Park, Gyuchul. Effects of cold rolling and induction casting on the phase decomposition and distribution of fission gas bubbles in U-10wt.%Mo alloys at low fluences.

Principal Investigator
First Name:
Last Name:
Purdue University
Graduate Student
Team Members:
Name: Institution: Expertise: Status:
Maria Okuniewski Purdue University Microstructure of Nuclear Fuels Faculty
Benjamin W. Beeler Idaho National Laboratory Nuclear Fuel Modeling Other
Experiment Details:
Experiment Title:
Effects of cold rolling and induction casting on the phase decomposition and distribution of fission gas bubbles in U-10wt.%Mo alloys at low fluences.
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 work will investigate how the cold rolling and induction casting affect to the phase decomposition and fission gas bubble distribution in U-10Mo alloys at low fluences and low irradiation temperatures. SEM images (BSE, EDS, and EBSD) will be obtained at the Irradiated Materials Characterization Laboratory at Idaho National Laboratory. Samples need to be polished before SEM imaging at Idaho National Laboratory. The samples will be polished with diamond paste followed by a vibratory polish for BSE imaging, EDS line scan, and EBSD. We have 13 samples to be examined. One is unirradiated, and twelve samples were irradiated to 0.01 dpa and 0.1 dpa at 150C, 250C, and 350 C, respectively.
Technical Abstract
The goal of the proposed research is to evaluate the effects of cold rolling and induction casting on the phase decomposition and distribution of fission gas bubbles in uranium-molybdenum (U-Mo) alloys at low fluences. According to the time-temperature-transition (TTT) diagram of U-Mo alloy, the phase transition is not expected in unirradiated U-10Mo alloy at low temperatures (below 350 °C at least for 100 hours). However, it is anticipated that the phase decomposition will be observed in the cold-rolled U-Mo alloy foil at low fluences and low irradiation temperatures. When compared to the U-Mo alloy that was induction cast, the U-Mo alloy rolled foil is expected to have a higher fraction of the decomposed phases (α and γ') at the same fluence and irradiation temperature. With the increasing irradiation temperature (up to 350°C), the fraction of the decomposed phases will be increased. This can potentially be attributed to the high density of dislocations that are introduced from cold rolling. These dislocations may produce low angle grain boundaries, resulting in smaller grain sizes. Accordingly, there will be more places for the decomposed phases to be nucleated, which leads to an increase in the driving force for the phase decomposition of γ during irradiation. Also, more fission gas bubbles will be nucleated in U-10Mo foil because smaller grain sizes, and therefore more grain boundaries, will provide more sites for the fission gas bubbles to be nucleated. Our recent synchrotron XRD data supports the hypothesis, indicating more extensive γ-phase decomposition in the low fluence irradiated rolled versus induction cast U-Mo. Complementary data is required to further support these findings through the identification of grain morphologies, phases, and fission gas bubble nucleation via SEM. Scanning electron microscopy (SEM), including (backscattered electron (BSE) imaging, electron backscattered diffraction (EBSD), and energy dispersive spectroscopy (EDS) line scans and maps will be used to characterize the unirradiated and irradiated U-10 Mo as-cast and as-rolled foils. EDS will assist in identifying the presence of decomposed phases (α and γ'), and EBSD will be used to measure and compare the phases, grain size, and orientation. It is proposed that the SEM, including BSE, EDS, and EBSD, is used for 10 days (~6 hrs/sample). The proposed research is essential because γ-phase was not expected to decompose into α and γ' at the very low doses and low temperatures. This may suggest a new design or new fabrication process for the next generation to improve the fuel performance under irradiation. The results will also provide valuable input parameters, including fabrication variations, into fuel behavior models to ultimately improve their predictability.