Compressive Creep of Porous Gamma Phase Uranium Metal
Abstract
The compressive deformation behavior of unirradiated depleted gamma phase uranium metal was investigated in support of new metal fueled fast reactor designs. Extended core residence times have raised questions about long term fuel performance under stress and at high temperatures. To enable this study, depleted uranium powder was created with a fine particle size (nominally 1 to 10 micrometers) using a hydride dehydride process. The powder was pressed and sintered to produce porous, metallic uranium cylindrical samples approximately 8.5 mm in diameter and 15 mm in length with porosity ranging from 12 to 22%. A compressive creep experiment apparatus was designed and purpose built for this study. Compression experiments were performed at 800°C, 850°C, and 900°C in a high purity argon atmosphere glovebox to minimize the impact of oxidation. Constant mechanical loads between 6.1 and 12.3 kg were used, approximately corresponding to stresses of 1.4 to 2.4 MPa, which are slightly higher than the estimated internal stresses in a tall porous fuel rod. Axial strain versus time and strain rate versus time data was collected for tests using two linear variable differential transducers. This enabled the estimation of a stress exponent near n=2.3 and activation energies ranging from 100 to 140 kJ/mol; the observed range of activation energies indicates a shift in conditions during the test. Image analyses from selected samples were performed to characterize the post-test pore size and distribution after deformation. The average pore radius was found to be 2.7 ± 0.6 micrometers. The experimental results and post-test analyses point to a compression mechanism consistent with diffusion assisted, dislocation motion controlled, power law creep.
Citation
Stern, Karyn (2022). Compressive Creep of Porous Gamma Phase Uranium Metal. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198153.