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DOE OSTI2014

Geoelectrical Measurement of Multi-Scale Mass Transfer Parameters

Mass transfer affects contaminant transport and is thought to control the efficiency of aquifer remediation at a number of sites within the Department of Energy (DOE) complex. An improved understanding of mass transfer is critical to meeting the enormous scientific and engineering challenges currently facing DOE. Informed design of site remedies and long-term stewardship of radionuclide-contaminated sites will require new cost-effective laboratory and field techniques to measure the parameters controlling mass transfer spatially and across a range of scales. In this project, we sought to capitalize on the geophysical signatures of mass transfer. Previous numerical modeling and pilot-scale field experiments suggested that mass transfer produces a geoelectrical signature—a hysteretic relation between sampled (mobile-domain) fluid conductivity and bulk (mobile + immobile) conductivity—over a range of scales relevant to aquifer remediation. In this work, we investigated the geoelectrical signature of mass transfer during tracer transport in a series of controlled experiments to determine the operation of controlling parameters, and also investigated the use of complex-resistivity (CR) as a means of quantifying mass transfer parameters in situ without tracer experiments. In an add-on component to our grant, we additionally considered nuclear magnetic resonance (NMR) to help parse mobile from immobile porosities. Including the NMR component, our revised study objectives were to: 1. Develop and demonstrate geophysical approaches to measure mass-transfer parameters spatially and over a range of scales, including the combination of electrical resistivity monitoring, tracer tests, complex resistivity, nuclear magnetic resonance, and materials characterization; and 2. Provide mass-transfer estimates for improved understanding of contaminant fate and transport at DOE sites, such as uranium transport at the Hanford 300 Area. To achieve our objectives, we implemented a 3-part research plan involving (1) development of computer codes and techniques to estimate mass-transfer parameters from time-lapse electrical data; (2) bench-scale experiments on synthetic materials and materials from cores from the Hanford 300 Area; and (3) field demonstration experiments at the DOE’s Hanford 300 Area. In a synergistic add-on to our workplan, we analyzed data from field experiments performed at the DOE Naturita Site under a separate DOE SBR grant, on which PI Day-Lewis served as co-PI. Techniques developed for application to Hanford datasets also were applied to data from Naturita. 1. Introduction The Department of Energy (DOE) faces enormous scientific and engineering challenges associated with the remediation of legacy contamination at former nuclear weapons production facilities. Selection, design and optimization of appropriate site remedies (e.g., pump-and-treat, biostimulation, or monitored natural attenuation) requires reliable predictive models of radionuclide fate and transport; however, our current modeling capabilities are limited by an incomplete understanding of multi-scale mass transfer—its rates, scales, and the heterogeneity of controlling parameters. At many DOE sites, long “tailing” behavior, concentration rebound, and slower-than-expected cleanup are observed; these observations are all consistent with multi-scale mass transfer [Haggerty and Gorelick, 1995; Haggerty et al., 2000; 2004], which renders pump-and-treat remediation and biotransformation inefficient and slow [Haggerty and Gorelick, 1994; Harvey et al., 1994; Wilson, 1997]. Despite the importance of mass transfer, there are significant uncertainties associated with controlling parameters, and the prevalence of mass transfer remains a point of debate [e.g., Hill et al., 2006; Molz et al., 2006] for lack of experimental methods to verify and measure it in situ or independently of tracer breakthrough. There is a critical need for new field-experimental techniques to measure mass transfer in-situ and estimate multi-scale and spatially variable mass-transfer parameters. The current lack of such techniques results in large parameter uncertainty, which in turn translates into enormous prediction uncertainty and cost to DOE. In this project, we considered three hydrogeophysical approaches for providing information about mass-transfer parameters: (1) the combination of electrical-resistivity tomography (ERT) and ionic tracer experiments to explore rates of exchange and relative mobile and immobile porosities; (2) complex resistivity (CR) measurements to infer the distribution of diffusive length scales active in a porous medium; and (3) nuclear magnetic resonance (NMR) to estimate mobile and immobile porosity.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2012

Evaluation of the Impact of Thin Pours on Saltstone Properties

The proposed Saltstone Disposal Unit 6 (SDU6) is a larger structure than the SDU4 cells and larger than the disposal units (SDU2, SDU3, and SDU5) currently in use or under construction. The additional capacity provided by SDU6 is desired to reduce life cycle costs and support site accelerated closure goals. The larger size of the planned SDU6 could result in saltstone being placed in thinner lifts as the unit is filled. This study was performed to determine whether thinner layers of saltstone negatively impact the performance of the waste form. A larger number of cold joints could potentially result in increased drying, salt deposition, and surface oxidation. A matrix of samples was prepared to simulate thin pours ranging from 0.5 to 6 inches thick. Each sample was cured for at least 28 days prior to further characterization. Leachability results showed that there is no obvious impact of the number of grout layers on the Leachability Index values for Na and NO 3 . The concentrations of Cr, NO 2 , and C 2 O 4 were below detection limits for all of the leachates. No attempt was made to evaluate the oxidation of these samples since no measureable Cr was leached, although this would appear to indicate that Cr in the samples remained reduced for cold joints with surfaces exposed for approximately four days. The results of hydraulic conductivity measurements showed that the number of cold joints in the samples did not have a significant impact on the measured values for the vertical lift orientation (i.e., when the flow path is perpendicular to the cold joints). For the horizontal lift orientation (i.e., when the flow path is parallel to the cold joints), the number of cold joints in the samples also did not appear to have a significant impact on hydraulic conductivity. The measured hydraulic conductivity was faster when the flow path was parallel to the cold joints as compared to when the flow path was perpendicular to the cold joints. Percolation testing showed increased flow when the number of cold joints was increased. Compressive strength testing showed that the maximum load at the onset of cracking was reduced by approximately 26% for those samples that contained cold joints as compared to the monolithic samples. The number of cold joints in the sample had no significant impact on the maximum load prior to cracking. The porosity of the samples was not influenced by cold joints. This result was expected as the porosity is a material property affected by the properties of the components (premix and salt solution) and the water to premix ratio. Overall, the only obvious impact of cold joints in the samples was to significantly increase hydraulic conductivity in the direction parallel to the cold joints. An increasing number of cold joints (thin layers) in the simulated saltstone samples did not exacerbate this effect, nor did it have a negative impact on the Leachability Indices or porosity for surfaces exposed for approximately four days. The presence of a cold joint reduced the compressive strength of the material, although this impact was seen regardless of the number of cold joints in the sample.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Advanced Technologies for Monitoring CO2 Saturation and Pore Pressure in Geologic Formations: Linking the Chemical and Physical Effects to Elastic and Transport Properties

Ultrasonic P- and S-wave velocities were measured over a range of confining pressures while injecting CO2 and brine into the samples. Pore fluid pressure was also varied and monitored together with porosity during injection. Effective medium models were developed to understand the mechanisms and impact of observed changes and to provide the means for implementation of the interpretation methodologies in the field. Ultrasonic P- and S-wave velocities in carbonate rocks show as much as 20-50% decrease after injection of the reactive CO2-brine mixture; the changes were caused by permanent changes to the rock elastic frame associated with dissolution of mineral. Velocity decreases were observed under both dry and fluid-saturated conditions, and the amount of change was correlated with the initial pore fabrics. Scanning Electron Microscope images of carbonate rock microstructures were taken before and after injection of CO2-rich water. The images reveal enlargement of the pores, dissolution of micrite (micron-scale calcite crystals), and pitting of grain surfaces caused by the fluid- solid chemical reactivity. The magnitude of the changes correlates with the rock microtexture – tight, high surface area samples showed the largest changes in permeability and smallest changes in porosity and elastic stiffness compared to those in rocks with looser texture and larger intergranular pore space. Changes to the pore space also occurred from flow of fine particles with the injected fluid. Carbonates with grain-coating materials, such as residual oil, experienced very little permanent change during injection. In the tight micrite/spar cement component, dissolution is controlled by diffusion: the mass transfer of products and reactants is thus slow and the fluid is expected to be close to thermodynamical equilibrium with the calcite, leading to very little dissolution, or even precipitation. In the microporous rounded micrite and macropores, dissolution is controlled by advection: because of an efficient mass transfer of reactants and products, the fluid remains acidic, far from thermodynamical equilibrium and the dissolution of calcite is important. These conclusions are consistent with the lab observations. Sandstones from the Tuscaloosa formation in Mississippi were also subjected to injection under representative in situ stress and pore pressure conditions. Again, both P- and S-wave velocities decreased with injection. Time-lapse SEM images indicated permanent changes induced in the sandstone microstructure by chamosite dissolution upon injection of CO2-rich brine. After injection, the sandstone showed an overall cleaner microstructure. Two main changes are involved: (a) clay dissolution between grains and at the grain contact and (b) rearrangement of grains due to compaction under pressure Theoretical and empirical models were developed to quantify the elastic changes associated with injection. Permanent changes to the rock frame resulted in seismic velocity-porosity trends that mimic natural diagenetic changes. Hence, when laboratory measurments are not available for a candidate site, these trends can be estimated from depth trends in well logs. New theoretical equations were developed to predict the changes in elastic moduli upon substitution of pore-filling material. These equations reduce to Gassmann’s equations for the case of constant frame properties, low seismic frequencies, and fluid changes in the pore space. The new models also predict the change dissolution or precipitation of mineral, which cannot be described with the conventional Gassmann theory.

Mavko, G.↗
DOE OSTI2013

Geoscience Perspectives in Carbon Sequestration - Educational Training and Research Through Classroom, Field, and Laboratory Investigations

The most effective mechanism to limit CO 2 release from underground Geologic Carbon Sequestration (GCS) sites over multi-century time scales will be to convert the CO 2 into solid carbonate minerals. This report describes the results from four independent research investigations on carbonate mineralization: 1) Colloidal calcite particles forming in Maramec Spring, Missouri, provide a natural analog to evaluate reactions that may occur in a leaking GCS site. The calcite crystals form as a result of physiochemical changes that occur as the spring water rises from a depth of more than 190'. The resultant pressure decrease induces a loss of CO 2 from the water, rise in pH, lowering of the solubility of Ca 2+ and CO 3 2- , and calcite precipitation. Equilibrium modelling of the spring water resulted in a calculated undersaturated state with respect to calcite. The discontinuity between the observed occurrence of calcite and the model result predicting undersaturated conditions can be explained if bicarbonate ions (HCO 3 - ) are directly involved in precipitation process rather than just carbonate ions (CO 3 2- ). 2) Sedimentary rocks in the Oronto Group of the Midcontinent Rift (MCR) system contain an abundance of labile Ca-, Mg-, and Fe-silicate minerals that will neutralize carbonic acid and provide alkaline earth ions for carbonate mineralization. One of the challenges in using MCR rocks for GCS results from their low porosity and permeability. Oronto Group samples were reacted with both CO 2 -saturated deionized water at 90°C, and a mildly acidic leachant solution in flow-through core-flooding reactor vessels at room temperature. Resulting leachate solutions often exceeded the saturation limit for calcite. Carbonate crystals were also detected in as little as six days of reaction with Oronto Group rocks at 90oC, as well as experiments with forsterite-olivine and augite, both being common minerals this sequence. The Oronto Group samples have poor reservoir rock characteristics, none ever exceeded a permeability value of 2.0 mD even after extensive dissolution of calcite cement during the experiments. The overlying Bayfield Group – Jacobsville Formation sandstones averaged 13.4 ± 4.3% porosity and a single sample tested by core-flooding revealed a permeability of ~340 mD. The high porosity-permeability characteristics of these sandstones will allow them to be used for GCS as a continuous aquifer unit with the overlying Mt. Simon Formation. 3) Anaerobic sulfate reducing bacteria (SRB) can enhance the conversion rate of CO 2 into solid minerals and thereby improve long-term storage. SRB accelerated carbonate mineralization reactions between pCO 2 values of 0.0059 and 14.7 psi. Hydrogen, lactate and formate served as suitable electron donors for SRB metabolism. The use of a 13 CO 2 spiked gas source also produced carbonate minerals with ~53% of the carbon being derived from the gas phase. The sulfate reducing activity of the microbial community was limited, however, at 20 psi pCO 2 and carbonate mineralization did not occur. Inhibition of bacterial metabolism may have resulted from the acidic conditions or CO 2 toxicity. 4) Microbialite communities forming in the high turbidity and hypersaline water of Storrs’ Lake, San Salvador Island, The Bahamas, were investigated for their distribution, mineralogy and microbial diversity. Molecular analysis of the organic mats on the microbialites indicate only a trace amount of cyanobacteria, while anaerobic and photosynthetic non-sulfur bacteria of the phyla Chloroflexi and purple sulfur bacteria of class Gammaproteobacteria were abundant.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

A New Method for Low Cost Production of Titanium Alloys for Reducing Energy Consumption of Mechanical Systems

This project investigated an innovative manufacturing process intended to minimize the cost of production of titanium materials and components, and increase the adoption of Ti components for energy consuming applications, such as automobiles. A key innovation of the proposed manufacturing approach is a novel Ti powder sintering technology for making titanium materials with ultrafine grain microstructure in the as-sintered state with minimum, or an absence, of post-sintering processes. The new sintering technology is termed Hydrogen Sintering and Phase Transformations (HSPT), and constitutes a promising manufacturing technology that can be used to produce titanium (Ti) materials and components in a near-net-shape form, thus also minimizing machining costs. Our objective was to meet, or possibly surpass, the mechanical property levels for ASTM B348 Grade 5 for wrought Ti-6Al-4V. Although specific applications call for varying mechanical property requirements, ASTM B348 was created for the demanding applications of the aerospace industry, and is the established standard for Ti-6Al-4V. While the primary goal was to meet, or exceed this standard, the team also had the goal of demonstrating this could be done at a significantly lower cost of production. Interim goals of the project were to fully develop this novel sintering process, and provide sufficient baseline testing to make the method practical and attractive to industry. By optimizing the process parameters for the sintering of titanium hydride (TiH 2 ) powders in a hydrogen atmosphere and controlling the phase transformations during and after sintering, the HSPT process was expected to reduce the energy consumption, and thus cost, of making Ti alloys and fabricating Ti components. The process was designed such that no high temperature melting is required for producing Ti alloys; little or no post-sintering processing is needed for producing desired microstructures (and therefore enhanced mechanical properties), and finally, minimum machining is needed to fabricate finished Ti components. An energy analysis within this report provides more detail, but calculated values indicate that the HSPT process is less than half as energy intensive as conventional wrought processing, while producing mechanical properties that are comparable. In addition to the energy savings anticipated from the industrial production of Ti components, a second prong of energy savings resides in the use phase of components produced, primarily from use in the transportation sector. Titanium has a number of material qualities appropriate for the auto industry, particularly low mass and corrosion resistance. By reducing the weight of automobiles and other vehicles, energy costs and CO 2 production will be reduced over the lifetime of the vehicles, and components in corrosive environments on vehicles, such as exhaust systems and other under carriage parts, may not have to be replaced during a vehicle’s lifetime. Our analysis indicates that by replacing only 5.6 kg of steel parts in an auto with Ti components across the entire US fleet would save approximately 486 million gallons of gasoline per year. This correlates to a reduction of 3.6 million metric tons of CO 2 per year. The potential for replacing many more of the steel parts in automobiles with lighter weight titanium components is clear. The project was very successful overall, meeting all milestones and surpassing project goals in terms of mechanical properties and microstructures produced. In addition to tensile properties, fatigue properties were emphasized in the project work. Powder metallurgy processes often have porosity to some degree in their final microstructure, and porosity is a well-known cause of crack initiation and low fatigue performance. Although many automobile applications do not undergo fatigue stress regimes, many others do encounter cyclic stress, and design criteria in the latter case require good fatigue properties. Production and testing of HSPT parts showed excellent tensile properties and fracture toughness, and fatigue properties that exceeded all previously reported powder metallurgy Ti methods, overlapping with wrought processed values. Fatigue limits exceeded 500 MPa and tensile strength exceeded 1,000 MPa while maintaining good ductility. Microstructures produced during the project period easily surpassed pre-project expectations. In addition to producing very fine grains in the as-sintered state (without post sintered thermo-mechanical work), porosity was reduced and industrially relevant microstructures previously undemonstrated in any other powder metallurgy titanium method were produced using HSPT materials. These microstructures, both bi-modal and globularized, were produced with simple post-sinter heat treatments, but without the need for energy intensive mechanical work. The employed heat treatments expanded the available mechanical property range (tensile strength vs. ductility) of the HSPT system in Ti-6Al-4V. The project has resulted in the publication, thus far, of five refereed journal articles and five conference proceedings papers, as well as a patent application, two dissertations and a master’s thesis. Two additional journal articles are currently under review, and at least three others are currently in preparation, with several additional students anticipated to graduate within the coming year. Presentations and papers were a particular focus of the second half of the project, once significant experimentation had been performed and analyzed. As part of our efforts to disseminate information of our results, the Ti research teams within Prof. Fang’s and Prof. Chandran’s research groups had a strong presence at the 13th World Conference on Ti, August 16-20, 2015, in San Diego. Several research groups in the US and in Europe are now performing experiments using the HSPT process. Accompanying efforts to bring HSPT to the Ti community at large, and industry in particular, work has continued with our partners and with other interested industrial Ti users and producers, including Boeing and GKN (a major powder metallurgy parts manufacturer). Commercialization has been a central focus of the final phase of the project, and Reading Alloys signed a provisional licensing agreement in summer of 2015. They are currently seeking an appropriate customer with which to pursue initial parts manufacturing efforts. Other licensing options and partners are continuing to be pursued. The promise of lightweight, strong and corrosion resistant Ti alloys with long fatigue lifetimes for automobile or transportation applications has been the vision of the metal industry since titanium came to the attention of scientists and engineers. The sole limitation of realizing these goals has been cost, which is primarily a function of energy used in production. The HSPT process was shown through this work to be capable of realizing this goal, and facilitating the practical use of titanium in US automotive and other industries.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

SECARB Commercial Scale CO 2 Injection and Optimization of Storage Capacity in the Southeastern United States

The Commercial Scale Project is a US DOE/NETL funded initiative aimed at enhancing the knowledge-base and industry’s ability to geologically store vast quantities of anthropogenic carbon. In support of this goal, a large-scale, stacked reservoir geologic model was developed for Gulf Coast sediments centered on the Citronelle Dome in southwest Alabama, the site of the SECARB Phase III Anthropogenic Test. Characterization of regional geology to construct the model consists of an assessment of the entire stratigraphic continuum at Citronelle Dome, from surface to the depth of the Donovan oil-bearing formation. This project utilizes all available geologic data available, which includes: modern geophysical well logs from three new wells drilled for SECARB’s Anthropogenic Test; vintage logs from the Citronelle oilfield wells; porosity and permeability data from whole core and sidewall cores obtained from the injection and observation wells drilled for the Anthropogenic Test; core data obtained from the SECARB Phase II saline aquifer injection test; regional core data for relevant formations from the Geological Survey of Alabama archives. Cross sections, isopach maps, and structure maps were developed to validate the geometry and architecture of the Citronelle Dome for building the model, and assuring that no major structural defects exist in the area. A synthetic neural network approach was used to predict porosity using the available SP and resistivity log data for the storage reservoir formations. These data are validated and applied to extrapolate porosity data over the study area wells, and to interpolate permeability amongst these data points. Geostatistical assessments were conducted over the study area. In addition to geologic characterization of the region, a suite of core analyses was conducted to construct a depositional model and constrain caprock integrity. Petrographic assessment of core was conducted by OSU and analyzed to build a depositional framework for the region and provide modern day analogues. Stability of the caprock over several test parameters was conducted by UAB to yield comprehensive measurements on long term stability of caprocks. The detailed geologic model of the full earth volume from surface thru the Donovan oil reservoir is incorporated into a state-of-the-art reservoir simulation conducted by the University of Alabama at Birmingham (UAB) to explore optimization of CO 2 injection and storage under different characterizations of reservoir flow properties. The application of a scaled up geologic modeling and reservoir simulation provides a proof of concept for the large scale volumetric modeling of CO 2 injection and storage the subsurface.

58 GEOSCIENCES↗
DOE OSTI2017

Structural and Stratigraphic Controls on Methane Hydrate occurrence and distribution: Gulf of Mexico, Walker Ridge 313 and Green Canyon 955: Final Report

The goal of this project was to determine structural and stratigraphic controls on hydrate occurrence and distribution in Green Canyon (GC) 955 and Walker Ridge (WR) 313 blocks using seismic and well data. Gas hydrate was discovered in these blocks in coarse- and fine-grained sediments during the 2009 Joint Industrial project (JIP) Leg 11 drilling expedition. Although the immediate interest of the exploration community is exclusively hydrate which is present in coarse–grained sediments, factors that control hydrate and free gas distribution in the two blocks and whether coarse and fine-grained hydrate-bearing units are related in any manner, formed the core of this research. The project spanned from 10/01/2012 to 07/31/2016. In the project, in both the leased blocks, the interval spanning the gas hydrate stability zone (GHSZ) was characterized using a joint analysis of sparse Ocean Bottom Seismic (OBS) and dense, surface–towed multichannel seismic (MCS) data. The project team had the luxury of calibrating their results with two well logs. Advance processing methods such as depth migration and full-waveform inversion (FWI) were used for seismic data analysis. Hydrate quantification was achieved through interpretation of the FWI velocity field using appropriate rock physics models at both blocks. The seismic modeling/inversion methodology (common to both GC955 and WR313 blocks) was as follows. First, the MCS data were depth migrated using a P-wave velocity (VP) model constructed using inversion of reflection arrival times of a few (four in both cases) key horizons carefully picked in the OBS data to farthest possible offsets. Then, the resolution of the traveltime VP model was improved to wavelength scale by inverting OBS gathers up to the highest frequency possible (21.75 Hz for GC955 and 17.5 for WR313) using FWI. Finally, the hydrate saturation (or the volume fraction) was estimated at the well location assuming one of the other hydrate morphology (filling the primary or the secondary porosity) was extrapolated out from the wells using the FWI VP as a guide. General outcomes were as follows. First and foremost, an imaging methodology using sparse seismic data, which is easily replicable at other sites with similar datasets, has been demonstrated. The end product of this methodology at both the leased blocks is quantitative estimates of hydrate distribution. Second, at both locations there is strong evidence that the base of the GHSZ, which does not appear as a clear Bottom Simulating Reflection (BSR), manifests in the VP perturbations created by FWI, suggesting that FWI is sensitive to subtle compositional changes in shallow sediments and establishes it as a valuable tool for investigations of hydrate-bearing basins. Third, through joint interpretation of the depth migrated image and the FWI VP model, how structure and stratigraphy jointly determine hydrate and free gas distribution in both blocks could be clearly visualized. The joint interpretation also suggests that the coarse and fine grained hydrate-bearing sediments at both leased are connected. Site specific results, in addition to general results, are as follows. At GC955 the overlying fine-grained hydrate-bearing unit could have been sourced from the underlying hydrate coarse-grained channel-levee complex through a chimney feature. The channel-levee system at GC955 is compartmentalized by faults, of which only a few may be impermeable. Although compartmentalized, the channel-levee system in the GC955 as a whole might be in communication except selected zones. At WR313 the overlying fine-grained fracture-filled hydrate unit appears to be sourced from below the GHSZ. The reason that only a particular fine-grained unit has hydrate, despite having lower porosity that the bounding units, could be the presence of secondary porosity (such as those formed from clay dewatering under compaction). In conclusion, the project was a pioneering effort in in joint analysis of OBS and MCS datasets for advancing the knowledge about a hydrate and free–gas system dynamics using advanced processing methods such as FWI and depth migration. Results obtained in this project can greatly advance the tools and techniques used for delineating specific hydrate prospects. Results obtained in this project can also be seamlessly incorporated into other DOE funded project on modeling the potential productivity and commercial viability of hydrate from sand-dominated reservoirs. The OBS and MCS data in this project were acquired in 2012 (after the JIP II drilling) by the USGS and therefore the results are a posteriori. Nonetheless, the seismic inversion workflow established through this project can be used to generate various what-if quantification scenarios even in absence of logs and serve as a valuable tool for guiding drilling operations. Results from this project can augment other DOE sponsored projects on determining the commercial viability of methane production from the Gulf of Mexico.

03 NATURAL GAS↗
DOE OSTI2018

Improved Characterization and Modeling of Tight Oil Formations for CO 2 Enhanced Oil Recovery Potential and Storage Capacity Estimation

Tight oil formations such as those in the Bakken petroleum system are known to hold hundreds of billions of barrels of oil in place; however, the primary recovery factor for these plays is typically less than 10%. Tight oil formations, including the Bakken Formation, therefore, may be attractive candidates for enhanced oil recovery (EOR) using CO 2 . Multiphase fluid behavior and flow in fluid-rich shales can vary substantially depending on the size of pore throats, and properties such as fluid viscosity and density are much different in nanoscale pores than in macroscale pores. Thus it is critical to understand the nature and distribution of nano-, micro-, and macroscale pores and fracture networks. To address these issues, the Energy & Environmental Research Center (EERC) has been conducting a research program entitled “Improved Characterization and Modeling of Tight Oil Formations for CO 2 Enhanced Oil Recovery Potential and Storage Capacity Estimation.” The objectives of the project are 1) the use of advanced characterization methods to better understand and quantify the petrophysical and geomechanical factors that control CO 2 and oil mobility within tight oil formation samples, 2) the determination of CO 2 permeation and oil extraction rates in tight reservoir rocks and organic-rich shales of the Bakken, and 3) the integration of the laboratory-based CO 2 permeation and oil extraction data and the characterization data into geologic models and dynamic simulations to develop predictions of CO 2 storage resource and EOR in the Bakken tight oil formation. A combination of standard and advanced petrophysical characterization techniques were applied to characterize samples of Bakken Formation tight reservoir rock and shales from multiple wells. Techniques included advanced computer tomography (CT) imaging, scanning electron microscopy (SEM) techniques, whole-core and micro x-ray CT imaging, field emission (FE) SEM, and focused ion beam (FIB) SEM. Selected samples were also analyzed for geomechanical properties. X-ray CT imaging yielded information on the occurrence of fractures, bedding planes, fossils, and bioturbation in core, as well as data on bulk density and photoelectric factor logs, which were used to interpret porosity, organic content, and mineralogy. FESEM was used for characterization of nano- and microscale features, including nanoscale pore visualization and micropore and pore throat mineralogy. FIBSEM yielded micro- to nanoscale visualization of fracture networks, porosity and pore-size distribution, connected versus isolated porosity, and distribution of organics. Results from the characterization activities provide insight on nanoscale fracture properties, pore throat mineralogy and connectivity, rock matrix characteristics, mineralogy, and organic content. Laboratory experiments demonstrated that CO 2 can permeate the tight matrix of Bakken shale and nonshale reservoir samples and mobilize oil from those samples. Geologic models were created at scales ranging from the core plug to the reservoir, and dynamic simulations were conducted. The data from the characterization and laboratory-based activities were integrated into modeling research activities to determine the fundamental mechanisms controlling fluid transport in the Bakken, which support EOR scheme design and estimation of CO 2 storage potential in tight oil formations. Simulation results suggest a CO 2 storage resource estimate range of 169 million to 1.5 billion tonnes for the Bakken in North Dakota, possibly resulting in 1.8 billion to 16 billion barrels of incremental oil.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2017

Assessment of the Idaho National Laboratory Remote-Handled Low-Level Waste Disposal Facility Vault Concrete Data

This document provides a summary of the concrete performance data collected during vault fabrication and installation. The report includes the process by which quality data was collected during vault fabrication and installation, the inspection requirements, and a summary of resulting test data with the potential to impact vault system durability. This report also includes quantitative data collected on cured concrete samples poured for random concrete batches throughout the concrete component fabrication process. Quantitative data includes total porosity, bulk density, absorption, effective porosity, and gas-phase permeability. Chloride diffusivity data collected during the concrete mix selection process are also included for completeness. Data shows that the vault quality assurance program resulted in components received insignificant defects and damaged areas during the fabrication stage and during the vault installation stage. Data collected on the cured concrete samples show the gas-phase permeability and effective porosity are slightly higher than the data used to select the concrete mix designs.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2018

Developing Novel Multifunctional Materials for High-Efficiency Electrical Energy Storage

This is the final report for the program “Developing Novel Multifunctional Materials for High-efficiency Electrical Energy Storage”, funded by The U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL), and performed by University of Tennessee, from September 01, 2013 to August 31, 2018. Securing a sustainable energy economy by developing affordable and clean energy from renewable energy is a central element to the mission of DOE/NETL. To further this mission, NETL funds research and development of novel multifunctional materials that can be used for high-efficiency electrical energy storage. The main objective of this research program is to conduct fundamental and applied research that lead to successful development and demonstration of novel multifunctional materials, which can improve the efficiency and reduce the cost of hydrogen production with water electrolysis. The specific objectives of this research program include: 1) Design, fabrication and demonstration of thin/well-tunable liquid/gas diffusion layer (TT-LGDLs) with different pore morphologies, including pore sizes and pore porosities. 2) Development of comprehensive computational models of proton exchange membrane water electrolyzer cell (PEMECs) for the investigation of influence of different operating conditions and physical design parameters on its performance. 3) Surface modification of TT-LGDLs for better catalyst access and product/reactant removal, and smaller interfacial contact resistance (ICR). To achieve the above challenging goals, a multidisciplinary research team was formed to work on fundamental and applied research on the following three major technical areas: 1) Design, fabrication and demonstration of thin/well-tunable LGDLs (TT-LGDLs) by using photolithography and wet etching of thin titanium (Ti) foils. During the project period, the team has successfully fabricated TT-LGDLs with different pore morphologies, including pore sizes and pore porosities. The manufacturing steps mainly include cleaning thin Ti foil, supporting the foils, applying photoresist, patterning the photoresist with designed mask, exposing and developing, etching, removing photoresist, and lift-off and cleaning. The manufactured TT-LGDLs were characterized with optical microscopies and scanning electron microscopies. Their pore morphologies, including pore size and porosity, were derived based on advanced image process. The feasibility for scale-up manufacturing has been demonstrated. The TT-LGDLs have been successfully investigated for water splitting in PEMECs, which showing better performance than their counterparts fabricated with the traditional fiber-based materials. 2) Comprehensive computational modeling of a PEMEC. A comprehensive computational model has been successfully developed, and the influence of different operating conditions and physical design parameters on its performance has been investigated, including operating temperature, pressure, exchange current density, electrode thickness, membrane thickness, and interfacial resistance. Results obtained from the present model provide a comprehensive understanding of design parameter effects and consequently improve the design/performance in a PEMEC. 3) Surface modification of TT-LGDLs. The proposed surface modifications of TT-LGDLs by sputter coating and/ electroplating have been successfully demonstrated. It has been found that the performance of PEMECs can be improved by both methods, and the thickness of the electroplated gold thin layer has limited effects on the performance. With the help of the surface modifications, the PEMECs achieved the best ever performance compared with the public literatures. In addition to completion of the proposed method, microporous layers (MPLs) with both irregular micro and sphere nano titanium particles on novel TT-LGDLs was developed for the first time. The MPLs were fabricated by a low-temperature air spraying method, which provide a better catalyst access and product/reactant removal. In summary, under the close collaborations among the research team, all the tasks have been completed and the proposed research objectives have been fulfilled. All the technical milestones have been achieved and the project has been completed successfully. The technical breakthroughs obtained under this project provide novel LGDLs with well-tunable pore morphologies that can significantly improve the performance of water splitting and energy storage. This development can be directly used in existing and next generation energy storage and fuel systems.

08 HYDROGEN↗
DOE OSTI2018

CarbonSAFE Rocky Mountain Phase I: Ensuring Safe Subsurface Storage of Carbon Dioxide in the Intermountain West

An integrated CCS pre-feasibility study, CarbonSAF E Rocky Mountain Phase I, was conducted by the U niversity of Utah and its partners as part of the US D epartment of Energy’s Carbon Storage Assurance a nd Facility Enterprise (CarbonSAFE) program. The a ssembled project team consisted of academic, indus try and governmental agencies covering the technic al and non- technical challenges of a commercial-sc ale CO 2 storage facility capable of storing 50 million tonnes of anthropogenically-sourced CO 2 . The Rock y Mountain CarbonSAFE team identified the Hunter Power Plant in central Utah as the primary source of CO 2 on which this study would be focused. The nea rby Huntington power plant, also operated by Rocky Mountain Power, was evaluated as a secondary sou rce of CO 2 . The Hunter plant was chosen because o f an interest in CO 2 capture technology by the plant operator, Rocky Mountain Power, and also because i t is a representative example of a typical coal-fired g enerating station in the Rocky Mountain west. Amine -based and cryogenic-based capture assessments w ere performed for approximately 3 million tonnes per year for one of the boiler units at the Hunter plant, yi elding cost of capture estimates of $\$56$/tonne and $\$4 1.50$/tonne. Transportation and intermediate compre ssion would increase the per tonne costs, but will be highly dependent on specific injection locations and available rights-of-way. A high-level technical sub-ba sinal evaluation was performed on the area surround ing the Hunter and Huntington power plants to verify CO 2 storage capacity and integrity. Initial geologic c haracterization efforts focused on sites immediately adjacent to the Hunter plant, including the deep eolia n Permian White Rim Sandstone, which in outcrop a nd core from other locations indicates high permeabi lity and high porosity. However, petrophysical logs fr om wells near Hunter indicate porosity of only 2-4%. As a result, potential injection sites were moved stru cturally down-dip (to the west), into the high permea bility (~200 mD) and high porosity (20%) Navajo san dstone. A comprehensive analysis of the reservoir a nd seals was conducted, providing data to the model , simulation and risk assessment groups on the proje ct. CO 2 capacity estimates for the Navajo Sandston e approximately 18 kilometers from the Hunter plant are well in excess of the 50 million tonnes goal of the project. Area of Review Delineation and Risk Asse ssment on the Navajo, associated seals and shallow groundwater aquifers identified the most significant risks and mitigation options. A non-technical assessment to a commercial-scale CO 2 storage facility in central Utah was conducted. EPA Underground Injection Control Class VI and National Environmental Policy Act permitting present particularly challenging issues related to the development of any saline aquifer for CO 2 storage, including the area around the Hunter plant. While surface and subsurface ownership and ri ghts are not straightforward, especially on any privat e land, many of the stakeholders in central Utah are accustomed and open to oil/gas/mineral-related activities similar to what would be required for CO 2 storage sites.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2019

Initial Simulations of Empty Room Collapse and Reconsolidation at the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) is a geologic repository for defense-related nuclear waste. If left undisturbed, the virtually impermeable rock salt surrounding the repository will isolate the nuclear waste from the biosphere. If humans accidentally intrude into the repository in the future, then the likelihood of a radionuclide release to the biosphere will depend significantly on the porosity and permeability of the repository itself. Room ceilings and walls at the WIPP tend to collapse over time, causing rubble piles to form on floors of empty rooms. The surrounding rock formation will gradually compact these rubble piles until they eventually become solid salt, but the length of time for a rubble pile to reach a certain porosity and permeability is unknown. This report details the first efforts to build models to predict the porosity and permeability evolution of an empty room as it closes. Conventional geomechanical numerical methods would struggle to model empty room collapse and rubble pile consolidation, so three different meshless methods, the Immersed Isogeometric Analysis Meshfree, Reproducing Kernel Particle Method (RKPM), and the Conformal Reproducing Kernel method, were assessed. First, the meshless methods and the finite element method each simulated gradual room closure, without ceiling or wall collapse. All three methods produced equivalent room closure predictions with comparable computational speed. Second, the Immersed Isogeometric Analysis Meshfree method and RKPM simulated two-dimensional empty room collapse and rubble pile consolidation. Both methods successfully simulated large viscoplastic deformations, fracture, and rubble pile rearrangement to produce qualitatively realistic results. In addition to geomechanical simulations, the flow channels in damaged salt and crushed salt were measured using micro-computed tomography, and input into a computational fluid dynamics simulation to predict the salt's permeability. Although room for improvement exists, the current simulation approaches appear promising.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Geothermal Deep Direct Use for Turbine Inlet Cooling in East Texas

The National Renewable Energy Laboratory (NREL), the Southern Methodist University Geothermal Laboratory (SMU), Eastman Chemical (Longview, TX), and TAS (Houston, TX) evaluated the feasibility of using geothermal heat to improve the performance of a natural-gas power plant in East Texas. The area of interest is the Eastman Chemical plant in Longview, Texas, which is on the northwestern margin of a geologic region known as the Sabine Uplift. The feasibility study focused on determining the potential for accessing a subsurface hot-water geothermal resource within a 10-km radius of the site to provide thermal energy for absorption chillers. Wells within a 20-km radius are included for broader geological comparison to determine the heat flow, temperature-at-depth, field porosity and permeability. The lithologies of most interest are the Lower Cretaceous Trinity Group and Upper Jurassic Cotton Valley Group. The deeper Cotton Valley formations are hotter (averaging 117 to 130°C), yet permeability and porosity are low. The shallower Trinity Group contains more variability in permeability and porosity and lower temperatures averaging about 98 to 117°C. The shallower formations are considered despite the lower temperature because of increased ability to produce larger volumes of water and extract enough heat before reinjection. The complete SMU analysis is available in the National Geothermal Data System (NGDS). Tapping such deep geothermal sources for direct heating (as opposed to power generation) is known as geothermal deep direct use (DDU). Geothermal DDU has potential across a wide swath of the United States but is underutilized due to challenging project economics associated with developing a deep geothermal resource for what are typically small-scale, variable-demand projects. This project examines the feasibility of geothermal energy integration in a natural-gas combined cycle power station in East Texas. The DDU resource is tapped to drive absorption chillers (24/7) for production of chilled water at 5-10°C (41-50°F). This chilled water is stored until needed, which allows for continuous operation with a relatively small-capacity geothermal/absorption chiller system. When conditions are favorable, the chilled water is dispatched to cool the air entering the compressor stage of a gas combustion turbine. This process, known as turbine inlet cooling (TIC), boosts power production during periods of high temperature and high-power demand. Such systems can enhance grid reliability and reduce the cost for peak-demand power. A simulation model of the power plant was developed in IPSEpro software and validated against operational data from the plant. This model allowed the team to estimate the additional power that could be produced by applying TIC under different operating and ambient conditions. Absorption chiller performance was estimated from vendor sources to determine the production rate of chilled water from the geothermal resource. Geothermal drilling and development costs were estimated using NREL's GEOPHIRES 2.0. The expected lower drilling costs in this region led to an estimated cost of geothermal heat of about $4/MMBtu (1.4 cents/kWh t ). The estimated cost for the absorption chillers and TIC hardware were obtained from literature sources and project partners. Hourly data were obtained for weather, natural gas and electricity prices, and plant operating state for 2017, which served as a representative year. NREL estimated the capital cost, operating cost, and additional electricity production and revenue for different combinations of geothermal capacity, chiller capacity, and water storage-tank size. The analysis drove toward smaller geothermal and chiller systems to reduce equipment cost. A relatively low-cost water storage tank accumulated the near-continuous chilled water output for later use when TIC was most valued.

15 GEOTHERMAL ENERGY↗
DOE OSTI2021

Nanoporous weakly coordinating anionic frameworks (Final Technical Report)

Under this award, we synthesized and characterized new weakly coordinating, anionic covalent organic frameworks. The motivation was to expand the class of covalent organic frameworks though the introduction of the first weakly coordinating anionic ones. The significance of the weakly coordinating anionic character of these frameworks is associated with the character of the counter (metal) cations in their pores. Those counter-cations, due to the inability to effectively coordinate to the pore walls, have a “naked”, and thus highly electrophilic, Lewis acidic character. Such properties are expected to translate to a number of interesting physical properties that can be potentially used for a range of energy-relevant applications. One of these applications is gas adsorption, separation, and storage. The electrophilic, Lewis acidic character of the counter-cations are expected to strongly bind to gas molecules entering the pores leading to higher gas sorption capacities. Other applications include heterogeneous catalysis, ion exchange, and solid state ion conduction. Within the project we explored a range of chemical blocks, and tested synthesis conditions to polymerize these building blocks to form the target materials. In particular, we focused on materials with group 15 elements like phosphorus in the oxidation state +5 and the coordination number 6, that have a formal -1 charge. The synthesis of such materials is challenging because its success depends on the absence of residual monomeric and oligomeric side-products in the pores, and the absence of significant framework interpenetration. Crystalline forms of these materials require sufficient reversibility of the polymerization reaction (which is difficult to achieve because group 15 elements like P tend to make strong covalent bonds with neighbored elements), as well as suitable polymerization rates that prevent the formation of kinetically controlled products. We had success with the preparation of anionic porous organic frameworks with anionic building blocks containing P(V)O6 octahedra synthesized through Yamamoto coupling reactions. These materials are non-crystalline because of the irreversible nature of the Yamamoto coupling reaction, but show porosity. The porosity and surface area can be significantly increased by co-reaction with electrostatically neutral co-reactants. Very high porosity and surface areas can be achieved when the materials are washed with hydrochloric acid. This method is commonly used to free products from Yamamoto coupling reactions from by-products. Indeed, this method removed by products from the pores of our materials, however it also led to the hydrolysis of the PO6 octahedra to form pending phosphonic acid groups (-PO3H)-groups in the frameworks (PA-POFs) which was actually not desired. Nonetheless, these materials showed high CO2 sorption capacities. In addition, they show extremely high (actually record) sorption capacities for the removal of a range of common micropollutants such as bisphenol A (BPA) and 4-nitrophenol in water. BPA is a wide-spread organic pollutant and a known endocrine disruptor. The maximum adsorption capacity of BPA at equilibrium is found to be as high as 3,366 mg g-1 by Langmuir adsorption model, which is more than 10 times greater than peer materials. The polymer also rapidly removes various other organic micropollutants with more than 90% removal efficiencies. In addition, the PA-POF material can be regenerated at least five times by mild washing using methanol without significant loss in removal efficiency. This is significant advantage over commonly used activated carbon materials (that are in Brita water faucet filters, for example). Comparison studies showed that only materials with the phosphonate groups show extreme sorption although the number of PA group is actually small according to solid state NMR and EDX data. More research would be needed to investigate why this is (a possibility is that the phosphonate groups have a multiplying effect in which a PA-induced initial adsorption leads to the adsorption of much more adsorbate). The extreme sorption capabilities can also be visually seen when colored adsorbates such as 4-nitrophenol are used, as the adsorption of the nitrobenzene leads to the decoloration of the solution. We have produced three short videos that illustrate the sorption capabilities compared to two peer materials (activated carbon from dismantled Brita water filters, and a electrostatically neutral, chemically related, porous organic polymer, respectively).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Demonstration of Dimensional and Microstructural Postirradiation Examination Capabilities on MiniFuel Disk Specimens

This work demonstrates two new MiniFuel postirradiation examination (PIE) capabilities, laser profilometry and serial sectioning, for future use on alpha-U specimens for the upcoming Mini-99 irradiation campaign. Representative U–Mo disk specimens—3 mm in diameter and approximately 0.75 mm in thickness—were subjected to dimensional measurements using standard calipers, as well as a new Keyence CL-3000 series laser profilometry system designed to measure the surface of both sides of the disk simultaneously. The laser profilometry system captured thickness gradients across the specimens as large as 0.2 mm. Additionally, because of the limitations inherent to the use of calipers, caliper measurements consistently overestimated the initial volume of MiniFuel disk specimens compared to the laser profilometry method by up to 5%. However, the results show that optimal data collection and analysis procedures are crucial to avoiding significant artifacts during data collection that can lead to large errors (approximately 10%). Serial sectioning using a combination of ion milling and electron imaging was also demonstrated for the analysis of micron-sized control volumes. Nanometer- to micron-scale porosity was resolved on a representative U–Mo specimen before irradiation, even when the surface of the specimen appeared free of porosity. Future efforts to relate microstructural features (porosity, fission product distributions, and so on) to macroscale effects (dimensional changes, thermal conductivity degradation) require accurate characterization methods such as those demonstrated in this work. These advanced PIE capabilities will be applied to optimized alpha-U specimens for the upcoming Mini-99 neutron irradiation campaign.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

3D printed Ni-Mn-Fe Bi-Functional Catalyst for Metal Air Batteries

Oxygen evolution catalyst with porous structures on the submillimeter and millimeter ranges have been shown to have high catalytic activity. Often, a limiting factor in the performance of a catalyst can be its specific surface area as this can limit the availability of active sites which encourage the desired reaction. As such, the inclusion of a hierarchical structure that include both meso-scale and nano-scale porosity can offer a means to greatly increase the performance of electrochemical catalysts. We have developed a method for manufacturing samples with such a hierarchical structure by combining techniques of direct ink writing (DIW), thermal sintering and free corrosion based dealloying. This allows us to prepare three-dimensionally structured samples with open-cell porosity at the macro-, micro- and nano-scales. Each level of porosity offers a different advantage to the overall functionality and applicability of this technology.

25 ENERGY STORAGE↗
DOE OSTI2022

Improved Understanding of Zircaloy Hydrogen Pickup Mechanisms in BWRs. NSUF Report (Final Report)

Using an instrumented autoclave operating at 288°C and 1100 psi, electrical impedance spectroscopy (EIS) measurements were taken from three neutron irradiated fuel channel samples (Zircaloy-2 and Zircaloy-4). The three high priority fuel channel samples were tested at 288°C using a simulated PWR water with the AC frequency range extending down through 10 -4 Hz, with corresponding DC measurements to validate the resistance measurements. EIS measurements were also taken at room temperature using a simulated PWR water from four neutron irradiated fuel channel samples (Zircaloy-2 and Zircaloy-4). and four water rod samples (Zircaloy-2). EIS measurements were also performed on unirradiated Zircaloy-2 tubes that were previously oxidized in autoclaves at various temperatures for different time durations to obtain oxide layers of different thicknesses. These experiments proved to be more challenging than anticipated because of the small size of the samples, which required development of fixtures to allow valid testing of the materials, some of which are radioactive, under pressure and temperature. Equivalent circuits were used to model the data. Some samples resulted in Nyquist plots where the arcs were too close to each other resulting in the inability to separate the different oxide morphological thicknesses. Microstructural characterization in the form of optical microscopy, scanning electron microscopy and (scanning) transmission electron microscopy was performed to document the microstructural features of the oxidized Zr-2 and Zr-4 samples (oxide and metal/oxide interface) and to interpret the EIS results. At the start of this work, it was assumed that despite the laminar cracks and porosity visible in both optical and SEM, the oxide scale is dense near the metal, effectively preventing the water from contacting the metal directly. While it is generally accepted that the large laminar cracks pores allow the water to percolate into the oxide film, it is unknown just how deep it can go, and how interconnected is the porosity, which will dictate how much the porosity is connected electrically to the water within the oxide scale. The EIS results demonstrated that there is in fact a distribution of oxide thicknesses over the various samples, and within each material condition, that are communicating to the liquid. This is derived from the fact that Nyquist plots have an arc radius whose center point is often below the Z’ axis, implying that instead of a single oxide thickness, these oxides have a distribution of thicknesses. This distribution of thicknesses produces arcs that are not clearly separable in most of the samples.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Evaluation of LPBF Steels for Nuclear Applications

This report provides an update on the prioritization of existing reactor materials for advanced manufacturing. This report is a Milestone 3 deliverable in FY2023, under work package CT-23AN130401 to support research and qualification activities supported by the Advanced Materials and Manufacturing Technologies (AMMT) program here at Argonne National Laboratory (ANL). The focus of FY23 for ANL included the determination of a decision criteria matrix for the prioritization of existing materials, the literature review of a select few Fe-based alloys, and working with vendors to obtain customized powders. The work package also includes fabricating test samples in a Renishaw AM400 Laser Powder Bed Fusion (LPBF) system and optimizing the process parameters. The major outcomes of this work package are: With collaborations from PNNL, ORNL, and INL, we were able to establish a decision criteria matrix containing a total of 6 categories and 31 different criteria. These will be used to downselect alloys for further evaluation; As part of that, 6 different Fe-based alloys were selected, 3 austenitic stainless steels (A709, D9, AFA) and 3 ferritic/martensitic steels (HT9, Grade 91, Grade 92). Customized powders were obtained from vendors in small quantities to fabricate initial prints to check printability of these specific alloys; A total of 72 single track experiments were performed on two alloy systems, 1 austenitic stainless steel (A709) and 1 ferritic/martensitic steel (Grade 91) in order to optimize the process parameters for the full 3d prints. The optimization led to the selection of 20 different processing conditions, 10 for each class of alloys; D9 and AFA alloys showed extensive cracking and porosity in the samples. This was due to less-than-ideal conditions present in the chamber during the deposition. A709 printed using the same process parameters showed almost fully dense samples with no noticeable porosity or any other defects. SEM and EBSD analysis revealed single phase FCC microstructure with cellular structure within the grains; HT9, Grade 91, Grade 92 alloys also showed no noticeable signs of cracking and ImageJ analysis showed porosity <0.5% in all conditions. While Grade 91 and Grade 92 showed single phase BCC microstructures, the presence of martensite laths was noted in HT9 alloy; Future work will include further characterization of these alloys to better understand the microstructural evolution during the 3d printing process.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗