Nuclear fuel element

Object: To facilitate the detection of failure of a nuclear fuel element by providing a detecting mechanism capable of non-reversibly changing the position in response to the pressure in the tube disposed within a space located in an upper portion of a cladding tube. Structure: When a cladding tube is failed, the internal pressure therein is increased up to a value equal to the coolant pressure, thus causing extension of a bellows. As a result, a plate spring is upwardly bent to cause rising of a movable body. With this rising, a coil of a differential transformer is fitted on the outer periphery of the end plug, whereby the failure is detected. (Yoshino, Y.)