Graphite oxidation modeling for application in MELCOR.

The Arrhenius parameters for graphite oxidation in air are reviewed and compared. One-dimensional models of graphite oxidation coupled with mass transfer of oxidant are presented in dimensionless form for rectangular and spherical geometries. A single dimensionless group is shown to encapsulate the coupled phenomena, and is used to determine the effective reaction rate when mass transfer can impede the oxidation process. For integer reaction order kinetics, analytical expressions are presented for the effective reaction rate. For noninteger reaction orders, a numerical solution is developed and compared to data for oxidation of a graphite sphere in air. Very good agreement is obtained with the data without any adjustable parameters. An analytical model for surface burn-off is also presented, and results from the model are within an order of magnitude of the measurements of burn-off in air and in steam

A review of Plutonium (Pu) combustion releases in air for inhalation hazard evaluation.

Experimental data are compiled and reviewed for aerosol particle releases due to combustion in air of Plutonium (Pu). The aerosol release fraction (ARF), which is the mass of Pu aerosolized, divided by the mass of Pu oxidized, is dependent on whether the oxidizing Pu sample is static (i.e. stationary) or dynamic (i.e. falling in air). ARF data are compiled for sample masses ranging from 30 mg to 1770 g, oxidizing temperatures varying from 113 C to {approx}1000 C, and air flow rates varying from 0.05 m/s to 5.25 m/s. The measured ARFs range over five orders of magnitude. The maximum observed static ARF is 2.4 x 10{sup -3}, and this is the recommended ARF for safety studies of static Pu combustion

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

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

Test plan for the irradiation of nonmetallic materials.

A comprehensive test program to evaluate nonmetallic materials use in the Hanford Tank Farms is described in detail. This test program determines the effects of simultaneous multiple stressors at reasonable conditions on in-service configuration components by engineering performance testing

Summary report : direct approaches for recycling carbon dioxide into synthetic fuel.

The consumption of petroleum by the transportation sector in the United States is roughly equivalent to petroleum imports into the country, which have totaled over 12 million barrels a day every year since 2004. This reliance on foreign oil is a strategic vulnerability for the economy and national security. Further, the effect of unmitigated CO{sub 2} releases on the global climate is a growing concern both here and abroad. Independence from problematic oil producers can be achieved to a great degree through the utilization of non-conventional hydrocarbon resources such as coal, oil-shale and tarsands. However, tapping into and converting these resources into liquid fuels exacerbates green house gas (GHG) emissions as they are carbon rich, but hydrogen deficient. Revolutionary thinking about energy and fuels must be adopted. We must recognize that hydrocarbon fuels are ideal energy carriers, but not primary energy sources. The energy stored in a chemical fuel is released for utilization by oxidation. In the case of hydrogen fuel the chemical product is water; in the case of a hydrocarbon fuel, water and carbon dioxide are produced. The hydrogen economy envisions a cycle in which H{sub 2}O is re-energized by splitting water into H{sub 2} and O{sub 2}, by electrolysis for example. We envision a hydrocarbon analogy in which both carbon dioxide and water are re-energized through the application of a persistent energy source (e.g. solar or nuclear). This is of course essentially what the process of photosynthesis accomplishes, albeit with a relatively low sunlight-to-hydrocarbon efficiency. The goal of this project then was the creation of a direct and efficient process for the solar or nuclear driven thermochemical conversion of CO{sub 2} to CO (and O{sub 2}), one of the basic building blocks of synthetic fuels. This process would potentially provide the basis for an alternate hydrocarbon economy that is carbon neutral, provides a pathway to energy independence, and is compatible with much of the existing fuel infrastructure

Design and Testing of a Micro Thermal Conductivity Detector (TCD) System

This work describes the design, simulation, fabrication and characterization of a microfabricated thermal conductivity detector to be used as an extension of the {micro}ChemLab{trademark}. The device geometry was optimized by simulating the heat transfer in the device, utilizing a boundary element algorithm. In particular it is shown that within microfabrication constraints, a micro-TCD optimized for sensitivity can be readily calculated. Two flow patterns were proposed and were subsequently fabricated into nine-promising geometries. The microfabricated detector consists of a slender metal film, supported by a suspended thin dielectric film over a pyramidal or trapezoidal silicon channel. It was demonstrated that the perpendicular flow, where the gas directly impinges on the membrane, creates a device that is 3 times more sensitive than the parallel flow, where the gas passed over the membrane. This resulted in validation of the functionality of a microfabricated TCD as a trace-level detector, utilizing low power. the detector shows a consistent linear response to concentration and they are easily able to detect 100-ppm levels of CO in He. Comparison of noise levels for this analysis indicates that sub part per million (ppm) levels are achievable with the selection of the right set of conditions for the detector to operate under. This detector was originally proposed as part of a high-speed detection system for the petrochemical gas industry. This system was to be utilized as a process monitor to detect reactor ''upset'' conditions before a run away condition could occur (faster than current full-scale monitoring systems were able to achieve). Further outlining of requirements indicated that the detection levels likely achievable with a TCD detector would not be sufficient to meet the process condition needs. Therefore the designed and fabricated detector was integrated into a detection system to showcase some technologies that could further the development of components for the current gas phase {micro}ChemLab as well as future modifications for process monitoring work such as: pressurized connections, gas sampling procedures, and packed columns. Component integration of a microfabricated planar pre-concentrator, gas-chromatograph column and TCD in the separation/detection of hydrocarbons, such as benzene, toluene and xylene (BTX) was also demonstrated with this system

Membranes for H2 generation from nuclear powered thermochemical cycles.

In an effort to produce hydrogen without the unwanted greenhouse gas byproducts, high-temperature thermochemical cycles driven by heat from solar energy or next-generation nuclear power plants are being explored. The process being developed is the thermochemical production of Hydrogen. The Sulfur-Iodide (SI) cycle was deemed to be one of the most promising cycles to explore. The first step of the SI cycle involves the decomposition of H{sub 2}SO{sub 4} into O{sub 2}, SO{sub 2}, and H{sub 2}O at temperatures around 850 C. In-situ removal of O{sub 2} from this reaction pushes the equilibrium towards dissociation, thus increasing the overall efficiency of the decomposition reaction. A membrane is required for this oxygen separation step that is capable of withstanding the high temperatures and corrosive conditions inherent in this process. Mixed ionic-electronic perovskites and perovskite-related structures are potential materials for oxygen separation membranes owing to their robustness, ability to form dense ceramics, capacity to stabilize oxygen nonstoichiometry, and mixed ionic/electronic conductivity. Two oxide families with promising results were studied: the double-substituted perovskite A{sub x}Sr{sub 1-x}Co{sub 1-y}B{sub y}O{sub 3-{delta}} (A=La, Y; B=Cr-Ni), in particular the family La{sub x}Sr{sub 1-x}Co{sub 1-y}Mn{sub y}O{sub 3-{delta}} (LSCM), and doped La{sub 2}Ni{sub 1-x}M{sub x}O{sub 4} (M = Cu, Zn). Materials and membranes were synthesized by solid state methods and characterized by X-ray and neutron diffraction, SEM, thermal analyses, calorimetry and conductivity. Furthermore, we were able to leverage our program with a DOE/NE sponsored H{sub 2}SO{sub 4} decomposition reactor study (at Sandia), in which our membranes were tested in the actual H{sub 2}SO{sub 4} decomposition step

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

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

Analytical Modeling of Fission Product Releases by Diffusion from Multicoated Fuel Particles

Three levels of fission product diffusional release models are solved exactly. First, the Booth model for a homogeneous uncoated spherical fuel particle is presented and an improved implementation is suggested. Second, the release from a fuel particle with a single barrier layer is derived as a simple alternative to account for a coating layer. Third, the general case of release from a multicoated fuel particle is derived and applied to a TRISO-coated fuel. Previous approaches required approximate numerical solutions for the case of an arbitrary number of coatings with arbitrary diffusivities and arbitrary coating interface conditions

The general dynamic equation for aerosols

This work focusses on developing and solving the conservation equations for a spatially homogeneous aerosol. We begin by developing the basic equations, and in doing so, a new form of the conservation equation or General Dynamic Equation (GDE), termed the discrete-continuous GDE, is presented. In this form, one has the ability to simulate aerosol dynamics in systems in which processes are occurring over a broad particle size spectrum, typical of those found in the atmosphere. All the necessary kinetic coefficients needed to solve the GDE are discussed and the mechanisms for gas-to-particle conversion are also elucidated. Particle growth rates limited by gas phase diffusion, surface and volume reactions are discussed. In the absence of coagulation, analytic solutions for the above particle growth rates, arbitrary initial and boundary conditions, arbitrary sources, and first order removal mechanisms are developed. To account for all processes, numerical solutions are required. Therefore, numerical techniques and the errors associated with the numerical solution of the GDE are discussed in detail. By comparing the numerical solution to both analytical solutions for simplified cases and smog chamber data, it is shown that the numerical techniques are highly accurate and efficient. Techniques for simulating a sulfuric acid and water aerosol are presented. By application of the discrete-continuous GDE, the effect of neglecting cluster-cluster agglomeration, and the effect of a preexisting aerosol on the nucleation rate of a sulfuric acid and water aerosol are studied. The effects of coagulation are also elucidated by simulating the system with the full continuous GDE and the analytic solution to the continuous GDE in the absence of coagulation. Fairly good agreement between the predicted and experimentally observed distributions is obtained. Finally, an exact solution to the continuous form of the GDE for a multicomponent aerosol for simplified cases is developed.</p