Safety basis analysts throughout the U.S. Department of Energy (DOE) complex rely heavily on the information provided in the DOE Handbook, DOE - HDBK - 3010, Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear Facilities, to determine radionuclide source terms. In calculating source terms, analysts tend to use the DOE Handbook's bounding values on airborne release fractions (ARFs) and respirable fractions (RFs) for various categories of insults (representing potential accident release categories). This is typically due to both time constraints and the avoidance of regulatory critique. Unfortunately, these bounding ARFs/RFs represent extremely conservative values. Moreover, they were derived from very limited small-scale bench/laboratory experiments and/or from engineered judgment. Thus, the basis for the data may not be representative of the actual unique accident conditions and configurations being evaluated. The goal of this research is to develop a more accurate and defensible method to determine bounding values for the DOE Handbook using state-of-art multi-physics-based computer codes. This enables us to better understand the fundamental physics and phenomena associated with the types of accidents in the handbook. In this year, this research included improvements of the high-fidelity codes to model particle resuspension and multi-component evaporation for fire scenarios. We also began to model ceramic fragmentation experiments, and to reanalyze the liquid fire and powder release experiments that were done last year. The results show that the added physics better describes the fragmentation phenomena. Thus, this work provides a low-cost method to establish physics-justified safety bounds by taking into account specific geometries and conditions that may not have been previously measured and/or are too costly to perform.
In this work we have presented a particle resuspension model implemented in the SNL code SIERRA/Fuego, which can be used to model particle dispersal and resuspension from surfaces. The method demonstrated is applicable to a class of particles, but would require additional parametric fits or physics models for extension to other applications, such as wetted particles or walls. We have demonstrated the importance of turbulent variations in the wall shear stress when considering resuspension, and implemented both shear stress variation models and stochastic resuspension models (not shown in this work). These models can be used in simulations with of physically realistic scenarios to augment lab-scale DOE Handbook data for airborne release fractions and respirable fractions in order to provide confidences for safety analysts and facility designers to apply in their analyses at DOE sites. Future work on this topic will involve validation of the presented model against experimental data and extension of the empirical models to be applicable to different classes of particles and surfaces.
In this work we have presented a particle resuspension model implemented in the SNL code SIERRA/Fuego, which can be used to model particle dispersal and resuspension from surfaces. The method demonstrated is applicable to a class of particles, but would require additional parametric fits or physics models for extension to other applications, such as wetted particles or walls. We have demonstrated the importance of turbulent variations in the wall shear stress when considering resuspension, and implemented both shear stress variation models and stochastic resuspension models (not shown in this work). These models can be used in simulations with of physically realistic scenarios to augment lab-scale DOE Handbook data for airborne release fractions and respirable fractions in order to provide confidences for safety analysts and facility designers to apply in their analyses at DOE sites. Future work on this topic will involve validation of the presented model against experimental data and extension of the empirical models to be applicable to different classes of particles and surfaces.
In a submerged environment, power cables may experience accelerated insulation degradation due to water-related aging mechanisms. Direct contact with water or moisture intrusion in the cable insulation system has been identified in the literature as a significant aging stressor that can affect performance and lifetime of electric cables. Progressive reduction of the dielectric strength is commonly a result of water treeing which involves the development of permanent hydrophilic structures in the insulation coinciding with the absorption of water into the cable. Water treeing is a phenomenon in which dendritic microvoids are formed in electric cable insulation due to electrochemical reactions, electromechanical forces, and diffusion of contaminants over time. These reactions are caused by the combined effects of water presence and high electrical stresses in the material. Water tree growth follows a tree-like branching pattern, increasing in volume and length over time. Although these cables can be “dried out,” water tree degradation, specifically the growth of hydrophilic regions, is believed to be permanent and typically worsens over time. Based on established research, water treeing or water induced damage can occur in a variety of electric cables including XLPE, TR-XLPE and other insulating materials, such as EPR and butyl rubber. Once water trees or water induced damage form, the dielectric strength of an insulation material will decrease gradually with time as the water trees grow in length, which could eventually result in failure of the insulating material. Under wet conditions or in submerged environments, several environmental and operational parameters can influence water tree initiation and affect water tree growth. These parameters include voltage cycling, field frequency, temperature, ion concentration and chemistry, type of insulation material, and the characteristics of its defects. In this effort, a review of academic and industrial literature was performed to identify: 1) findings regarding the degradation mechanisms of submerged cabling and 2) condition monitoring methods that may prove useful in predicting the remaining lifetime of submerged medium voltage power cables. The research was conducted by a multi-disciplinary team, and sources included official NRC reports, national laboratory reports, IEEE standards, conference and journal proceedings, magazine articles, PhD dissertations, and discussions with experts. The purpose of this work was to establish the current state-of-the-art in material degradation modeling and cable condition monitoring techniques and to identify research gaps. Subsequently, future areas of focus are recommended to address these research gaps and thus strengthen the efficacy of the NRC’s developing cable condition monitoring program. Results of this literature review and details of the testing recommendations are presented in this report.
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. NASA has prepared an Environmental Impact Statement (EIS) in accordance with the National Environmental Policy Act. The EIS includes information on the risks of mission accidents to the general public and on-site workers at the launch complex. The Nuclear Risk Assessment (NRA) addresses the responses of the MMRTG option 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 the MMRTG option for the EIS. This paper provides a summary of the methods and results used in the NRA.
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. NASA has prepared an Environmental Impact Statement (EIS) in accordance with the National Environmental Policy Act. The EIS includes information on the risks of mission accidents to the general public and on-site workers at the launch complex. The Nuclear Risk Assessment (NRA) addresses the responses of the MMRTG option 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 the MMRTG option for the EIS. This paper provides a summary of the methods and results used in the NRA.
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.
Spent nuclear fuel reprocessing may involve some hazardous liquids that may explode under accident conditions. Explosive accidents may result in energetic dispersion of the liquid. The atomized liquid represents a major hazard of this class of event. The magnitude of the aerosol source term is difficult to predict, and historically has been estimated from correlations based on marginally relevant data. A technique employing a coupled finite element structural dynamics and control volume computational fluid dynamics has been demonstrated previously for a similar class of problems. The technique was subsequently evaluated for detonation events. Key to the calculations is the use of a Taylor Analogy Break-up (TAB) based model for predicting the aerodynamic break-up of the liquid drops in the air environment, and a dimensionless parameter for defining the chronology of the mass and momentum coupling. This paper presents results of liquid aerosolization from an explosive event.
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.
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.
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.
American Nuclear Society Embedded Topical Meeting - 2007 International Topical Meeting on Safety and Technology of Nuclear Hydrogen Production, Control, and Management
As part of the US DOE Nuclear Hydrogen Initiative, Sandia National Laboratories is designing and constructing a process for the conversion of sulfuric acid to produce sulfur dioxide. This process is part of the thermochemical Sulfur-Iodine (S-I) cycle that produces hydrogen from water. The Sandia process will be integrated with other sections of the S-I cycle in the near future to complete a demonstration-scale S-I process. In the Sandia process, sulfuric acid is concentrated by vacuum distillation and then catalytically decomposed at high temperature (850°C) to produce sulfur dioxide, oxygen and water. Major problems in the process, corrosion, and failure of high-temperature connections of process equipment, have been eliminated through the development of an integrated acid decomposer constructed of silicon carbide. The unit integrates acid boiling, superheating and decomposition into a single unit operation and provides for exceptional heat recuperation. The design of acid decomposition process, the new acid decomposer, other process units, and materials of construction for the process are described and discussed.
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.
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.