Author(s):

Theodore M. Chu, & Lane B. Carasik.

Abstract:

In sodium-cooled fast reactors, transient thermal stratification of the sodium coolant within the reactor components can cause severe thermal stresses. This thermal stress phenomena after related occurrences and/or during severe accident conditions can lead to vessel/component structure failure. Therefore, a thorough understanding of thermal stratification phenomena is critical to operational reliability and licensing efforts.

Turbulent scaling theories can be used to describe the underlying mechanics contributing to stratification. In particular, Bolgiano-Obukhov (BO59) scaling is of interest in liquid-metal flows for its inclusion of buoyancy in the flow. However, the instantaneous velocity and temperature time series data required for investigating the presence of BO59 scaling is lacking. In an effort to augment the data sets available, the use of high-fidelity computational fluid dynamics (CFD) simulations to generate data capable of observing BO59 scaling is of interest.

This study focuses on efforts in modeling the Gallium Thermal-hydraulic Experiment (GaTE) facility using large eddy simulations in Nek5000. The GaTE facility was designed as a scaled-down model of the Advanced Burner Test Reactor plenum to investigate thermal stratification within liquid-metal flows under a variety of operational conditions. Instantaneous temperature and velocity data are generated by the CFD model of GaTE during a forced flow transient exhibiting mixed convection with Ri = 0.722.

In general, the data have shown evidence of BO59 scaling throughout the plenum, especially with the momentum spectra and cospectra, indicating that the simulation is likely capable of generating the necessary instantaneous velocity and temperature data required for observing the BO59 microscale in liquid-metal flows. It has been determined that future investigation is needed to understand the lack of agreement in the spectra for the lower plenum height region and to assess the presence of BO59 scaling in mixed convection regimes with greater influence of natural convection effects.

Full Article:

https://www.tandfonline.com/doi/full/10.1080/00295639.2026.2688037#abstract 

Author(s):

Arturo Cabral, Cody S. Wiggins, Jesse D. East, Lane B. Carasik.

Abstract:

Heat transfer efficiency can be improved with the use of tight- and loose-fitting twisted tape inserts in coolant channels of high heat flux components across various flow regimes. This improvement has been explored in literature including the development of correlations that provide empirical matching to measured data for heat transfer coefficients (Nusselt numbers). Good agreement is observed in the turbulent regime however existing laminar and transitional correlations only match data within cited bounds and vary in performance. This paper compares the predictive ability of existing correlations to newly developed empirical methodologies for three different loose-fitting twisted tape insert configurations. A modification of existing Nusselt number correlations using a functional coefficient, C, is demonstrated to be more accurate than a static value of C = 0.2 found in existing literature. Additionally, we observe improved heat transfer performance with greater twisted tape insert pitches. These experiments used water with Reynolds numbers of 3000 to 24 000 and a Prandtl number of approximately 6.8 at the inlet. The twisted tapes have a pitch of 1.9, 2.86, or 3.81 diameters per 180° turn, placing them at and below the lower bounds of existing correlations. We lastly highlight needs for exploring varying Prandtl numbers in future work and potential modifications of previously derived correlations.

Full Article:

Experimental studies of loose-fitting twisted tape inserts as heat transfer enhancements - ScienceDirect 

Author(s):

Haomin Yuan, Yu-Hsiang Lan, Misun Min, Dezhi Dai, Dillon Shaver, John Acierno, Michael Seneca, Elia Merzari, Sierra Tutwiler, Lane Carasik, & Nathaniel Hoyt.

Abstract:

For both coolant and fueled variants of molten salt reactors (MSRs), the corrosion of structural materials is a significant challenge. The corrosion stems from chemical and electrochemical reactions initiated by fissile material, fission products, and impurities in the salt. Lower-fidelity models rely on empirical correlations for mass transfer, simplified lumped temperature profiles, and similar assumptions. They do not capture detailed spatial variations in complex geometries, creating the need for high-fidelity modeling to bridge this gap.

As we approach the demonstration and possible deployment of MSRs in this decade, the development of a high-fidelity, high-performance simulator becomes imperative. To simulate the complex electrochemical environment and corrosion within molten salt systems, we have developed the Molten Salt Chemistry And TranspOrt (MOSCATO) code. This endeavor is comprised of three essential components. First, mass transfer equations are coupled with the Navier-Stokes equations in order to account for the transport of species in the salt. Second, the diffusion of alloy constituents, such as Cr, Fe, Ni, etc. is simulated within the structural metals. Third, the alloy and salt domains are coupled to account for the heterogeneous chemical and electrochemical reactions that occur at the salt-alloy interface.

MOSCATO manages all three components within the framework of the highly scalable, open-source spectral element method computational fluid dynamics code Nek5000/NekRS. This integration enables MOSCATO to harness the immense computational power of modern high-performance computing resources, ensuring both high fidelity and computational speed.

In addition to code development, we have initiated a comprehensive verification and validation campaign, utilizing data from diverse sources. First, MOSCATO’s electrochemical solver was verified with reference numerical data. Then validation occurred against experiments: one of a thermal galvanic cell and the other for corrosion in flowing molten salt of FLiNaK (LiF-NaF-KF). This campaign verified and validated MOSCATO as a reliable tool for simulating electrochemical environments and corrosion in molten salt systems.

Full Article:

Full article: Development of MOSCATO: A CFD-Level Electrochemistry and Corrosion Simulator for Molten Salt Systems 

Author(s):

Trevor Franklin, Ryan P. McGuire, Sierra  Tutwiler, A. M. Coxe, Lane B. Carasik.

Abstract:

Fusion energy sources have garnered private and public interest around the world in attempts to reach net-zero carbon emissions. Current fusion energy system designs involve solid or liquid blanket systems that serve the purposes of tritium (fuel) management, neutron multiplication, and heat removal for power conversion. The use of fluoride molten salts in fusion breeder blankets is an option worthy of investigation because molten salts such as FLiBe can serve all three major roles.

Although there have been past studies on FLiBe- and FLiNaBe-based breeder blankets, known as liquid immersion breeder blankets, there are no published designs or analyses of entire notional breeder blanket systems using molten salts. The existing public information on molten salt breeder blankets has mostly focused on the blanket vessel, with minimal information on the systems.

To address this issue, a preliminary design for a prototypical molten salt breeder blanket system was investigated using the U.S. Department of Energy’s Nuclear Energy Advanced Modeling and Simulation–developed SAM (System Analysis Module) code for heat exhaust/transport systems. Existing SAM capabilities involving thermal-hydraulic modeling were used to perform critical system design activities.

In this work, we present the performance of the heat removal system and identify potential gaps in research to further the liquid immersion breeder blanket system design. To address different major design aspects for liquid immersion systems, three transient cases are studied: minimum power transient, startup transient, and shutdown transient. For the three transient cases, two different materials, V-4Cr-4Ti and Inconel-718, are investigated to determine the impact on the temperature profile and operating limits of the loop. The data produced by this study will provide a foundation for future designs of molten salt-based fusion energy concepts, allowing for the deployment of a future fusion pilot plant.

Full Article:

Design Study of a Fusion Liquid Immersion Blanket Heat Exhaust/Transport System Using SAM: Fusion Science and Technology: Vol 82 , No 3 - Get Access 

Author(s):

Colin Bailey, Connor Donlan, Matthew Glace, Gabrielle Broussard, Someshwar Nagamalla, Lane B. Carasik, Thomas D. Roper.

Abstract:

This study presents a kinetic model that simulates the consumption of 4-hydroxybenzoic acid (4-HBA), the formation of di-isopropyl benzoic acid (DIPBA) via a Friedel–Crafts alkylation reaction, and the generation of key impurities. The model provides valuable insights into reaction dynamics by capturing the intricate interplay between reaction kinetics and competing pathways. In addition, we introduce a cost-effective, scalable reactor design that overcomes the limitations of traditional laboratory-based reactor systems. The reactor system enhances safety, efficiency, and adaptability, making it ideal for large-scale, highly acidic reactions in laboratory settings. Together, this work underscores the insights and limitations of conventional kinetic modeling for solvolysis-mediated Friedel–Crafts reactions and lays the foundation for more efficient and innovative approaches to chemical process development.

This study presents a kinetic model that simulates the consumption of 4-hydroxybenzoic acid (4-HBA), the formation of di-isopropyl benzoic acid (DIPBA) via a Friedel–Crafts alkylation reaction, and the generation of key impurities.

Full Article:

https://pubs.rsc.org/re/article/11/3/757/1225405/Reactor-and-kinetic-study-advances-for-highly

Author(s):

Sierra A. Tutwiler, Dillon R. Shaver, Lane B. Carasik.

Abstract:

For liquid immersion blankets (LIBs), the heat removal within different plasma-facing components (PFCs) requires substantial heat removal capabilities that could benefit from the usage of heat transfer enhancements. Of consideration are twisted tape insert heat transfer enhancements that are ribbon-like metal pieces inserted within cooling channels that increase fluid mixing, resulting in higher heat transfer and pressure drop. Unlike traditional applications, PFCs such as divertor coolant tubes experience a significantly higher heat flux on one side versus the other or entirely one-sided heating. These conditions are not well studied for molten salts where the higher Prandtl numbers characteristic of the fluids are significantly higher than water, gases, and liquid metals. As an effort to study this knowledge gap, large eddy simulations were done with Prandtl numbers representative of FLiBe at proposed operating conditions. In this study, the effects of applying a surface heat flux to one side of a tube versus the entire tube with a twisted tape insert were investigated for the heat transfer coefficient and effects on the temperature profile. The findings of the study suggest that for Prandtl number fluids above unity, the Nusselt number was largely unaffected by the change in boundary condition. Both boundary conditions showed good agreement with the Manglik and Bergles Nusselt number correlation for tight-fitting twisted tapes. The outcomes of this study will be useful for future design studies of LIBs to provide fundamental guidance implementing twisted tape inserts and their performance in one-sided–heated conditions.

Full Article:

Full article: CFD Simulations of Molten Salts Within Plasma-Facing Components with Twisted Tape Inserts Under One-Sided–Heated Conditions 

Author(s):

Trevor C. Franklin, Sierra A. Tutwiler, Dillon Shaver, Lane B. Carasik.

Abstract:

Fluid-induced vibration remains a dominant mechanism for long-term damage in tube bundles for nuclear power plants. The GO-VIKING project was created to better understand and predict FIV behavior in nuclear power plants; furthermore, the GOKSTAD experiment was created to collect datasets at high Reynolds numbers for cross-flow inline tube bundles. In this work, large eddy simulations were performed for flow-only simulations of the GOKSTAD experimental bundle for experimental benchmarking. Average velocity and turbulent kinetic energy are compared between the simulations and the experiments. Overall, the LES showed good agreement with the velocity profiles in the experiment, but generally predicted higher values of TKE compared to the experiment. Furthermore, two different inlet conditions were compared to understand the sensitivity of the results. First, an inlet with a reduced length was chosen, limiting the generation of turbulence in the inlet channel. Second, a longer inlet length was chosen along with the use of a precursor simulation, allowing for fully developed turbulent flow before reaching the bundle area. Comparing the two inlet conditions shows that the choice of inlet conditioning does not have a significant impact on the TKE profiles (and subsequently the average velocity profile) after the third row of tubes. This implies that fully developed turbulent inlet generation is only necessary for accurately capturing near inlet development, and simpler and less computationally expensive inlet conditions can be used when concerned with the bulk crossflow region beyond the entrance rows.

Full Article:

Experimental Comparison of the GOKSTAD Tube Bundle using Large Eddy Simulations by Trevor C. Franklin, Sierra A. Tutwiler, Dillon Shaver, Lane B. Carasik :: SSRN 

Author(s):

Connor F. Donlan, Arturo Cabral, Colin Bailey, Jerel Houston, Lane B. Carasik, Floren Rubio.

Abstract:

Different types of molten salts are proposed or in use for nuclear fission, fusion, and concentrated solar power, such as fluorides, chlorides, carbonates, and nitrate-based salts. For the different clean energy technologies, the components that interface with the molten salts as coolants and/or nuclear/fusion fuels require research and development before deployment. This research and development includes experimental validation where lower cost and lower hazard surrogate fluids can be used for specific sets of physics. These surrogate fluids can emulate the heat transfer and fluid mechanics phenomena of molten salts at reduced temperature scales, safety requirements and as a result, costs. Previously, certain surrogate fluids have been proposed for fluorides, chloride, and nitrate salts; however, better surrogate fluids in terms of the aforementioned benefits and enhanced scaling of behavior are sought after. In this work, the Dynalene family of fluids was investigated and shown to work as surrogate fluids for fluoride, chloride, and nitrate based salts. The most important outcome is that these Dynalene fluids are demonstrated to scale well to molten salts. This is as compared to the previously identified surrogate fluids, specifically, Dowtherm-A and Therminol VP-1, at reduced cost and improved material compatibility.

Full Article:

Identification of Lower Cost Industrial Available Heat Transfer Fluids as Surrogate Fluids for Separate & Integral Effects Testing of Molten Salts by Connor F. Donlan, Arturo Cabral, Colin Bailey, Jerel Houston, Lane B. Carasik, Floren Rubio :: SSRN 

Author(s):

Briana R. Schrage, Joshua E. Leach, Ethan Villarreal, Jisue Braatz, Kristian G. Myhre.

Abstract:

Mediated electrochemical oxidation (MEO) is a low-temperature, low-pressure, aqueous mineralization process used to treat organic waste. A powerful metal oxidant is used as a mediator in an acidic solution. Although Ce and Co are thoroughly studied mediators, Ag is a preferred choice because of the higher efficiency rates of mineralization observed with this system. Importantly, the quantification methodology and spectroscopic characteristics of the Ag(ii) ion must be obtained. In this study, we determined molar extinction coefficients of the primary absorption band associated with the Ag(ii) ion in 2–9 M HNO3 solution. The optimization of Ag(ii) electrooxidation was also determined by altering parameters such as HNO3 concentration, mediator concentration, and temperature. The optimization studies and extinction coefficient data provide parameters for implementation of Ag as a suitable mediator for MEO processing of organic waste.

The extinction coefficient of silver(ii) has been obtained. Titration quantification methods were then used to optimize electrochemical silver(ii) generation as a function of temperature, silver(i) concentration, and HNO3 concentration.

Full Article:

Optimization and quantification of silver(ii) for mediated electrochemical oxidation applications | Dalton Transactions | The Royal Society of Chemistry