Effect of external gamma irradiation on dissolution of the spent UO2 fuel matrix

Jégou, Christophe; Muzeau, B.; Broudic, V.; Peuget, S.; Poulesquen, Arnaud; Roudil, D.; Corbel, C.

doi:10.1016/j.jnucmat.2005.01.008

Cited by 66 publications

(48 citation statements)

References 23 publications

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“…[4][5][6] In addition, hydrogen peroxide strongly affects the oxidative dissolution of SNF and UO 2 , by oxidizing the U(IV) of the solid to more soluble U(VI) species.…”

Section: Introductionmentioning

confidence: 99%

Determination of the equilibrium formation constants of two U(vi)–peroxide complexes at alkaline pH

et al. 2011

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The formation of uranyl-peroxide complexes was studied at alkaline media by using UV-Visible spectrophotometry and the STAR code. Two different complexes were found at a H 2 O 2 /U(VI) ratio lower than 2. A graphical method was used in order to obtain the formation constants of such complexes and the STAR program was used to refine the formation constants values because of its capacity to treat multiwavelength absorbance data and refining equilibrium constants. The values obtained for the two complexes identified were:At hydrogen peroxide concentrations higher than 10 -5 mol dm -3 , and in the absence of carbonate, the UO 2 (O 2 ) 2 (OH) 2 4-complex is predominant in solution, indicating the significant peroxide affinity of peroxide ions for uranium and the strong complexes of uranium(VI) with peroxide.

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“…[4][5][6] In addition, hydrogen peroxide strongly affects the oxidative dissolution of SNF and UO 2 , by oxidizing the U(IV) of the solid to more soluble U(VI) species.…”

Section: Introductionmentioning

confidence: 99%

Determination of the equilibrium formation constants of two U(vi)–peroxide complexes at alkaline pH

et al. 2011

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“…Studtite was a major alteration phase of fuel-element claddings, and also occurred on the basin floor and in canister sludge (12). Studtite also formed on spent fuel in deionized water under laboratory conditions (13), and on UO 2 doped with alpha emitters or irradiated by an external source in water (2,(14)(15)(16)(17).Where seawater flow is relatively stagnant in the FukushimaDaiichi systems, peroxide will accumulate, it will increase corrosion rates of exposed UO 2 , and it will complex uranyl ions in solution. The seawater, with a pH of approximately 8, will provide abundant Na and lesser K to balance the charge of the resulting uranyl peroxide complexes that form in solution and in precipitates.…”

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confidence: 99%

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confidence: 99%

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Armstrong

Nyman

Shvareva

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

134

177

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The Fukushima-Daiichi nuclear accident brought together compromised irradiated fuel and large amounts of seawater in a high radiation field. Based on newly acquired thermochemical data for a series of uranyl peroxide compounds containing charge-balancing alkali cations, here we show that nanoscale cage clusters containing as many as 60 uranyl ions, bonded through peroxide and hydroxide bridges, are likely to form in solution or as precipitates under such conditions. These species will enhance the corrosion of the damaged fuel and, being thermodynamically stable and kinetically persistent in the absence of peroxide, they can potentially transport uranium over long distances.F ailed cooling systems in the reactors and spent fuel cooling ponds at the Fukushima-Daiichi nuclear power plants resulted in compromised irradiated fuel and release of radionuclides. Copious amounts of seawater were subsequently used to cool the fuel. The collocation of large quantities of damaged fuel, an intense radiation field, and massive amounts of seawater has created a highly heterogeneous and presumably rapidly evolving system that has the potential to release vast quantities of radionuclides to the environment. Currently, large quantities of contaminated water remain onsite (1), and presumably some has been released to the subsurface as well as to the Pacific Ocean.The fuel matrix at the Fukushima-Daiichi site is mainly UO 2 , whose behavior will largely dictate release of matrix-incorporated plutonium and various other radionuclides into water used as a coolant. The intense radiation field of the fuel will cause radiolysis of water and formation of peroxide (as well as other species) (2). Peroxide enhances the corrosion rate of UO 2 by oxidizing U (IV) to the much more soluble U(VI) that exists as the linear dioxo uranyl cation, ðUO 2 Þ 2þ . Peroxide strongly complexes uranyl (3), which increases its aqueous solubility under alkaline conditions.Simple uranyl peroxide complexes contain a single uranyl ion coordinated by as many as three peroxide groups that, each being bidentate, define the equatorial edges of hexagonal bipyramidal coordination polyhedra (4) (Fig. 1). These small complexes associate with counterions locally to balance charge in solution and readily crystallize as alkali metal salts (4-6). When peroxide bridges uranyl ions, the configuration is bent (7-9) and nanoscale cage clusters containing as many as 60 uranyl ions self-assemble in aqueous systems (10) (Fig. 1). These soluble clusters carry negative charges, are associated with counterions in solution, and can be crystallized. Under acidic conditions in deionized water, the combination of uranyl and peroxide causes the precipitation of studtite, ½ðUO 2 ÞðO 2 ÞðH 2 OÞ 2 ðH 2 OÞ 2 (11).Some insight into the geochemical interactions of uranium and peroxide that may occur in the Fukushima-Daiichi systems emerge from cases where deionized water, UO 2 , and ionizing radiation have been combined. Irradiated fuel was stored in the K-East Basins of the plutonium-productio...

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“…A significant H 2 pressure has been predicted to be generated due to the anoxic corrosion of the iron canisters. Dissolved hydrogen can significantly contribute to establishing reducing conditions in the near field [21][22][23] and effectively suppressing the UO 2 oxidation process even in the presence of a high alpha field. …”

Section: Discussionmentioning

confidence: 99%

Simulation of alpha dose for predicting radiolytic species at the surface of spent nuclear fuel pellets

Becker

Kienzler

2014

Open Chemistry

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In many countries, spent nuclear fuel is considered as a waste form to be disposed of in underground disposal. Under deep host rock conditions, a reducing environment prevails. In the case of water contact, long-term radionuclide release from the fuel depends on dissolution processes of the UO 2 matrix. The dissolution rate of irradiated UO 2 is controlled by oxidizing processes facilitated by dissolved species formed by alpharadiolysis of water in contact with spent nuclear fuel. To understand the effect of the radiation, the information of the dose rate at the surface of the fuel and its proximity is needed. α particles contribute strongly due to their high linear energy transfer. However, their dose rate and the energy deposition at the fuel surface are difficult to measure. Cylindrical fuel pellets as used in fuel rods show specific features, such as the rim zone, where a higher Pu concentration and a different porosity of the fuel matrix is present. The a particle dose rate was determined by simulations with the code MCNPX with focus on the rim zone of a pellet. As a result a 40% increased dose level in the rim zone exists in comparison to the center of a pellet. The potential dominant and inhomogeneous α-dose distribution is supposed to have a strong impact on radiolysis phenomena and in turn on an inhomogeneous dissolution of elements over the surface.

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Effect of external gamma irradiation on dissolution of the spent UO2 fuel matrix

Cited by 66 publications

References 23 publications

Determination of the equilibrium formation constants of two U(vi)–peroxide complexes at alkaline pH

Determination of the equilibrium formation constants of two U(vi)–peroxide complexes at alkaline pH

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Simulation of alpha dose for predicting radiolytic species at the surface of spent nuclear fuel pellets

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