CHEMICAL SIGNATURES FOR UNKNOWN AND INTERDICTED SAMPLES IN THE ENVIRONMENT FOR NUCLEAR FORENSIC ANALYSIS
Open Access
- Author:
- Durrant, Chad Bredthauer
- Graduate Program:
- Nuclear Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 02, 2017
- Committee Members:
- Dr. Kenan Unlu, Dissertation Advisor/Co-Advisor
Dr. Kenan Unlu, Committee Chair/Co-Chair
Dr. Jack Brenizer, Committee Member
Dr. Marek Flask, Committee Member
Dr. Peter Heaney, Outside Member
Dr. Annie Kersting, Special Member
Dr. Dawn Shaughnessy, Special Member - Keywords:
- Radiochemistry
Sorption
Desorption
Cesium
Plutonium
Rapid Separations - Abstract:
- Irradiation of materials may produce unique signatures that can be measured and identified through the various types of radiation particles emitted from the materials. The emitted particles may be characteristic to specific radioisotopes thereby allowing the identification and characterization of the irradiated material. The characterization of a potentially radioactive material and then determining its origin is useful in diverse applications including nuclear forensics samples. This thesis investigates problems associated with two areas, improving the understanding of radionuclide transport in the environment and improving the speed with which samples can be chemically separated. Both topics are relevant to increasing the ability to apply nuclear forensics techniques to unknown samples in the environment. Understanding sorption and desorption processes is essential to predicting the mobility of radionuclides in the environment. Typically, such sorption reactions are studied in single mineral binary systems. This work investigates adsorption/desorption of cesium (Cs) in both binary and two-mineral “ternary” systems in order to study component additivity, desorption kinetics and sorption reversibility in the presence of two competing minerals. First, binary Cs sorption experiments were performed with the clay minerals, illite, montmorillonite, and kaolinite, in a NaHCO3 solution over a Cs concentration range of 10-3 to 10-11 M to quantify the non-linear (illite) and linear (kaolinite and montmorillonite) sorption behavior. The binary sorption experiments were followed by desorption experiments to test for sorption reversibility. Cesium exhibits partial irreversible sorption to illite whereas Cs sorption to kaolinite and montmorillonite is reversible. In the ternary experiments, Cs was separately sorbed to illite, iv montmorillonite or kaolinite for ~14 days, and then Cs-free illite was place inside a dialysis bag (Float-a-lyzer®) inside the beaker with the pre-sorbed clays to induce desorption of the originally adsorbed Cs. Results from these ternary experiments show significantly greater Cs desorption compared to the binary desorption experiments. The ternary experiments confirm batch desorption findings of irreversible sorption of some Cs to illite and reversible sorption of Cs to kaolinite and montmorillonite. Plutonium (Pu), which has significantly more complex aqueous chemistry than Cs, is another radionuclide of chief concern in environmental contamination and transport scenarios. The dialysis bag experimental setup and procedure, which was designed and tested in the Cs experiments, was then applied to experiments using Pu to investigate the sorption and long-term desorption behavior of Pu in the presence of two minerals. These experiments were specifically designed to look at the long-term (7 months) reversibility of Pu sorption to montmorillonite in the presence of goethite, both common minerals in a variety of geologic environments. The distribution coefficient, Kd, of Pu sorption to montmorillonite continued to increase over the duration of the experiment, indicating that equilibrium in a ternary system is a long process occurring over several months to years. Results suggest that Pu on montmorillonite is reversible at pH 8, with up to 14 percent of the Pu desorbing from the montmorillonite and sorbing to the goethite. This would suggest that goethite may be the more important mineral influencing long-term colloid-facilitated transport of Pu. Additional studies were undertaken to explore the development and testing of an automated chemical separation system for post-detonation nuclear forensic related samples. The development of this chemical separation system entailed identifying a v suitable chemical separation sequence to sequentially separate eight elements; europium (Eu), gadolinium (Gd), neptunium (Np), plutonium (Pu), promethium (Pm), terbium (Tb), uranium (U), and zirconium (Zr), elements that may be of interest for post-detonation nuclear forensic analysis. A likely post-detonation situation could be in an urban environment where many samples could have a significant cement matrix associated with the sample. The chemical separation scheme would need to account for this given matrix and the large mass of associated material. To this end, batch sorption and separation experiments were conducted to examine the sorption behavior of Pu and U on AG 1x8 resin in varying concentrations of hydrochloric acid (HCl) and dissolved cement. These batch experiments were used to determine possible interferences or adverse separation effects that may result from a high concentration cement matrix. Similar batch sorption experiments with varying acid and cement concentrations were also conducted with Eu and Eichrom’s LN® and TRU® resins in order to determine possible adverse consequences as a result of interferences caused by the cement. The hardware for the separation system consisted of several pumps, valves, ion-exchange columns, and a fraction collector. A software program written in LabVIEW was developed to control the hardware. A test separation experiment was conducted with uranium (U), lead (Pb), and tin (Sn) isotopes to troubleshoot and test the ability of the system to sequentially separate elements. The trial run successfully separated the elements; however, several changes were made afterwards including the addition of an injection loop, a fraction collector, and changing the tubing such that eluents flowed through a more chemically inert material that was less susceptible to corrosion. vi After developing the chemical separation scheme and system design was finished, it was tested with five surrogate samples. The purpose of using the automated chemical separation system was to shorten the time necessary to effectively separate the eight elements of interest. The total run-time for the system was 160 minutes including sample injection, sequential separation, and wash/regeneration steps. Four of the samples had a known composition, including one that had a cement-like matrix. The elemental fractions recovered were consistent across each sample including the cement-like sample. This consistency is indicative of the robustness of the system and its ability to handle even samples with significant background mass. The final sample was of unknown composition and used to demonstrate the ability of the automated chemical separation system to sequentially separate the elements of interest and accurately determine the initial sample composition. This automated chemical separation system was a proof of concept that the eight specified elements could successfully be separated using automation and used to determine the composition of an unknown sample. Actinide recoveries were around 90% and lanthanide recoveries were around 30%.