Freezing phenomena of ceramic alumina melts flowing in pin bundles

This paper reports that the potential for recriticalities and high energetics during the transition phase of the a hypothetical core-disruptive 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