Measuring Neptunium Concentration using Optical Spectrometry for the Pu-238 Supply Program

Targets containing ²³⁷Np are irradiated at the High Flux Isotope Reactor at Oak Ridge National Laboratory to produce ²³⁸Pu, as plutonium dioxide (PuO₂), a heat source material for use in future NASA space missions. Kilogram quantities of Np are processed yearly and developing methods to efficiently characterize and monitor the Np processing streams with optical spectroscopy and real-time monitoring software is a critical aspect of this effort. Here, we evaluate how ultraviolet/visible/near-infrared (UV-Vis-NIR) absorbance and Raman spectroscopic techniques are applicable to characterizing concentrated Np solutions and provide proof-of-principle and proof-of-concept results for each technique. Both techniques were tested in lab-scale studies and should improve the timeliness of production efforts. However, spectrophotometry is the more mature option and has been successfully demonstrated in a hot cell environment. An overview of the initial findings, a brief demonstration, and areas for future work will be highlighted in this report.