Fuel inventory codes are used to predict the effect the composition of radioactive material following periods of irradiation and/or radioactive decay.
FISPIN (UK code) is a fuel inventory/depletion code. It calculates the changes in the numbers of atoms of the nuclides of various species – heavy isotopes or actinides, fission products, and structural or activation materials – as a sample of nuclear fuel element is subjected to periods of irradiation and cooling.
ORIGEN (US code) forms part of the SCALE suite of codes.