Leakage detection device for fuel cladding tube

Gamma-ray spectrum are measured by a measuring means disposed on the surface of pipelines thereby continuously measuring the intensity of radioactivity from radioactive nuclides. The leakage of a fuel cladding tube is detected by the change of the intensity of radioactivity. The gamma-ray spectrum are stored in memory means and the extend of the change of the gamma spectrum intensity is calculated by calculating means, thereby enabling to detect leakage from a plurality of fuel cladding tubes. Further, the position of the failed fuels can be calculated and specified by using an intensity ratio of gamma spectrum for two different nuclides and reactor operation process signals as process signals from process calculating means. Then, rapid countermeasure can be taken if a fuel is failed, thereby improving the plant safety. (I.S.)