A nuclear-characteristic calculating program for calculating a nuclear characteristic of a fuel rod that contains nuclear fuel and burnable poison includes a first scattering model that can represent a simple scattering of the neutron and a second scattering model that can represent a complicated scattering of the neutron. The nuclear-characteristic calculating program includes step of calculating, when a burnup of the fuel rod is before a set burnup at which the burnable poison is considered to lose neutron absorption capability, the nuclear characteristic of the fuel rod by using the second scattering model, step of switching, when the burnup of the fuel rod is the set burnup, the scattering model from the second scattering model to the first scattering model, and step of calculating, after performing step of switching, the nuclear characteristic of the fuel rod by using the first scattering model.