Accelerated Materials Evaluation for Nuclear Applications Utilizing Irradiation and Integrated Modeling: Poster Session
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Assel Aitkaliyeva, University of Florida; Peter Hosemann, University of California - Berkeley; Samuel Briggs, Oregon State University; David Frazer, Los Alamos National Laboratory

Monday 5:30 PM
February 24, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr

Session Chair: Assel Aitkaliyeva, University of Florida


H-1 (Invited): Modeling the Uranium-Silicon Phase Equilibria: Tashiema Ulrich1; Sven Vogel1; Joshua White1; Theodore Besmann2; 1Los Alamos National Laboratory; 2University of South Carolina
    The uranium-silicide compound, U3Si2 , is under consideration as a potential replacement for conventional uranium dioxide fuel. Despite the large number of studies on the uranium-silicon system, there is concern regarding the accuracy and completeness of our understanding of the 40-66 at.% silicon region of phase diagram. The Uranium-Silicon phase diagram is characterized by seven intermetallic compounds (U3Si, U3Si2, USi, U3Si5 , USi1.88 , USi2 , and USi3) of which only U3Si is well understood. In this work, experimental techniques for thermal and compositional analysis, and crystal structure determination were coupled with computational predictions for the characterization of the six intermetallic compounds U3Si2 , USi,U3Si5 , USi1.88, USi2 , USi3, and additional compounds between U3Si2 , and USi2 . Information such as phase transitions, homogeneity ranges, and crystal structures were used, along with critically assessed literature data, to construct a thermodynamic database describing the U-Si system utilizing the CALPHAD method.

H-2: Characterization of Helium Implanted Single Crystal Titanium: Sarah Stevenson1; Mehdi Balooch1; Andrew Scott1; Peter Hosemann1; Frances Allen1; Saryu Fensin2; 1University of California, Berkeley; 2Los Alamos National Laboratory
    Helium bubble development in materials due to plasma exposure or transmutation is an ongoing concern for the structural integrity of nuclear components. Numerous studies have been performed on a range of materials to analyze degradation phenomena involving helium bubbles. In this work, helium ion microscopy (HIM), featuring a nanometer-sized ion beam allowing precise local implantation of near-surface helium, was used to implant single crystal titanium samples of varying crystallographic orientations. For each sample, multiple implantations were performed using a range of doses and dose rates. The implantations were characterized using a multi-technique approach. The swelling and surface topography changes of the implanted areas were investigated by atomic force microscopy (AFM) with sub nanometer height resolution. Nano-indentation was used to determine the variation of local hardness and elastic modulus with depth. Transmission electron microscopy (TEM) allowed for the characterization of defects and bubble distributions.

H-3: Femtosecond Laser Machining of Micro-Scale Structures: Sebastian Lam1; Andrew Dong1; Jack Peterson1; Peter Hosemann1; Quinn Mcculloch2; Jonathan Gregory Gigax2; 1University of California, Berkeley; 2Los Alamos National Laboratory
     Currently FIB based sample preparation is the standard for micro-mechanical samples and TEM foils as well as residual stress measurements. However, larger and mesoscale samples can only be tackled using plasma based FIB machines or femto second laser ablation techniques. A femto second laser ablation system allows for extremely efficient material removal with sufficient precision for sample preparation with subsequent FIB based cleaning procedures for a fraction of the cost of a conventional or advanced FIB system.The primary goal of this work is the development of micro-scale structures with the use of a femto second laser. Damage mitigation strategies such as the optimization of parameters like pulse frequency, fabrication velocity, and power are suggested to give a reduction in ablation as well as reduced cleaning times at a focused ion beam. The results given show that femtosecond laser preparation techniques hold great promise for rapid material analysis.

Cancelled
H-4: Direct Compaction of Dispersion Fuels Using a Matrix Deposition on the Fuel Particles: Sunghwan Kim1; Kyu Hong Lee1; Won Jae So1; Yong Jin Jeong1; Kinam Kim1; Jong Man Park1; 1Korea Atomic Energy Research Institute
    The high uranium loading, indispensable for the LEU conversion, has an effect on the homogeneity of dispersion fuels relating substantial variation in fuel product yields. In this study, atomized U-7Mo powders were coated with pure Al, a matrix material, by PVD to avoid the problems of homogeneity. Varying thicknesses of Al was homogeneously deposited on the surface of U-7Mo particles. Al-deposited powders were directly compacted in various densities of compacts without a blending process. The porosity of compacts was measured by the Archimedes method, and the results compared to those of a general compact.

H-5: Effects of Helium Ion Irradiation on Single Crystal Vanadium: Andrew Scott1; Peter Hosemann1; Mehdi Balooch1; Marco Sebastiani2; Muhammad Mughal2; Sarah Stevenson1; 1University of California, Berkeley; 2Universitą degli studi Roma Tre
     Helium Bubbles in metals present several challenges to the design of materials for nuclear reactors. The high neutron flux causes displacement damage and Helium accumulation via (n, alpha) reactions, and direct implantation in fusion environments. Fusion presents uniquely difficult challenges, as PFC materials must withstand the combined thermal stresses and multi-species bombardment. It is crucial to understand the fundamental nature of Helium in metals to engineer materials that withstand these harsh environments. In this work, Helium Ion Microscopy is employed to implant and characterize single crystal Vanadium, building on previous research utilizing this method. HIM implantation allows for precise control of irradiation conditions with rapid and reproducible variability to investigate effects of temperature, fluence, flux, and irradiation area. AFM, TEM, and Nanoindentation are employed to probe surface and microstructural phenomenon, blistering, swelling, hardening, and embrittlement. FIB-DIC is further employed to characterize residual stresses from irradiation,revealing strong correlation with dose.

Cancelled
H-6: Fabrication of Low-enriched Uranium Dispersion Targets with a High Uranium Density for Mo-99 Production: Kinam Kim1; Jong Hwan Kim1; Tae Won Cho1; Sunghwan Kim1; Kyuhong Lee1; Yong Jin Jeong1; Jong Man Park1; 1Korea Atomic Energy Research Institute
    Mo-99 decays to Tc-99m, which is the most widely used radiopharmaceutical isotope for medical diagnostic purposes. Recently, Mo-99 producers have been attempting to replace conventional highly enriched uranium (HEU) targets with low enriched uranium (LEU) targets by international non-proliferation policies. As a result, it is necessary to develop high-uranium-density targets with LEU to improve the Mo-99 production efficiency of LEU targets. Korea Atomic Energy Research Institute (KAERI) has been developing commercial LEU targets with a uranium density of 2.6 gU/cm3 and high-density LEU targets using atomized U-Al alloy powder. We successfully mass-produced uranium alloy powder for high-density targets through centrifugal atomization and fabricated high density targets with a uranium density of 3.2 and 4.1 gU/cm3. Thermomechanical treatment (hot rolling + heat treatment) was conducted to prevent deformation due to phase transformation in the targets.

H-8: Mechanical Properties of Ion Irradiated and Helium Implanted HT9 Micropillars: Ryan Schoell1; Ce Zheng1; Khalid Hattar2; Djamel Kaoumi1; 1North Carolina State University; 2Sandia National Laboratory
    Micropillars of F/M steel HT9 were processed using Focused Ion Beam (FIB). The pillars were subject to 1.7 MeV Au3+ and/or implanted with 10 keV He+ at 470 °C in-situ in a TEM. After the in-situ irradiation, the pillars were then subject to compression tests at a displacement rate of 5 × 10-4 s-1 at room temperature using a pico-indenter in-situ in a TEM. Snapshots, video and stress-strain curve were recorded for each tested pillar. The changes in the microstructure were tracked during irradiation and during compression in-situ in the TEM to understand the radiation hardening due to radiation damage and the impact of the He bubbles in HT9.

H-9: Microstructure and Mechanical Behavior of Directed Energy Deposition Laser Additively Manufactured T-91: Jack Peterson1; Adi Benartzy1; Stuart Maloy2; Thomas Lienert2; Peter Hosemann1; 1University of California, Berkeley; 2Los Alamos National Laboratory
    The diverse capabilities of additive manufacturing (AM) make it a highly attractive processing method for the nuclear engineering community. Direct energy deposition selective laser melting (DED-SLM) process was used to manufacture T-91, a creep and radiation resistant martensitic stainless steel. The AM steel was found to be tempered martensite, with residual compositional gradients induced by the heat-affected zone of the laser process. Tensile testing showed that the as AM material had a slight decrease in yield stress and a major increase in elongation to fracture in comparison to wrought T-91. Tempering of the AM material induced a reduction in both properties. It was established that AM using DED-SLM might be an effective processing method for T-91. The data on T-91 is further compared to 420SS as well as a more common material.

H-10: Radiation Response of HT9 Ferritic/Martensitic Alloys as a Function of Interstitial Content: Eda Aydogan1; Jonathan Gigax2; Scott Parker2; Benjamin Eftink2; Yongqiang Wang2; Stuart Maloy2; 1Sabanci University; 2Los Alamos National Laboratory
    HT-9 ferritic/martensitic steels are one of the best candidates for structural materials in nuclear applications such as the fuel cladding and fuel ducts for fast reactors. Effect of interstitial elements on swelling, radiation induced segregation and damage has been investigated extensively back in 70s and 80s. However, it is still unclear how it effects hardening and void swelling. In this study, HT9 alloys having various nitrogen contents have been ion irradiated up to ~23 dpa at 300 °C. Transmission electron microscopy (TEM), nano-indentation and atom probe tomography (APT) analyses have shown that the dislocation loop size and density, radiation induced hardening and second phase precipitation mechanisms are different in low and high nitrogen alloys. This study sheds light on any discrepancies in the literature and paves the way to improvements in both modelling and structural material development efforts for next generation reactors.