Evidence of Trivalent Am Substitution into U3O8.
U3O8is considered to be the most stable phase for uranium oxide. Its structural properties must be accurately understood to foresee and manage aspects such as its leaching behavior when spent nuclear fuel is stored in an oxidative environment. Moreover, as fuel irradiation causes the formation of fission products and activation products such as plutonium and minor actinides, it is probable that U3O8will be mixed with other chemical elements under real conditions of oxidation. The storage issue can be extended to americium transmutation, where the irradiated compounds are mixed oxides composed of uranium and americium. This study thus focused on determining the structural properties of a solid solution containing uranium and trivalent americium (U/Am ratio = 90/10) and synthesized so as to obtain conventional U3O8oxide. This paper presents the possibility of combining trivalent americium with uranium in a U3O8mixed oxide for the first time, despite the high valence and atomic ratio differences, and proposes novel structural arrangements. X-ray diffraction measurements reveal americium substitution in U3O8uranium cationic sites, leading to phase transformation into a U3O8high-temperature structure and general lattice swelling. X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure experiments highlight an excess of U+VIorganized in uranyl units as the main consequence of accommodation.
CEA, DEN, DTEC/SECA/LFC , F-30207 Bagnols-sur-Cèze Cedex, France.|CEA, DEN, DRCP/SERA/LCAR , F-30207 Bagnols-sur-Cèze Cedex, France.|Institut Européen des Membranes, UMR 5635 CNRS-ENSCM-UM2, CC047, Université Montpellier 2 , F-34095 Montpellier Cedex 5, France.
Marie
M
Caisso
Unité de Catalyse et Chimie du Solide, UMR 8012 CNRS , 59652 Villeneuve d'Ascq Cedex, France.
Pascal
P
Roussel
Institut de Chimie de Nice, Université Nice Sophia Antipolis, UMR 7272 , F-06108 Nice cedex 2, France.
Christophe
C
Den Auwer
CEA, DEN, DRCP/SERA/LCAR , F-30207 Bagnols-sur-Cèze Cedex, France.
Sébastien
S
Picart
HZDR, Institute of Resource Ecology , 01314 Dresden, Germany.
Christoph
C
Hennig
HZDR, Institute of Resource Ecology , 01314 Dresden, Germany.|Rossendorf Beamline, ESRF , 38043 Grenoble, France.
Andreas C
AC
Scheinost
CEA, DEN, DRCP/SERA/LCAR , F-30207 Bagnols-sur-Cèze Cedex, France.
Thibaud
T
Delahaye
Institut Européen des Membranes, UMR 5635 CNRS-ENSCM-UM2, CC047, Université Montpellier 2 , F-34095 Montpellier Cedex 5, France.
André
A
Ayral