Cécile Gueudré

Geometric characterization of a circumferential seam by automatic segmentation of digitized radioscopic images

The present study deals with the nondestructive control of a circumferential seam by digital radioscopy. A series of images for one complete revolution of the welded component is available. We first resort to a joint approach by simulation and experimentation. This approach allows the detection of the molten zone limits for an initial image. We then develop a segmentation method that permits automatic extraction of the geometric characteristics of the set of images representative of the weld. These measures supply fast and automatic control of the weld quality. Results are shown for real components.

DETERMINATION OF THE ORDER OF PASSES OF AN AUSTENITIC WELD BY OPTIMIZATION OF AN INVERSION PROCESS OF ULTRASOUND DATA

Multipass welds made in austenitic stainless steel, in the primary circuit of nuclear power plants with pressurized water reactors, are characterized by an anisotropic and heterogeneous structure that disturbs the ultrasonic propagation and challenge the ultrasonic non‐destructive testing. The simulation in this type of structure is now possible thanks to the MINA code which allows the grain orientation modeling taking into account the welding process, and the ATHENA code to exactly simulate the ultrasonic propagation. We propose studying the case where the order of the passes is unknown to estimate the possibility of reconstructing this important parameter by ultrasound measures. The first results are presented.

Study of Ultrasonic Characterization And Propagation In Austenitic Welds: The MOSAICS Project

Regulatory requirements enforce a volumetric inspection of welded components of nuclear equipments. However, the multi-pass austenitic welds are characterized by anisotropic and heterogeneous structures which lead to numerous disturbances of the ultrasonic beam. The MOSAICS project supported by the ANR (French National Research Agency) aims at matching various approaches to improve the prediction of the ultrasonic testing in those welds. The first stage consists in characterizing the weld structure (determination of the columnar grain orientation and measurements of elastic constants and attenuation coefficients). The techniques of characterization provide input data for the modeling codes developed in another task of the project. For example, a 3D version of the finite elements code ATHENA is developed by EDF R&D to take into account anisotropic texture in any direction. Semi-analytical models included in CIVA software are also improved to better predict the ultrasonic propagation in highly anisotropic and heterogeneous structures. The last stage deals with modeling codes validation based on experimental inspections on representative mock-ups containing calibrated defects. The objective of this paper is to give an overview of the MOSAICS project and to present specific results illustrating the various tasks.

Towards nonlinear ultrasonic characterization of air microbubbles in water

The characterization of argon microbubbles in liquid sodium is currently being investigated in connection with the development of Generation IV nuclear reactors. It seems that nonlinear acoustic techniques can be used to determine the void fraction (volumetric fraction of free gas) and the histogram of the bubble radii. We discuss the first stage of our work here: the development of an experimental test bench suitable for generating air microbubbles in water and then measuring them optically, before attempting an acoustic characterization. The bubble clouds generated have a radius distribution centred on about 20 microns.