Investigation of the Cs₂(Mo,Te)O₄Solid Solution and Implications on the Joint Oxyde-Gaine System in Fast Neutron Reactors

The formation of a thin layer, the so-called Joint Oxyde-Gaine (JOG), between the (U,Pu)O2 fuel pellets and the cladding has been observed in fast neutron reactors, due to the accumulation of volatile fission products. Cs2MoO4 is known to be one of the major components of the JOG, but other elements are also present, in particular tellurium...

A new approach for coupled modelling of the structural and thermo-physical properties of molten salts. Case of a polymeric liquid LiF-BeF₂

The (Li,Be)F_x fluoride salt is an ionic liquid with complex non-ideal thermodynamic behaviour due to the formation of short-range order. In this work, we explore the relationship between local structure, thermo-physical and thermodynamic properties in this system using a multidisciplinary approach that couples molecular dynamics...

Report of the Double-Molybdate Phase Cs₂Ba(MoO₄)₂ with a Palmierite Structure and Its Thermodynamic Characterization

The existence of a novel double-molybdate phase with a palmierite-type structure, Cs2Ba(MoO4)2, is revealed in this work, and its structural properties at room temperature have been characterized in detail using X-ray and neutron diffraction measurements. In addition, its thermal stability and thermal expansion are investigated in the...

Structural and thermodynamic study of Cs₃Na(MoO₄)₂: Margin to the safe operation of sodium cooled fast reactors

Neutron diffraction measurements of the double molybdate Cs₃Na(MoO₄)₂ have been performed for the first time in this work and the crystal structure refined using the Rietveld method. The thermal expansion of this trigonal phase, in space group P3¯m1, measured using high temperature X-ray diffraction (XRD),...

Thermodynamic assessment of the LiF-NiF₂, NaF-NiF₂ and KF-NiF₂ systems

Using the modified quasi-chemical model in the quadruplet approximation, three new thermodynamic assessments of binary systems useful for the detailed operational design of the Molten Salt Reactor are presented: AF-NiF₂ (A = Li, Na, K). These systems are particularly relevant for the study of the molten salt-structural materials...

In situ high-temperature EXAFS measurements on radioactive and air-sensitive molten salt materials

The development at the Delft University of Technology (TU Delft, The Netherlands) of an experimental set-up dedicated to high-temperature in situ EXAFS measurements of radioactive, air-sensitive and corrosive fluoride salts is reported. A detailed description of the sample containment cell, of the furnace design, and of the measurement...

Thermodynamic study of Cs3Na(MoO4)2: Determination of the standard enthalpy of formation and standard entropy at 298.15 K

The enthalpy of formation at 298.15 K and low temperature heat capacity of Cs3Na(MoO4)2 have been measured for the first time in this work using solution calorimetry and thermal-relaxation calorimetry in the temperature range T = (1.9–299.6) K, respectively. The solution calorimetry measurements, performed in 2 M HNO3 solution, have yielded an...

Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs

A thermodynamic model for the Na-O system was developed for the first time using the CALPHAD method after review of the structural, thermodynamic, and phase diagram data available on this system. Differential Scanning Calorimetry measurements were moreover performed to assess the phase equilibria and liquidus temperature in the Na<sub>2</sub...

A New Look at the Structural and Magnetic Properties of Potassium Neptunate K₂NpO₄ Combining XRD, XANES Spectroscopy, and Low-Temperature Heat Capacity

The physicochemical properties of the potassium neptunate K₂NpO₄ have been investigated in this work using X-ray diffraction, X-ray absorption near edge structure (XANES) spectroscopy at the Np-L₃ edge, and low-temperature heat capacity measurements. A Rietveld refinement of the crystal structure is reported...

Structural Properties and Charge Distribution of the Sodium Uranium, Neptunium, and Plutonium Ternary Oxides: A Combined X-ray Diffraction and XANES Study

The charge distributions in α-Na₂UO₄, Na₃NpO₄, α-Na₂NpO₄, Na₄NpO₅, Na₅NpO₆, Na₂PuO₃, Na₄PuO₅, and Na₅PuO₆ are investigated in this work using X-ray absorption near-edge...

Mössbauer spectroscopy, magnetization, magnetic susceptibility, and low temperature heat capacity of α-Na₂NpO₄

The physical and chemical properties at low temperatures of hexavalent disodium neptunate α-Na₂NpO₄ are investigated for the first time in this work using Mössbauer spectroscopy, magnetization, magnetic susceptibility, and heat capacity measurements. The Np(VI) valence state is confirmed by the isomer shift value of the...

Thermodynamic assessment of the neptunium-oxygen system:: Mass spectrometrics studies and thermodynamic modelling

Crystal-Field and Covalency Effects in Uranates: An X-ray Spectroscopic Study

The electronic structure of U^V- and U^VI-containing uranates NaUO₃and Pb₃UO₆was studied by using an advanced technique, namely X-ray absorption spectroscopy (XAS) in high-energy-resolution fluorescence-detection (HERFD) mode. Due to a significant reduction in core–hole lifetime broadening,...