Chemical residues, generally resulting from material preparation, exist in the volume of polymer insulations and impact their dielectric properties. This is particularly the case in XLPE, where by-products from cross-linking and antioxidants exist. In the presence of an electric field, these chemical species can dissociate or ionize, giving rise to ionic charges. Like electronic charges, ions contribute to conduction and to space charge accumulation in the insulation under DC stress. However, it is difficult experimentally to distinguish the role of electronic and ionic species. In this paper, we simulate the impact of the presence of ions by modeling their generation and transport in an XLPE containing dissociable by-products. Ionic phenomena are combined with electronic ones in a bipolar charge transport model, assuming that ionic charges result from dissociation of neutral species in the insulation volume. The model is described, and simulation results are presented and discussed as regards the impact of the presence of ionic species on space charge and current.