The goal of Raman and vis-NIR spectroscopic measurements of the dis­solved ATM-109 fuel solutions was to assess the utility of optical process monitoring methods employing Raman and vis-NIR for the direct measure­ment of dissolved fuel feed, 30% TBP/n-dodecane extraction, and raffinate phases under the conditions of complex composition of the dissolved com­mercial fuel containing multiple light-absorbing species potentially interfer­ing with detection and quantification of the target analytes.

Direct Raman measurements of the aqueous nitric acid feed and raffinate solutions performed on commercial fuel ATM-109 are shown in Fig. 4.10 (left). This figure also contains a spectrum of the Simple Feed fuel simulant (containing 1.3 M UO2(NO3)2/0.8 M HNO3) for comparison of the Raman response between simulants and actual fuel samples. The spectral features responsible for the UO22+ and NO3- bands (870 and 1047 cm-1, respectively) in the fuel feed and raffinate samples are in excellent agreement with those contained within the Simple Feed simulant. The TBP/n-dodecane extract phase of ATM-109 fuel was also measured by Raman spectroscopy. Figure

4.10 (right) compares the Raman spectra of TBP/n-dodecane extracts of ATM-109 feed and Simple Feed simulant. No shift of the UO22+ and NO3- bands Raman bands (858 and 1029 cm-1, respectively) between the extrac­tion phases loaded using actual commercial fuel and simulant solutions was observed. Other bands observed in the extraction phase Raman spectra were assigned to the solvent (TBP and n-dodecane).

Spectrophotometric measurements of the aqueous feed solutions of the ATM-109 commercial fuel samples were performed using the vis-NIR spec­tral region. Plutonium in both Pu(IV) and Pu(VI) oxidation states was observed in the commercial fuel feed, with varying concentrations depend­ing on the HNO3 concentration, as is apparent in Fig. 4.11. Neptunium as Np(V) was evident in the ATM-109 fuel (Fig. 4.11).

Figure 4.12 (top) shows the vis-NIR spectra of the organic extraction phase from ATM-109 in 5.1 M HNO3. The spectral bands observed in

Fig. 4.12 are those diagnostic for Pu(IV). For comparison, a fuel simulant containing a feed composition of 1.33 M UO2(NO3)2 in 0.8 M HNO3 with a Pu(IV) concentration of 2 mM was contacted with the 30% TBP/n-dodecane PUREX solvent followed by spectroscopic measurement by vis-NIR spec­troscopy, with the resulting spectra shown in Fig. 4.12 (bottom). There is excellent agreement in comparing the Pu(IV) bands between the actual commercial fuel extract (Fig. 4.12, top) and fuel simulant extract (Fig. 4.12, bottom).

The Raman and vis-NIR spectra of the ATM-109 feeds were subjected to chemometric analysis and standard Beers Law spectral analysis to deter­mine the concentrations of U, Pu, and Np present in solution. The resulting concentrations are contained in Table 4.1. For comparison, the ICP-MS results are also displayed, along with both the ORIGEN code calculations for these fuel samples and the computed ratios of analytical results for ORIGEN/ICP and Spectroscopic/ICP data. From this table, it is evident that the spectroscopic method is in excellent agreement with the standard ICP-MS analysis.