4 research outputs found
Reducing Uncertainties Affecting the Assessment of the Long-Term Corrosion Behavior of Spent Nuclear Fuel
Reducing
the uncertainties associated with extrapolation to very long term
of corrosion data obtainable from laboratory tests on a relatively
young spent nuclear fuel is a formidable challenge. In a geologic
repository, spent nuclear fuel may come in contact with water tens
or hundreds of thousands of years after repository closure. The corrosion
behavior will depend on the fuel properties and on the conditions
characterizing the near field surrounding the spent fuel at the time
of water contact. This paper summarizes the main conclusions drawn
from multiyear experimental campaigns performed at JRC-ITU to study
corrosion behavior and radionuclide release from spent light water
reactor fuel. The radionuclide release from the central region of
a fuel pellet is higher than that from the radial periphery, in spite
of the higher burnup and the corresponding structural modifications
occurring at the pellet rim during irradiation. Studies on the extent
and time boundaries of the radiolytic enhancement of the spent fuel
corrosion rate indicate that after tens or hundreds of thousands of
years have elapsed, very small or no contribution to the enhanced
corrosion rate has to be expected from α radiolysis. A beneficial
effect inhibiting spent fuel corrosion due to the hydrogen overpressure
generated in the near field by iron corrosion is confirmed. The results
obtained so far point toward a benign picture describing spent fuel
corrosion in a deep geologic repository. More work is ongoing to further
reduce uncertainties and to obtain a full description of the expected
corrosion behavior of spent fuel
Complexation of Europium(III) by Bis(dialkyltriazinyl)bipyridines in 1-Octanol
The present work focuses on highly selective ligands
for An<sup>III</sup>/Ln<sup>III</sup> separation: bis(triazinyl)bipyridines
(BTBPs). By combining time-resolved laser-induced fluorescence spectroscopy,
nanoelectrospray ionization mass spectrometry, vibronic sideband spectroscopy,
and X-ray diffraction, we obtain a detailed picture of the structure
and stoichiometry of the first coordination sphere of Eu<sup>III</sup>-BTBP complexes in an octanolic solution. The main focus is on the
1:2 complexes because extraction studies revealed that those are the
species extracted into the organic phase. The investigations on europium(III)
complexes of BTBP with different triazin alkylation revealed differences
in the formed complexes due to the bulkiness of the ligands. Because
of the vibronic sidebands in the fluorescence spectra, we were able
to detect whether or not nitrate ligands are coordinated in the first
coordination sphere of the Eu-BTBP complexes. In solution, less sterically
demanding BTBP offers enough space for additional coordination of
anions and/or solvent molecules to form 9-coordinated Eu-BTBP 1:2
complexes, while bulkier ligands tend to form 8-fold-coordinated structures.
We also report the first crystal structure of a Ln-BTBP 1:2 complex
and that of its 1:1 complex, both of which are 10-coordinated
Complexation of Europium(III) by Bis(dialkyltriazinyl)bipyridines in 1-Octanol
The present work focuses on highly selective ligands
for An<sup>III</sup>/Ln<sup>III</sup> separation: bis(triazinyl)bipyridines
(BTBPs). By combining time-resolved laser-induced fluorescence spectroscopy,
nanoelectrospray ionization mass spectrometry, vibronic sideband spectroscopy,
and X-ray diffraction, we obtain a detailed picture of the structure
and stoichiometry of the first coordination sphere of Eu<sup>III</sup>-BTBP complexes in an octanolic solution. The main focus is on the
1:2 complexes because extraction studies revealed that those are the
species extracted into the organic phase. The investigations on europium(III)
complexes of BTBP with different triazin alkylation revealed differences
in the formed complexes due to the bulkiness of the ligands. Because
of the vibronic sidebands in the fluorescence spectra, we were able
to detect whether or not nitrate ligands are coordinated in the first
coordination sphere of the Eu-BTBP complexes. In solution, less sterically
demanding BTBP offers enough space for additional coordination of
anions and/or solvent molecules to form 9-coordinated Eu-BTBP 1:2
complexes, while bulkier ligands tend to form 8-fold-coordinated structures.
We also report the first crystal structure of a Ln-BTBP 1:2 complex
and that of its 1:1 complex, both of which are 10-coordinated
High-Resolution Solid-State Oxygen-17 NMR of Actinide-Bearing Compounds: An Insight into the 5f Chemistry
A massive interest has been generated
lately by the improvement of solid-state magic-angle spinning (MAS)
NMR methods for the study of a broad range of paramagnetic organic
and inorganic materials. The open-shell cations at the origin of this
paramagnetism can be metals, transition metals, or rare-earth elements.
Actinide-bearing compounds and their 5f unpaired electrons remain
elusive in this intensive research area due to their well-known high
radiotoxicity. A dedicated effort enabling the handling of these highly
radioactive materials now allows their analysis using high-resolution
MAS NMR (>55 kHz). Here, the study of the local structure of a
series of actinide dioxides, namely, ThO<sub>2</sub>, UO<sub>2</sub>, NpO<sub>2</sub>, PuO<sub>2</sub>, and AmO<sub>2</sub>, using solid-state <sup>17</sup>O MAS NMR is reported. An important increase of the spectral
resolution is found due to the removal of the dipolar broadening proving
the efficiency of this technique for structural analysis. The NMR
parameters in these systems with numerous and unpaired 5f electrons
were interpreted using an empirical approach. Single-ion model calculations
were performed for the first time to determine the <i>z</i> component of electron spin on each of the actinide atoms, which
is proportional to the shifts. A similar variation thereof was observed
only for the heavier actinides of this study