FISCHOOSE ncho fischo(i) i=1,ncho
FISCHOOSE affects the choice of actinides included in the pathways analysis, not the actinides included in the activation calculation. USEFISSION and FISYIELD are the keywords to use to alter the treatment of actinides in the activation calculation.
When actinides are included as trace elements in a material then dominant nuclides that can be formed as a result of the fission of an actinide will be considered in the calculation of pathway information. Although uranium and thorium may have been the only actinides input, neutron-induced reactions and decay will create many other fissionable actinides and the user may wish to specify which of these actinides are considered as possible parents when calculating the pathways. By default all actinides are considered, but by setting ncho and specifying the identifiers of the actinides the user can limit the nuclides to be included.
In most cases minor actinides are unlikely to have significant impact on the total radiological quantities and so are unlikely to be part of the important pathways. Also this keyword only affects the calculation of pathways, all actinides are considered during the calculation of inventories (unless the use of other keywords indicates otherwise).
An example to include any pathways with the fission of U238, Pu239, Pu240 and Pu242 in the pathways analysis would be:
< -- Control phase -- > ... FISPACT * Title of the simulation < -- Initial phase -- > ... USEFISSION FISYIELD 4 U235 Pu239 Pu240 Pu242 FISCHOOSE 4 U235 Pu239 Pu240 Pu242 ... < -- Inventory phase -- > ...