Available on-demand - *S.CT03.06.04
The JRC Surface Science Labstation—A Unique Set-Up to Investigate Actinides in Support of Nuclear Safety and Non-Power Application of Nuclear Materials
Rachel Eloirdi1,Thomas Gouder1,Ghada El Jamal2,Concettina Andrello1,Frank Huber1,Roberto Caciuffo1
JRC Karlsruhe1,KTH Royal Institute of Technology2
Show Abstract
Knowledge about the interaction of UO2 with the environment is of high importance to assess its stability in oxidizing and in reducing condition. For this reason, understanding the UO2 oxidation process is central to the performance assessment of nuclear fuels. Oxidizing condition can convert UO2 into U3O8 leading, in some cases, to powdering of the fuel matrix or to failure of the cladding [1]. The redox behaviour of UO2 is also relevant for the management of nuclear waste forms, as oxidation results in the production of soluble uranyl cations, UO22+, that can easily migrate in the biosphere.
This talk summarizes surface science research activities carried out at JRC Karlsruhe in support of nuclear safety and non-power application of nuclear materials. I will also describe a unique set-up developed in-house, the Labstation [2], including sample preparation modules, by DC Sputtering or evaporation, and several surface characterisation techniques. Among the latter, High-resolution X-ray Photoelectron Spectroscopy (XPS) and Bremstrahlung Isochromat Spectroscopy (BIS) are particularly useful to characterize the uranium oxidation state in single and mixed oxides. In a first example, I will show the process of oxidation and reduction of U oxides using O2, H2O and H2, plasma. For the first time, U2O5 films [3-4] could be produced and studied, filling a gap in the knowledge about U5+ oxidation state. While U4+, U5+ and U6+ have representative satellite peaks positioned, respectively, at 7, 8 and 4 & 10 eV out of the main 4f5/2,7/2 excitation lines, a satellite peak at 9 eV is observed when UO2+x in contact with sodium is heated at 400 °C under oxygen. In a second example, we report the first in-situ preparation of ThF4 [5] whose band gap of 10.2(2) eV is significantly larger than the 229mTh excitation energy, making ThF4 a possible candidate material for a solid-state nuclear clock based on the vacuum ultraviolet γ decay.
References
[1] NEA (2005), The Safety of the Nuclear Fuel Cycle, 3rd Edition, OECD, Paris.
[2] T. Gouder, F. Huber, R. Eloirdi, R. Caciuffo, R. J. Vis. Exp. 144, e59017b, (2019)
[3] T. Gouder, R. Eloirdi, R. Caciuffo, Scientific Reports 8, 8306 (2018)
[4] N. A. Brincat, S. C. Parker, M. Molinari, G. C. Allen and M. T. Storr, Dalton Trans. 44, 2613–2622, (2015) Molinari, M., Brincat, N. A., Allen, G. C. & Parker, S. C. Structure and properties of some layered U2O5 phases: A density functional theory study. Inorg. Chem. 56, 4468 (2017). Molinari, M., Brincat, N. A., Allen, G. C. & Parker, S. C. Structure and properties of some layered U2O5 phases: A density functional theory study. Inorg. Chem. 56, 4468 (2017). Molinari, M., Brincat, N. A., Allen, G. C. & Parker, S. C. Structure and properties of some layered U2O5 phases: A density functional theory study. Inorg. Chem. 56, 4468 (2017). Molinari, M., Brincat, N. A., Allen, G. C. & Parker, S. C. Structure and properties of some layered U2O5 phases: A density functional theory study. Inorg. Chem. 56, 4468 (2017).
[5] T. Gouder, R. Eloirdi, R. L. Martin, M. Osipenko, M. Giovannini, and R. Caciuffo, Phys. Rev. Research 1, 033005, (2019)