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|Title:||Structural Investigation of Minor Actinide-bearing Fuels|
|Authors:||VESPA MARIKA; RINI MATTEO; SOMERS Joseph|
|Citation:||ACTA Mineralogica-Petrographica vol. 6 p. 362|
|Publisher:||The Departament of Mineralogy, Geochemistry and Petrology, University of Szeged|
|Type:||Articles in periodicals and books|
|Abstract:||Fast reactors (e.g. as outlined in the Gen IV initiative and in the Sustainable Nuclear Energy Technology Platform (SNETP)) provide a means by which nuclear energy sustainability is ensured. Furthermore, they make a positive step forward in the destruction of the minor actinide (MA) waste that they produce. Novel nuclear fuels will be needed and, in a likely first step, they should be based on actinides-U mixed oxides. Fuel development is a lengthy process, and little is known about MA-bearing fuels, which needs to be treated through experimental and theoretical approaches at the molecular level. The Strategic Research Agenda (SRA) of the SNETP (www.snetp.eu) clearly indicates the need to establish fundamental properties and irradiation behaviour of these new and largely untested materials. Nuclear fuel research is facing a paradigm shift from "Observe and Validate" towards "Design and Control" and is being driven by advances in multiscale modelling, and in particular ab initio calculations and molecular dynamics. Though tremendous advances have been made in these areas, there is a clear need for validation by experiments. Local structure investigation, by means of X-ray absorption spectroscopy (EXAFS and XANES), is one method poised to make important contribution towards the validation of such codes. An important fuel parameter, which has to be taken into consideration, is the oxygen potential and the corresponding O/M (oxygen to metal) ratio of the Am containing-mixed oxides. Since the O/M will increase during the irradiation time, an increase in the oxygen potential may limit the fuel burn-up due to possible fuel-cladding interactions. During this process Am is expected to be reduced to its trivalent state, a requirement to limit cladding oxidation. Consequently, the thermal conductivity should decrease due to the defects and distortion in the cubic structure [1-4]. In this study (U, Am)O2 samples with different O/M, have been prepared and investigated at the beamline for radioactive materials (INE-beamline) at the ANKA-synchrotron light source. EXAFS measurements were performed on the U- and Am-LIII edges. These first measurements demonstrated the feasibility of analysing highly radioactive materials (7.93x108 Bq/g), and will aid in developing and improving future nuclear fuels. In the next steps, it is planned to complement the EXAFS investigations with magic angle spinning nuclear magnetic resonance (MAS NMR) measurements. The combination of these spectroscopic methods will lead to an accurate determination of the coordination number and bond length change within the structure, and the evolution thereof as the sample undergoes self irradiation damage.  Walter M., Nästren C., Somers J., Jardin R., Denecke M. A., Brendebach B. (2007) Local atomic structure of a zirconia based americium transmutation fuel. J. Solid State Chem. 180, 3130-3135  Walter M., Somers J., Bouëxière D., Gaczynski P., Brendebach B. (2009) Oxidation behaviour of uranium and neptunium in stabilised zirconia. J. Solid State Chem. 182, 3305-3311  Walter M., Somers J., Fernández¿Carretero A., Rothe J. (2008) Local atomic structure in (Zr1-xUx)N. J. Nucl. Mater 373, 90-93  Walter M., Somers J. , Fernandez A., Haas D., Dardenne K., Denecke M. A. (2007) Structural investigation on an aged americium transmutation fuel. J. Nucl. Mater. 362, 343¿349|
|JRC Directorate:||Nuclear Safety and Security|
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