TY - JOUR
T1 - Synthesis, Characterization, and Enthalpies of Formation of Uranium Substituted Zirconolites
AU - Subramani, Tamilarasan
AU - Baker, Jason
AU - Xu, Hongwu
AU - Navrotsky, Alexandra
N1 - Funding Information:
Research presented in this article was supported by the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory (LANL) under project number 20180007 DR. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. LANL, an affirmative action/equal opportunity employer, is managed by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract 89233218CNA000001.
Publisher Copyright:
© 2020 American Chemical Society.
PY - 2020/10/15
Y1 - 2020/10/15
N2 - Uranium substituted zirconolite samples based on CaZrTi2O7 have been synthesized by a conventional solid-state method in air and structurally characterized by powder X-ray diffraction. The uranium substituted compounds crystallize in a monoclinic C2/m structure like the parent phase. The oxidation state of uranium has been confirmed to be mostly UVI by X-ray absorption spectroscopy (XAS). The enthalpies of formation from oxides (H°f,ox) determined by high temperature oxide melt solution calorimetry of uranium substituted compounds are more exothermic than that of the parent CaZrTi2O7. The enthalpies of decomposition of uranium substituted zirconolites into perovskite (CaTiO3), UO3, and other binary oxides are endothermic by about 20 kJ/mol, implying that decomposition is probably thermodynamically unfavorable. The results show that zirconolite is a thermodynamically stable host for uranium in high level nuclear waste.
AB - Uranium substituted zirconolite samples based on CaZrTi2O7 have been synthesized by a conventional solid-state method in air and structurally characterized by powder X-ray diffraction. The uranium substituted compounds crystallize in a monoclinic C2/m structure like the parent phase. The oxidation state of uranium has been confirmed to be mostly UVI by X-ray absorption spectroscopy (XAS). The enthalpies of formation from oxides (H°f,ox) determined by high temperature oxide melt solution calorimetry of uranium substituted compounds are more exothermic than that of the parent CaZrTi2O7. The enthalpies of decomposition of uranium substituted zirconolites into perovskite (CaTiO3), UO3, and other binary oxides are endothermic by about 20 kJ/mol, implying that decomposition is probably thermodynamically unfavorable. The results show that zirconolite is a thermodynamically stable host for uranium in high level nuclear waste.
KW - actinides
KW - high level nuclear waste immobilization
KW - stability
KW - thermochemistry
KW - zirconolite
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U2 - 10.1021/acsearthspacechem.0c00182
DO - 10.1021/acsearthspacechem.0c00182
M3 - Article
AN - SCOPUS:85096290322
SN - 2472-3452
VL - 4
SP - 1878
EP - 1887
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 10
ER -