Detecting liq. metal leakages from nuclear reactor circuit components

A sub-assembly for the detection of leakages of a liq. metal circulating in a component of a circuit, e.g. a pipe or a valve or contd. in a vessel, e.g. liq. sodium circulating in the circuits of a nuclear reactor, incorporates electrically conducting elements placed inside an electrically insulating material. The insulating material consists of a rigid shell, the inner face of which conforms in shape to the outer face of the component. Open grooves are formed on the inner face of the shell to receive the conducting elements. The grooves have a widened part away from the inner face of the shell, receiving the elements, and a part of reduced width between the widened part and the inner face of the shell, keeping the elements sepd. from the inner face. The device avoids faults of existing devices comprising e.g. wires, plates or grids associated with an insulating support constituted by a fabric of silica threads or by a layer of permeable felt, of which the time of response is too long and which are fragile and difficult to handle. The device according to the invention has a very short response time and handling is very easy.