NSUF 18-1570: Phase Evolution of Uranium-Zirconium Alloys Under In-Situ TEM Heating
The binary uranium-zirconium (U-Zr) and the ternary uranium-plutonium-zirconium (U-Pu-Zr) alloys are considered candidate fuel for any future U.S. Fast Reactor, including the Versatile Test Reactor. Advanced characterization on these fuel types is needed to substantially lessen the reliance on empirical models currently being used. The Nuclear Science User Facilities (NSUF) has fabricated U-Zr foils for such a study through the Disc Irradiation for Separate Effects Testing with Control of Temperature (DISECT) project. It is well known that both the binary and ternary metallic fuels have four primary phenomena that govern the potential fuel lifetime: fuel cladding chemical interactions, fuel cladding mechanical interaction, fuel swelling and growth, and constituent redistribution. Understanding the microstructural evolution of these samples, including phase stability, texture, crystal structure, and mechanical properties is crucial to tailor and accommodate these phenomena in our fuel systems and models. The U-Zr phase diagram agrees with the observed fine structured α-U and δ-Zr at room temperature. However, the fast reactor operating conditions often exceed this α-δ phase?s temperature range and operate in the γ phase region above ~720 °C. In order to gain insight on the in-pile U-Zr system through post-irradiation examination it is vital to understand the kinetics involved in the transformation from γ to the α-δ phase during reactor shut down as well as the microstructural evolution that takes place during the transformation. Additionally, it has been shown in other metallic fuels, such as U-Mo, the in-pile phase transitions and kinetics can differ greatly from that of out of pile. DISECT uranium-zirconium foils are 6, 10, 20, and 30 weight percent (13.28, 22.48, 39.48, and 52.79 atomic percent), compositions that are seen following constituent redistribution. The U-Zr foils were fabricated using hot and cold rolling; a technique that has never been applied to this fuel system. We have shown that through post-roll annealing, the foils achieve a similar microstructure to that of homogenized induction casted fuel rods and are suitable for phase transformation studies. By utilizing in-situ heating on the JEOL-2010 TEM/STEM 200 kV microscope, equipped with a LaB6 filament and a Gatan UltraScan 1000 digital camera located at the Irradiated Materials Characterization Laboratory of Idaho National Laboratory, we will be able to draw precise conclusions on the out-of-pile phase transformation kinetics and subsequent microstructural evolution that would be seen during reactor shut down. This experiment would allow for the samples to be characterized at room temperature α-δ phases, through intermediate phases, and in the γ phase observed during normal reactor operating conditions. This would allow for the ability to infer in-pile microstructure and behavior from post-irradiated characterization of identical samples that are slated for reactor insertion in SCK·CEN?s BR2. Additionally, we will be able to quantify dislocation migration and crystallite evolution by using damage rich un-annealed rolled samples that are also available.
Additional Info
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|---|---|
| Abstract | The binary uranium-zirconium (U-Zr) and the ternary uranium-plutonium-zirconium (U-Pu-Zr) alloys are considered candidate fuel for any future U.S. Fast Reactor, including the Versatile Test Reactor. Advanced characterization on these fuel types is needed to substantially lessen the reliance on empirical models currently being used. The Nuclear Science User Facilities (NSUF) has fabricated U-Zr foils for such a study through the Disc Irradiation for Separate Effects Testing with Control of Temperature (DISECT) project. It is well known that both the binary and ternary metallic fuels have four primary phenomena that govern the potential fuel lifetime: fuel cladding chemical interactions, fuel cladding mechanical interaction, fuel swelling and growth, and constituent redistribution. Understanding the microstructural evolution of these samples, including phase stability, texture, crystal structure, and mechanical properties is crucial to tailor and accommodate these phenomena in our fuel systems and models. The U-Zr phase diagram agrees with the observed fine structured α-U and δ-Zr at room temperature. However, the fast reactor operating conditions often exceed this α-δ phase?s temperature range and operate in the γ phase region above ~720 °C. In order to gain insight on the in-pile U-Zr system through post-irradiation examination it is vital to understand the kinetics involved in the transformation from γ to the α-δ phase during reactor shut down as well as the microstructural evolution that takes place during the transformation. Additionally, it has been shown in other metallic fuels, such as U-Mo, the in-pile phase transitions and kinetics can differ greatly from that of out of pile. DISECT uranium-zirconium foils are 6, 10, 20, and 30 weight percent (13.28, 22.48, 39.48, and 52.79 atomic percent), compositions that are seen following constituent redistribution. The U-Zr foils were fabricated using hot and cold rolling; a technique that has never been applied to this fuel system. We have shown that through post-roll annealing, the foils achieve a similar microstructure to that of homogenized induction casted fuel rods and are suitable for phase transformation studies. By utilizing in-situ heating on the JEOL-2010 TEM/STEM 200 kV microscope, equipped with a LaB6 filament and a Gatan UltraScan 1000 digital camera located at the Irradiated Materials Characterization Laboratory of Idaho National Laboratory, we will be able to draw precise conclusions on the out-of-pile phase transformation kinetics and subsequent microstructural evolution that would be seen during reactor shut down. This experiment would allow for the samples to be characterized at room temperature α-δ phases, through intermediate phases, and in the γ phase observed during normal reactor operating conditions. This would allow for the ability to infer in-pile microstructure and behavior from post-irradiated characterization of identical samples that are slated for reactor insertion in SCK·CEN?s BR2. Additionally, we will be able to quantify dislocation migration and crystallite evolution by using damage rich un-annealed rolled samples that are also available. |
| Award Announced Date | 2018-09-17T12:06:44.57 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Alina Zackrone |
| Irradiation Facility | None |
| PI | Walter Williams |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1570 |