Measuring Hydroxylammonium, Nitrate, and Nitrite Concentration with Raman Spectroscopy for ²³⁸Pu Supply Program

Optical spectroscopy has great potential to improve the timeliness of important analytical measurements for the ²³⁸Pu Supply Program by enabling real-time analysis of process solutions within radiochemical hot cells. Hydroxylammonium (H₃NOH⁺]), nitrate (NO₃^-), and nitrite (NO₂^-) are three important molecular species present in multiple aqueous streams throughout the program’s flow sheet. The concentration of each species normally goes uncharacterized during processing. However, rapid quantification may benefit the program because uncertainties in kinetic redox expressions describing hydroxylammonium (HA) and nitrite reactions with Np and Pu leads to uncertainty in process model predictions for solvent extraction runs. HA concentration is normally quantified using ion chromatography, a technique that requires diluted grab samples taken out of the hot cell and analyzed off-line. Here we evaluate Raman spectroscopy for determining the concentration of H₃NOH⁺, NO₃^-, and NO₂^- in benchtop tests to determine limits of detection. We also consider the possibility of using Raman spectroscopy in both glove box and hot cell environments for rapid analysis and pinpoint additional development opportunities needed to make this application successful.