Abstract: The credit nuclide selection is the key step in burnup credit for spent fuel storage criticality safety analysis. Based on typical PWR fuel assembly with different enrichment, burnup and cooling time combinations, important nuclides in criticality safety analysis were selected according to nuclide importance ranking in terms of their fractional neutron absorptions. The results show that 47 nuclides can bound 99% nuclides which affect the spent fuel storage system reactivity during 0.20 a after shutdown. The validation analysis shows that the selection method is reasonable and the selected nuclides can adequately represent all dominant nuclides in system reactivity calculation.