Matthew Weathered's THETA experiment offers high fidelity data for nuclear reactor computer code development within one of METL's 71-cm diameter test vessels at Argonne.
All U.S. nuclear reactors, which currently provide more than half of the nation's carbon-free power, are first- or second-generation light water reactors. This means they use water as both a coolant and neutron moderator to control the nuclear reaction and produce useful electricity.
However, the growing need for more clean energy is prompting scientific experts, policy makers and members of private industry to excitedly pursue all kinds of reactor designs.
A new generation of nuclear reactors, "Gen-IV," aims to improve safety while optimizing efficiency and cost. One Gen-IV reactor design at the vanguard of development is the sodium-cooled fast reactor (SFR). SFRs with metallic-alloy fuel are garnering a significant amount of interest because they have intrinsic passive safety and can produce more nuclear fuel material than they consume. This can reduce the amount of waste generated over the lifetime of the reactor.
At the U.S. Department of Energy's (DOE) Argonne National Laboratory—famously charged with peaceful expansion of Enrico Fermi's successful Chicago Pile-1 fission experiment—fast reactor technology is nothing new.
In fact, Argonne designed, built and operated the full-scale Experimental Breeder Reactor-II (EBR-II) and tested and validated molten sodium technology for 30 years until the lab safely shut down EBR-II in 1994.
Information used by the nuclear industry almost everywhere in the world to validate reactor designs and by American industry to proceed with licensing applications and obtain Nuclear Regulatory Commission approvals are still strongly influenced by or directly produced from EBR-II operations and testing data and other Argonne research.
Today, Argonne's primary SFR experiments and component testing take place in an innovative high-bay facility on the lab's campus just outside of Chicago: the Mechanisms Engineering Test Loop (METL) facility. At METL, scientists like principal nuclear engineer Matthew Weathered work with federal sponsors and industry partners to pursue a common goal: testing and validating a new generation of sodium fast reactor designs.
A tradition of expertise and innovation
Weathered earned his Ph.D. in nuclear engineering and has almost a decade of work experience. But at Argonne, where engineers like Earl Feldman (who worked on EBR-II in 1974) still conduct research, Weathered is considered "early career." Just like Feldman, however, his focus is thermal hydraulics.
"Thermal hydraulics is the study of heat transfer," Weathered explained.
"We transfer heat produced by sustained nuclear fission to something that can produce electricity, such as steam spinning a turbine. In Gen-IV reactors, we look at optimizing systems—like pumps, heat exchangers and the reactor core—so that we are transferring heat efficiently to get the best return on investment. We also want to understand how these systems will behave during an accident scenario."
Weathered's primary experiment is the Thermal Hydraulic Experimental Test Article (THETA), a 500-liter pool-type sodium facility offering high fidelity data for nuclear reactor computer code development and validation.
THETA is approximately one-sixth the size of an actual reactor but possesses all the main components found in a typical SFR. It can validate a scaled-down analysis in nuclear reactor design software. THETA operates neatly within one of METL's 71-cm diameter test vessels and has an electrically heated core, mechanical pumps, one-of-a-kind electromagnetic flow meter instrumentation, optical sensors and an intermediate heat exchanger that dissipates heat to a secondary sodium circuit.
Using various means of measuring, Weathered is able to simulate what happens during steady state operations or accident-like conditions of a full-sized SFR.
The commercial nuclear industry likes this capability a lot. THETA can test and validate new software codes and components of new designs, allowing stakeholders to inform what tests should be performed to best suit their needs in real-time. This is a capability that data from historical reactor experiments cannot offer.
"The unprotected loss-of-flow tests conducted from full power on the EBR-II reactor to demonstrate intrinsic passive safety are fundamental to today's innovations," said Feldman. "The capabilities provided by THETA should contribute to the development of future SFRs."
Weathered recently completed more than 100 different tests in a test matrix in THETA to validate reactor design software in a number of simulated scenarios. THETA can test and validate other emerging SFR designs as well.
"With the Gen-IV reactors, most of this technology is not yet 'off the shelf,'" said Weathered, who added that designing and implementing solutions to complex fast reactor issues is part of what intrigues him about his research. "That's really the most fascinating part—the cutting-edge stuff that we work on, moving from first principles to operating concepts in a reactor environment."
Will it be enough to keep him at Argonne for another 40 years, inspiring the next pipeline of early career scientists to embark on a career in nuclear engineering? Weathered certainly appreciates that he is at the forefront of a new era.
"It's a really exciting time right now and I think it's going to get even more exciting in the next few decades," he said. "There will be a lot of energy demand with respect to computational resources for artificial intelligence, and nuclear energy is a clean energy system. That's going to be really attractive to the next generation."
