DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The structure of liquid UO2-x in reducing gas atmospheres

Journal Article · · Applied Physics Letters
DOI: https://doi.org/10.1063/1.4977035 · OSTI ID:1389313
ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [3];  [4];  [5];  [6];  [6]
  1. Materials Development Inc., Arlington Heights, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division
  2. Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division
  3. Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division; Stony Brook Univ., NY (United States). Mineral Physics Inst.
  4. Materials Development Inc., Arlington Heights, IL (United States)
  5. Materials Development Inc., Arlington Heights, IL (United States)A
  6. Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering

High energy X-ray diffraction experiments performed on hypostoichiometric UO2-x liquids in reducing gas mixtures of 95%Ar:5%CO and 95%Ar:5%H2 are compared to that conducted in a pure Ar atmosphere [Skinner et al., Science 346, 984 (2014)]. The measurements are pertinent to severe accident scenarios at nuclear reactors, where core melts can encounter reducing conditions and further shed light on the oxide chemistry of the low valence states of uranium, particularly U(III), which become stable only at very high temperatures and low oxygen potentials. The radioactive samples were melted by floating small spheres of material using an aerodynamic levitator and heating with a laser beam. In the more reducing environments, a 1.7% shift to lower Q-values is observed in the position of the principal peak of the measured X-ray structure factors, compared to the more oxidizing Ar environment. This corresponds to an equivalent elongation in the U-U nearest neighbor distances and the U-U periodicity. The U-O peak (modal) bond-length, as measured from the real-space total correlation functions, is also observed to expand by 0.9–1.6% under reducing conditions, consistent with the presence of 15–27% U3+ cations, assuming constant U-O coordination number. The slightly larger U-U elongation, as compared to the U-O elongation, is interpreted as a slight increase in U-O-U bond angles. Difficulties concerning the determination of the hypostoichiometry, x, are discussed, along with the future directions for related research.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1389313
Alternate ID(s):
OSTI ID: 1349361
Journal Information:
Applied Physics Letters, Vol. 110, Issue 8; ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

References (29)

Development and operating experience of a short-period superconducting undulator at the Advanced Photon Source journal April 2015
Area detector corrections for high quality synchrotron X-ray structure factor measurements
  • Skinner, Lawrie B.; Benmore, Chris J.; Parise, John B.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 662, Issue 1 https://doi.org/10.1016/j.nima.2011.09.031
journal January 2012
Accident tolerant fuels for LWRs: A perspective journal May 2014
Molecular-dynamic simulation of the thermophysical properties of liquid uranium journal June 2010
Molecular Dynamics study of the effects of non-stoichiometry and oxygen Frenkel pairs on the thermal conductivity of uranium dioxide journal February 2013
Ab initio investigation on oxygen defect clusters in UO2+x journal November 2008
Thermophysical properties of uranium dioxide journal March 2000
High-Temperature Levitated Materials book January 2010
Continuous Structural Transition in Glass-Forming Molten Titanate BaTi 2 O 5 journal November 2016
Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides journal September 1976
Experimental evidence of Xe incorporation in Schottky defects in UO 2 journal March 2015
Aerodynamic levitator for in situ x-ray structure measurements on high temperature and molten nuclear fuel materials journal July 2016
Determination of solidus-liquidus temperatures in the uo2 + x system (−0.50<0.20) journal May 1970
Melting of stoichiometric and hyperstoichiometric uranium dioxide journal June 2005
High-temperature studies of UO2 and ThO2 using neutron scattering techniques journal January 1987
Taking the measure of molten uranium oxide journal November 2014
Thermal Transport in Off-Stoichiometric Uranium Dioxide by Atomic Level Simulation journal April 2009
Neutron diffraction by germania, silica and radiation-damaged silica glasses journal February 1969
Progress in the thermodynamic modelling of the O–U binary system journal May 2002
Iron K-edge X-ray absorption near-edge structure spectroscopy of aerodynamically levitated silicate melts and glasses journal March 2017
Current knowledge on core degradation phenomena, a review journal April 1999
Low Cation Coordination in Oxide Melts journal April 2014
Chemical thermodynamic representation of journal February 1985
Premelting transition in uranium dioxide journal March 1993
Local structural variation with oxygen fugacity in Fe2SiO4+ fayalitic iron silicate melts journal April 2017
Extracting the pair distribution function from white-beam X-ray total scattering data journal June 2011
Molten uranium dioxide structure and dynamics journal November 2014
Molecular dynamics simulation of premelting and melting phase transitions in stoichiometric uranium dioxide journal September 2007
Two-dimensional detector software: From real detector to idealised image or two-theta scan journal January 1996

Cited By (3)

Corium lavas: structure and properties of molten UO2-ZrO2 under meltdown conditions journal February 2018
Temperature gradients for thermophysical and thermochemical property measurements to 3000 °C for an aerodynamically levitated spheroid journal January 2019
Influence of calcium content on the atomic structure and phase formation of alkali-activated cement binder journal August 2018