1. Field of the Invention
The present invention relates to a fastening device for structures which employ bolts and nuts, and more particularly, to a fastening device suitable for use in, for example, repair work in a nuclear reactor pressure vessel.
2. Description of the Invention
In the conventional fastening method of structures using bolts and nuts, performed in a structure making or repair work in a nuclear reactor pressure vessel, after the bolts and nuts have been fastened to the structures, welding is performed to fix the structures to the nuts or the nuts to the bolts to prevent loosening of the nuts.
Structure fastening using bolts and nuts which does not employ welding may be performed 1) by using a spring washer, 2) by using a lock nut, 3) by deforming a split nut with a small screw, 4) by abutting a metal piece to a side surface of the nut, 5) by passing a split pin through the bolts and nuts, 6) by bending or caulking part of a washer having a claw which is brought into engagement with the bolt or a portion of the structure to fix the nut, 7) by using a nut having a structure in which an end surface thereof which faces the structure is elastically deformed or 8) by striking part of the nut to bite it into the bolt. These methods are described from page 731 to page 733 in the Handbook of Machine Design edited by the editorial committee of Handbook of Machine Design and published by Maruzen.
When any of the above-mentioned conventional methods is applied to, for example, the repair work of structures in a nuclear reactor pressure vessel, it is difficult to introduce a welding device into the reactor, because the interior of the reactor is narrow. Further, since the welding work must be performed in air to secure reliability of the welding, if the welding device is of the type having a waterproof operation and thus has a large size, it is difficult to introduce it into the reactor. Where a welding device having no waterproof operation is employed, the draining operation of water in the nuclear reactor is necessary, thus prolonging the repair work.
When any of the above-described methods from 1) to 6) is applied to, for example, the repair work of a nuclear reactor pressure vessel, parts, such as washers or split pins, must be mounted to prevent rotation of the nut relative to the structure or the bolt in a remote controlled operation, making the repair work complicated and producing lost articles in the reactor.
The conventional methods shown in 1), 2), 3), 7) and 8) involve fixing the rotation of the nut by an increase in the frictional force between the nut and the structure or between the nut and the bolt. However, loosening of the nut may occur during use due to changes in the frictional force with time caused by, for example, vibrations of the structure, making semi-permanent maintenance of the structure in the reactor unreliable.