This allows neutron radiography to be effectively utilized for the study of even small quantities of hydrogen ingress in the cladding, which is an important mechanism for cladding embrittlement, as depicted in Figure Furthermore, through proper characterization and with the aid of digital radiographs, Nrad allows for the investigation of the absolute hydrogen content and its distribution. Nrad-studies are the only way to investigate and understand the phenomenon of hydrogen ingress in the Zr TM cladding. Additionally, it was found that rapid hydrogen absorption takes place in the absence of the oxide layer covering the metallic surface of the Zr TM cladding Grosse et al.
Figure 16 displays the results of in-situ Nrad investigations of hydrogen uptake during steam oxidation with the time dependence of hydrogen concentration of Zr TM -4 materials at K and higher, where a very rapid hydrogen uptake was found in the first couple of seconds after the steam flow was switched on. At temperatures of about K a phase transformation occurs and is accompanied by a volume change and the formation of a pronounced crack structure. When the cracks are formed, the hydrogen uptake increases by nearly an order of magnitude Grosse et al.
Pebble bed modular reactor PBMR fuel. Figure 17 shows the composition of a 60 mm outer diameter high-temperature reactor HTR fuel pebble consisting of thousands of 0. The pebble was analysed using X-ray tomography technique prior to irradiation at the. The aim of the investigation was to observe the homogeneity of the TRISO particles within the carbon matrix and to direct the manufacturing process to ensure the centralization of the fuel within the carbon matrix Necsa, Figure 18 shows the misalignment of the fuel within the carbon matrix of the fuel pebble as well as the location and identification of a TRISO particle within the fuel-free zone.
The inhomogeneous distribution of the TRISO particles at the top of the fuel pebble can be clearly seen. Three-dimensional quantitative data of the misalignment of the fuel particles becomes available in the tomograms and is presented in Figure 19 , showing the extent of correction in X-, Y- and Z-directions to be introduced in the manufacturing process of the fuel pebble. A sphere-type fuel element from the high-temperature reactor HTR programme was studied with neutron tomography. This sample is 6 cm in diameter and contains about individual fuel pebbles diameter 0.
No shielding of the fresh fuel element was necessary for the tomographic inspection. The investigation was aimed at the visualization of the 3D distribution of the fuel particles in the graphite matrix in order to determine its uniformity and the fuel sphere's content of fissile material.
Each layer performs specific functions. The fuel kernel, consisting of uranium or uranium carbide, provides the fissile material and retains some of the fission products. The buffer layer, a highly porous carbon structure, provides some free volume for gaseous fission products, and protects the SiC layer from damage by high-energy fission products.
The IPyC layer provides structural support for the subsequent SiC layer and prevents the chlorine compounds required for SiC deposition interacting with the fuel kernel. The SiC layer forms the main diffusion barrier for fission products.
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It acts as a pressure vessel, providing mechanical strength for the particle during manufacture of the nuclear fuel compact or pebble bed. Lowe et al. An understanding of the thermal performance and mechanical properties of TRISO fuel requires a detailed knowledge of pore sizes, their distribution, and interconnectivity. Direct comparison with SEM sections indicates that destructive sectioning can introduce significant levels of coarse damage, especially in the pyrolytic carbon layers.
Since it is non-destructive, multi-scale time-lapse X-ray CT opens the possibility of intermittently tracking the degradation of TRISO structure under thermal cycles or radiation conditions in order to validate models of degradation such as kernel movement. X-ray CT in situ experimentation on TRISO particles under load and temperature could also be used to understand the internal changes that occur in the particles under accident conditions. Research reactor control rod verification.
Nrad is being applied as a verification and analytic technique at the SAFARI-1 nuclear research reactor on the control rods. The quality control assurance test entails the verification of the neutron attenuation cross-section of the control rod against a standard consisting of Cd.
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The inspection entails a visual clarification of the attenuation of the thermal neutrons by inspection of the neutron radiograph of the control rod. Additionally, due to the digital radiography capability of the neutron camera detection system, the first-order neutron transmission calculation can be made using the pixel greyscale values on the radiographs of both the standard and control rod sample.
Pixel greyscale values represent a linear relationship in the neutron attenuation of materials. Neutron radiographs of the Cd standard and a control rod are depicted in Figure Radioactive waste. Low- and intermediate-level nuclear waste is normally encapsulated in in some form of barrier to protect the waste from the environment and vice versa. Intermediate-level nuclear waste is firstly encapsulated in a steel drum, compressed, and finally embedded normally in a concrete drum and safely stored underground in a remote location such as Vaalputs in the Karoo region in South Africa Necsa, n.
A site is normally chosen with low rainfall and suitable surface and groundwater conditions. Concrete is a porous medium and the characterization of transport of water through concrete structures is well described by De Beer, Strydom and Griesel and De Beer, Le Roux and Kearsley It is especially important to understand the transport of water through concrete because nearly all concrete structures contain steel reinforcing, and in the case of nuclear waste, intermediate-level nuclear waste in compressed steel drums.
When cracks in the concrete, caused by the transport of liquid through it, reach the reinforcing, an environment conductive to the corrosion of steel is created. Corrosion affects the strength of the structural members, as the steel is a major contributor to the tensile and compressive strength of the members. Severe leakage of radioactive materials into the surrounding environment is thus possible if the integrity of the concrete barrier is compromised. Neutron radiography studies of concrete and mortars enable the direct physical visualization and quantitative detection of water inside concrete structures.
The physical properties of concrete such as porosity, permeability, and sorping characteristics are obtained through applying neutron radiography as a non-destructive analytic tool. The aim of these investigations is to maximize the properties to prevent water sorption and leaching of concrete structures and optimize one of the physical properties which is sometimes neglected in the criteria to develop structures for nuclear waste encapsulation De Beer, Strydom and Griesel, ; De Beer, Le Roux and Kearsley, To improve the durability of concrete, the capillary and pore size within the concrete matrix must be restricted to a minimum.
The visualization of the sorption of water by means of neutron tomography of a laboratory-size concrete structure is depicted in Figure X-ray and neutron radiography in two or three dimensions play an important role in many dedicated areas within the nuclear fuel cycle. The advantage of these methods is their completely non-destructive nature. Visualization of the structure of samples, as well as quantitative description, are important aspects in materials research. X-rays and neutrons are produced by very different methods, and also interact with materials in different manners.
In the nuclear environment, each type of radiation has its own field of utilization due to their different characteristics, but in some instances their applications complement each other to reveal comprehensive information.
Neutron transmission analysis is a very helpful tool to obtain information on the properties of, and changes in, nuclear fuel material. Scientists and researchers in the geosciences in South Africa have, in the availability of the tomography facilities at Necsa, the capabilities to conduct quantitative analytical measurements at state-of-the-art radiation imaging facilities that compare to similar facilities elsewhere in the world.
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Within the mining area, 3D computer tomography shows potential for further development, and can be already used to complement and add value to current conventional 2D mineralogical techniques. Neutron radiography analysis is able to derive the hydrogen content in fuel cladding both qualitatively and quantitatively, with high sensitivity and precision. The results presented here illustrate how recent advances in laboratory-based X-ray CT instruments allow the examination of TRISO particles at the nano- and micro-scales in 3D.
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In this case study, high-resolution X-ray CT has been shown to be a viable tool for profiling the TRISO particles in two important aspects; to characterize the individual TRISO layers with variations in thickness and their subsequent interactions, thus allowing manufacturing validation as well as assisting in working towards a mechanistic understanding of fabrication and in-service issues. The availability of these techniques in South Africa opens new possibilities for research, quantitative analysis, and nondestructive evaluation.
National capacity as well as international trends shows the ability for non-destructive testing of nuclear materials utilizing penetrating X- ray- and neutron radiation in more comprehensive and unique ways than before. African NTD Centre. Oxford University Press. Chetty, D. The use of 3D X-ray computed tomography for gold location in exploration drill cores. Role of NDT in condition based maintenance of nuclear power plant components. Neutron, X-ray and dual gamma-ray radiography and tomography of geomaterial - a South African perspective.
Leading Edge, June Special Edition Africa. De Beer, F. Neutron radiography of porous rocks and iron ore.
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Applied Radiation and Isotopes, vol. The drying process of concrete: a neutron radiography study. Testing the durability of concrete with neutron radiography. Domanus, J. Practical Neutron Radiography. Kluwer Academic Publishers. Frajtag, P. Not dated. Ghosh, J.
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Monitoring plutonium enrichment in mixed-oxide fuel pellets inside sealed nuclear fuel pins by neutron radiography. NDT International, vol. DOI: Neutron radiography-a powerful tool for fast, quantitative and non- destructive determination of the hydrogen concentration and distribution in zirconium alloys. Grosse, M. Nuclear Instruments and Methods in Physics Research, vol. Kinetics of hydrogen absorption and release in zirconium alloys during steam oxidation.
In addition, the mechanism of release and impact on the atmosphere of elements such as Se, As, Sb, Cd, In, and Pb was investigated.
Areas of atmospheric chemistry that have been of interest to Zoller involved the collection and chemical analysis of particles and gases from remote areas of the earth's atmosphere. His studies focussed on identifying the sources of these particles and gases and on assessing the impact of anthropogenic emissions to the atmosphere in these remote areas. Some of these projects involved fieldwork in Washington, Alaska, and Hawaii. Special emphasis was placed upon the sulfur cycle and the cycles of the volatile metals Se, Sb, and As in the marine atmosphere, with particular emphasis upon the source of these natural enriched elements in the atmosphere.
Zoller's work attempted to answer the question as to how the ocean, or organisms in the ocean, effected the concentration of the elements in remote areas. Other areas of activity may be arranged within the broad spectrum of expertise in the Department of Chemistry and Chemical Engineering. Candidates for the degrees; Master of Science, Master of Applied Science, Master of Engineering or Doctor of Philosophy will be admitted under the general admission requirements.