The Dual Fluid Reactor – A novel concept for a fast nuclear reactor of high efficiency

The Dual Fluid Reactor, DFR, is a novel concept of a fast heterogeneous nuclear reactor. Its key feature is the employment of two separate liquid cycles, one for fuel and one for the coolant. As opposed to other liquid-fuel concepts like the Molten-Salt Fast Reactor (MSFR), both cycles in the DFR can be separately optimized for their respective purpose, leading to advantageous consequences: A very high power density resulting in remarkable cost savings, and a highly negative temperature feedback coefficient, enabling a self-regulation without any control rods or mechanical parts in the core. In the current reference design the fuel liquid is an undiluted actinide trichloride based on isotope-purified Cl-37, circulating at an operating temperature of 1000 °C. It can be processed on-line in a small internal processing unit utilizing fractional distillation or electro refining. Medical radioisotopes like Mo-99/Tc-99m are by-products and can be provided right away. In a more advanced design, an actinide metal alloy melt with an appropriately low solidus temperature is also possible which enables a reduction of the core size and allows a further increase in the operating temperature due to its high heat conductivity. For the reference design, pure Lead as coolant is the best choice. It yields a very hard neutron spectrum, fostering a very good neutron economy and therefore making the DFR a preferred thorium breeder but also a very effective waste incinerator and transmuter. With its high coolant temperature the DFR achieves the same ambitions as the Generation IV concept of the very high temperature reactor (VHTR), with all its advantages like electricity production with high efficiency and the synthesis of carbon-free fuels, but with overall production costs competitive with today’s refined oil. The specific combination of the liquids in the very high temperature regime requires structural materials withstanding corrosive attacks. Because of the small size of the reactor core the utilization of these expensive materials would have no significant impact on the overall energy (and also economic) efficiency, measured by the EROI (Energy Return on Investment), which is more than 20 times higher than for a light-water reactor (LWR). The DFR inherits the positive properties of the lead-cooled reactor (LFR) and of the MSFR, especially its outstanding passive safety features.