As some structural properties, like generative families of positive P-invariants, can only be computed in P/T nets, unfolding of Colored Petri Nets is of interest. However, it may generate huge nets that cannot be stored concretely in memory. In some cases, removing the dead parts of the unfolded net can dramatically reduce its size, but this operation requires the unfolded net to be represented anyway. This paper presents a symbolic representation of unfolded nets using Data Decision Diagrams. This technique allows to store very large models and manipulate them for optimization purpose.