Large-scale molecular dynamics of cascade production of the primary damage state are performed in nanocrystalline nickel with an average grain diameter of 12 nm and primary knock-on atom kinetic energies ranging from 5 to 30 keV. The role of the grain boundary during the cascade production of irradiated NC Ni is discussed in terms of grain-boundary structure. It is shown that regions of misfit in the grain boundaries can absorb self-interstitials and that stacking-fault tetrahedra are formed in the neighbourhood of the grain boundary.