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European Commission

Short description of the work
A series of different composition prototypical corium materials were synthesised at the JRC-ITU and Laser heated (and cooled) at controlled atmosphere simulating high temperature phase changes during severe accidents. In order to fully understand the behaviour of such materials, oxidation state, geometric and electronic structure data, X-ray methods available at ESRF were used to understand the local electronic structure (determined by EXAFS) and the chemical state (from XANES).
In addition, samples with Pu content typical of corium formed from a melted
MOX fuel was analysed in a similar manner.
In summary a total of 16 samples were measured over 4 days shift.
compositions included: 3xUO2 reference, melted under argon and in air;
3x U(0.5)Zr(0.5)O2 reference, melted under argon and in air; 3x U(0.2)Zr(0.8)O2 reference, melted under argon and in air; 2x U(0.6)Zr(0.4)O2 reference and melted in air; 2x U(0.8)Zr(0.2)O2 reference and melted in air; 3xU(0.44)Pu(0.08)Zr(0.48)O2 reference, melted under argon and in air.
For all samples Zr K and U L edge data were collected.

 

Short description of the work
In the context of studies concerning the long term behaviour of nuclear glasses and in order to understand the influence of radioactivity on the glass leaching especially on the residual rate step, two different R7T7-type borosilicate glasses with a different alpha dose rate were leached in the shielded line C19 in ATALANTE facility. Solution analyses showed a drop in the alteration tracer releases indicating the formation of a protective alteration layer at the solid - solution interface. The current project objective was to better understand the nature and the morphology of this protective alteration layer formed on the radioactive glass surfaces, particularly concerning the behaviour of radionucleides, by analysing radioactive glass powders previously leached by transmission electron microscopy and secondary electron microscopy.
The two different samples of altered doped glasses have been sent to ITU for solid characterizations. The TEM grids have been prepared by grounding the glass powders into very thin fractions. For both glasses, we were able to observe the different parts of the alteration layers by TEM: alteration gel and phyllosilicates. Their quantities were different from one glass to the other one. Some black "grains" have also been observed on the most doped sample leached, and seem to be enriched in rare earth elements. Some complementary TEM and SEM characterizations are now needed to complete these observations

 

Short description of the work
This joint research project has studied Np(V)-U(VI) cation-cation interactions (CCIs) in organic solution (TBP/TPH), which are relevant to solvent reprocessing applications. CCIs are characteristic of pentavalent actinyl ions, and it is thought that the formation of a Np(V)-U(VI) species may synergistically enhance the extraction of Np(V) in the PUREX process, as well as affecting the redox rates of reactions. Spectroscopic techniques (UV-vis-nIR and Raman) available at CEA Marcoule (Atalante) have been used to study organic solutions (TBP/TPH) containing Np(V) in the presence and absence of U(VI). An additional opportunity arose to analyse these organic solutions by EXAFS at the European Synchrotron Radiation Facility. EXAFS data acquired at the ERSF is currently undergoing analysis, which is challenging due to difficulties faced with controlling Np(V) disproportionation (results presented in TALI-C05-01).
UV-vis-nIR spectroscopy results have shown that many different Np(V) species can exist in organic solution, for example Np(V)-TBP, Np(V)-Np(IV)-TBP, Np(V) U(VI)-TBP and possibly Np(V)-U(VI)-DBP depending on the solution conditions. However, for the recorded Raman spectra of Np(V)-, Np(VI) and Np(V)-U(VI) in 30 % TBP, no spectral shift of the Raman bands was observed. The Raman band for NpO2+ may have been observed at 770 cm-1 in 30 % TBP/TPH; however, further Raman spectroscopy must be performed to determine the vibrational bands due to nitrate and TBP. Additionally, more concentrated Np and U solutions in TBP/TPH could be prepared to try to observe the Raman vibrational peaks for the Np(V) U(VI) CCI.

 

Short description of the work
Exchange interaction through interface between a ferromagnet and an antiferromagnet may result in the magnetic exchange bias (EB) effect [1]. The EB manifests itself as a shift of the magnetic hysteresis loops along the field direction when the sample is field cooled below the Néel temperature (TN) of the antiferromagnet. This property has become of great technological value for applications in magnetic sensors based on spin-valves or tunnel junctions [2]. In this project, we prepared several types of samples.

 

Short description of the work
During this stay, X-ray Absorption Spectroscopy measurements on nuclear fuel samples at high temperature and under controlled atmospheres were performed. We modified our experimental set-up to accept slices of sintered nuclear fuel pellets. Initially, UO2 and (U,Am)O2 samples were planned for this experiment but due to safety issues, no sample containing plutonium could be sent to ANKA-INE. Nevertheless, in situ XANES (X-ray Absorption Near Edge Structure) spectra were successfully collected on UO2 samples and also on U0.75La0.25O2 and U0.50La0.50O2 samples as surrogates for (U,Am)O2 compounds. During this experiment, data at uranium L3 edge were collected for the 3 compositions from 300 K up to 2023 K for a wide range of oxygen partial pressure: from air (pO2=0.21 atm) to Ar-4% H2 (pO2=1.7E-26 atm). Based on XANES data, the evolution of uranium oxidation state, thus the O/U ratio, could be determined in situ as a function of both temperature and µO2. These data will be compared to thermodynamic modelling.

 

Short description of the work
The associated pooled facility (APF) CEA – ATALANTE was visited by the Ph.D. student Sebastian Bahl from 28/09/15 – 03/10/15. All proposed work could be carried out successfully. Before this time period, 4 Pu glass samples were cut from glass rods, embedded in a resin and optically polished for the planed experiments. One day was required to record Raman spectra of all four Pu doped borosilicate glasses in the box line of the ATALANTE facility. The evaluation of the data will be performed in Karlsruhe. The Pu glasses were then cleaned and transferred to a preparation glovebox. The sample holder cells, designed and constructed at KIT-INE, were on-site modified according to the preparation process requirements. The Pu glass specimens were mounted by Mr. Delrieu in the cells and all surfaces were checked for contamination. As one surface revealed a small increase in activity, the cell was replaced by a backup sample holder on which no contamination was detected after the preparation. The procedure required also one day. The last day, the U doped alumosilicate glasses were mounted in a similar sample holder. No contamination was determined. In addition organizational paperwork was done to prepare the visit of the Ph.D. student Pierrick Chevreux at INE for X-ray absorption measurements (XAS).
All sample holder containing glass specimens were finally prepared for transport and arrived safely and in time in Karlsruhe at INE. Samples were analyzed by high energy resolution X-ray absorption near edge structure (HR-XANES) spectroscopy in November 2015 at INE-Beamline by the help of young scientist Mr. Chevreux. The evaluation of the data will be done in collaboration of Ph.D. students Chevreux and Bahl.

 

Short description of the work
During this stay, the first X-ray Absorption Spectroscopy measurements on nuclear fuel samples at high temperature and under controlled atmospheres were performed. We modified our experimental set-up to accept slices of sintered nuclear fuel pellets. Initially, UO2 and (U,Pu)O2 samples were planned for this experiment but due to safety issues, no sample containing plutonium could be sent to ANKA-INE. Nevertheless, in situ XANES (X-ray Absorption Near Edge Structure) spectra were successfully collected on UO2 samples and also on U0.75Ce0.25O2 and U0.50Ce0.50O2 samples as surrogates for (U,Pu)O2 compounds. During this experiment, data at uranium L3 edge were collected for the 3 compositions from 300 K up to 2023 K for a wide range of oxygen partial pressure: from air (pO2=0.21 atm) to Ar-4% H2 (pO2=1.7E-26 atm). Based on XANES data, the evolution of uranium oxidation state, thus the O/U ratio, could be determined in situ as a function of both temperature and µO2. These data will be compared to thermodynamic modelling.

 
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