[en] The device provides automatic control of coolant flow through the fuel assembly. It consists of a fixed assembly part and of an adjustable throttle element mounted at the assembly outlet. A flexible force element (a spring or a bellow containing compressed gas) and parallel to that a bellow are fitted between the movable part of the throttle element and the fuel assembly. The space formed between the force element and the bellow is filled with a liquid with a pressure of saturated vapours lower than the coolant operating pressure. (M.D.)