Structural changes of Nd- and Ce-doped ammonium diuranate microspheres during the conversion to U1-y Ln yO2±x

JOURNAL OF NUCLEAR MATERIALS

卷:542

Article

Schreinemachers, Christian^1,2  Leinders, Gregory¹  Podor, Renaud³  Lautru, Joseph³  Clavier, Nicolas³  Modolo, Giuseppe⁴  Verwerft, Marc¹  Binnemans, Koen²  Cardinaels, Thomas^1,2 

[1] Belgian Nucl Res Ctr SCK CEN, Inst Nucl Mat Sci, Boeretang 200, B-2400 Mol, Belgium

[2] Katholieke Univ Leuven, Dept Chem, Celestijnenlaan 200F,POB 2404, B-3001 Heverlee, Belgium

[3] Univ Montpellier, Bagnols Ceze, ENSCM, ICSM,CNRS,CEA, Bagnols Sur Ceze, France

[4] Forschungszentrum Julich, Inst Energy & Climate Res, IEK Nucl Waste Management & Reactor Safety 6, D-52425 Julich, Germany

关键词: Nuclear fuel fabrication;    Co-conversion;    Sol-gel;    Internal gelation;    GenIV;   

DOI  :  10.1016/j.jnucmat.2020.152454

来源: Elsevier

【 摘 要 】

The structural changes of ammonium diuranate (ADU) microspheres, prepared by the sol-gel route via internal gelation, were investigated during thermal treatments in oxidative and reducing conditions. In particular, in-situ simultaneous thermogravimetric analyses and in-situ high-temperature scanning electron microscopy investigations were carried out on un-doped ADU microspheres, and ADU microspheres doped with 10 mol% neodymium or 10 mol% cerium. Calcination in air caused the surface of the particles to crack, but with increasing temperature up to 900 degrees C some healing, and additionally, shrinkage occurred. The extent of the fractures and the amount of shrinkage was, however, significantly more pronounced in a particle prepared with a tetravalent Ce precursor, as compared to particles prepared with a trivalent Nd or Ce precursor. The macroscopic behaviour could be related to the release of volatile decomposition products and the calcined compositions were identified as (Ln-doped) alpha-U3O8 by X-ray powder diffraction. During thermal treatment in reducing conditions a transition from a (Ln-doped) alpha-U(3)O98 phase to a (Ln-doped) UO2 +/- x phase was observed. After exposure to a hydrogen containing gas mixture, this transition occurred rapidly in un-doped particles, and in particles prepared with trivalent Nd or Ce dopant precursors at 700 degrees C. Despite the fast reduction reaction, severe fractures appeared in the particles above temperatures of 850 degrees C, indicating that such behaviour is mainly attributed to sintering effects and less to the phase transition. In contrast, a more delayed reduction reaction was observed in particles prepared with a tetravalent dopant precursor and the described effects appeared less severe. (C) 2020 Elsevier B.V. Allrightsreserved.

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