POTENTIOMETRIC SENSOR FOR REAL-TIME REMOTE SURVEILLANCE OF ACTINIDES IN MOLTEN SALTS

A potentiometric sensor is being developed at the Idaho National Laboratory for real-time remote surveillance of actinides during treatment of spent nuclear fuel. This sensor will be used for process control and safeguarding by monitoring the concentrations of actinides in a molten salt. The work presented focuses on developing a solid-state cation conducting ceramic sensor for detecting varying concentrations of trivalent actinide metal cations in eutectic LiCl-KCl molten salt. To understand the basic mechanisms for actinide sensor applications in molten salts, gadolinium was used as a surrogate for actinides. Polycrystalline ß - Al2O3 was selected as the solid-state electrolyte for sensor fabrication based on multivalent cationic conductivity and other factors. In the present work Gd 3+ -ß -Al2O3 was prepared by ion exchange reactions between K + -, Na + -, and Sr 2+ -ß -Al2O3 precursors and trivalent Gd 3+ from GdCl3. Scanning electron microscopy (SEM) was used for characterization of Gd 3+ -ß -Al2O3 samples. Microfocus X-ray diffraction (µ- XRD) was used in conjunction with SEM energy dispersive X-ray spectroscopy (EDS) to identify phase content and elemental composition. The Gd 3+ -ß -Al2O3 materials were tested for mechanical and chemical stability by exposing them to molten LiCl-KCl based salts. The effect of annealing on the exchanged material was studied to determine improvements in material integrity post ion exchange. The stability of the ß -Al2O3 phase after annealing was verified by µ-XRD. Preliminary sensor tests with different assembly designs will also be presented.