Daniel Bouëxière

Contrasting immobilization behavior of Cs+ and Sr2+ cations in a titanosilicate matrix

ETS-10 titanosilicate was tested as an adsorbent for the removal of Cs+ and Sr2+ cations from radioactive waters, considering both the ion exchange and the behaviour of the loaded adsorbent during thermal conditioning. The studies indicate that ETS-10 has a high and similar affinity for both Cs+ and Sr2+ cations reaching the ion exchange capacity of ETS-10 at a concentration of about 50 milliequivalents gram per liter. Thermal treatment of Cs+- and Sr2+-exchanged ETS-10 materials results in melting at approximately 700 °C. The melting temperature increases with the initial Cs+ and Sr2+ concentration and is higher for Sr2+ than for Cs+ exchanged ETS-10. Recrystallisation occurs only in the presence of Sr2+ as evidenced by the exothermic effects between 800 and 900 °C. After calcination of Cs+- and Sr2+-exchanged ETS-10 in air at 800 °C, two types of materials were obtained: an amorphous glass material with homogeneous Cs+ distribution and a strontium fresnoites glass–ceramic material.

Synthesis and electronic properties of Th-N films

Abstract Thin layers of Th, ThN, and Th 3 N 4 were synthesized by sputter deposition of Th in an Ar atmosphere with variable nitrogen partial pressure. The phase purity and crystal structure of the nitrides were confirmed by X-ray diffraction. Photoelectron spectroscopy studies demonstrate that ThN is metallic, with a rather high density of 6d states at the Fermi level, while Th 3 N 4 is non-metallic.

Structural chemistry of the neptunium–silicon binary system

Abstract The structural chemistry of the complete binary neptunium–silicon system has been investigated by means of X-ray diffraction. This system is characterised by the existence of six different compounds, whereas only three were previously reported in the literature. The formation and the crystal structure of the NpSi 3 compound (AuCu 3 type) and of the richest in neptunium binary Np 3 Si 2 compound (U 3 Si 2 type) were confirmed. The ThSi 2 type of compound was also confirmed but, as usually observed in the rare-earth or actinide systems, with a slight defect on the silicon site. The hexagonal AlB 2 type compound was isolated for the first time, showing, as expected, a higher silicon defect than in the ThSi 2 type of compounds. The last phase observed in this system was found to crystallise with the NpSi composition showing a polymorphic transformation. Depending on the annealing process a primitive orthorhombic FeB type, as observed with the rare-earth systems, or a C-centered orthorhombic new crystal structure type are obtained. These new results are described and compared with the recently revised Np–Ge and uranium homologue systems.

Synthesis and Characterisation of BaMIV(PO4)2 in the View of Conditioning of the Actinides

We present here a systematic study on the BaMIV(PO4)2 double phosphates. We successfully synthesized the compounds with MIV = Ti, Zr, Hf, Ge, Sn and Th. Several attempts to obtain the compounds with MIV = Pb, Re, Ce, U and Np have been also performed and the preliminary findings are discussed here. In agreement with previous studies, the BaMIV(PO4)2 (MIV = Ti, Zr, Hf, Ge and Sn) compounds crystallize in the C1 2/m 1 space group (yavapaiite structure), while BaTh(PO4)2 exhibit a different structure. The results on the stability of the BaZr(PO4)2 and BaHf(PO4)2 yavapaiite-like compounds upon heating and cooling are presented.

A low-temperature synthesis method for AnO2 nanocrystals (An = Th, U, Np, and Pu) and associate solid solutions

Production of actinide oxide powder via dry thermal decomposition of corresponding oxalates is currently carried out on the industrial scale at temperatures exceeding 500 °C. Although it is simple, this method presents some disadvantages such as high decomposition temperature with a direct effect on the surface area, pre-organised morphology of the nanoparticles affecting the sintering behaviour, etc. We have recently proposed the decomposition of AnIV-oxalates under hot compressed water conditions as a straightforward way to produce reactive actinide oxide nanocrystals. This method could be easily applied at low temperatures (95–250 °C) in order to generate highly crystalline nano-AnO2. We present here the formation conditions of AnO2 (An = Th, U, Np, and Pu) and some associated solid solutions, their stability, and grain growth during thermal treatment. The involvement of water molecules in the mechanism of the oxalate decomposition under the hot compressed water conditions has been demonstrated by an isotopic exchange reaction during the thermal treatment of the hydrated oxalate in H2[17O] through MAS-NMR and Raman techniques.

Electronic Properties of ζ-U-Pu Alloys

The ζ-phase, existing between 35 and 70% U in Pu, belongs to the high density phases seen from the point of view of systematics of allotropic modifications of Pu metal. Despite the volume per actinide atom only slightly higher than for α-Pu, it magnetic susceptibility is much higher than for α-Pu and exceeds even the δ-Pu value. Similarly, the Sommerfeld coefficient γ > 40 mJ/mol Pu K 2 exceeds the experimental δ-Pu value. The data confirm that the volume is not the primary control parameter affecting the situation around the Fermi level of common Pu phases and they point against the traditional belief that they are essentially narrow 5 f band systems.