Engineering topics

Middlemas, Scott

Publications and source records attributed to Middlemas, Scott.

5 records

DOE OSTI2024

Determining the effects of U/Pu ratio on subsolidus phase transitions in U-Pu-Zr metallic fuel alloys

Here, ternary alloys consisting primarily of uranium, plutonium, and zirconium (U-Pu-Zr) are among the leading candidate fuel systems considered for fast spectrum nuclear reactors. Despite historical operation data from the testing of U-Pu-Zr rods in the Experimental Breeder Reactor-II, considerable uncertainty about the evolution of phases and microstructure across the ternary composition space exists. Due to sluggish kinetics and other difficulties in handling metal actinide specimens, quantitative measurements of phase-transitions in U-Pu-Zr alloys remain sparse in scientific literature, with most investigators reporting either phase-transition temperatures or phase identification data, but not both from the same specimens. The purpose of this paper is to critically compare experimental and calculated phase transition data and correlate with the microstructure and phase characterization data of as-cast and annealed U-Pu-Zr alloys. Phase transition peaks were measured using differential scanning calorimetry in the subsolidus regions (723-948 K) of three ternary U-Pu-Zr alloys with the same zirconium concentration but various U/Pu ratios. Overlapping peaks were deconvoluted using a Frazier-Suzuki peak fitting algorithm, and the critical peak temperatures and enthalpies were calculated. In general, increasing concentrations of Pu were associated with enhanced thermal stability of the body-centered cubic γ phase upon both heating and cooling. Experimental phase transition temperatures in this study tended to agree well with the predictions of the established ternary phase diagrams and other reported phase transition temperatures in literature. Additionally, the TAF-ID thermodynamic database was used to calculate a U-Pu-40 at.% Zr pseudobinary diagram as well as ternary diagrams from 773 to 973 K. The equilibrium phase transition temperatures tended to be considerably lower than measured peak temperatures upon both heating and cooling. Recommendations for improving the quality of data in future U-Pu-Zr characterization studies are also discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2020

Aluminum Spent Fuel Performance in Dry Storage Task 4 Aluminum Oxide Sampling of ATR Dry Stored Fuel

Milestone report on sampling of long-term dry-stored ATR spent fuel elements. It describes tooling, sample acquisition methods and analysis of the aluminum oxide samples by scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and transmission electron microscopy. The observations provide input to projections on controls necessary for maintaining the integrity of the fuel during extended interim storage.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2019

Producing a titanium product

A method (400) for producing a titanium product is disclosed. The method (400) can include obtaining TiO.sub.2-slag (401), and producing a titanium product from the TiO.sub.2-slag using a metallic reducing agent (402) at a moderate temperature and a pressure to directly produce a titanium product chemically separated from metal impurities in the TiO.sub.2 slag (403). The titanium product can comprise TiH.sub.2 and optionally elemental titanium. Impurities in the titanium product can then removed (404) by leaching, purifying and separation to form a purified titanium product.

Fang, Zhigang Zak↗

DOE OSTI2017

Evaluation of The Thermophysical Properties and Microstructure of UPu{sub 24}Zr{sub 15} Metallic Fuel

Featuring high burn-up, high fissile and fertile isotopic density, inherent safety characteristics, and favorable thermal response, actinide transmutation metallic fuels are considered to be among the most promising fuel classes for next generation fast reactors. During reactor operation, it is anticipated that fluctuations in chemical potential along the temperature gradient will lead to migration and redistribution of constituents between radial zones of the cylindrical fuel pin, resulting in compositional inhomogeneity and hence unpredictable fuel performance. Limited experimental fuel performance data is available for fuel selection and certification, therefore different compositions of options uranium-plutonium-zirconium (UPu- Zr) alloys have been investigated. Several complementary techniques, including scanning and transmission electron microscopy (SEM and TEM, respectively), differential scanning calorimetry (DSC), and laser flash diffusivity (LFD) techniques were used to characterize the phase distribution, microstructure, and thermophysical properties of unirradiated U-Pu-Zr fuels in both the as-cast and annealed condition. This information is necessary to understand the irradiated microstructure, properties, and performance of U-Pu-Zr fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

Phase Verification and Thermophysical Properties Evaluation of Pu-Zr alloys

Pu-Zr alloys have been investigated for almost 60 years, with much of the experimental data collected during the 1950's and 1960's'. Key features of the Pu-Zr phase diagram include continuous solubility between the body-centered cubic phases {beta}-Zr and {epsilon}-Pu, extensive solubility of Zr in {delta}-Pu and limited solubility in {alpha}-Pu, {beta}-Pu, {gamma}-Pu, and {delta}'-Pu, and the existence of {theta}-(Pu-Zr) as an intermediate phase that is stable at room-temperature. The available experimental data were synthesized by Okamoto to produce a single phase diagram. However, many details of the phase diagram remain poorly known, particularly those involving temperatures below {approx}400 deg. C or concentrations of Zr below {approx}30 at% or above {approx}65 at%. Thermal property measurements and microstructural characterization on Pu-Zr alloys are complicated by sluggish kinetics, high sensitivity to low concentrations of oxygen and other impurities leading to the possible formation of oxygen-stabilized low-temperature phases, and the metallurgical complexity and unique characteristics of Pu. As a result of these difficulties, the identities of some possible Pu-Zr phases are controversial, and there is little published data on phase transformations or thermophysical properties.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗