Failed fuel detection for nuclear reactor

Apparatus for locating failed fuel assemblies in a nuclear reactor cooled by upward flow of liquid coolant through the fuel assemblies, comprising gas source means for supplying gas at a pressure greater than the pressure of liquid coolant at the outlet of each assembly, emulsion producing means for producing an emulsion between the gas and the liquid coolant, the emulsion producing means including an enclosed flow path for each assembly adapted to receive a portion of the liquid coolant flowing from the outlet thereof, the emulsion producing means further including gas diffusion means connected to the flow path and adapted to receive gas from the gas source means and introduce the gas into liquid coolant flowing through the flow path, selector means for successively supplying gas to each gas diffusion means one at a time, means for separating the gas from the liquid coolant, and means for detecting the presence of radioactivity in the separated gas, each flow path including a tube with one end near the outlet of a fuel assembly, said tube being adapted to enable the liquid coolant to flow upwardly therein, the gas diffusion means including a gas chamber bounded on one side by said tube and on the other side by a supporting plate connected to the selector means, the portion of the tube that bounds the gas chamber being laterally disposed and including a plurality of gas inlet apertures therein.