Patent ID: 6879653

Claim:
A method of measuring a diameter of a peripheral rod of a fuel assembly of a nuclear reactor cooled by light water, the fuel assembly comprising a bundle of fuel rods and a framework for supporting the fuel rods, the framework comprising spacer grids distributed in an axial longitudinal direction of the bundle of rods, guide tubes disposed in certain positions of the rods inside the bundle, and end nozzles, the measuring being performed underwater in a pool in which the fuel assembly is placed so that the fuel assembly longitudinal axis extends vertically, and being performed between two successive spacer grids along a longitudinal segment of a rod situated at a periphery of the fuel assembly, the method comprising the steps of: placing a measuring tool at a level situated between the two successive spacer grids, the tool having two measuring fingers with freedom to move relative to each other in a first horizontal direction, the fingers being urged towards each other by a resilient return arrangement and extending in a second horizontal direction perpendicular to the first horizontal direction; moving the measuring fingers in the second horizontal direction towards the rod so as to put two contact pieces into contact with two zones of the segment of rod occupying diametrically opposite generator lines, the contact pieces being secured to respective ones of the measuring fingers; moving the two measuring fingers such that the contact pieces are pressed against the rod in two zones situated on the diametrically opposite generator lines, so that the fingers travel in a vertical axial direction of the rod along the segment situated between the two spacer grids; and using an electromagnetic sensor to measure a distance between the contact pieces of the measuring fingers in the first horizontal direction perpendicular to an axial displacement of the measuring fingers.