[en] An analytic logic system is described that can be used to define the state of a reactor core with respect to the probability of the loss of fuel rod cladding hermeticity. The cladding flaw growth index (CFGI) logic for computing the probability of cladding failure as a function of axial location along each fuel rod depends on the calculated linear heat generation rate (LHGR) variation of this specified length of the fuel rod as a function of irradiation. It also assumes that the probability of failure depends on both a current power maneuver and all previous power change events (i.e., it assumes that failure can result from a cumulative process). This logic system can be used to aid in the location (detection) of failed fuel bundles and as part of a computational system to evaluate and anticipate the effects of power change maneuvering (duty cycle) on fuel rod reliability