Stabilization and Solidification of Beryllium Waste: Influence of the Cement Composition on the Corrosion of Be Metal.

Beryllium metal is used as neutron moderator and reflector or multiplier in certain types of fission or fusion reactors. Dismantling of these reactors will produce radioactive beryllium waste, classified as low- or intermediate-level waste, that will need to be stabilised and solidified before being sent to disposal. The cementation process is under consideration because it may offer a good compromise between simplicity of implementation, cost, and quality of the final cemented wasteform.

Grain growth of NpO and UO nanocrystals.

We report on the crystallite growth of nanometric NpO and UO powders. The AnO nanoparticles (An = U and Np) were synthesized by hydrothermal decomposition of the corresponding actinide(iv) oxalates. NpO powder was isothermally annealed between 950 °C and 1150 °C and UO between 650 °C and 1000 °C.

Synthesis of Nanocrystalline PuO by Hydrothermal and Thermal Decomposition of Pu(IV) Oxalate: A Comparative Study.

In recent years, the hydrothermal conversion of actinide (IV) oxalates into nanometric actinide dioxides (O) has begun to be investigated as an alternative to the widely implemented thermal decomposition method. We present here a comparison between the hydrothermal and the conventional thermal decomposition of Pu(IV) oxalate in terms of particle size, morphology and residual carbon content. A parametric study was carried out in order to define the temperature and time applied in the hydrothermal conversion of tetravalent Pu-oxalate into PuO and to optimize the reaction conditions.

Coprecipitation of actinide peroxide salts in the U-Th and U-Pu systems and their thermal decomposition.

The uranium and plutonium co-conversion process constitutes a continuous subject of interest for MOx fuel fabrication. Among the various routes considered, chemical coprecipitation by the salt effect has been widely investigated regarding its simplicity of integration between the partitioning and purification steps of the PUREX process, and the straightforward recovery of precursors that are easily converted into oxide phases by thermal decomposition. The present study focuses on the coprecipitation behavior of U-Th and U-Pu actinide peroxide mixed systems by examining the precipitation yields and settling properties for nitric acidity in the range of 1 to 3 M and hydrogen peroxide concentration in the range of 4.

Zirconium Oxalates: Zr(OH)(CO), (HO)[Zr(CO)(HO)], and MM'[Zr(CO)]·HO with M and M' = Ammonium, Alkali Metal, and Hydroxonium Ion HO ( = 2, 3, 4).

Crystallized powder of dihydroxide zirconium oxalate Zr(OH)(CO) () was obtained by precipitation and the structure determined from powder X-ray data. The three-dimensional (3D) framework observed in () results from the interconnection of zirconium hydroxide chains [Zr(OH)] and zirconium oxalate chains [{Zr(CO)}]. Single crystals of (HO)[Zr(CO)(HO)] () were obtained by evaporation.

Structural Variations of 2D and 3D Lanthanide Oxalate Frameworks Hydrothermally Synthesized in the Presence of Hydrazinium Ions.

Depending on the nature of the 4f element, six different lanthanide oxalate families were hydrothermally synthesized in the presence of hydrazinium ions. Four of them correspond to the general formula NH[(CO)]·HO but have different structural formulas according to the number of coordinated water molecules or hydrazinium ions and the structural arrangement, NH[La(CO)] (); NH[{(NH)}(CO)]·4HO, = Ce, Pr, Nd, and Sm (); NH[{(HO)}(CO)], = Sm, Eu, Gd, Tb, Dy, and Ho (); NH[(CO)]·HO, = Yb, = 3, and Lu, = 2 (). The two others do not contain hydrazinium ions.

Crystal Growth in the Thorium-TEDGA-Oxalate-Nitrate System: Description and Comparison of the Main Structural Features.

This paper reports the synthesis and characterization of four new compounds based on thorium and tetraethyldiglycolamide (TEDGA), [Th(TEDGA)(CO)][NO][HCO].6HO (1), [Th(TEDGA)(CO)][HCO].2HO (2), [Th(TEDGA)][NO].

Insight into the Uranyl Oxyfluoride Topologies through the Synthesis, Crystal Structure, and Evidence of a New Oxyfluoride Layer in [(UO)F][Sr(HO)](NO)·HO.

A new strontium uranyl oxyfluoride, [(UO)F][Sr(HO)](NO)·HO, was synthesized under hydrothermal conditions. The single-crystal X-ray structure was determined. This compound crystallizes in the triclinic space group P1̅ (No.

Characteristics of chemical bonding of pentavalent uranium in La-doped UO.

The effect of La doping on the electronic structure of U in UO was studied using an advanced technique, namely, X-ray absorption spectroscopy (XAS) in the high-energy-resolution fluorescence-detection (HERFD) mode, at the U 3d (M) edge. Thanks to a significant reduction of the core-hole lifetime broadening and distinct chemical shifts of the HERFD-XAS lines, the U(v) formation as a result of La doping was identified. The isolated contribution of U(v) in the M HERFD-XAS spectrum reveals the so-called charge-transfer satellites due to the U 5f-O 2p hybridization.

Use of HERFD-XANES at the U L3- and M4-Edges To Determine the Uranium Valence State on [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3].

We report and discuss here the unambiguous uranium valence state determination on the complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using high-energy-resolution fluorescence detection-X-ray absorption near-edge structure spectroscopy (HERFD-XANES). The spectra at both U L3- and M4-edges confirm that all five nonequivalent U atoms are solely in the hexavalent form in this compound, as previously suggested by bond-valence-sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the preedge feature, due to the 2p3/2-5f quadrupole transition, has been observed in the U L3-edge HERFD-XANES spectrum, in agreement with theoretical and experimental observations of other uranium-based compounds.

Hydrazinium lanthanide oxalates: synthesis, structure and thermal reactivity of N2H5[Ln2(C2O4)4(N2H5)]·4H2O, Ln = Ce, Nd.

New hydrazinium lanthanide oxalates N2H5[Ln2(C2O4)4(N2H5)]·4H2O, Ln = Ce (Ce-HyOx) and Nd (Nd-HyOx), were synthesized by hydrothermal reaction at 150 °C between lanthanide nitrate, oxalic acid and hydrazine solutions. The structure of the Nd compound was determined from single-crystal X-ray diffraction data, space group P2₁/c with a = 16.315(4), b = 12.

Crystal growth and first crystallographic characterization of mixed uranium(IV)-plutonium(III) oxalates.

The mixed-actinide uranium(IV)-plutonium(III) oxalate single crystals (NH4)0.5[Pu(III)0.5U(IV)0.

Linear alkyl diamine-uranium-phosphate systems: U(VI) to U(IV) reduction with ethylenediamine.

Mild-hydrothermal reactions in acidic medium using 1,3-diaminopropane, 1,4-diaminobutane, and 1,5-diaminopentane as structure directing agents led to three-dimensional (3D) uranyl phosphates (CH₂)₃(NH₃)₂{[(UO₂)(H₂O)][(UO₂)(PO₄)]₄} (C3U5P4), (CH₂)₄(NH₃)₂{[(UO₂)(H₂O)][(UO₂)(PO₄)]₄} (C4U5P4) and (CH₂)5(NH₃)₂{[(UO₂)(H₂O)][(UO₂)(PO₄)]₄} (C5U5P4). The structures of (C4U5P4) and (C5U5P4) were solved in the space group Cmc2₁ using single-crystal X-ray diffraction data. The compounds are isostructural to the corresponding uranyl vanadates and contain the same 3D inorganic framework built from uranyl-phosphate layers of uranophane-type anion topology pillared by [UO₆(H₂O)] pentagonal bipyramids.

X-Ray diffraction and mu-Raman investigation of the monoclinic-orthorhombic phase transition in Th(1-x)U(x)(C(2)O(4))(2).2H(2)O solid solutions.

A complete Th(1-x)U(x)(C(2)O(4))(2).2H(2)O solid solution was prepared by mild hydrothermal synthesis from a mixture of hydrochloric solutions containing cations and oxalic acid. The crystal structure has been solved from twinned single crystals for x = 0, 0.