Contribution of energetically reactive surface features to the dissolution of CeO2 and ThO2  analogues for spent nuclear fuel microstructures

Claire L. Corkhill, Emmi Myllykyla, Daniel J. Bailey, Stephanie M. Thornber, Jiahui Qi, Pablo Maldonado, Martin C. Stennett, Andrea Hamilton, Neil C. Hyatt

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

In the safety case for the geological disposal of nuclear waste, the release of radioactivity from the repository is controlled by the dissolution of the spent fuel in groundwater. There remain several uncertainties associated with understanding spent fuel dissolution, including the contribution of energetically reactive surface sites to the dissolution rate. In this study, we investigate how surface features influence the dissolution rate of synthesised CeO2 and ThO2, spent nuclear fuel analogues which approximate as closely as possible the mineral structure characteristics of fuel-grade UO2 but are not sensitive to changes in oxidation state of the cation. The morphology of grain boundaries (natural features) and surface facets (specimen preparation-induced features) were investigated during dissolution. The effects of surface polishing on dissolution rate was also investigated. We show that preferential dissolution occurs at grain boundaries, resulting in grain boundary decohesion and enhanced dissolution rates. A strong crystallographic control was exerted, with high misorientation angle grain boundaries retreating more rapidly than those with low misorientation angles, which may be due to the accommodation of defects in the grain boundary structure. The data from these simplified analogue systems support the hypothesis that grain boundaries play a role in the so-called "instant release fraction" of spent fuel, and should be carefully considered, in conjunction with other chemical effects, in safety performance assessements for the geological disposal of spent fuel. Surface facets formed during the sample annealing process also exhibited a strong crystallographic control and were found to dissolve rapidly on initial contact with dissolution medium. Defects and strain induced during sample polishing caused an overestimation of the dissolution rate, by up to 3 orders of magnitude.
LanguageEnglish
Pages12279–12289
Number of pages11
JournalACS Applied Materials and Interfaces
Volume6
Issue number15
Early online date7 Jul 2014
DOIs
Publication statusPublished - 13 Aug 2014

Fingerprint

Spent fuels
Nuclear fuels
Dissolution
Microstructure
Grain boundaries
Polishing
Radioactive Waste
Specimen preparation
Defects
Radioactivity
Radioactive wastes
Waste disposal
Minerals
Cations
Groundwater
Positive ions
Annealing
Oxidation

Keywords

  • energetically reactive
  • surface features
  • geological disposal
  • dissolution of CeO2
  • ThO2 analogues
  • spent nuclear fuel microstructures
  • nuclear waste
  • safety case
  • release of radioactivity
  • grain boundaries
  • specimen preparation-induced features
  • crystallographic control

Cite this

Corkhill, Claire L. ; Myllykyla, Emmi ; Bailey, Daniel J. ; Thornber, Stephanie M. ; Qi, Jiahui ; Maldonado, Pablo ; Stennett, Martin C. ; Hamilton, Andrea ; Hyatt, Neil C. / Contribution of energetically reactive surface features to the dissolution of CeO2 and ThO2  analogues for spent nuclear fuel microstructures. In: ACS Applied Materials and Interfaces. 2014 ; Vol. 6, No. 15. pp. 12279–12289.
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abstract = "In the safety case for the geological disposal of nuclear waste, the release of radioactivity from the repository is controlled by the dissolution of the spent fuel in groundwater. There remain several uncertainties associated with understanding spent fuel dissolution, including the contribution of energetically reactive surface sites to the dissolution rate. In this study, we investigate how surface features influence the dissolution rate of synthesised CeO2 and ThO2, spent nuclear fuel analogues which approximate as closely as possible the mineral structure characteristics of fuel-grade UO2 but are not sensitive to changes in oxidation state of the cation. The morphology of grain boundaries (natural features) and surface facets (specimen preparation-induced features) were investigated during dissolution. The effects of surface polishing on dissolution rate was also investigated. We show that preferential dissolution occurs at grain boundaries, resulting in grain boundary decohesion and enhanced dissolution rates. A strong crystallographic control was exerted, with high misorientation angle grain boundaries retreating more rapidly than those with low misorientation angles, which may be due to the accommodation of defects in the grain boundary structure. The data from these simplified analogue systems support the hypothesis that grain boundaries play a role in the so-called {"}instant release fraction{"} of spent fuel, and should be carefully considered, in conjunction with other chemical effects, in safety performance assessements for the geological disposal of spent fuel. Surface facets formed during the sample annealing process also exhibited a strong crystallographic control and were found to dissolve rapidly on initial contact with dissolution medium. Defects and strain induced during sample polishing caused an overestimation of the dissolution rate, by up to 3 orders of magnitude.",
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Contribution of energetically reactive surface features to the dissolution of CeO2 and ThO2  analogues for spent nuclear fuel microstructures. / Corkhill, Claire L.; Myllykyla, Emmi ; Bailey, Daniel J.; Thornber, Stephanie M.; Qi, Jiahui ; Maldonado, Pablo ; Stennett, Martin C. ; Hamilton, Andrea; Hyatt, Neil C.

In: ACS Applied Materials and Interfaces, Vol. 6, No. 15, 13.08.2014, p. 12279–12289.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Contribution of energetically reactive surface features to the dissolution of CeO2 and ThO2  analogues for spent nuclear fuel microstructures

AU - Corkhill, Claire L.

AU - Myllykyla, Emmi

AU - Bailey, Daniel J.

AU - Thornber, Stephanie M.

AU - Qi, Jiahui

AU - Maldonado, Pablo

AU - Stennett, Martin C.

AU - Hamilton, Andrea

AU - Hyatt, Neil C.

PY - 2014/8/13

Y1 - 2014/8/13

N2 - In the safety case for the geological disposal of nuclear waste, the release of radioactivity from the repository is controlled by the dissolution of the spent fuel in groundwater. There remain several uncertainties associated with understanding spent fuel dissolution, including the contribution of energetically reactive surface sites to the dissolution rate. In this study, we investigate how surface features influence the dissolution rate of synthesised CeO2 and ThO2, spent nuclear fuel analogues which approximate as closely as possible the mineral structure characteristics of fuel-grade UO2 but are not sensitive to changes in oxidation state of the cation. The morphology of grain boundaries (natural features) and surface facets (specimen preparation-induced features) were investigated during dissolution. The effects of surface polishing on dissolution rate was also investigated. We show that preferential dissolution occurs at grain boundaries, resulting in grain boundary decohesion and enhanced dissolution rates. A strong crystallographic control was exerted, with high misorientation angle grain boundaries retreating more rapidly than those with low misorientation angles, which may be due to the accommodation of defects in the grain boundary structure. The data from these simplified analogue systems support the hypothesis that grain boundaries play a role in the so-called "instant release fraction" of spent fuel, and should be carefully considered, in conjunction with other chemical effects, in safety performance assessements for the geological disposal of spent fuel. Surface facets formed during the sample annealing process also exhibited a strong crystallographic control and were found to dissolve rapidly on initial contact with dissolution medium. Defects and strain induced during sample polishing caused an overestimation of the dissolution rate, by up to 3 orders of magnitude.

AB - In the safety case for the geological disposal of nuclear waste, the release of radioactivity from the repository is controlled by the dissolution of the spent fuel in groundwater. There remain several uncertainties associated with understanding spent fuel dissolution, including the contribution of energetically reactive surface sites to the dissolution rate. In this study, we investigate how surface features influence the dissolution rate of synthesised CeO2 and ThO2, spent nuclear fuel analogues which approximate as closely as possible the mineral structure characteristics of fuel-grade UO2 but are not sensitive to changes in oxidation state of the cation. The morphology of grain boundaries (natural features) and surface facets (specimen preparation-induced features) were investigated during dissolution. The effects of surface polishing on dissolution rate was also investigated. We show that preferential dissolution occurs at grain boundaries, resulting in grain boundary decohesion and enhanced dissolution rates. A strong crystallographic control was exerted, with high misorientation angle grain boundaries retreating more rapidly than those with low misorientation angles, which may be due to the accommodation of defects in the grain boundary structure. The data from these simplified analogue systems support the hypothesis that grain boundaries play a role in the so-called "instant release fraction" of spent fuel, and should be carefully considered, in conjunction with other chemical effects, in safety performance assessements for the geological disposal of spent fuel. Surface facets formed during the sample annealing process also exhibited a strong crystallographic control and were found to dissolve rapidly on initial contact with dissolution medium. Defects and strain induced during sample polishing caused an overestimation of the dissolution rate, by up to 3 orders of magnitude.

KW - energetically reactive

KW - surface features

KW - geological disposal

KW - dissolution of CeO2

KW - ThO2 analogues

KW - spent nuclear fuel microstructures

KW - nuclear waste

KW - safety case

KW - release of radioactivity

KW - grain boundaries

KW - specimen preparation-induced features

KW - crystallographic control

U2 - 10.1021/am5018978

DO - 10.1021/am5018978

M3 - Article

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SP - 12279

EP - 12289

JO - ACS Applied Materials and Interfaces

T2 - ACS Applied Materials and Interfaces

JF - ACS Applied Materials and Interfaces

SN - 1944-8244

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ER -