Ultrasonic simulation tools have been gathered in the Civa software developed at CEA (the French Atomic Energy Commission), in order to conceive, optimise and predict the performances of various inspection techniques. Those models are based on semi-analytical kernels and numerical integration, so that realistic 3D and time transient configurations may be dealt with, and specific emphasis is made to optimise time computations, so that these models can be used for parametric studies in spite of potentially complex configurations. These simulation tools include beam propagation and defect scattering models, thus the whole inspection performances may be predicted for a wide range of applications (phased arrays, complex specimen geometry and/or materials, various flaws). This paper addresses some experimental validations of those models, in the frame of collaboration with the French Institute for Radiological Protection and Nuclear Safety (IRSN). Applications concerned include validation of inspection predictions over realistic configurations in terms of probes, specimens, and flaws, for which developments have been achieved to deal with complex shapes (planar flaw with a contour defined by CAD and multi-facetted flaws). This paper addresses some experiments carried out with mock-ups containing calibration reflectors (side drilled hole, flat bottomed holes) or artificial complex shaped defects, for which complex phenomenon may occur in the echo formation. Comparison with simulated results is presented and discussed in order to assess the validity range of the simulation models.