Modelling the Oxidative Dissolution of UO<sub>2</sub>

King, Fraser; Kolář, Miroslav; Shoesmith, David W.

doi:10.1557/proc-556-463

Cited by 11 publications

(14 citation statements)

References 5 publications

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“…However, these models do not model the formation of oxidants directly but rather assume constant values. Indeed, only H 2 O 2 generation was considered in the model in the 1999 version of the mixed potential model developed by King et al (1999) and Sunder (1998); hence, this model could be improved with a more comprehensive radiolysis component. Most radiolysis modeling has concentrated on gamma irradiation rather than alpha irradiation, and there are few, if any, examples in the literature of radiolytic species predictions under alpha radiolysis.…”

Section: Modeling Concepts and Processesmentioning

confidence: 99%

Radiolysis Process Model

Buck¹,

Wittman²,

Skomurski³

et al. 2012

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SUMMARYThis report satisfies the Used Fuel Disposition M3 Milestone, Radiolysis Products Modeling Results for Scenarios, (M3FT-12PN080651).Assessing the performance of Spent (or Used) Nuclear Fuel (UNF) in geological repository requires quantification of time-dependent phenomena that may influence its behavior on a time-scale up to millions of years. A high-level waste repository environment will be a dynamic redox system because of the time-dependent generation of radiolytic oxidants and reductants and the corrosion of Fe-bearing canister materials. One major difference between used fuel and natural analogues, including unirradiated

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Section: Modeling Concepts and Processesmentioning

confidence: 99%

Radiolysis Process Model

Buck¹,

Wittman²,

Skomurski³

et al. 2012

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“…Recently, a mixed-potential model (MPM) for UO 2 fuel dissolution has been developed [9,10]. The MPM also uses the established dissolution current versus potential relationship mentioned above, but predicts both corrosion potentials and corrosion rates.…”

Section: Dissolution Ratesmentioning

confidence: 99%

The effects of alpha-radiolysis on UO₂ dissolution determined from electrochemical experiments with ²³⁸Pu-doped UO₂

Stroes-Gascoyne¹,

King²,

Betteridge³

et al. 2002

Radiochimica Acta

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Alpha-radiolysis / 238 Pu-doped UO 2 / Electrochemistry / Corrosion potential / Dissolution rate Summary. The long-term stability of spent nuclear fuel under deep geologic repository conditions will be determined mostly by the influence of α-radiolysis, since the dose-rate for α-radiolysis will exceed that for γ/β-radiolysis beyond a fuel age of ∼ 100 years and will persist for more than 10 000 years. Dissolution rates derived from studies with currently available spent fuel include radiolysis effects from γ/β-as well as α-radiolysis. The use of external α-sources and chemically added H 2 O 2 in UO 2 studies has provided much information on the basic chemistry/electrochemistry of α-radiolysis effects on UO 2 fuel dissolution. Here, alpha-radiolysis effects were measured directly by performing electrochemical experiments with α-doped UO 2 . The 238 Pu-doped UO 2 pellets, produced by milling, pressing and sintering, had activities of approximately 0.01 and 0.1 Ci/g. Discs cut from these pellets were fabricated into electrodes. Corrosion potentials (E corr ) were measured for these electrodes, in glass cells containing deaerated 0.1 M NaClO 4 (pH 9.5) for periods up to 1600 h. The effects of carbonate and Fe(II) on E corr values were also investigated. Preliminary results showed that E corr values correlated with doping levels, and were slightly higher than E corr values obtained with UO 2 electrodes in the presence of external α-sources. The presence of carbonate reduced E corr values considerably. Addition of Fe(II) caused generally small reductions in E corr values, suggesting that Fe(II) affects the dissolution process, either by scavenging radiolytic oxidants, reducing oxidized surface states, or reducing dissolved U(VI). These effects were often transient due to depletion of the added Fe(II). Accurate dissolution rates could not be determined from measured solution and surface concentrations because of material entering the solutions during the electroreduction procedure, probably due to the dissolution of fines present on the electrode surface after polishing. Experiments are continuing in order to confirm the preliminary findings, with greater attention being paid to determining accurate dissolution rates.

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“…This tends to suggest that bubble growth and migration may have resulted in interconnected porosity that may have allowed increased fission gas release. Increases in porosity within the rim will increase the surface area that can be contacted by moisture (Wasywich et al 1992), and there may be an increase of the generation rate of a-radiolytic oxidants in the microporous regions (King et al 1999). Both of these effects would tend to increase the rate of spent fuel corrosion and radionuclide release from the matrix.…”

Section: Burn-up Effectsmentioning

confidence: 99%

“…Moreover, the production rate of OH" radicals is lower in an o~-radiation field compared to a [3-,3,-field. The heterogeneous nature of spent fuel, particularly the occurrence of Pu-enriched rims (Matzke & Spino 1997), may continue to allow radiolytic species to form under moist-air (vapour) conditions even after the decay of the [3-,~/-field (King et al 1999). Performance assessment codes for HLW repositories require a rate for spent nuclear fuel corrosion; yet, in over 25 years of fuel research, such a relationship has been difficult to obtain.…”

Section: Radiolysismentioning

confidence: 99%

“…Oversby (1999) summarized much of the scientific community's data on UO2 fuel corrosion and demonstrated the difficulty in obtaining a mechanistic dependency for the spent fuel corrosion rate. New models that include dependence on the effective generation rates of H202 from c~-radiolysis in an aged fuel/canister environment are providing improvements in our models for spent fuel behaviour in a geological repository (King et al 1999).…”

Section: Radiolysismentioning

confidence: 99%

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The geochemical behaviour of Tc, Np and Pu in spent nuclear fuel in an oxidizing environment

Buck

Hanson

McNamara

2004

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Spent fuel from commercial nuclear reactors consists mainly of uranium oxide. However, the changes that occur during reactor operations have a profound effect on chemical and physical properties of this material. Heat build-up in the fuel pellet during reactor operations can cause redistribution of fission products. The fission products may aggregate in one of three types of precipitates; gaseous, metallic, or oxide, depending on the burn-up and in-core treatment. Radiation damage and variations in fission and neutron capture yields across the fuel pellets lead to Pu enrichment and increased porosity with increasing burn-up. A more porous surface may make the fuel more susceptible to oxidative dissolution. As the level of actinides and fission products increases, the fuel may become more resistant to oxidation. These changes may limit the usefulness of natural uraninite (U02) analogues for predicting the geological behaviour of spent fuel disposed in a high-level waste (HLW) repository. In this Chapter, an overview of spent fuel microstructure, radiolytic effects, and alteration processes is presented. Evidence for Np incorporation into U 6+ phases, the nature of Pu surface precipitates on spent fuel, and evidence for the preferential removal of 4d-metals from e-particles in corroded spent fuel is discussed. Understanding the potential mechanisms of radionuclide attenuation through sorption and/or incorporation requires techniques with both high spatial resolution and excellent elemental sensitivity.

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Modelling the Oxidative Dissolution of UO₂

Cited by 11 publications

References 5 publications

Radiolysis Process Model

Radiolysis Process Model

The effects of alpha-radiolysis on UO₂ dissolution determined from electrochemical experiments with ²³⁸Pu-doped UO₂

The geochemical behaviour of Tc, Np and Pu in spent nuclear fuel in an oxidizing environment

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Modelling the Oxidative Dissolution of UO2

Cited by 11 publications

References 5 publications

Radiolysis Process Model

Radiolysis Process Model

The effects of alpha-radiolysis on UO2 dissolution determined from electrochemical experiments with 238Pu-doped UO2

The geochemical behaviour of Tc, Np and Pu in spent nuclear fuel in an oxidizing environment

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Modelling the Oxidative Dissolution of UO₂

The effects of alpha-radiolysis on UO₂ dissolution determined from electrochemical experiments with ²³⁸Pu-doped UO₂