Intrasubassembly incoherencies affecting the fuel pin failure pattern within a fast test reactor (FTR) subassembly during an unprotected transient overpower/hypothetical core disruptive accident have been investigated using the COBRA-III/MELT code. Two dominant intrasubassembly incoherencies in an FTR subassembly were studied, namely, (a) the hydraulic effect, or the variation in pin-power-to-effective-coolant ratio between pins in the inner region and those in the outer region of the sub-assembly, and (b) the power skew, or variation in pinwise power density for pins throughout the subassembly. The hydraulic effect study concluded that a one-pin representation as used in SAS3A and MELT-IIIA does not represent the fuel pin failure characteristic of any pin in the inner or outer region of the subassembly, but only the failure characteristic of some hypothetical “average” pin, which generally fails much later than most of the pins that actually would fail in the subassembly during the postulated accident. From the power-skew study, it was found that the domain of fuel pin failure times is further widened by the power-skew incoherency. A widened domain of failure times can alleviate molten fuel/coolant interaction by not squirting molten fuel into all coolant subchannels simultaneously. The power skew also produces an eccentric failure pattern within the subassembly that reduces the possibility of a complete fuel blockage.