Doctoral Dissertations
Date of Award
12-2023
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Nuclear Engineering
Major Professor
Jason P. Hayward, Jamie B. Coble
Committee Members
Louise Evans, Steven Skutnik, Ondrej Chvala
Abstract
Liquid-fueled molten salt reactors (MSRs) are an advanced reactor design concept with material accountancy challenges due to continuously circulating fuel in bulk form with online additions of fresh fuel. With more than 24 distinct liquid-fueled MSR designs being pursued by companies around the world, facility operators and the International Atomic Energy Agency need approaches and technologies to quantify nuclear material within MSR facilities for safeguards and security purposes. Safeguards technical objectives were defined across a prospective liquid-fueled MSR. One high-priority objective for facility operators and the IAEA will likely be quantifying nuclear material in fresh initial salt (i.e., salt added to the MSR at the beginning of life) and makeup salt additions to the reactor system (i.e., salt added over time while the MSR is operational), which was selected for further analysis. Computational simulations combining fresh fuel source terms from SCALE/ORIGEN into MCNP models were run for different MSR design parameters as well as different gamma- and neutron-based measurement techniques to determine the expected impact of each parameter on the feasibility of radiation monitoring on the outside of fresh fuel salt in piping for material accountancy. MSR design parameters analyzed were a fluoride-based and chloride-based salt, four uranium enrichments, two pipe materials, several pipe outer diameters and thicknesses, and the optional presence of insulation and aluminum jacketing external to the piping. Measurement modalities including NaI and high-purity germanium gamma detector systems, total passive neutron counting in a moderated 3He collar, coincident neutron counting in a moderated 3He collar, and coincident neutron counting in in a moderated 3He collar with an interrogating neutron source were assessed for feasibility. Although no measurement technique worked well for both salt types and all design parameters assessed, passive gamma spectrometry and total passive neutron counting in a moderated neutron detector collar are promising, especially for salts with high-assay low-enriched uranium salt and larger diameters. Active neutron interrogation with a neutron coincidence collar counting thermal neutrons in 3He exhibited high relative uncertainties due to high accidental coincidences. A neutron coincidence collar using liquid scintillators counting fast neutrons will likely be a promising alternative for quantifying 235U within unirradiated, uranium-bearing fuel salts within piping because of the expected lower accidental coincidence rate.
Recommended Citation
Hogue, Karen K., "Feasibility Study of Fresh Fuel Feed Monitoring for Liquid-Fueled Molten Salt Reactor Safeguards. " PhD diss., University of Tennessee, 2023.
https://trace.tennessee.edu/utk_graddiss/9005