction with nanoporous materials.

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“…Experimental study of MAnO 2 is limited by the intense radioactivity of Np, Am, and Cm. Experimental studies of bulk MAnO 2 , which have the calcium fluorite (CaF 2 ) structure with Fm 3 m symmetry, − have focused on heat capacity, thermal expansion, and vaporization behavior − as well as the band structure. − The actinide 5f and 6d orbitals and the O 2p orbitals contribute to the valence and conduction bands of both dioxides, and the valence band of NpO 2 has more actinide character than that of AmO 2 . , Theoretical studies of bulk MAnO 2 have employed modified density functional theory (DFT) methods, such as DFT + U and screened hybrid DFT, to give reasonable results. − For example, the lattice constants of MAnO 2 calculated with the PBE + U method are close to experimental data, ,, and calculations correctly predict the band structure and the insulating behavior. , …”

Section: Introductionmentioning

confidence: 99%

Computational Study of the Bulk and Surface Properties of Minor Actinide Dioxides MAnO₂ (MAn = Np, Am, and Cm); Water Adsorption on Stoichiometric and Reduced {111}, {110}, and {100} Surfaces

Chen

Kaltsoyannis

2019

J. Phys. Chem. C

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Hubbard U-corrected generalized gradient approximation density functional theory is used to study the bulk and surface properties of minor actinide dioxides NpO 2 , AmO 2 , and CmO 2 . Comparison of lattice parameters, band gaps, and density of states with experimental data indicates that PBE + U (U = 4.50 eV, J = 0.50 eV) is the best approach of those considered. Stoichiometric and oxygen vacancy defect {111}, {110}, and {100} surfaces are investigated, including the molecular and dissociative adsorptions of water. Comparison with previous work by our group on UO 2 and PuO 2 leads to the conclusion that the oxygen defect generation energy is essentially linearly correlated with the An(IV)/(III) redox potential across the AnO 2 series from U to Cm. The geometries of water adsorption are similar across the series, whereas adsorption energies generally decrease, with the exception of certain PuO 2 surfaces, in agreement with the very hygroscopic nature of PuO 2 . Surface defects promote dissociative water adsorption.

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Thermal conductivities of ThO2, NpO2 and their related oxides: Molecular dynamics study

Cited by 17 publications

References 33 publications

Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

Thermal Conductivity of a Fluid-Filled Nanoporous Material: Underlying Molecular Mechanisms and the Rattle Effect

Computational Study of the Bulk and Surface Properties of Minor Actinide Dioxides MAnO₂ (MAn = Np, Am, and Cm); Water Adsorption on Stoichiometric and Reduced {111}, {110}, and {100} Surfaces

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Thermal conductivities of ThO2, NpO2 and their related oxides: Molecular dynamics study

Cited by 17 publications

References 33 publications

Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

Thermal Conductivity of a Fluid-Filled Nanoporous Material: Underlying Molecular Mechanisms and the Rattle Effect

Computational Study of the Bulk and Surface Properties of Minor Actinide Dioxides MAnO2 (MAn = Np, Am, and Cm); Water Adsorption on Stoichiometric and Reduced {111}, {110}, and {100} Surfaces

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Computational Study of the Bulk and Surface Properties of Minor Actinide Dioxides MAnO₂ (MAn = Np, Am, and Cm); Water Adsorption on Stoichiometric and Reduced {111}, {110}, and {100} Surfaces