Monitoring of Spent Nuclear Fuel Reprocessing Studies via UVVisible Spectroscopy

1
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

2
Outline

• Introduction
• ANL experiments
• Experimental Setup
• Results
• UNLV
• Experimental Setup
• Results
• Conclusions

3
Introduction

• 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

4
Background

• 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
Solvent TBP in dodecane
Scrub Aqueous HNO3
Strip Aqueous HNO3
Extraction Section
Scrub Section
Strip Section
Raffinate Aqueous HNO3 Pu, FP
Product Aqueous HNO3 U, Tc
Spent Solvent
5
Centrifugal Countercurrent Contactors

• 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

Scrub
Scrub
Feed
Spent solvent
Strip
Raffinate
Solvent
Product
6
Centrifugal Countercurrent Contactors

• Housed as one
• Fast
• Efficient

Spinning Rotor with Indicator
Separation Zone
Mixing Zone
7
Fiber optic dip probe (ANL)

• 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
• solution

7
8
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

9
Results

• 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
10
Summary

• 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

10
11
Flow-thru Cuvettes (UNLV)

• 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 pumps (UNLV) range is 0.5-4 mL/min
• Industrial scale will be L/min
• Slight variations due to tightness of clamps and
  tubing size

11
12
Experimental Setup
Flow-through cuvette connected to peristaltic pump
Cuvette placed inside UV-Visible spectrometer
13
A, B, D Pathlength Normalized

• 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.
14
E, G, H Pathlength normalized

• Calculation of U
• E 0.57 M (0.63 M)
• G 0.96 M (1.01 M)
• H 1.28 M (1.26 M)

15
Summary

• 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 e10 M-1cm-1 provides method
  and experimental check

16
Influence of Acid 0.01 M 0.1 M H
16
17
Influence of Acid 0.5 M 1 M H
17
18
Influence of Acid 3 M H
18
19
Influence of Acid 6 M H
19
20
Summary

• 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

21
Calculation of e, 426 nm
22
Conclusions

• 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 e 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.
22
23
Future Work

• Titration cell setup with flow-through cuvettes
• 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

23
24
Acknowledgements

• 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
  Securitys Domestic Nuclear Detection Office and
  the U.S. Department of Defenses Domestic Threat
  Reduction Agency

24