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CdAs crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Cd2+ is bonded to four equivalent As2- atoms to form a mixture of edge and corner-sharing CdAs4 tetrahedra. There are a spread of Cd–As bond distances ranging from 2.69–2.99 Å. As2- is bonded in a 5-coordinate geometry to four equivalent Cd2+ and one As2- atom. The As–As bond length is 2.48 Å.
Sr(CdAs)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent As3- atoms to form SrAs6 octahedra that share corners with twelve equivalent CdAs4 tetrahedra, edges with six equivalent SrAs6 octahedra, and edges with six equivalent CdAs4 tetrahedra. All Sr–As bond lengths are 3.21 Å. Cd2+ is bonded to four equivalent As3- atoms to form CdAs4 tetrahedra that share corners with six equivalent SrAs6 octahedra, corners with six equivalent CdAs4 tetrahedra, edges with three equivalent SrAs6 octahedra, and edges with three equivalent CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 17–54°. There are three shorter (2.76 Å) and one longer (2.87 Å) Cd–As bond lengths. As3- is bonded to three equivalent Sr2+ and four equivalent Cd2+ atoms to form a mixture of distorted corner and edge-sharing AsSr3Cd4 pentagonal bipyramids.
Ba(CdAs)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ba2+ is bonded to six equivalent As3- atoms to form BaAs6 octahedra that share corners with twelve equivalent CdAs4 tetrahedra, edges with six equivalent BaAs6 octahedra, and edges with six equivalent CdAs4 tetrahedra. All Ba–As bond lengths are 3.35 Å. Cd2+ is bonded to four equivalent As3- atoms to form CdAs4 tetrahedra that share corners with six equivalent BaAs6 octahedra, corners with six equivalent CdAs4 tetrahedra, edges with three equivalent BaAs6 octahedra, and edges with three equivalent CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–52°. There are three shorter (2.78 Å) and one longer (2.85 Å) Cd–As bond lengths. As3- is bonded to three equivalent Ba2+ and four equivalent Cd2+ atoms to form a mixture of distorted corner and edge-sharing AsBa3Cd4 pentagonal bipyramids.
Eu(CdAs)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent As3- atoms to form EuAs6 octahedra that share corners with twelve equivalent CdAs4 tetrahedra, edges with six equivalent EuAs6 octahedra, and edges with six equivalent CdAs4 tetrahedra. All Eu–As bond lengths are 3.15 Å. Cd2+ is bonded to four equivalent As3- atoms to form CdAs4 tetrahedra that share corners with six equivalent EuAs6 octahedra, corners with six equivalent CdAs4 tetrahedra, edges with three equivalent EuAs6 octahedra, and edges with three equivalent CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 15–56°. There are three shorter (2.75 Å) and one longer (2.86 Å) Cd–As bond lengths. As3- is bonded to three equivalent Eu2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing AsEu3Cd4 pentagonal bipyramids.
Yb(CdAs)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Yb2+ is bonded to six equivalent As3- atoms to form YbAs6 octahedra that share corners with twelve equivalent CdAs4 tetrahedra, edges with six equivalent YbAs6 octahedra, and edges with six equivalent CdAs4 tetrahedra. All Yb–As bond lengths are 3.06 Å. Cd2+ is bonded to four equivalent As3- atoms to form CdAs4 tetrahedra that share corners with six equivalent YbAs6 octahedra, corners with six equivalent CdAs4 tetrahedra, edges with three equivalent YbAs6 octahedra, and edges with three equivalent CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–57°. There are three shorter (2.73 Å) and one longer (2.90 Å) Cd–As bond lengths. As3- is bonded to three equivalent Yb2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing AsYb3Cd4 pentagonal bipyramids.
CaCd2As2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent As3- atoms to form CaAs6 octahedra that share corners with twelve equivalent CdAs4 tetrahedra, edges with six equivalent CaAs6 octahedra, and edges with six equivalent CdAs4 tetrahedra. All Ca–As bond lengths are 3.09 Å. Cd2+ is bonded to four equivalent As3- atoms to form CdAs4 tetrahedra that share corners with six equivalent CaAs6 octahedra, corners with six equivalent CdAs4 tetrahedra, edges with three equivalent CaAs6 octahedra, and edges with three equivalent CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–56°. There are three shorter (2.74 Å) and one longer (2.89 Å) Cd–As bond lengths. As3- is bonded to three equivalent Ca2+ and four equivalent Cd2+ atoms to form a mixture of distorted edge and corner-sharing AsCa3Cd4 pentagonal bipyramids.
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This project investigated the cyber-security impacts of moving from an all analog, point-to-point, instrumentation and control (I&C) system to a digital I&C system based on Modbus and a shared communication medium. A formalism called a hybrid attack graph was expanded to support the nuclear research reactor system. The hybrid attack graph allows one to check a system for vulnerabilities, in this case cyber-security vulnerabilities, and to document the attack vectors (scenarios) causing those vulnerabilities. In parallel, a simulation of the system was developed to model both the physical reactor parameters and operations, as well as the network interconnects and communications. This simulation platform was modeled on the nuclear research reactor located at Washington State University. The simulation platform provided a sandbox to evaluate and quantify the impact of identified and proposed vulnerabilities in the system and to determine the effectiveness of countermeasures at stopping these attacks. The simulation and hybrid attack graph tools were integrated to provide a streamlined process of generating attack scenarios, playing those scenarios out in the simulation, and then analyzing the results to correlate system state to states in the hybrid attack graph. This process was used to (1) quantify the impact of attack scenarios and (2) to determine if the system moved through the hybrid attack graph as anticipated. The hybrid attack graph tool was extended and customized to produce a tool to automatically identify critical assets (CAs) and critical digital assets (CDAs) as defined by NRC Regulatory Guide 5.71. This tool was verified using the nuclear research reactor at Washington State University. Finally, a series of educational modules covering the findings of the different aspects of this research have been created.
Progress of the modern day condensed matter physics is to a large extent driven by the synthesis of new materials, advances in their experimental characterization and theoretical description. Recent discoveries of novel gapless Weyl semimetals, such as NaBi,CdAs, and BiTe-based films, in which magnetic dopants essentially suppress the gap, have added to the family of graphene and topological insulators actively investigated over the past decade. With the field of novel semimetals rapidly maturing, its focus necessarily shifts from demonstrations of the feasibility of such materials to their quantitative characterization. While the transport and optical properties of graphene and topological insulators are well captured within the picture of free non-interacting electrons, gapless 3D Weyl semimetals and narrow-gap 2D semiconductors with Dirac spectrum are known to be extremely susceptible to disorder and electron-electron interactions. This susceptibility obscures the manifestations of nontrivial band structure -- like quantum anomalous Hall effect -- of the new topological materials. Among particular projects to be addressed are: 1) optical conductivity of 3D gapless Dirac fermions in the presence of smooth disorder, 2) interplay of disorder and Coulomb interactions in the spectral properties of such fermions, 3) formation and structure of the impurity band with Coulomb supercritical clusters, 4) Coulomb interaction-driven renormalization of the electron spectrum and of the transport response in the presence of strong magnetic field, 5) instanton approach to the disorder-induced fluctuation states in zero-gap 3D materials, and 6) the role of disorder in quantum anomalous Hall effect. The proposal relies upon the investigators' previous broad expertise in interacting and disordered electron systems. The methods to be employed include perturbative diagrammatic technique, non-perturbative instanton and self-consistent approximations, hydrodynamics of electron liquid. Both analytical as well as numerical approaches are to be employed. The anticipated broader outcome of the proposal includes gaining an in-depth understanding of the interplay of the disorder and interactions under the conditions when this interplay has the most dramatic impact on observables. Traditionally, interaction effects are among the most challenging and interesting problems of condensed matter physics. Similarly, disordered systems typically present very difficult but extremely rich problems in the description of various materials. Importantly, understanding the spectral and transport properties of such materials not only presents the fundamental objective, but is also of particular interest for many applications, such as computation, memory, optics, plasmonics. In particular realization of the quantum anomalous Hall effect may lead to the development of low-power-consumption electronics. Indeed, a major constraint for practical use of the quantum Hall effect is limited by the requirement of the quantizing magnetic field. At the same time, the quantum anomalous Hall effect samples exhibit non-dissipative edge quantum transport in a zero magnetic field.
Operational lifetime extensions of existing research reactors have emphasized the need for refurbishment, replacements, and upgrades to supporting equipment and instrumentation. The Advanced Test Reactor (ATR) at Idaho National Laboratory (INL), which entered service in 1967, has recently completed the sixth core internals change-out and has scheduled operations until at least 2040. Reactor maintenance and operational risk management is critically important in the research reactor community, however supporting measurement systems sometimes get overlooked when maintenance is planned. The Fission Wire Measurement System (FWMS) is a custom measurement system designed in the 1960s to measure the beta-particle activity of irradiated uranium-aluminum fission wires. This measurement is conducted to determine the fission rate profile of the Advanced Reactor Test Critical (ATR-C) facility. The ATR-C is an open-pool, low-power test reactor that was purpose driven to resemble ATR and is used to qualify experiment configurations and verify core models prior to full-power experiment irradiations in ATR. A power distribution measurement in ATR-C uses uranium-aluminum wires that are distributed throughout the ATR-C core to validate simulation and modeling results. These measurements require 340 to 1500 wires to be irradiated and measured within a 12-hour window. The activity of the wires is measured in the required time with the FWMS, which was put into service in 1965 at the Radiation Measurements Laboratory (RML). The system consists of 4 measurement channels and one reference channel, each with a 2-pi proportional gas flow detector and the measurement channels each have an automated sample changer. This legacy system is crucial to the continued operations of ATR and has undergone some minor hardware upgrades since 1965, however the system presently relies on custom control boards, custom gas ion chambers, analog amplifiers/discriminators, and a user interface (UI) for the system written in outdated code. Much of the equipment and software is custom with no commercial replacements or support and limited documentation. The existing control software requires an operating system that is no longer supported, creating more vulnerabilities to continued operations. A project is underway with a third-party vendor to design, build, and document a new control and data acquisition system (CDAS) for the FWMS. The new upgrade will replace the control system, computer, UI, sample changer motors, and main power supply while maintaining the interface with existing detector hardware. The upgraded system will be operated in parallel with the current hardware and software to conduct validation testing. This equipment upgrade demonstrates the commitment at ATR to ensuring successful operations and potential future research reactors at INL.