Patent Number: 054328284
Section: claims

1. Method of replacing an adaptor (3) for penetrating the vessel head (1) of a nuclear reactor, of rounded shape, disposed, after dismounting, so as to have a convex outer surface (1a) facing upwards and a concave inner surface (1b) facing downwards, each of the adaptors (3) having a vertical disposition and being fixed in a penetration opening (2) in the head (1) by means of a weld (5) in the vicinity of the concave inner surface (1b) and carrying an item of equipment (13, 4) resting on one end of the adaptor (3, 3'), this end projecting outside the head (1), the method consisting in machining a lower portion of the adaptor (3) to be replaced, in the vicinity of the inner surface (1b) of the head (1), and at least one portion of the weld (5) for fixing the adaptor (3), in extracting the adaptor (3) to be replaced from the opening in the head (1), in inserting a replacement adaptor (50) into the opening and fixing it therein, and in welding the replacement adaptor (50) to the head, characterized in that the replacement is performed from a repair area located above the convex face (1a) of the head and in that at least one of the operations of machining the adaptor to be replaced (3') after dismounting the item of equipment (4, 13) resting on its upper end and of welding the replacement adaptor (50) is carried out by inserting a repair means (14) via the upper end of the adaptor (3, 50). 2. Method according to claim 1, characterized in that the item of equipment resting on the upper part (3a) of the adaptor to be replaced (3') is constituted by a mechanism (13) for driving a reactivity control rod and by a thermal sleeve (4) disposed inside the adaptor (3). 3. Method according to claim 2, characterized in that, in order to install the repair means (14) in the adaptor to be replaced (3'), at least one drive mechanism (13) resting on an adaptor (3) other than the adaptor (3) being replaced is dismounted. 4. Method according to any one of claims 1 to 3, characterized in that a portion of the repair means (14) is mounted from beneath the head, in a manual manner, from inside a biological-shield chamber (11). 5. Method according to any one of claims 1 to 3 characterized in that the lower portion of the adaptor to be replaced (3) and a portion of the weld (5) are removed by machining by means of a boring tool (40). 6. Method according to any one of claims 1 to 3, characterized in that a narrow bevel (36) is machined in the metal of the weld (5), after removal by machining of the lower portion of the adaptor (3) to be replaced and of a portion of the weld (5). 7. Method according to claim 6, characterized in that a weld is formed by deposition of filler metal in the narrow bevel (36) using a welding head (49, 59) rotating at a speed which can be varied during the welding. 8. Method according to any one of claims 1 to 3, characterized in that, after removal by machining of the lower portion of the adaptor (3) and of a portion of the weld (5) of the adaptor to be replaced, that portion of the adaptor (3) remaining inside the opening (2) of the head is rebored. 9. Method according to claim 8, characterized in that, after reboring the remaining portion of the adaptor (3), a wall (47) of the adaptor (3), obtained after reboring, is compressed so as to separate the wall (47) from the penetration opening (2) of the head (1). 10. Method according to claim 1, characterized: in that the head (1) is positioned on a repair stand (6) with its convex outer surface facing upwards;  in that the item of equipment (4, 13) resting on the upper portion of the adaptor (3, 3') being replaced is dismounted;  in that the repair means (14) is installed on the upper portion of the adaptor (3), at least one portion of which means is inserted into the bore of the adaptor (3, 3');  in that a first machining tool is fixed to that portion of the repair means (14) inserted into the adaptor (3, 3') from beneath the head (1);  in that a lower portion of the adaptor (3, 3') and a portion of the weld (5) are removed by machining;  in that the first machining tool is replaced by a second tool and in that a welding bevel (36) is machined in a remaining portion of the weld (5);  in that the second machining tool is replaced by a third tool and in that that portion of the adaptor (3, 3') remaining in the opening (2) of the vessel head (1) is rebored;  in that the rebored portion of the adaptor (3, 3') remaining in the opening (2) of the head (1) is compressed and in that the remaining portion of the adaptor (3, 3') is removed from the opening (2) in the head (1);  in that a replacement adaptor (50) is installed at a low temperature and in that it is shrink-fitted to the opening (2); and  in that the welding bevel (36) is filled with filler metal.