Dissolution kinetics of Indian PHWR natural UO2 fuel pellets in nitric acid – Effect of initial acidity and temperature

Desigan, N.; Augustine, Elizabeth; Murali, Remya; Pandey, N. K.; Mudali, U. Kamachi; Natarajan, R.; Joshi, Jyeshtharaj B.

doi:10.1016/j.pnucene.2015.03.001

Cited by 17 publications

(5 citation statements)

References 24 publications

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“…Claparede et al [51], Desigan et al [52] and Tocino et al [54] have found that the activation energy values they have calculated do not correspond to the expected values for a diffusion-controlled processes, and have concluded that the dissolution reaction is likely to take place under chemical control. Nevertheless, this conclusion relies on a serial transport, diffusion and reaction mechanism, which could not take place during uranium dioxide dissolution.…”

Section: Conclusion On the Influence Of The Physicochemical Parametermentioning

confidence: 99%

Dissolution of uranium dioxide in nitric acid media: what do we know?

Marc

Magnaldo

Vaudano

et al. 2017

EPJ Nuclear Sci. Technol.

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Abstract. This article draws a state of knowledge of the dissolution of uranium dioxide in nitric acid media. The chemistry of the reaction is first investigated, and two reactions appear as most suitable to describe the mechanism, leading to the formation of monoxide and dioxide nitrogen as reaction by-products, while the oxidation mechanism is shown to happen before solubilization. The solid aspect of the reaction is also investigated: manufacturing conditions have an impact on dissolution kinetics, and the non-uniform attack at the surface of the solid results in the appearing of pits and cracks. Last, the existence of an autocatalytic mechanism is questionned. The second part of this article presents a compilation of the impacts of several physico-chemical parameters on the dissolution rates. Even though these measurements have been undertaken under a broad variety of conditions, and that the rate determining step of the reaction is usually not specified, general trends are drawn from these results. Finally, it appears that several key points of knowledge still have to be clarified concerning the dissolution of uranium dioxide in nitric acid media, and that the macroscopic scale which has been used in most studies is probably not suitable.

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Section: Conclusion On the Influence Of The Physicochemical Parametermentioning

confidence: 99%

Dissolution of uranium dioxide in nitric acid media: what do we know?

Marc

Magnaldo

Vaudano

et al. 2017

EPJ Nuclear Sci. Technol.

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“…The result values of E a related to our experimental conditions agree with the results proposed by several investigators. Some authors, as presented in the Table 3 obtained nearly the same activation energy values of UO 2 pellets dissolution [16,18,22,32,33]. Finally, from plots of the kinetic Eq.…”

Section: Activation Energy Evaluationmentioning

confidence: 57%

“…The temperature dependency of the dissolution rate is governed by the Arrhenius equation which is given by Desigan et al [18]: where k is the overall rate constant, A is the frequency factor, E a is the activation energy (J/mol), R is the universal gas constant (8.314 kJ mol −1 ), and T is the reaction temperature (K). The rate constants for different temperatures were calculated from the plots in Fig.…”

Section: Activation Energy Evaluationmentioning

confidence: 99%

“…Desigan et al [18] have investigated the dissolution kinetics of Indian PHWR natural UO 2 fuel pellets in nitric acid: Effect of initial acidity and temperature. The results showed that the apparent activation energy estimated from the temperature effect of the chemical reaction was found to be about 90.5 kJ/mol and dissolution rate of UO 2 pellets was controlled by chemical reaction under the experimental conditions.…”

Section: Introductionmentioning

confidence: 99%

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Recycling Scrap from Un-Irradiated Nuclear Fuel by HNO3 Leaching

2020

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The work describes the wet chemical route process to recover and recycle a defective un-irradiated uranium dioxide sintered pellets. The optimal conditions of the un-irradiated UO 2 sintered pellets dissolution in Nitric acid solutions has been examined. The effects of acid concentration, contact time and temperature on dissolution action have been studied. The samples were exposed to leaching over a range of nitric acid concentrations 2-8 mol/L and temperatures from 20 to 70 °C. The stoichiometry of the dissolution reaction depends on the acidity of the solution. The shrinking core model (product diffusion control model and chemical reaction control model) was used to correlate the experimental results. Kinetics study shows that the chemical reaction model controls the dissolution of UO 2 sintered pellets in nitric acid solution. The average value of apparent activation energy estimated from the temperature effect of the chemical reaction was found to be about 101.40 kJ/ mol. The optimal conditions to dissolve the UO 2 sintered pellets in nitric acid solution have been proposed.

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“…Cordara et al 27 performed dissolution experiments in less concentrated nitric acid solutions (0.1 to 4 mol.L -1 ) and observed that the duration of the induction period was variable depending on temperature and nitric acid concentration, but ended systematically after a UO 2 weight loss of 0.5%, indicating that the required concentration of catalytic species might be reached at this stage. Nitrous acid is suspected to be the species increasing the dissolution rate of UO 2 [28][29][30][31][32] .…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Microstructural evolution of UO2 pellets containing metallic particles of Ru, Rh and Pd during dissolution in nitric acid solution: 3D-ESEM monitoring

et al. 2019

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Uranium dioxide containing 3 mol.% platinum group metals (PGMs) (Ru, Rh, Pd) was synthesized by hydroxide precipitation. The powders were converted to oxides, pelletized and sintered to prepare dense pellets of UO 2 incorporating PGMs particles. The characterization techniques performed revealed a microstructure similar to that of spent nuclear fuel (SNF). Dissolution tests in nitric acid demonstrated that in the presence of PGMs, the uranium dissolution rate was increased and the induction period was shortened. We used a new method based on the acquisition of Environmental Scanning Electron Microscopy (ESEM) micrographs recorded at three tilt angles and at different dissolution times. This method allowed the reconstruction of the topography of the solid/liquid interface. By monitoring the evolution of the solid/liquid interface during dissolution by means of 3D reconstructions, we were able to observe preferential dissolution zones in the vicinity of the PGMs particles and to determine microscopic dissolution rates for several regions of interest. PGMs particles were found mainly at the grain boundaries. In 0.1 M HNO 3 solution at 60˚C, the normalized dissolution rate for uranium at the grain boundaries reached R L (U) = (7 ± 1)×10-2 g.m-2 .d-1 , a value similar to the normalized dissolution rate determined for the whole image over the first 30 days of the experiment. This result showed that the dissolution occurred mainly at the UO 2 grain boundaries in the vicinity of PGMs particles. Furthermore, the 3D reconstructions of the solid/liquid interface were used to determine the evolution of the surface area of the pellet. By combining the weight losses determined at the macroscopic scale using the uranium concentrations in solution with the reactive surface area values, it was possible to estimate an effective normalized dissolution rate for the whole pellet.

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Dissolution kinetics of Indian PHWR natural UO2 fuel pellets in nitric acid – Effect of initial acidity and temperature

Cited by 17 publications

References 24 publications

Dissolution of uranium dioxide in nitric acid media: what do we know?

Dissolution of uranium dioxide in nitric acid media: what do we know?

Recycling Scrap from Un-Irradiated Nuclear Fuel by HNO3 Leaching

Microstructural evolution of UO2 pellets containing metallic particles of Ru, Rh and Pd during dissolution in nitric acid solution: 3D-ESEM monitoring

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