One of the main issues concerning a cobalt 60 irradiator is the optimization of the source. This optimization concerns the homogeneity of the dose distribution inside the product, the geometrical contribution of each pencil, the yield etc. Such an optimization can be done easily using a simulation tool. One simulation tool is the 3D Monte Carlo software RayXpert®. With it you can build from scratch a complete cobalt 60 facility with the source, the product and the bunker. For complex facilities, some interesting functionalities are available such as the scripting module that can create hundreds of sources from a file, or the step import in order to insert a complex geometry from a CAD tool. Among others, RayXpert® offers you the possibility to calculate absorbed dose rate (Gy/h) or kerma water rate (Gy/h). Thus, you can easily test different configurations of source placement, including source overlap or product overlap issues, in order to quantify the impact on the dose distribution inside the product and select the one that offers the best homogeneity. A lot of industrials already use RayXpert® to make dose distribution calculation in complex industrial context.