Real-time Neutron Radiography Research Articles

Electrolyte layer gas triggers cathode potential instability in CO2 electrolyzers

Electrolytic carbon dioxide (CO2) reduction is becoming increasingly promising for managing anthropogenic CO2 emissions; however, issues related to unstable performance and ineffective gas management are still not fully accounted for in the field. Here, we identify two instability modes that are directly linked to the electrolyte layer gas saturation for an anion exchange membrane CO2 reduction flow cell circulating a neutral pH electrolyte (KHCO3). The cathode potential exhibits a semi-stable mode with low electrolyte layer gas saturations and a detrimental secondary mode with high gas saturations and a highly noisy, non-stationary potential. We illustrate that the gas saturation has a profound, direct impact on the mode of instability with a direct correlation between the coefficient of variation in cathode potential and the electrolyte layer gas saturation measured with real-time neutron radiography. This correlation is indicative of reaction site gas blockage that results in performance instability and reduced energy efficiency.

Determination of moisture distributions in porous building bricks by neutron radiography

Water transport into construction building materials is an important subject since it may deteriorate them because it can carry harmful biological and chemical substances. Some of the reported results in literature for moisture transport in construction building materials follow Fick's law of diffusion while others show anomalous diffusion. There is not enough reliable and accurate data in the literature to discuss this issue. Therefore, in the present work moisture transport into four different kinds of brick samples was studied using the real time neutron radiography method. Neutron radiography images were registered continuously during the moisture absorption process. Simple procedures based on the Cd-umbrella method were used for the first time to correct for the neutron scattering during the water absorption process. The images showed clearly that the absorption process is different from one sample to another. The water content distribution along the flow direction, x (profiles) and positions of water front as the time of moisture absorption elapses were determined from the images obtained. The results obtained showed that the water front positions do not scale with the square root of the absorption time. It was shown that moisture diffusion processes in the samples investigated could be described by an anomalous diffusion approach of the sub-diffusive type. The moisture diffusivities were determined for every sample. The neutron radiography method and the neutron scattering correction procedures used are proven to be a powerful and effective for studying transport process in porous media.

Estimation of volumetric water content during imbibition in porous building material using real time neutron radiography and artificial neural network

Abstract Movement of fluids through porous media is of great significance in different sciences such as civil engineering and chemical technology. When a fluid is introduced to a porous media, the fluid starts moving and diffusing through that. In this condition, the amount of fluid in each position of the porous material is a function of the distance between the desired position and the fluid movement starting point as well as the elapsed time. In this research, a novel methodology is proposed for estimating the volumetric water content in different times and positions during the water imbibition inside the porous building materials using a combination of real time neutron radiography technique and artificial neural network (ANN). For this purpose, a brick as a porous construction sample was positioned in contact with a water container and 145 neutron radiographs were recorded during the water imbibition inside the brick. To extract the required data for training, testing and validating the ANN, a line of pixels in the center of brick’s image along with the water movement direction inside the sample was considered. The calculated volumetric water content in each position of the mentioned line was used as the output of the ANN. In addition, the elapsed time and position were utilized as the two inputs of the ANN. After training, the proposed ANN model could estimate the volumetric water content in different times and positions in direction of water movement inside the brick with a mean square error (MSE) of less than 8.4 × 10−4.

Flow visualization of heavy oil in a packed bed using real-time neutron radiography

Neutron radiography can visualize heavy oil flows in metallic reactors used to upgrade heavy oils. Thus, we visualized heavy oil flows in a packed bed using real-time neutron radiography to support its capability and to offer basic experimental data necessary for verification and validation of numerical simulations. Atmospheric residue was used as the heavy oil sample and heavy oil and N2 gas were concurrently supplied into a packed bed from above a reactor simulating a trickle bed reactor. Reactor temperatures were set at either 100°C or 250°C to change heavy oil viscosity. The heavy oil flow rate was kept constant at 2.5 mL/min and the N2 gas flow rate was set at either 1 L/min or 3 L/min at 25°C. A series of neutron radiography experiments was conducted at the B-4 neutron imaging facility in the Kyoto University Research Reactor (KUR) with a thermal neutron flux of 5 × 107 n/cm2⋅s. We performed image processing for the neutron radiographs to calculate neutron beam attenuation and clarify flow behavior. Visualization results show differences in flow behavior depending on operating factors. Temperature had a particularly substantial effect on flow behavior because heavy oil viscosity depends strongly on temperature. The flows also showed different behaviors for 1 mm and 3 mm packed particle sizes because the void ratios in the packed bed, which were preliminarily observed by X-ray computational tomography (CT), change with particle size. Channeling flow was observed with 3 mm particles and a temperature of 250°C. Furthermore, this work suggests that neutron radiography can be used to investigate heavy oil flows in metallic reactors.

Visualization of Crust in Metallic Piping Through Real-Time Neutron Radiography Obtained with Low Intensity Thermal Neutron Flux

Abstract The presence of crust on the inner walls of metallic ducts impairs transportation because crust completely or partially hinders the passage of fluid to the processing unit and causes damage to equipment connected to the production line. Its localization is crucial. With the development of the electronic imaging system installed at the Argonauta/Nuclear Engineering Institute (IEN)/National Nuclear Energy Commission (CNEN) reactor, it became possible to visualize crust in the interior of metallic piping of small diameter using real-time neutron radiography images obtained with a low neutron flux. The obtained images showed the resistance offered by crust on the passage of water inside the pipe. No discrepancy of the flow profile at the bottom of the pipe, before the crust region, was registered. However, after the passage of liquid through the pipe, images of the disturbances of the flow were clear and discrepancies in the flow profile were steep. This shows that this technique added the assembled apparatus was efficient for the visualization of the crust and of the two-phase flows.

Ex Situ and In Situ Neutron Imaging of Enzymatic Electrochemical Cells

Neutron imaging provides a route for studying the effect of environmental conditions on enzymatic electrochemical cell (EEC) performance. Here, the application of 2D and 3D neutron imaging is demonstrated as a means to investigate effects of environmental conditions on EEC performance. Changes in aqueous solutions that are vital to the operation of EECs have been directly observed in real time using neutron radiography (NR). These changes include uptake of aqueous solutions in electrode materials and in situ observation of water content during operation. The EEC structure has also been observed using ex situ neutron tomography. Initially samples constructed to simulate EEC geometry were imaged, and aqueous buffer solution uptake behavior was observed in carbon paper cell components. In follow-on studies neutron tomography was used to map regions of enzyme catalyst inks, defining active regions within the EEC electrode. The higher neutron attenuation of polymeric ink components enables this observation. Finally, in situ imaging of a prototype EEC pouch cell was performed using a standard chronoamperometry arrangement while performing real time neutron radiography. Neutron radiographs acquired during operation show a clear variation in transmission behavior, primarily due to drying. Together these studies demonstrate the applicability and attendant challenges of neutron imaging for the study of EEC performance and reliability.

A Review of Significant Advances in Neutron Imaging from Conception to the Present

Abstract This review summarizes the history of neutron imaging with a focus on the significant events and technical advancements in neutron imaging methods, from the first radiograph to more recent imaging methods. A timeline is presented to illustrate the key accomplishments that advanced the neutron imaging technique. Only three years after the discovery of the neutron by English physicist James Chadwick in 1932, neutron imaging began with the work of Hartmut Kallmann and Ernst Kuhn in Berlin, Germany, from 1935-1944. Kallmann and Kuhn were awarded a joint US Patent issued in January 1940. Little progress was made until the mid-1950's when Thewlis utilized a neutron beam from the BEPO reactor at Harwell, marking the beginning of the application of neutron imaging to practical applications. As the film method was improved, imaging moved from a qualitative to a quantitative technique, with applications in industry and in nuclear fuels. Standards were developed to aid in the quantification of the neutron images and the facility's capabilities. The introduction of dynamic neutron imaging (initially called real-time neutron radiography and neutron television) in the late 1970's opened the door to new opportunities and new challenges. As the electronic imaging matured, the introduction of the CCD imaging devices and solid-state light intensifiers helped address some of these challenges. Development of improved imaging devices for the medical community has had a major impact on neutron imaging. Additionally, amorphous silicon sensors provided improvements in temporal resolution, while providing a reasonably large imaging area. The development of new neutron imaging sensors and the development of new neutron imaging techniques in the past decade has advanced the technique's ability to provide insight and understanding of problems that other non-destructive techniques could not provide. This rapid increase in capability and application would not have been possible without the advances in computer processing speed and increased memory storage. For example, images with enhanced contrast are created by using the reflection, refraction, diffraction and ultra small angle scattering interactions. It is somewhat ironic that, like the first development of neutron images, the technique remains limited by the availability of high-intensity neutron sources, both in the facility cost and portability.

Design of Real-time Neutron Radiography at China Advanced Research Reactor

Abstract A real-time detector system for neutron radiography based on CMOS camera has been designed for the thermal neutron imaging facility under construction at China Advanced Research Reactor (CARR). This system is equipped with a new scientific CMOS camera with 5.5 million pixels and speed up to 100 fps at full frame. The readout noise is below 2.4 e/pixel. It is capable of providing images with much higher resolution and sensitivity at high frame rate. With optimized optical design and custom-built lens, the capture of quantitative information may be greatly enhanced. The maximum photon received by detector is calculated to be 2.1 × 10 3 /pixel, while the camera resolution is 0.2 mm at 30 fps according to the expected flux (5 × 10 7 n/cm 2 /s) at the sample position.

GEANT4 used for neutron beam design of a neutron imaging facility at TRIGA reactor in Morocco

Neutron imaging has a broad scope of applications and has played a pivotal role in visualizing and quantifying hydrogenous masses in metallic matrices. The field continues to expand into new applications with the installation of new neutron imaging facilities. In this scope, a neutron imaging facility for computed tomography and real-time neutron radiography is currently being developed around 2.0MW TRIGA MARK-II reactor at Maamora Nuclear Research Center in Morocco (Reuscher et al., 1990 [1]; de Menezes et al., 2003 [2]; Deinert et al., 2005 [3]). The neutron imaging facility consists of neutron collimator, real-time neutron imaging system and imaging process systems. In order to reduce the gamma-ray content in the neutron beam, the tangential channel was selected. For power of 250 kW, the corresponding thermal neutron flux measured at the inlet of the tangential channel is around 3×1011 ncm2/s. This facility will be based on a conical neutron collimator with two circular diaphragms with diameters of 4 and 2 cm corresponding to L/D-ratio of 165 and 325, respectively. These diaphragms' sizes allow reaching a compromise between good flux and efficient L/D-ratio. Convergent–divergent collimator geometry has been adopted. The beam line consists of a gamma filter, fast neutrons filter, neutron moderator, neutron and gamma shutters, biological shielding around the collimator and several stages of neutron collimator. Monte Carlo calculations by a fully 3D numerical code GEANT4 were used to design the neutron beam line (http://www.info.cern.ch/asd/geant4/geant4.html [4]). To enhance the neutron thermal beam in terms of quality, several materials, mainly bismuth (Bi) and sapphire (Al2O3) were examined as gamma and neutron filters respectively. The GEANT4 simulations showed that the gamma and epithermal and fast neutron could be filtered using the bismuth (Bi) and sapphire (Al2O3) filters, respectively. To get a good cadmium ratio, GEANT 4 simulations were used to define the design of the moderator in the inlet of the radiation channel. A graphite block of 22 cm thickness seems to be the optimal neutron moderator. The results showed that the combination of 5 cm of bismuth with 5 cm of sapphire permits the filtration of gamma-rays, epithermal neutrons as well as fast neutrons in a considerable way without affecting the neutron thermal flux.

Electronic imaging system for neutron radiography at a low power research reactor

This paper describes an electronic imaging system for producing real time neutron radiography from a low power research reactor, which will allow inspections of samples with high efficiency, in terms of measuring time and result analysis. This system has been implanted because of its potential use in various scientific and industrial areas where neutron radiography with photographic film could not be applied. This real time system is installed in neutron radiography facility of Argonauta nuclear research reactor, at the Instituto de Engenharia Nuclear of the Comissão Nacional de Energia Nuclear, in Brazil. It is adequate to perform real time neutron radiography of static and dynamic events of samples.

Detection of drugs and explosives using neutron computerized tomography and artificial intelligence techniques

In this study the development of a methodology to detect illicit drugs and plastic explosives is described with the objective of being applied in the realm of public security. For this end, non-destructive assay with neutrons was used and the technique applied was the real time neutron radiography together with computerized tomography. The system is endowed with automatic responses based upon the application of an artificial intelligence technique. In previous tests using real samples, the system proved capable of identifying 97% of the inspected materials.

Nondestructive Evaluation of Multiply Connected Electrical Arc Furnace Graphite Rod Electrodes

The low quality of graphite electrodes in a small electrical arc furnace causes many problems on furnace operation. High temperature and erosion at the remote electrode tip, and defects in the electrode increase the probability of electrode failure due to ageing phenomena such as thermal stress cracking. Most measurement techniques cannot determine the electrode quality under such conditions as the high temperature is highly destructive to the device. Nondestructive sensing techniques such as ultrasonics can possibly be used. Experimental studies on the feasibility of using mechanically connected and chemically bonded graphite rod electrodes as a sensing medium for an ultrasonic signal are performed. Graphite rod porosity and defects are inspected using ultrasonic, infrared, and Real-Time Neutron Radiography nondestructive inspection techniques. The acoustic characteristics of the graphite rods are determined, and the soundwave velocity of the graphite rods is measured to be 2529.4 m/s. Ultrasonic frequencies from 60.0 kHz to 10.0 MHz are studied. The optimum ultrasonic frequency for propagation through graphite rods, hence quality inspection, are 500.0 kHz and 1.0 MHz. The effect of electrode length and the number of mechanical joints on the operating ultrasonic frequency are discussed in detail.

Neutron radiography determination of water diffusivity in fired clay brick

The real time neutron and gamma radiography station at Maria reactor, Institute of Atomic Energy, Świerk, Poland, was used to investigate the isothermal water absorption into fired clay brick samples. The investigated brick is different from the bricks reported in El Abd and Milczarek [2004. Neutron radiology study of water absorption in porous building materials: anomalous diffusing analysis. J. Phys. D: Appl. Phys. 37, 2305–2313] in density and chemical composition. Neutron radiography images were acquired regularly as the absorption time elapses. The water content, θ, along the flow direction, x, namely the water profiles θ( x, t) and the water front position as a function of the absorption time, t, were extracted from neutron radiography images. The results were discussed in terms of the macroscopic theory of water infiltration in unsaturated porous media. It was shown that the water front position followed the t -scaling ( x m = ϕ m t ) and the profiles ( θ−ϕ) converged to a universal one master curve. The water diffusivity was analytically determined from the experimental results. It has the so-called hypo-diffusive character, namely its gradient with respect to the water content is positive. Neutron radiography is a powerful method to distinguish among the unsaturated flow in different porous construction materials.

Finned Fuel Element Two-Phase Flow Parameter Measurements Using Real-Time Neutron Radiography

The measurement of two-phase flow parameters for development of constitutive relationships for the HANARO/MAPLE type finned fuel using Real-Time Neutron Radiography (RTNR) is discussed in this paper. A single element finned Fuel Element Simulator (FES) was used with Freon 134a as the working fluid. To observe the effect of a spacer device on void distribution, single pin tests were performed with and without a spacer present. By analyzing the RTNR images using image processing, the effects of the spacer on the time-averaged and instantaneous void fraction distribution were studied. For the experimental results without a spacer, the time-averaged local void distribution is radially asymmetric and the degree of void fluctuation increases with a decreasing frequency along the heated channel, where the observed asymmetry may be caused by flow induced vibration. For the experimental results with a spacer, the spacer clearly limits any significant vibration and the local void distribution becomes more symmetrical. The spacer however does generate an axial void fraction maximum at the upstream of the spacer with a small depletion zone at the exit of the spacer. By analysis of the instantaneous local void distribution, void fluctuation at the heated wall due to boiling was clearly observed. Also, the agglomeration and breakup of the cold-wall void was evident. The dynamic effects of the local void transients will be discussed in detail.

Applications for real-time neutron radiography for convection driven flow pattern transition studies

Thermal hydraulics design of nuclear reactors require extensive studies on two-phase flow pattern. In particular, for reactors using convection driven flow, such as advanced heavy water reactor being designed by the Bhabha Atomic Research Centre (BARC), Bombay, India, very little data exists on flow pattern behavior. Also such reactors using natural circulation face the problem of flow pattern instabilities due to various reasons and no data exists for such instabilities. We have used real-time neutron radiography methods in order to study flow pattern instability and develop thermal hydraulics model for such a reactor. A real time neutron imaging system has been developed for the visualization and measurement of void fraction inside metallic pipes. The system has been installed at the APSARA Reactor, BARC, Bombay, India. Experiments have been conducted on subsystems (SS) test sections of different diameters at pressure ranging from 1 to 40 bar and at various power levels. We report in this paper on the method and components used for this imaging system and some preliminary results of these experiments on void fraction measurement using this system.

Performance and calibration of a neutron image intensifier tube based real-time radiography system

Image calibration is central to extending the capabilities of neutron radiography beyond mere visualization. However, the effects of scattered neutrons and variations in background image intensity adversely affect quantitative radiography. We describe the calibration of a real-time neutron radiography system that limits these effects and which is applicable to systems with variable digitizer gain and offset. A neutron image intensifier tube coupled to a vidicon camera with a capture rate of 30 frames/s was used. The system could account for 10 ml of water entering the field of view to within 2% and could measure the variation in thickness of a graphite wedge to within 2.3%. The spatial resolution was 450 /spl mu/m for a field of view of 410 cm/sup 2/. The image persistence half life was /spl sim/0.3 s and the system was functional for quantitative radiography with neutron fluxes above /spl sim/5*10/sup 5/n/cm/sup 2//s.

Measurement of fluid contents and wetting front profiles by real-time neutron radiography

Few methods exist for measuring rapidly changing fluid contents at the pore scale that simultaneously allow whole flow field visualization. We present a method for using real-time neutron radiography to measure rapidly changing moisture profiles in porous media. The imaging technique monitors the attenuation of a thermal neutron beam as it traverses a flow field and provides measurements every 30 ms with an image area >410 cm 2 and a spatial resolution ∼0.05 cm. The technique is illustrated by measuring the variation in moisture content across a wetting front moving at constant velocity through SiO 2 sand. The relative contributions of the hydraulic conductivity and diffusivity terms in Richards' equation to the total fluid flux within the wetting front region were also measured. The diffusivity was found to rise from zero to a peak value within the wetting front region before falling off while the conductivity was found to rise monotonically. The reliability of the technique was checked via mass balance.

Real-time neutron radiography at the IEA-R1m nuclear research reactor

A LIXI(Light Intensifier X-ray Image) device has been employed in a real-time neutron radiography system. The LIXI is coupled to a video camera and the real-time images can be observed in a TV monitor, and processed in a computer. In order to get the real-time system operational, the neutron radiography facility installed at the IEA-R1m nuclear research reactor of the IPEN-CNEN/SP has been optimized. The most important improvements were the neutron/gamma ratio, the effective energy of the neutron beam, decrease of the scattered radiation at the irradiation position, and the additional shielding of the video camera. Several one-frame as well as computer processed images are presented. The overall Modulation Transfer Function for the real-time system was obtained from the resolution parameter p = 0:44 ± 0:04mm; the system sensitivity, evaluated for a Perspex step wedge, was determined and the average value is 0:70 ± 0:09mm.

A rapidly pulsed triga reactor for neutron radiography

Many TRIGAR reactors are used as the source of thermal neutrons for neutron radiography. The majority of these applications involve steady state operation of the reactor which provides sufficient fluence for radiographic plates or real-time imaging. Many real-time applications would benefit from substantially increased fluences in a single frame (1/30 sec) or in a few frames if the number is limited by motion of the NR target. A pulsed TRIGA reactor can be useful in such cases. The low repetition rate for the standard pulsed TRIGA reactor (∽6/hour) has seriously limited this application. owever, the modern control rod drives and related digital instrumentation have made it possible to produce 60MW pulses at the rate of 1 at least every 5 to 6 seconds (∽10/ min or at least 100 times more frequent). The increased fluence in each of such pulses provides the capability to use electronic imaging with substantially increased resolution and signal-to-noise in a single frame. As an example. a 250kw steady state TRIGA reactor with L/D= 100 can provide a NR fiuence of about 1.8 x 109 n/cm2 in 3 minutes i.e., with 45000 kw sec). A single frame of an electronic imaging system receives a fiuence from the same reactor corresponding to about 8.3 kw-sec, A TRIGA reactor pulsed every 6 seconds to 60MW will give a fluence in a single pulse corresponding to about 1800kw sec. This will allow a single frame to receive the fluence corresponding to the integration of more than 200 frames from the referenced steady state operation but without the electronic noise that accompanies extended frame integration. At least two areas of improved neutron radiography can result from use of the proposed rapidly pulsed TRIGA reactor. Not only would there be significant improvements in spatial and temporal resolution for radioscopy of moving NR objects but real-time cold neutron radiography would become more easily achievable.

Present Status on the Development of a High-Frame-Rate Neutron Radiography System in Jrr-3M

Because of the limitation on the temporal resolution, standard real-time (30 frames/s) neutron radiography systems can not be used for observation of rapid transient phenomena. To overcome this limitation, a high-frame-rate neutron radiography system which enables imaging over 1000 frames/s has been developed and made available in the thermal neutron radiography facility in the JRR-3M. This system consists of a fluorescent converter, two quartz-glass mirrors, a lens, an image intensifier and a high speed digital video camera. In addition, seeking for higher temporal resolution, fluorescent converters are being developed and scintillation decay characteristics partially examined by the ultra-violet exposure test.