Patent Number: 
Section: claims

1. A method of inspecting an operation of sealed closure by welding an end opening of a filling channel axially traversing an upper plug for closing a cladding of a fuel rod for a nuclear reactor, the cladding of the rod configured to contain a plurality of pellets of nuclear fuel stacked in an axial direction of the cladding and two closure plugs, at least one of the plugs and an upper plug traversed by the channel for filling the cladding of the rod with an inert pressurized gas and the sealed closure by welding of the filling channel of the upper plug after filling the cladding with the inert pressurized gas, in a filling apparatus, by melting an end central part of the plug adjacent to the opening of the filling channel comprising: prior to the sealed closure of the filling channel, acquiring images of an end surface of the plug on which the filling channel emerges by the substantially circular inlet opening to obtain a digitized image, wherein the rod is in a position for filling and for sealed welding of the upper plug in the filling apparatus and wherein the inlet opening is configured to be substantially circular;  determining a position of a center of the circular inlet opening of the filling channel with respect to a reference position and a diameter of the inlet opening of the filling channel through analyzing the digitized image;  deducing whether it is possible to weld the filling channel; and  acquiring images of the end of the plug after welding and determining a presence and position of a spot weld for sealed closure of the filling channel, where the sealed closure of the filling channel is carried out by welding. 2. The method according to  claim 1 , wherein the reference position consists of a center of a reticule comprising a horizontal axis and a vertical axis, the position of the center of the reticule corresponding to a position for adjusting a welding arrangement for carrying out the sealed closure by welding of the filling channel of the plug, the method further comprising: claim 1 seeking the edges of the inlet opening of the filling channel on the end surface of the plug along a first axis of the reticule;  deducing a first position of the center of the circular inlet opening of the filling channel and a first value of the diameter of the inlet opening;  seeking the edges of the opening along a second axis perpendicular to the first axis of the reticule passing through the center deduced position;  deducing a second position of the center of the circular opening of the filling channel and a second value of the diameter of the circular inlet opening of the filling channel;  seeking the edges of the circular opening along a third axis perpendicular to the second axis passing through the second position of the center;  deducing a third position of the center of the circular opening and a third value of the diameter of the circular opening, the third position of the circular opening considered as an actual center of the opening;  comparing the second value of the diameter and the third value of the diameter to deduce a consistency of the second and the third parameter values considered as parameters of the circular opening;  determining a distance between the third position of the center of the opening and the center of the reticule; and  comparing the distance calculated between the centers of the circular opening and of the reticule together with the calculated value of the diameter of the circular inlet opening of the filling channel to threshold values to determine a compliance of the inlet opening of the filling channel and of a filling channel position and a possibility of carrying out sealed closure by welding. 3. The method according to  claim 2 , wherein the edges of the inlet opening of the filling channel are sought along each of the axes from a graph providing gray levels along at least one of the mean gray levels along N rows and N columns of the digitized image parallel to the axis along which a search is carried out and which are located on each side of the axis. claim 2 4. The method according to  claim 3 , wherein the edges of the circular inlet opening of the filling channel are determined by using a threshold value of the gray levels constituting a mean between the gray levels of the image of the filling channel and the gray levels of the surface of the upper plug around the circular inlet opening of the filling channel. claim 3 5. The method according to  claim 1 , wherein a reflection of the spot weld, having a central part in the shape of a crater reflecting light directed axially is sought on the digitized image of the end surface of the plug after carrying out the sealed closure of the filling channel of the upper plug, and determining a position of the center and the size of the reflection. claim 1 6. The method according to  claim 5 , wherein the position of the center of the reflection is determined with respect to a center of a reticule defined by two horizontal and vertical axes, respectively, on the digitized image, corresponding to a welding position and a diameter of the reflection, and in that the distance from the center of the reflection to the center of the reticule and a calculated diameter of the reflection are compared to threshold values to define whether the upper plug of the fuel rod is compliant after welding. claim 5 7. The method according to  claim 6 , further comprising: claim 6 seeking the edges of the reflection along a first axis of the reticule;  deducing a first position of the center and a first value of the diameter of the reflection;  seeking the edges of the reflection along a second axis perpendicular to the first axis passing through the first center of the reflection;  deducing a second position of the center and a second value of the diameter of the reflection;  comparing the first and second diameters in order to verify a consistency of the values obtained;  determining a distance between the second position of the center of the reflection and the center of the reticule; and  comparing a distance between the center of the reflection and the center of the reticule and the calculated diameter of the reflection to threshold values to determine a compliance of carrying out the sealed closure by welding the filling channel of the upper plug of the rod. 8. The method according to  claim 7 , wherein the edges of the reflection are sought along each of the first and second axes by determining a graph providing grey levels along a mean row parallel to the first and second axes respectively, corresponding to a mean of the gray levels along at least one of several rows and columns of the digitized image which are parallel to one of the first and second axes respectively and placed on each side of one of the first and second axes. claim 7