PNNL

Abstract

Nuclear energy represents one of the stronger candidates to meet the worlds’ ever-growing energy needs. However, the nuclear fuel cycle faces many challenges; in particular improved methods for monitoring radioactive materials throughout the cycle are needed to maintain proper safeguards and ensure safe and efficient processing of materials. Development of more effective, reliable, and fast methods for monitoring radioactive materials is integral to the continued development of the nuclear fuel cycle. The advancement of microfluidics and lab-on-a-chip designs has provided a pathway of experimentation that utilizes volumes which are orders of magnitude less than previous techniques. For radioactive applications the benefits of lower dose to workers and equipment, smaller feedstock volumes, and less waste make these techniques of significant interest. With these benefits come the complication of solution analysis, as conventional spectroscopic techniques require much larger volumes. An example is Raman spectroscopy, which has been used extensively for solution analysis; of key interest to the nuclear field is measurement of species such as actinide dioxocations, organic solvent components and complexants, inorganic oxo-anions (NO3-, CO32-, OH-, SO42-, etc), and pH/acid concentration. Typical Raman probes require a minimum solution volume on the order of mLs in order to obtain quantifiable measurements of solution components, especially those with low concentrations. A new micro-Raman probe has been developed which significantly reduces the focal region of the excitation beam and allows for the interrogation of reduced sample volumes. The micro-Raman probe focal region readily fits into most microfluidic chip channels as well as micro flow cells. Instrument performance was tested on a variety of solution systems including a flowing stream of uranyl nitrate in nitric acid. A micro-Raman probe was used to measure the uranyl nitrate and nitric acid sequentially injected through the microfluidic cell. The application of chemometric analysis was performed to quantify the uranyl, nitric acid, and total nitrate within the system based on the Raman spectra. Probe performance for monitoring two-phase systems including complications with interfering species was also explored. Overall, this novel spectroscopic probe has successfully enabled the on-line analysis of a variety of streams on the microscale. This paper focuses on our current progress in on-line, real-time process monitoring. Advances in spectroscopic technology and our analytical approach will be discussed. An overview of the successful application within microfluidic systems will be discussed.