Time at Temperature Abstract and Intern Poster

Saroufil Ishak, Caroline Emad [Idaho National Laboratory]; Colldeweih, Aaron William [Idaho National Laboratory] (ORCID:0000000200545276)

DOE OSTI · 3364036

Time at Temperature Abstract and Intern Poster

Saroufil Ishak, Caroline Emad [Idaho National Laboratory]·Colldeweih, Aaron William [Idaho National Laboratory] (ORCID:0000000200545276)

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Abstract

Current NRC regulations for BWR operations dictate that any occurrence reaching the point of Departure from Nucleate Boiling (DNB) disqualifies the use of the fuel rod for further reactor operation. That criteria does not account for duration of rate of the power increase, the corresponding effects on material properties or rewetting that may occur. Previous Anticipated Operational Occurrences (AOOs) show short durations power increase that may require limited amounts of heat removal. Industrial experience has shown evidence that fuel can reach dryout yet continue to safely operate in regular reactor conditions. The gap in research into such occurrences is the motivation for a series of experiments, including this current work. Time-at-Temperature experiments aim to identify and characterize the microstructural changes in Zircaloy-2 under oxygen-free high temperatures. This work uses the FlashDSC instrument to rapidly ramp up and down the temperature of a focus ion beam (FIB) prepared large area lift-out (LALO) of Zircaloy-2 at a rate of 10,000 K/s to desired values. The focus is to characterize the microstructure evolution, if any, of Zircaloy-2 that may impact its performance under typical BWR conditions. This characterization includes analyzing grain structure and size, secondary phase particle (SPPs) size, shape, composition, and location using Transmission Electron Microscopy (TEM). Further data collection and analysis is in progress including diffraction pattern indexing and 4D STEM processing. While current results focus on the testing and characterizing unirradiated material, future plans include expansion to irradiated material to explore the effects of rapid transition rates seen in DNB and dryout conditions on irradiationg damage and defect annealing.

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36 - MATERIALS SCIENCE BWR FIB/SEM FlashDSC SPPs TEM Zircaloy-2

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Saroufil Ishak, Caroline Emad [Idaho National Laboratory], Colldeweih, Aaron William [Idaho National Laboratory] (ORCID:0000000200545276). 2025-08-05. Time at Temperature Abstract and Intern Poster. https://www.osti.gov/biblio/3364036

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