Date of Award

Fall 2021

Document Type

Open Access Thesis


Mechanical Engineering

First Advisor

Theodore Besmann


Molten salt reactors are being deployed as one of the Generation IV nuclear reactor concepts starting in 2025. While their applications and safety potential are considered extremely advantageous, there is a lack of operating history to draw on, so thorough understanding of proposed molten salt materials’ thermochemical behavior is crucial to their successful implementation.

The most prominent fissile fuel proposed for molten salts is uranium tetrafluoride (UF4) using 233U of the thorium fuel cycle. UF4 is extremely hygroscopic, meaning it will react with moisture and oxygen in its environment, so as-received powders contain significant levels of impurity. In order to have UF4 for use in experimental thermochemical assessments of UF4-containing binary and ternary systems, the powder must be purified prior to experimentation. In this work, a process for purification of asreceived uranium tetrafluoride is developed using the solid-state reaction between ammonium bifluoride and uranium oxides at elevated temperatures. This process required the selection of a compatible reaction vessel, the creation of a KOH off-gas scrubbing system for the produced HF gas, and a reaction system as devoid of oxygen as possible to prevent further oxidation. Special attention had to be paid to materials interaction between the volatile gaseous products and system components at all points past the reaction vessel. The purification process and its results are explored using various experimental methods, including DSC, XRD, and TGA. Variables explored in the process of purification optimization include powder ratio, ramp rate, and reaction time.