This study considers a fast-reactor concept in which the recirculating molten plutonium alloy fuel is externally cooled by direct contact with an immiscible coolant fluid. An example of one such design is given using sodium as the coolant and Pu/Co/Ce ternary as the fuel. Operational characteristics are discussed showing the self-regulating features of the system. Some fission-product-removal mechanisms are considered together with their effect on core life and system safety. The principal problem areas are fuel pumping, phase separation, and containment-materials compatability.