Ongoing research projects

EU project NOMAD

The European research project NOMAD – Nondestructive Evaluation (NDE) System for the Inspection of Operation-Induced Material Degradation in Nuclear Power Plants – pursues the goal of developing a test system to quantify neutron-induced material embrittlement in nuclear power plants in a non-destructive manner, particularly for the non-replaceable reactor pressure vessels with a limited service life. The research consortium consists of 10 European partners from Belgium (SCK-CEN), Germany (Fraunhofer IZfP, Eurice), Finland (VTT), United Kingdom (Coventry University), Spain (Tecnatom), Hungary (MTA-EK, Hepenix) and Switzerland (PSI, SVTI). Six different NDT processes based on various physical principles are used in the research project for the development of the non-destructive testing system – the NDE tool. These are assessed in terms of their sensitivity to neutron embrittlement on samples that were exposed to different irradiation cycles in the research reactor. The samples, which were made from four different types of base material, also have different geometries – from impact samples to cladded test samples. The innovative approach of the research project involves not only combining the different processes but developing the combination into an NDE tool that also makes use of the opportunities offered by machine learning. Four technical work packages were defined:

• WP1: ‘Description and delivery of the sample sets (including cladded material) and irradiation conditions, sample provision, microstructure characterisation and determination of the mechanical properties’
• WP2: ‘Non-destructive materials characterisation (MC) and evaluation of the progression of the material properties’
• WP3: ‘Advanced non-destructive evaluation tool for demonstration of materials characterization’
• WP4: ‘Application and validation’

Due to the wide range of experiences from the qualification of non-destructive testing systems (Swiss non-destructive testing qualification body), the SVTI has taken over the management of work package 4 ‘Application and validation’. The challenge now faced by the European research project is, among other things, to validate a test system under the most realistic possible boundary conditions based on machine learning approaches. Determining the performance of such test systems, the functionality of which is only partially understood due to machine learning, will also be relevant in the future for further qualifications, particularly with regard to the reliability of test systems in field applications with varying boundary conditions.

The project is funded by the EU under the Euratom research and training programme 2014-2018 under grant agreement no. 755330.

PIONIC

The international research project PIONIC continues the investigations into the performance of current and new NDT processes and testing techniques carried out in the previous research programmes PINC (International Program for Inspection of Nickel-alloy Components) and PARENT (Program to Assess the Reliability of Emerging Nondestructive Techniques). The overall goal of these activities between the United States (NRC, PNNL, EPRI), Sweden (SSM, SQC), Finland (VTT, Aalto University), Korea (SKKU, KINS), Japan (MHI, JAPEIC) and Switzerland (ENSI, PSI, SVTI) is to determine the performance of the NDT testing techniques used (ultrasound and eddy current) for the verification and characterisation of simulated stress corrosion cracks (SCC).  Furthermore, the understanding of influencing factors such as defect and weld seam properties must be expanded to include defect detection and defect size determination. Series of international round robin tests (RRT) were therefore carried out on open test samples and blind test samples of different geometries with austenitic weld seams and mixed weld seams with the involvement of commercial providers, laboratories and universities. The applied testing techniques were quantitatively assessed and compared using the ‘hit-miss’ probability of detection (POD) approach. In order to expand the number of test defects for the performance evaluation, artificial stress corrosion cracks – generated by modelling and simulation as well as by the reproduction of real crack indications – were examined in addition to the creation of real stress corrosion cracks. Both sources serve to refine the POD calculation and thus the performance evaluation through a larger number of test defects. Based on the empirical tests and the update of the POD analyses through artificial test defect responses, a procedure will be developed to realistically quantify performance. Furthermore, the assessment of the data should be supported by artificial intelligence. The developed procedure must be summarised in a nuclear-specific guide for the implementation of POD analyses for the assessment of test techniques in nuclear technology.

The following task groups were established in the PIONIC research project:

• Task Group 1 ‘NDE modelling and simulation’
• Task Group 2 ‘Flaw relevance evaluation’
• Task Group 3 ‘Materials degradation monitoring’
• Task Group 4 ‘Probability of detection analysis’
• Task Group 5 ‘Machine learning’

The international research project with contributions from supervisory authorities, companies, universities and research institutions is financed by ‘in-kind contributions’ from the project partners.

ASTRA research project – ‘Detection and location of gravel pockets in concrete components’

To ensure the stability and durability of reinforced concrete structures, careful construction is of key importance in addition to the structural dimensioning of the design to permanently ensure the corrosion protection of the inserted reinforcement against environmental influences, among other things. This also includes the defect-free concreting of the concrete components. The verification of fault-free concreting or the detection of defective areas in the form of gravel pockets or segregation (which can occur, for example, with densely reinforced component cross-sections, high concreting heights or complex geometries) has so far only been carried out as quality control after concreting in a few individual cases. The aim of this research project is to determine the practical building boundary conditions of reinforced concrete components under which gravel pockets or segregation can be reliably detected and quantified without destruction. For this purpose, the first step involves determining typical gravel pocket characteristics, which are then simulated experimentally. These artificial gravel pockets are then examined using acoustic methods such as the ultrasound technique or the impact echo method. These experimental examinations are supported by initial test problem modelling approaches. Finally, recommendations are formulated with boundary conditions under which a gravel pocket or segregation can be reliably detected in practice.

The following work packages are being executed in the project:

• Literature research on typical gravel pocket characteristics and associated signal responses
• Creation of test samples and practical studies
• Modelling of test samples and theoretical examinations
• Recommendations for the detectability of gravel pockets or for an optimal NDT system

The national research project, managed together with the project partner TFB AG (Swiss company specialising in technology and research in concrete construction), is funded by the Federal Roads Office (FEDRO) under project number AGB 2018/006 ‘Non-destructive detection of gravel pockets in reinforced concrete components’.