The ability of models to deal with accurate descriptions of the piece geometry and materials (by CAD) is a key-point for simulation work. Availability of semi-analytical models for simulating sensor and actuator behaviours and the interaction of the “field” with the piece allows both versatility and efficiency. Simulation tools developed at CEA for NDT of realistic configurations have been presented. Ultrasonic, radiographic and eddy-current techniques are considered. They are based on semi-analytical formulations for efficiency. Numerical integration is performed wherever necessary for generality. They are included in a general software CIVA allowing the processing, the imaging and the simulation of NDT data. Simulations are used as laboratory tools for conceiving and qualifying methods and demonstrating their performance, teaching and training operators. They are also used in field work context for in-service inspections to help experts' interpretation, by direct simulation of their guess for immediate comparison with actual data or by means of model-based inversion algorithms. (4 pages)