Sal B. Rodriguez

Transient Analysis of Sulfur-Iodine Cycle Experiments and Very High Temperature Reactor Simulations Using MELCOR-H2

Abstract MELCOR is a thermal-hydraulic code used by the United States and the international nuclear community for the modeling of both light water and gas-cooled reactors. MELCOR was extended in order to model nuclear reactors that are coupled to the sulfur-iodine (SI) cycle for cogeneration of hydrogen. This version of the code is known as MELCOR-H2, and it includes modular secondary system components (e.g., turbines, compressors, heat exchangers, and generators), a point-kinetics model, and a graphical user interface. MELCOR-H2 allows for the fully coupled, transient analysis and design of the nuclear thermochemical SI cycle for the purpose of maximizing the production of hydrogen and electricity. Recent work has demonstrated that the hydrogen generation rate calculated by MELCOR-H2 for the SI cycle was within the expected theoretical yield. In order to benchmark MELCOR-H2, we simulated a set of sulfuric acid decomposition experiments that were conducted at Sandia National Laboratories during 2006. We also used MELCOR-H2 to simulate a 2004 Japan Atomic Energy Research Institute SI experiment. The simulations compared favorably with both experiments; most measured and calculated outputs were within 10%. The simulations adequately calculated O2, SO2, and H2 production rate, acid conversion efficiency, the relationship between solution mole percent and conversion efficiency, and the relationship between molar flow rate and efficiency. We also simulated a 6-stage turbine and a 20-stage compressor. Our results were mostly within 1 or 2% of the literature. Then, we simulated a pebble bed very high temperature reactor (VHTR) and compared key MELCOR-H2 results with the literature. The comparison showed that the results were typically within 1 or 2%. Finally, we compared the MELCOR-H2 point-kinetics model with the exact Inhour reactivity solution for various cases, including a 1.0

Modeling of a Z-IFE Hydrogen Plant Using MELCOR-H2.

step reactivity insertion. We were able to employ a large time step while successfully matching the theoretical power level. These comparisons demonstrate MELCOR-H2’s unique ability to simulate fully coupled VHTRs for the production of hydrogen.

Recent Advances in Modeling Axisymmetric Swirl and Applications for Enhanced Heat Transfer and Flow Mixing

Abstract A hypothetical Z-Inertial Fusion Energy (IFE) plant was coupled to a sulfur iodine (SI) thermochemical cycle using a new version of MELCOR called MELCOR-H2. MELCOR-H2 was designed to model nuclear reactors that are coupled to thermochemical plants for the production of electricity and hydrogen. The Z-IFE input model consisted of three major system components - a fusion heat source control volume with several types of boundary conditions, an SI loop, and a Brayton secondary system. The components were coupled in order to investigate system feedback and hydrogen production. The input model was modified so that various parametric studies could be conducted. Particular emphasis was placed on plant operating temperature and maximizing hydrogen production. This paper summarizes the results of the SI system model as it was driven by temperature changes in the primary circuit that simulated those that would occur in a Z-IFE driven reactor.

Cooling of an Isothermal Plate Using a Triangular Array of Swirling Air Jets

The concept of enhanced heat transfer and flow mixing using swirling jets has been investigated for nearly seven decades (Burgers, 1948; Watson and Clarke, 1947). Many practical applications of swirling jets include combustion, pharmaceuticals, tempering of metals, electrochemical mass transfer, metallurgy, propulsion, cooling of high-power electronics and computer chips, atomization, and the food industry, such as improved pizza ovens. Recently, swirling jet models have been applied to investigate heat transfer and flow mixing in nuclear reactors, including the usage of swirling jets in the lower plenum (LP) of generation-IV very high temperature gas-cooled reactors (VHTRs) to enhance mixing of the helium coolant and eliminate the formation of hot spots in the lower support plate, a safety concern (Johnson, 2008; Kim, Lim, and Lee, 2007; Laurien, Lavante, and Wang, 2010; Lavante and Laurien, 2007; Nematollahi and Nazifi, 2007; Rodriguez and El-Genk, 2008a, b, c, and d; Rodriguez, Domino, and El-Genk, 2010; Rodriguez and El-Genk, 2010a and b; Rodriguez and El-Genk, 2011). There are many devices and processes for generating vortex fields to enhance flow mixing and convective heat transfer. Figure 1 shows a static helicoid device that can be used to generate vortex fields based on the swirling angle, θ. Recent advances in swirling jet technology exploit common characteristics found in axisymmetric vortex flows, and these traits can be employed to design the vortex flow field according to the desired applications; among these are the degree of swirl (based on the swirl number, S) and the spatial distributions of the radial, azimuthal, and axial velocities. For a 3D helicoid, the vortex velocity in Cartesian coordinates can be approximated as:

Investigation of Argon Gas as a Potential Shock Attenuator in Z-IFE Chambers Using ALEGRA

Cooling with swirling jets is an effective means for enhancing heat transfer and improving spatial uniformity of the cooling rate in many applications. This paper investigates cooling a flat, isothermal plate at 1,000 K using a single and a triangular array of swirling air jets, and characterizes the resulting flow field and the air temperature above the plate. This problem was modeled using the Fuego computational fluid dynamics (CFD) code that is being developed at Sandia National Laboratories. The separation distance to jet diameter, L/D, varied from 3 to 12, Reynolds number, Re, varied from 5×103 –5×104 , and the swirl number, S varied from 0 to 2.49. The formation of the central recirculation zone (CRZ) and its impact on heat transfer were also investigated. For a hubless swirling jet, a CRZ was generated whenever S ≥ 0.67, in agreement with experimental data and our mathematical derivation for swirl (helicoid) azimuthal and axial velocities. On the other hand, for S ≤0.058, the velocity field closely approximated that of a conventional jet. With the azimuthal velocity of a swirling jet decaying as 1/z2 , most mixing occurred only a few jet diameters from the jet nozzle. Highest cooling occurred when L/D = 3 and S = 0.12 to 0.79. Heat transfer enhancement increased as S or Re increased, or L/D decreased.Copyright

Towards a Unified Swirl Vortex Model

Abstract The Z-IFE (inertial fusion energy) plant is a unique, inertial confined, fusion energy concept in which high yield targets will be ignited to fusion, yielding brief energy bursts in the 3 to 20-gigajoule range. The fusion reaction yields an energetic burst that consists principally of neutrons, X rays, and charged particles. The X rays rapidly attenuate in matter, causing the material to expand rapidly, thus generating a strong shock wave. This shock wave must be mitigated if the Z-IFE chamber is to last for a period of 30 to 50 years. ALEGRA simulations were conducted for a hypothetical Z-IFE chamber filled with argon gas and ionized by an X ray source. The calculations employed a set of sophisticated models, including Saha ionization, XSN and CDF opacities, bremsstrahlung radiation, linearized diffusion of X ray photons for a blackbody, fully-coupled magnetohydrodynamic models, electron thermal conduction, Spitzer thermal conductivity with cold material interpolation, and Mie-Gruneisen EOS. In order to obtain confidence in the results, a laser experiment from UCSD was simulated. In the experiment, laser photons were used to ionize argon gas. The simulations showed that ALEGRA quite successfully calculated the measured temperature, level of ionization, and spatial evolution of the argon plasma.

Z-Pinch Power Plant Shock Mitigation Experiments, Modeling, and Code Assessment

A review of the literature shows the existence of dozens of single-cell, axisymmetric, Newtonian-fluid vortices that, in one form or another, are solutions to the Navier-Stokes Equation. However, little research has been conducted in the literature to investigate common traits that are shared by these vortices. This research lays out a foundation of common mathematical traits, with a focus on the azimuthal velocity v. Notwithstanding their diverse mathematical and physical origin, it can be shown that these vortices are diverse manifestations of a single vortex family—they are united by a set of at least seven common mathematical traits. As a first common trait, we show that there are only four possible categories of single-cell, axisymmetric, Newtonian-fluid vortices. Next, by normalizing and overlaying the vortices into a single figure, three additional traits are noted, namely that v(r=0) = 0; they have similar azimuthal velocity profiles; and the azimuthal velocity is asymmetric about r. Thereafter, a fifth trait is noted by doing a series expansion for the azimuthal velocity of each vortex (as found in the literature), and expressing it as an alternating series that expands geometrically with odd exponents (truncated Laurent series with real coefficients). Finally, two more traits are noted by taking limit bounds for each series, thus showing that one bound is the Rankine (solid body) vortex, and the other is a Lamb-Oseen sine-like bound. In brief, we note that the vortices have seven traits in common, and hereby propose that these vortices are essentially diverse manifestations of a single vortex family.

Numerical investigation of potential elimination of ‘hot streaking’ and stratification in the VHTR lower plenum using helicoid inserts

Abstract We are investigating attenuation techniques to mitigate the powerful shock that occurs inside the Z-Pinch Power Plant. For this purpose, we conducted a series of experiments at the University of Wisconsin. These experiments consisted of shock waves traveling at greater than Ma 1 that impacted aluminum foam under various configurations. In turn, ABAQUS, ALEGRA, CTH, and DYNA3D were used to simulate one of the experiments in order to validate the codes. Although the behavior of foamed solid and liquid metal is fundamentally different, we considered foamed metal because some disposable components of the ZP-3 (i.e. the RTL) may be designed with metal foam. In addition, the relatively simple experiments should help us determine which codes can better simulate shock waves. In the near future, we will conduct shock experiments using foamed materials such as water, oils, and other metals.