Seaborg Institutes: Emerging Topics in Actinide Materials and Science: Metallurgy
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: J. Rory Kennedy, Idaho National Laboratory; Taylor Jacobs, Helion Energy; Krzysztof Gofryk, Idaho National Laboratory; Assel Aitkaliyeva, University of Florida; Don Wood, Idaho National Laboratory
Thursday 2:00 PM
March 23, 2023
Room: 28A
Location: SDCC
Session Chair: Ladia Havela, Charles University ; Krzysztof Gofryk, Idaho National Laboratory; Rory Kennedy, INL
2:00 PM Invited
Magnetic Dichroism in Ga-stabilized d-Pu: Jason Jeffries1; Alexander Baker1; G Fabbris2; Daniel Haskel2; 1Lawrence Livermore National Laboratory; 2Argonne National Laboratory
A prevailing model of Pu invokes a spin and orbital cancellation model to predict structural evolution. The hallmark of this spin/orbit cancellation model is the presence of anti-parallel, on-atom spin and orbital moments of identical magnitude (or nearly so) near 3 Bohr magnetons each. Such an offsetting magnetic configuration would be nearly invisible to bulk probes that see only the total moment but x-ray magnetic circular dichroism (XMCD) can offer a glimpse into the local, atomic magnetic configuration. Herein, we will discuss the results of dichroism measurements at the M4 and M5 edges of Ga-stabilized d-Pu acquired at a temperature of 2 K and in magnetic fields up to 60 kOe.This work was performed by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This research used resources of the APS; a DOE/OS user facility operated by ANL under Contract No. DE-AC02-06CH11357.
2:30 PM Invited
Understanding Self-irradiation Damage Mechanisms in δ-Pu from First-principles: Sarah Hernandez1; 1Los Alamos National Laboratory
Nuclear applications of Pu are inherently accompanied by real-world challenges such as self-irradiation and damage evolution, which are further complicated with six allotropic phase transitions, melting temperature of 900K, extreme reactivity, phases with negative thermal expansion, etc. Fortunately, in application the high-temperature face-centered-cubic δ-phase can be stabilized to room temperature with the addition of a few atomic percent of elements located in Group IIIA, but the mechanism for phase stabilization remains elusive. Using density functional theory (DFT), we are able to obtain insight into these physics, chemistry and materials science challenges dominated by heterogeneity and crystalline symmetry breaking from a first-principles perspective. This talk will be an overview of DFT calculations ranging from point defect formation and migration in δ-Pu-Ga alloys in order to determine the rate of Ga segregation for δ-phase metastability that may be induced by self-irradiation damage.
3:00 PM
Recovery in Stabilized Delta Pu and Its Effects on Thermal Expansion: Najeb Abdul-Jabbar1; Shane Mann1; Jeremy Mitchell1; 1Los Alamos National Laboratory
The kinetics and thermodynamics that drive the delta Pu stabilization mechanism via tri-valent cations are still not fully understood. Renewed efforts at Los Alamos National Laboratory (LANL) have focused on probing recovery effects of aged and pre-conditioned delta alloys at temperatures in the vicinity of eutectoid decomposition in the Pu-Ga phase diagram. In both scenarios, noticeable thermal contraction is observed (via dilatometry) across temperatures ranging from 125-225 °C. Analogous behavior in Pu has been observed via electrical resistivity measurements, which has been attributed to migration of point defects, dislocations, and vacancy clusters. Whether interactions between defects produced by pre-conditioning or natural aging can develop into alpha-like embryos that facilitate eutectoid decomposition remains to be seen. Consequently, ongoing thermal analysis work is being conducted at LANL on a comprehensive series of pre-conditioned and naturally aged Pu-Ga alloys and the ensuing results in the context of delta phase stability will be discussed.
3:20 PM
A Time-of-Flight Neutron Diffraction Study of δ-phase 239PuGa Alloys at Cryogenic Temperatures: Alice Smith1; Franz Freibert1; Sven Vogel1; Bjorn Clausen1; Jianzhong Zhang1; Donald Brown1; Joan Siewenie1; Travis Carver1; Scott Richmond1; Michael Ramos1; 1Los Alamos National Laboratory
Self-irradiation damage in Pu-Ga alloys results in lattice distortions, void swelling, He bubble formation, and daughter product ingrowth (Am/U/Np). For a more detailed picture of the less understood processes of defect accumulation and damage evolution, dose, dose rate, thermal history and alloy composition must be considered. This work is a time-of-flight neutron diffraction investigation at cryogenic temperatures of δ-phase 239Pu-Ga alloys as associated with a varied history of storage time at ambient temperature, elevated temperature annealing, and different Ga concentrations. Measurements were collected using the High-pressure Preferred Orientation (HIPPO) and the Spectrometer for Materials Research at Temperature and Stress (SMARTS) diffractometers at Lujan Neutron Scattering Center facility, Los Alamos National Laboratory. Structural changes, in particular the evolution of the lattice parameter, as a function of temperature will be discussed. The collected data contributes to a better understanding of the δ-phase 239Pu-Ga alloys average structure evolution at low temperatures.
3:40 PM Break
4:00 PM Invited
Hydrogen Embrittlement in Uranium: From Hydrides to Plastic Effects: Mary O'Brien1; Jason Cooley1; Samantha Lawrence1; 1Los Alamos National Laboratory
Hydrogen embrittlement is a long-standing challenge in metallurgy due to unpredictable failures observed in numerous metallic systems exposed to hydrogen-containing environments. Ductility loss is attributed to any combination of the following: formation of brittle hydrides upon supersaturation, decohesion along boundaries attributed to trapped hydrogen, or hydrogen-enhanced localized plasticity due to soluble hydrogen. Hydrogen has been observed to localize plasticity by reducing dislocation spacing at pile-ups, but additional effects of hydrogen on plasticity are possible. Diffusible hydrogen may depress the stress necessary for dislocation movement and, by extension, result in early-onset plasticity. Uranium, with its low symmetry crystal structure, presents a unique opportunity to observe the proposed hydrogen-induced early-onset plasticity without added complications of slip system interactions that occur in most engineering materials. This talk will discuss current research frontiers in hydrogen/uranium interactions, with emphasis on recent investigations into the effect of soluble hydrogen on plasticity in uranium.
4:30 PM Invited
Experimental Investigation of the U-Mo Solidus and Liquidus: Kara Luitjohan1; Seth Imhoff1; 1Los Alamos National Laboratory
Low enriched uranium (U)-10 wt% molybdenum (Mo) is of interest as a monolithic fuel material to replace highly enriched uranium dispersion fuels in high performance nuclear reactors. A proposed manufacturing route for the U- 10wt% Mo fuels begins with casting. Knowledge of the liquidus and solidus phase boundaries is crucial for successful castings in both the design of processing parameters and for predicting the degree of microsegregation. In the current literature, numerous U-Mo phase diagrams are available, but they differ significantly in their definitions of the solid/liquid boundary, specifically on the U-rich side. In an attempt to better define that boundary, an experimental strategy utilizing thermal analysis was employed. The data collected and presented here focuses not on proving a singular point but attempts to provide points with highly characterized uncertainty.
5:00 PM
Thermal Stability of Alpha-phase Plutonium: Jeremy Mitchell1; Najeb Abdul-Jabbar1; 1Los Alamos National Laboratory
Monoclinic α is the room-temperature phase of plutonium. With the addition of as little as 1 atomic % gallium, the face-centered cubic δ phase is stable at room temperature. In δ-phase Pu alloys with less than 3 atomic % Ga, various types of α phase can coexist depending on their thermal and mechanical history. Residual α-Pu may be present following post-casting homogenization and can persist despite prolonged annealing times. Pressure-induced α´ may be present following isostatic compression or as a result of sample preparation. Thermally-induced α´ is produced cryogenically and is characterized by a large volume contraction and large hysteresis loop. Here we will discuss the thermal stability regimes of these various types of α-Pu based on thermal analysis experiments and describe the transformation mechanisms that allow them to be present in these various conditions.
5:20 PM Concluding Comments