Patent Number: 054065950
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT A tubular lead-through in the form of a neutron detector housing arranged in the bottom of a reactor vessel in a nuclear power plant and with a seal designed according to the invention is shown in FIG. 1. A neutron detector housing 1 is, according to the invention, adapted to be closed and sealed off by means of a device comprising a cone 2 comprising a head 21 a rod-shaped part 22 and a sealing surface 23 arranged between the head 21 and the rod-shaped part 22, wherein the cone 2 is arranged with the head 21 inserted into the neutron detector housing 1, PA1 an annular flange 3 attached to the lead-through 1 and around the rod-shaped cone 2, inserted into the lead-through 1, for retaining the head 21 of the cone in the lead-through 1, whereby the annular flange 3 comprises a sealing surface 31, corresponding to the sealing surface 23 of the cone, in the form of a seat 31 with which the sealing surface 23 arranged on the cone is adapted to make contact to close and seal the lead-through 1, PA1 means for fixing and retaining the sealing surface 23, provided on the cone, to the seat-shaped sealing surface 31 in the form of a sealing washer 41 and a so-called neutron detector nut 42 comprising a teflon seal 43 and an intermediate drainage 44, PA1 the flush pipe 5 is connected to the cone 2, PA1 the flush pipe 5 is attached and a force is applied by means of the attachment member 55, whereby the cone 2 is retained in closed position with the sealing surface 23 of the cone sealingly making contact with the seat-shaped sealing surface 31, PA1 the means comprising a neumron detector nut 42 and a sealing washer 41, applied for fixing and retaining the cone, are detached and removed, the teflon seal 43 being already removed, PA1 temporarily during the mounting of the flush bottle 6, when the attachment 55 of the flush pipe has to be released, a nut divided into two parts is preferably mounted for fixing the cone 2, PA1 the attachment is detached such that the flush bottle 6 can be moved up over the flush pipe 5, PA1 the attachment 55 is again applied to the flush pipe 5 before the flush bottle 6 is moved up and is connected to the annular flange 3, PA1 the drainage connection 65 of the flush bottle 6 is connected, PA1 the attachment 55 is again detached and a member 56 for operation of the flush pipe 5 and the cone 2 is connected to the flush pipe 5; and PA1 flushing water is connected to the flushing water connection of the flush pipe 5. wherein the rod-shaped part 22 of the cone 2, in the end opposite to the head 21, comprises a member 24 for connecting the cone 2 to a flush pipe 5 arranged in the form of an extension of the rod-shaped part of the cone. The first end of the above-mentioned flush pipe 5, which end is fixed to the cone 2 by means of a connection member 24 arranged on the cone 2 and an attachment 51 arranged on the flush pipe, is provided with a plurality of holes 52, and the second end of the flush pipe is provided with means 54 for connection of flushing water and means 55 for connecting an attachment (not shown) by means of which a retaining force is applied to the flush pipe 5 and the cone 2 connected to the flush pipe. As shown in the figures, both the flushing water and the attachment can be connected by means of the same pin 54, 55 projecting from the flush pipe 5. During cleaning, the cone 2 and the connected flush pipe 5 are operated by means of an operating member 56. The second end of the flush pipe 5 is preferably made with a reduced diameter. In its free end, the above-mentioned annular flange 3 is provided with means 33 for connecting a flush bottle 6 arranged around the cone 2 and the flush pipe 5. In its first end the flush bottle 6 comprises means 62 for connection to the annular flange 3 and corresponding connection means 33 arranged on the annular flange 3. In the second end of the flush bottle, an internal sliding seal 64 is arranged for sealing against the flush pipe 5 and a drainage connection 65 is arranged for drainage of contaminated water. Before cleaning a neutron detector housing 1, which when no neutron detector is mounted is arranged with a seal according to the invention, the following steps are taken: While cleaning the detector housing 1, the flush pipe 5 and the cone 2 are operated by means of the connected operating member 56 which is capable of moving the flush pipe 5 up and down in the lead-through 1 and to rotate the flush pipe 5. In connection with the cone 2 being lifted by the operating member 56 and leaving the seat-shaped sealing surface 31, the supply of flushing water through the flush pipe 5 is opened immediately after the flush holes 52 have been maneuvered into the lead-through 1. The flushing proceeds while operating the flush pipe 5 with the cone 2 until it can be determined by activity measurement that the lead-through 1 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 5 and the cone 2. After completed cleaning, the supply of flushing water is closed while at the same time the sealing surface 23 arranged on the cone is again fixed to the seat-shaped sealing surface 31 and closes the seal 1. After that, the flush bottle 6 and the flush pipe 5 are removed while carrying out the above-mentioned operations in reverse order, the cone 2 again being fixed in the seat and retained by means of a sealing washer 41 and a neutron detector nut 42.