Roles of Radiolytic and Externally Generated H<sub>2</sub> in the Corrosion of Fractured Spent Nuclear Fuel

Liu, Nazhen; Wu, Linda; Qin, Z.; Shoesmith, David W.

doi:10.1021/acs.est.6b04167

Cited by 21 publications

(14 citation statements)

References 30 publications

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“…Radiolytic oxidants produced by radiation--induced water radiolysis may cause the oxidative dissolution of a UO 2 matrix. In particular, under alpha irradiation, the most important species to be considered regarding UO 2 dissolution is H 2 O 2 (Ekeroth et al, 2006;Lousada et al, 2013;Liu et al, 2016). The generation of H 2 O 2 (aq) was introduced in the model according to the following rate law:…”

Section: Production Of Radiolytic H 2 O 2 (Aq)mentioning

confidence: 99%

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Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

Odorowski

Jégou

Windt

et al. 2017

Geochimica et Cosmochimica Acta

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In the hypothesis of direct disposal of spent fuel in a geological nuclear waste repository, interactions between the fuel mainly composed of UO 2 and its environment must be understood. The dissolution rate of the UO 2 matrix, which depends on the redox conditions on the fuel surface, will have a major impact on the release of radionuclides into the environment. The reducing conditions expected for a geological disposal situation would appear to be favorable as regards the solubility and stability of the UO 2 matrix, but may be disturbed on the surface of irradiated fuel. In particular, the local redox conditions will result from a competition between the radiolysis effects of water under alpha irradiation (simultaneously producing oxidizing species like H 2 O 2, hydrogen peroxide, and reducing species like H 2, hydrogen) and those of redox active species from the environment. In particular, Fe 2+ , a strongly reducing aqueous species coming from the corrosion of the iron canister or from the host rock, could influence the dissolution of the fuel matrix. The effect of iron on the oxidative dissolution of UO 2 was thus investigated under the conditions of the French disposal site, a Callovian-Oxfordian clay formation chosen by the French National Radioactive Waste Management Agency (Andra), here tested under alpha irradiation. For this study, UO 2 fuel pellets doped with a radioactive alpha emitter (238/239 Pu) were leached in synthetic Callovian-Oxfordian groundwater (representative of the French waste disposal site groundwater) in the presence of a metallic iron foil to simulate the steel canister. The pellets had varying levels of alpha activity, in order to modulate the concentrations of species produced by water radiolysis on the surface and to simulate the activity of aged spent fuel after 50 and 10000 years of alpha radioactivity decay. The experimental data showed that whatever the sample alpha radioactivity, the presence of iron inhibits the oxidizing dissolution of UO 2 and leads to low uranium concentrations (between 4x10-10 and 4x10-9 M), through a reactional mechanism located in the very first microns of the UO 2 /water reactional interface. The mechanism involves consumption of oxidizing species, in particular of H 2 O 2 by Fe 2+ at the precise place where these species are produced, and is accompanied by the precipitation of an akaganeite-type Fe 3+ hydroxide on the surface. The higher the radioactivity of the samples, the greater the precipitation induced. Modeling has been developed, coupling chemistry with transport and based on the main reactional mechanisms identified, which enables accurate reproduction of the mineralogy of the system under study, giving the nature of the phases under observation as well as the location of their precipitation.

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Section: Production Of Radiolytic H 2 O 2 (Aq)mentioning

confidence: 99%

“…The position of this threshold is also strongly dependent on the environmental conditions. It has thus been shown that the presence of redox active species like hydrogen in the environmental water (anoxic corrosion of the containers) or iron may counteract the water radiolysis effects (Spahiu et al, 2004a;Liu et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

Odorowski

Jégou

Windt

et al. 2017

Geochimica et Cosmochimica Acta

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“…For UO 2 -based materials the competition between oxidation of the UO 2 matrix and catalytic decomposition has sometimes been assigned to two different types of surface sites [17]. In simulations of radiation-induced dissolution of spent nuclear fuel, a constant ratio between oxidation and catalytic decomposition is sometimes used to handle the competing reactions [18].…”

Section: Introductionmentioning

confidence: 99%

The role of surface-bound hydroxyl radicals in the reaction between H₂O₂ and UO₂

Fidalgo

Kumagai

Jönsson

2018

Journal of Coordination Chemistry

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In this work, we have studied the reaction between H 2 O 2 and UO 2 with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of H 2 O 2 consumption and uranium dissolution at different initial H 2 O 2 concentrations. The results show that the consumption rates at a given H 2 O 2 concentration are different depending on the initial H 2 O 2 concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The dissolution yield given by the amount of dissolved uranium divided by the amount of consumed hydrogen peroxide was used to compare the different cases. For all initial H 2 O 2 concentrations, the dissolution yield increases with reaction time. The final dissolution yield decreases with increasing initial H 2 O 2 concentration. This is expected from the mechanism of catalytic decomposition of H 2 O 2 on oxide surfaces. As the experiments were performed in solutions containing 10 mM HCO − 3 and a strong concentration dependence was observed in the 0.2-2.0 mM H 2 O 2 concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.

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“…Species such as Fe(0) and hydrogen can inhibit the oxidative dissolution of fuels and promote the retention of redox-sensitive radionuclides by stabilizing the less soluble reduced forms [119][120][121][122][123][124]. Hydrogen is produced in the initial phase by oxidation of metals such as zirconium during the accident and temperature rise or by anoxic corrosion of iron containers under geological disposal conditions.…”

Section: V-3) the Role Of Electroactive Redox Speciesmentioning

confidence: 99%

Ten years after the NPP accident at Fukushima : review on fuel debris behavior in contact with water

Grambow

Nitta

Shibata

et al. 2021

Journal of Nuclear Science and Technology

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Following the NPP accident, several hundred tons of heat-generating corium and fuel debris have been cooled permanently by millions of m 3 of flowing. Knowledge on the interaction with water is crucial for any decommissioning planning.Starting from knowledge on the evolutions of the accident in the three reactor cores and associated fuel debris formations and some additional isotopic and physio-chemical information on debris fragments collected in Fukushima soils, we review the temporal evolution of the chemistry and leached radionuclide contents of the cooling water, comparing measured concentration ratios of the actinides and fission products in the water to reported results of laboratory leaching studies with either spent nuclear fuel or simulated fuel debris.As for spent fuel leaching, the fractions of inventories of 134,137 Cs in the cooling water are orders of magnitude larger than that of the actinides. After more than 10 years of fuel debris/ water contact, 137 Cs release rates have decreased by about a factor of 100. The total release of actinides from the fuel debris is orders of magnitude lower than that of 134,137 Cs or of 90 Sr. This high stability makes direct disposal of fuel debris in suitable containers after decommissioning a viable option.

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Roles of Radiolytic and Externally Generated H₂ in the Corrosion of Fractured Spent Nuclear Fuel

Cited by 21 publications

References 30 publications

Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

The role of surface-bound hydroxyl radicals in the reaction between H₂O₂ and UO₂

Ten years after the NPP accident at Fukushima : review on fuel debris behavior in contact with water

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Roles of Radiolytic and Externally Generated H2 in the Corrosion of Fractured Spent Nuclear Fuel

Cited by 21 publications

References 30 publications

Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

Effect of metallic iron on the oxidative dissolution of UO2 doped with a radioactive alpha emitter in synthetic Callovian-Oxfordian groundwater

The role of surface-bound hydroxyl radicals in the reaction between H2O2 and UO2

Ten years after the NPP accident at Fukushima : review on fuel debris behavior in contact with water

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Product

Resources

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Roles of Radiolytic and Externally Generated H₂ in the Corrosion of Fractured Spent Nuclear Fuel

The role of surface-bound hydroxyl radicals in the reaction between H₂O₂ and UO₂