NSUF 24-4978: Analysis of FCCI and phase decomposition on Zr-lined U-10Mo specimens using Transmission Electron Microscopy and Atom Probe Tomography

For the past decades, the U.S. department of energy (DOE) has deployed programs for the design and evaluation of high-assay low-enriched uranium (HALEU) fuels, such as Uranium-molybdenum (U-Mo), which are required for the development of advance nuclear reactor technology. The U-Mo fuels for commercial applications were proposed in the 1960s for fast reactor operation, but due to the high swelling observed in the fuel, the U-Mo alloy was not suggested for the integral fast reactor (IFR) campaign. However, the development of new fuel designs, as well as fabrication and characterization techniques has prompted the revisitation of U-Mo fuels for commercial reactor applications. Thus, U-Mo fuels in solid and annular designs are being evaluated as part of the Advanced Fuels Campaign (AFC). From the historical irradiation experience, U-Mo fuels exhibited high swelling at temperatures within ~300-450ºC due to the presence of the high swelling α-U phase. On the other hand, the γ phase exhibits more resistance to swelling. By quenching in the γ phase, U-Mo fuels for research applications have achieved high fission densities with little swelling. Yet, these experiments were performed at low temperatures (<150ºC) were the supersaturated γ phase is still stable. Due to the higher temperatures in commercial reactors, the phase decomposition from γ →α-U+ γ could take place following the equilibrium transformations identified in the equilibrium diagram. However, the temperature threshold and radiation parameters for phase decomposition in U-Mo are not well defined. Thus, experimental information of the irradiation behavior of U-Mo at higher temperatures (300-450ºC) is required to understand phase decomposition and its effect in the irradiation performance of the fuel. Similarly, fuel-cladding chemical interaction (FCCI) is a concern for U-Mo fuels. A Zr barrier has proven effective to prevent the FCCI in U-Mo fuels for research reactors applications. Yet again, these fuels operate at low temperatures, where thermal diffusion is not as significant as irradiation induced diffusion. In the case of commercial operation fuels, the high temperatures allow for both thermal and irradiation enhanced diffusion to occur, causing significant FCCI. Thus, this proposal aims to test the following hypotheses: (1) are the Zr liners capable of preventing FCCI in U-10wt.%Mo at high temperatures? And (2) is there evidence of phase decomposition in the irradiated fuel at this temperature and irradiation dose? To test the hypotheses, we propose to characterize a Zr lined FAST U-10wt.%Mo specimen irradiated to 4.29%FIMA using both transmission electron microscopy (TEM) and atom probe tomography (APT). We propose TEM to identify the crystallography of the phases via selected area electron diffraction (SAED) and the potential changes in elemental composition via energy dispersive spectroscopy (TEM-EDS) in the fuel bulk, as well as in the FCCI region to determine cladding degradation. Moreover, the APT will provide three-dimensional (3-D) compositional distribution of the specimens including not only the compositional content but also the isotopic nature of the constituents. Similarly, APT can provide local burn-up information of utility to understand the specific effects of irradiation dose in the microstructure evolution.

Additional Info

Field	Value
Award Announced Date	2024-05-28T17:14:02.267
Awarded Institution	Purdue University
Facility Tech Lead	Alina Montrose
Irradiation Facility
PI	Nicole Rodriguez Perez
PI Email	[email protected]
Project Type	RTE
RTE Number	None