In this paper, the possibilities and advantages of loading mixed used nuclear fuel (UNF) assemblies into canisters for final repository are presented from a criticality aspect within the burnup credit approach (BUC). UNF coming from a Swiss reactor are taken into account at the pin-by-pin level and two canister loading patterns are studied: mixed and homogeneous (i.e. mixing UNF with various burnup values and enrichments, or not). The advantages of the mixed cases are presented in terms of criticality, together with the impact of assembly axial and radial rotations. The main outcome of the mixed loading is that a variety of UNF assemblies can be safely loaded together, including those which were previously not allowed in the homogeneous case.