JRP CALL information
Supported By

European Commission

Short description of the work
The aim of the study is to obtain new experimental data on the high temperature behaviour of crucial systems involved in a nuclear reactor severe accident. The U-Zr-O and Fe-Zr-O systems were studied using the laser heating setup at ITU. Three samples within the U-Zr-O system and six samples within the Fe-Zr-O system were investigated. A need of data exists especially in the oxygen-poor region of the aforementioned systems. The samples were heated using a Nd:YAG laser above the melting point using different experimental atmospheres (compressed air and argon). The laser was then switched off and the samples quenched to ambient temperature. Several cycles of heating-cooling were used in order to have a good statistics and to test the reproducibility of the results. Using a pyrometer working at 650 nm the radiance temperature was measured. In parallel a 256-channel spectrometer working between 450-1000 nm was used to obtain an estimation of the emissivity of the samples. A clear effect of the experimental atmosphere on the melting results was observed. In fact, especially when Fe and Zr-containing samples are concerned, the oxygen potential of the buffer gas may drive an overwhelming oxidation of the samples.
Part of the post-experiment analyses (SEM-EDS, XRD) will be performed at ITU. The Fe-Zr-O samples will be analysed at the CEA Saclay using the same techniques.
The measured transition temperatures will be used for a thermodynamic modelling of the investigated systems using the CALPHAD method. The thermodynamic reassessment of these systems will be then integrated to the TAF-ID thermodynamic database for the description of the in-vessel corium formed during a severe accident in a nuclear reactor.

 

Short description of the work
The determination of complexation constants by traditional methods such as solvent extraction, potentiometry, spectrophotometry, and calorimetry can be quite time consuming, labor intensive, and typically require work with larger quantities of materials. Methods that minimize the time, effort, and use of hazardous and/or radioactive materials are more cost-effective, and improve safety. This project is focused on developing a different approach for determining complexation constants that is much more rapid than the more established methods, and that requires minimal volume of solution. In this work, capillary electrophoresis (CE) is used to correlate mobilities of metal-ligand complexes with solution conditions, including ligand concentration.
For this initial visit, we investigated the complexation constants between alpha-hydroxyisobutyric acid (HIBA) and actinides of various oxidation states in solvent media composed of water and methanol. CE was coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS). CE-ICP-MS allows for the rapid, simultaneous detection of elements in solution matrices, such as the 10% (v/v) methanol media used in these experiments. The actinides used in the experiments were curium (III), plutonium (IV), neptunium (V), and uranium (VI). We were able to determine that mobilities of the actinides decreased with an increasing concentration of the ligand. This behavior indicates that the speciation of the each actinide is changing as the mobility is dependent on both the size and charge of the analyte. As the ligand concentration is increased, the prevalence of higher order species is increased, which in turn decreases the charge on the overall actinide-ligand complex as well as increasing the size of the complex.

The main goal of this work is to use the experimental data collected at INE to estimate stability constants in this mixed aqueous-methanol system. The experimental results are currently being evaluated for the estimation of the stability constants between the indicated actinides and HIBA.

 

Short description of the work
Seven samples of 1 mM Am(III) in the presence of 0.03 M lactate at varying pH value (1-7) have been prepared at the Institute of Nuclear Waste Disposal (KIT, Karlsruhe, Germany). Due to the stable operation at the ESRF it was possible to measure 12-15 scans of sample 1-6. Due to a clearly visible precipitation in sample 7, possibly a result of hydrolysis at pH 7, 7 scans were measured of both the clear solution and the precipitate.
The obtained EXAFS spectra will now be analyzed to obtain the molecular structure (coordination numbers and Am-O, Am-C distances) of the Am(III) lactate species as a function of the pH value. Furthermore, the experimental EXAFS spectra will be treated by iterative transfortmation factor analysis and the results will be compared to speciation calculations using tabulated thermodynamic data. The results will add to a general molecular-level understanding of the geochemical behavior of trivalent actinides.
The results will be presented at national and international conferences and meetings. Furthermore, publication of the data in a peer review journal is planned.

 

 

Short description of the work
In the framework of the partitioning and transmutation, the Am recycling is one of the milestones requiring notably a full understanding of the Am electronical properties. Different XANES studies at LIII edges have shown different charge distribution in uranium-americium mixed oxides. U(IV) and Am(III/IV) were found in sol-gel synthesized materials while U(IV/V) and Am(III) were observed in powder metallurgy prepared compounds. In order to understand this discrepancy, the U and Am oxidations states in uranium-americium oxides have been studied using high resolution XANES (HRXANES) at M4 edge. Compared to L3 XANES, M4 HR XANES allows a significant improvement of the spectrum resolution by overcoming the core-hole lifetime broadening ffects leading then to sharper spectral features. In this context, the M4 XANES spectra of U reference compounds (UO2, U3O8, UO3), Am reference compounds (AmO2) and uranium-americium mixed oxides have been collected. Comparing these latter spectra with the U and Am reference samples, it has been established that Am is purely trivalent in uranium-americium mixed oxides while U is tetra- and pentavalent.

 

 

Short description of the work

This project is focused on the comparative study of Pu(IV) intrinsic colloids obtained by sonolysis of PuO2 in pure water and by hydrolysis of Pu(IV) nitric acid solutions. Ultrasonic treatment of PuO2 calcined at 520°C (SBET=13.6 m2•g-1) and 600°C (SBET=13.3 m2•g-1) in contact with air for 12h has been performed using 20 kHz ultrasound at the acoustic power of 0.34W•mL-1 in pure water saturated with argon or Ar/10%CO. Temperature of 25°C inside the sonoreactor during sonolysis was controlled by a cryostat. The reactor was installed in the hot glove box at ATALANTE research facility. Hydrolytic Pu(IV) colloids were prepared by the dilution of concentrated Pu(IV) nitric solutions in pure water. The obtained colloids have been characterized by UV/Vis, SEM and XAFS spectroscopy. XAFS measurements at Pu L3 edge (XANES and EXAFS), have been performed at ROBL beamline (ESRF Grenoble). Soft NEXAFS spectrum and STXM measurements have been performed at MES Beamline 11-0-2 (ALS Berkeley) to probe plutonium N4,5 edges. The samples of Pu colloids have been sent to JRC-ITU for HRTEM analysis. The preliminary TEM analysis confirmed the STXM data that sonochemical colloid is composed of 20-30 round shaped nanoparticles. Further HRTEM study will be performed in 2015 to identify the atomic structure of both, sonochemical and hydrolytic colloids.

 

Short description of the work

In the event case of a clad breach in a Sodium-cooled Fast Reactor (SFR), sodium will enter the pin and react with the (U1-xPux)O2 fuel to form compounds of general formula Na3U1-xPuxO4. One main goal of the International Generation IV program is moreover to incorporate minor actinides (Np,Am) to the fuel so as to recycle them and reduce the burden for future generations. This will introduce a more complex chemistry with sodium, for which many data are missing. As part of our program of research, we are currrently investigating the structural, thermomechanical and thermodynamic properties of the numerous compounds in the Na-Np-O, Na-Pu-O systems and Na-(U,Pu)-O systems: Na2MO3, Na3MO4, Na2MO4, Na4MO5, Na2M2O7, Na5MO6 (M=U,Pu,Np). The later compounds present many oxidation states, namely IV, V, VI and VII, which define the oxygen potential required for their formation. In the present work, we have characterized those different oxidation states, and local structures of the uranium, neptunium, and plutonium cations using X-ray Absorption Structure (XAS) at the HZDR Rossendorf Beamline (ROBL). Such a study is of primary importance for the thermodynamic modeling of the system for SFRs, which is the ultimate goal of our research.

 

Short description of the work

The aim of these EXAFS measurements is to determine the nature of uranium (VI) species extracted in an ionic liquid (IL) by two kinds of extractant molecules: a neutral malonamide-base extracting molecule (DMDBMA) and an ionic liquid functionalized with a CMPO group (FIL-CMPO), from acidic aqueous solutions (HNO3 or HClO4). The extraction of charged complexes, instead of neutral complexes formed in the usual organic solvents, was postulated from our previous experimental. We now want to determine experimentally the structure of extracted uranyl species, i.e. the stoichiometry, ligands nature and number.
During the allocated beam time, we have analysed 15 samples at the uranium L3 edge in transmission and fluorescence detection. 8 solutions are reference samples containing a known [extractant molecule]/[NO3- or ClO4-]/[UO22+] ratio, the others were obtained by liquid liquid extraction of uranium in different experimental conditions (nature and concentration of the acid, nature of the extractant molecule).
The preliminary analysis of the spectra show that uranyl is extracted as a bivalent cationic complex at low acidic concentration, whatever the extraction molecule. Using DMDBMA, the nature of the extracted species in the IL phase changes when the aqueous acidic concentration increases, but this is not the case when the extraction is made using the FIL-CMPO molecule. A precise data analysis will allow us to determine precisely the nature of those complexes, and thus, determine the mechanism leading to their extraction in the studied ionic liquid.

 
More Articles...