A key safety issue in the operation of any nuclear reactor or nuclear waste management site is the control and containment of radioactive material, making risk assessment and management by means of regular inspection a vital element as much as a regulatory requirement.
By Yoldas Askan, Nuclear Future, 4/2011
Given the challenges of working in radiation controlled environments and with limited choice of non-contact, remote examination techniques available, visual inspection has so far been most widely used technique despite its limitations to the detecting of obvious flaws, requiring good eyesight and illumination, and findings are often subjective and dimensionally uninformative.
In recent years, remote deployment of laser scanners in contaminated environments has allowed acquisition of more precise survey data. By the systematic emission of millions of laser beams, a 3D Laser Scanner (e.g. FARO’s Focus3D) collates accurate measurements of distances to objects, producing a 3D model often referred to as the “Point Cloud”.
Figure 1: A Point Cloud is generated by using a 3D laser scanner. In radioactive controlled environment robot mounted scanners can be driven to position.
Meshing of individual points of the Point Cloud can be used to extrapolate the shape of the object under consideration. As with other physical measurement systems, all data collected is subject to statistical noise and a surface profile drawn by meshing raw Point Cloud data can exhibit significant surface roughness, obscuring the overall geometrical representation of the object.
Point Cloud engineering is an innovative new technology pioneered by Geopticks Ltd which deals with determination and eradication of the statistical noise on Point Cloud data. The technique achieves smooth Point Cloud surfaces without altering the true object shape. Mathematically speaking, the benefit of Point Cloud engineering is that each minute meshed plane normal of four neighbouring points on a square lattice intersect an adjacent plane normal at far greater distances.
Figure 2: A close-up view of the Point Cloud reveals the extent of statistical noise. Under optimum scanning conditions standard error of ±2mm on the Point Cloud surface is commonly observed.
Steve Foster, Technical Manager (Encapsulation) at Sellafield Ltd. comments:
“Condition monitoring of plant, equipment and products at Sellafield site is a key element in the overall management of the site, enhancing equipment reliability and enabling the demonstration of nuclear safety. The need for a non-contact method of measuring dimensional changes over several years to a precision of 1mm or better was identified to assist with the ongoing condition monitoring of radioactive waste packages. Because the Laser Scanner is required to operate in a radioactive environment it is necessary to remove it for its own protection when not in use. The work done by Geopticks on point cloud smoothing and comparative scanning after long time periods without the requirement for precise positioning of both the Laser Scanner and the target object is a welcome development which has significantly enhanced the usefulness of laser scanning to the nuclear industry wherever small but significant dimensional changes need to be measured by non-contact means. We are pleased to have this new technology available to us.”
Superior surface formulation enable mathematical operations to be performed – subtracting the overlapping normal lengths allows the distance between two meshed surfaces to be calculated, or in other words, identification of the surface deflection or deformation widths.
Figure 4 shows accurate superimposition of two engineered Point Cloud models. Comparing the Point Cloud from a previous scan reveals surface defects that have occurred. The 2D display of Figure 4 shows all of the deformations exhibited, expansion and contraction.
Figure 4: Map of Waste Container Deformation caused by Thermal Expansion of Fuel Rod in contact with the Drum Inner Wall – Images generated via Point Cloud Engineering can reveal deformations of 0.1 – 15 mm
The precision of surface defects identified for an engineered scan can range from staggering 0.1mm to 1000mm using a midrange phase-shift laser scanner.
Geopticks’ unique S-DELTA software for precise mapping of surfaces by a non-contact method is a recent accomplishment that can detect surface imperfections, deformations and topographical features. S-DELTA’s ability to detect minute surface deflections allows for damage to be identified and quantified as soon as it becomes apparent. In addition to providing important safety information, the comprehensive surface deformation mappings also provide useful insight to future engineering design of critical components.
Laser scanning and the S-DELTA software increases precision in deformation analysis, efficiency in installation, maintenance and aid decommissioning process and is a significant compliment to safety standards in the safety critical nuclear sector.
Figure 5: Point clouds are 3D models and can be displayed in 3D. By rotating and zooming into the Point Cloud can reveal a realistic picture of the object before and after any surface deformation.
About Geopticks Ltd. Laser Scanning Services :
Geopticks is a laser scanning company located in Bedford, UK. Geopticks pride themselves on their scientific approach to 3D laser scanning and point cloud engineering to create noise free point cloud. As a result, bring previously unseen technologies and capabilities such as accurate deformation modeling, to the heart of surveying industry and the engineering science.
Geopticks’ widely acknowledged bespoke software S-Delta is a success story. S-Delta is the only software tool in existence that can map surface deformations by using 3D laser scanners as e.g. FARO’s Laser Scanner Photon or Focus3D. Geopticks’ applications: nuclear, transport, accident & CSI, heritage, geological survey, routine surveying and verification.
More information: www.Geopticks.com