TY - CONF A1 - Prabhakara, Prathik T1 - Simulation and construction of a focussing borehole probe for ultrasonic investigations at sealing structures for radioactive waste repositories N2 - A novel ultrasonic borehole probe is developed for the quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The aim is to analyse the sealing structures made of salt concrete concerning potential cracks, delamination, and embedded objects. A first prototype of the probe uses 12 individual dry point contact (DPC) shear horizontal wave transducers separated by equidistant transmitter/receiver arrays, each consisting of six individual transducers. It is operated with a commercial handheld ultrasonic testing device used in civil engineering. In order to increase the generated sound pressure of the borehole probe, the number of transducers will be increased to 32 for the novel probe. In addition, a time-controlled excitation of the individual probes is used to steer a focused sound beam to a certain angle and focus on a certain distance based on calculated time delays. Hence, the sensitive test volume is more limited, and the signal-to-noise ratio of the received signals improved. This paper presents the validation of the newly developed phased array borehole probe by beam simulation and experimentally on a half-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction method, an optimised radiation characteristic of the probe, an improved signal quality and thus an increased reliability of the results in imaging is expected. This is of great importance to construct safe sealing structures needed for radioactive or toxic waste disposal. T2 - NDT UT-Online 21 CY - Online meeting DA - 01.11.2021 KW - Borehole probe KW - Engineered Barrier System (EBS) KW - SealWasteSafe KW - Phased array technique KW - Monitoring PY - 2021 AN - OPUS4-54500 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Prabhakara, Prathik A1 - Mielentz, Frank A1 - Stolpe, Heiko A1 - Behrens, Matthias A1 - Lay, Vera A1 - Niederleithinger, Ernst T1 - Ultrasonic Investigation for the Quality Assurance of Sealing Structures in Radioactive Waste Repositories N2 - The structural integrity of sealing structures in underground repositories for radioactive waste is a major concern regarding safe disposal. Non-destructive testing plays a very important role in the safety of this sealing structures. Ultrasonic pulse echo technology has been established in the construction industry as a non-destructive testing method for locating potential defects and material characterization of concrete structures. A borehole probe is an ultrasonic pulse-echo device used to investigate the internal structures of salt concrete. A prototype borehole probe is successfully demonstrated with the existing research borehole in the test site using a commercially available flaw detector. A novel phased array borehole probe that allows the beam to be focused based on the delay law was constructed and tested. The directivity measurements on the semi-cylindrical concrete sample agree well with the simulation results for the different focusing angles. In combination with geophysical reconstruction methods, the optimized radiation pattern of the probe is expected to improve the signal quality and thus increase the reliability of the imaging results. In addition, a unique large aperture ultrasound system (LAUS) is expected to provide enhanced images of possible cracks and embedded objects in in-situ structures. LAUS will be optimized to reliably detect objects at depths greater than 9 m and, at the same time, provide good resolution. Modeling studies show the potential to increase the distance between the transducer arrays further, and the same configuration has been successfully tested on a thick concrete wall. Overall, the paper shows that quality assurance using ultrasonic testing is crucial for constructing safe sealing structures to dispose of radioactive or toxic waste. T2 - NDE 2022 CY - Gandhinagar, India DA - 24.12.2022 KW - Ultrasonic Testing KW - Engineered barrier KW - Phased array technique KW - Non-destructive testing civil engineering KW - Quality assurance PY - 2022 AN - OPUS4-56802 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Prabhakara, Prathik A1 - Lay, Vera A1 - Mielentz, Frank A1 - Niederleithinger, Ernst A1 - Behrens, Matthias T1 - Enhancing the Performance of a Large Aperture Ultrasound System (LAUS): A Combined Approach of Simulation and Measurement for Transmitter–Receiver Optimization N2 - The Large Aperture Ultrasound System (LAUS) developed at BAM is known for its ability to penetrate thick objects, especially concrete structures commonly used in nuclear waste storage and other applications in civil engineering. Although the current system effectively penetrates up to ~9 m, further optimization is imperative to enhance the safety and integrity of disposal structures for radioactive or toxic waste. This study focuses on enhancing the system’s efficiency by optimizing the transducer spacing, ensuring that resolution is not compromised. An array of twelve horizontal shear wave transducers was used to find a balance between penetration depth and resolution. Systematic adjustments of the spacing between transmitter and receiver units were undertaken based on target depth ranges of known reflectors at depth ranges from 5 m to 10 m. The trade-offs between resolution and artifact generation were meticulously assessed. This comprehensive study employs a dual approach using both simulations and measurements to investigate the performance of transducer units spaced at 10 cm, 20 cm, 30 cm, and 40 cm. We found that for depths up to 5 m, a spacing of 10 cm for LAUS transducer units provided the best resolution as confirmed by both simulations and measurements. This optimal distance is particularly effective in achieving clear reflections and a satisfactory signal-to-noise ratio (SNR) in imaging scenarios with materials such as thick concrete structures. However, when targeting depths greater than 10 m, we recommend increasing the distance between the transducers to 20 cm. This increased spacing improves the SNR in comparison to other spacings, as seen in the simulation of a 10 m deep backwall. Our results emphasize the critical role of transducer spacing in achieving the desired SNR and resolution, especially in the context of depth imaging requirements for LAUS applications. In addition to the transducer spacing, different distances between individual sets of measurement positions were tested. Overall, keeping the minimal possible distance between measurement position offsets provides the best imaging results at greater depths. The proposed optimizations for the LAUS in this study are primarily relevant to applications on massive nuclear structures for nuclear waste management. This research highlights the need for better LAUS efficiency in applications such as sealing structures, laying the foundation for future technological advances in this field. KW - Engineered barrier system KW - Phased array technique KW - Ultrasonic testing KW - Non-destructive testing in civil engineering KW - Seismic migration PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-592426 DO - https://doi.org/10.3390/s24010100 VL - 24 IS - 1 SP - 1 EP - 23 PB - MDPI CY - Basel, Switzerland AN - OPUS4-59242 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Prabhakara, Prathik A1 - Mielentz, Frank A1 - Stolpe, Heiko A1 - Behrens, Matthias A1 - Lay, Vera A1 - Niederleithinger, Ernst T1 - Construction and validation of a novel phased array borehole probe for ultrasonic investigations at sealing structures in radioactive repositories N2 - A new type of ultrasonic borehole probe is currently under development for the quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The goal is to examine the sealing structures made of salt concrete for possible cracks, delamination, and embedded objects. Earlier prototype probes use 12 or 16 individual dry point contact (DPC) horizontal shear wave transducers grouped into a transmitter and a receiver array, each made up of six or eight individual transducers. They are operated with a commercially available portable ultrasonic flaw detector used in the civil engineering industry. To increase the generated sound pressure of the borehole probe, the number of transducers in the novel probe is increased to 32. In addition, timed excitation of each probe is used to direct a focused sound beam to a specific angle and distance based on calculated time delays. Hence, the sensitive test volume is limited, and the signal-to-noise ratio of the received signals is improved. This paper presents the validation of the newly developed phased array borehole probe by beam computation in CIVA software and experimental investigations on a semi-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction techniques, an optimised radiation pattern of the probe is expected to improve the signal quality and thus increase the reliability of the imaging results. This is of great importance for the construction of safe sealing structures needed for the disposal of radioactive or toxic waste. T2 - NDT-CE 2022 CY - Zurich, Switzerland DA - 16.08.2022 KW - Borehole probe KW - Phased array technique KW - SealWasteSafe KW - Monitoring KW - Engineered barrier; PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-568016 SN - 1435-4934 SP - 1 EP - 4 PB - NDT.net AN - OPUS4-56801 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Prabhakara, Prathik T1 - Construction and Simulation of a Novel Phased Array Borehole Probe for Ultrasonic Investigations at Sealing Structures in Radioactive Repositories N2 - A novel ultrasonic borehole probe is developed for the quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The goal is to examine the sealing structures made of salt concrete for possible cracks, delamination, and embedded objects. A prototype probe uses 12 individual horizontal dry point contact (DPC) shear wave transducers separated by equidistant transmitter/receiver arrays of six individual transducers each. It is operated with a commercially available portable ultrasonic flaw detector used in the civil engineering industry. To increase the generated acoustic pressure of the borehole probe, the number of transducers in the novel probe is increased to 32. In addition, a timed excitation of each probe directs a focused beam of sound to a specific angle and distance based on calculated time delays. This limits the sensitive test volume and improves the signal-to-noise ratio of the received signals. This paper presents the validation of the newly developed phased array borehole probe by investigating the directivity through beam computation in the CIVA software and experimental investigations on a semi-cylindrical test specimen. It is expected that an optimised radiation pattern of the probe in combination with geophysical reconstruction methods will improve the signal quality and thus increase the reliability of the imaging results. This is of great importance for the construction of safe sealing structures needed for the disposal of radioactive or toxic waste. T2 - ISNT NDE 21 CY - Online meeting DA - 09.12.2021 KW - Borehole probe KW - Engineered barrier KW - Phased array technique KW - SealWasteSafe KW - Monitoring PY - 2022 AN - OPUS4-54498 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -