Gamma-ray Tomography Research Articles

On-Stream Pipe Scale Inspection Using Gamma-Ray Tomography Technique: Field Experiment in Karaha Geothermal Power Plant, Indonesia

Pipe scaling is a common problem in geothermal power plants. Currently, the pipeline withinside the Karaha Telaga Bodas geothermal subject is indicated to incorporate scale because of pressure anomalies. On-stream pipe scale inspection techniques are needed to maintain the production process. This research aims to apply the gamma-ray transmission tomography technique to pipelines in geothermal fields. The gamma-ray tomography system consists of a 137Cs (2.96 GBq) gamma radiation source, a scintillation detector, mechanical parts, control parts, and data acquisition. Scanning was performed at three predetermined points: brine pipe 1, two-phase pipe, and brine pipe 2. The system scans half of the pipe circumference (180°) and divides it into 32 projections (5.625°). Each projection performs a translational scan with a resolution of 4 mm. Three cross-sectional images of the pipe were obtained, showing the inside condition. Pipe scale was observed at three scanning points with a thickness of 12 mm-48 mm. Gamma tomography can potentially be a tool for examining pipe scale thickness in geothermal fields. The use of a single detector is a limitation that needs to be improved. Apart from that, the stability of the control and mechanical parts must also be improved.

Characterization of multiphase flow through Venturi nozzle using gamma-ray tomography

Venturi-based differential pressure flow meters have proven to be robust and well suited to measure the flowrate of multiphase flow in combination with other measurement techniques. However, important challenges remain in order to reduce the effect of flow regime dependent measurement uncertainties from non-homogeneous flow.Understanding the complexities of multiphase flow through a Venturi is critical, not only for the Venturi flow measurement but also for the potential implications it might have on adjacent measurements affected by the constriction-induced flow perturbations.In this study, we examine the evolution of multiphase flow through a vertically oriented Venturi situated downstream of a T-bend, with a particular emphasis on the effects this might have on associated measurements within a multiphase metering context. Using Gamma-ray tomography, we conducted measurements at the inlet, throat, outlet, and downstream of the Venturi across a wide range of flow rates and Gas Volume Fractions (GVFs). We evaluated gas fraction (GF), slip, and cross-sectional distribution, quantified using measures of asymmetry and annularity.Our findings suggest that deviations between GF and GVF, relative slip velocity, annularity, and asymmetry are generally less at the outlet and downstream of the Venturi compared to the inlet and throat. Notably, annularity exhibits a greater impact than asymmetry on the estimation of bulk fractions from cord measurements.Overall, the study suggests that there may be more favorable conditions for measurements that require a homogeneous mix and less difference between GF and GVF at the outlet or a short distance downstream of the Venturi. However, despite the inlet results showing larger deviations due to inhomogeneous flow compared to the outlet and downstream, these results demonstrate a more predictable pattern in line with predictive models, offering potential benefits for the application of corrective models.

Measurement of Local Void Fraction of Air-Water Flow in an 8 × 8 Rod Bundle Using High-Resolution Gamma-Ray Tomography

High-resolution two-phase flow data in the rod bundle are important in the development and validation of high-fidelity models for computational fluid dynamics and subchannel codes, in particular, those pertaining to light water reactor cooling systems. The Michigan Adiabatic Rod Bundle Flow Experiment (MARBLE) has been constructed as a modular assembly of an 8 × 8 lattice rod bundle to simulate scaled pressurized water reactor and boiling water reactor subchannel assemblies. To establish a high-spatial resolution database of the void fraction in the reactor fuel assembly geometries, tomographic measurements were performed with the High-Resolution Gamma-ray Tomography System, which was designed and built in house; the detector system has a spatial resolution of less than 1.0 mm using 240 LYSO (Lu1.8Y0.2SiO5) scintillators with a fan-beam array. In the present study, the local void fraction was measured with the MARBLE facility under various air-water flow conditions (jg = 0.04 to 0.85 m/s and jl = 0.12 to 0.77 m/s) covering from bubbly to cap-turbulent flows. The local void fraction was also successfully measured under nonuniform and asymmetric air bubble distribution conditions with an investigation of the effect of spacer grids and mixing vanes on void drift across subchannels.

Multi-modal tomographic imaging system for poolside characterization of nuclear test fuels: Design considerations and studies

Testing and qualification of advanced nuclear fuels involve an iterative process of prototyping, in-pile irradiation testing, and in/ex situ examination. Fuel restructuring and fission product migration during burnup are among the most important aspects of fuel evolution and affect several important performance characteristics (e.g., heat removal, accident tolerance, and fission product retention). Poolside nondestructive characterization techniques provide fuel developers with tools to understand fuel evolution at different time points of burnup. A design for a compact, submersible, and multi-modal (transmission and emission) gamma-ray tomography system for imaging irradiated nuclear fuel is presented herein. Detector selection, collimator geometry and fabrication, mechanical design, imaging protocol, and acquisition protocol are discussed. Modeling calculations showed that sub-millimeter resolution could be achieved in a matter of hours in both transmission and emission tomography images. Several design compromises and fabrication challenges are discussed to further the development of future submersible gamma-ray tomography instruments.

Accelerated radiation transport modeling techniques for pencil beam computed tomography using gamma rays

Monte Carlo radiation transport modeling studies were performed for a compact, and high-resolution gamma-ray computed tomography system designed for imaging irradiated nuclear fuel. The system comprises a 60Co source – chosen for its highly penetrating 1173 keV and 1332 keV gamma rays – a pair of high-aspect-ratio pencil beam collimators, and an inorganic scintillator detector. Two acceleration methods are proposed to rapidly model a transmission type gamma-ray tomography system. The first, a variance reduction technique, is based on performing Monte Carlo simulations with a monodirectionally-biased source, sampled from a characteristic sub-volume of the full source volume. The second acceleration method is based on the deterministic calculations using the Beer–Lambert law and detector response characteristics. Comparison of simulations using acceleration approaches with analog simulations of the fully isotropic, full-volume equivalent, show that the Monte Carlo variance reduction technique gives quantitatively accurate predictions for large collimator aspect ratios while the deterministic calculations are semi-quantitative but converge close to the correct result as the collimator aspect ratio increases. As such, these techniques can be used to reduce the computational cost in generating simulated radiographs and tomographs by several orders of magnitude. Experimental validation efforts are currently underway and will be demonstrated in future work.

Hydrodynamic force analysis of magnetite medium inside dense medium cyclone using multiphase GPU parallelized ASM model

In order to tackle the high compute cost of the multiphase simulations for dense medium cyclones, the development of an open source high fidelity LES based algebraic slip mixture multiphase flow solver is presented. The solver is parallelized on a general purpose GPU using a full load model, which provides around 13 times speed up as compared to a CPU implementation thereby, making design explorations using the current solver more feasible and less time consuming. The traditional ASM model was improved upon using more realistic slurry viscosity model and polydispersed hindered correlation for dense medium operation. The performance of the developed solver for dense medium cyclone operation was validated with the literature based gamma ray tomography (GRT) experimental results. The solver was then used to study the implication of variation in the key aspects of DMC operation such as pressure head, underflow diameter and feed particle concentration. The medium segregation is explained based on a novel non-dimensional force analysis of the drag, shear lift and turbulent dispersion. Finally, the response of the DMC in terms of hydrodynamic force analysis and density differential with the variation in design and operating variables has discussed. Based on the comprehensive force analysis of the medium a justification is provided as to why a lower pressure head is preferred for DMCs used in mineral processing.

A novel method to improve Electrical Resistance Tomography measurements on slurries containing clays

Electrical Resistance Tomography (ERT) is a robust and proven technique for slurry flow measurements. The presence of surface-active clays in mineral tailings makes it difficult to make accurate solids concentration measurements using ERT. To evaluate ERT performance under such conditions, measurements on pipeline flows of concentrated clay/water/sand mixtures were performed using ERT. Traversing gamma-ray densitometry and Gamma-Ray Tomography (GRT) systems installed on the pipe loop were used as reference instruments. The results showed that ERT performance is sensitive to clay concentration and is more accurate at lower clay and higher coarse solids (sand) concentrations. A concentration correction model based on a modified Archie's law was developed to compensate for the effect of clay on ERT measurements. The implementation of the correction model was found to significantly improve the accuracy of the ERT measurements on slurries containing clays.

Improved scatter correction model for high attenuation gamma-ray tomography measurements

In this study a state-of-the-art gamma-ray tomography (GRT) unit was used to measure the solids concentration distributions of high density, high attenuation clay/water/sand slurries in a 4 in. (100 mm) diameter recirculating pipe loop. The presence of neighbouring radiation sources on the GRT results in a scattered radiation contribution to the total intensity measured at each detector. The scattered radiation decreases the signal-to-noise ratio of the measured radiation intensity and introduces error in the measured tomography data and the reconstructed tomograms (Maad et al 2008 Meas. Sci. Technol. 19 6). Because of the high attenuation of the materials being measured, the scatter contribution was a significant fraction of the total radiation measured at each detector. To correct for the scattered radiation contribution in the measurements, a test campaign was undertaken to characterize and model the scattering behaviour of the GRT at the Saskatchewan Research Council. The scattered radiation was measured experimentally from empty pipe, water filled pipe and a number of flowing clay/water/sand slurries at densities ranging from 1206 kg m−3 to 1580 kg m−3. A semi-empirical scatter correction model has been developed which allows the scattered contribution at each detector to be calculated iteratively based on the measured uncorrected attenuated radiation intensity. This article is an extension of the work presented at the 9th World Congress for Industrial Process Tomography (Spelay et al 2018 Proc. 9th World Congress Industrial Process Tomography p 14).

Performance of the X-ray powder diffraction (XRD), X-ray fluorescence (XRF) and the industrial computed tomography used for characterization of the vesicular volcanic rock.

Volcanic rock is a designation in geology given to extrusive igneous rocks. One type of igneous rock of interest, in economic terms, is vesicular, since, besides the knowledge of the morphology (positioning, size, direction, and interconnectivity of the vesicles) of these structures within the spill, there is also an economic interest regarding the possibility of this rock as a reservoir of fluids (water and hydrocarbons). In this work, samples of vesicular volcanic rock from the Paraná Basin were studied for their characterization, aiming to contribute to the knowledge of this rock proprieties as a reservoir of fluids. The elements present inside the rocks were identified and quantified by X-ray fluorescence and X-ray diffraction. The dimensions of the vesicles and the interconnection between them could be clearly observed in the reconstructed images of the rocks measured by the third generation gamma-ray industrial tomography technique.

Coupling gamma ray spectrometry and tomography in a Bayesian frame

To investigate the possibility to characterize radioactive wastes using available information and measurements in a coherent frame, a Bayesian formalism is built to couple gamma-ray spectrometry and tomographic scans. The gamma ray spectrometry is performed with four High Purity Germanium (HPGe) detectors placed around the waste and scanning 2 cm thick slices of a radioactive waste drum in a Gamma Scanning mode. The tomography provides the density of the drum matrix and identifies heterogeneities. The unknown chemical composition of the matrix and heterogeneities is handled with two parameters that represent the mass fractions of carbon and hydrogen of a fictive {C; Sn; H} material that would show a gamma ray attenuation behavior similar to that of the true material. The approach is tested by simulating the measurement of 239Pu gamma rays produced by a PuO2 sphere placed in a drum slice in which two distinctive zones have been identified by tomography, in presence of 137Cs background. With the studied simulated examples, depending on the sphere position, the use of the density prior information allows decreasing the plutonium mass uncertainty by up to a factor 3 compared to the case when the density prior is not used. In addition, the use of the density prior information provides a posterior plutonium mass distribution having a significant number of event related to the true plutonium mass, which is not the case when the density prior information is not used.

Multimodal Two-Phase Flow Measurement Using Dual Plane ECT and GRT

This work assesses the accuracy of two-phase flow measurement, based on cross correlation (XC) and cross-spectrum (CS) velocity computation, using dual plane nonintrusive electrical capacitance tomography (ECT), over a broad spectrum of horizontal flow configurations, combined with fraction distribution measurements from gamma-ray tomography (GRT). The measurement of two-phase flow encompasses the measurement of both the velocity and the phase concentration of the flow components. The accuracy of the flow velocity is still an open discussion and remains a key challenge in the field of multiphase flow measurement. The velocities of the two-phase components vary, both in between them and across the pipe cross section. This study assesses the use of XC techniques as methods for calculating the cross-sectional velocity distribution by deriving the transit time of the fluid flowing through two parallel ECT sensor arrays mounted on the perimeter of a pipe. The spectral distribution of the velocities is assessed for improved accuracy of individual component velocities. A dual-plane ECT is adopted for the velocity measurements and is combined with state-of-the-art density-based cross-sectional phase fraction distribution from a GRT system to measure the volumetric flow rates of the two phases. The results show that the CS method provides enhanced velocity estimation for both flow phases over the conventional XC technique. Further improvement was reported using a simple predictive correction model resulting in flowrate estimation accuracy of ±10%. The method for two-phase flow measurement suggested in this work leverages the accuracy of the tomography systems on accurate fraction measurement and fast data acquisition to lead to potential enhancement in process control by enabling a more accurate prediction of components velocities.

Comparison of novel imaging sensor and gamma ray tomography imaging of grout deficiencies in external post-tensioned structural tendons

A relatively simple and economical novel NDT method (Tendon Imaging Unit, TIU) for imaging grout anomalies in external post-tensioned structural tendons combines magnetic and impedance measurements. Validation comparison was conducted against a well-established but more resource intensive NDT technology, gamma-ray tomography (GRT), on test tendons with steel strands and grout voids, unhydrated grout, and excess water. GRT could resolve individual strands but TIU still provided viable strand envelope data. Both TIU and GRT detected full voids, outer voids, and unhydrated grout but neither adequately sensed a small inner void. TIU provided only limited detection of a water filled void compared with better GRT identification. Results support TIU deployment for wide range screening inspections that would otherwise be prohibitively costly, reserving advanced techniques like GRT for more focused targets.

Passive gamma emission tomography with ordered subset expectation maximization method

Gamma-ray emission tomography (GET) was developed as a potential verification tool to visualize the passive gamma-ray emitter sources of fuel rods. In GET, maximum likelihood–expectation maximization (MLEM) was employed as an iterative reconstruction method. However, as convergence iteration in the algorithm is proportional to the pixel size, convergence is slow and the calculation cost for practical application is high. Therefore, an ordered subset expectation maximization method (OSEM) was used, and the rod-wise relative gamma-ray emitter distribution of a BWR 10 × 10 mock-up fuel assembly was reconstructed to evaluate the performance of the OSEM. The OSEM enabled reconstruction comparable to that of MLEM with an effective decrease in the number of iterations.

Development of data acquisition and control software for gamma-ray process tomography system

Data acquisition (DAQ) and control software has been developed for gamma-ray process tomography system in Malaysian Nuclear Agency. The gamma-ray computed tomography (CT) system uses Computer Automated Measurement and Control (CAMAC) standard for nuclear counting and data acquisition instead of the common Nuclear Instrumentation Module (NIM) standard. For scanning configuration, the system consists of an array of NaI(Tl) scintillation detectors that moves in a small degree of angle by using a stepper motor. The gamma-ray CT software comprises of graphical user interface (GUI) for the system automation that includes CAMAC modules setup, motor and scanning control, data acquisition from CAMAC crate controller via ethernet interface and data recording. The software is developed by using National Instruments LabView development package.

Fast reconstruction of Bayesian iterative approximation in passive gamma-ray tomography

ABSTRACTMedian root prior expectation maximization (MRPEM) algorithm that belongs to the Bayesian iterative approximation is used in passive gamma emission tomography (GET) to reconstruct passive gamma emitter distribution. The algorithm converges slowly and may involve iterations of 50–200. Fast processing of the algorithm was integrated into MRPEM to accelerate the convergence. Then, the integrated MRPEM reconstructed a passive distribution of gamma emissions within a mock-up boiling water reactor (BWR) assembly. It was found that the reconstructions in GET using the integrated MRPEM could result in a 20% reduction in the mean absolute error (MAE) compared to the standard MRPEM.

A gamma-ray tomography system to determine wax deposition distribution in oil pipelines.

Monitoring wax deposition in pipelines is of particular importance for oil extraction companies. In this work, a new gamma-ray tomography system based on using a rod CsI(Na) scintillator and 137Cs gamma source was developed to view the cross section of oil pipelines. The system can estimate the interaction position of gamma-rays by measuring light attenuation in the rod scintillator using two photomultiplier tubes coupled to its ends. Therefore, despite the simple structure of the employed detector, it can act as a position-sensitive instrument. In order to test the proposed tomography system, a selection of desired polyethylene round-bar pieces (as different wax thicknesses) was prepared to be placed in iron pipes, and their projections at different angles were acquired to construct cross-sectional images as well. The results showed that the designed system had the ability to scan the interior of the pipes and determine wax thickness with an error between 2.4% and 11.4%.

Cross-Sectional Imaging of Tree Stem Density Distribution using Gamma-Ray Tomography Technique

Cavities in the tree stem increase the potential of the tree to collapse and threaten the safety of people. The stem needs to be checked to determine whether the tree is safe or not. The option of tree stem inspection techniques without destructing it is still very limited. Gamma-ray tomography techniques was used to image tree stem density distributions. A collimated 2.96 GBq 137Cs emits gamma photons through the wood phantom as the object and received by the NaI(Tl) scintillation detector on the other side. The object was scanned with the parallel beam method. The data was built into the image using filtered back projection (FBP) algorithm. The results show the cross-sectional of the wood phantom include the cavities (holes) inside it. Density patterns of wood phantom can be observed. Finally, the use of gamma-ray tomography provided a non-destructive and accurate method for investigation of tree stem density distribution. The results in images form make it easier to be interpreted.

Industrial gamma computed tomography using high aspect ratio scintillator detectors (A Geant4 simulation)

Gamma-ray Computed Tomography is an important tool for accessing the internal details of large objects in different industries such as oil, gas, petrochemical, etc. In this paper, a Geant4 study was performed to develop a new approach for this type of tomography by using high aspect ratio scintillators. In this method, a NaI(Tl) rectangular cube scintillator, coupled to a PMT on each side in a coincidence setup, was considered as a position sensitive detector. Different responses of the detector including the scintillation processes in presence of 662 keV gamma-rays of a Cs-137 were simulated. Spectral response, position and energy resolutions were obtained and compared to the experimental data. The comparisons showed a good agreement between the simulation results and experimental data. Furthermore, the detector was simulated in a gamma-ray tomography setup and the related projections and cross sectional images of a standard phantom were obtained. The obtained results showed that the high aspect ratio scintillator detector can be used instead of array detector in industrial applications where there is no need to very high position resolutions.

Integration of phase distribution from gamma-ray tomography technique with monolith reactor scale modeling

In this work, a monolith reactor model was developed to study the effect of phase distribution on the performance of the monolith reactors by integrating phase distribution data from the experiments. To obtain the phase distribution at the reactions conditions, gamma ray computed tomography (CT) was used. Effect of gas density, surface tension of liquid and operating conditions on the phase distribution were studied using gamma-ray computed tomography. Experiments were conducted in Taylor flow regime. With the increase in gas density, uniformity increases. Surface tension has little effect on the distribution in the investigated conditions. Liquid with lower surface tension and gas with lower density has higher cross-sectional liquid saturation. Further, the monolith reactor model with uniform phase distribution and actual distribution were compared. It was found that at higher velocities both gives the same reactor performance irrespective of the maldistribution, however at low velocities, they differ significantly due to the maldistribution. If the maldistribution is present at both low and high velocities, catalyst utilization plays a major role, thus it is recommended to operate at higher velocities where catalyst utilization is high due to high mass transfer.

Advanced process-synchronized computed tomography for the investigation of periodic processes

Computed tomography (CT) is known for giving cross-sectional images of a body. As tomographic scans require mechanical movement of components, data acquisition is commonly too slow to capture dynamic processes, which are faster than the acquisition time for a single image. Time-averaged angle-resolved CT imaging is a more recent method, which has demonstrated a capability to sharply image fast rotating machinery components by synchronizing data acquisition with rotation. However, in this modality, all information on static parts disappears. In this paper, a novel data acquisition approach is introduced that combines both CT imaging methods. Eventually, the developed method is exemplarily applied to the study of gas-liquid flow in an industrial centrifugal pump using high-resolution gamma-ray tomography imaging.