For long-term use of the nuclear energy program, control and management of nuclear waste generated in a reactor are essential. In recent decades, the transmutation of long-lived fission products (LLFPs) into some stable or short-lived nuclei by accelerator driven systems (ADS) has been investigated and developed as one of the methods to reduce the radioactive contamination of spent fuel. In MCNPX code, the interaction tally calculates the transmutation rate of nuclei for which tabulated data exist, but does not score in the model physics regime. To circumvent this problem, this study proposes a response function that is consistent with the physics models used in the MCNPX code. This is used to estimate the transmutation rate of 129I in an ADS containing protons and spallation neutrons with energies up to 1500 MeV. To generate this response function, a very thin 129I target is used, the small size of the target allows attenuation and energy loss to be ignored. To do so, for neutrons, 168 energy bins from 10 MeV to 1500 MeV, and for protons, 120 energy bins from 1 MeV to 1500 MeV are considered.
