Austin Williams’ senior design project involved the impending arrival of the Flexible Neutron Source at the University of Tennessee. Williams and his team created a model that simulated how the subcritical system would operate once the Zeanah Engineering Complex opened a few months later in 2021.
Now a fourth-year graduate student and research assistant in the Department of Nuclear Engineering, Williams is finally able to see the system at work. NE faculty and students started running measurements with the FNS for the first time in December.
“Getting to be here when it’s starting to become real is very rewarding,” Williams said. “It took a little while with the approvals and certifications that were necessary, so it’s cool I still get to be a part of the startup experience.”
The FNS laboratory, named in honor of TCE alumnus Samuel E. Beall II (BSIE ’42), provides a much-needed experimental facility that supports a series of nuclear experiments, especially for advanced reactor design. It is not a nuclear reactor, but rather a “core” that features a reconfigurable design. The reconfigurable design provides the flexibility to mimic the neutron spectrum of a sodium-, molten salt-, or lead-cooled advanced reactor.
The FNS allows students and researchers to simulate neutron spectra of future reactors to improve modeling codes and capabilities.
“There are not that many subcritical facilities, especially not at the university level, that could go as flexibly from high to low energies like we can here now,” said NE Assistant Professor Sandra Bogetic. “The few subcritical-condition facilities that exist are mainly thermal systems, which are incredibly valuable, but no university will be able to build a facility like that.”
Meeting an Important Need
The FNS, which uses a deuterium-deuterium (DD) neutron generator to drive a subcritical thermal/fast coupled pile, is situated in the Samuel E. Beall II Neutron Source Laboratory, a shielded vault in the ZEC with high-level security and safety standards.
UT developed the FNS concept in conjunction with leaders and researchers at Oak Ridge National Laboratory (ORNL) and Idaho National Laboratory (INL) to meet a current national need. The nuclear reaction cross sections of many materials proposed for use in fast reactor applications are poorly understood and computational modeling and simulation of future nuclear systems is unreliable without accurate nuclear reaction data.
To meet the national need of providing more accurate data, the Beall FNS facility was designed to facilitate both integral and differential cross section measurements. Westinghouse, TerraPower, and several other companies have expressed interest in the data UT’s facility will generate at a lower cost.
Running tests at major facilities can be expensive and the demand exceeds the availability. Having the Beall FNS gives UT the ability to provide initial data at a lower level to provide a benchmark of materials with measurements of different fluxes and different configurations in different positions.
“What we are trying to do is be sort of a surrogate,” Bogetic said. “We want to create experimental capabilities within our boundaries of licensing enough neutrons. There are a lot of needs to have integral measurement capability.”
Training for the Future
The FNS positions UT in a unique role to provide training for students to become familiar with using a generator source to induce fission events in natural uranium.
To run experiments, UT students have been using the first available uranium rods and poly blocks inside the cassettes, where they can put material configurations to model and change the neutron spectrum.
“The idea is start multiplying the number of neutrons using our uranium rods to increase how many particles we can have,” Bogetic said. “Then, thanks to the flexibility of our construction and the symmetry using those cassettes, the goal is for material compositions to be able to represent different configurations of a reactor spectra, for example.”
In the future, UT could potentially use the FNS to study the recycling of fuel by trying to reduce the activity level of certain materials for waste or for different space applications among other projects.
Williams and his classmates are grateful for the opportunity to utilize the FNS to enhance their educational experience and position them for future success in the industry.
“It’s a good experience because I’ve been on the simulation side for my first three years, and then this year, I’ve been able to look at the physical side and actually running detectors,” he said. “Getting the hands-on, cutting-edge opportunity and seeing how things change when you go from a computer model to reality is very useful to me.”
Contact
Rhiannon Potkey (865-974-0683, rpotkey@utk.edu)