The uranium extraction (UREX) solvent system was selected as a model flowsheet for testing Raman and absorbance spectroscopic techniques for process monitoring and safeguarding purposes and served as a guide for selecting the various feed concentrations and solvent system bounding the choice of spectroscopic measurements. The initial effort was directed toward evaluation of current UREX flowsheet specifications received from Argonne National Laboratory (ANL) (Vandegrift 2004). Based on this report evaluation, specifications were developed for preparing solutions that simulate the UREX process flowsheet streams. These solutions were used to evaluate capabilities for testing in-house instrumentation applicable for on-line process monitoring. To demonstrate the feasibility of using spec­troscopic techniques for the process monitoring and control of the UREX flowsheet, a 0.8 M HNO3 solution matrix was selected. The simple baseline feed solution contained 1.33 M UO2(NO3)2 in 0.8 M HNO3 (labeled Simple Feed). The Simple Feed simulant served as a matrix for the Pu(IV, VI) and Np(V) measurements at variable concentrations in the 0-10 mM range. The organic solvent extraction solution containing 30 vol% TBP in n-dodecane was prepared and loaded with actinide nitrates by the batch contact equili­bration with the UREX feed simulant solutions.

Raman spectra were collected on an InPhotonics, Inc. RS2000 echelle spectrograph. The system was equipped with a stabilized 670 nm, 150 mW visible diode laser as the excitation source. Data were collected at 1 cm-1 spectral resolution over a range of 200-4000 cm-1 stokes shift (Raman shift from 670 nm). Samples were measured with an InPhotonics focused fiber-optic probe (RamanProbeTM) with a thermoelectrically cooled CCD detector, normal operating temperature -55°C. The laser beam was coupled to the sample through a 10m fiber-optic cable and probe assembly which focused the excitation beam directly into the sample; this also precluded any air gap between the laser source and the sample. The focal point of the laser beam was 5 mm beyond the end of the laser probe tip, the measured laser intensity at the sample was typically 50 mW, and the excitation laser beam diameter at the sample was measured as 3 mm. Molecue® acquisition software with GRAMS 32® data manipulation software was used to process the Raman data. Typically, an integration time of 2 to 20 seconds was used for each acquisition. Vis-NIR measurements were performed using a 400 series dual source reflectance fiber-optic probe (SI Photonics) coupled with an LS-1 Tungsten Halogen Light Source (Ocean Optics) and a USB2000- vis-NIR spectrophotometer (Ocean Optics). SpectraSuite (Ocean Optics) software was used for collection and processing of the spectrophotometric data.