Patent Number: 050698613
Section: claims

1. Apparatus for the remote unscrewing and extraction of a fastening screw of an element of a fuel assembly (1) of a nuclear reactor, the head of which is damaged, the screw being engaged by means of its head part (16b) in a bore (18) of a first piece (8) of the assembly (1) and by means of its threaded body (16a) in an internally threaded bore passing through a second piece (10), this apparatus comprising a C-shaped frame (34) having two branches (35, 36) substantially parallel to one another and a joining part (37) between the two branches (35) and (36), an extraction screw (40, 40', 40") engaged in an internally threaded hole passing through one branch of the frame (34) and having one end (50) forming a punch directed towards the inside of the frame (34), and a bearing and centring piece (51), the diameter of which is smaller than the diameter of the internally threaded bore of the second piece (10) and which is fastened to the second branch (36) of the frame (34) and is directed towards the inside of the frame in the axial direction of the extraction screw (40, 40', 40"), characterized in that it also possesses: a pole (32) to the end of which the C-shaped frame (34) is fastened,  a ring (47) for centring the extraction screw (40) relative to the screw to be extracted (16), arranged round the extraction screw (40) over a smooth part (45) of this screw located between its threaded part and its end part (50) forming the punch,  and a means (43) for the remote actuation of the extraction screw (40, 40', 40") by screwing or unscrewing. 2. Apparatus according to claim 1, characterized in that the centring ring (47) has a diameter corresponding to the diameter of the bore (18), the centring of the extraction screw (40) relative to the screw to be extracted (16) being obtained by means of the bore (18). 3. Apparatus according to claim 2, characterized in that the centring ring (45) is fastened to the extraction screw (40) adjustably in the axial direction. 4. Apparatus according to claim 1, characterized in that the centring ring (55, 62) has an inside diameter slightly larger than the diameter of the screw (16) to be extracted in its damage part, and in that a spring pushing axially towards the end (50', 50") of the screw (40', 40") is fastened to the screw and bears on the ring (55, 62). 5. Apparatus according to claim 4, characterized in that the smooth part (60) of the screw, round which the centring ring (62) is fastened, has a diameter larger than the running diameter of the screw (40") and possesses a bearing shoulder (61), on which a corresponding shoulder (63) of the centring and positioning ring (62) comes to rest. 6. Apparatus according to claim 1, characterized in that the extraction screw (40, 40', 40"), at its end opposite the punch (50), has an engagement profile (41) for the remote engagement of a screwdriver and a widened insertion part (42) for the guidance of the screwdriver in the direction of the profile (41). 7. Apparatus according to claim 1, characterized in that the screw (16) to be extracted is a fastening screw for springs (7, 27) retaining a fuel assembly (1) of a pressurized-water nuclear reactor, the first piece consisting of a flange (8), under which one end of the springs (7, 27) is engaged, and the second piece (10) consisting of a frame of the upper connector (5) of the fuel assembly (1), and in that the frame (34) is fastened to the end of the pole in such a way that its joining part (37) is in the extension of the pole (32), making it possible to carry out the unscrewing of the fastening screw (16) from the upper platform of a fuel-assembly deactivation pool. 8. Apparatus according to claim 1, for when the screw to be extracted is in a horizontal or inclined position, characterized in that the frame (34) is connected to the pole (32) in a corresponding position, and in that the means for the remote actuation of the extraction screw possesses means for adaptation and inclination in order to reach the engagement profile of the extraction screw (40).