National Nuclear Security Agency Research Articles

Mykonos: A pulsed power driver for science and innovation

Sandia National Laboratories has been operating the Mykonos linear transformer driver (LTD) in a five-cavity configuration since 2014. The machine operates at 1MA output current, 500kV output voltage, with a 10–90% current rise time of 85ns, which enables small scale physics and engineering pulsed power experiments. Mykonos provides hands-on pulsed power experimental training for students and staff alongside senior Sandia scientists in an environment that is more accessible than the Z Facility. Over the years, we have fielded and accumulated a wide variety of optical, x-ray and electrical diagnostics and we are preparing to open this facility to outside users. Here, we are presenting the pulsed power and diagnostic capability of Mykonos as well as some recent experiments that have been performed on the facility. The goal of this publication is to attract researchers across the pulsed power and high energy density (HED) community to collaborate with Sandia on exciting, innovative science and to train the next generation of researchers for the National Nuclear Security Agency (NNSA) and the nation. As such, we have established a Mykonos Academic Access Program (MAAP) as part of ZNetUS to enable academic utilization of the Mykonos Pulsed Power Facility.

LANSCE Accelerator Update and Future Plans

Several multi-year accelerator system upgrades have recently been completed at LANSCE that will ensure the long-term future of beam operations to its users and to prepare for a planned next-generation signature facility (MaRIE) based on multi-probe capabilities. Present LANSCE accelerator operations will be discussed. A summary of the recent upgrades completed and future plans will also be presented. This work is supported by the United States Department of Energy, National Nuclear Security Agency, under contract DE-AC52-06NA25396.

Optimization and Characterization of Plasma Sprayed Zirconium Diffusion Barriers on Uranium-Molybdenum Monolithic Nuclear Fuel Plates

In this report, the CONVERT MP-1 team at Los Alamos National Laboratory (LANL) presents the development work for an industrial plasma spraying method to affix zirconium (Zr) metal fuel diffusion barriers on uranium-molybdenum alloy nuclear fuel plates, in order to prevent a reaction between the U-Mo fuel and the eventual aluminum cladding. The United States government is continually committed to strengthening nuclear security and nonproliferation to reduce the threat of radioactive materials acquisition by terrorists. To meet this important mission, the US Department of Energy and National Nuclear Security Agency’s (NNSA) Office of Material Management and Minimization (M3) Reactor Conversion Program (CONVERT) seeks to minimize the use of highly enriched uranium (HEU) in civilian applications through work with governments and facilities around the world to convert research reactors to the use of non-weapons-usable low enriched uranium (LEU) fuels. Currently, the CONVERT Program is committed to development of a high-density U-Mo fuel that will be able to convert high performance research reactors, while establishing an efficient and economic fabrication capability to manufacture the fuel. A micron scale Zr metal diffusion barrier is deposited onto bare U-10Mo (uranium-10% molybdenum alloy) monolithic metal foils by plasma spraying. Zr metal powders are heated in a high energy DC plasma and accelerated toward the foil substrate. The molten metal particle impact and deform on the substrate, to form a uniform dense coating. (Figure 1A) Multiple passes of the plasma torch increase the coating thickness layer by layer. In initial experiments, the DU-10Mo foil was significantly preheated, which promoted oxidation of the foil surface. Microscopic analysis showed a thin (100’s of nanometer) interaction layer rich in oxygen (Figure 1B).[1] The integrity of the Zr diffusion barrier deposition is determined by tensile strength adhesion testing and destructive cross-sectional metallography and microscopy.[2, 3] Despite best efforts of ensuring a quality vacuum and oxygen free environment, trace amounts of oxygen were present in the Ar-He plasma. During the preheating passes (i.e. no metal powder), the uranium surface was slightly oxidized. During deposition, uranium and molybdenum, as well as zirconium, would diffuse into this oxide, forming the oxygen rich interaction layer. This became a point of weakness and led to a temperature dependent bond strength. Post coating annealing shows nano-scale phase segregation and reduced strength. Further experiments eliminated the preheating steps; the Zr powder was deposited onto the foil immediately, then the plasma torch was used to heat the coated foils following deposition. With this approach, there is almost no oxide formation and minimal interaction at the interface. Contrary to expectations, this minimal diffusion and interaction leads to improved tensile adhesion strength. This improved bonding strength seems to be less dependent on the deposition temperature. The effects of processing on bond adhesion strength are reported in Figure 1C. A successful diffusion barrier requires adequate Zr layer thickness, uniform coverage, sufficient bonding at the Zr/fuel and Zr/aluminum cladding interface, and maintenance of the original nuclear fuel properties i.e. physical dimensions, alloy composition and dispersion, crystallographic phase concentration, neutronics, etc. This work outlines development of the Zr plasma spray processing techniques, parameters affecting the diffusion barrier/nuclear fuel bond strength, and characterization of the Zr diffusion barrier. Works Cited. 1. Cummins, D.R., et al., Plasma Sprayed Zirconium Diffusion Barrier Development for Monolithic U-Mo Metallic Fuel, in RRFM European Research Reactor Conference 2016. 2016: Berlin, Germany. 2. Hollis, K.J., et al., Bond Characterization of Plasma Sprayed Zirconium on Uranium Alloy by Microcantilever Testing. Journal of Thermal Spray Technology, 2013. 22(2-3): p. 233-241. 3. Cummins, D.R., K.J. Hollis, and D.E. Dombrowski, Bond Strength of Plasma Sprayed Zr Diffusion Barrier on U-Mo Fuels. Trans. Amer. Nucl. Soc., 2016. Figure 1. A) Cross-sectioned backscattered SEM (BS-SEM) of typical U-10Mo foil with both sides coated with Zr metal via plasma spray. B) BS-SEM image detailing the interface between the Zr layer and the U-10Mo foil when the sample is preheated by plasma, prior to Zr spray. C) Relation between average substrate temperature during plasma spraying (°C) and the measured bond adhesion tensile strength (MPa). Black squares show the bond strength results of the conventional twelve preheating passes prior to Zr powder depositions. The red circle present the results of the post heating treatment at 750°C for 1 hour of these same foils. The blue square relates to the experiment with only four preheating passes before Zr powder is introduced into the plasma spray system. The green squares show the results of no preheating passes. Figure 1

Using Statistical Methods to Assess a Surveillance Program

ABSTRACTThree metrics have been been developed to assess the National Nuclear Security Agency (NNSA) Surveillance Program against its objectives of detecting defects, determining margins and validating predictions. The surveillance metrics use statistical methods and are probabilities or confidences that produce quantitive assessments on a 0 to 1 scale—from no confidence that a given data stream achieves its surveillance program objectives to complete confidence that the data stream fulfills the objectives. These metrics may be compared and rolled up to support NNSA Surveillance Program management decisions.

5.3.2 Integrating the Life‐cycle Process Utilizing SysML

AbstractSandia National Laboratories is developing and applying an Integrated Phase Gate (IPG) project structure to execute critical programs such as nuclear weapon Life Extension Projects (LEP) that require the utmost attention to reliability, function and other stakeholder requirements including safety and security. This emphasis on project rigor reflects a new directive from the Department of Energy's National Nuclear Security Agency (NNSA) to develop robust processes in order to ensure that the nation's nuclear deterrence will be effective and available for decades to come. To this end, Sandia's Advanced and Exploratory Systems Department is developing a SysML model of an integrated Product Lifecycle Management (PLM) environment with the intent of providing project teams with direct access to program templates, requirements, tools (both program and technical) and related databases. This paper will describe the current state and future direction of the integrated PLM environment SysML model.

Lunch with the head of the National Nuclear Security Administration and the under secretary of state for arms control

Last Friday at the Fairmont Hotel in downtown Washington, DC, I was among a group of reporters who'd been invited to a lunchtime question-and-answer session with Thomas D'Agostino, the head of the National Nuclear Security Agency, and Ellen Tauscher, the under secretary of state responsible for arms control and international security affairs.

Universal Tritium Transmitter

At the Savannah River Site and throughout the National Nuclear Security Agency (NNSA) tritium is measured using Ion or Kanne Chambers. Tritium flowing through an Ion Chamber emits beta particles generating current flow proportional to tritium radioactivity. Currents in the 1x 10-15 A to 1x 10-6 A are measured. The distance between the Ion Chamber and the electrometer in NNSA facilities can be over 100 feet. Currents greater than a few microamperes can be measured with a simple modification. Typical operating voltages of 500 to 1000 Volts and piping designs require that the Ion Chamber be connected to earth ground. This grounding combined with long cable lengths and low currents requires a very specialized preamplifier circuit. In addition, the electrometer must be able to supply “fail safe” alarm signals which are used to alert personnel of a tritium leak, trigger divert systems preventing tritium releases to the environment and monitor stack emissions as required by the United States federal Government and state governments. Ideally the electrometer would be “self monitoring”. Self monitoring would reduce the need for constant checks by maintenance personnel. For example at some DOE facilities monthly calibration and alarm checks must be performed to ensure operation. NNSA presently uses commercially available electrometers designed specifically for this critical application. The problems with these commercial units include: ground loops, high background currents, inflexibility and susceptibility to Electromagnetic Interference (EMI) which includes RF and Magnetic fields. Existing commercial electrometers lack the flexibility to accommodate different Ion Chamber designs required by the gas pressure, type of gas and range. Ideally the electrometer could be programmed for any expected gas, range and high voltage output. Commercially available units do not have “fail safe” self monitoring capability. Electronics used to measure extremely low current must have sufficient time to thermally equilibrate. Amplifiers, transistors, resistors all need time to stabilize before the electrometer circuit will measure accurately in the 10-15 and 10-14 ampere range. Existing electrometers give the user no indication when the unit has stabilized and is acceptable for low level measurements. Savannah River National Laboratory (SRNL) funded through the NNSA Plant Directed Research and Development (PDRD) program, has developed a truly Universal Tritium Transmitter (UTT) capable of solving many known problems with existing commercial electrometers. This UTT pushes the state-of-the-art in electrometer design and incorporates solutions to deficiencies found in commercial electrometers.

Technical Report: Absolute Radiometric Calibration at NSLS

For nearly 20 years the U3c and X8a beamlines at the National Synchrotron Light Source (NSLS) have been used for absolute calibration and X-ray characterization of detectors and optics. The motivation behind this capability has been the need of the U.S. Department of Energy's National Nuclear Security Agency (DOE-NNSA) programs at other U.S. national laboratories (Livermore, Sandia, and Los Alamos) to provide diagnostics capabilities for high-temperature plasma physics experiments. For example, specific applications of regularly NSLS-calibrated diagnostics are found at Livermore's National Ignition Facility (NIF) and Sandia's Z machine.

Software Project Management and Quality Engineering Practices for Complex, Coupled Multiphysics, Massively Parallel Computational Simulations: Lessons Learned From ASCI

Many institutions are now developing large-scale, complex, coupled multiphysics computational simulations for massively parallel platforms for the simulation of the performance of nuclear weapons and certification of the stockpile, and for research in climate and weather prediction, magnetic and inertial fusion energy, environmental systems, astrophysics, aerodynamic design, combustion, biological and biochemical systems, and other areas. The successful development of these simulations is aided by attention to sound software project management and software engineering. We have developed “lessons learned” from a set of code projects that the Department of Energy National Nuclear Security Agency has sponsored to develop nuclear weapons simulations over the last 50 years. We find that some, but not all, of the software project management and development practices (rather than processes) commonly employed for non-technical software add value to the development of scientific software and we identify those that we judge add value. Another key finding, consistent with general software industry experience, is that the optimal project schedule and resource level are solely determined by the requirements once the requirements are fixed.

The national ignition facility

The National Ignition Facility (NIF) currently under construction at the University of California Lawrence Livermore National Laboratory (LLNL) is a 192-beam, 1.8-Megajoule, 500-Terawatt laser being built by the Department of Energy and the National Nuclear Security Agency (NNSA) for inertial confinement fusion and high-energy-density experimental studies. The stadium-sized facility is currently activating systems for first light and will be completed in 2008.The facility is controlled by the Integrated Computer Control System (ICCS), a layered architecture of 300 front-end processors (FEP) coordinated by supervisor subsystems. The FEP's are distributed computers that interface to physical devices through VME-bus and PCI-bus crates. The functional subsystems - beam control including automatic beam alignment and wavefront correction, laser pulse generation and pre-amplification, diagnostics, pulse power, and shot timing - implement the actions of operators at eight graphic consoles, coordinate control, and display and archive data in a database. The software architecture mimics the hardware design levels: software devices in FEP's model hardware control points and supervisory objects model the line replaceable units that modularize the laser system. Graphic user interfaces are provided to make status and control of each level accessible to operators.The ICCS software is based on an object-oriented framework that incorporates services for archiving, machine configuration, graphical user interface, status monitoring, event logging, scripting, alert management, and access control. Software code development uses a mixed language environment of Ada (for functional controls) and Java (for user interface and database backend). CORBA is used to communicate between languages and processors. Substantial benefits credited to using Ada include the formality of controlled interfaces that rely on Ada's type model, easy-to-construct exception processing and the robustness of Ada's tasks.A strategy of incremental cycles of construction and formal test has been used since project inception. The project has completed more than 30 planned cycles of deployment into testbeds and is now integrating with the first 4 operational beamlines in the facility. Fifty of the planned 300 FEP's have been installed and tested with facility equipment. These implement nearly 200 classes that model physical control hardware - some 2500 software objects. Nearly all of the top-level functional subsystems, embodying some 110 application classes, have been commissioned in the facility. The integrated control system has successfully executed shots into test diagnostics in support of laser integration. The first coordinated facility shots to the 10-m diameter target chamber are expected in early 2003.Issues of robustness and scaling arise as the system integrates larger ensembles of control points and serves an increasing number of operators. The system comprises some 60 intercommunicating processes, and since none of these are known to be defect free, techniques for replacement and restart of individual processes are required. The most common communication pattern - publish and subscribe - is supported by a connection management framework that adds exception handlers to the ORB in order to restore broken connections and restart failed processes without explicit action by application client codes.This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.