| Description |
Pyroprocessing is an innovative process designed to reprocess spent nuclear fuel. In order to make it cost competitive advancements must be made in the process to increase its efficiency. This work aimed to increase the efficiency of a part of pyroprocessing by mitigating the amount of Li2O transferred from the oxide reduction step to the electrorefining step. It did so by studying the effects that various process variables had on Li2O entrainment in the cathode basket. Drying techniques for LiCl and Li2O are described in this work. In addition, it was found that adding metallic lithium to the salt was an effective way to remediate LiOH in the electrolyte. Though convenient for salt sampling, the dip method consistently underestimated the concentration of Li2O by about 8% (wt%/wt%). Tests were performed proving the feasibility of measuring the concentration of Li2O in situ, via open circuit potential. Titration was used to measure Li2O entrainment in the cathode product, which was validated. Rotating the basket at a high rotation rate at a temperature of 650oC was effective at removing the majority of the salt in the cathode basket, allowing direct titration of the cathode product. MgO in the titration cell resulted in a background titration, accompanied by qualitative indicators: slow settling rate and color change. The TGA was found to be effective for measuring the reduction extent, and was validated using pure uranium. The reductions performed for the process variable studies passed 150% theoretical charge, resulting in an average reduction extent of 82% and an average current efficiency of 55%. Particle size, in the range of 106 to 1000 mm, had no perceptible effect on Li2O entrainment. Applying current in cycles reduced the amount of entrained Li2O; however, the reduction was mostly attributed to rest time. Also, as the cycle frequency was increased, the entrainment increased as well. The largest effect on entrainment was the reduction mechanism. When the UO2 was chemically reduced, via lithium metal, the entrainment increased substantially. Stirring had a negative effect, increasing entrainment. |
