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The microstructure investigations of a U 3 Si 2 specimen implanted by 84 MeV Xe ions at 450∘C are reported here. In the region that corresponds to the highest irradiation dose, U 3 Si 2 was found to decompose into a Si-enriched nanocrystalline USi matrix phase and a U-enriched amorphous inclusion phase. Density functional theory (DFT) calculations were used to help understand the decomposition mechanism. Xe bubbles of different morphologies were observed in USi nano-grains, on USi grain boundaries, and phase boundaries. Original U 3 Si 2 micro-grains were preserved on both sides of the irradiation damage peak region within the sample, implying a radiation dose threshold for decomposition of approximately 150 dpa at 450∘C. In the preserved U 3 Si 2 region beneath the irradiation damage peak, where significant amount of Xe ions were deposited, a monomodal size distribution of intragranular Xe bubbles with an average size of 2.68 nm formed. In both decomposed and preserved U 3 Si 2 , the size of Xe bubbles was found to be lower than 50 nm. Based on this observation, the fission gas behavior of U 3 Si 2 is controllable and free of run-away swelling despite the occurrence of decomposition at this irradiation temperature. [ABSTRACT FROM AUTHOR]

Abstract Uranium-molybdenum (U-Mo) particles dispersed in an aluminum matrix is the most promising candidate fuel to convert high-power research and test reactors in Europe from using high-enriched to using low-enriched fuel. However, chemical interaction between the U-Mo and the Al matrix leads to undesirable fuel behavior. Zirconium nitride (ZrN) is used as a diffusion barrier between the U-Mo fuel particles and the Al matrix. To understand the potential microstructural evolution of ZrN during irradiation, a high-energy heavy ion (84 MeV Xe) irradiation experiment was performed on atomic layer deposited (ALD) nanocrystalline ZrN deposited on an Al plate. A fluence of 1.86 × 1017 ions/cm2, or 90.3 dpa was reached during this experiment. Both analytic transmission electron microscopy (TEM) and synchrotron microbeam X-ray diffraction (μ XRD) techniques were utilized to investigate the kinetics of radiation-induced grain growth of ZrN at various radiation doses based on the Williamson-Hall analyses. The grain growth kinetics can be described by a power law expression, D n − D 0 n = K ϕ , with n = 5.1. The Al-ZrN interaction products (Al 3 Zr and AlN) created by radiation-induced ballistic mixing/radiation-enhanced diffusion and their corresponding formation mechanism were determined from electron diffraction and elemental composition analysis. These experimental results were confirmed by first principle thermodynamic density functional theory (DFT) calculations. The results from this ion irradiation study were also compared to in-pile irradiation data from physical vapor deposited (PVD) ZrN samples for a comprehensive evaluation of the interaction between Al and ZrN and its influence on diffusion barrier performance. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The microstructure investigations on a high-energy Xe-implanted U 3 Si 2 pellet were performed. The promising accident tolerant fuel (ATF) candidate, U 3 Si 2 , was irradiated by 84 MeV Xe ions at 600 °C at Argonne Tandem Linac Accelerator System (ATLAS). The characterizations of the Xe implanted sample were conducted using advanced transmission electron microscopy (TEM) techniques. An oxidation layer was observed on the sample surface after irradiation under the ∼ 10 -5  Pa vacuum. The study on the oxidation layer not only unveils the readily oxidation behavior of U 3 Si 2 under high-temperature irradiation conditions, but also develops an understanding of its oxidation mechanism. Intragranular Xe bubbles with bimodal size distribution were observed within the Xe deposition region of the sample induced by 84 MeV Xe ion implantation. At the irradiation temperature of 600 °C, the gaseous swelling strain contributed by intragranular bubbles was found to be insignificant, indicating an acceptable fission gas behavior of U 3 Si 2 as a light water reactor (LWR) fuel operating at such a temperature. [ABSTRACT FROM AUTHOR]

The microstructure modifications of a high-energy Xe implanted U 3 Si 2 , a promising accident tolerant fuel candidate, were characterized and are reported upon. The U 3 Si 2 pellet was irradiated at Argonne Tandem Linac Accelerator System (ATLAS) by an 84 MeV Xe ion beam at 300 °C. The irradiated specimen was then investigated using a series of transmission electron microscopy (TEM) techniques. A dense distribution of bubbles were observed near the range of the 84 MeV Xe ions. Xe gas was also found to accumulate at multiple types of sinks, such as dislocations and grain boundaries. Bubbles aggregated at those sinks are slightly larger than intragranular bubbles in lattice. At 300 °C, the gaseous swelling strain is limited as all the bubbles are below 10 nm, implying the promising fission gas behavior of U 3 Si 2 under normal operating conditions in light water reactors (LWRs). [ABSTRACT FROM AUTHOR]