| Description |
The thermodynamic and electrochemical properties of rare earth chlorides in molten salt solutions are of interest from the standpoint of both pyrochemical processing of spent nuclear fuel and for the development of Generation IV nuclear reactors. Knowledge of key properties like activity coefficients, phase diagrams and reliable waste disposal methods will accelerate the development of safe reliable carbon free energy. In this work, three conduits of research have been pursued and reported within the larger theme of minimization of waste in spent fuel reprocessing and associated technology development. First a novel process for the disposal of chloride salts using H-Y zeolite has been studied. In this process, a protonated Y zeolite is used to occlude the LiCl-KCl eutectic salt. In the process, the proton and the chloride ions react to evolve HCl gas that can be easily captured and neutralized. Hence the final waste form will be lighter compared to the baseline process. Results indicate that the proton and chloride react to form HCl gas which was captured and neutralized. Up to 50% of theoretical ion exchange was achieved based on the total HCl evolution. The activity of four rare earth chlorides was determined electrochemically in LiCl-KCl eutectic salt. These rare earth chlorides are: LaCl3, NdCl3, GdCl3, and CeCl3. The activity was determined using two distinct experimental set-ups: using a Ag/AgCl reference electrode and an analyte reference electrode. Broadly it is noted that the activity coefficient of the rare earth chlorides changes with concentration of the analyte in solution. From the data of all of the four rare earth chlorides it was concluded that as the ionic size of the rare earth reduces, the species shows a larger negative deviation from ideal solution behavior. The presence of large concentrations of CsCl seems to influence the activity of some of the rare earths. The solidus and liquidus temperatures for quaternary LiCl-KCl-CsCl-RECl 3 systems were determined using a differential scanning calorimetry. It is observed that the presence of CsCl depresses the melting temperature for all of the rare earth chlorides tested. The LiCl-KCl-CsCl-LaCl3 system departs from eutectic behavior and manifests peritectic behavior. The LiCl-KCl-CsCl-GdCl3 system shows peritectic behavior at only low GdCl 3 and high CsCl concentrations. The LiCl-KCl-CsCl-NdCl3 system continues to exhibit purely eutectic behavior for all of the concentration windows tested for this work. |
