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

Abstract

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.

Applying Two-Dimensional Correlation Spectroscopy and Principal Component Analysis to Understand How Temperature Affects the Neptunium(V) Absorption Spectrum

“…The dominant peak at 979.5 nm is outside the dynamic range of the spectrophotometer at the Np concentration reported in Figure 1. Several distinct absorption bands were also observed at 433, 476.5, 616.4, 687.0, 769.5, 914, 1023, 1095, 1116, and 1616 nm with molar absorptivity values ranging from 2.5-27 M −1 •cm −1 [3]. Several peaks, like the sharp 616 nm band and low-intensity peaks from 500-600 nm, are complex and confounded by overlapping peaks that are difficult to resolve.…”

“…Neptunium-237 (t 1 2 = 2.14 × 10 6 years) is the isotope most suitable for laboratory handling, and a large inventory has been accumulated worldwide as a by-product of the neutron irradiation of uranium fuel. Neptunium-237 is an important precursor to the production of 238 Pu, a heat source material used by the National Aeronautics and Space Administration to power deep space missions [2,3]. The chemistry of Np is complex with respect to redox properties and coordination chemistry.…”

“…The temperature-induced effects on other peaks in the spectrum have not been documented in the literature. Accounting for dynamic temperature conditions is highly relevant to operations taking place in glove box and hot cell environments where temperatures can vary by more than 20 • C compared with benchtop operations [2,3] Characterizing the entire spectrum will bolster the spectrophotometric approach for the quantification of Np(V) in processing solutions to support various fuel cycle applications and Np processing operations for the 238 Pu Supply Program [3].…”

Feasibility Study of Spectrophotometry to Support a Promethium Production Program at ORNL

“…Fiber-optic cables can transmit light over large distance (e.g., hundreds of meters) to enable ultraviolet/visible/near infrared (UV-Vis-NIR) absorption measurements in hot cells while personnel operate equipment in a control room. This allows spectroscopic measurements of materials located in the hot cells at the Radiochemical Engineering Development Center at Oak Ridge National Laboratory (ORNL) without transferring samples out of the cells for the 238 Pu Supply Program at ORNL [1][2][3][4][5][6]. The developed approach can readily be adapted to other isotope production programs [7].…”

Evaluating Optical Techniques to Characterize Solid State Samples for the Pu-238 Supply Program

“…Spectrophotometry is an important component of the 238 Pu Supply Program for measuring Np and Pu concentrations, oxidation state(s), and monitoring separations. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Spectrophotometry, or absorption spectroscopy, is a technique that quantifies the amount of light absorbed by a sample as a function of wavelength. Ultraviolet (UV)-visible (Vis)-near-infrared (NIR) spectrometers collect spectra at relatively rapid intervals (e.g., 10-1,000 ms) and contain a wealth of information.…”