Showing papers by "Westinghouse Electric published in 2021"

Evidence of hydrogen trapping at second phase particles in zirconium alloys.

Abstract: Zirconium alloys are used in safety-critical roles in the nuclear industry and their degradation due to ingress of hydrogen in service is a concern. In this work experimental evidence, supported by density functional theory modelling, shows that the α-Zr matrix surrounding second phase particles acts as a trapping site for hydrogen, which has not been previously reported in zirconium. This is unaccounted for in current models of hydrogen behaviour in Zr alloys and as such could impact development of these models. Zircaloy-2 and Zircaloy-4 samples were corroded at 350 °C in simulated pressurised water reactor coolant before being isotopically spiked with 2H2O in a second autoclave step. The distribution of 2H, Fe and Cr was characterised using nanoscale secondary ion mass spectrometry (NanoSIMS) and high-resolution energy dispersive X-ray spectroscopy. 2H- was found to be concentrated around second phase particles in the α-Zr lattice with peak hydrogen isotope ratios of 2H/1H = 0.018-0.082. DFT modelling confirms that the hydrogen thermodynamically favours sitting in the surrounding zirconium matrix rather than within the second phase particles. Knowledge of this trapping mechanism will inform the development of current understanding of zirconium alloy degradation through-life.

Full-field microscale strain measurements of a nitinol medical device using digital image correlation.

Abstract: Computational modeling and simulation are commonly used during the development of cardiovascular implants to predict peak strains and strain amplitudes and to estimate the associated durability and fatigue life of these devices. However, simulation validation has historically relied on comparison with surrogate quantities like force and displacement due to barriers to direct strain measurement-most notably, the small spatial scale of these devices. We demonstrate the use of microscale two-dimensional digital image correlation (2D-DIC) to directly characterize full-field surface strains on a nitinol medical device coupon under emulated physiological and hyperphysiological loading. Experiments are performed using a digital optical microscope and a custom, temperature-controlled load frame. Following applicable recommendations from the International DIC Society, hardware and environmental heating studies, noise floor analyses, and in- and out-of-plane rigid body translation studies are first performed to characterize the microscale DIC setup. Uniaxial tension experiments are also performed using a polymeric test specimen to characterize the strain accuracy of the approach up to nominal stains of 5%. Sub-millimeter fields of view and sub-micron displacement accuracies (9nm mean error) are achieved, and systematic (mean) and random (standard deviation) errors in strain are each estimated to be approximately 1,000μϵ. The system is then demonstrated by acquiring measurements at the root of a 300μm-wide nitinol medical device strut undergoing fixed-free cantilever bending motion. Luders-like transformation bands are observed originating from the tensile side of the strut that spread toward the neutral axis at an angle of approximately 55°. Despite the inherent limitations of optical microscopy and 2D-DIC, simple and relatively economical setups like that demonstrated herein could provide a practical and accessible solution for characterizing cardiovascular implant micromechanics, validating computational model strain predictions, and guiding the development of next-generation material models for simulating superelastic nitinol.

On the effect of manual rework in AFP quality control for a doubly-curved part

Abstract: It is widely thought that considerable manual rework is a necessity in the production of aerospace composite structures manufactured through automated fiber placement (AFP). However, there is limited availability of information regarding the precise quality control outcomes obtained through manual rework and defect removal. Given the large amounts of cycle time dedicated to the rework process, it may be fruitful to investigate in what ways rework may improve part quality, shift defect distributions, or in some cases, fail at improvement and make the resulting structure worse. To provide insights into these questions, a ply of a doubly-curved part was produced by AFP, inspected using an automated inspection system, manually repaired, and then inspected again. Through a multi-faceted analysis of the inspection data, trends including changes in defect number and significance, repair suggestions, and a previously unreported new defect type associated with manual rework can be observed.

Monolithic Nanoporous Gold Foams with Catalytic Activity for Chemical Vapor Deposition Growth of Carbon Nanostructures.

Abstract: While bulk gold is generally considered to be a catalytically inactive material, nanostructured forms of gold can in fact be highly catalytically active. However, few methods exist for preparing high-purity macroscopic forms of catalytically active gold. In this work, we describe the synthesis of catalytically active macroscopic nanoporous gold foams via combustion synthesis of gold bis(tetrazolato)amine complexes. The resulting metallically pure porous gold nanoarchitectures exhibit bulk densities of <0.1 g/cm3 and Brunauer-Emmett-Teller (BET) surface areas as high as 10.9 m2/g, making them among the lowest-density and highest-surface-area monolithic forms of gold produced to date. Thanks to the presence of a highly nanostructured gold surface, such gold nanofoams have also been found to be highly catalytically active toward thermal chemical vapor deposition (CVD) growth of carbon nanotubes, providing a novel method for direct synthesis of carbon nanostructures on macroscopic gold substrates. In contrast, analogous copper nanofoams were found to be catalytically inactive toward the growth of graphitic nanostructures under the same synthesis conditions, highlighting the unusually high catalytic propensity of this form factor of gold. The combustion synthesis process described herein represents a never-wet approach for directly synthesizing macroscopic catalytically active gold. Unlike sol-gel and dealloying approaches, combustion synthesis eliminates the time-consuming diffusion-mediated steps associated with previous methods and offers multiple degrees of freedom for tuning morphology, electrical conductivity, and mechanical properties.

Credibility Assessment of Machine Learning in a Manufacturing Process Application

Abstract: We present a framework for establishing credibility of a machine learning (ML) model used to predict a key process control variable setting to maximize product quality in a component manufacturing application. Our model coupled a purely data-based ML model with a physics-based adjustment that encoded subject matter expertise of the physical process. Establishing credibility of the resulting model provided the basis for eliminating a costly intermediate testing process that was previously used to determine the control variable setting.

Assessment of parallel simulated annealing performance with the nexus/anc9 core design code system

Abstract: The method of parallel simulated annealing is being considered as a loading pattern optimization method to be used within the framework of the latest Westinghouse core design code system NEXUS/ANC9. A prototype version of NEXUS/ANC9 that incorporates the parallel simulated annealing method was developed. The prototype version was evaluated in terms of robustness, performance and results. The prototype code was used to optimize LPs for several plants and cycles, including 2-loop, 3-loop and 4-loop Westinghouse plants. Different fuel assembly lattices with IFBA, WABA and Gadolinium burnable absorbers were also exercised in these cores. Different strategies were evaluated using different options in the code. Special attention was paid to the robustness and performance when different number of parallel processes were used with different size of Markov chain.

Unveiling damage mechanisms of chromium-coated zirconium-based fuel claddings at LWR operating temperature by in-situ digital image correlation

Abstract: Here, we investigate the coupled thermomechanical fracture mechanisms of coated nuclear fuel claddings at Light Water Reactor (LWR) operating temperatures. These coated claddings are a highly attractive, near-term solution that address the demands for accident-tolerant fuel systems that provide greater oxidation resistance. However, the fracture mechanisms of these coatings, which may create channels for oxidation ingression, must be fully understood prior to implementation. Thus, high-temperature expanding plug experiments were conducted on coated cladding specimens at a temperature of 315 °C, consistent with the operating environment of LWRs. In-situ thermomechanical deformation was measured with stereo digital image correlation during heating and mechanical testing to separately resolve contributions of thermal and mechanical strain. Image correlation, supported by acoustic emissions (AE) detection, was also leveraged to track cracking activity during loading. Coating fracture was found to initiate at total hoop strains of 0.34%. The thermal deformation of the coated claddings was investigated via finite element simulations, revealing a bidirectional stress-state within the coating with axial and circumferential strains of 0.026 and 0.031%. This bidirectional stress-state was attributed with the generation of off-axis fracture pattern within the coating as identified via post-experiment scanning electron microscopy. Thus, this study unveiled critical, coupled thermomechanical mechanisms governing the coating fracture of coated claddings at LWR temperatures.

Liquid metal current collectors for homopolar machines

Abstract: Results of theoretical and experimental studies of liquid metal current collectors, primarily for segmented-magnet (SEGMAG) drum-type homopolar generators, are presented. Current collectors evaluated are of the rotating disk-stationary concentric channel design The liquid metal is the eutectic sodium-potassium alloy (NaK-78). Power losses and disturbing pressures in the liquid metal were either analyzed or evaluated experimentally in terms of rotor speed, temperature, electric current, and magnetic field for prototypic size current collectors. Specific-contact resistance measurements made using these collectors are reported here.

On the Interactions of Molybdenum and Graphite, a Promising Material System for Microreactors

Abstract: Critical components for many microreactor designs include the core, heat pipe cladding, fuel, and moderator. This article reviews the interactions between graphite and Mo in order to assess the practicability of using Mo as a cladding heat pipe material in a graphite monolith core microreactor. The current literature data on the carburization of Mo are examined and confirmed with new experimental data. The available data for the diffusion of carbon through Mo are summarized, and calculations are performed to showcase the feasibility of such a system, assuming a nominal alkali metal heat pipe design. Finally, material options for protective coatings that could be applied to Mo in order to mitigate unwanted interactions with carbon are reviewed and key data on the thermal expansion coefficient match with Mo as well as the available carbon diffusion rate data for these materials are summarized.

Vehicle advisory system

Abstract: A vehicle advisory system and method determine whether a vehicle system moving along a route is within a designated distance of a feature of interest, initiate a distance-based alert sequence of an advisory device of the vehicle system in response to determining that the vehicle system is at or within the designated distance of the feature of interest, and generate advisory signals using the advisory device according to the distance-based alert sequence. The advisory signals are indicative of passage of the vehicle system by the feature of interest during the distance-based alert sequence. The distance-based alert sequence dictates one or more of plural different commencement locations or commencement distances at which advisory signals are generated by the advisory device. The distance-based alert sequence also dictates one or more of plural different termination locations or termination distances where generation of the advisory signals by the advisory device is terminated.

Vehicle brake cylinder monitoring system and method

Abstract: A system and method for monitoring air pressure applied to a brake cylinder of a braking assembly of a railway vehicle, including an empty-load device, and an RFID transducer in communication with the empty-load device, wherein the RFID transducer is configured to measure the air pressure delivered to the brake cylinder of the braking assembly, and generate data on the air pressure delivered to the brake cylinder of the braking assembly; and a remote data monitor configured to read data from the RFID transducer.