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New Research Advances Understanding of Critical Heat Flux Events

Nick Brown and Richard Hernandez.

Nick Brown, left, and Richard Hernandez

The concept behind transient testing of nuclear fuels involves exposing these materials to short bursts of powerful radiation within the core of test reactors in order to study physical phenomenon that could ultimately improve design and safety of advanced nuclear fuel materials.

The Transient Reactor Test (TREAT) Facility provides unique transient testing capabilities of nuclear fuels to understand fuel melting behavior, interactions between fuel materials and coolants, and the potential for fuel failure to spread to adjacent fuel pins under a range of reactivity-initiated accident conditions.

NE Associate Professor Nicholas Brown has contributed to new research that leveraged the 2018 restart of the TREAT Facility at Idaho National Laboratory (INL), which was in use for a decade before stalling operations in 1994. In 2019, the research team helped design experiments that were successfully inserted in the TREAT reactor.

Now they’ve conducted a series of sensitivity analyses which were led by Brown’s doctoral student and recent graduate Richard Hernandez (’21) who conducted the research as part of his dissertation. They published findings in the Annals of Nuclear Energy that contribute to understanding the impacts of critical heat flux (CHF) events.

This most recent study attempts to understand fuel-to-coolant heat transfer mechanisms under transient heating irradiation conditions, which is is an important aspect of pressurized-water reactor safety. Specifically, the team was interested in the potential impacts of critical heat flux events on nuclear fuel systems.

They utilized the heat transfer time constant (HTTC) as the fundamental basis and established a set of thermophysical material and heat transfer coolant properties to represent the HTTCs of two experimental fuel/cladding designs located at the TREAT facility.

“The heat removal performance of light-water reactors is limited by the critical heat flux,” said Hernandez. “The contributions of this study present a unique approach to better characterize the cladding-to-coolant heat transfer under the complex nature of this physical phenomenon.”

Using a variance-based Sobol sensitivity analysis along with the Reactor Excursion and Leak Analysis Program code to investigate the most important thermophysical heat transfer properties towards peak outer cladding temperatures.

“Research contributions from our university partners has been crucial to many successes already gained at the TREAT facility,” said Colby Jensen, National Technical Lead for Transient Testing at INL. “Dr. Brown’s research is a prime example of this success with research impacts on critical heat flux that reach industry while training the next generation of bright researchers, like Richard.”

These results offer unique contributions to the study of the effects of thermophysical properties on flow boiling transient CHF.