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Monitoring of Spent Nuclear Fuel Reprocessing Studies via UV-Visible Spectroscopy. Jamie L. Warburton Radiochemistry PhD Candidate University of Nevada, Las Vegas Harry Reid Center for Environmental Studies. Outline. Introduction ANL experiments Experimental Setup Results UNLV

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Monitoring of spent nuclear fuel reprocessing studies via uv visible spectroscopy

Monitoring of Spent Nuclear Fuel Reprocessing Studies via UV-Visible Spectroscopy

Jamie L. Warburton

Radiochemistry PhD Candidate

University of Nevada, Las Vegas

Harry Reid Center for Environmental Studies

Outline UV-Visible Spectroscopy

  • Introduction

  • ANL experiments

    • Experimental Setup

    • Results

  • UNLV

    • Experimental Setup

    • Results

  • Conclusions

Introduction UV-Visible Spectroscopy

  • Process monitoring can improve safeguards in spent nuclear fuel reprocessing

  • Several parameters can be monitored

    • Mass, temperature, flow rate, pH, concentration

  • UV-Vis is an effective technique for concentration monitoring

    • Portable

    • On-line capability

    • Very fast spectral acquisition

    • Rapid analysis possible to confirm process chemistry and for materials accountability

      • Peak to peak ratio measurements

      • Significant changes in absorbance

Background UV-Visible Spectroscopy

  • Argonne has conducted bench scale demos of UREX+ flowsheets

  • Experiments used a 24-stage bank of 2 cm contactors

  • Process variables include

    • Concentrations

      • Feed

      • Solvent

      • Scrub

      • Strip

    • Flow rates

      • Feed

      • Solvent

      • Scrub

      • Strip

    • Temperatures

      • Extraction, scrub, strip

Fuel Derived Feed

Aqueous HNO3


TBP in dodecane


Aqueous HNO3


Aqueous HNO3

Extraction Section

Scrub Section

Strip Section


Aqueous HNO3

Pu, FP


Aqueous HNO3

U, Tc

Spent Solvent

Centrifugal countercurrent contactors
Centrifugal Countercurrent Contactors UV-Visible Spectroscopy

  • In the UREX process, UO22+ is extracted from the feed into the solvent

  • Next, the scrub section scrubs the loaded solvent, now containing UO22+, of any fission products that may have co-extracted with the UO22+

  • The dilute HNO3 strip solution extracts the UO22+ species from the loaded solvent, exiting the scrub section




Spent solvent





Centrifugal countercurrent contactors1

Aqueous UV-Visible Spectroscopy








Centrifugal Countercurrent Contactors

  • Housed as one

  • Fast

  • Efficient

Spinning Rotor with Indicator

Separation Zone

Mixing Zone

Fiber optic dip probe anl
Fiber optic dip probe (ANL) UV-Visible Spectroscopy

  • Range of probe 0.005-0.566 M U conservatively

  • Resolution of system found to be

    0.002 ± 0.0001 M U

  • Aqueous 0.09, 0.10 & 0.11 M Nd(NO3)3

    used in qualitative time response study

    • Acquisition time of 300 μs

    • Instantaneous spectral

      changes seen when probe

      put alternately in each



Experimental setup

20-stage 2-cm unit UV-Visible Spectroscopy

Experimental Setup

  • Probe measuring product stream via Swagelok flow-through cell

  • OmniDriver integrated into LabVIEW controller

    • Spectral acquisition time of 250 microseconds

  • Cold feed used to achieve steady-state in contactors

    • Hot run after steady state ~3.5 hours

  • 1.002 ± 0.001 M HNO3, 28.1 ± 1.41 g/L U feed

Results UV-Visible Spectroscopy

  • Characteristic peaks evident at 403, 414, & 426 nm

  • Uranyl grows into product stream due to 20-stage contactors and time needed to achieve steady-state

  • Reducing the strip solution flow rate causes the UO22+ to be incompletely stripped from the loaded solvent and results in a higher concentration in the product stream

Graph illustrating the growth of the UO22+ in the product stream exiting stage 17 over time1

1 Image courtesy of J.F. Krebs, ANL

Summary UV-Visible Spectroscopy

  • Fiber optic probe setup is successful in monitoring product conditions in simulated UREX run

    • Varying flow rate does not affect spectral acquisition, but does affect product concentration

  • UV-Vis monitoring used in conjunction with flow rate meters to identify source of absorbance changes

    • Intended vs. unintended flow rate alterations

    • Material diversion

  • Acquisition time of 250 ms

    • Online automated monitoring of peaks as well as peak to peak comparison is needed – user monitoring is too slow

  • Flow rates result in slugs of solution in product stream


Flow thru cuvettes unlv
Flow-thru Cuvettes (UNLV) UV-Visible Spectroscopy

  • Hellma flow-through cuvettes instead of fiber optic dip probe

    • Utilizing robust UV-Vis while peristaltic pump provides sample flow

    • Sample “stock” is outside UV-Vis and can be changed during absorbance measurements

    • Various pathlengths available (1 cm, 0.5 cm, 0.1 cm)

      • Disassemble setup to change pathlength

  • Flow rates

    • Previously (ANL) looking at 5-40 mL/min

    • Peristaltic pump’s (UNLV) range is ~0.5-4 mL/min

    • Industrial scale will be ~ L/min

    • Slight variations due to tightness of clamps and tubing size


Experimental setup1
Experimental Setup UV-Visible Spectroscopy

Flow-through cuvette connected to peristaltic pump

Cuvette placed inside UV-Visible spectrometer

A b d pathlength normalized
A, B, D Pathlength Normalized UV-Visible Spectroscopy

  • Allows for direct comparison across varying pathlength samples2

  • Calculation of [U]

    • A ~ 0.008 M (0.01 M)

    • B ~ 0.10 M (0.12 M)

    • D ~ 0.22 M (0.26 M)

[2] Theoretical Basis of Bouguer-Beer Law of Radiation Absorption, F.C. Strong, 1952.

E g h pathlength normalized
E, G, H Pathlength normalized UV-Visible Spectroscopy

  • Calculation of [U]

    • E ~ 0.57 M (0.63 M)

    • G ~ 0.96 M (1.01 M)

    • H ~ 1.28 M (1.26 M)

Summary UV-Visible Spectroscopy

  • Loss of peak resolution evident at 6 M HNO3 across uranyl concentrations

  • Peak ratio changes throughout uranyl concentrations for [H+] ≥ 3 M

  • At highest uranyl (1.26 M) shouldering in spectra across [H+] range

  • Calculation assuming ε=10 M-1cm-1 provides method and experimental check

Influence of acid 0 01 m 0 1 m h
Influence of Acid UV-Visible Spectroscopy 0.01 M & 0.1 M [H+]


Influence of acid 0 5 m 1 m h
Influence of Acid UV-Visible Spectroscopy 0.5 M & 1 M [H+]


Influence of acid 3 m h
Influence of Acid UV-Visible Spectroscopy 3 M [H+]


Influence of acid 6 m h
Influence of Acid UV-Visible Spectroscopy 6 M [H+]


Summary UV-Visible Spectroscopy

  • No change across

    • 0.01 M & 0.1 M [H+]

    • 0.5 M & 1 M [H+]

    • Trends in peak ratios remain similar

  • Rapid changes seen at 3 M & 6 M [H+]

    • Complete loss of peak resolution

    • Significant trend alterations in peak ratios

       No distinct peaks at 6 M [H+]

Calculation of 426 nm
Calculation of UV-Visible Spectroscopyε, 426 nm

Conclusions UV-Visible Spectroscopy

  • Alleviated slug flow obstacle seen in fiber optic dip probe via cuvette flow-through cell

  • At high [HNO3] (or high [NO3-]) and high [UO22+]

    • Still see loss of peak definition as expected3

  • Calculations of ε confirm [HNO3] and [U] dependence

  • UV-Vis spectroscopy can be used effectively in process monitoring to demonstrate a more proliferation-resistant fuel reprocessing plant

[3] The Simultaneous Analysis of Uranium and Nitrate, D.T. Bostick et al, 1978.


Future work

Titration cell setup with flow-through cuvettes UV-Visible Spectroscopy

Can precisely alter [H+], [NO3-], [UO22+]

Single-user interface

Evaluate sensitivity to rate of change of acid and nitrate

Identify change from UREX to PUREX

Confidence level?

8 kg Pu or 25 kg HEU

Future Work


Acknowledgements UV-Visible Spectroscopy

  • Dr. Kenneth Ronald Czerwinski

  • Dr. Patricia Paviet-Hartmann

  • Dr. Gary Steven Cerefice

  • Nick Smith

  • Amber Wright

  • Dr. John F. Krebs, ANL

  • This work was performed under the Nuclear Forensics Graduate Fellowship Program which is sponsored by the U.S. Department of Homeland Security’s Domestic Nuclear Detection Office and the U.S. Department of Defense’s Domestic Threat Reduction Agency