Mentor: Lei Zhang

Location of Research: Notre Dame

Category of Research: Chemistry

Working Title: Thermodynamics of U(SO4)2(H2O)4

Topic/problem: ‍Thermodynamic analysis of U(SO4)2(H2O)4

Research Plan:

The management of nuclear waste is not just a major economic issue, but also a critical environmental issue. Annually, the nuclear industry produces 2,000 - 2,300 metric tons of used nuclear fuel. In the past four decades, 74,258 metric tons of used nuclear fuel has been produced. Due to the long half-lives of some radioactive elements, the dangers of much of this waste will not be negated for hundreds, thousands, or even millions of years.
The messes we make with radioactive waste have the potential to last for long stretches of time, possibly even longer than we will last. Having the opportunity to be under the mentorship of some of the leading experts in nuclear waste management is not only thrilling to me from an experience point of view, but also from a moral perspective. Being able to contribute at all to a project that's impact could be felt by people for generations to come motivated me to choose this project.
The goal of this research is to develop the understanding of the impact of the tetravalent cation on the stability of U(SO4)2(H2O)4 that crystallizes in orthorhombic space groups, α- (Fddd) and/or β- (Pnma) polymorphs which are structurally related.
U4+(SO4)2(H2O)4 crystallizes in two structures with identical stoichiometry, the UO4(H2O)4 square antiprisms share corners with SO4 tetrahedra to produce sheets parallel to (001) (α-form) and (100) (β-form), with the difference being the local coordination environment about the tetravalent U4+ by the arrangement of SO4 tetrahedra and water molecules (Jayadevan).
Systematic thermochemical studies will be performed on the compound U4+(SO4)2(H2O)4 with both or either α- and β-forms, to understand the thermodynamics of these compounds with varying tetravalent cations. First, to obtain a large quantity of pure crystals of this compound, many reactions will occur with varying amounts of the reagents Uranyl acetate dehydrate and H2SO4 in order to find the most consistent solution. The compound will then be studied through the use of calorimetry. To measure the compound’s heat of formation, the solution will be placed in a Heat Balance calorimeter which will measure any heat changes the solution will go through during reaction. After the solution forms crystals, these crystals will then be placed in a high temperature calorimeter, which can go up to 1000 degrees Celsius to burn the substance, and give values as to the total enthalpy of the system. Using these two tools the thermodynamics of the compound U4+(SO4)2(H2O)4 with both or either α- and β-forms will be compared (Majzlan).
Work on this experiment will involve the use of many potentially hazardous materials. Radioactive materials and dangerous chemicals can be found in the solutions of Uranyl acetate dehydrate and H2SO4. To mitigate these risks, proper safety clothing (such as lab coats, gloves, goggles, and badges to detect radiation) will be worn, proper training on working in a lab with potentially dangerous materials will be given, and time spent directly working with dangerous substances will be minimized.
The data gathered from this research will strengthen the research community’s understanding of the impact of (001) (α-form) and (100) (β-form) formations in the structures of transuranic compounds.

Literature Cited
Albrecht, A. J.; Sigmon, G. E.; Moore-Shay, L.; Wei, R.; Dawes, C.;
Charushnikova, I. A.; Krot, N. N.; Starikova, Z. A. Radiokhymiya 2000, 42, 42.
Jayadevan, N. C.; Mudher, K. D. S.; Chackraburtty, D. M. Z. Kristallogr. 1982, 161, 7.
Majzlan, J.; Sejkora, J.; Machovič, V.; Talla, D. Mineralogical Magazine 2011, 75(6), 2739.
"On-Site Storage of Nuclear Waste." Nuclear Waste Amounts & On-Site Storage. NEI, n.d. Web. 22 Oct. 2015.
Wilson, R. E. Inorganic Chemistry 2011, 50, 5663.