Investigations of the thermodynamic behavior of reactor fuel elements require out-of-pile experiments to be carried out on fuel element mockups made up of electrical heater rods. The results of these experiments depend strongly on the similarity of thermodynamic behavior between heater rods applied and nuclear fuel rods to be simulated. Typical requirements for the heater rods that simulate the nuclear fuel rods of interest are, for example, heat flux density and the associated heat flux density distribution in case of nonuniform coolant conditions and heat capacity. Because of the various modes of heat production in nuclear fuel rods, electrically heated rods in experiments are able to only partially meet these requirements. A type I heater with a nickel-chromium conductor, maximum rod power up to 340 W/cm at cladding temperatures up to 1200 K, and a type II heater with a tantalum-tungsten conductor, rod powers up to 1000 W/cm at cladding temperatures of 1200 K, were examined experimentally in a liquid sodium flow and showed lifetimes up to 10 h and more. They can be fabricated with different geometrical dimensions (e.g., diameters, heated and unheated lengths) and varying axial heat production.