Effect of Xe bubble size and pressure on the thermal conductivity of UO2—A molecular dynamics study

Abstract

Abstract

Thermal Energy Transport in Oxide Nuclear Fuel

“…Clearly, more accurately accounting for nanovoids requires models that consider the atomic structure of the defects. In parallel with grain boundaries, recent molecular dynamics modeling work has aimed to understand the role of atomic structure at pore/bubble boundaries [642,646]. Zhu et al [646] used non-equilibrium molecular dynamics to study the impact of Xe bubbles on thermal transport in UO2.…”

“…638−641 However, because grain boundaries serve as sinks for point defects, it is expected that the impediment to thermal transport caused by grain boundaries will increase under irradiation. 407,552 MD simulations have been used to investigate the degradation of thermal conductivity due to porosity 553 and the accumulation of fission gas (Xe) 642 or decay gas (He) 643 into bubbles. As expected, increased porosity reduces the thermal conductivity; however, Chen et al 642 and Lee et al 643 both showed a decrease in thermal conductivity as the voids were filled with Xe and He, respectively.…”

“…407,552 MD simulations have been used to investigate the degradation of thermal conductivity due to porosity 553 and the accumulation of fission gas (Xe) 642 or decay gas (He) 643 into bubbles. As expected, increased porosity reduces the thermal conductivity; however, Chen et al 642 and Lee et al 643 both showed a decrease in thermal conductivity as the voids were filled with Xe and He, respectively. For He this was attributed to the resolution of He into the lattice, whereas resolution did not occur for Xe and the decrease was attributed to UO 2 atom distortion at the bubble−UO 2 interface.…”

“…For example, the reduction in thermal conductivity of UO 2 for several concentrations of edge dislocations has been predicted to develop an analytical form suitable for use in a fuel performance code . The impact of grain boundaries on UO 2 thermal conductivity has also been estimated and extrapolated from MD simulations, revealing only a small impact for micrometer-sized grains (as are typically present in fresh fuel). − However, because grain boundaries serve as sinks for point defects, it is expected that the impediment to thermal transport caused by grain boundaries will increase under irradiation. , MD simulations have been used to investigate the degradation of thermal conductivity due to porosity and the accumulation of fission gas (Xe) or decay gas (He) into bubbles. As expected, increased porosity reduces the thermal conductivity; however, Chen et al and Lee et al both showed a decrease in thermal conductivity as the voids were filled with Xe and He, respectively.…”

“…The impact of grain boundaries on UO 2 thermal conductivity has also been estimated and extrapolated from MD simulations, revealing only a small impact for micrometer-sized grains (as are typically present in fresh fuel). − However, because grain boundaries serve as sinks for point defects, it is expected that the impediment to thermal transport caused by grain boundaries will increase under irradiation. , MD simulations have been used to investigate the degradation of thermal conductivity due to porosity and the accumulation of fission gas (Xe) or decay gas (He) into bubbles. As expected, increased porosity reduces the thermal conductivity; however, Chen et al and Lee et al both showed a decrease in thermal conductivity as the voids were filled with Xe and He, respectively. For He this was attributed to the resolution of He into the lattice, whereas resolution did not occur for Xe and the decrease was attributed to UO 2 atom distortion at the bubble–UO 2 interface.…”