Patent Number: 054065950
Section: summary

TECHNICAL FIELD The invention relates to a device intended for closing and sealing a lead-through, wherein the sealing permits the lead-through to be opened, washed clean and closed again. Preferably, the invention relates to sealing of a lead-through in the form of a so-called neutron detector housing which is arranged in a reactor vessel for a nuclear power plant. BACKGROUND ART The vessel of a reactor in a nuclear power plant is provided with a number of lead-through which, where necessary, are prepared for mounting of various sensors or equipment. A number of such lead-throughs are mostly not utilized and then usually closed and sealed by a conventional sealing flange. After a period of one or a few operating seasons, active material, for example in the form of solid corrosion products, accumulates in these lead-throughs sealed by sealing flanges in such a quantity that a noticeable radiation level can be detected from them. This results in drawbacks, especially since the mentioned lead-throughs are usually arranged at the bottom of the reactor vessel close to, inter alia drive devices, on which maintenance is continuously being performed, so personnel are regularly present in the area around the lead-throughs sealed by sealing flanges. Cleaning of a lead-through sealed by a sealing flange is admittedly possible, but must then be carried out by means of complex and difficult methods which, in addition, must be carried out from inside the reactor vessel. The object of the invention is to suggest a device intended to seal the lead-through which enables the lead-through, by means of a simple method, to be opened, washed clean and closed again. SUMMARY OF THE INVENTION With a device applied to close and seal a lead-through in a reactor vessel and designed according to the invention, the lead-through can, when necessary, be opened, cleaned, and closed again. A seal for a tubular lead-through designed according to the invention comprises at least a cone comprising a head, a rod-shaped part and a sealing surface arranged between the head and the rod-shaped part, wherein the cone is arranged with the head inserted into the lead-through, PA1 an annular flange attached to the lead-through and around the rod-shaped cone inserted into the lead-through for retaining the head of the cone in the lead-through, whereby the annular flange comprises a sealing surface, corresponding to the sealing surface of the cone, in the form of a seam with which the sealing surface arranged on the cone is adapted to make contact to close and seal the lead-through, PA1 means for fixing and retaining the sealing surface, provided on the cone, to the seat-shaped sealing surface of the annular flange, in the form of a sealing washer and a so-called detector nut comprising a teflon seal and an intermediate drainage, PA1 the flush pipe is connected to the cone, PA1 the flush pipe is attached and a force is applied which retains the cone in closed position with the sealing surface of the cone sealingly making contact with the seat-shaped sealing surface of the annular flange, PA1 the means comprising a neutron detector nut and a sealing washer, applied for fixing and retaining the cone, are detached and removed, PA1 temporarily during the installation of the flush bottle, when the attachment of the flush pipe has to be released, a nut divided into two parts is preferably mounted for fixing the cone, PA1 the attachment is detached such that the flush bottle can be moved up over the flush pipe, PA1 the flush pipe is again attached before the flush bottle is moved up and is connected to the annular flange, PA1 the drainage connection of the flush bottle is connected, PA1 the attachment is again detached and replaced by a member for operation of the flush pipe and the cone, and PA1 flushing water is connected to the flush pipe. wherein the rod-shaped part of the cone, in the end opposite to the head, comprises a member for connecting the cone to a flush pipe arranged in the form of an extension of the rod-shaped part of the cone. The first end of the above-mentioned flush pipe, which end is fixed to the cone by means of a connection member arranged on the cone, is provided with a number of holes and the second end of the flush pipe is provided with means for connection of flushing water and means for attaching and operating the flush pipe and the cone connected to the flush pipe. In its second end, the flush pipe is preferably arranged with a reduced diameter. The above-mentioned annular flange is provided in its free end with means for connecting a flush bottle arranged around the cone and the flush pipe. In its first end the flush bottle comprises means for connection to the annular flange corresponding to the connection member arranged on the annular flange, and in its second end it is provided with an internal sliding seal for sealing against the flush pipe and with a drainage connection. Before flushing clean a lead-through which is arranged with a seal according to the invention, the following steps are taken: While cleaning the detector housing, the flush pipe and the cone are operated by means of the connected operating member which is capable of moving the flush pipe up and down in the lead-through and to rotate the flush pipe. In connection with the cone being lifted by the operating member and leaving the sealing surface of the seat, the supply of flushing water through the flush pipe is opened after the flush holes of the flush pipe have been maneuvered into the lead-through. The flushing proceeds while operating the flush pipe until it can be determined by activity measurement that the lead-through has been cleaned from contaminated material. The cleaning can be made even more efficient by supplementing the equipment by means for mechanical cleaning by brushing, for example by means of a cleaning brush arranged between the flush pipe and the cone. After completed cleaning, the supply of flushing water is closed while at the same time the sealing surface of the cone is again fixed to the sealing surface of the seat and closes the seal. After that, the flush bottle and the flush pipe are removed while carrying out the above-mentioned operations in reverse order, the cone again being fixed in the seat and retained by means of a sealing washer and a neutron detector nut.