This keyword causes fission reactions for which ssion yield data are stored in the fission yield library to be self-consistently included in the matrix describing the inventory equations. It should be used in conjunction with FISYIELD whenever actinides (or other heavy elements that are transmuted to actinides) are speci ed in the target material. When it is absent, all fission reactions are omitted from the inventory equations, leading to much faster calculations which remain accurate when there are no actinides in the initial inventory and none is produced. If there are actinides in the initial inventory and the USEFISSION keyword has not been used, then warning messages are written to both the output and runlog files.
An example where the fission of U238, Pu239, Pu240 and Pu242 will produce fission products in the simulation would be:
< -- Control phase -- > ... FISPACT * Title of the simulation < -- Initial phase -- > ... USEFISSION FISYIELD 4 U235 Pu239 Pu240 Pu242 ... < -- Inventory phase -- > ...