1. A non-transitory computer readable media, comprising a nuclear-characteristic calculating program executable by a processor for calculating a nuclear characteristic of a fuel rod that contains nuclear fuel and burnable poison that loses neutron absorption capability with a neutron absorption reaction of absorbing a neutron, wherein the nuclear-characteristic calculating program includes: a first scattering model that can represent a simple scattering of the neutron with light calculation load as a scattering model for representing a scattering of the neutron; a second scattering model that can represent a complicated scattering of the neutron with heavy calculation load compared to the first scattering model as a scattering model for representing a scattering of the neutron; a first nuclear-characteristic calculating of calculating, when a burnup of the fuel rod is before a set burnup at which the burnable poison is considered to lose the neutron absorption capability, the nuclear characteristic of the fuel rod by using the second scattering model; a scattering-model switching 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 a second nuclear-characteristic calculating of calculating, after switching the scattering model, the nuclear characteristic of the fuel rod by using the first scattering model.