UNLV Theses, Dissertations, Professional Papers, and Capstones 12-2010 Speciation and spectroscopy of the uranyl and tetravalent plutonium nitrate systems: Fundamental studies and applications to used fuel reprocessing Nicholas A. Smith University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Atomic, Molecular and Optical Physics Commons, Nuclear Commons, and the Radiochemistry Commons Repository Citation Smith, Nicholas A., "Speciation and spectroscopy of the uranyl and tetravalent plutonium nitrate systems: Fundamental studies and applications to used fuel reprocessing" (2010). UNLV Theses, Dissertations, Professional Papers, and Capstones. 776. http://dx.doi.org/10.34917/2044437 This Dissertation is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). 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SPECIATION AND SPECTROSCOPY OF THE URANYL AND TETRAVALENT PLUTONIUM NITRATE SYSTEMS: FUNDAMENTAL STUDIES AND APPLICATIONS TO USED FUEL REPROCESSING by Nicholas Alexander Smith Bachelor of Science Lake Superior State University 2005 A dissertation submitted in partial fulfillment of the requirements for the Doctor of Philosophy Degree in Radiochemistry Department of Chemistry College of Sciences Graduate College University of Nevada, Las Vegas December 2010 Copyright by Nicholas Alexander Smith 2011 All Rights Reserved THE GRADUATE COLLEGE We recommend the dissertation prepared under our supervision by Nicholas Alexander Smith entitled Speciation and Spectroscopy of the Uranyl and Tetravalent Plutonium Nitrate Systems: Fundamental Studies and Applications to Used Fuel Reprocessing be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Radiochemistry Department of Chemistry Kenneth Czerwinski, Committee Chair Alfred Sattelberger, Committee Member Gary Cerefice, Committee Member Ralf Sudowe, Graduate Faculty Representative Ronald Smith, Ph. D., Vice President for Research and Graduate Studies and Dean of the Graduate College December 2010 ii ABSTRACT Speciation and Spectroscopy of the Uranyl and Tetravalent Plutonium Nitrate systems: Fundamental Studies and Applications to Used Fuel Reprocessing by Nicholas Alexander Smith Dr. Kenneth R. Czerwinski, Examination Committee Chair Professor of Chemistry Chair of the Department of Radiochemistry University of Nevada, Las Vegas This dissertation explores the use of UV-Visible spectroscopy and Time Resolved Laser Induced Fluorescence spectroscopy as near real time process monitors of uranium and plutonium concentrations in aqueous reprocessing trains. The molar absorptivities and linear ranges of these metals were investigated under total nitrate and acid concentrations similar to those found in current reprocessing systems. Concurrent to this, a new multiple wavelength monitor was derived that is capable of determining the total nitrate concentration spectroscopically. This method uses the uranium absorbance spectrum to calculate the nitrate concentration in solution. When used as part of an Advanced Safeguard suite, this technique can provide information on the process chemistry in use. The fundamental chemistry of the uranyl nitrate system was investigated to add to the thermodynamic data set. A combination of spectroscopic measurements, Density Functional Theory calculations, Extended X-ray Absorption Fine Structure spectroscopy, and observations of solvent extraction studies were used to theorize a new model of uranyl-nitrate speciation. In this model, the dominant species at low nitrate iii + concentrations is UO 2(NO 3)2 and the UO 2NO 3 species is de-emphasized. Spectrophotometric titrations of the uranyl system were used to determine the log β2,1 values for this system at multiple ionic strengths and the zero ionic strength stability constants were calculated using the Specific Ion Interaction Theory. The UV-Visible spectroscopy of the tetravalent plutonium nitrate system was investigated as a function of nitric acid concentration. Two pseudo-isobestic points were identified in the spectra which can be used to determine the total Pu IV concentration. Factor analysis was then used to investigate the speciation of the system; a total of 5 species exist between 2 and 10 M HNO 3. This information can be used to focus future studies. iv ACKNOWLEDGMENTS There is a long list of people that I would like to thank as the process of completing a doctoral degree is so overwhelming that without support anyone would crack under the pressure long before the defense. I want to thank my wife, Heather, first and foremost; she has put up with more than anyone else during this long ordeal and I can only hope that I can repay her for all of the time and energy she has expended to support me. Next, I would like to thank my dissertation committee, Drs. Ken Czerwinski, Gary Cerefice, Al Sattelberger, and Ralf Sudowe. They were instrumental in shaping both my research and my theories throughout my time at UNLV. My family deserves to be mentioned as they all have followed my academic career closely and have always been both interested in my work and encouraging of my endeavors. I would like to thank Tom O’Dou, Trevor Low and Julie Bertoia for maintaining and managing the group laboratories; these individuals make possible the work that all of us do and we would be lost without them. Thanks are in order for Drs. Patricia Paviet-Hartmann and Thomas Hartmann who provided unique viewpoints and welcomed suggestions due to their experiences outside of academia. Finally, I would like to thank my cadre-mates: Craig Bias, Rich & Julie Gostic, Kiel Holliday, Chinthaka Silva, and Amber Wright: without other students to guide us we guided ourselves through this ordeal and I thank you all. v TABLE OF CONTENTS ABSTRACT .................................................................................................................. iii ACKNOWLEDGEMENTS ............................................................................................. v LIST OF TABLES ...................................................................................................... viii LIST OF FIGURES ........................................................................................................ix CHAPTER 1 INTRODUCTION .............................................................................. 1 1.1 Dissertation Overview .................................................................................... 2 1.2 Motivation for Research ................................................................................. 2 1.3 Project Goals .................................................................................................. 5 CHAPTER 2 BACKGROUND ................................................................................ 6 2.1 Definitions and Formulae ............................................................................... 6 2.2 Review of the Uranyl Nitrate Literature........................................................ 13 2.3 Review of the Plutonium(IV) Nitrate Literature ............................................ 28 2.4 Ionic Strength Effects ................................................................................... 34 2.5 Theoretical Modeling of Thermodynamic Quantities .................................... 36 2.6 Solvent Extraction of Actinides .................................................................... 36 2.7 Process Monitoring and IAEA/DOE Safeguards ........................................... 39 CHAPTER 3 ANALYTICAL ................................................................................ 44 3.1 Titrations ...................................................................................................... 44 3.2 Ultraviolet-Visible Spectroscopy .................................................................. 51 3.3 Time Resolved Laser Induced Fluorescence Spectroscopy (TRLFS) ............ 57 3.4 Inductively Couples Plasma – Atomic Emission Spectroscopy ..................... 63 3.5 X-Ray Absorption Fine Structure Spectroscopy ........................................... 66 3.6 Radiometric Techniques ............................................................................... 69 CHAPTER 4 EXPERIMENTAL............................................................................ 73 4.1 UV-Visible Spectroscopy Batch Experiments ............................................... 73 4.2 TRLFS Batch Experiments ........................................................................... 88 4.3 Potentiometric Titrations .............................................................................. 90 4.4 Spectrophotometric Titrations ...................................................................... 92 4.5 EXAFS Spectroscopy ................................................................................... 95 CHAPTER 5 MODELING ...................................................................................