Fred Gelbard

Sectional representations for simulating aerosol dynamics

Abstract A general method for simulating aerosol size distribution dynamics is developed. The method, based on dividing the particle size domain into sections and dealing only with one integral quantity in each section (e.g., number, surface area, or volume), has the advantages that the integral quantity is conserved within the computational domain and coagulations between all particle sizes are properly accounted for. To demonstrate the simplicity and accuracy of the method for a practical problem, the evolution of a power plant plume aerosol undergoing coagulation is simulated.

Modeling Multicomponent Aerosol Particle Growth By Vapor Condensation

A new “moving-sectional” method is presented to solve the dynamics of multicomponent aerosol particle growth by vapor condensation in a closed system. The method controls numerical diffusion and stiffness by adapting the method of characteristics to a sectional representation of the aerosol. An exact solution for a closed system is presented, and the “moving-sectional” method gives excellent agreement when tested against this solution. Four cases are presented to demonstrate the importance of the solute, Kelvin, and latent heat effects.

A one-dimensional sectional model to simulate multicomponent aerosol dynamics in the marine boundary layer: 3. Numerical methods and comparisons with exact solutions

We present the theoretical framework and computational methods that were used by Fitzgerald et al. [this issue (a), (b)] describing a one-dimensional sectional model to simulate multicomponent aerosol dynamics in the marine boundary layer. The concepts and limitations of modeling spatially varying multicomponent aerosols are elucidated. New numerical sectional techniques are presented for simulating multicomponent aerosol growth, settling, and eddy transport, coupled to time-dependent and spatially varying condensing vapor concentrations. Comparisons are presented with new exact solutions for settling and particle growth by simultaneous dynamic condensation of one vapor and by instantaneous equilibration with a spatially varying second vapor.

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

Status of initial testing of the H2SO4 section of the ILS experiment.

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.

Development of design and simulation model and safety study of large-scale hydrogen production using nuclear power.

A sulfuric acid catalytic decomposer section was assembled and tested for the Integrated Laboratory Scale experiments of the Sulfur-Iodine Thermochemical Cycle. This cycle is being studied as part of the U. S. Department of Energy Nuclear Hydrogen Initiative. Tests confirmed that the 54-inch long silicon carbide bayonet could produce in excess of the design objective of 100 liters/hr of SO{sub 2} at 2 bar. Furthermore, at 3 bar the system produced 135 liters/hr of SO{sub 2} with only 31 mol% acid. The gas production rate was close to the theoretical maximum determined by equilibrium, which indicates that the design provides adequate catalyst contact and heat transfer. Several design improvements were also implemented to greatly minimize leakage of SO{sub 2} out of the apparatus. The primary modifications were a separate additional enclosure within the skid enclosure, and replacement of Teflon tubing with glass-lined steel pipes.

A new method for determining hydrodynamic effects on the collision of two spheres

Before this LDRD research, no single tool could simulate a very high temperature reactor (VHTR) that is coupled to a secondary system and the sulfur iodine (SI) thermochemistry. Furthermore, the SI chemistry could only be modeled in steady state, typically via flow sheets. Additionally, the MELCOR nuclear reactor analysis code was suitable only for the modeling of light water reactors, not gas-cooled reactors. We extended MELCOR in order to address the above deficiencies. In particular, we developed three VHTR input models, added generalized, modular secondary system components, developed reactor point kinetics, included transient thermochemistry for the most important cycles [SI and the Westinghouse hybrid sulfur], and developed an interactive graphical user interface for full plant visualization. The new tool is called MELCOR-H2, and it allows users to maximize hydrogen and electrical production, as well as enhance overall plant safety. We conducted validation and verification studies on the key models, and showed that the MELCOR-H2 results typically compared to within less than 5% from experimental data, code-to-code comparisons, and/or analytical solutions.

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

A sphere falling in a fluid may collide with another sphere falling more slowly if, when the spheres are far apart vertically, the horizontal distance between their centers is less than or equal to a critical radius. Accurate prediction of aerosol particle coagulation requires a good understanding of this process. Previously reported optical techniques for measuring hydrodynamic effects on this phenomenon have inherent difficulties detecting grazing collisions and hence in determining the critical radius. In this work, a novel detection technique is demonstrated and it is shown that the critical radius may be determined from the sound generated by the collision of two spheres in a viscous liquid. The technique is shown to provide a more precise and decisive indication of when hard spheres collide.

Nuclear risk assessment for the Mars 2020 mission environmental impact statement.

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.

Predicted Liquid Atomization from a Spent Nuclear Fuel Reprocessing Pressurization Event.

In the summer of 2020, the National Aeronautics and Space Administration (NASA) plans to launch a spacecraft as part of the Mars 2020 mission. One option for the rover on the proposed spacecraft uses a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) to provide continuous electrical and thermal power for the mission. An alternative option being considered is a set of solar panels for electrical power with up to 80 Light-Weight Radioisotope Heater Units (LWRHUs) for local component heating. Both the MMRTG and the LWRHUs use radioactive plutonium dioxide. NASA is preparing an Environmental Impact Statement (EIS) in accordance with the National Environmental Policy Act. The EIS will include information on the risks of mission accidents to the general public and on-site workers at the launch complex. This Nuclear Risk Assessment (NRA) addresses the responses of the MMRTG or LWRHU options to potential accident and abort conditions during the launch opportunity for the Mars 2020 mission and the associated consequences. This information provides the technical basis for the radiological risks of both options for the EIS. SAND2013-10589, January 2014 NRA for Mars 2020