Oxidation Behaviour of Uranium and Neptunium in Stabilised Zirconia

Yttria stabilised zirconia (YSZ) based (Zr,Y,U)O2-x and (Zr,Y,Np)O2-x solid solutions with 6 and 20 mol% actinide were prepared with Y/Zr ratios ranging from 0.2 to 2.0 to investigate uranium and neptunium oxidation behaviour in dependence of the oxygen vacancies in the defect fluorite lattice. Sintering in at 1600°C in Ar/H2 yields a cubic, fluorite type structure with U(IV) and Np(IV). Annealing (Zr,Y,U)O2-x with Y/Zr = 0.2 at 800°C in air results in a tetragonal phase, whereas (Zr,Y,U)O2-x with higher Y/Zr ratios and (Zr,Y,Np)O2-x retain the cubic structure. XANES and O/M measurements indicate mixed U(V)¿U(VI) and Np(IV)¿Np(V) oxidation states after oxidation. Based on X¿ray diffraction, O/M and EXAFS measurements different oxidation mechanisms are identified for U and Np doped stabilised zirconia. In contrast to U, excess oxygen vacancies are needed to oxidise Np in (Zr,Y,Np)O2-x as the oxidation process competes with Zr for oxygen vacancies. As a consequence U(VI) and Np(V) can only be obtained in stabilised zirconia with Y/Zr =1 but not in YSZ with Y/Zr = 0.2.

WALTER Marcus;  SOMERS Joseph;  BOUEXIERE Daniel;  BRENDENBACH Boris; 

2009-12-07

ACADEMIC PRESS INC ELSEVIER SCIENCE

JRC52952

0022-4596,   

www.elsevier.com/locate/jssc,    https://publications.jrc.ec.europa.eu/repository/handle/JRC52952,   

10.1016/j.jssc.2009.09.022,