Three-dimensional bubble reconstruction in high burnup UO2

Casey McKinney; Rachel Seibert; Grant Helmreich; Assel Aitkaliyeva; Kurt Terrani

doi:10.1016/j.jnucmat.2020.152053

Three-dimensional bubble reconstruction in high burnup UO₂

Casey McKinney, Rachel Seibert, Grant Helmreich, Assel Aitkaliyeva, Kurt Terrani

Research output: Contribution to journal › Article › peer-review

9 Scopus citations

Abstract

In light water reactor (LWR) UO₂ fuels, the evolution of volatile fission products is one of the critical areas of fuel behavior that is yet to be fully understood. In UO₂ irradiated to high burnups, it is well known that most released fission gases come from the central region of the fuel as opposed to the highly porous high burnup structure (HBS) on the periphery of the pellets. However, fuels with and without interconnected bubble networks at the fuel center showed high to moderate release fractions, which conceals the mechanisms responsible for the gas release in the latter scenario. In this work, focused ion beam tomography was used to investigate the three-dimensional bubble structure in an irradiated LWR UO₂ fuel pellet with high degree of fission gas retention so that the degree of bubble interconnection could be assessed. Six radial locations with different burnups and temperatures were serially sectioned and imaged to reconstruct the three-dimensional bubble structure. As expected, the highest porosity was observed at the periphery of the fuel (HBS). The porosity then decreased towards the pellet center, except for the centermost location. This location had a slightly higher porosity than its adjacent mid-radial location, which was attributed to the temperature difference between the two locations. This study provides a first-time volumetric evaluation of the porosity at different radial locations on a UO₂ fuel pellet. During this investigation, no significant bubble interconnection was noted at any of the six radial locations.

Original language	English
Article number	152053
Journal	Journal of Nuclear Materials
Volume	532
DOIs	https://doi.org/10.1016/j.jnucmat.2020.152053
State	Published - Apr 15 2020

Funding

The authors of this work are grateful to the many people involved in the specimen preparation and handling at the hot-cell and radiological facilities at Oak Ridge National Laboratory. Authors acknowledge Joseph Burns for burnup calculations, and Andrew Nelson, Tyler Gerczak, and Jason Harp for their support and critical review of the manuscript prior to publication. This research was supported in part by an appointment to the Oak Ridge National Laboratory Higher Education Research Experience Program, sponsored by the US Department of Energy and administered by the Oak Ridge Institute for Science and Education. The authors of this work are grateful to the many people involved in the specimen preparation and handling at the hot-cell and radiological facilities at Oak Ridge National Laboratory. Authors acknowledge Joseph Burns for burnup calculations, and Andrew Nelson, Tyler Gerczak, and Jason Harp for their support and critical review of the manuscript prior to publication. This research was supported in part by an appointment to the Oak Ridge National Laboratory Higher Education Research Experience Program , sponsored by the US Department of Energy and administered by the Oak Ridge Institute for Science and Education .

Funders	Funder number
Joseph Burns for burnup calculations
Oak Ridge National Laboratory
US Department of Energy
U.S. Department of Energy
Oak Ridge National Laboratory
Oak Ridge Institute for Science and Education

Keywords

3D reconstruction
FIB tomography
Fission gas release
High burnup fuel
Uranium dioxide

Access to Document

10.1016/j.jnucmat.2020.152053

Cite this

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title = "Three-dimensional bubble reconstruction in high burnup UO2 ",

abstract = "In light water reactor (LWR) UO2 fuels, the evolution of volatile fission products is one of the critical areas of fuel behavior that is yet to be fully understood. In UO2 irradiated to high burnups, it is well known that most released fission gases come from the central region of the fuel as opposed to the highly porous high burnup structure (HBS) on the periphery of the pellets. However, fuels with and without interconnected bubble networks at the fuel center showed high to moderate release fractions, which conceals the mechanisms responsible for the gas release in the latter scenario. In this work, focused ion beam tomography was used to investigate the three-dimensional bubble structure in an irradiated LWR UO2 fuel pellet with high degree of fission gas retention so that the degree of bubble interconnection could be assessed. Six radial locations with different burnups and temperatures were serially sectioned and imaged to reconstruct the three-dimensional bubble structure. As expected, the highest porosity was observed at the periphery of the fuel (HBS). The porosity then decreased towards the pellet center, except for the centermost location. This location had a slightly higher porosity than its adjacent mid-radial location, which was attributed to the temperature difference between the two locations. This study provides a first-time volumetric evaluation of the porosity at different radial locations on a UO2 fuel pellet. During this investigation, no significant bubble interconnection was noted at any of the six radial locations.",

keywords = "3D reconstruction, FIB tomography, Fission gas release, High burnup fuel, Uranium dioxide",

author = "Casey McKinney and Rachel Seibert and Grant Helmreich and Assel Aitkaliyeva and Kurt Terrani",

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AU - Seibert, Rachel

AU - Helmreich, Grant

AU - Aitkaliyeva, Assel

AU - Terrani, Kurt

PY - 2020/4/15

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N2 - In light water reactor (LWR) UO2 fuels, the evolution of volatile fission products is one of the critical areas of fuel behavior that is yet to be fully understood. In UO2 irradiated to high burnups, it is well known that most released fission gases come from the central region of the fuel as opposed to the highly porous high burnup structure (HBS) on the periphery of the pellets. However, fuels with and without interconnected bubble networks at the fuel center showed high to moderate release fractions, which conceals the mechanisms responsible for the gas release in the latter scenario. In this work, focused ion beam tomography was used to investigate the three-dimensional bubble structure in an irradiated LWR UO2 fuel pellet with high degree of fission gas retention so that the degree of bubble interconnection could be assessed. Six radial locations with different burnups and temperatures were serially sectioned and imaged to reconstruct the three-dimensional bubble structure. As expected, the highest porosity was observed at the periphery of the fuel (HBS). The porosity then decreased towards the pellet center, except for the centermost location. This location had a slightly higher porosity than its adjacent mid-radial location, which was attributed to the temperature difference between the two locations. This study provides a first-time volumetric evaluation of the porosity at different radial locations on a UO2 fuel pellet. During this investigation, no significant bubble interconnection was noted at any of the six radial locations.

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