Speciation Model Selection by Monte Carlo Analysis of Optical Absorption Spectra: Plutonium(IV) Nitrate Complexes

Berg, John M.; Veirs, D. K.; Vaughn, R.B.; Cisneros, Michael R.; Smith, Craig W.

doi:10.1366/0003702001950436

Cited by 21 publications

(16 citation statements)

References 19 publications

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“…A PCA analysis by Berg et al. 16 indicates that there are three Pu(IV) nitrate species < 2 M. These species, in combination with temperature and disproportionation, would lead to a total of five LVs for the model (temperature and disproportionation providing the other two PCs). However, in Berg’s analysis the third LV is associated with only 0.17% of the spectral variance, suggesting that the third species is only present in trace quantities in this acidity region.…”

Section: Resultsmentioning

confidence: 99%

“…Up to five different Pu(IV) nitrate complexes (Pu(NO 3 ) n 4–n , n = 0, 1, 2, 4, 6) are present across this range, with typically two to three complexes present at any one time. 15,16 As acidity increases, and higher nitrate complexes form, significant changes are observed across the entire spectrum. These changes are particularly notable for the strong absorbance peak that appears at 470 nm at low acidity.…”

Section: Introductionmentioning

confidence: 99%

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A Piecewise Local Partial Least Squares (PLS) Method for the Quantitative Analysis of Plutonium Nitrate Solutions

2017

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We have developed a piecewise local (PL) partial least squares (PLS) analysis method for total plutonium measurements by absorption spectroscopy in nitric acid-based nuclear material processing streams. Instead of using a single PLS model that covers all expected solution conditions, the method selects one of several local models based on an assessment of solution absorbance, acidity, and Pu oxidation state distribution. The local models match the global model for accuracy against the calibration set, but were observed in several instances to be more robust to variations associated with measurements in the process. The improvements are attributed to the relative parsimony of the local models. Not all of the sources of spectral variation are uniformly present at each part of the calibration range. Thus, the global model is locally overfitting and susceptible to increased variance when presented with new samples. A second set of models quantifies the relative concentrations of Pu(III), (IV), and (VI). Standards containing a mixture of these species were not at equilibrium due to a disproportionation reaction. Therefore, a separate principal component analysis is used to estimate of the concentrations of the individual oxidation states in these standards in the absence of independent confirmatory analysis. The PL analysis approach is generalizable to other systems where the analysis of chemically complicated systems can be aided by rational division of the overall range of solution conditions into simpler sub-regions.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Piecewise Local Partial Least Squares (PLS) Method for the Quantitative Analysis of Plutonium Nitrate Solutions

2017

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“…Subtle spectral effects may subsequently arise from changes in the spheres of hydration surrounding the analyte. 11 Note that uranium oxidation state is not expected to change in these solutions due to the presence of Fe 2+ .…”

Section: +mentioning

confidence: 96%

On Line Spectrophotometric Measurement of Uranium and Nitrate in H Canyon

Lascola¹

2002

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Successful and timely completion of the Highly Enriched Uranium Blend Down Project requires an aggressive processing schedule. One of the requirements for meeting the schedule is the use of on-line instrumentation to eliminate the delays associated with the analysis of samples extracted from process tanks. The Analytical Development Section of the Savannah River Technology Center has developed on-line spectrophotometers to measure uranium and nitric acid concentrations in tanks in H Canyon. Development areas addressed in this report include air-lift samplers, instrument control and analysis software, and diode array spectrophotometers. A total of nine tanks will be analyzed using two spectrophotometers. The acquired spectra are interpreted using partial leastsquares models which are valid for solutions with uranium concentrations up to 11 g/L and nitrate concentrations as high as 6 M. Concentration-dependent measurement uncertainities (2σ) are less than 0.30 g/L for uranium and 0.32 M for nitrate, and are comparable to the uncertainties of available diode array spectroscopy methods at the Analytical Laboratory (AL) facility. The models incorporate corrections for the spectral effects of Fe (<3 g/L) and Hg (<1 g/L), which are expected to be present in some process streams. Analyses with the on-line instrumentation can be performed in less than one minute, a large time savings compared to the many hours required for sampling, transport, and analysis of grab samples by AL. Other benefits of the on-line instrumentation include the reduction of radiological exposure to personnel and cost savings associated with fewer demands on AL and faster processing rates. SUMMARYThis report describes the on-line instrumentation developed by the Analytical Development Section of Savannah River Technology Center (SRTC) in support of Highly Enriched Uranium (HEU) Blend Down processing in H Canyon. The system provides measurements of uranium and nitrate concentrations for nine tanks located before and after the mixer-settler separation banks. An air-lift sampler/flow cell system attached to each tank provides access to the contents of each tank. Absorption spectra of the solutions are obtained with one of two diode-array spectrophotometers that are coupled to the flow cells by fiber optics. The spectra are analyzed using partial least-squares analysis models, and the results are reported to the H Canyon Distributed Control System. This instrument replaces a spectrophotometer system developed and installed in the late 1980's 1 which was eventually abandoned after a redefinition of the site's priorities. Recent development work at SRTC incorporated improvements to the samplers, spectrophotometers, control software, and analysis models. This report describes those technical improvements and serves as an operating, design, and performance guide for the system. INTRODUCTION Measurement PrincipleThe basis of diode array spectroscopy as an analytical technique is the determination of the concentration-and wavelength-dependent li...

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“…The equilibrium between the Pu nitrate species, and thus the absorbance spectrum, is independent of total Pu concentration for these process conditions. [21] Since the overall magnitude of the spectrum is dependent on Pu concentration, normalizing the spectra to unit area allows the effects of shape change to be isolated from the effects of Pu concentration. Table 4-1 summarizes the three acidity classification models that are used in the analysis scheme.…”

Section: Pu Calibration -Acidity Classification Modelsmentioning

confidence: 99%

Spectrophotometers for plutonium monitoring in HB-line

Lascola

O'Rourke

Kyser

et al. 2016

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Management (EM). standards. Gary Dobos streamlined the procurement process for instrument components and absorbance standards. Lindsay Roy, in addition to providing technical review of this document, helped us communicate the sometimes esoteric technical details of the project to our customers. Deanna Stimac, Chris Loyal, and James Therrell in HB-Line Engineering helped keep the project on track, facilitated communication between SRNL and HB-Line stakeholders, and provided important insight into process requirements. Ed Sadowski and Jeff Schaade provided critical programmatic support in promoting the benefits of this instrumentation and keeping enthusiasm and facility support of this project at a high level even during the challenges of process startup.

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Speciation Model Selection by Monte Carlo Analysis of Optical Absorption Spectra: Plutonium(IV) Nitrate Complexes

Cited by 21 publications

References 19 publications

A Piecewise Local Partial Least Squares (PLS) Method for the Quantitative Analysis of Plutonium Nitrate Solutions

A Piecewise Local Partial Least Squares (PLS) Method for the Quantitative Analysis of Plutonium Nitrate Solutions

On Line Spectrophotometric Measurement of Uranium and Nitrate in H Canyon

Spectrophotometers for plutonium monitoring in HB-line

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