Thank you for agreeing to this interview! Please tell us about yourself, what is your current position?
My name is Julien Margate, I am 26 years old and I come from Paris, France. I am currently doing a PhD in the physical chemistry of actinides at the Institute for Separation Chemistry in Marcoule (ICSM) in the Laboratory for Sonochemistry in Complex Fluids (LSFC). My thesis is conducted under the supervision of Sergey Nikitenko and Matthieu Virot from ICSM and is carried out in collaboration with Philippe Moisy and Thomas Dumas from CEA Marcoule. I am in the third and final year of my thesis, which deals with the preparation, structural characterization, and reactivity of actinide peroxides. My research involves studies with uranium, which are performed at ICSM, while experiments with plutonium are performed at the Atalante facility in a dedicated glove box.
What does your research into uranium involve?
My research focuses first on the formation of uranyl peroxide. Recent studies show that the formation of mineral uranyl peroxides, metastudtite and studtite, can be observed in geological storage conditions (by oxidation of uranium dioxide) or following a nuclear accident, e.g., Fukushima. The formation of uranyl peroxides resulting from radiolysis can thus lead to the corrosion of nuclear fuel and the release of radionuclides in the surroundings. Sonochemistry, which deals with the effect of powered ultrasound on chemical reactions, is known to share some similarities with radiolysis particularly through the in-situ generation of hydrogen peroxide resulting from water molecule splitting. Therefore, this approach can be used as an original alternative to evaluate the effect of hydrogen peroxide on actinide materials, and has been investigated for several years by the ICSM sonochemistry group. Careful choice of parameters can give a dramatic spike of hydrogen peroxide production under mild conditions with observation of additional physical effects, e.g., erosion of solids, mass transfer, fragmentation, etc.
Tell us more about your investigations using sonolysis
I have been studying the sonolysis of uranium dioxide in pure water and slightly acidic media under oxygenated atmosphere. After the preparation of well-characterized uranium dioxide platelets using the oxalic route, we observed complete conversion into metastudtite under ultrasound. Detailed investigations on the remaining solutions using UV-Vis. absorption spectroscopy and ICP-OES and solid residues using SEM, XRD, and FTIR techniques allowed us to attribute this behavior to the sonochemical generation of hydrogen peroxide. The formation of crystalline studtite structures was observed on the surface of uranium dioxide platelets with a preservation of morphology, suggesting a complex formation mechanism other than classical dissolution/reprecipitation. Interestingly, under specific sonochemical conditions, center-holed platelets are observed. We proposed a mechanism based on a sonocapillary effect giving rise to circulation of the reactants within the oxide. This lead to a publication in the Journal of Hazardous Materials in 2023 and a poster prize at the conference Plutonium Futures 2022.
Can you tell us about your plutonium work?
My plutonium studies examine the formation of plutonium peroxide species. Over five decades ago, the formation of plutonium peroxo complexes was described through the addition of hydrogen peroxide to acidic plutonium(IV) solutions, leading to the creation of colored complexes, which transition from brown to red as the concentration of hydrogen peroxide increases. Excessive quantities of hydrogen peroxide relative to plutonium result in the formation of green precipitates, which have been used as precursors for plutonium dioxide or in waste management processes. Various structures have been proposed for these complexes and solid compounds, but definitive evidence has remained elusive until now. During my thesis, we synthesized a new peroxo-based compound of tetravalent plutonium by adding dilute solutions of plutonium(IV) previously stabilized in nitric media into highly concentrated hydrogen peroxide solutions at a pH of 1–2. The as-prepared solution of green color was found to be very stable. Vibrational and spectroscopic investigations confirmed the peroxide and polynuclear structure of the compound. The latter bears striking similarities to the green solid compound used historically in the nuclear industry and during the Manhattan project. This discovery sheds new light on a chapter of science deeply intertwined with the history of nuclear research. A publication on this work is currently under submission.
How did you become an actinide scientist?
I started my academic journey by pursuing a degree in chemistry with a specialization in physical chemistry and spectroscopy at the University of Paris-Saclay in France. I successfully graduated with distinction, obtaining a comprehensive understanding of physical chemistry, complemented by a robust grounding in geoscience. As my academic path unfolded, I directed my focus towards nuclear sciences, choosing relevant study projects and optional subjects to align with this interest.
Diving into the realm of scientific research, I undertook multiple internships in research laboratories, exploring diverse areas such as materials under irradiation, spectroscopy, and geochemistry. Subsequently, I enrolled in the nuclear engineering master's program at University of Paris-Saclay and the ChimieParisTech engineering school. This internationally renowned program, conducted in partnerships with
research institutes such as IJClab and CEA, as well as prominent nuclear industry players like EDF, CEA, Orano, and Framatome. Delivered in English, this program attracts high-caliber students worldwide and covers a broad spectrum of nuclear-related topics, ranging from the nuclear fuel cycle to reactor physics, nuclear power plant design, and waste management. During this program, I learned a lot about nuclear science, including radiochemistry, chemistry under radiation, nuclear physics, and nuclear engineering, and received the EDF Excellence Scholarship. In my final year, I specialized in actinide chemistry and chemistry under radiation, and I proudly completed my master's degree with honors.
What first drew you to study plutonium?
I find this a complex question. I have always loved science and how it shapes our world. When I was studying physical chemistry, I got into some cool subjects like the physicochemistry of d- and f-block elements, nuclear physics, and radiation chemistry. That is when I discovered a real interest in actinide chemistry. After doing research at IJCLab (Laboratoire de Physique des deux Infinis Irène Joliot-Curie) in Orsay, France, during an internship, my interest in this field got even stronger. Therefore, I decided to pursue a master's in nuclear studies based on my professors' advice. I delved deeper into nuclear sciences, focusing on fundamental physicochemistry, especially in radiation and actinide chemistry. Later on, I chose to continue with research, going for a PhD. I got a thesis topic on actinide peroxides at CEA Marcoule, recommended by one of my professors. It perfectly matched my interests, so I went for it. This topic examines the chemistry and structure of actinide peroxides, with a focus on uranium and plutonium due to their use in industries and the military. Lastly, what makes plutonium truly beautiful is not just its scientific importance but also the mesmerizing colors it displays in different oxidation states. From vibrant yellows to striking reds and purples, these colors result from the interplay between plutonium's electronic structure and its surroundings, adding an artistic touch to its exploration in the periodic table.