Passive detection of special nuclear material (SNM) at long range or under heavy shielding can only be achieved by observing the penetrating neutral particles that it emits: gamma rays and neutrons in the MeV energy range. The ultimate SNM standoff detector system would have sensitivity to both gamma and neutron radiation, a large area and high efficiency to capture as many signal particles as possible, and good discrimination against background particles via directional and energy information. Designing such a system is a daunting task. Using timemodulated collimators could be a transformative technique leading to practical gamma-neutron imaging detector systems that are highly efficient with the potential to exhibit simultaneously high angular and energy resolution. A new technique using time encoding to make a compact, high efficiency imaging detector was conceived. Design considerations using Monte Carlo modeling and the construction and demonstration of a prototype imager are described.
Next-generation exascale systems, those capable of performing a quintillion (10{sup 18}) operations per second, are expected to be delivered in the next 8-10 years. These systems, which will be 1,000 times faster than current systems, will be of unprecedented scale. As these systems continue to grow in size, faults will become increasingly common, even over the course of small calculations. Therefore, issues such as fault tolerance and reliability will limit application scalability. Current techniques to ensure progress across faults like checkpoint/restart, the dominant fault tolerance mechanism for the last 25 years, are increasingly problematic at the scales of future systems due to their excessive overheads. In this work, we evaluate a number of techniques to decrease the overhead of checkpoint/restart and keep this method viable for future exascale systems. More specifically, this work evaluates state-machine replication to dramatically increase the checkpoint interval (the time between successive checkpoint) and hash-based, probabilistic incremental checkpointing using graphics processing units to decrease the checkpoint commit time (the time to save one checkpoint). Using a combination of empirical analysis, modeling, and simulation, we study the costs and benefits of these approaches on a wide range of parameters. These results, which cover of number of high-performance computing capability workloads, different failure distributions, hardware mean time to failures, and I/O bandwidths, show the potential benefits of these techniques for meeting the reliability demands of future exascale platforms.
Discrimination of benign sources from threat sources at Port of Entries (POE) is of a great importance in efficient screening of cargo and vehicles using Radiation Portal Monitors (RPM). Currently RPM's ability to distinguish these radiological sources is seriously hampered by the energy resolution of the deployed RPMs. As naturally occurring radioactive materials (NORM) are ubiquitous in commerce, false alarms are problematic as they require additional resources in secondary inspection in addition to impacts on commerce. To increase the sensitivity of such detection systems without increasing false alarm rates, alarm metrics need to incorporate the ability to distinguish benign and threat sources. Principal component analysis (PCA) and clustering technique were implemented in the present study. Such techniques were investigated for their potential to lower false alarm rates and/or increase sensitivity to weaker threat sources without loss of specificity. Results of the investigation demonstrated improved sensitivity and specificity in discriminating benign sources from threat sources.
There is national interest in the development of sophisticated materials that can automatically detect and respond to chemical and biological threats without the need for human intervention. In living systems, cell membranes perform such functions on a routine basis, detecting threats, communicating with the cell, and triggering automatic responses such as the opening and closing of ion channels. The purpose of this project was to learn how to replicate simple threat detection and response functions within artificial membrane systems. The original goals toward developing 'smart skin' assemblies included: (1) synthesizing functionalized nanoparticles to produce electrochemically responsive systems within a lipid bilayer host matrices, (2) calculating the energetics of nanoparticle-lipid interactions and pore formation, and (3) determining the mechanism of insertion of nanoparticles in lipid bilayers via imaging and electrochemistry. There are a few reports of the use of programmable materials to open and close pores in rigid hosts such as mesoporous materials using either heat or light activation. However, none of these materials can regulate themselves in response to the detection of threats. The strategies we investigated in this project involve learning how to use programmable nanomaterials to automatically eliminate open channels within a lipid bilayer host when 'threats' are detected. We generated and characterized functionalized nanoparticles that can be used to create synthetic pores through the membrane and investigated methods of eliminating the pores either through electrochemistry, change in pH, etc. We also focused on characterizing the behavior of functionalized gold NPs in different lipid membranes and lipid vesicles and coupled these results to modeling efforts designed to gain an understanding of the interaction of nanoparticles within lipid assemblies.
This is the final report for the President Harry S. Truman Fellowship in National Security Science and Engineering (LDRD project 130813) awarded to Dr. Bryan Kaehr from 2008-2011. Biological chemistries, cells, and integrated systems (e.g., organisms, ecologies, etc.) offer important lessons for the design of synthetic strategies and materials. The desire to both understand and ultimately improve upon biological processes has been a driving force for considerable scientific efforts worldwide. However, to impart the useful properties of biological systems into modern devices and materials requires new ideas and technologies. The research herein addresses aspects of these issues through the development of (1) a rapid-prototyping methodology to build 3D bio-interfaces and catalytic architectures, (2) a quantitative method to measure cell/material mechanical interactions in situ and at the microscale, and (3) a breakthrough approach to generate functional biocomposites from bacteria and cultured cells.
This report provides a detailed overview of the work performed for project number 130781, 'A Systems Biology Approach to Understanding Viral Hemorrhagic Fever Pathogenesis.' We report progress in five key areas: single cell isolation devices and control systems, fluorescent cytokine and transcription factor reporters, on-chip viral infection assays, molecular virology analysis of Arenavirus nucleoprotein structure-function, and development of computational tools to predict virus-host protein interactions. Although a great deal of work remains from that begun here, we have developed several novel single cell analysis tools and knowledge of Arenavirus biology that will facilitate and inform future publications and funding proposals.
Most topic modeling algorithms that address the evolution of documents over time use the same number of topics at all times. This obscures the common occurrence in the data where new subjects arise and old ones diminish or disappear entirely. We propose an algorithm to model the birth and death of topics within an LDA-like framework. The user selects an initial number of topics, after which new topics are created and retired without further supervision. Our approach also accommodates many of the acceleration and parallelization schemes developed in recent years for standard LDA. In recent years, topic modeling algorithms such as latent semantic analysis (LSA)[17], latent Dirichlet allocation (LDA)[10] and their descendants have offered a powerful way to explore and interrogate corpora far too large for any human to grasp without assistance. Using such algorithms we are able to search for similar documents, model and track the volume of topics over time, search for correlated topics or model them with a hierarchy. Most of these algorithms are intended for use with static corpora where the number of documents and the size of the vocabulary are known in advance. Moreover, almost all current topic modeling algorithms fix the number of topics as one of the input parameters and keep it fixed across the entire corpus. While this is appropriate for static corpora, it becomes a serious handicap when analyzing time-varying data sets where topics come and go as a matter of course. This is doubly true for online algorithms that may not have the option of revising earlier results in light of new data. To be sure, these algorithms will account for changing data one way or another, but without the ability to adapt to structural changes such as entirely new topics they may do so in counterintuitive ways.
Oxygen gas injection has been studied as one method for rapidly generating hydrogen gas from a uranium hydride storage system. Small scale reactors, 2.9 g UH{sub 3}, were used to study the process experimentally. Complimentary numerical simulations were used to better characterize and understand the strongly coupled chemical and thermal transport processes controlling hydrogen gas liberation. The results indicate that UH{sub 3} and O{sub 2} are sufficiently reactive to enable a well designed system to release gram quantities of hydrogen in {approx} 2 seconds over a broad temperature range. The major system-design challenge appears to be heat management. In addition to the oxidation tests, H/D isotope exchange experiments were performed. The rate limiting step in the overall gas-to-particle exchange process was found to be hydrogen diffusion in the {approx}0.5 {mu}m hydride particles. The experiments generated a set of high quality experimental data; from which effective intra-particle diffusion coefficients can be inferred.
Recent work has shown that graphene, a 2D electronic material amenable to the planar semiconductor fabrication processing, possesses tunable electronic material properties potentially far superior to metals and other standard semiconductors. Despite its phenomenal electronic properties, focused research is still required to develop techniques for depositing and synthesizing graphene over large areas, thereby enabling the reproducible mass-fabrication of graphene-based devices. To address these issues, we combined an array of growth approaches and characterization resources to investigate several innovative and synergistic approaches for the synthesis of high quality graphene films on technologically relevant substrate (SiC and metals). Our work focused on developing the fundamental scientific understanding necessary to generate large-area graphene films that exhibit highly uniform electronic properties and record carrier mobility, as well as developing techniques to transfer graphene onto other substrates.
This report details efforts to deploy Agile Components for rapid development of a peridynamics code, Peridigm. The goal of Agile Components is to enable the efficient development of production-quality software by providing a well-defined, unifying interface to a powerful set of component-based software. Specifically, Agile Components facilitate interoperability among packages within the Trilinos Project, including data management, time integration, uncertainty quantification, and optimization. Development of the Peridigm code served as a testbed for Agile Components and resulted in a number of recommendations for future development. Agile Components successfully enabled rapid integration of Trilinos packages into Peridigm. A cost of this approach, however, was a set of restrictions on Peridigm's architecture which impacted the ability to track history-dependent material data, dynamically modify the model discretization, and interject user-defined routines into the time integration algorithm. These restrictions resulted in modifications to the Agile Components approach, as implemented in Peridigm, and in a set of recommendations for future Agile Components development. Specific recommendations include improved handling of material states, a more flexible flow control model, and improved documentation. A demonstration mini-application, SimpleODE, was developed at the onset of this project and is offered as a potential supplement to Agile Components documentation.
This report summarizes the progress made as part of a one year lab-directed research and development (LDRD) project to fund the research efforts of Bryan Marker at the University of Texas at Austin. The goal of the project was to develop new techniques for automatically tuning the performance of dense linear algebra kernels. These kernels often represent the majority of computational time in an application. The primary outcome from this work is a demonstration of the value of model driven engineering as an approach to accurately predict and study performance trade-offs for dense linear algebra computations.
Time-reversal is a wave focusing technique that makes use of the reciprocity of wireless propagation channels. It works particularly well in a cluttered environment with associated multipath reflection. This technique uses the multipath in the environment to increase focusing ability. Time-reversal can also be used to null signals, either to reduce unintentional interference or to prevent eavesdropping. It does not require controlled geometric placement of the transmit antennas. Unlike existing techniques it can work without line-of-sight. We have explored the performance of time-reversal focusing in a variety of simulated environments. We have also developed new algorithms to simultaneously focus at a location while nulling at an eavesdropper location. We have experimentally verified these techniques in a realistic cluttered environment.
The discipline of computer science is built on indirection. David Wheeler famously said, 'All problems in computer science can be solved by another layer of indirection. But that usually will create another problem'. We propose that every computer security vulnerability is yet another problem created by the indirections in system designs and that focusing on the indirections involved is a better way to design, evaluate, and compare security solutions. We are not proposing that indirection be avoided when solving problems, but that understanding the relationships between indirections and vulnerabilities is key to securing computer systems. Using this perspective, we analyze common vulnerabilities that plague our computer systems, consider the effectiveness of currently available security solutions, and propose several new security solutions.
This paper presents an extension to generalized blockmodeling where there are more than two types of objects to be clustered based on valued network data. We use the ideas in homogeneity block modeling to develop an optimization model to perform the clustering of the objects and the resulting partitioning of the ties so as to minimize the inconsistency of an empirical block with an ideal block. The ideal block types used in this modeling are null, complete and a new type that is related to that developed in Ziberna (2007). Three case studies are presented, two based on the Southern Women dataset (Davis et al. 1941) and a third based on passenger air travel in the Continental United States.
Vertical-cavity surface-emitting lasers (VCSELs) are well suited for emerging photonic microsystems due to their low power consumption, ease of integration with other optical components, and single frequency operation. However, the typical VCSEL linewidth of 100 MHz is approximately ten times wider than the natural linewidth of atoms used in atomic beam clocks and trapped atom research, which degrades or completely destroys performance in those systems. This report documents our efforts to reduce VCSEL linewidths below 10 MHz to meet the needs of advanced sub-Doppler atomic microsystems, such as cold-atom traps. We have investigated two complementary approaches to reduce VCSEL linewidth: (A) increasing the laser-cavity quality factor, and (B) decreasing the linewidth enhancement factor (alpha) of the optical gain medium. We have developed two new VCSEL devices that achieved increased cavity quality factors: (1) all-semiconductor extended-cavity VCSELs, and (2) micro-external-cavity surface-emitting lasers (MECSELs). These new VCSEL devices have demonstrated linewidths below 10 MHz, and linewidths below 1 MHz seem feasible with further optimization.
This document summarizes the results from a level 3 milestone study within the CASL VUQ effort. It demonstrates the application of 'advanced UQ,' in particular dimension-adaptive p-refinement for polynomial chaos and stochastic collocation. The study calculates statistics for several quantities of interest that are indicators for the formation of CRUD (Chalk River unidentified deposit), which can lead to CIPS (CRUD induced power shift). Stochastic expansion methods are attractive methods for uncertainty quantification due to their fast convergence properties. For smooth functions (i.e., analytic, infinitely-differentiable) in L{sup 2} (i.e., possessing finite variance), exponential convergence rates can be obtained under order refinement for integrated statistical quantities of interest such as mean, variance, and probability. Two stochastic expansion methods are of interest: nonintrusive polynomial chaos expansion (PCE), which computes coefficients for a known basis of multivariate orthogonal polynomials, and stochastic collocation (SC), which forms multivariate interpolation polynomials for known coefficients. Within the DAKOTA project, recent research in stochastic expansion methods has focused on automated polynomial order refinement ('p-refinement') of expansions to support scalability to higher dimensional random input spaces [4, 3]. By preferentially refining only in the most important dimensions of the input space, the applicability of these methods can be extended from O(10{sup 0})-O(10{sup 1}) random variables to O(10{sup 2}) and beyond, depending on the degree of anisotropy (i.e., the extent to which randominput variables have differing degrees of influence on the statistical quantities of interest (QOIs)). Thus, the purpose of this study is to investigate the application of these adaptive stochastic expansion methods to the analysis of CRUD using the VIPRE simulation tools for two different plant models of differing random dimension, anisotropy, and smoothness.
Bowman, Christopher; Adzima, Brian J.; Anderson, Benjamin J.
This project examines the utility of cycloaddition reactions for the synthesis of polymer networks. Cycloaddition reactions are desirable because they produce no unwanted side reactions or small molecules, allowing for the formation of high molecular weight species and glassy crosslinked networks. Both the Diels-Alder reaction and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) were studied. Accomplishments include externally triggered healing of a thermoreversible covalent network via self-limited hysteresis heating, the creation of Diels-Alder based photoresists, and the successful photochemical catalysis of CuAAC as an alternative to the use of ascorbic acid for the generation of Cu(I) in click reactions. An analysis of the results reveals that these new methods offer the promise of efficiently creating robust, high molecular weight species and delicate three dimensional structures that incorporate chemical functionality in the patterned material. This work was performed under a Strategic Partnerships LDRD during FY10 and FY11 as part of a Sandia National Laboratories/University of Colorado-Boulder Excellence in Science and Engineering Fellowship awarded to Brian J. Adzima, a graduate student at UC-Boulder. Benjamin J. Anderson (Org. 1833) was the Sandia National Laboratories point-of-contact for this fellowship.
Events of interest to data analysts are sometimes difficult to characterize in detail. Rather, they consist of anomalies, events that are unpredicted, unusual, or otherwise incongruent. The purpose of this LDRD was to test the hypothesis that a biologically-inspired anomaly detection algorithm could be used to detect contextual, multi-modal anomalies. There currently is no other solution to this problem, but the existence of a solution would have a great national security impact. The technical focus of this research was the application of a brain-emulating cognition and control architecture (BECCA) to the problem of anomaly detection. One aspect of BECCA in particular was discovered to be critical to improved anomaly detection capabilities: it's feature creator. During the course of this project the feature creator was developed and tested against multiple data types. Development direction was drawn from psychological and neurophysiological measurements. Major technical achievements include the creation of hierarchical feature sets created from both audio and imagery data.
The purpose of this LDRD is to develop technology allowing warfighters to provide high-level commands to their unmanned assets, freeing them to command a group of them or commit the bulk of their attention elsewhere. To this end, a brain-emulating cognition and control architecture (BECCA) was developed, incorporating novel and uniquely capable feature creation and reinforcement learning algorithms. BECCA was demonstrated on both a mobile manipulator platform and on a seven degree of freedom serial link robot arm. Existing military ground robots are almost universally teleoperated and occupy the complete attention of an operator. They may remove a soldier from harm's way, but they do not necessarily reduce manpower requirements. Current research efforts to solve the problem of autonomous operation in an unstructured, dynamic environment fall short of the desired performance. In order to increase the effectiveness of unmanned vehicle (UV) operators, we proposed to develop robots that can be 'directed' rather than remote-controlled. They are instructed and trained by human operators, rather than driven. The technical approach is modeled closely on psychological and neuroscientific models of human learning. Two Sandia-developed models are utilized in this effort: the Sandia Cognitive Framework (SCF), a cognitive psychology-based model of human processes, and BECCA, a psychophysical-based model of learning, motor control, and conceptualization. Together, these models span the functional space from perceptuo-motor abilities, to high-level motivational and attentional processes.
This guide describes the R&A process, Common Look and Feel requirements, and preparation and publishing procedures for communication products at Sandia National Laboratories. Samples of forms and examples of published communications products are provided. This guide takes advantage of the wealth of material now available on the Web as a resource. Therefore, it is best viewed as an electronic document. If some of the illustrations are too small to view comfortably, you can enlarge them on the screen as needed. The format of this document is considerably different than that usually expected of a SAND Report. It was selected to permit the large number of illustrations and examples to be placed closer to the text that references them. In the case of forms, covers, and other items that are included as examples, a link to the Web is provided so that you can access the items and download them for use. This guide details the processes for producing a variety of communication products at Sandia National Laboratories. Figure I-1 shows the general publication development process. Because extensive supplemental material is available from Sandia on the internal web or from external sources (Table I-1), the guide has been shortened to make it easy to find information that you need.
This report documents our first year efforts to address the use of many-core processors for high performance cyber protection. As the demands grow for higher bandwidth (beyond 1 Gbits/sec) on network connections, the need to provide faster and more efficient solution to cyber security grows. Fortunately, in recent years, the development of many-core network processors have seen increased interest. Prior working experiences with many-core processors have led us to investigate its effectiveness for cyber protection tools, with particular emphasis on high performance firewalls. Although advanced algorithms for smarter cyber protection of high-speed network traffic are being developed, these advanced analysis techniques require significantly more computational capabilities than static techniques. Moreover, many locations where cyber protections are deployed have limited power, space and cooling resources. This makes the use of traditionally large computing systems impractical for the front-end systems that process large network streams; hence, the drive for this study which could potentially yield a highly reconfigurable and rapidly scalable solution.
The number of PDF files with embedded malicious code has risen significantly in the past few years. This is due to the portability of the file format, the ways Adobe Reader recovers from corrupt PDF files, the addition of many multimedia and scripting extensions to the file format, and many format properties the malware author may use to disguise the presence of malware. Current research focuses on executable, MS Office, and HTML formats. In this paper, several features and properties of PDF Files are identified. Features are extracted using an instrumented open source PDF viewer. The feature descriptions of benign and malicious PDFs can be used to construct a machine learning model for detecting possible malware in future PDF files. The detection rate of PDF malware by current antivirus software is very low. A PDF file is easy to edit and manipulate because it is a text format, providing a low barrier to malware authors. Analyzing PDF files for malware is nonetheless difficult because of (a) the complexity of the formatting language, (b) the parsing idiosyncrasies in Adobe Reader, and (c) undocumented correction techniques employed in Adobe Reader. In May 2011, Esparza demonstrated that PDF malware could be hidden from 42 of 43 antivirus packages by combining multiple obfuscation techniques [4]. One reason current antivirus software fails is the ease of varying byte sequences in PDF malware, thereby rendering conventional signature-based virus detection useless. The compression and encryption functions produce sequences of bytes that are each functions of multiple input bytes. As a result, padding the malware payload with some whitespace before compression/encryption can change many of the bytes in the final payload. In this study we analyzed a corpus of 2591 benign and 87 malicious PDF files. While this corpus is admittedly small, it allowed us to test a system for collecting indicators of embedded PDF malware. We will call these indicators features throughout the rest of this report. The features are extracted using an instrumented PDF viewer, and are the inputs to a prediction model that scores the likelihood of a PDF file containing malware. The prediction model is constructed from a sample of labeled data by a machine learning algorithm (specifically, decision tree ensemble learning). Preliminary experiments show that the model is able to detect half of the PDF malware in the corpus with zero false alarms. We conclude the report with suggestions for extending this work to detect a greater variety of PDF malware.
Packet switched data communications networks that use distributed processing architectures have the potential to simplify the design and development of new, increasingly more sophisticated satellite payloads. In addition, the use of reconfigurable logic may reduce the amount of redundant hardware required in space-based applications without sacrificing reliability. These concepts were studied using software modeling and simulation, and the results are presented in this report. Models of the commercially available, packet switched data interconnect SpaceWire protocol were developed and used to create network simulations of data networks containing reconfigurable logic with traffic flows for timing system distribution.
Currently there is a substantial lack of data for interactions of shock waves with particle fields having volume fractions residing between the dilute and granular regimes, which creates one of the largest sources of uncertainty in the simulation of energetic material detonation. To close this gap, a novel Multiphase Shock Tube has been constructed to drive a planar shock wave into a dense gas-solid field of particles. A nearly spatially isotropic field of particles is generated in the test section by a gravity-fed method that results in a spanwise curtain of spherical 100-micron particles having a volume fraction of about 19%. Interactions with incident shock Mach numbers of 1.66, 1.92, and 2.02 were achieved. High-speed schlieren imaging simultaneous with high-frequency wall pressure measurements are used to reveal the complex wave structure associated with the interaction. Following incident shock impingement, transmitted and reflected shocks are observed, which lead to differences in particle drag across the streamwise dimension of the curtain. Shortly thereafter, the particle field begins to propagate downstream and spread. For all three Mach numbers tested, the energy and momentum fluxes in the induced flow far downstream are reduced about 30-40% by the presence of the particle field. X-Ray diagnostics have been developed to penetrate the opacity of the flow, revealing the concentrations throughout the particle field as it expands and spreads downstream with time. Furthermore, an X-Ray particle tracking velocimetry diagnostic has been demonstrated to be feasible for this flow, which can be used to follow the trajectory of tracer particles seeded into the curtain. Additional experiments on single spherical particles accelerated behind an incident shock wave have shown that elevated particle drag coefficients can be attributed to increased compressibility rather than flow unsteadiness, clarifying confusing results from the historical database of shock tube experiments. The development of the Multiphase Shock Tube and associated diagnostic capabilities offers experimental capability to a previously inaccessible regime, which can provide unprecedented data concerning particle dynamics of dense gas-solid flows.
The U.S. is currently re-evaluating the policy on high-level radioactive waste (HLW) management and has been studying generic disposal system environment (GDSE) concepts to support the development of a long-term strategy for geologic disposal of HLW. The GDSE study focuses on the analysis of different GDSE options, and a salt repository is one of the options currently under study. The immediate goal of the generic salt repository study is to develop the necessary modeling tools to evaluate and improve understanding on the repository system response and processes relevant to long-term HLW disposal in salt. An initial version of the salt GDSE performance assessment model and the preliminary analysis results are discussed, emphasizing key attributes of a salt repository that are potentially important to the long-term safe disposal of HLW. Also discussed are the preliminary results on the repository response to the effects of different waste types (commercial UNF, existing DOE HLW, and hypothetical reprocessing HLW), and radionuclide release scenarios (undisturbed and human intrusion). Soluble, non- to weakly sorbing fission products, particularly 129I, 79Se, and 26Ra are the major dose contributors. However, the conservative assumptions made about their geochemical behaviors contribute to their calculated dose. The paper elaborates on the identified knowledge gaps and path forwards for future R&D efforts to advance understanding of salt repository system performance for HLW disposal.
In the saturated zone transport model for the Yucca Mountain repository, the transport of the long lived radionuclides is explicitly modeled, while the concentrations of the short-lived decay products are inferred from the concentrations of their respective parent radionuclides. When assessing dose from 226Ra and its decay products, it is important to consider radioactive disequilibrium between the concentrations of 226Ra in the groundwater and the concentrations of its short-lived decay product, 222Rn caused by the preferential sorption of 226Ra on mineral grains in the aquifer. This paper discusses behavior of radon in the groundwater, 222Rn transfer to indoor and outdoor air, and the resulting transport and exposure pathways for the groundwater enriched in 222Rn. The processes considered include the buildup of radon decay products in the soil, the transfer of radon from groundwater to outdoor and indoor air, and the consequent radionuclide transfer to other environmental media, such as plants and animal products. The increased concentrations of radon and its decay products in the environmental media (water, soil, air, crops, animal products, and fish) result in additional exposure pathways that should be taken into account when evaluating the dose to the receptor. It is concluded that the unsupported 222Rn can have a significant effect on the dose from 226Ra and its decay products.
Given the uncertain future of the proposed Yucca Mountain Repository for final disposal of used light water reactor fuel, the tactical strategy is to store used nuclear fuel (UNF) at utility sites in either pool or dry cask storage systems. Although no time threshold has been defined, the current recommendation for long-term management of UNF is 300 years. This presents possible regulatory and technical issues for both storage safety and security. This paper discusses ongoing work in address security for long-term storage of UNF. Previous work focused on an assessment of security requirements for the U.S. Nuclear Regulatory Commission and the U.S. Department of Energy. In addition, it has been determined that the dose rates for UNF will fall below the current 100 rem/hour self-protection threshold after 70 to 120 years. Work continues to address issues associated with maintaining security for long-term storage of UNF. Extending the self-protection concept and plans for performing assessments of the long-term security risk will be discussed. This work is part of a larger effort to develop concepts for a demonstration UNF storage site and to develop a technical basis for long-term storage of UNF and the associated transportation.
Published results of performance assessments for deep geologic disposal of high-level radioactive waste and spent nuclear fuel provide insight into those aspects of the waste form that are potentially important to the long-term performance of a repository system. Alternative waste forms, such as might result from new technologies for processing spent fuel and advances in nuclear reactor design, have the potential to affect the long-term performance of a geologic repository. This paper reviews relevant results of existing performance assessments for a range of disposal concepts and provides observations about how hypothetical modifications to waste characteristics (e.g., changes in radionuclide inventory, thermal loading, and durability of waste forms) might impact results of the performance assessment models. Disposal concepts considered include geologic repositories in both saturated and unsaturated environments. Specifically, we consider four recent performance assessments as representative of a range of disposal concepts. We examine the extent to which results of these performance assessments are affected by (i) thermal loading of the waste proposed for disposal; (ii) mechanical and chemical lifetime of the waste form; and (iii) radionuclide content of the waste. We find that peak subsurface temperature generally is a constraint that can be met through engineering solutions and that processing of wastes to reduce thermal power may enable more efficient use of repositories rather than improved repository performance. We observe that the rate of radionuclide release is often limited by geologic or chemical processes other than waste form degradation. Thus, the effects on repository performance of extending waste-form lifetime may be relatively small unless the waste form lifetime becomes sufficiently long relative to the period of repository performance. Finally, we find that changes to radionuclide content of waste (e.g., by separation or transmutation processes) do not in general correspond to proportional effects on repository performance. Rather, the effect of changes to radionuclide content depends on the relative mobility of various radionuclides through the repository system, and consequently on repository geology and geochemistry.
The safe management and disposition of used nuclear fuel and/or high level nuclear waste is a fundamental aspect of the nuclear fuel cycle. The United States currently utilizes a once-through fuel cycle where used nuclear fuel is stored on-site in either wet pools or in dry storage systems with ultimate disposal in a deep mined geologic repository envisioned. However, a decision not to use the proposed Yucca Mountain Repository will result in longer interim storage at reactor sites than previously planned. In addition, alternatives to the once-through fuel cycle are being considered and a variety of options are being explored under the U.S. Department of Energy's Fuel Cycle Technologies Program. These two factors lead to the need to develop a credible strategy for managing radioactive wastes from any future nuclear fuel cycle in order to provide acceptable disposition pathways for all wastes regardless of transmutation system technology, fuel reprocessing scheme(s), and/or the selected fuel cycle. These disposition paths will involve both the storing of radioactive material for some period of time and the ultimate disposal of radioactive waste. To address the challenges associated with waste management, the DOE Office of Nuclear Energy established the Used Fuel Disposition Campaign in the summer of 2009. The mission of the Used Fuel Disposition Campaign is to identify alternatives and conduct scientific research and technology development to enable storage, transportation, and disposal of used nuclear fuel and wastes generated by existing and future nuclear fuel cycles. The near-and long-term objectives of the Fuel Cycle Technologies Program and its ' Used Fuel Disposition Campaign are presented.
The implementation of a project for the long-term disposal of nuclear waste (e.g., spent nuclear fuel, high-level radioactive waste) has proven to be one of the most challenging technical and political endeavors facing modern societies. The process of moving the project from site selection and characterization to licensing nuclear waste management facilities places shifting and, in some cases, conflicting demands on the community of technical experts engaged in providing the conceptual and quantitative bases for assessing facility safety and demonstrating regulatory compliance. At the same time, the accumulation and preservation of site-specific knowledge, data and modeling concerning the relevant components of the site is of urgent importance for the success of the overall process. To date, the evolving demands placed on these technical communities have received little systematic attention. The US efforts to site nuclear waste management facilities have faced significant challenges in developing and maintaining appropriate technical staffing, and based on recent policy shifts those challenges are likely to grow larger. This paper employs interviews with technical professionals from the US nuclear waste disposal program to analyze ways in which technical, social and political factors influence the performance of technical experts in lengthy, complex projects such as one for the long-term disposal of nuclear waste. The focus is on the interaction of the organizational and professional culture with evolving technical and professional demands. Recommendations are made for the design of sustainable technical organizations for performance of long-term risk analyses for nuclear waste management project.
Thermal analyses of disposal strategies in a generic salt repository with high-level nuclear waste (HLW) have been completed. These studies were undertaken primarily to examine details of temperature distribution as a function of time for disposal concepts of wastes resulting from the recycling of spent nuclear fuel from a light water reactor. These analyses confirm that a conceptual salt repository for HLW appears feasible and worthy of more detailed evaluation. The analyses examined the temporal temperature distribution near a HLW package, as well as the far-field thermal response due to its transient heat pulse. The sensitivity of temperature distribution to several variations of primary features (e.g. the waste emplacement rate, waste configuration, etc.) was also determined. The principal observations of the study include the following. The temperatures involved ensure sufficient time for waste emplacement within a panel and adequate time to mine adjacent panels without adverse consequences. The modeled concept of a single level repository is workable. Thermal loading is the primary driver of repository-wide (far-field relative to the waste canister) heat effects. Decay storage, decreasing the loading of the waste package and changing the waste configuration are viable methods for reducing the peak waste and salt temperatures. The results of the thermal analyses show that with application of informed heat management strategies, thermal front migration rates are slow enough that a feasible design of the repository can be implemented. Peak temperatures within the waste package can be controlled with modest engineering considerations.
An in-package chemistry model is presented to calculate pH in the pore space of degradation products inside a breached waste package in the unsaturated environment of the Yucca Mountain repository. The pH is calculated as a function of liquid influx rate, partial pressure of carbon dioxide, solid-water volume ratio in the porous degradation products (provided by a coupled water balance model), and the relative rate of steel and waste form degradation. The EQ3/6 code is used to calculate pH at high liquid influx rates and zero liquid influx rates (vapor influx only). For mid-range liquid influx rates, a Damkohler ratio is defined and used to interpolate between the pH values calculated at the two extremes. This approach allows the in-package pH to be calculated over broad ranges of key parameters in a total system performance assessment.
Waste heat generation, repository temperature, and waste radiotoxicity were evaluated using three idealized fuel cycle cases (Table I) in addition to reference UNF. Heat output was normalized to electrical energy produced, simplifying thermal analysis of alternative fuel cycles, especially if waste mass and volume can be accommodated using various container and engineered barrier system configurations. Using a reference repository thermal model, the peak near-field temperature for these cases is shown to be in the range 100 to 130°C, indicating that any of the cases considered can be thermally "fine tuned" (line loading density, decay storage) to limit temperatures as required. Whereas transmutation of TRUs has been proposed to limit repository temperatures after decay of short-lived fission products, the repository concept of operations (drift spacing, decay storage, waste packaging, active ventilation, etc.) can be readily adjusted to accomplish the same effect. The potential radiotoxicity from long-lived fission products, normalized to electricity produced, is effectively the same for all three fuel cycle cases. This is especially important for a repository in clay or shale, where LLFPs are the major contributors to projected dose. Thus, burning of TRUs (conversion to fission products) may decrease overall radiotoxicity, but without significantly changing the toxicity of fission products, or the projected dose for a clay/shale repository, if electrical energy is produced and taken into account (Figure 5). Separation of long-lived fission products, and direct transmutation, have limited applicability with attendant technical and economic challenges.11 Whatever approach is taken to manage long-lived fission products, it should consider the entire system including geologic disposal, and the impacts should be normalized to the benefits, i.e., to the useable energy produced.
This paper reviews how the risks of transporting very radioactive materials are modeled and how the resulting doses to the public compare with commonly experienced radiation doses like background radiation. Both routine, incident-free transportation and transportation accidents are discussed. Only transportation of used nuclear fuel and high-level radioactive waste is discussed.
Hydrologic characterization at the Waste Isolation Pilot Plant (WIPP), near Carlsbad, New Mexico, has historically focused on collection of geologic data, such as cores and borehole geophysical logs, and the estimation of hydrologic parameters from single- and multi-well aquifer tests. These data have resulted in a detailed understanding of the depositional and alteration processes that have affected the hydrologie units of interest at WIPP. The hydrologie conceptual model has been used to create a groundwater flow and radionuclide transport model used in WIPP performance assessment (PA). Long-term monitoring of a large network of monitoring wells between testing events has produced millions of high-frequency, long-duration water level records. Hydrologie analysis techniques associated with barometric, Earth tide, and precipitation signals, these long-term data have the potential to reveal additional insights about the large-scale hydrogeology of the formations near WIPP. This study emphasizes that hydrological and geophysical data and analysis is important on multiple temporal and spatial scales in order to achieve effective characterization.
The possible effects of epistemic uncertainty in the seismic hazard curve used in the 2008 performance assessment (PA) for the proposed repository for high-level radioactive waste at Yucca Mountain (YM), Nevada, are investigated. The analysis establishes that it is possible to propagate epistemic uncertainty in the seismic hazard through the computational structure used in the 2008 YM PA and to investigate the effects of this uncertainty on expected dose to a reasonably maximally exposed individual from seismic ground motion events with sensitivity analysis procedures based on Latin hypercube sampling, partial rank correlation, and stepwise rank regression. The dominant analysis inputs affecting the epistemic uncertainty in the indicated dose were found to be the residual stress level at which stress corrosion initiates in the Alloy 22 outer corrosion barrier for waste packages and the seismic hazard curve.
The PUREX process is one of the most widely adopted approaches of industrial-scale liquid-liquid extraction (LLE) methods for the separation and recovery of U and Pu from dissolved used nuclear fuel. This paper documents the application of chemical equilibrium approaches to the modeling of LLE for the PUREX process at 25°C. In this work, we focus on modeling the extraction of HNO3 and UO2(NO3)2 by the non-electrolyte organic liquid phase Tri-n-butyl Phosphate (TBP) plus a diluent (Amsco 125-82). Six chemical reactions representing the equilibria between the concentrated HNO3-UO2(NO3)2 electrolyte and TBP-diluent organic phase is sufficient to accurately generate the extraction isotherms for the extracted components for a wide range of TBP and acid concentrations in the non-electrolyte and electrolyte phases, respectively. The Pitzer approach is used to compute the activity coefficients of the HNO3 electrolyte phase. No activity coefficient model is adopted for TBP organic complexes where these were assigned unity values. Even with this assumption, the predicted isotherms are in very good agreement with the experimental data and such result serves as a preamble to extend this modeling approach to more compositionally complex systems relevant to LLE of radionuclides.
13th International High-Level Radioactive Waste Management Conference 2011, IHLRWMC 2011
Ross Kirkes, G.; Wagner, S.W.
The Waste Isolation Pilot Plant (WIPP) is a deep geologic repository sited in salt beds in Southeast New Mexico for the permanent disposal of defense-related Transuranic (TRU) waste operated by the U.S. Department of Energy (DOE). Conceptual designs, governing rules and statutes for the WIPP have historically included requirements for waste retrieval or waste removal. This paper discusses the rationale for waste retrieval and removal requirements and how the concept of waste retrieval and removal has evolved as the mission of WIPP progressed from a pilot project to an operational disposal facility.
The U.S. Department of Energy has developed the Waste Isolation Pilot Plant in southeastern New Mexico for the geologic disposal of transuranic waste. Performance assessment is the analysis methodology used to demonstrate that WIPP radionuclide release probabilities fall below limits designated by the U.S. Environmental Protection Agency, ensuring the protection of the public and environment. The most recent WIPP PA demonstrates that cumulative releases continue to lie entirely below specified limits. Therefore, WIPP continues to be in compliance with containment requirements. Analysis of the results shows that total releases are dominated by radionuclide releases that could occur during an inadvertent penetration of the repository by a future drilling operation. The natural and engineered barrier systems of the WIPP provide robust and effective containment of transuranic waste even if the repository is penetrated by multiple borehole intrusions.
13th International High-Level Radioactive Waste Management Conference 2011, IHLRWMC 2011
Williams, Jeffrey R.; Cotton, Thomas A.; Rechard, Rob P.
At the early stages of a repository program an important decision is the selection of a system development strategy that will lead effectively and efficiently to a final operating system in the face of inevitable technical and institutional uncertainties about how the future will unfold. The approach to designing the repository can contribute to the flexibility required to allow a repository program to adapt to unforeseen developments. The evolution of the Yucca Mountain repository design from a large integrated facility optimized for a single reference development and operation scenario to a modular design that is more readily adaptable to a wide range of alternative futures is an example of both the importance of and an approach to designing flexibility into a repository system.
13th International High-Level Radioactive Waste Management Conference 2011, IHLRWMC 2011
Jenkins-Smith, Hank C.; Silva, Carol L.; Herron, Kerry G.; Rechard, Rob P.
Public attitudes in the United States toward spent nuclear fuel (SNF) management options are sensitive to specified policy design elements. Retrievability is generally preferred, both because the public views SNF as a possible future resource and because the public prefers to retain the option to revise SNF storage strategies in light of new learning. The public favors in the United States retaining the option for reprocessing SNF by a two-to-one majority. Expressed public support for a SNF repository is increased substantially if it is combined with a national laboratory focused on increasing safety of SNF storage, or with a facility for reprocessing SNF. Overall, it appears that bundling repository facilities with other SNF management junctions holds substantial promise to reduce the traditionally negative, stigmatizing imagery attached to SNF management facilities that treat these materials as a "waste".
Given the uncertain future of the proposed Yucca Mountain Repository for final disposal of used light water reactor fuel, the tactical strategy is to store used nuclear fuel (UNF) at utility sites in either pool or dry cask storage systems. Although no time threshold has been defined, the current recommendation for long-term management of UNF is 300 years. This presents possible regulatory and technical issues for both storage safety and security. This paper discusses ongoing work in address security for long-term storage of UNF. Previous work focused on an assessment of security requirements for the U.S. Nuclear Regulatory Commission and the U.S. Department of Energy. In addition, it has been determined that the dose rates for UNF will fall below the current 100 rem/hour self-protection threshold after 70 to 120 years. Work continues to address issues associated with maintaining security for long-term storage of UNF. Extending the self-protection concept and plans for performing assessments of the long-term security risk will be discussed. This work is part of a larger effort to develop concepts for a demonstration UNF storage site and to develop a technical basis for long-term storage of UNF and the associated transportation.
We report direct observation of an unexpected anisotropic swelling of Si nanowires during lithiation against either a solid electrolyte with a lithium counter-electrode or a liquid electrolyte with a LiCoO2 counter-electrode. Such anisotropic expansion is attributed to the interfacial processes of accommodating large volumetric strains at the lithiation reaction front that depend sensitively on the crystallographic orientation. This anisotropic swelling results in lithiated Si nanowires with a remarkable dumbbell-shaped cross section, which develops due to plastic flow and an ensuing necking instability that is induced by the tensile hoop stress buildup in the lithiated shell. The plasticity-driven morphological instabilities often lead to fracture in lithiated nanowires, now captured in video. These results provide important insight into the battery degradation mechanisms.
Complex Adaptive Systems of Systems, or CASoS, are vastly complex ecological, sociological, economic and/or technical systems which we must understand to design a secure future for the nation and the world. Perturbations/disruptions in CASoS have the potential for far-reaching effects due to pervasive interdependencies and attendant vulnerabilities to cascades in associated systems. Phoenix was initiated to address this high-impact problem space as engineers. Our overarching goals are maximizing security, maximizing health, and minimizing risk. We design interventions, or problem solutions, that influence CASoS to achieve specific aspirations. Through application to real-world problems, Phoenix is evolving the principles and discipline of CASoS Engineering while growing a community of practice and the CASoS engineers to populate it. Both grounded in reality and working to extend our understanding and control of that reality, Phoenix is at the same time a solution within a CASoS and a CASoS itself.