The melting behaviour of uranium/neptunium mixed oxides

The melting behaviour in the pseudo-binary system UO2 – NpO2 has been experimentally assessed for the first time in this work with the help of laser heating under controlled atmosphere. It has been observed that the solidus and liquidus lines of this system follow an ideal solution behaviour (negligible mixing enthalpy) between the well-established solid/liquid transition temperatures of pure UO2 (3130 K) and that recently assessed for NpO2 (3070 K). Pre- and post-melting material characterization performed with the help of x-ray diffraction and Raman spectroscopy is also consistent with ideal mixing of the two end members. Such behaviour is well consistent with the similar ionic radii of tetravalent uranium and neptunium and with the similar melting points of the two oxides. The interest of this investigation is twofold. From a technological viewpoint, it indicates that the incorporation of NpO2 in UO2 fertile blankets is a viable option to recycle neptunium without inducing any relevant change in the chemical or thermal stability of the uranium dioxide matrix, even up to the melting point. From a more fundamental perspective, it confirms that actinide dioxides, and particularly UO2, tend to mix in a more ideal way, the closer are the atomic numbers, 5-f electron shell filling, atomic radii and oxygen potentials of the metals forming the pure dioxides.

CHOLLET Melanie;  PRIEUR Damien;  BÖHLER Robert;  BELIN R.C.;  MANARA Dario; 

2015-12-15

ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD

JRC91577

0021-9614,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC91577,   

10.1016/j.jct.2015.04.031,