A study of various core designs was conducted to investigate design features pertaining to the preclusion of energetic hypothetical core disruptive accidents. The design data and core layouts for different designs are described. A summary of the nuclear performance predicted for several typical low sodium void worth cores is presented. It appears that the tightly coupled heterogeneous core configuration offers a substantial reduction in prompt void worth and flux level at the expense of greater inventory, large flux gradients, and large changes in internal blanket power over the operating cycle.