Patent Number: 050842285
Section: summary

FIELD OF THE INVENTION The invention relates to a sealing device for an instrumentation column and, in particular, for a thermocouple column penetrating the head of a vessel of a pressurized-water nuclear reactor. BACKGROUND OF THE INVENTION In pressurized-water nuclear reactors, the vessel enclosing the core of the reactor has a head with a substantially hemispherical shape having openings in which followers are fastened enabling the passage of the control rods of the reactor and of instrumentation columns such as thermocouple columns; a set of thermocouples enabling the temperature of the cooling fluid to be measured at the outlet of the assemblies of the core of the reactor is arranged in each of the thermocouple columns. Each of the followers has a part projecting beneath the head ensuring the guidance of the thermocouple column and a part projecting above the head having means for connecting a tubular bearing and sealing unit of the thermocouple column which may be fastened in the extension of the follower. Inside the bearing unit fastened to the follower, a shoulder is provided against which part of the thermocouple column may bear, a sealing strip being placed therebetween. The thermocouple column which traverses the bores of the bearing unit and of the follower, situated in each other's extension, has an end which engages with a pulling device resting on the end of the bearing unit. By virtue of the pulling device, the thermocouple column may be displaced between a low position where its sealing surface is at a distance from the shoulder of the corresponding bearing unit and a high position where the sealing surface of the thermocouple column is applied against the shoulder with a degree of contact pressure which ensures sealing. The bearing unit of the thermocouple column generally has two parts placed in each other's extension which are assembled, a sealing strip being placed therebetween, and held in place in their assembled position by a clamping bracket engaged on corresponding tapered areas of the two parts of the bearing unit. The lower part of the bearing unit is connected to the follower by its joining means which generally consists of a threaded part onto which is engaged a corresponding tapped bore of the lower part of the bearing unit. The joint between the follower and the lower part of the bearing unit is completed by welding two circular seams placed to coincide in order to ensure the sealing of the screwed joint. The upper end part of the bearing unit including the sealing area of the thermocouple column has an upper end surface against which the pulling device of the instrumentation column bears. When it is desired to raise the vessel head, after having performed the depressurization, the tensile force exerted on the thermocouple column is relaxed and the two parts are separated from the bearing unit by disassembling the clamping brackets. The pulling device on the thermocouple column may be separated from the latter, enabling the upper part of the bearing unit to slide in order to separate it from the thermocouple column. The thermocouple column may then be removed completely from the follower and from the lower part of the bearing unit. This procedure is also necessary when it is desired to change the sealing strip of a thermocouple column. These various operations take a relatively long time to perform and may even prove impossible when the clamping pieces seize up. SUMMARY OF THE INVENTION The object of the invention is therefore to provide a sealing device for an instrumentation column and, in particular, for a thermocouple column penetrating the head of a pressurized-water nuclear reactor vessel, inside a tubular follower fastened in a penetration opening of the vessel head and projecting inwardly and outwardly from the head, having a tubular bearing unit fastened to the end of the follower situated outside the head and in its extension, in which a leaktight bearing area is provided for the instrumentation column traversing the bore of the tubular bearing unit and of the follower, as well as a means for pulling on one end of the instrumentation column projecting outwardly from the bearing unit and resting on the end of this bearing unit, this sealing device enabling the thermocouple column to be extracted quickly and easily, even when the clamping and bracketing parts of the bearing unit have seized up. To this end, the bearing unit has an end part in which is provided the bearing area of the thermocouple column and on which the means for pulling the instrumentation column rests, consisting of two successive sections in the axial direction: a first section being fastened to the outer end of the follower and having an outer, peripheral annular throat and at least three openings traversing the first section in an axial direction so as to open into the peripheral throat, a second section being superposed on the first and having openings in the extension of the openings of the first section and the bearing area of the instrumentation column, a mounting piece consisting of two half-rings being introduced into the peripheral throat of the first section and having tapped openings in the extension of the openings of the first and second sections in an assembled position where screws are introduced into the coinciding openings of the first and of the second sections and screwed into the tapped openings of the mounting piece so as to assemble the first and the second sections, a sealing strip being placed therebetween.