LDRD Seminar Series: ‘Levitating Liquids — Probing Nuclear Fuels at Extreme Conditions’
Physicist Chris Benmore (XSD) will discuss his Laboratory-Directed Research and Development (LDRD) sponsored work at the LDRD Seminar Series presentation Tuesday, Jan. 17, 2017.
“Levitating Liquids — Probing Nuclear Fuels at Extreme Conditions” will begin at 12:30 p.m. in the Bldg. 203 Auditorium. All are welcome to attend.
The Fukushima Daiichi nuclear reactor accident, containment and subsequent clean-up process underscores the need for understanding nuclear fuel interactions at the atomic level. To date, these rare but catastrophic events have coexisted with national needs for nuclear energy, and emphasize the importance of characterizing the fundamental properties and behavior of nuclear fuels under severe accident conditions. The experimental challenges associated with measuring radioactive materials at the extremely high temperatures, in excess of 3000 degrees Kelvin, have until recently prevented liquid state structural characterization studies. The majority of nuclear reactors use mixed oxide fuels with UO2 and PuO2 as their main constituents. Their melting points and high temperature structures therefore represent important engineering parameters, since they define the operational limits of the nuclear material in its environment and are key factors in determining fuel performance and safety.
Benchmark structural data on nuclear fuel components such as UO2 and PuO2 are also critical in developing realistic interatomic potentials that describe changes in atomic interactions prior to and during melting. Understanding correlations between uranium and other atoms in “corium”, epitomized by the Chernobyl “lavas” that form during core meltdown, are essential for modeling severe accident scenarios. One of the most important interactions in the radioactive lava is that of the molten fuel and its cladding material, which is commonly represented by the UO2-ZrO2 system.
Traditional furnace heating experiments of nuclear fuel materials are often affected by extensive interactions between the samples and their containers. In this presentation we will demonstrate how the demanding experimental requirements of very high temperatures and elimination of container contamination have been met through the development of a laser-heated aerodynamic levitation system. Integrating this system on a high-energy beamline at the Advanced Photon Source (APS), we have conducted the first measurement of the structure of molten uranium dioxide, and obtained a realistic assessment of the multitude of atomistic models in the literature. This unique instrumentation also enables advancements in ultra-high temperature crystallography. For example, insights can be made into the pre-melting behavior of the oxygen sub-lattice in UO2, which is believed to be associated with a second order λ-transition at 2670K. We will show that Rietveld refinements of X-ray data enable an accurate assessment of the thermal expansion of nuclear materials at high temperatures, an important factor in the design of new cladding materials. Deviations from stoichiometry in different atmospheres can also be explored by changing the levitation gas enabling a wide range of accident conditions to be replicated. Specifically, this LDRD is aimed at providing the methodology to address the U.S. Department of Energy’s interests in pursuing the characterization and development of accident tolerant fuels, defined as those fuels which could operate with the loss of active cooling and maintain reactor performance under normal operating conditions.
Chris Benmore joined Argonne in 2000 as the instrument scientist for Glass, Liquid and Amorphous Materials Diffractometer at the Intense Pulsed Neutron Source. For the past decade he has worked on high energy X-ray diffraction beamlines at the APS. Benmore is best known for his experiments on quantum effects in liquid water and amorphous materials at extreme conditions. He has been an adjunct professor in the physics department at Arizona State University since 2008 and works closely with the company Materials Development Incorporated in Chicago. In 2012 he received the University of Chicago medal for distinguished performance. Benmore was educated in England receiving his Ph.D. in experimental physics in from the University of East Anglia. He was postdoctoral fellow in Canada and a neutron scattering scientist at the Rutherford Appleton Laboratory in the UK prior to coming to Argonne.