Thermophysical properties of USi to 1673 K

Abstract

Consideration of uranium silicide compounds as candidate nuclear reactor fuels requires the accurate knowledge of their thermophysical properties as a function of temperature. Stoichiometric USi has received little attention in the literature with regard to property characterization. This absence of data prevents modeling and simulation communities from predicting performance of uranium silicide fuels that are either nominally USi itself, or are designed with other uranium silicide phases but may include appreciable fractions of USi introduced as a result of the fuel synthesis or fabrication process. This study was undertaken to quantify the thermal expansion coefficient, specific heat capacity, thermal diffusivity, and thermal conductivity of USi from ambient conditions to just below the peritectic decomposition of the compound. Stoichiometric samples that were prepared by arc melting and powder metallurgical routes for thermophysical property measurements exhibited 94% USi phase, with the balance being U 3 Si 5 phase that likely formed during the solidification process. An energetic phase transformation was observed at 723 K, which is attributed to the inclusion of the secondary U 3 Si 5 phase.

Overview of lower length scale model development for accident tolerant fuels regarding U₃Si₂ fuel and FeCrAl cladding

“…For USi, the mode prediction agrees well with experimental measurements at low temperatures, and the discrepancy increases with elevating temperature. It has been suspected that the USi sample used in the experiments could possibly be non-stoichiometric, U 34 Si 34.5 instead of USi [31]. Therefore, actual sample may contain some lattice defects and extra scattering should be considered which brings the model prediction down (dash green curve in Fig.7) and much closer to the experimental results.…”

“…This assumption is supported by the nearly linear increasing conductivity over temperature, and the linearly decreasing electronic density of state (DOS) with respect to Si content in several compounds including U 3 Si, U 3 Si 2 and U 3 Si 5 . To construct the model, we used the experimentally measured data for U [26], Si [27], U 3 Si 2 [28] and U 3 Si 5 [29] for fitting, and those for U 3 Si [30] and USi [31] as validation.…”

Oxidation behavior of U-Si compounds in air from 25 to 1000 C

“…The preparation methodology, resulting phase purity and microstructure of the U 3 Si 5 , USi, and U 3 Si 2 match those presented in previous investigations. [4][5][6] In addition, U metal was included as a baseline. Uranium metal used in this study (Aero-Jet Rocketdyne, Jonesborough, TN) was prepared before oxidation testing by hand grinding using SiC metallography paper and cleaned with DI water to remove surface contamination.…”

“…This comparison was included due to the customary use of arc melting as the primary means of synthesizing novel intermetallic compounds for initial experimental characterization. Although use of powder metallurgy methods for production of regular geometries is possible and has been demonstrated for these systems, [4][5][6] processing and sintering to obtain high-density regular geometries represents significant effort. A more simple route to sample preparation is desirable if only initial or screening properties are necessary.…”

“…The unirradiated thermal conductivity advantages of each of the above compounds have been verified relative to UO 2 . [3][4][5][6] However, a large number of basic properties remain unknown. One fundamental behavior of high importance to many avenues of nuclear fuel performance is the susceptibility of a nuclear fuel compound to oxidation.…”