Liu, Xiang. Investigation of fission gas bubble distribution, phase transformations, and bubble growth kinetics in a FFTF-irradiated U-10Zr fuel

Principal Investigator
First Name:
Last Name:
Idaho National Laboratory
Postdoctoral Research Associate
Team Members:
Name: Institution: Expertise: Status:
Tiankai Yao Idaho National Laboratory TEM, Corrosion, Environmental Degradation, Ceramics, Characterization, spark plasma sintering, Amorphization, High Density Fuels, uranium compounds, grain growth, High Burnup Fuel, nuclear waste, Nuclear Fuel Post Doc
Luca Capriotti Idaho National Laboratory PIE, Metal Fuels, Irradiated Fuels, Oxide Fuels Other
Maria Okuniewski Purdue University nuclear fuels, U-Zr metallic fuel, microstructure characterization, TEM, fission gas behavior. Faculty
Lingfeng He Idaho National Laboratory TEM, Radiation Effects, Ceramics, Nuclear Fuel Other
Experiment Details:
Experiment Title:
Investigation of fission gas bubble distribution, phase transformations, and bubble growth kinetics in a FFTF-irradiated U-10Zr fuel
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
This project will perform first-time detailed nano-scale characterization of the fission gas bubbles in different phases in a U-10Zr fuel irradiated in FFTF to 12.4% burnup. After preliminary EBSD and EDS characterization, 4 TEM lamellae will be prepared from different radial locations of the fuel disc using the FIB lift-out technique. Conventional room-temperature TEM characterization will be performed. More importantly, phase transformations and growth kinetics of fission gas bubbles will be studied in situ during subsequent thermal annealing at 730C. One FFTF-irradiated U-10Zr fuel sample will be investigated.
Technical Abstract
This project aims to investigate the fission gas bubble distribution in different phases in a FFTF-irradiated U-10wt.%Zr fuel, and study the phase transformations and growth kinetics of gas bubbles during thermal annealing. The fission gas behavior has huge impacts on the fuel performance in two different ways: accumulation of gas bubbles inside the fuel leads to gaseous swelling and the release of fission gas bubbles requires a long plenum to accommodate the released fission gas. The formation of fission bubbles not only alters the dimension of the fuel slug, but also changes a series of material properties of the fuel. In particular, thermal conductivity of the fuel suffers significant degradation due to the gaseous fuel swelling. The gaseous swelling also leads to loss of reactivity of the fuel and therefore the fuel performance is compromised. The gas bubble distribution was found dependent on the crystal structure of the host matrix, as demonstrated by the anisotropic swelling behavior of metallic U-Zr fuel. The anisotropic swelling causes mismatched growth stress at grain boundaries, leading to plastic flow and possible cavitation. On the other side, significant amount of fission gas release requires a low smear density to avoid premature cladding failure and a long plenum to contain the released fission gas. These requirements compromise the overall fuel utilization and economics of advanced reactors. In summary, the fission gas behavior is an important phenomenon that affects multiple aspects of fuel performance and therefore must be comprehensively understood. However, the fission gas release and retention mechanisms for the candidate fast reactor U-10Zr metallic fuel has not been well studied experimentally. Understanding this phenomenon is of paramount importance for the safety assessment and qualification of this nuclear fuel system. The accurate spatially resolved experimental data is also critical for the development of high-fidelity fission gas models. This project will address these challenges by systematic investigation of the fission gas bubbles of U-10Zr fuel after in-pile irradiation, and provide critical spatially-resolved gas bubble kinetics data that can be used for the validation of fission gas models that are being developed by the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program.