Effect of pores and He bubbles on the thermal transport properties of UO2 by molecular dynamics simulation

Abstract

The thermal conductivities of UO 2 single crystals containing nanoscale size pores and He gas bubbles are calculated using non-equilibrium molecular dynamics as a function of pore size and gas density in the bubble. As expected, the thermal conductivity decreases as pore size increases, while the decrease in thermal conductivity is determined to be more substantial than the predictions of traditional analytical models by Loeb and Maxwell-Eucken. However, the recent model of Alvarez, which is applicable when the phonon mean-free path is comparable to the pore size, is able to quantitatively reproduce the simulation results. The thermal conductivity of UO 2 of the small pores considered here is reduced further when the pore is filled with He gas. This surprising result is due to the penetration of the helium atoms into the lattice where they act as phonon scattering centers.

Non-stoichiometry in U3Si2

“…Specifically relating to 259 fission gas distribution, it is possible that any secondary phases of U 5 Si 4 /USi that precipitate due 260 to burnup induced variations in stoichiometry, may act as multiple nucleation sites for fission gas 261 bubbles. If these precipitates reside as intra-granular inclusions, their formation may contribute 262 to the highly dense fission gas bubble microstructure observed experimentally [34] [38]. 263…”

“…The phase diagram of Domagala is reproduced in Figure 1 (the β→γ U 3 Si 36 phase transition at 1048 K as reported by Remschnig et al [6] is shown as a green dashed 37 line). 38 39…”

Impact of irradiation induced dislocation loops on thermal conductivity in ceramics

“…Another irradiation induced defect known to impact thermal transport are voids . While the majority of vacancies created under displacement damage recombine with interstitials, a very small fraction of them is expected to cluster into voids .…”

Investigation of thermal transport in composites and ion beam irradiated materials for nuclear energy applications

“…These latter phenomena have been actively investigated by computational methods 19,45,46 and very little experimental data exist and are a subject of future work. 47,48 The stopping and range of ions in matter (SRIM) code was used to estimate the displacement damage.…”