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Enhancing Nuclear Safety


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Development of Eddy Current Simulation Features within CIVA for the Analysis of Steam Generator Tubing Inspection Safety Issues


Congress title :6th International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components
Congress location :Budapest
Congress date :08/10/2007

Summary

The assessment of Steam Generator (SG) tubes integrity is a challenging task with respect to the numerous degradation mechanisms observed worldwide and to the number of tubes in service. In the framework of extended cycles and optimization of their maintenance programs, utilities may revise their Technical Specifications for SG inspections. These Technical Specifications revisions and other current SG safety related issues such as Tube Support Plate (TSP) blockage have to be evaluated by the safety authorities. IRSN carries out research and analysis on the risk related to radioactivity for the French Safety Authority (ASN). Since many years, IRSN has contributed to the development of simulation tools for the evaluation and expertise of Non-Destructive Testing techniques used by the nuclear industry. These developments, among other from various contributors (industries, research institutes, academics) belonging to diverse industrial branches (nuclear, aeronautics, automotive, metallurgy ...) have been appended to the CIVA NDT platform developed by CEA. In this paper, the main features of CIVA for SG tube inspection are reviewed and commented through typical applications. The first example presents the bobbin coil inspection configuration. The bobbin coil response to longitudinal notches, transversal notches and volumetric flaws such as flat bottom holes or loss of material (defined in cylindrical coordinates) can be simulated. The effect of possible probe eccentricity on probe sensitivity might also be assessed. Those simplified configurations might be used to model SG tube degradation mechanisms like Stress Corrosion Cracking (SCC) and, to a certain extent, wear. Although great care has to be taken to extrapolate simplified modelled degradations to realistic industrial configurations, simulation gives valuable information for overall estimation of the probe performances. The second example addresses rotating probe configurations which, as a matter of fact, can be modelled using a planar configuration considering the usually small dimensions of rotating probes with respect to the tube radius. The performances of probes for simplified flaws (notches) can be estimated and the effect of perturbations factors on EC signal can be evaluated. The perturbation factors might be related to the tube environment (e.g. tube fouling) or to the inspection process (e.g. probe tilt and lift-off). For quantitative assessment, the validation of the simulation tools is a key point thus great care has been taken for the comparison between numerical results and experimental data on a set of artificial flaws. The validation approach and the conclusions are presented. The main prospects of future developments within CIVA for SG inspection safety issues are presented: modelling of TSP, tube fouling and clogging of the TSP by magnetite. The developments will address first the bobbin coil and then the rotating probes.

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