JP6239891B2 - Apparatus and method for removing top cover of reactor pressure vessel - Google Patents

Description

  The present invention relates to a technique for removing an upper cover of a reactor pressure vessel, and more particularly to an apparatus and method for removing an upper cover of a reactor pressure vessel on the premise of a nuclear power plant decommissioning.

  The reactor pressure vessel is configured such that an upper lid is placed on top of a cylindrical pressure vessel main body. In addition, a body plate flange and an upper cover flange are formed on the peripheral surfaces where the pressure vessel main body and the upper lid come into contact with each other, and penetrate through the body plate flange on the pressure vessel main body side and the upper lid flange on the upper cover side in the height direction. A hole is provided and a stud bolt is embedded in the through hole. Furthermore, the head portion of the stud bolt protruding above the upper lid flange on the upper lid side is tightened and tightened with a nut. The peripheral surface where the pressure vessel main body and the upper lid abut is fixed by a number of stud bolts.

  Therefore, a fastening device called a stud bolt tensioner for performing tightening and loosening operations is installed on the upper cover of the stud bolt. When removing the upper lid from the main body of the pressure vessel for the purpose of inspection, etc., the stud bolt is pulled up by the stud bolt tensioner to extend the stud bolt so that the upper lid tightening force by the nut is relaxed. Then, the nut is rotated and removed.

  On the other hand, in the case of a reactor pressure vessel that has experienced severe accidents such as earthquakes and tsunamis, the stud bolt and nut are stuck due to the temperature history and pressure history at the time of the severe accident, and the nut can be loosened and removed. It may not be possible.

  Even if the nut can be loosened and removed, the reactor pressure vessel body and upper lid are deformed, and the upper lid cannot be removed without the nut, or the stud bolt cannot be removed from the reactor pressure vessel. There is a possibility.

  For example, in Patent Document 1, a stud bolt that is fixed to the body plate flange on the pressure vessel body side is formed in the through portion of the body plate flange in order to deal with the problem that these may not be removed. The technique to remove without showing is shown.

JP-A-8-243944

  The above prior art is based on the premise that each of the reactor pressure vessel main body, the upper lid, the stud bolt, and the nut is maintained in a normal state. For this reason, it may not be applicable to a reactor pressure vessel after a severe accident.

  For example, Patent Literature 1 is a technique for removing a stud bolt that has been fixed to a body plate flange on the pressure vessel main body side at a through-hole of the body plate flange without damaging the screw. However, as a premise of this explanation, the nut can be removed, and the processing when the fixation is found in the scene where the removal of the upper cover is completed successfully and then the stud bolt is removed is a problem.

  However, in a reactor pressure vessel after a severe accident, the stud bolt and nut are stuck, and the nut cannot be loosened and removed. Even if the nut can be loosened and removed, the reactor pressure vessel It is assumed that the main body and the upper lid are deformed and that the upper lid cannot be removed even without the nut, or that the stud bolt cannot be removed from the reactor pressure vessel.

  It is reasonable to assume that it is more likely that the reactor pressure vessel after a severe accident will not reach the scene of removing the stud bolt (it will fail in the previous stage).

  On the other hand, in general industrial products, when the bolt and nut are fixed and the nut cannot be loosened, the nut breaker is used to drive the wedge from the side of the nut to break and remove the nut. There is no size that can be applied to the stud bolt diameter of a reactor pressure vessel. In addition, since the stud bolt of the reactor pressure vessel has a small interval between adjacent nuts, even if there is a nut breaker corresponding to the stud bolt diameter, it is determined that the stud bolt cannot be used because it interferes with the adjacent nut.

  As for the cutting position of the stud bolt, cutting at the bottom surface of the nut can be considered, but there is a high risk of damage to the vicinity of the nut seat surface of the upper lid flange, and the bolt is cut integrally with the nut, so the cutting length Since the stud bolt remains in the through hole of the upper lid flange, the deformation of the reactor pressure vessel main body and the upper lid cannot cope with the situation in which the upper lid cannot be removed even without the nut.

  From the above, in the present invention, a bolt cutting device is inserted from the gap between the flange joint surface of the reactor pressure vessel main body and the upper lid, and the stud bolt is cut, thereby loosening and removing the stud bolt and nut. It is an object of the present invention to provide an apparatus and method for removing an upper cover of a reactor pressure vessel that removes an upper cover without removing the cover.

  From the above, in the present invention, the body plate flange provided around the cylindrical pressure vessel main body and the upper lid flange provided around the pressure vessel upper lid come into contact with each other to form a flange portion. The stud bolt is screwed into the through hole formed in the vertical direction, the head of the stud bolt protruding from the pressure vessel upper lid is fastened with a nut, and the flange portion is in contact with the inner peripheral side of the through hole, and the through hole An apparatus for removing the top cover of a reactor pressure vessel that is prevented from coming into contact with the outer peripheral side, and positioning the cutting device and the cutting device positioned in a gap formed by not contacting the outer peripheral side of the flange portion And a cutting device including a fixing means for fixing the positioning means to the reactor pressure vessel, and the stud bolt is cut at the gap by a cutting device. To.

  According to the present invention, it is possible to remove the RPV upper cover without loosening the stud bolt and the nut by cutting the stud bolt tightening the RPV flange by using the remote-operated bolt cutting device.

The figure which shows the whole structure of a nuclear reactor pressure vessel, and the enlarged view of a flange part. The figure which shows the circumferential direction moving mechanism using the rail by the side of a bulkhead. The figure which shows the circumferential direction movement mechanism using the stay by the side of a nuclear reactor containment vessel. The figure which shows a suction-type circumferential direction moving mechanism. The figure which shows the cutting device which uses electric discharge machining. The figure which shows the cutting device which uses an abrasive water jet. The figure which shows the cutting device which uses a mechanical cutting means.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an overall configuration of a reactor pressure vessel as an object of the present invention and an enlarged view of a flange portion. According to the overall configuration of the reactor pressure vessel on the left side of FIG. 1, the reactor pressure vessel upper lid 2 is installed on the upper portion of the cylindrical reactor pressure vessel body 1.

  In FIG. 1, a reactor well 26 is formed in the upper part of the reactor containment vessel, and water is stored in this portion to shield radiation. For this reason, an annular space between the reactor pressure vessel 1 and a reactor containment vessel (not shown, specifically, the inner surface of the top slab 25) provided outside the reactor pressure vessel 1 is closed by the well seal device 27. The bottom of the reactor well 26 is used. The bulkhead 7 is a part of the well seal device 27 and is an annular platform provided around the reactor pressure vessel 1. The height position of the bulkhead 7 is in the vicinity of the contact portion between the pressure vessel main body 1 and the pressure vessel upper lid 2 and is disposed around the pressure vessel main body 1.

  The flange portion A of the reactor pressure vessel on the right side of FIG. 1 is formed on the peripheral surface where the pressure vessel main body 1 and the pressure vessel upper lid 2 are in contact with each other, and the flange flange 3 on the pressure vessel main body 1 side and the pressure vessel upper lid 2 side. The upper lid flange 4 is partially in contact. That is, the inner peripheral side 21a is in contact with the face of the body plate flange 3 and the upper lid flange 4, but the outer peripheral side 21b of the opposing face is not in contact. Thereby, when the opposing surface is viewed from the outside, a gap G is formed.

  Further, through holes 20 are formed in the height direction at a plurality of locations on the upper and lower flanges around the pressure vessel, and the positions of the through holes 20 are located on the outer peripheral side 21 b from the contact surface of the body plate flange 3. A stud bolt 5 is screwed in the through hole 20. In other words, the stud bolt 5 is internally threaded in the through hole 20 formed on the outer peripheral side 21 b from the contact surface of the body plate flange 3, and the stud bolt 5 inserted and fixed in the through hole 20 is studded. The male thread for the bolt 5 implantation is cut. The screw must be formed at least on the bottom 5b of the stud bolt 5.

  With the above configuration, in the assembly process of the reactor pressure vessel, the stud bolts 5 are inserted into the through holes 20 formed at various locations around the barrel flange 3 on the cylindrical pressure vessel main body 1 side and fixed with screws. The pressure vessel upper lid 2 is suspended in accordance with the position of the stud bolt 5 of the body plate flange 3 and inserted into the through hole 20 on the pressure vessel upper lid side 2. After the suspension installation, the top portion 5a of the stud bolt 5 that finally protrudes from the through hole 20 of the pressure vessel upper lid 2 is tightened with a nut 6 so as to function as a reactor pressure vessel. When the assembly is completed, a part of the stud bolt 5 is exposed in the gap G on the outer peripheral side from the contact surface of the body plate flange 3 and the upper lid flange 4.

  The reactor pressure vessel assembly process as described above can be basically performed in the reverse order of the above assembly, but in the case of a reactor pressure vessel that has experienced severe accidents such as earthquakes and tsunamis, There is a possibility that the stud bolt 5 and the nut 6 are fixed in response to the temperature history and pressure history, and the nut 6 cannot be loosened and removed.

  Even if the nut 6 can be loosened and removed, the reactor pressure vessel main body 1 and the upper lid 2 are deformed, and the upper lid 2 cannot be removed without the nut 6 or the stud bolt 5 can be removed by the atom. There is a possibility that it cannot be removed from the furnace pressure vessel body 1.

  Therefore, the present invention provides a method and apparatus for inserting a cutting device into the gap G and cutting the stud bolt 5. In the present invention, the cutting device is guided to the gap portion G of the flange portion and fixed at the installation position, and the stud bolt 5 can be cut at the position, and after completion, the work is performed by moving to another gap portion G. Provide a method and apparatus that can be continued. For this purpose, a fixing means for fixing the cutting device at a predetermined position and enabling work is indispensable. Hereinafter, a configuration example of a cutting apparatus including specific fixing means will be described.

  FIG. 2 uses a bulkhead 7 as an installation example of a cutting device. The bulkhead 7 closes an annular space between the reactor pressure vessel 1 and a reactor containment vessel (not shown; specifically, the inner surface of the top slab 25) provided on the outside thereof. It is a part of the well seal device, and is an annular platform provided on the upper part of the reactor pressure vessel 1.

  In the embodiment of FIG. 2, rails 8 are laid along the outer periphery of the flange portion on a platform 7 (bulk head) which is an annular base. A cutting device 30 is mounted on the rail 8. The cutting device 30 includes a cutting device 9, a vertical positioning axis adjustment unit 15 that adjusts the height position as the positioning of the cutting device 9, and a front-rear machining axis adjustment unit 16 that adjusts the front-rear direction position as the positioning of the cutting device 9. The insertion depth of the cutting device 9 is adjusted in accordance with the progress of the cutting of the stud bolt 5 by using the cutting device 9 positioned in the gap G by adjusting the height. Thus, by mounting the cutting device 30 on the rail 8, the cutting device 9 can circulate along the rail 8 with a certain distance around the outer periphery of the flange portion. In FIG. 2, the circulation direction is represented by W.

  The cutting device 9 is, for example, a rotary blade, and the rotary blade enters the gap G on the outer peripheral side from the contact surface of the body plate flange 3 and the upper lid flange 4 to cut the stud bolt 5. For this reason, the cutting device 9 includes a front / rear machining axis adjustment unit 16 as a lateral movement mechanism for causing the rotary blade to enter and retreat in the gap portion G direction. In FIG. 2, the lateral movement direction is represented by Y. Further, the height direction position is represented by X and is positioned by the vertical positioning axis adjustment unit 15.

  Thereby, the cutting device 9 is fixed in proximity to the gap G by the circular movement, and the stud bolt 5 is cut by the lateral movement and the rotation of the rotary blade. In the embodiment of FIG. 2, since it moves along the rail 8, it is easy to ensure the positioning accuracy of the cutting device 9, and continuous work in the circumferential direction is possible. The reaction force at the time of cutting the stud bolt has a structure in which the rail 8 is loaded.

  FIG. 3 illustrates a method of holding the cutting device using the stay 10 attached to the stud bolt 5 and the upper lid flange 4 as an installation example of the cutting device. Here, the stay 10 is formed by upper and lower lateral members 10 a and 10 b and a height member 10 c, and one top of the upper lateral member 10 a rises from the flange portion of the pressure vessel upper lid 2. The other is fixed to the height direction member 10c. Then, the lower lateral member 10b extends from the intermediate portion of the height direction member 10c in the direction of the pressure vessel upper lid 2, and the other end of the lower lateral member 10b is fixed to the pressure vessel upper lid 2.

  Moreover, the cutting device 30 is arrange | positioned inside the lower end (pressure vessel upper cover 2) of the height direction member 10c. 2, the cutting device 30 adjusts the position in the front-rear direction as the positioning of the cutting device 9, the vertical positioning axis adjustment unit 15 that adjusts the height position as the positioning of the cutting device 9, and the positioning of the cutting device 9. It is preferable that the front / rear machining axis adjustment unit 16 be configured. In FIG. 3, only the connection relationship between one stud bolt 5 and one stay 10 is illustrated, but the stay 10 is preferably installed for all stud bolts 5. It is preferable to arrange a circumferential member (not shown) for connecting and fixing the stay 10 in the circumferential direction.

  In this case, a circumferential movement mechanism 12 that can move along the circumferential direction is installed on the inner side of the lower end of the height direction member 10 c (pressure vessel upper lid 2), and the cutting device 30 is attached to the circumferential movement mechanism 12. By mounting, the cutting device 30 can be moved to a flange portion at an arbitrary place. The circumferential movement mechanism 12 performs the same function as the rail 8 of FIG.

  As described above, when the stay 10 extends over the entire outer circumference of the flange, as in the case of using the rail 8 of FIG. 2, continuous work is possible in the circumferential direction. After the work in the area covered by the stay 10 is finished, the work is performed by changing the installation position of the stay 10, so that the stud bolt 5 can be cut all around. In this case, the stay 10 is loaded with a reaction force when the stud bolt is cut.

  FIG. 4 illustrates an adsorption-type cutting device that can be attracted to the upper lid flange 4 and moved in the circumferential direction. The suction-type cutting device 30 includes a suction mechanism 13, a traveling mechanism 14, and a cutting device 30, and these are integrally mounted. The adsorption-type cutting device is adsorbed on the outer peripheral surface of the upper lid flange 4 by the adsorption mechanism 13 and moved in the circumferential direction of the upper lid flange 4 by the traveling mechanism 14. As an adsorption method here, a method using magnetism or a method using negative pressure can be considered.

  However, in the case of the suction-type cutting device shown in FIG. 4, it is difficult to ensure positioning accuracy as compared with the case where the rail 8 of FIG. 2 or the stay 10 of FIG. 3 is used. For this reason, it is preferable to add equipment such as inserting a guide into the gap G between the body plate flange 3 and the upper lid flange 4. In addition, since the traveling mechanism 14 loads the reaction force at the time of cutting the stud bolt, it is necessary to select the cutting device 9 that has a higher adsorption force of the traveling mechanism 14 than the reaction force at the time of cutting.

  FIG. 5 shows an example of a cutting device 9 using electric discharge machining (EDM). In this case, since the cutting device 9 has a feature, any one of FIGS. 2 to 4 can be employed as a positioning method. However, in the figure, an example in which the positioning method of FIG. 2 is adopted will be described.

  Under this premise, in the embodiment of FIG. 5, in order to insert the electric discharge machining electrode 17 into the gap G between the body plate flange 3 and the upper lid flange 4, vertical positioning is performed using the vertical positioning shaft adjustment unit 15. The insertion depth of the electric discharge machining electrode 17 is adjusted in accordance with the progress of cutting of the stud bolt 5 by using the front / rear machining axis adjusting unit 16.

  FIG. 6 shows an example of a cutting device 9 using an abrasive water jet. Since this example also has a feature in the cutting device 9, any one of FIGS. 2 to 4 can be adopted as a method for positioning. However, in the figure, an example in which the positioning method of FIG. 2 is adopted will be described.

  Under this premise, in the embodiment of FIG. 6, in order to inject an abrasive water jet into the gap between the body plate flange 3 and the upper lid flange 4, the vertical water positioning nozzle 15 is used to position the abrasive water jet nozzle 18 in the vertical direction. . The circumferential position of the abrasive water jet nozzle 18 is adjusted according to the progress of the cutting of the stud bolt 5 using the circumferential movement mechanism 12. In this case, since the irradiation position of the abrasive water jet nozzle 18 can be adjusted, the front / rear machining axis adjustment unit 16 need not be provided.

  FIG. 7 shows an example of a cutting device 9 using mechanical cutting. In this example, since the cutter 19 is inserted into the gap between the body plate flange 3 and the upper lid flange 4, the vertical positioning shaft 15 is used to perform vertical positioning. Moreover, the insertion depth of the cutter 19 is adjusted according to the progress of the cutting of the stud bolt 5 by using the front and rear machining shaft 16.

  As described above, the present invention cuts a stud bolt using a bolt cutting device in which a cutting device is mounted on a carriage that is movable in the circumferential direction along the outer surface of a reactor pressure vessel flange.

  In this case, the cutting equipment can be selected by using an abrasive water jet when there is a possibility of hydrogen explosion, and by EDM or mechanical cutting means when there is no danger of hydrogen explosion. Even when it is considered that the possibility of hydrogen explosion is low, it is preferable to release hydrogen by cutting the vent nozzle pipe at the top of the reactor pressure vessel top lid in advance.

  As a result, according to the present invention, even when the stud bolt and the nut are fixed and the nut cannot be removed, the reactor pressure vessel main body and the upper lid are deformed, and the upper lid can be removed even without the nut. Even if it cannot be removed or the stud bolt cannot be removed from the reactor pressure vessel, the top cover can be removed.

  According to the present invention, it is possible to remove the reactor pressure vessel top cover without loosening the stud bolt and nut by cutting the stud bolt tightening the reactor pressure flange using a remotely operated bolt cutting device. become. Moreover, since the cut stud bolt upper part and the nut are removed together with the reactor pressure vessel upper cover, it is possible to reduce the work man-hours and the exposure of the worker.

  Because of the above effects, when the stud bolt that fastens the reactor pressure vessel top lid is stuck due to severe accidents and the nut cannot be loosened, or the reactor pressure vessel body and top lid are deformed, and the top lid can be removed even without the nut. Even if the stud bolt cannot be removed from the reactor pressure vessel, it is possible to cut the stud bolt and remove the upper lid.

1: Reactor pressure vessel body 2: Reactor pressure vessel upper lid 3: Body plate flange 4: Upper lid flange 5: Stud bolt 6: Nut 7: Bulkhead 8: Rail 9: Cutting device 10: Stay 12: Circumferential movement mechanism 13: Traveling mechanism 14: Suction mechanism 15: Vertical positioning shaft 16: Front / rear machining shaft 17: Electrical discharge machining electrode 18: Abrasive water jet nozzle 19: Cutter 20: Through hole 21a: Inner peripheral side 21b of flange facing surface: Flange facing Outer surface side 25: Top slab 26: Reactor well 27: Well seal device 30: Cutting device G: Gap

Claims (6)

In the through-hole formed in the height direction of the flange portion, the body plate flange provided around the cylindrical pressure vessel body and the upper lid flange provided around the pressure vessel upper lid abut to form a flange portion. The stud bolt is screwed to the upper end of the pressure vessel, and the head of the stud bolt protruding from the pressure vessel top cover is fastened with a nut. The flange portion abuts on the inner peripheral side with respect to the through hole, and contacts the outer peripheral side with respect to the through hole. An apparatus for removing a top cover of a reactor pressure vessel that is not in contact with the reactor,
A cutting device including a cutting device and positioning means for positioning the cutting device in a gap formed by not contacting the outer peripheral side of the flange portion, an upper and lower lateral member, and a height member. One of the lateral members is fixed to the top of the stud bolt, the other is fixed to the height direction member, and the lower lateral member extends from the middle portion of the height direction member toward the pressure vessel upper lid. The other end of the lower lateral member includes a stay fixed to the pressure vessel upper lid,
An apparatus for removing an upper lid of a reactor pressure vessel, wherein the cutting device is disposed on the pressure vessel upper lid side at a lower end of the height direction member, and the stud bolt is cut at the gap by the cutting device. An apparatus for removing an upper cover of a reactor pressure vessel according to claim 1,
The cutting device includes moving means that can move along the outer periphery of the flange portion, and after cutting the stud bolt, guides the cutting device to the gap portion at another outer peripheral portion position. Reactor pressure vessel top cover removal device. An apparatus for removing a top cover of a reactor pressure vessel according to claim 1 or 2,
The cutting device of the cutting device, electrical discharge machining (EDM), abrasive water jet, top cover removal device of the reactor pressure vessel, characterized in that is due to either mechanical cutting. An apparatus for removing an upper cover of a reactor pressure vessel according to claim 3,
An apparatus for removing an upper lid of a reactor pressure vessel, wherein a cutting device of the cutting device is selected according to an ambient environment. In the through-hole formed in the height direction of the flange portion, the body plate flange provided around the cylindrical pressure vessel body and the upper lid flange provided around the pressure vessel upper lid abut to form a flange portion. The stud bolt is screwed to the top of the pressure vessel, and the head of the stud bolt protruding from the pressure vessel upper lid is fastened with a nut. The flange portion is inward of the through hole and the body plate flange and the upper lid flange are in contact with each other. An upper lid removing method for a reactor pressure vessel in which the body flange and the upper lid flange are prevented from coming into contact with each other on the outer peripheral side of the through hole,
An upper horizontal member and an upper horizontal member are fixed to the top of the stud bolt, the other is fixed to the height member, and an intermediate portion of the height member. A lower lateral member extends in the direction of the pressure vessel upper lid, and the other end of the lower transverse member is fixed to the pressure vessel upper lid, on the pressure vessel upper lid side of the lower end of the height direction member , Positioning means for positioning the cutting device and the cutting device in the gap formed by not contacting the outer peripheral side of the flange portion, and the gap portion formed by not contacting the outer peripheral side of the flange portion The method of removing an upper cover of a reactor pressure vessel, comprising cutting the stud bolt. A method for removing an upper lid of a reactor pressure vessel according to claim 5,
The method of removing a top cover of a reactor pressure vessel, wherein the cutting of the stud bolt is performed in a state where a nut is attached to a head portion of a stud bolt protruding from the top cover of the pressure vessel.

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