Analysis and design considerations for a real-time system for non-destructive evaluation in the nuclear industry

This paper studies the feasibility of implementing a real-time system for non-destructive evaluation of nuclear reactors based on the principles of synthetic aperture processing. A detailed analysis of the computational requirements and simulation and benchmarking work on several computers seems to suggest the design of a special purpose processor as the most viable solution to the problem. The paper concludes with a discussion of the parameters affecting field design and some preliminary design considerations of the overall system.     

A new ultrasonic technique for the measurement of liquid level

A new design of pulse-echo ultrasonic liquid level gauge is described in which the ultrasonic pulse (here a Rayleigh or a Lamb wave) travels down a metal bar or strip towards the liquid surface, where, through a double mode-conversion process and a special reflecting structure, a strong echo is generated which travels back up the bar to the receiving transducer.The geometry of the special reflecting structure is outlined, and it is shown how this affects the basic accuracy of measurement. Inaccuracies arising from other effects like temperature variation, viscosity and poor signal-to-noise ratio are also discussed. Some mechanical variants, like using the wall of the tank in place of the metal bar carrying the ultrasonic wave and the use of corner reflectors as part of the reflecting structure, are also considered.A note in the Appendix briefly describes one method which has been used successfully for the generation of Rayleigh and Lamb waves.     

An EDXRF method for determination of uranium and thorium in AHWR fuel after dissolution

A fast energy dispersive x‐ray fluorescence (EDXRF) method requiring only microgram amounts of analytes, i.e. uranium (U) and thorium (Th), in their mixtures in solution form is described. Calibration solutions and samples covering the fuel composition range (0–5% of U in U + Th) of advanced heavy water reactor (AHWR) were prepared by mixing uranium and thorium solutions. A known fixed amount of internal standard yttrium (Y) was added to these solutions. EDXRF spectra of calibration solutions and samples were measured by taking 20 µl aliquots on 30 mm diameter filter papers, after drying, using a Rh target tube operated at 40 kV and 500 µA. Calibration plots were made by plotting U/Y, U/Th and Th/Y amount ratios against the respective intensity ratios of Th Lα, U Lα and Y Kα. In the first set, U was determined using Y as an internal standard, and for Th determination, U, thus determined, was used as an internal standard since the amounts of Th and Y were kept constant in the calibration solutions and samples. In the second set, both U and Th were varied and determined using Y as internal standard. The results of U and Th determinations showed a precision of about 3% (1s) and the results deviated from the expected values by <3% in most of the cases. This approach has an advantage that it requires only microgram amounts of sample, thus mitigating radiation hazards associated with radioactive samples as well as the amount of radioactive analytical waste generated is quite less. Copyright © 2009 John Wiley & Sons, Ltd.     

A high-efficient method for generating radially and azimuthally polarized Bessel beams using biaxial crystals

As was shown previously, in propagation of a circularly polarized Bessel light beam along the optical axes of a biaxial crystal, there takes place the conversion of the order of Bessel function. In this paper, a new result is presented which is obtained by varying the polarization state of an input beam. Namely, a linearly polarized beam can be transformed into a beam with the radial or azimuthal polarization state. At that the order-transformation also occurs. The switching between radial and azimuthal polarization states of the output beam is performed by the proper switching between two orthogonal linear polarization states of the input beam. The efficiency of polarization conversion is high and can be practically full at an appropriate choice of the cone angle of the input beam or crystal length.     

A note on the elastic constants of sodium bromate from 350 K to 77 K

The elastic constantsC ₁₁,C ₁₂ andC ₄₄ of sodium bromate single crystals have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC ₁₁=5.57₈,C ₁₂=1.07₅,C ₄₄=1.51₀ (×10¹⁰ N/m²) at 290 K and 6.35, 1.98 and 1.65 (×10¹⁰ N/m²) at 77 K. The present room temperature values agree closely with the recent values of Gluyaset al. but the other earlier measurements show some scatter. A comparison between the elastic constants of sodium bromate and sodium chlorate is also made.     

超声波在液体中相速与群速的测量

简要叙述了相速与群速的定义,并用实验测量了超声波在不同液体中的相速与群速.     

Optical propagation of the HE11 mode and Gaussian beams in hollow circular waveguides

The propagation of the HE₁₁ mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE₁₁ mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength.     

A simple model of ultrasound propagation in a cavitating liquid. Part II: Primary Bjerknes force and bubble structures

In a companion paper, a reduced model for propagation of acoustic waves in a cloud of inertial cavitation bubbles was proposed. The wave attenuation was calculated directly from the energy dissipated by a single bubble, the latter being estimated directly from the fully nonlinear radial dynamics. The use of this model in a mono-dimensional configuration has shown that the attenuation near the vibrating emitter was much higher than predictions obtained from linear theory, and that this strong attenuation creates a large traveling wave contribution, even for closed domain where standing waves are normally expected. In this paper, we show that, owing to the appearance of traveling waves, the primary Bjerknes force near the emitter becomes very large and tends to expel the bubbles up to a stagnation point. Two-dimensional axi-symmetric computations of the acoustic field created by a large area immersed sonotrode are also performed, and the paths of the bubbles in the resulting Bjerknes force field are sketched. Cone bubble structures are recovered and compare reasonably well to reported experimental results. The underlying mechanisms yielding such structures is examined, and it is found that the conical structure is generic and results from the appearance a sound velocity gradient along the transducer area. Finally, a more complex system, similar to an ultrasonic bath, in which the sound field results from the flexural vibrations of a thin plate, is also simulated. The calculated bubble paths reveal the appearance of other commonly observed structures in such configurations, such as streamers and flare structures.     

A hybrid FDTD-Rayleigh integral computational method for the simulation of the ultrasound measurement of proximal femur

The development of novel quantitative ultrasound (QUS) techniques to measure the hip is critically dependent on the possibility to simulate the ultrasound propagation. One specificity of hip QUS is that ultrasounds propagate through a large thickness of soft tissue, which can be modeled by a homogeneous fluid in a first approach. Finite difference time domain (FDTD) algorithms have been widely used to simulate QUS measurements but they are not adapted to simulate ultrasonic propagation over long distances in homogeneous media. In this paper, an hybrid numerical method is presented to simulate hip QUS measurements. A two-dimensional FDTD simulation in the vicinity of the bone is coupled to the semi-analytic calculation of the Rayleigh integral to compute the wave propagation between the probe and the bone. The method is used to simulate a setup dedicated to the measurement of circumferential guided waves in the cortical compartment of the femoral neck. The proposed approach is validated by comparison with a full FDTD simulation and with an experiment on a bone phantom. For a realistic QUS configuration, the computation time is estimated to be sixty times less with the hybrid method than with a full FDTD approach.     

Surface wave propagation in wood: prospective method for the determination of wood off-diagonal terms of stiffness matrix

Overall elastic properties of wood can be studied by ultrasonic methods. Orthotropic symmetry is assumed (nine constants). This article describes two methods developed for the determination of three off-diagonal terms of the stiffness matrix. The first method deals with bulk waves (BAW), and the second with surface wave (SAW) measurements. The BAW method requires repeated off-axis measurements and an optimization criterion for selecting the C_ij-terms. The SAW method gives the value of the C_ij-term corresponding to a specific plane of symmetry, from only one on-axis measurement. The six diagonal terms of the stiffness matrix can be obtained easily from on-axis bulk wave measurements. From the nine terms of the matrix, the compliance terms (S_ij) and corresponding technical terms are calculated. Technical constants determined from ultrasonic measurements are in agreement with those obtained by classical statistical methods. The experiments were performed on beech and spruce. The SAW technique is expected to be of more interest for further investigations of wood mechanical properties.     

Development of yttria-doped thoria solid electrolyte for use in liquid sodium systems

Electrolytic grade yttria-doped thoria (YDT) was synthesized by a novel combustion method. Sintering studies were carried out with polyvinyl alcohol as binder or ZnO as sintering aid to obtain high-density product. The sintering temperature has been optimized as 1,923 K. The results showed that when ZnO was used and sintered at 1,923 K, high-density YDT pellets were obtained, which met the required helium leak rate of the order of ∼10⁻⁹ std. l/s. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006     

一种测量液膜高度的方法

给出一种测量液膜高度的新方法,利用此方法测定液体表面张力系数时发现,计算液膜重量时,液膜厚度不能用金属丝直径代替,否则液体表面张力系数会出现负值。     

A methodology for structural health monitoring with diffuse ultrasonic waves in the presence of temperature variations

Diffuse ultrasonic waves for structural health monitoring offer the advantages of simplicity of signal generation and reception, sensitivity to damage, and large area coverage; however, there are the serious disadvantages of no accepted methodology for analyzing the complex recorded signals and sensitivity to environmental changes such as temperature and surface conditions. Presented here is a methodology for applying diffuse ultrasonic waves to the problem of detecting structural damage in the presence of unmeasured temperature changes. This methodology is based upon the prediction and observation that the first order effect of a temperature change on a diffuse ultrasonic wave is a time dilation or compression. A multi-step procedure is implemented to (1) record a set of baseline waveforms from the undamaged specimen at temperatures spanning the expected operating range, (2) select a waveform from the baseline set whose temperature is the closest to that of a subsequently measured signal, (3) adjust this baseline waveform to best match the signal, and (4) calculate an error parameter between the signal and the adjusted waveform and compare this parameter to a threshold to determine the structural status. This procedure is applied to experimental data from aluminum plate specimens with artificial flaws. Probability of detection and the minimum flaw size detected are presented as a function of the size of the baseline waveform set. It is shown that a probability of detection of over 95% can be achieved with a small number of baseline waveforms.     

New fluorimetric reagents, sodium pyrophosphate, sodium trimetaphosphate, and sodium tetrametaphosphate, for the determination of cerium(III)

Three sensitive and selective new alternatives for fluorometric determination of cerium(III) are described in this study. Ce(III) is highly fluorescent in sodium pyrophosphate, sodium trimetaphosphate, and sodium tetrametaphosphate solutions. For these reagents, the maximum excitation/emission wavelengths are 300/350, 297/340, and 299/352 nm, respectively. Maximum fluorescence intensities are obtained by irradiating Ce(III) dissolved in 0.033 g L⁻¹ sodium pyrophosphate, 41.4 g L⁻¹ sodium trimetaphosphate, and 0.96 g L⁻¹ sodium tetrametaphosphate at room temperature. The fluorescence intensities are linear over the range 0.001–30, 0.001–75, and 0.001–70 μg ml⁻¹. The detection limits are calculated as 9.5 × 10⁻³, 1.1/10⁻³, and 3.8 × 10^-3 μg ml⁻¹ Ce(III), respectively. The relative standard deviations for 15/0.05 Μg ml⁻¹ Ce(III) are 1.1/1.2, 1/1.1, and 1.2/1.3%, respectively. Quenching effects of other lanthanides and some inorganic anions were investigated. The methods have been applied to rare earth mixtures with a good accuracy.     

On algorithms of the Monte-Carlo method for solving problems in the theory of propagation of narrow light beams. I

The characteristic features of the application of the Monte-Carlo method to one class of problems in atmospheric physics are discussed. Using an analysis of one of the programs in the most general form, we establish some characteristic features of the method of simulating radiation transport processes in narrow collimated light beams. An estimate is made of the advantages of semianalytic modifications of the Monte-Carlo method by comparison with direct simulation; and the results of test calculations are presented, confirming the feasibility of such modifications.     

A new method for the determination of surface tension from molecular dynamics simulations applied to liquid droplets

For the determination of surface tension of liquid droplets by molecular dynamics simulations, the most time-consuming part is the calculation of pressure tensor in the transition layer, which makes it difficult to enhance the precision of the computation. A new method for the calculation of surface tension of liquid droplets to reduce the calculation quantity of pressure tensor in transition layer to the minimum is proposed in this paper. Two thousand particles are taken as example to show how to carry out our scheme.     

A feasibility study of the use of bounded beams resembling the shape of evanescent and inhomogeneous waves

Plane waves are solutions of the visco-elastic wave equation. Their wave vector can be real for homogeneous plane waves or complex for inhomogeneous and evanescent plane waves. Although interesting from a theoretical point of view, complex wave vectors normally only emerge naturally when propagation or scattering is studied of sound under the appearance of damping effects. Because of the particular behavior of inhomogeneous and evanescent waves and their estimated efficiency for surface wave generation, bounded beams, experimentally mimicking their infinite counterparts similar to (wide) Gaussian beams imitating infinite harmonic plane waves, are of special interest in this report. The study describes the behavior of bounded inhomogeneous and bounded evanescent waves in terms of amplitude and phase distribution as well as energy flow direction. The outcome is of importance to the applicability of bounded inhomogeneous ultrasonic waves for nondestructive testing.     

A method for determining the location and depth of cracks in double-cracked beams

The influence of two transverse open cracks on the antiresonances of a double cracked cantilever beam is investigated both analytically and experimentally. It is shown that there is a shift in the antiresonances of the cracked beam depending on the location and size of the cracks. These antiresonance changes, complementary with natural frequency changes, can be used as additional information carrier for crack identification in double cracked beams. Experimental results from tests on plexiglas beams damaged at different locations and different magnitudes are found to be in good agreement with theoretical predictions. Based on the results of the present work, an efficient prediction scheme for crack localization and characterization in double cracked beams is proposed.     

Calculations of the reflection and transmission of ultrasound by cracks in steel filled with liquid sodium

The ultrasonic reflection and transmission amplitudes of idealized cracks in steel filled with liquid sodium are calculated as a function of the angle of incidence and crack width for an incident compression wave of frequency 2.25 MHz. It is concluded that it should be no more difficult to detect a liquid-sodium filled crack than an air filled crack for widths greater than 0.01 mm, which is typical of fatigue crack widths.