ANS Student Conference, April 3 rd, 2009 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

ANS Student Conference, April 3 rd, Outline Introduction ANL experiments Experimental Setup Results UNLV Experimental Setup Results Conclusions

ANS Student Conference, April 3 rd, 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

ANS Student Conference, April 3 rd, 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 Background Extraction SectionScrub SectionStrip Section Solvent TBP in dodecane Scrub Aqueous HNO 3 Strip Aqueous HNO 3 Raffinate Aqueous HNO 3 Pu, FP Product Aqueous HNO 3 U, Tc Spent Solvent Fuel Derived Feed Aqueous HNO 3

ANS Student Conference, April 3 rd, Centrifugal Countercurrent Contactors In the UREX process, UO 2 2+ is extracted from the feed into the solvent Next, the scrub section scrubs the loaded solvent, now containing UO 2 2+, of any fission products that may have co-extracted with the UO 2 2+ The dilute HNO 3 strip solution extracts the UO 2 2+ species from the loaded solvent, exiting the scrub section Solvent Feed Scrub Raffinate Strip Spent solvent Product

ANS Student Conference, April 3 rd, Fresh Solvent Loaded Solvent Aqueous Product Centrifugal Countercurrent Contactors Housed as one Fast Efficient Aqueous Feed Mixing Zone Separation Zone Spinning Rotor with Indicator

ANS Student Conference, April 3 rd, Fiber optic dip probe (ANL) Range of probe M U conservatively Resolution of system found to be ± M U Aqueous 0.09, 0.10 & 0.11 M Nd(NO 3 ) 3 used in qualitative time response study Acquisition time of 300 μs Instantaneous spectral changes seen when probe put alternately in each solution

ANS Student Conference, April 3 rd, 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 ± M HNO 3, 28.1 ± 1.41 g/L U feed 20-stage 2-cm unit

ANS Student Conference, April 3 rd, Results Graph illustrating the growth of the UO 2 2+ in the product stream exiting stage 17 over time 1 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 UO 2 2+ to be incompletely stripped from the loaded solvent and results in a higher concentration in the product stream 1 Image courtesy of J.F. Krebs, ANL

ANS Student Conference, April 3 rd, 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 s 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

ANS Student Conference, April 3 rd, 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 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

ANS Student Conference, April 3 rd, Experimental Setup Flow-through cuvette connected to peristaltic pump Cuvette placed inside UV-Visible spectrometer

ANS Student Conference, April 3 rd, A, B, D Pathlength Normalized Allows for direct comparison across varying pathlength samples 2 Calculation of [U] A ~ 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.

ANS Student Conference, April 3 rd, 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)

ANS Student Conference, April 3 rd, Summary Loss of peak resolution evident at 6 M HNO 3 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 -1 cm -1 provides method and experimental check

ANS Student Conference, April 3 rd, Influence of Acid 0.01 M & 0.1 M [H + ]

ANS Student Conference, April 3 rd, Influence of Acid 0.5 M & 1 M [H+]

ANS Student Conference, April 3 rd, Influence of Acid 3 M [H+]

ANS Student Conference, April 3 rd, Influence of Acid 6 M [H+]

ANS Student Conference, April 3 rd, 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 + ]

ANS Student Conference, April 3 rd, Calculation of ε, 426 nm

ANS Student Conference, April 3 rd, Conclusions Alleviated slug flow obstacle seen in fiber optic dip probe via cuvette flow-through cell At high [HNO 3 ] (or high [NO 3 - ]) and high [UO 2 2+ ] Still see loss of peak definition as expected 3 Calculations of ε confirm [HNO 3 ] 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.

ANS Student Conference, April 3 rd, Future Work Titration cell setup with flow-through cuvettes Can precisely alter [H + ], [NO 3 - ], [UO 2 2+ ] 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

ANS Student Conference, April 3 rd, 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 Security’s Domestic Nuclear Detection Office and the U.S. Department of Defense’s Domestic Threat Reduction Agency