Ultrasonic detection and sizing of intergranular stress corrosion cracks (IGSCC) in nuclear reactor cooling systems is a difficult practical problem due to the complicated geometry of these defects and to the variety of other reflectors (e. g., welds) which produce competing ultrasonic indications. The use of models of scattering from such defects can help in improving physical insight into ultrasonic scattering from IGSCC’s and may ultimately be of use in defining inspection protocols and signal processing algorithms which can lead to improved inspection reliability and discrimination between IGSCC’s and other geometrical reflectors. This paper will discuss the application of a model of ultrasonic scattering from a simple Y-shaped crack based upon the Kirchhoff approximation. In this model, the ultrasonic beam is approximated by a Gaussian profile which includes the effects of diffraction and allows calculation of the full ultrasonic radiation pattern which may be used, for example, to simulate a scanned inspection. Included in this paper will be a brief description of the model and a presentation of simulated IGSCC results. Comparisons of the model to experimental measurements will then be addressed followed by an application to the problem of IGSCC sizing based upon the dB-drop and PAT (pulse-arrival-time) techniques.