SUBJECT: Ph.D. Dissertation Defense
BY: Peter Sobel
TIME: Thursday, January 12, 2023, 1:00 p.m.
PLACE: MS Teams, N/a
TITLE: Design of Experimental Systems for a Liquid-fueled Molten Salt Reactor
COMMITTEE: Dr. Steven Biegalski, Chair (NRE)
Dr. Anna Erickson (NRE)
Dr. Bojan Petrovic (NRE)
Dr. Preet Singh (MSE)
Dr. Timothy Head (ACU)


Molten salt reactors (MSR’s) represent the next step in the production of nuclear power through neutron fission. They provide inherent benefits over solid fueled reactors through the use of liquid salts as a working fluid. The reactor pressure can be kept low and temperature high, leading to enhanced safety and better thermal properties. There are challenges however, as working with high temperature salts requires monitoring of both the nuclear properties of a traditional reactor and the chemistry as well. It will be of the upmost importance for the next generation of MSR’s to include monitoring systems for the status of the reactors many characteristics during operation. The measurements collected from these systems can then be used to provide data and experience for the construction of future MSR’s. The purpose of this work is to perform experiments and gather data that provide a basis for the design of experimental systems for an MSR. An analytical procedure was developed based on the original Molten Salt Reactor Experiment literature and the modern day ongoing research involving molten salts and their effluent. This procedure considers the combination of gamma, alpha, optical, electrochemical and mass measurements as sufficient for developing broad knowledge of the changing properties of the operating reactor. Reactor operators with the information from these measurements will be able to better understand the reactor throughout its lifetime. Two experiments were performed to gather data about how to design a modern day MSR sampler system and in-situ gamma-ray spectroscopy system. A laboratory scale molten salt sampler was designed and built to determine the challenges and effectiveness of different sampling techniques when working with molten salts. Data gathered from the small scale sampler experiment showed that a vacuum extraction method was able to repeatably acquire a controlled volume of salt (0.1-0.5 grams) without introducing moisture or oxygen to the sample. The second experiment performed looked the feasibility of measuring some short-lived (t1/2 < 3 days) isotopes generated in the fission of 235U. The measurements were performed with a gamma-ray spectrometer over the course of a 24 hour period and found a selection of 14 isotopes that could be used for forensic analysis. Calculations were performed to determine the minimum detectable activity of those analytes. The results of these experiments lead to two design reports as a compilation of recommendations for designing full-scale molten salt samplers and in-situ gamma-ray spectrometer experiments. The designs were modeled in computer aided drafting programs and provided with information about their material requirements.