The potential for recriticalities and high energetics during the transition phase of a hypothetical coredisruptive accident in a liquid-metal fast breeder reactor is strongly dependent on the fissile fuel inventory remaining in the core region. To investigate the ability of the fuel to penetrate unblocked flow paths, a series of experiments with pin bundle geometry has been performed at the THEFIS facility using alumina and alumina-iron melts as fuel simulants. Several series of similar experiments were done previously with tubes, annuli, and three-pin bundles using alumina, iron, and mixtures of alumina and iron melts. In this new series, seven-pin bundles with wire wrappers and grid spacers defining the cooling channels between the single pins have been investigated. These bundles are a more realistic representation of the upper blanket structure. These out-of-pile experiments have been analyzed with the PLUGM code, which is based on the assumption of stable crust growth during the penetration and freezing process. The differences in results between out-ofpile experiments using alumina and those using UO2 are discussed, and an explanation for these discrepancies is indicated.