A system for detecting a leak in a cladding tube in a nuclear reactor that has a plurality of cladding tubes housed in a plurality of horizontally arranged channels. A plurality of tubes are positioned adjacent to the channels. A plurality of solid state radiation detectors are in each of the tubes. The detectors are spaced from each other along the length of each tube. The detectors can detect the presence of radiation from a selected fission product within a channel. A processor calculates a leak location by receiving signals above a base line level from the detectors, determining differences in signal strength from the detectors over a period of time, and identifying location of the detector emitting the strongest signal.