Leaching behaviour of unirradiated high temperature reactor (HTR) UO2–ThO2 mixed oxides fuel particles

Alliot, Cyrille; Grambow, Bernd; Landesman, Catherine

doi:10.1016/j.jnucmat.2005.05.018

Cited by 8 publications

(9 citation statements)

References 12 publications

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“…The geometrical surface area of the spheres is used for S as the reference because S is too low to be measured by the gas adsorption method. In many cases, the geometric surface area estimations of ceramics are good estimates of the experimental values . The normalized dissolution rate (in g·m −2 ·day −1 ) is then calculated with the following equation: NLR = normalΔ NL normalΔ italict where Δ t signifies an interval in the contact time (days) and ΔNL variation of the normalized mass loss in this interval.…”

Section: Data Treatmentmentioning

confidence: 99%

Discrepancies in Thorium Oxide Solubility Values: Study of Attachment/Detachment Processes at the Solid/Solution Interface

2010

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The solubility of thorium under oxide and/or hydroxide forms has been extensively studied for many years. Nevertheless, a large discrepancy in the solubility values is noticed in the literature. We study Th atom exchange between thorium oxide surfaces and various aqueous solutions (0.01 mol·L(-1) NaCl for 0.0 < pH < 5.2) to address this issue. By solid-state characterization [X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and atomic force microscopy], we determined that 80% of the XPS accessible near the surface region of sintered thorium oxide is represented by the less reactive ThO(2)(cr) grains. The remaining 20% corresponds to ThO(x)(OH)(y)(H(2)O)(z), which is largely associated with grain boundaries. Only the latter fraction is involved in solid/solution exchange mechanisms. Local conditions (thorium concentrations, pH values, etc.) in grain boundaries lead to an adjustment of the "local solubility constraints" and explain the thorium concentration measured in our experiments. For pH <5.2, the thorium concentration and pH gradient between the bulk solution and grain-boundary regions imply that the solubility values mainly depend on the availability and accessibility of ThO(x)(OH)(y)(H(2)O)(z). We have performed two solubility experiments with a (232)ThO(2)(cr) solid in a 0.01 mol·L(-1) NaCl solution for 300 days. In a first experiment, we measured (232)Th concentrations in dissolution experiments in order to determine the detachment rates of Th atoms from the solid surface. In a subsequent step, we added (229)Th to the solution in order to measure the surface attachment rate for dissolved Th atoms. This allowed an assessment of the net balance of Th atom exchange at the solid/solution interface. The empirical solubility data do not correspond to the thermodynamic bulk phase/solution equilibrium because measured solution concentrations are controlled by site-specific exchange mechanisms at the solid/solution interface. Therefore, for sparingly soluble solids, one needs to quantify site-specific surface attachment and detachment rates if one wants to assess solubility constraints.

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Section: Data Treatmentmentioning

confidence: 99%

Discrepancies in Thorium Oxide Solubility Values: Study of Attachment/Detachment Processes at the Solid/Solution Interface

2010

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“…These electrodes were specially engineered for our experiment [11]. Because U(IV) readily oxidizes into U(VI) in the presence of O 2 both during the experiment and sampling, the removal of the oxygen traces of about 0.1 ppm in nitrogen gas was ensured using a redox cycle [11,15]. The nitrogen gas, containing oxygen traces (o100 ppb) was splashed through a NH 4 VO 3 solution containing a ZnHg amalgam.…”

Section: Synthesis Methodsmentioning

confidence: 99%

Synthesis and characterization of nanometric powders of UO2+x, (Th,U)O2+x and (La,U)O2+x

Rousseau¹,

Fattahi²,

Grambow³

et al. 2009

Journal of Solid State Chemistry

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“…The geometrical surface area (Table 1) of the spheres was used as reference, because it is too low to be measured by gas adsorption methods. In many cases, geometric surface area estimations of ceramics are good estimates of experimental values [15].…”

Section: Methodsmentioning

confidence: 99%

“…These spheres are originating from TRISOcoated (Tri-isotropic or multi-layered high-and low-density pyrolytic carbon and silicon carbide coatings) fuel particles of the german HTR (High Temperature Reactor) test programme. In fact, only a few data exist concerning dissolution properties of these spheres [15,16]. We have chosen these materials because they were made using a well defined protocol [17] allowing to obtain spherical solid samples with similar and strictly controlled surface.…”

Section: Introductionmentioning

confidence: 99%

Discrepancies in thorium oxide solubility values: a new experimental approach to improve understanding of oxide surface at solid/solution interface

2008

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The solubility of ThO 2 (cr) was studied since many years but a large discrepancy in solubility values is noticed in the literature. The present work suggests that this discrepancy is related to differences in the surface properties of thorium oxide. To understand the role of surface properties on solubility values, we conducted experiments with ThO 2 (cr) spheres with reproducable surface properties. Batch dissolution experiments were conducted in 0.01 M NaCl solution at pH = 3.0 and 4.0 for periods of time up to 270 days. The solutions were spiked with 229 Th to determine precipitation (sorption) rates of thorium, while dissolution rates were determined by measuring 232 Th released from ThO 2 (cr) spheres. We assume that 229 Th atoms are exchanged only with active sites involved in Th-dissolution. Using 229 Th as local sensor of attachement and detachment processes at the ThO 2 (cr) surface under close-to-equilibrium conditions, allows to assess surface reactivity of the solid during solubility experiments.

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Leaching behaviour of unirradiated high temperature reactor (HTR) UO2–ThO2 mixed oxides fuel particles

Cited by 8 publications

References 12 publications

Discrepancies in Thorium Oxide Solubility Values: Study of Attachment/Detachment Processes at the Solid/Solution Interface

Discrepancies in Thorium Oxide Solubility Values: Study of Attachment/Detachment Processes at the Solid/Solution Interface

Synthesis and characterization of nanometric powders of UO2+x, (Th,U)O2+x and (La,U)O2+x

Discrepancies in thorium oxide solubility values: a new experimental approach to improve understanding of oxide surface at solid/solution interface

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