Fabrication and Characterization of a Silicon Carbide Alpha Detector for Molten Salt Application Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Joshua T. Jarrell, B.S., M.S. Graduate Program in Nuclear Engineering The Ohio State University 2018 Dissertation Committee Dr. Lei R. Cao, Advisor Dr. Thomas Blue Dr. Marat Khafizov 1 Copyrighted by Joshua T. Jarrell 2018 2 Abstract There exists a need for monitoring the actinide concentrations in elevated temperature molten salt environments. Reprocessing of used nuclear fuel through pyroprocessing is being investigated as a viable method to manage the growing stockpile of used nuclear fuel. Idaho National Laboratory has demonstrated the ability to reprocess both breeder and blanket fuel from the Experimental Breeder Reactor II using an electrorefining system. This system uses a molten eutectic salt mixture of lithium chloride and potassium chloride. This electrorefining system can produce high purity uranium ingots and mixed uranium- plutonium ingots. The fundamental electrochemistry used for this process precludes the separation of high purity plutonium when operated within the suggested process limits. However, special nuclear material may be diverted by operating outside of the normal process. Complete draw down of the uranium dissolved into the molten salt would allow for the subsequent removal of high purity plutonium. Monitoring of the operational history of the electrorefiner is therefore essential to address these non-proliferation and safeguard concerns. There is thus a need to monitor the concentrations of individual elements and isotopes present in the electrorefiner salt. Currently, such assays require time on the order of weeks to provide an accurate description of isotopic concentrations within the salt. Thus, a near real-time measurement system for the actinide isotopic concentrations within the salt is needed. All actinide isotopes of interest to non-proliferation and safeguards interests ii emit characteristic alpha particles. Semiconductor radiation detectors have been shown to provide a compact, high energy resolution solution to spectroscopic measurement needs. Silicon carbide, a wide band-gap semiconductor, provides elevated temperature operation capability and corrosion resistance in the molten salt environment that is superior to silicon. As a result, for this work, alpha radiation detectors comprised of 4H-SiC with Schottky barrier contacts have been fabricated and shown to operate above 500oC. Detector contact compositions of nickel-platinum was explored as possible Schottky contact structures. The electrical and diode characteristics of the detectors were measured. Alpha spectra from multiple source isotopes and source geometries were obtained in vacuum with the detector heated from 20oC to 500oC. The resulting detector behavior including alpha spectrum centroid position and detector energy resolution were measured. To avoid energy attenuation in the molten salt, a repeatable method for depositing actinides to the surface of the detector was devised that allows for repeated spectroscopic measurements by a single detector. The resilience of detector performance to submersion in a molten salt was investigated as well as energy resolution during elevated temperature operation. Detectors were characterized prior to being submerged in a 500oC molten LiCl-KCl eutectic salt for increasing time intervals. After submersion, the detectors were again characterized to identify any degradation. Detector packaging capable of withstanding the corrosive 500oC molten salt environment was developed which allows for electrical connections between the detector and spectrometry equipment. The packaging was designed to allow for actinide deposition on the active area of the detector, allowing for accurate calculations of the actinide mass deposited by a known current. Additionally, nuclear forensic applications of iii 4H-SiC alpha detectors in conjunction with electrodeposited source fabrication were explored. A method was determined to calculate the 235U enrichment in the product stream of an enrichment facility through measurement of the 234U and 235U enrichments in an electrodeposited source fabricated from depleted uranium. iv Dedication This is dedicated to my loving wife Jennifer. v Acknowledgments This work would not be possible without the assistance and support of many individuals. Foremost among these are Dr. Raymond Cao and Dr. Thomas Blue. Their guidance, suggestions, and feedback proved indispensable in my development as a graduate student. I would also like to acknowledge Dr. Lei Wang and Sha Xue for their work which contributed to the outcome of this research. Additionally, I would like to acknowledge Dr. Marat Khafizov for serving on my thesis defense committee. I would like to acknowledge Dr. Timothy Garcia, Dr. Benjamin Reinke and the staff of Nanotech West for their assistance with the development of the equipment and processes which were invaluable in the research presented in this work. I would also like to acknowledge the National Academy for Nuclear Training Fellowship and the Nuclear Regulatory Commission Fellowship programs. Their financial support of my stipend made this work possible. Additionally, I would like to thank the Nuclear Energy University Program for their support of the project on which I worked. vi Vita November 7, 1990 ……………… Born – Orange, VA, USA 2013 …………………….…...….. B.S Physics, James Madison University 2015 …………………………..… M.S. Nuclear Engineering, The Ohio State University 2016-Present ……………………. NRC Fellow, The Ohio State University Publications 1. Josh Jarrell, Milan Stika, Michael Simpson, Thomas E. Blue, and Lei R. Cao, “4H-SiC Alpha Spectrometry for Nuclear Forensics with Electrodeposited Sources”, J. of Radioanalytical and Nuclear Chemistry (accepted) 2. Josh Jarrell, Thomas E. Blue, and Lei R. Cao “Development of A Ni-Pt Schottky Diode for High Temperature Alpha Spectroscopy”. IEEE 2017 NSS/MIC/RTSD, 00(2):277– 287, Oct 2017. 3. Josh Jarrell, Milan Stika, Michael Simpson, Thomas E. Blue, Lei R. Cao. “Depleted Uranium and Th-232 Decay Chain Daughter Isotope Identification with 4H-SiC Alpha Spectroscopy”. Transactions of American Nuclear Society, 00(2):277–287, Oct 2017. 4. Lei Wang, Josh Jarrell, Sha Xue, Thomas Blue, Lei R. Cao. “The Fast Neutron Sensitivity of a SiC Detector”. Transactions of American Nuclear Society, 00(2):277– 287, Oct 2017. vii 5. Lei Cao, Josh Jarrell, Andrew Kauffman, Susan White, Kevin Herminghuysen, Douglas E. Hardtmayer, Jeff Sanders, Shelly Li “A Radioactive Tracer Dilution Method to Determine the Mass of Molten Salt”. Journal of Radioanaltyical and Nuclear Chemistry, https://doi.org/10.1007/s10967-017-5417-5, Aug 2017. 6. Lei Cao, Eric Moore, Josh Jarrell “Heteroepitaxial Diamond Growth on 4H-SiC using Microwave Plasma Chemical Vapor Deposition”. Heliyon, Sep 2017. 7. Joshua Jarrell, Eric Moore, Thomas Blue, Lei Cao “Elevated Temperature Alpha Spectroscopy with Nickel-Platinum 4H-SiC Schottky Diodes”. Transactions of American Nuclear Society, 116 (1). 123-125, Jun 2017. 8. M. Stika, S. Padilla, J. Jarrell, T. Blue, L. R. Cao, M. Simpson “Thin-Layer Elec- trodeposition of Thorium Metal from Molten LiCl-KCl”. Journal of Electrochemical Society, vol. 164, no. 8, 2017. 9. Josh Jarrell, Milan Stika, Max Chaiken, Michael Simpson, Thomas E. Blue, Lei R. Cao “Determination of the thickness of an electrodeposited thorium film with SiC alpha detectors”. J. Radioanalytical and Nuclear Chemistry, 1127-1133 Vol. 311, no. 2., Nov 2016. 10. Milan Stika, Max Chaiken, Josh Jarrell, Thomas Blue, Lei Raymond Cao, Michael Simpson “Thin-Layer Electrodeposition of Thorium and Uranium from Molten LiCl- KCl”. ECS Transactions, 603-608 volume 75, issue 15, 2016. 11. Milan Stika, Max Chaiken, Joshua Jarrell, Thomas Blue, Lei R. Cao, Michael Simpson “Electrodeposition of Actinides on a Semiconductor Detector for Concentration Monitoring”. Transactions of American Nuclear Society, 114 (1). 340-344, Jun 2016. 12. Josh Jarell, Benjamin Reinke, Max Chaiken, Brandon Wilson, Wolfgang Windl, Brian Esser, Lei Cao, Thomas Blue “Charge Carrier Diffusion Length Determination in 4H- SiC Schottky Alpha Detectors”. Transactions of American Nuclear Society, 114 (1). 300- 304, Jun 2016. 13. Benjamin Reinke, Joshua Jarrell, Max Chaiken, Brandon A. Wilson, Thomas E. Blue, Wolfgang Windl, Bryan D. Esser, Lei Cao “Long-term 500 C testing of high- temperature 4H-SiC Schottky diode alpha article detectors for pyroprocessing”. Transactions of American Nuclear Society, 113 (1). 489-491, Nov 2015. viii Fields of Study Major Field: Nuclear Engineering ix Table of Contents Abstract ............................................................................................................................... ii Dedication ........................................................................................................................... v Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii List of Tables ................................................................................................................... xiii List of Figures .................................................................................................................