Abstract: The apparatus is for internal inspection of a guide tube of a nuclear fuel assembly and measurement of deformations of a zone of smaller diameter in a terminal portion of the tube. The apparatus has a stick whose distal portion presents, in succession, starting from a distal end of the stick-shaped means, a guiding swelling having an easy fit in the zone of smaller diameter and two projections. The first projection carries two sets of diametrically opposite strain sensors provided with conductors linking them to a proximal end of the stick. A sleeve slides in a running portion of the guide tube above the zone of smaller diameter and slides over the stick. The sleeve and said stick-shaped means have mutually cooperating abutments for limiting displacement of the sleeve towards the distal portion to a position where the sleeve surrounds the stick.

Abstract: The assembly (1) is immersed in the water of a pool and placed in vertical position. Detection of the rods (6) of the assembly exhibiting cracks giving rise to leakage is ensured by transmission of ultrasonic waves along the length of each of the rods (6) and by measuring the attenuation of the ultrasonic waves due to the presence of water inside the rods (6) whose cladding is cracked. The ultrasonic waves are picked up after propagation on the cladding of the rods (6) of the assembly along their length, below the lower end fitting (5) in place on the assembly (1). The detecting device comprises an ultrasonic transducer (11) capable of transmitting ultrasonic waves along the length of the rod from its upper part, and a receiver probe (16) for the ultrasonic waves, placed under the lower end fitting (5).