Woodruff School of Mechanical Engineering

NRE 8011/8012 and MP 6011/6012 Seminar

Nuclear & Radiological Engineering and Medical Physics Programs


Property Characterization of Uranium-Silicide Compounds for Light Water Reactor Applications


Dr. Andy Nelson


Los Alamos National Laboratory (LANL)


Thursday, January 16, 2014 at 11:00:00 AM


Boggs Building, Room Room 3-47


Dr. Chaitanya Deo


The uranium-silicon binary system possesses a range of compounds that have been historically investigated and utilized to a limited extent as nuclear reactor fuels. Of the multiple compounds, U3Si and U3Si2 are most familiar; their high uranium densities have made them an intriguing choice for incorporation into composite plate fuels in research reactors and other low power core redesigns where retained neutronic performance was desired at lower enrichments. This increased uranium density compared with uranium dioxide has made them attractive to a new generation of nuclear fuels research driven by the renewed push for accident-tolerant light water reactor (LWR) fuels prompted by the events at Fukushima. A higher uranium density may motivate incorporation of U-Si phases into composite fuels that utilize secondary phases with the goal of increasing coping time during a cladding breach before fission products and/or actinides are released. However, surveys of the existing property databases of candidate U-Si compounds revealed that very little is known of even the more common uranium silicides with respect to their thermophysical and thermodynamic performance under steady state or possible transient LWR conditions.

The historic applications of U3Si and U3Si2 prompted limited investigation of the properties of these compounds, but the limitations in the existing data will be highlighted from the perspective of translation to LWR service. The results of fundamental thermophysical property studies at Los Alamos National Laboratory to provide the thermal conductivity, heat capacity, and thermal expansion data for U3Si, U3Si2, USi and U3Si5 from ambient conditions through melting will be presented. Compatibility of these compounds with both conventional nuclear fuels (i.e. UO2 and UN) and other oxidation resistant materials at high temperature will be discussed. New data relevant to the thermodynamic aspects of uranium silicide operation in an LWR environment will be summarized, including oxidation kinetics under water vapor atmospheres as well as stability under nitrogen and hydrogen environments at high temperatures. Finally, issues and potential solutions encountered during scaling of techniques employed for fabrication of high-purity uranium-silicides in the laboratory (10-2 kg) to the test irradiation environment (10 kg), and finally to possible commercial use (106 kg) will be examined.


Andrew T. Nelson is a senior research scientist in the Materials Science and Technology Division at Los Alamos National Laboratory, where he has worked since 2007. He received his B.S. in Engineering Mechanics followed by his M.S. and Ph.D. in Nuclear Engineering from the University of Wisconsin-Madison. His research interests are focused on the study of thermophysical properties of both metals and ceramics at high temperatures, with an emphasis on materials for nuclear applications and development of advanced experimental techniques. Nelson is also active in the characterization of materialsí performance in spallation environments as well as the design of materials systems for spallation target applications. Currently, Nelson is the Ceramic Fuels Irradiation Testing Lead within the DOE-NE Fuel Cycle Research and Development program and leads the Fuels Research Laboratory at Los Alamos.