Directly related to the key technological issues identified within FINESSE are basic material interactions. These material interactions arise from material property changes and lead to interactive effects which have been identified for several first wall/blanket concepts. Emphasis has been placed upon those interactive effects which are directly related to accumulated neutron damage. For testing purposes the minimum accumulated neutron fluence needed to substantially reduce the uncertainty associated with an anticipated material interaction must be defined. A method of projecting uncertainties associated with interactive effects has been developed to determine these fluence goals for selected issues.