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Zivanovic R.,University of Adelaide | Bokov P.M.,Necsa
Annals of Nuclear Energy | Year: 2010

This paper discusses the use of the dimension-wise expansion model for cross-section parameterization. The components of the model were approximated with tensor products of orthogonal polynomials. As we demonstrate, the model for a specific cross-section can be built in a systematic way directly from data without any a priori knowledge of its structure. The methodology is able to construct a finite basis of orthogonal polynomials that is required to approximate a cross-section with pre-specified accuracy. The methodology includes a global sensitivity analysis that indicates irrelevant state parameters which can be excluded from the model without compromising the accuracy of the approximation and without repetition of the fitting process. To fit the dimension-wise expansion model, Randomised Quasi-Monte-Carlo Integration and Sparse Grid Integration methods were used. To test the parameterization methods with different integrations embedded we have used the OECD PBMR 400 MW benchmark problem. It has been shown in this paper that the Sparse Grid Integration achieves pre-specified accuracy with a significantly (up to 1-2 orders of magnitude) smaller number of samples compared to Randomised Quasi-Monte-Carlo Integration. © 2010 Elsevier Ltd. All rights reserved.


Prinsloo R.H.,Necsa | Tomasevic D.I.,Necsa | Moraal H.,North West University South Africa
Annals of Nuclear Energy | Year: 2014

Transverse-integrated nodal diffusion methods currently represent the standard in full core neutronic simulation. The primary shortcoming of this approach is the utilization of the quadratic transverse leakage approximation. This approach, although proven to work well for typical LWR problems, is not consistent with the formulation of nodal methods and can cause accuracy and convergence problems. In this work, an improved, consistent quadratic leakage approximation is formulated, which derives from the class of higher-order nodal methods developed some years ago. Further, a number of iteration schemes are developed around this consistent quadratic leakage approximation which yields accurate node average results in much improved calculational times. The most promising of these iteration schemes results from utilizing the consistent leakage approximation as a correction method to the standard quadratic leakage approximation. Numerical results are demonstrated on a set of benchmark problems and further applied to a realistic reactor problem, particularly the SAFARI-1 reactor, operating at Necsa, South Africa. The final optimal solution strategy is packaged into a standalone module which may simply be coupled to existing nodal diffusion codes. © 2014 Elsevier Ltd. All rights reserved.


De Beer F.C.,Necsa | De Beer F.C.,North West University South Africa
Journal of the Southern African Institute of Mining and Metallurgy | Year: 2015

A number of important areas in nuclear fuel cycle, at both the front end and back end, offer ideal opportunities for the application of nondestructive evaluation techniques. These techniques do not only provide opportunities for non-invasive testing of e.g. irradiated materials, but also play an important role in the development of new materials in the nuclear sector. The advantage of penetrating radiation used as probe in the investigation and testing of nuclear materials makes X-ray and neutron radiography (2D) and tomography (3D) suitable for various applications in the total nuclear fuel cycle. The unique and different interaction modes of the two radiation probes with materials provide several opportunities. Their complementary nature and non-destructive character makes them most suitable for nuclear material analyses, analytical method development, and the evaluation of the performance of existing nuclear material compositions. This article gives an overview of the X-ray and neutron radiography/tomography applications in the field of nuclear material testing, and highlights a few of the success stories. Several selected areas of application in the nuclear fuel cycle are discussed to illustrate the complementary nature of these techniques as applied to nuclear materials. © The Southern African Institute of Mining and Metallurgy, 2015.


Roos T.H.,South African Council for Scientific and Industrial Research | Quin R.L.,RLQ Design | De Beer F.C.,Necsa | Nshimirimana R.M.,Necsa
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

Probably the most common method of reverse engineering in mechanical engineering involves measuring the physical geometry of a component using a coordinate measuring machine (CMM). Neutron tomography, in contrast, is used primarily as a non-destructive testing technique. This paper, however, explores the use of this technique in its tomographic application (neutron CAT scanning mode) as a reverse engineering tool, particularly for complex internal geometries, as it has the added advantage of being a non-destructive and non-invasive method. Several components from an IS-60 Rover gas turbine were scanned using neutron tomography and through the analyses it was demonstrated that the technique may be promising for reverse engineering purposes. © 2011 Elsevier B.V. All rights reserved.


De Beer F.C.,Necsa | Gruenauer F.,Necsa | Radebe J.M.,Necsa | Modise T.,Necsa | Schillinger B.,TUM
Physics Procedia | Year: 2013

The final scientific design for an upgraded neutron radiography/tomography facility at beam port no.2 of the SAFARI-1 nuclear research reactor has been performed through expert advice from Physics Consulting, FRMII in Germany and IPEN, Brazil. A need to upgrade the facility became apparent due to the identification of various deficiencies of the current SANRAD facility during an IAEA-sponsored expert mission of international scientists to Necsa, South Africa. A lack of adequate shielding that results in high neutron background on the beam port floor, a mismatch in the collimator aperture to the core that results in a high gradient in neutron flux on the imaging plane and due to a relative low L/D the quality of the radiographs are poor, are a number of deficiencies to name a few. The new design, based on results of Monte Carlo (MCNP-X) simulations of neutron- and gamma transport from the reactor core and through the new facility, is being outlined. The scientific design philosophy, neutron optics and imaging capabilities that include the utilization of fission neutrons, thermal neutrons, and gamma-rays emerging from the core of SAFARI-1 are discussed. © 2013 The Authors. Published by Elsevier B V.


Franklyn C.B.,Necsa | Torok G.,Hungarian Academy of Sciences
AIP Conference Proceedings | Year: 2011

To maintain a competitive edge in the wool and mohair industry, a detailed knowledge and understanding of the properties of wool fibres is essential. Standard techniques are used to determine fibre diameter, length and strength; however, properties such as hydroscopicity, lustre and changes in fibre structure following chemical or mechanical treatment are not so well understood. The unique capabilities of small angle neutron scattering to study changes in the supermolecular structure of wool fibres, particularly at the level of the microfibril-matrix complex, have been used to provide previously unknown features of the fibres. The results of these studies are presented. © 2011 American Institute of Physics.


Franklyn C.B.,Necsa
AIP Conference Proceedings | Year: 2011

A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >1011ns-1. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine. © 2011 American Institute of Physics.


Franklyn C.B.,Necsa
AIP Conference Proceedings | Year: 2011

Since natural coloured sapphire (α-Al2O3) commands a high gem stone market price there is a need for a reliable method of identifying artificially coloured sapphire that has an inherently lower value. Diffusing beryllium into sapphire at high temperatures results in a coloured stone virtually indistinguishable from a natural one. Beryllium can occur naturally in sapphire but at levels of <1ppma. Beryllium diffused sapphire typically contains >10ppma, which is difficult to determine in a non destructive way. It is possible to utilize nuclear reaction analysis techniques to determine the beryllium content in a macroscopically non destructive way. Kinematically ideal reactions are Be(p,α) and Be(p,d) which, for Ep=0.5 to 0.9 MeV, exhibit distinct reaction product signatures well separated from other proton induced reactions in aluminium or oxygen. Due to the lack of comprehensive cross section data for the Be(p,α) and Be(p,d) reactions in the energy range of interest, a series of measurements were made at the Van de Graaff accelerator facility at Necsa to create a new data base. A further outcome of these measurements was a deviation in reported values for the non-Rutherfordian proton back-scatter cross section. These new data bases, which extend to Ep=2.6MeV, can now facilitate a procedure for determining beryllium content in sapphire. © 2011 American Institute of Physics.


Adam R.,Necsa
World Nuclear Association 35th Annual Symposium - The Nuclear Resurgence: Fulfilling Our Potential | Year: 2010

The South African government took an in-principle decision to convert the SAFARI-1 research reactor to LEU fuel in 1999. This was fully implemented in 2009, followed by a conversion to LEU target plates for radioisotopes production in 2010. The first shipments of such product to international customers took place in July 2010. Full conversion has not been without significant technical hurdles, but nevertheless constitutes an important step towards freeing the world of HEU-based production processes, in line with commitments made by heads of state at the April 2010 Nuclear Security Summit in Washington. It is expected that regulatory systems in countries purchasing significant quantities of radioisotopes will respond by giving preferential treatment to LEU-origin products.


Prinsloo R.H.,Necsa | Tomasevic D.I.,Necsa
International Conference on the Physics of Reactors 2012, PHYSOR 2012: Advances in Reactor Physics | Year: 2012

Transverse integrated nodal diffusion methods currently represent the standard in full core neutronic simulation. The primary shortcoming in this approach is the utilization of the quadratic transverse leakage approximation. This approach, although proven to work well for typical LWR problems, is not consistent with the formulation of nodal methods and can cause accuracy and convergence problems. In previous work, an improved, consistent quadratic leakage approximation was formulated, which derived from the class of higher order nodal methods developed some years ago. In this paper a number of iteration schemes are developed around this consistent quadratic leakage approximation which yield accurate node average results in much improved calculational times. The developed consistent leakage approximation is extended in this work via a number of numerical schemes, the most promising of which results from utilizing the consistent leakage approximation as a correction method to the standard quadratic leakage approximation. Numerical results are demonstrated on a set of benchmark problems, such as the 3D IAEA LWR and MOX C5 problems.

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