NuFuel & MMSNF 2015

First Workshop on Research into Nuclear Fuel in Europe
and Materials Modeling and Simulation for Nuclear Fuels Workshop
Karlsruhe, Germany, November 16th to 18th, 2015

Updated: Tue 08 Dec 2015, 14:27

Poster 3.4: Further insight into the chemistry of the Bi-U-O system

Karin Popa1, D. Prieur1, D. Manara1, J.F. Vigier1, P. Martin2, O. Dieste Blanco1, J. Somers1, R.J.M. Konings1, P.E. Raison1
  • 1: European Commission, Joint Research Centre, Institute for Transuranium Elements (ITU), Hermann-von-Helmholtz Platz 1, PO Box 2340, DE–76125 Karlsruhe, Germany
  • 2: CEA, DEN, DEC/SESC, F–13108 Saint Paul Lez Durance Cedex, France

Abstract

Safety assessment for a lead-bismuth eutectic (LBE) cooled reactor requires detailed knowledge of potential lead and bismuth uranate phases that could form in the event of a pin breach. Thus, we studied the phase relations in the Pb-U-O and Bi-U-O systems to identify possible phases that could be formed, and in a second step to determine their properties. Cubic fluorite-type phases have been reported in the U(IV) system, UO(2+x)-Bi2O3, over the entire compositional range. However, a non-linear evolution of the lattice parameter with relative stoichiometry has been observed, in contrast to other M(III)-U(IV)-O systems. This unusual behaviour was explained previously based on the fact that the substitution increases the amount of anionic vacancies than going towards higher Bi2O3 content. In these extensive investigations on the UO(2+x)-Bi2O3 system, we have confirmed the unusual behaviour of the lattice parameter with composition, but have found that, even under inert atmosphere at 800ºC, U(IV) is oxidised to U(V)/U(VI) as a function of the substitution degree. Thus, using a combination of three methods (XRD, XANES and Raman) we have identified the formation of the BiU(V)O4 and Bi2U(VI)O6 compounds, within this series.