Filtern
Dokumenttyp
- Vortrag (52)
- Beitrag zu einem Tagungsband (43)
- Zeitschriftenartikel (36)
- Posterpräsentation (8)
- Buchkapitel (4)
- Beitrag zu einem Sammelband (2)
- Handbuch (1)
- Forschungsbericht (1)
Schlagworte
- Ultrasound (56)
- Concrete (54)
- Monitoring (38)
- Coda wave interferometry (15)
- Ultraschall (10)
- NDT (9)
- Non-destructive testing (9)
- Bridge (8)
- Imaging (8)
- Structural health monitoring (8)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (147) (entfernen)
Paper des Monats
- ja (2)
Eingeladener Vortrag
- nein (52)
Technology selection is an important part of the planning process when setting
up a waste management programme. This continues to be crucial during
implementation of the programme to evaluate if suitable technologies are being
implemented. This Domain Insight document provides guidance on the assessment
and selection of potential technologies for implementation during the pre-disposal
phase of the waste management lifecycle, considering factors such as cost-benefit ratio and availability (EURAD Pre-disposal theme overview, domain 2.1.3, Technology Selection), as a part of the sub-theme “Planning pre-disposal
management of radioactive waste in close cooperation with waste generators”
(Planning) and, on the broader theme 2 “Pre-disposal Activities prior to geological disposal” (Pre-disposal).
In the planning process for a waste management programme, it is critical for the waste owner to assess the feasibility of technologies for processing, storage, and monitoring, taking economic constraints into account and considering subsequent stages in the waste management lifecycle, including final disposal. In addition, technology selection must be based on the waste inventory that has been generated, planned waste stream composition and the evolution of resulting waste packages in storages. The accuracy, effectiveness and efficiency of the technologies deployed in a facility require periodic review and update, as needed, throughout the lifetime of the facility.
The ultrasonic echo technique is broadly applied in non‐destructive testing (NDT) of concrete structures involving tasks such as measuring thickness, determining geometry and locating built‐in elements. To address the challenge of enhancing ultrasonic imaging for complex concrete constructions, we adapted a seismic imaging algorithm – reverse time migration (RTM) – for NDT in civil engineering. Unlike the traditionally applied synthetic aperture focusing technique (SAFT), RTM takes into account the full wavefield including primary and reflected arrivals as well as multiples. This capability enables RTM to effectively handle all wave phenomena, unlimited by changes in velocity and reflector inclinations. This paper concentrates on applying and evaluating a two‐dimensional elastic RTM algorithm that specifically addresses horizontally polarized shear (SH) waves only, as these are predominantly used in ultrasonic NDT of concrete structures. The elastic SH RTM algorithm was deployed for imaging real ultrasonic echo SH‐wave data obtained at a concrete specimen exhibiting a complex back wall geometry and containing four tendon ducts. As these features are frequently encountered in practical NDT scenarios, their precise imaging holds significant importance. By applying the elastic SH RTM algorithm, we successfully reproduced nearly all reflectors within the concrete specimen. In particular, we were capable of accurately reconstructing all vertically oriented reflectors as well as the circular cross sections of three tendon ducts, which was not achievable with traditional SAFT imaging. These findings demonstrate that elastic SH RTM holds the ability to considerably improve the imaging of complex concrete geometries, marking a crucial advancement for accurate, high‐quality ultrasonic NDT in civil engineering.
To safely dispose of nuclear waste in underground facilities, engineered barrier systems are needed to seal shafts and galleries. The material used in these barriers must be adapted to the host rock parameters. Shrinking and cracking must be avoided to provide a barrier with almost zero permeability. For repositories in salt rock environments, several types of salt concrete (SC) are possible construction materials.
Within the project SealWasteSafe, we compared the behavior of an innovative alkali-activated material (AAM) with standard SC in their hydration and hardening phase. To monitor the microstructural changes within the two materials SC and AAM, acoustic emission (AE) signals have been recorded for up to ~250 days on 340-liter-cubic specimens.
The phenomenon of AE is defined as the emission of elastic waves in materials due to the release of localized internal energy. Such energy release can be caused by the nucleation of micro-fracture, e.g., in concrete while curing or when exposed to load. The occurrence of AE events gives first rough indications of microstructural changes and potentially occurring cracking and thus, provides insights for structural health monitoring (SHM).
The results show, that for the first 28 days after casting, less AE activity was detected in the AAM compared to SC. After 61 days, in the AAM material, the number of AE events exceeded those observed in the SC. However, the majority of the AE detected and located in AAM was related to surface effects, and not to microstructural changes or occurring cracks within the bulk volume. Additionally, the source location analysis indicated, that despite lower activity in SC, we observed some clustering of the events. In contrast, in AAM, the activity inside the specimen is randomly distributed over the whole volume. The monitoring results help to estimate the material’s sealing properties which are crucial to assess their applicability as sealing material for engineered barriers.
One of the major tasks in nuclear waste management is to design safe and reliable sealing structures for radioactive waste repositories. Particularly for salt as a host rock, engineered barrier systems for underground waste disposal must be constructed of well-understood (cementitious) materials that will sustain environmental conditions and ensure high durability.
Within the SealWasteSafe project, we studied two materials with a potential for sealing structures for nuclear waste repositories: an innovative alkali-activated material (AAM) and standard salt concrete (SC). To analyze the development of microstructural changes within the materials, we monitored microseismicity (aka acoustic emission monitoring) occurring during the hardening and setting period in two 340-liter-cubic specimens for up to ~250 days.
The monitoring results showed, that in the first 61 days, fewer events occurred in AAM compared to SC. After this time the number of events in AAM sharply increased and significantly exceeded those observed in SC. However, the source localization analysis revealed that the increase of microseismicity in AAM material was not related to the formation of macro-cracks within the material but was mainly caused by the surface effects. Accompanying analysis of the test specimens with additional methods (such as e.g., X-ray CT) proved that no macro-cracks were observed inside the AAM specimen. Further analysis in the time and frequency domains helped to characterize the tested materials and to estimate their potential to be used for engineered barriers in nuclear waste repositories.
Overall, our study shows the potential of microseismicity monitoring for feasibility studies and quality assurance in a broad range of applications, also in structural health monitoring.
Ultra-High-Performance Fiber-Reinforced Cementitious Composite (UHPFRC) offers several advantages compared to concrete, notably due to the strain hardening behavior under tensile actions. Structures made of this composite material are lightweight and highly durable, thanks to the UHPFRC waterproofing quality. Nonetheless, the tensile behavior leads to a different cracking pattern than conventional concrete and is not fully understood yet. This paper presents a combined approach using both passive ultrasonic (US) stress wave (or acoustic emission) and active US stress wave monitoring to localize and quantify damage progression in a full-scale UHPFRC beam during experimental load testing. The proposed monitoring approach involves 24 US transducers that are embedded randomly throughout a 4.2- meter-long laboratory UHPFRC T-beam. Continuous monitoring enabled accurate localization of US stress sources caused by loading-induced cracking as well as from pulses generated by the embedded US transducers. This study shows that it is possible to predict the location and shape of the macro-crack that is linked to structural failure early on, i.e., just after the end of the elastic domain. This combined approach opens new possibilities to monitor the structural behavior and detect damage on UHPFRC structures before they affect the structural behavior in terms of deflection and strain.
To safely dispose of nuclear waste in underground facilities, engineered barrier systems are needed to seal shafts and galleries. The material used in these barriers must be adapted to the host rock parameters. Shrinking and cracking must be avoided to provide a barrier with almost zero permeability. For repositories in salt rock environments, several types of salt concrete (SC) are possible construction materials. Within the project SealWasteSafe, we compared the behavior of an innovative alkali-activated material (AAM) with standard SC in their hydration and hardening phase. To monitor the microstructural changes within the two materials SC and AAM, acoustic emission (AE) signals have been recorded for up to ~250 days on 340-litercubic specimens. The phenomenon of AE is defined as the emission of elastic waves in materials due to the release of localized internal energy. Such energy release can be caused by the nucleation of micro-fracture, e.g., in concrete while curing or when exposed to load. The occurrence of AE events gives first rough indications of microstructural changes and potentially occurring cracking and thus, provides insights for structural health monitoring (SHM). The results show, that for the first 28 days after casting, less AE activity was detected in the AAM compared to SC. After 61 days, in the AAM material, the number of AE events exceeded those observed in the SC. However, the majority of the AE detected and located in AAM was related to surface effects, and not to microstructural changes or occurring cracks within the bulk volume. Additionally, the source location analysis indicated, that despite lower activity in SC, we observed some clustering of the events. In contrast, in AAM, the activity inside the specimen is randomly distributed over the whole volume. The monitoring results help to estimate the material’s sealing properties which are crucial to assess their applicability as sealing material for engineered barriers.
Combined passive ultrasonic (US) stress wave [better known as acoustic emission (AE)] and active US stress wave monitoring has been shown to provide a more holistic picture of ongoing fracture processes, damage progression, as well as slowly occurring aging and degradation mechanisms in concrete structures. Traditionally, different data analysis techniques have been used to analyze the data generated from these two monitoring techniques. For passive US stress wave monitoring, waveform amplitudes, hit rates, source localization, and b-value analysis, among others, have been used to detect and locate cracking. On the other hand, amplitude tracking, magnitude squared coherence (MSC), and coda wave interferometry (CWI) are examples of analyses that have been employed for active US stress wave monitoring. In this paper, we explore some of these data analysis techniques and show where their respective applications and limitations might be. After providing an overview of the monitoring approach and the different data analysis techniques, results and observations from selected laboratory experiments are discussed. Finally, suggestions for further work are proposed.
A monitoring and surveillance system is a mandatory element to ensure that a radioactive waste disposal facility provides and meets the required level of safety during both its operational and closure periods. In this study an innovative approach for the identification and monitoring of the structural integrity of stored radioactive drums is presented. The activities were carried out in the context of the European Project PREDIS, whose goal is the development of a robust and reliable sensing technology for monitoring and long-term storage of radioactive waste packaging systems.
Specifically, the focus was set on the development of innovative and smart sensor technologies, non-destructive examination tools, and/or devices capable to improve the safety of the storage by minimizing the number of interventions of cemented waste packages. Both conventional and innovative techniques, such as muon-tomography, SiLiF neutron and SciFi gamma detection, or contactless and smart radio transceiver technology provided with radiation monitoring sensors, have been considered and adapted for the use under repository conditions. Indeed, gamma and neutron detection techniques exploit the radiological information coming from inside the drums, while imaging techniques proved to be effective in spotting high density objects embedded inside the concrete: together, they allow to improve safety and security and can provide an early alert on behavioral changes hinting at anomalies in the drums.
A reliable monitoring and oversight system is essential to guarantee the safe operation and eventual closure of radioactive waste disposal facilities. With recent technological advancements, there is now the capability to deploy distributed wireless sensor networks that are cost-effective and low in power consumption. Such networks are versatile, finding applications in several civil, environmental, and industrial sectors. This work presents a novel system and method for identifying and continuously monitoring the integrity of stored radioactive waste packages. The proposed approach, developed by the University of Pisa in the context of the H2020 European Project PREDIS, employs a network of wireless node devices, provided with solid-state micro-power radiation detectors tasked with the measurement of gamma-rays and thermal neutrons coming from within cemented waste drums. Collected data are automatically transmitted across the storage site via Long Range radio technology and forwarded to cloud-based or offline platforms, allowing for further visualization, data processing, and safe storage. The system highlights the feasibility of autonomously and passively gathering data from radioactive waste drums over extended distances (more than 250 m in non-line-of-sight conditions), decreasing the reliance
on portable or automated scanning mechanisms. In line with its capability for autonomous, long-range data collection, the system satisfies the requirement for structural integrity, containment, and confinement of packaging throughout both interim and long-term disposal of radioactive wastes, thereby playing a key role in reinforcing the safe management of radioactive waste.