Jeffrey W. Griffin

Circularly polarized millimeter-wave imaging for personnel screening

A novel polarimetric millimeter-wave imaging technique has been developed at the Pacific Northwest National Laboratory (PNNL) for concealed weapon detection applications. Wideband millimeter-wave imaging systems developed at PNNL utilize low-power, coherent, millimeter-wave illumination in the 10-100 GHz range to form high-resolution images of personnel. Electromagnetic waves in these frequency ranges easily penetrate most clothing materials and are reflected from the body and any concealed items. Three-dimensional images are formed using computer image reconstruction algorithms developed to mathematically focus the received wavefronts scattered from the target. Circular polarimetric imaging can be employed to obtain additional information from the target. Circularly polarized waves incident on relatively smooth reflecting targets are typically reversed in their rotational handedness, e.g. left-hand circular polarization (LHCP) is reflected to become right-hand circular polarization (RHCP). An incident wave that is reflected twice (or any even number) of times prior to returning to the transceiver, has its handedness preserved. Sharp features such as wires and edges tend to return linear polarization, which can be considered to be a sum of both LHCP and RHCP. These characteristics can be exploited for personnel screening by allowing differentiation of smooth features, such as the body, and sharper features present in many concealed items. Additionally, imaging artifacts due to multipath can be identified and eliminated. Laboratory imaging results have been obtained in the 10-20 GHz frequency range and are presented in this paper.

Damage Assessment Technologies for Prognostics and Proactive Management of Materials Degradation

Abstract The U.S. Nuclear Regulatory Commission has undertaken a program to lay the groundwork for defining proactive actions to manage degradation of materials in light water reactors (LWRs). This proactive management of materials degradation (PMMD) program examines LWR component materials and the degradation phenomena that affect them. Of particular interest is how such phenomena can be monitored and data can be used to predict degradation and prevent component failure. Some forms of degradation, including some modes of stress corrosion cracking, are characterized by a long initiation time followed by a rapid growth phase, and monitoring such long-term degradation will require new nondestructive evaluation methods and measurement procedures. As reactor lifetimes are extended, degradation mechanisms previously considered too long-term to be of consequence (such as concrete and wiring insulation degradation) may become more important. This paper explains the basic principles of PMMD and its relationship to in-service inspection, condition-based maintenance, and advanced diagnostics and prognostics. It then reviews the phases for degradation development and technologies with potential for sensing and monitoring degradation in its early stages.

Materials issues in high temperature ultrasonic transducers for under-sodium viewing

Liquid sodium is used as the coolant in some fast spectrum nuclear reactors. This material is optically opaque. To facilitate operations and maintenance activities, an ultrasonic under-sodium viewing system has been developed. In the USA, the technology was successfully demonstrated in the 1970s and, over the intervening 30+ years, the capability was lost. This paper reports materials challenges encountered in developing both single-element and linear phased-array 2-MHz transducers that must operate at temperatures up to 260°C. The critical issues are fundamentally material selection: the ability of a transducer to be immersed into liquid sodium and function at 260°C, to achieve wetting and transmission of ultrasound into the sodium, and to be able to be removed and re-used.

High temperature ultrasonic transducers for in-service inspection of liquid metal fast reactors

In-service inspection of liquid metal (sodium) fast reactors requires the use of ultrasonic transducers capable of operating at high temperatures (>;200°C), high gamma radiation fields, and the chemically reactive liquid sodium environment. In the early- to mid-1970s, the U.S. Atomic Energy Commission supported development of high-temperature, submersible single-element transducers, used for scanning and under-sodium imaging in the Fast Flux Test Facility and the Clinch River Breeder Reactor. Current work is building on this technology to develop the next generation of high-temperature linear ultrasonic transducer arrays for under-sodium viewing and in-service inspections.

Infrared Fiber Optic Sensors For The Remote Detection Of Hydrocarbons Operating In The 3.3 To 3.36 Micron Region

A novel class of spectrochemical sensors for remote sensing of hydrocarbons is investigated. This class of sensors exploits the excellent near infrared transmission properties of commercial zirconium fluoride optical fibers that have only recently been available. Several different remote spectrochemical sensors are discussed which incorporate these IR transmitting fiber optics; they include a gas absorption cell, a photoacoustic cell, and an inexpensive FT-IR interface to a remote gas analysis cell. Design characteristics and experimental data on sensitivity and linearity are presented. Potential areas of application for the new class of sensors are also discussed.

Fiber Optic Spectrochemical Emission Sensors: A Detector For Chlorinated And Fluorinated Compounds

Prior work on fiber optic spectrochemical emission sensor (FOSES) concepts1,2 has been extended to the design and fabrication of a prototype fiber optic chemical sensor system for chlorinated compounds. The sensor performs analyte dissociation and atomic excitation via a radio-frequency-excited helium plasma. The device has been configured for field measurements of vadose-zone concentrations of carbon tetrachloride on the Hanford Reservation in southeastern Washington state. Detection and quantification of other atomic species may be achieved by varying the analytical wavelength. The sensor system design incorporates an RF excitation source; a metered, sub-atmospheric pressure helium supply system; an optical detection system; and a fiber optic umbilical to transmit analyte emissions to a central detection/data acquisition system. Sensor system design is summarized as well as performance data relating to detection limits and dynamic range.

Radiation Source Replacement Workshop

This report summarizes a Radiation Source Replacement Workshop in Houston Texas on October 27-28, 2010, which provided a forum for industry and researchers to exchange information and to discuss the issues relating to replacement of AmBe, and potentially other isotope sources used in well logging.

Fiber-optic spectrochemical emissions sensor: a detector for volatile chlorinated compounds

Abstract We present a fiber-optic sensor developed to measure volatile chlorine-containing compounds in the gas phase. This unique sensor, called the HaloSnif TM , is based on the atomic emission of chlorine. The HaloSnif sensor uses a critical orifice air inlet (a 50 μm capillary tube) and a radio frequency (r.f.) excited helium plasma to excite the ambient air sample. A fiber-optic cable transmits the chlorine emission intensity to a signal-processing module, where it is optically filtered and amplified. The HaloSnif system consists of a miniaturized probe (∼ 10 cm × 4 cm), fiber-optic cable, r.f. power supply, and a flow-control and signal-processig module. The compact robust system has been successfully field-tested at several waste-remediation sites. The detection limit for trichloroethylene in air is 1 ppm, with over four orders of linear response. Furthermore, HaloSnif is capable of measuring concentrations of any gas-phase chlorine-containing compound.

Relative importance of surface and volume scattering in all-dielectric mirrors

Total integrated scattering techniques are used to study power losses at 633 nm from bare and aluminized dielectric mirrors.(AIP)

DIAGNOSTIC AND PROGNOSTIC TOOLS FOR RESIDUAL LIFE ESTIMATION IN AGING NUCLEAR POWER PLANT COMPONENTS

A central issue in life extension for the current fleet of light water nuclear power reactors (LWR) is the early detection and monitoring of significant materials degradation. To meet this need, nondestructive methods that are suitable for continuous monitoring over extended time periods (months to years) are needed. A related issue is the ability to estimate remaining useful life (RUL) of components and systems based on condition assessment or degradation information. Monitoring for early detection of materials degradation requires novel sensors and enhanced data integration techniques. A range of acoustic and electromagnetic measurement methods may be suitable, including acoustic microscopy, eddy current and magnetic Barkhausen emission. Prognostic methods that predict rate of degradation and remaining life based on phenomena that can be described by linear elastic fracture mechanics have been reported by several researchers. However, the challenge of predicting remaining life starting from earlier phases of degradation is largely unsolved. This paper discusses an assessment of selected diagnostic techniques, and the application of Bayesian prognostic algorithms to detection of early degradation and rate of degradation/life prediction. Such measurement and modeling methods are expected to form the basis for a new range of advanced diagnostic and prognostic approaches for assessing and monitoring life extension of ageing light water reactors.A central issue in life extension for the current fleet of light water nuclear power reactors (LWR) is the early detection and monitoring of significant materials degradation. To meet this need, nondestructive methods that are suitable for continuous monitoring over extended time periods (months to years) are needed. A related issue is the ability to estimate remaining useful life (RUL) of components and systems based on condition assessment or degradation information. Monitoring for early detection of materials degradation requires novel sensors and enhanced data integration techniques. A range of acoustic and electromagnetic measurement methods may be suitable, including acoustic microscopy, eddy current and magnetic Barkhausen emission. Prognostic methods that predict rate of degradation and remaining life based on phenomena that can be described by linear elastic fracture mechanics have been reported by several researchers. However, the challenge of predicting remaining life starting from earlier phas...