Analysing the impact of autocatalysis on the dissolution kinetics of uranium and plutonium mixed oxide powders by optical microscopy

• Published in: Hydrometallurgy Vol. 216; p. 106010
• Main Authors: Garzon Losik, German, Lalleman, Sophie, Giraud, Martin, Magnaldo, Alastair, Schaer, Eric
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2023; Elsevier
• Subjects: Autocatalysis; Chemical engineering; Chemical Sciences; Dissolution; Optical microscopy; Spent nuclear fuel; Spent nuclear fuel; Optical microscopy; Autocatalysis; Dissolution
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2022.106010

Spent fuel dissolution is a key step in the recycling of nuclear fuel as it must ensure the production of a liquid solution consisted of concentrated nitric acid and the reusable fissile materials (uranium and plutonium), and decrease the fissile material hold-up in the system. This approach needs the understanding of chemical kinetic phenomena involved in the solid-liquid reaction. Optical microscopy was implemented to determine the dissolution rates of U-Pu-mixed oxides in nitric acid at different concentrations and temperatures for the first time. Mass transfer resistance was found negligible during dissolution indicating a process limited by the chemical reaction. Results showed a decrease in dissolution rate of the different oxides studied mainly due to the increment of plutonium content in the solids. Moreover, dissolution kinetics of solid U0.70Pu0.3O2 seems to improve when a catalyst is present in solution. Thus, the autocatalytic behaviour for the dissolution of spent fuel might occur for solids with 0% and up to 30%PuU+Pu of content. •Use of optical microscopy for the in-situ evolution of particles during dissolution.•Intrinsic dissolution kinetics determination for plutonium bearing solids.•Impact of the dissolution products on the mixed oxide consumption rate.