A new approach for monitoring radionuclides in hydrometallurgical separation processes based on Raman spectroscopy

The reprocessing of nuclear fuel offers unique advantages regarding both, the best use of the resource and the minimization of the radioactive wastes, and for the success of this challenge, the partitioning of radionuclides contained is essential. Nowadays, the most advanced technology is focused on the hydrometallurgical separation concept, based on liquid-liquid extraction methods. This approach, built on the use of selective extractants, is well-established for U and Pu separation, by the industrial process PUREX (Plutonium Uranium Reduction Extraction). The current international research efforts are addressed to the recovering of minor actinide elements, for which, different strategies are being demonstrated at different Technology Readiness Level (TRL). In this work, we propose the use of the fluorescence of key radionuclides measured by Raman spectroscopy (RS) as a tool to monitor processes performance of at laboratory scale. It should be noted that this tool is envisioned for in situ analysis, allowing it to be used for online monitoring of radionuclides, in the stream solutions of the reprocessing plants for safety purposes. As proof-of-concept we show in this work how Eu and Nd can be successfully monitored in an i-SANEX (Innovative-Selective Actinide Extraction)-like process by using the RS. For this aim we follow these radionuclides in three steps: i) extraction of Nd and Eu from an aqueous nitric acid solution (3 M) with N,N,N',N'-tetraoctyl-diglycolamide, TODGA (0.2 M in OK), ii) stripping actinides with 2,6-bis[1-(propan-1-ol)-1,2,3-triazol-4-yl)]pyridine, PTD (0.04 M in 2.1 M HNO₃ and iii) stripping lanthanides with 0.01 M HNO₃. (authors)