LAWRENCE BERKELEY NATIONAL LABORATORY
The design of advanced nuclear fuels poses considerable challenges in terms of understanding the physical phenomena occurring in complex systems under extreme conditions, with length scales from the atomic to the macroscopic, and over time scales from femtoseconds to years. After irradiation, fuels exhibit a complex nano- and micro-scale structure with multiple chemical components, oxidation states, and crystal phases. Controlling this structure may reduce the potential for failure of nuclear fuels by providing pathways for fission gas release, enhancing radiation tolerance, and improving heat transfer capabilities. Improvements in the performance of advanced nuclear fuels will require new strategies for actinide nanomaterials synthesis, coupled with an improved understanding of how nanoscale structure is both an advantage and a limitation to fuel designs.
This presentation will describe our recent efforts to use actinide synthesis, synchrotron spectroscopy, and first-principles calculations to develop a basis for the rational design of advanced nuclear fuels. Work began by developing an intuitive theoretical framework for relating actinide electronic structure and physical properties. This included spectroscopic analyses of the actinyl ions, which are perhaps the most ubiquitous high-valent molecules in nuclear chemistry. Our approach also included extended structures such as actinide–aluminum alloys, which are relevant to strategies for stabilizing delta-plutonium. These molecular-level insights were used to invent new synthetic methodologies that provide control over the mechanisms of formation, chemical reactivities, and physical properties of actinide materials. The discussion will also include preliminary results demonstrating how nanoscale structure can impact the physical properties most relevant to fuel performance.
Dr. Stefan Minasian received a B.A. in Chemistry from Reed College in 2002 with Prof. Margaret Geselbracht before coming to the University of California, Berkeley as a graduate student in the Department of Chemistry with Prof. John Arnold. His interest in nuclear chemistry began while developing syntheses for the first molecular compounds to exhibit unsupported metal–metal bonds between uranium and group 13 elements (e.g., aluminum and gallium). These discoveries ignited new theoretical discussions regarding heavy element structure–property relationships, in particular the relative roles of the 5f and 6d orbitals in controlling physical phenomena. Following completion of his Ph.D. in 2010, Dr. Minasian joined research groups at Los Alamos National Laboratory (LANL) and Lawrence Berkeley National Laboratory (LBNL), and held two concurrent Seaborg Fellowships in the Seaborg Institute at LANL and the Glenn T. Seaborg Center at LBNL. During this joint appointment, he led a collaborative effort to develop direct spectroscopic probes of actinide bonding and was at the forefront of a growing movement in nuclear chemistry that has changed how scientists formulate models of electronic structure. He became a Staff Scientist in the Heavy Elements Chemistry group in the Chemical Sciences Division at LBNL in 2014, where his current research occurs at the interface of materials design, inorganic spectroscopy, and theory. Controlling the chemical and physical properties of the poorly-understood transuranium elements (e.g., neptunium and plutonium) is of particular concern given their central role in scientific and technological applications for actinides in nuclear fuels, separations, and waste forms. The collaborative effort brings together scientists at multiple universities and DOE National Laboratories, and leverages access to cutting-edge instrumentation at several user facilities including the Advanced Light Source, Molecular Foundry, Stanford Synchrotron Radiation Lightsource, and Canadian Light Source.