The incident that occurred in Dampierre nuclear power plant (France) in April 2001 and consisted in the introduction of the 26th assembly of the reloading sequence in the reactor vessel instead of the 25th, was due to a human error and resulted in 113 assemblies located at the wrong position in the core before detection. This incident highlighted the importance of the parameters that could cause the reactor divergence during reloading operations. The analysis pointed out a potential criticality risk under less favorable circumstances. It was also noticed that neutron source range channels could not detect a local increase in reactivity unless a reactive pattern was formed closely to one of the channels. Analysis of this incident brought about preventive measures concerning fuel handling and higher reactor vessel boron concentration prescriptions. However, other fuel reloading errors occurred after that, even if they were detected almost immediately. Thus, incidents during the reloading operation need to be considered as a possible precursor of a reactivity accident. This paper presents the criticality calculations performed at IRSN with CRISTAL package, for different core configurations with a single mistake during the sequence of reloading. These calculations identify, for the most reactive pattern of assemblies placed at the wrong position, the margin existing from a criticality point of view. Moreover, the reactivity effects of different parameters like fuel enrichment, moderator density, boron concentration, etc. are evaluated.