NachhaltigMaschinenbau und MechatronikZeitschriftenartikel
T. Mull, T. Wagner, Giuseppe Bonfigli, S. Buchholz, Frank Schäfer, E. Schleicher, C. Schuster, M. Sporn
Safety cases for design-basis accidents in LWRs featuring passive systems
[In Press]
Nuclear Engineering and Design, no. Available online 26 February 2021
2021
DOI: 10.1016/j.nucengdes.2021.111095
Abstract anzeigen
This paper presents results from a series of integral tests performed at Framatome’s INKA test facility in Karlstein (Germany) which simulates a KERENA boiling water reactor (BWR). The scope of the test series was on the behaviour of and interaction between the different passive systems and components under the conditions of extended loss of alternating power (ELAP). These SBO-like conditions were aggravated in three out of four tests by parallel LOCA (Loss of Coolant Accident). The scenarios of all four tests fully correspond to Design Basic Conditions (DBC). They were: main steam line break, feed water line break, reactor pressure vessel (RPV) bottom leak and station blackout (SBO, non-LOCA).
In the tests, the passive systems integrated in KERENA and INKA, respectively, have fulfilled their design functions fully satisfactorily and as follows:
The Passive Pressure Pulse Transmitter (PPPT) triggered the RPV depressurization without delay. The Emergency Condenser (EC) system removed decay heat along with stored energy from the RPV to the containment. The Containment Cooling Condenser (CCC) system forwarded said power to a heat sink outside of the containment. The passive containment pressure suppression system kept the containment pressure within the design range, partially displacing surplus thermal energy from the drywell to the wetwell, in particular in the early phases after occurrence of LOCA. The passive core flooding system replenished the coolant inventory of the RPV thereby ensuring water levels in the RPV which are fully sufficient for core cooling.
Moreover, the systems have cooperated as anticipated by the designers, quietly and without perturbing each other.
Hence the test results, which are reported and discussed more in detail within this paper, soundly confirm the underlying design and its passive features.
Said tests were carried out as a part of the joint research project EASY (Evidence of Design Basis Accidents Mitigation solely with passive safety Systems), the overarching objective of which was the development and validation of the code system AC2 of GRS (Gesellschaft für Anlagen- und Reaktorsicherheit gGmbH).
NachhaltigMaschinenbau und MechatronikZeitschriftenartikel
Giuseppe Bonfigli, S. Buchholz, F. Schäfer, Nadine Kaczmarkiewicz, C. Schuster, M. Sporn
Safety cases for design-basis accidents in LWRs featuring passive systems Part 2 – Numerical investigations
Nuclear Engineering and Design, vol. 372, no. February
2021
DOI: 10.1016/j.nucengdes.2020.110996
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This paper deals with the improvement and validation of numerical tools for the simulation of design basis accidents in nuclear power plants equipped with passive safety systems. Numerical models are implemented in the framework of the 1-D thermal–hydraulic system code ATHLET developed by GRS. Experimental reference data for the validation were obtained at the INKA test facility, a model of the KERENA reactor, reproducing the passive safety systems nearly at full scale.
The validation effort focuses firstly on the accuracy of the models for the single passive components, and secondly on the ability of the numerical simulation to reproduce the interaction of all components of the KERENA design under realistic conditions as reproduced in the INKA test facility. Thermal-hydraulic models are presented and validated for two passive components of the KERENA reactor: the passive pressure pulse transmitter and the pressure-controlled flooding valve. Finally, the full model of the INKA facility, including these and other passive components, is discussed and numerical results for simulations reproducing three different design basis accidents are validated by comparison with the corresponding experimental data.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
F. Heilmeier, R. Koos, M. Singer, C. Bauer, Peter Hornberger, Jochen Hiller, W. Volk
Evaluation of Strain Transition Properties between Cast-In Fibre Bragg Gratings and Cast Aluminium during Uniaxial Straining
Sensors, vol. 20, no. 21
2020
DOI: 10.3390/s20216276
Abstract anzeigen
Current testing methods are capable of measuring strain near the surface on structural parts, for example by using strain gauges. However, stress peaks often occur within the material and can only be approximated. An alternative strain measurement incorporates fibre-optical strain sensors (Fiber Bragg Gratings, FBG) which are able to determine strains within the material. The principle has already been verified by using embedded FBGs in tensile specimens. The transition area between fibre and aluminium, however, is not yet properly investigated. Therefore, strains in tensile specimens containing FBGs were measured by neutron diffraction in gauge volumes of two different sizes around the Bragg grating. As a result, it is possible to identify and decouple elastic and plastic strains affecting the FBGs and to transfer the findings into a fully descriptive FE-model of the strain transition area.We thus accomplished closing the gap between the external load and internal straining obtained from cast-in FBG and generating valuable information about the mechanisms within the strain transition area.It was found that the porosity within the casting has a significant impact on the stiffness of the tensile specimen, the generation of excess microscopic tensions and thus the formation of permanent plastic strains, which are well recognized by the FBG. The knowledge that FBG as internal strain sensors function just as well as common external strain sensors will now allow for the application of FBG in actual structural parts and measurements under real load conditions. In the future, applications for long-term monitoring of cast parts will also be enabled and are currently under development.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
Jochen Hiller, Peter Landstorfer, Philipp Marx, Matthias Herbst
Evaluation of the impact of faulty scanning trajectories in robot-based x-ray computed tomography
Measurement Science and Technology, vol. 32, no. 1
2020
DOI: 10.1088/1361-6501/abaf2a
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X-ray computed tomography (CT) imaging for industrial applications is limited to certain physical conditions to be fulfilled. The size of the measuring object and the accumulated wall thickness are two fundamental conditions. An omission of these conditions by not capturing object attenuation information by the x-ray detector leads to missing data in the 3D reconstruction process and results as a consequence in image degradation and artifacts. Conventional industrial x-ray CT is based on cone-beam projections and circular or helical scanning trajectories using linear axis and a rotary (lift) table. For many inspection tasks on big-sized or unusually shaped objects the physical limits for obtaining a sufficient high image quality are reached very quickly when using conventional CT systems. Industrial six-axis robots offer much more flexibility with respect to the conditions mentioned earlier and can overcome the limitations of conventional scanners. In the present work we characterized an industrial six-axis robot in its working space following ISO 9283 in terms of pose accuracy and pose repeatability. These results are then used to simulate faulty scanning trajectories in terms of pose deviations where a single robot is used as an object manipulator to rotate virtual specimens on a circular trajectory resulting in different (faulty) reconstruction datasets. These datasets are evaluated visually and by using performance parameters and geometrical features in order to determine the reproduction fidelity (performance) of a one arm robot-based CT system depending on different pose errors. With the results obtained it was shown that a robot-based CT system of type B (in our classification scheme) using one robot as object manipulator should be able to reach a spatial resolution power in the range of the voxel size (in our case 200 µm) and smaller (neglecting effects from focal spot size, detector unsharpness from x-ray to light conversation and scatter radiation) if systematic pose errors are compensated using appropriate calibration methods.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
S. Zabler, M. Maisl, Peter Hornberger, Jochen Hiller, C. Fella, R. Hanke
X-ray imaging and computed tomography for engineering applications
tm - Technisches Messen, vol. 87, no. Online veröffentlicht: 08.04.2020
2020
DOI: 10.1515/teme-2019-0151
Abstract anzeigen
After an incremental development which took place over four decades, X-ray imaging has become an important tool for non-destructive testing and evaluation. Computed Tomography (CT) in particular beholds the power of determining the location of flaws and inclusions (e. g. in castings and composites) in three-dimensional object coordinates. Therefore, and thanks to a speed-up of the measurement, CT is now routinely considered for in-line inspection of electronics, castings and composites. When precision and not speed is important, Micro-CT (μCT) can be employed for Dimensional Measurements (DM, e. g. quality assurance and shape verification), as well as for in situ testing, and for characterizing micro-structures in metals and composites. Using appropriate image processing and analysis μCT can determine the local fibre orientation in composites, the granular morphology of battery cathodes or the inter-connectivity of certain phases in casting alloys.
Today, the large variety of X-ray instruments and methods poses an application problem which requires experience and a lot of knowledge for deciding which technique applies best to the task at hand. Application-specific guidelines exist for X-ray radiography testing (RT) only, whereas standardization has been applied to CT, unfortunately leaving out high resolution subμ CT, and nano-CT. For the latter exist an equally high number of NDT applications, however these instruments still necessitate a profound expertise. The task is to identify key industrial applications and push CT from system standardization to application specific automation.
DigitalNachhaltigFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
Gabriel Herl, Jochen Hiller, A. Maier
Scanning trajectory optimisation using a quantitative Tuybased local quality estimation for robot-based X-ray computed tomography
Nondestructive Testing and Evaluation, vol. (Published 21 June 2020), no. 6, pp. 1-17
2020
DOI: 10.1080/10589759.2020.1774579
Abstract anzeigen
Robotic CT systems allow complex scanning trajectories. This work presents a workflow to automatically calculate optimised scanning trajectories for robotic CT systems. In particular, as a local quality estimation, this work introduces a quantitative measure to quantify local reconstruction quality based on the Tuy conditions. The proposed method is tested in two summation experiments using an STL model of a motorcycle. In both experiments, a trajectory is calculated using a quantitative Tuy-based local quality estimation and the reconstruction result is then compared to reconstructions using conventional scanning trajectories. The comparison results indicate that the proposed approach automatically finds trajectories that enable 3D reconstructions with high image quality using much less projection data, which allows a significant reduction of scanning time.
DigitalNachhaltigFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
A. Stock, Gabriel Herl, T. Sauer, Jochen Hiller
Edge-preserving compression of CT scans using wavelets
Insight - Non-Destructive Testing and Condition Monitoring (The British Institute of Non-Destructive Testing), vol. 62, no. 6, pp. 345-351
2020
DOI: 10.1784/insi.2020.62.6.345
Abstract anzeigen
This work addresses the subject of efficient storage of computed tomography (CT) data with an emphasis on the quality of surfaces. Industrial dimensional metrology often requires high measurement accuracy and it is shown that this is retained using wavelet-based compression methods. The applied techniques include a tensor product wavelet transform and soft wavelet shrinkage. In these tests, performed on real objects, dimensional CT measurements of compressed and uncompressed volumes were compared. The necessary storage space was reduced significantly with a negligible loss of accuracy. The storage space required for a multi-sphere phantom was decreased to 4.7% (from 638 MB to 30 MB), with an average deviation below 1 μm from the original volume.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
F. Heilmeier, R. Koos, Peter Hornberger, Jochen Hiller, K. Weraneck, M. Jakobi, A. Koch, W. Volk
Calibration of cast-in Fibre-Bragg-Gratings for internal strain measurements in cast aluminium by using neutron diffraction
Measurement, vol. 163, no. 15 October 2020
2020
DOI: 10.1016/j.measurement.2020.107939
Abstract anzeigen
Fibre Bragg gratings (FBGs) are utilized to function as internal strain sensors during casting, solidification and cooling of two hypoeutectic Al alloys and technically pure Al. In situ neutron diffraction experiments were conducted simultaneously onsite the STRESS-SPEC instrument at the Research-Neutron Source (MLZ) in Garching. The experimental data correlated with structural finite element simulation and X-ray micro tomography (CT) elucidates the mechanisms of this measurement system.
The presented work offers a new practical approach to measure in-situ strains during casting of Al alloys by using FBG-based sensors. The FBG strain results correlate with the Al(311) peak obtained by neutron diffraction which is furthermore used for calibration. The examination of interactions between fibres and surrounding cast Al by finite element simulation and CT of the cast specimens enables the application of the sensors for unequivocal strain measurements in castings as well as the characterization of alloys during solidification.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikBeitrag (Sammelband oder Tagungsband)
Peter Landstorfer, Jochen Hiller, Matthias Herbst
Investigation of positioning accuracy of industrial robots for robotic-based X-ray computed tomography
iCT 2019 9th Conference on Industrial Computed Tomography (iCT) [13-15 February, 2019; Padua, Italy]
2019
Abstract anzeigen
In this research work we investigated the accuracy of a standard industrial robot. We wanted to find out, how accurate an X-RayComputed Tomography (CT) scan can be performed when using such a robot as a manipulator. The accuracy was measuredusing a laser-interferometer. The measured deviations were used to run an X-Ray simulation via Fraunhofer EZRT’s ScorpiusX-Lab. Metrological analysis was performed as a measure for the quality of the simulated CT-scan. The metrological deviationsreflect the feasible accuracy of a CT-scan in a real CT-setup.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikBeitrag (Sammelband oder Tagungsband)
Gabriel Herl, Jochen Hiller, T. Sauer
Artifact reduction in X-ray computed tomography by multipositional data fusion using local image quality measures
iCT 2019 9th Conference on Industrial Computed Tomography (iCT) [13-15 February, 2019; Padua, Italy]
2019
Abstract anzeigen
Metal artifacts are still a major problem in X-ray industrial computed tomography. In order to reduce metal artifacts and increase the image quality of X-ray CT-scans, we suggest using projection data from multiple scans with differently positioned object orientations. We present two different approaches for multipositional CT, which are especially effective for multimaterial objects with high absorbing metal parts. On one hand, we reconstruct the different scans separatly, estimate the local quality of the resulting volumes and then fuse these volumes to an optimized volume. On the other hand, we introduce smART (shrinking merged Algebraic Reconstruction Technique) and merge sinograms of different scans, estimate the reliability of each projection pixel and then reconstruct the merged sinogram with an adapted SART reconstruction method. We demonstrate our approaches on simulations and on measurement data and are able to show a significant reduction of image artifacts qualitatively and quantitatively with the help of dimensional measurement results.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikZeitschriftenartikel
Gabriel Herl, Jochen Hiller, S. Kasperl, A. Maier
Reduktion von Metallartefakten durch multipositionale Datenfusion in der industriellen Röntgen-Computertomographie
tm - Technisches Messen, vol. 87, no. 2
2019
DOI: 10.1515/teme-2019-0137
Abstract anzeigen
Metallartefakte stellen eine große Herausforderung für das Messen mit Röntgen-Computertomographie dar. Dieser Beitrag stellt die Methode der multipositionalen Datenfusion zur Reduktion von Metallartefakten vor. Dazu werden mehrere Scans desselben Objekts bei unterschiedlicher Objekt-positionierung durchgeführt, aufeinander registriert und zur Fusion gemeinsam unter Betrachtung eines lokalen Gütemaßes rekonstruiert. In praxisnahen Experimenten wird der Mehrwert der Methode gezeigt. Insbesondere wird dargestellt, wie mit wenig Aufwand und ohne Vorwissen Kunststoffstrukturen trotz starker Metallartefakte sichtbar gemacht werden können, womit das Verfahren ein Alleinstellungsmerkmal gegenüber den existierenden Metallartefaktreduktionsverfahren aufweist.
NachhaltigElektrotechnik und MedientechnikIQMAMaschinenbau und MechatronikZeitschriftenartikel
L. Jiang, Jonas Weber, F. Puglisi, P. Pavan, L. Larcher, Werner Frammelsberger, Günther Benstetter, M. Lanza
Understanding Current Instabilities in Conductive Atomic Force Microscopy
Materials, vol. 12, no. 3
2019
DOI: 10.3390/ma12030459
Abstract anzeigen
Conductive atomic force microscopy (CAFM) is one of the most powerful techniques in studying the electrical properties of various materials at the nanoscale. However, understanding current fluctuations within one study (due to degradation of the probe tips) and from one study to another (due to the use of probe tips with different characteristics), are still two major problems that may drive CAFM researchers to extract wrong conclusions. In this manuscript, these two issues are statistically analyzed by collecting experimental CAFM data and processing them using two different computational models. Our study indicates that: (i) before their complete degradation, CAFM tips show a stable state with degraded conductance, which is difficult to detect and it requires CAFM tip conductivity characterization before and after the CAFM experiments; and (ii) CAFM tips with low spring constants may unavoidably lead to the presence of a ~1.2 nm thick water film at the tip/sample junction, even if the maximum contact force allowed by the setup is applied. These two phenomena can easily drive CAFM users to overestimate the properties of the samples under test (e.g., oxide thickness). Our study can help researchers to better understand the current shifts that were observed during their CAFM experiments, as well as which probe tip to use and how it degrades. Ultimately, this work may contribute to enhancing the reliability of CAFM investigations.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikBeitrag (Sammelband oder Tagungsband)
A. Stock, Gabriel Herl, T. Sauer, Jochen Hiller
Edge preserving compression of CT scans using wavelets
SHM-NDT 2018 International Symposium on Structural Health Monitoring and Nondestructive Testing 4-5 Oct 2018, Saarbrücken – Germany
2018
Abstract anzeigen
This work addresses the subject of efficient storage of computed tomography (CT) data with an emphasis on the quality of surfaces. Industrial dimensional metrology often requires high measurement accuracy and we show that this is retained using wavelet-based compression methods. The applied techniques include a tensor product wavelet transform and soft wavelet shrinkage. In our tests on real objects, we compared dimensional CT measurements of compressed and uncompressed volumes. We were able to reduce the necessary storage space significantly with a minimal loss of accuracy. For a multi sphere phantom, we decreased the storage space to 4.7% (from 638 MB to 30 MB) with an average deviation below 1 µm from the original volume.
DigitalFraunhofer AWZ CTMTMaschinenbau und MechatronikBeitrag (Sammelband oder Tagungsband)
A. Stock, Gabriel Herl, T. Sauer, Jochen Hiller
Metal artifact reduction by fusion of CT scans from different positions using the unfiltered backprojection
iCT 2018 8th Conference on Industrial Computed Tomography (iCT) 2018, 6-9 Feb, Wels, Austria
2018
Abstract anzeigen
Metal objects or metal parts in an object are still a major problem of X-ray computed tomography (CT) because of so called metal artifacts. We propose a new method – a multipositional data fusion – for automatically fusing multiple CT volumes from different positions to reduce these metal artifacts. After scanning a specimen several times at different positions and reconstruction of every scan (e.g. by the filtered backprojection), we also perform an unfiltered backprojection. Based on the assumption that metal artifacts occur the most wherever X-rays are attenuated a lot, the unfiltered backprojection is used to autonomously estimate the likelihood of metal artifacts in every voxel of every scan. The different volumes are registered and then fused by weighted sum preferring the voxels with low values in the unfiltered backprojection results. In our tests on real objects, our method fully automatically created optimized volumes with significantly less metal artifacts. The multipositional data fusion was compared to the commercially multi spectra fusion of Werth Messtechnik GmbH and outperformed it in one of the use cases.
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