Dissertation Defense: Fabrication and Characterization of a Molten Salt Application Silicon Carbide Alpha Detector

Committee Members

• Dr. Raymond Cao, Chair (NE)
• Dr. Thomas Blue (NE)
• Dr. Marat Khafizov (NE)
• Dr. Chi-Chih Chen (ECE)

Abstract

There exists a need for monitoring the actinide concentrations in elevated temperature molten salt environments. Reprocessing of used nuclear fuel through pyroprocessing in an electrorefiner is being investigated as a viable method to manage the growing stockpile of used nuclear fuel. 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. 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. 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. 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 resilience of detector performance to submersion in a molten salt was investigated as well as energy resolution during elevated temperature operation. 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. Additionally, nuclear forensic applications of 4H-SiC alpha detectors in conjunction with electrodeposited source fabrication were explored.