Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) The finite element model of polycrystalline UO2 used in the present study. The circular holes in the model represent pores. (b) In the 2D finite element model, grains are set to connect with each other via a narrow gap. (c) Simple illustration of the computational procedure to calculate temperature profiles of UO2 pellet during service.

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Polycrystal simulation model with different grain size: 5 μm, 10 μm, 20 μm, and 40 μm. (b) The effective thermal conductivity κeff with different grain size. (c) Effective thermal conductivity of polycrystalline UO2 at 1000 K with different grain size. The solid line represents the effective thermal conductivity calculated by Eq.(7), where the value of κ0 is 3.94 W/m·K, and Rk is 1.14 × 10−7 m2 K/W.

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Radial temperature profile of UO2 pellets (radium = 0.4 cm) with different grain sizes and (b) temperature distribution inside the UO2 pellet

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Polycrystalline UO2 models with different topological entropies:3.5, 2.96, and 2.31. The grain size is 5 μm, and the porosity is zero. (b) Thermal conductivity of polycrystalline UO2 with different topological entropies. (c) Enlarged view of thermal conductivity of polycrystalline UO2 with different topological entropies.

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Polycrystalline UO2 models with grain growth directions of 0 deg, 30 deg, 60 deg, and 90 deg. The dimension of each grain is approximately 40 μm × 10 μm. (b) Thermal conductivities of polycrystalline UO2 models with grain growth directions of 0 deg, 30 deg, 60 deg, and 90 deg. The thermal conductivity of polycrystal with no certain grain growth direction (d = 20 μm) is also shown for comparison.

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Polycrystalline UO2 models with porosity of 3%, 5%, and 7%. Pores are distributed randomly in the polycrystals. (b) Thermal conductivities of polycrystalline UO2 with different porosities. (c) Comparison of thermal conductivity curves of polycrystalline UO2 with 5% porosity computed in this study (solid line) and Eq. (8) (the shaded region). (d) The differences of thermal conductivity between polycrystals with grain size of 40 μm and 5 μm.

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Polycrystalline UO2 models pores with in different locations and (b) thermal conductivities of polycrystalline UO2 with different pore locations

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: (a) Polycrystalline UO2 models pores with in different pore sizes. Pores are distributed randomly in the polycrystals. (b) Thermal conductivities of polycrystalline UO2 with different pore sizes. The solid lines represent the polycrystals that all pores are randomly distributed, and the dashed lines represent the polycrystals that all pores are along GBs. (c) Radial temperature profile of UO2 pellets with different pore sizes. Pores are along the GBs. (d) Temperature distribution inside the UO2 pellet.

Date of download: 12/27/2017 Copyright © ASME. All rights reserved. An Finite Element Method Study of the Thermal Conductivity of Polycrystalline UO2 ASME J of Nuclear Rad Sci. 2017;3(4):041006-041006-10. doi:10.1115/1.4037189 Figure Legend: Thermal conductivities of polycrystals with different topological entropies under the condition of pore existence. The dashed lines represent the polycrystals that all pores are randomly distributed, and the solid lines represent the polycrystals that all pores are along GBs.