The main coolant line (MCL) is a part of the primary coolant boundary and it is the key factor for the reactor safety. In order to guarantee the integrity of the primary circuit, full volumetric ultrasonic examination is required for the MCL welds of the European Pressurized Reactor (EPR) according to the RSE-M code 2010 Version. The difficulties for application of the ultrasonic inspection on the MCL welds are mainly caused by limited access space and coarse austenitic grain structure. In this study, inspection system including automated scanner and transmitter/receiver longitudinal wave technique has been developed in consideration of the multiple constraints. The qualification process of the ultrasonic examination on the test mock-ups including flaw sizing results is also presented and commented.