(547g) The Design of Organic Simulants to Model Various Nuclear Reprocessing Fluids

The reprocessing of irradiated nuclear fuel to extract Uranium and Plutonium from other compounds is facilitated through a liquid-liquid separation technique called the Plutonium Uranium Reduction EXtraction (PUREX) process. Since mass transfer occurs only where the two immiscible liquids meet (at the interface), a central goal when designing unit operations for PUREX is to promote a high surface area to droplet volume ratio. The three types of contacting equipment used in this unit operation are the mixer-settler, centrifugal contactor, and pulse column.

Though many designs for these devices exist, they all encourage the breakup of one liquid phase into droplets dispersed within the other to elicit a high interfacial area and, subsequently, transfer metal ions between phases. Understanding the subtle balance between flow rates, droplet size, mechanical power input, and coalescence time is highly complex and necessitates fundamental knowledge of the materials used. The most common liquids for this process are dilute nitric acid (1M - 3M) and a tributylphosphate (TBP, 30 vol%) mixture in n-dodecane. It has also been documented that key physical attributes change significantly due to increases in Uranium loading. Therefore, no system displays only a single set of physical properties because the PUREX fluids experience a wide range of changes in physiochemical properties. While it would be ideal to engage studies of the unit operations directly with the actual materials (i.e., uranium, plutonium, TBP), feasibility becomes an increasingly significant hurdle when handling radioactive materials. Therefore, economics, chemical compatibility, hazard prevention, and general intrigue orient the goal of this research to identify a selection of material substitutes for the traditional set of liquids to assist in prototyping and mock-up testing of the PUREX unit operation.

While many factors influence the performance of the unit operations and interfacial area of droplets, three vital ones are viscosity, interfacial tension (IFT), and density. Therefore, this document aims to explore and enhance the flexibility of experimental capacity by understanding, measuring, and controlling organic surrogates that span a wide array of the properties listed above. With these chemical systems, the separation equipment can be more robustly tested and scrutinized by surveying their limits while maintaining a safer and more cost-effective environment.