JP7504266B1 - Dismantling method for reactor pressure vessel - Google Patents

Abstract

A reactor pressure vessel is dismantled while covered with a thermal shield wall.
[Solution] A method for dismantling a reactor pressure vessel according to an embodiment is a method for dismantling a reactor pressure vessel having a nozzle to which a connecting pipe is connected while the vessel is surrounded and covered with a thermal shielding wall. The method for dismantling a reactor pressure vessel according to an embodiment includes a step of cutting the connecting pipe along an outer periphery of the thermal shielding wall, a step of forming a cut piece having no remaining part of the connecting pipe and a cut piece having the remaining part of the connecting pipe, each having a size sufficient to transport the reactor pressure vessel, a first removal step of removing the cut piece having no remaining part of the connecting pipe from the reactor containment vessel, a step of moving the cut piece having the remaining part of the connecting pipe in the direction of the gap after removing the cut piece having no remaining part of the connecting pipe to pull out the remaining part from the thermal shielding wall, and a second removal step of removing the cut piece having the remaining part of the connecting pipe from the reactor containment vessel.
[Selected figure] Figure 4

Description

The present invention relates to a method for dismantling a nuclear reactor pressure vessel.

When decommissioning a nuclear power plant, the reactor pressure vessel, which contains high levels of radiation, is dismantled by remote control. The typical dismantling method used involves cutting the cylindrical reactor pressure vessel into pieces of transportable size, which are then lifted and removed by a crane.

A thermal shield wall that shields against gamma rays is installed around the reactor pressure vessel. The reactor pressure vessel has multiple nozzles connected to pipes that penetrate the thermal shield wall. When dismantling the structures inside the reactor pressure vessel, the pipes connected to the nozzles are cut along the outer periphery of the thermal shield wall and closed. This leaves uncut pipes around the reactor pressure vessel penetrating the thermal shield wall. In this state, when the cut reactor pressure vessel is lifted by a crane remotely and removed, the uncut pipes will get caught on the thermal shield wall. Therefore, a method is being considered to dismantle the reactor pressure vessel after hollowing out and removing the uncut pipes and nozzles from the reactor pressure vessel so that they do not get caught on the thermal shield wall.

JP 2002-311195 A

However, when removing the remaining piping and nozzle sections from the reactor pressure vessel, the work will be carried out close to the vessel without the thermal shielding wall, which poses the problem of increased radiation exposure for workers.

The present invention was made under the above circumstances, and aims to dismantle a reactor pressure vessel while it is covered with a thermal shield wall.

The dismantling method for a reactor pressure vessel according to the embodiment for solving the above problem is a method for dismantling a reactor pressure vessel having a nozzle to which a connecting pipe is connected while the vessel is surrounded by a thermal shielding wall. The dismantling method for a reactor pressure vessel according to the embodiment includes a step of cutting the connecting pipe along the outer periphery of the thermal shielding wall, a step of forming a cut piece having no remaining part of the connecting pipe and a cut piece having the remaining part of the connecting pipe, each of which is large enough to transport the reactor pressure vessel, a first removal step of removing the cut piece having no remaining part of the connecting pipe from the reactor containment vessel, a step of moving the cut piece having the remaining part of the connecting pipe in the direction of the gap after removing the cut piece having no remaining part, thereby pulling out the remaining part from the thermal shielding wall, and a second removal step of removing the cut piece having the remaining part of the connecting pipe from the reactor containment vessel.

FIG. 1 is a configuration diagram of a reactor containment vessel according to an embodiment. FIG. 2 is a partially enlarged view of a reactor pressure vessel according to an embodiment. 1 is a cross-sectional view of a reactor pressure vessel according to an embodiment. 1 is a flowchart showing a method for dismantling a reactor pressure vessel according to an embodiment. FIG. 2 is a diagram for explaining a method for dismantling a reactor pressure vessel according to an embodiment. FIG. 2 is a diagram for explaining a method for dismantling a reactor pressure vessel according to an embodiment. FIG. 2 is a diagram for explaining a method for dismantling a reactor pressure vessel according to an embodiment. FIG. 2 is a diagram for explaining a method for dismantling a reactor pressure vessel according to an embodiment. FIG. 2 is a diagram for explaining a method for dismantling a reactor pressure vessel according to an embodiment. FIG. 2 is a diagram for explaining a method for dismantling a reactor pressure vessel according to an embodiment.

The method for dismantling a reactor pressure vessel according to an embodiment will be described below with reference to the drawings. In the description, an XYZ coordinate system consisting of mutually perpendicular X-axis, Y-axis, and Z-axis will be used as appropriate.

Figure 1 is a schematic diagram of a reactor containment vessel 2 that contains a reactor pressure vessel (hereinafter, RPV) 10 according to this embodiment. Figure 2 is an enlarged view of the portion surrounded by the dashed line in Figure 1. The RPV 10 is surrounded by a thermal shield wall (hereinafter, RSW) 30 and an RPV thermal insulation material 40, and is installed in a reactor building 1 while being contained within the reactor containment vessel 2.

The RPV 10 is an iron vessel used to store nuclear fuel. The RPV 10 has a number of connection pipes 22 around it, which are connected to an RPV nozzle 20 that is connected to various pipes (not shown). The +Z side of the RPV 10 is covered by an upper end 15. The RSW 30 is a wall for blocking gamma rays. The RSW 30 is made of iron, concrete, etc. The RPV thermal insulation material 40 is provided for the purpose of insulating the heat generated by the RPV 10. The RPV thermal insulation material 40 is made of a material containing aluminum. The connection pipes 22 pass through the RSW 30 while covered by the RPV thermal insulation material 40.

When dismantling the RPV 10, the connection pipe 22 is cut along the outer periphery of the RSW 30. FIG. 3 is a cross-sectional view taken along line AA in FIG. 1 when the connection pipe 22 is cut at the cut plane K shown in FIG. 2. An uncut portion 21 of the connection pipe 22 remains around the periphery of the RPV 10, with a length from the outer periphery of the RPV 10 to the outer periphery of the RSW 30.

Next, a method for dismantling a reactor pressure vessel (RPV) 10 according to an embodiment will be described with reference to the flowchart shown in FIG. 4. The RPV 10 is dismantled by remotely operating a crane or the like.

First, the connection pipe 22 is cut along the outer periphery of the RSW 30 (step S11). As shown in FIG. 3, an uncut portion 21 of the connection pipe 22 that is covered with the RPV thermal insulation material 40 and penetrates the RSW 30 remains around the RPV 10.

Next, the RPV 10 is cut into pieces of a size that can be transported. Specifically, as shown by line B in FIG. 5, a cut is made in the side of the RPV 10, and the cut portion is cut to form a cut piece 11 (step S12). The cut piece 11 is made to not include the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipes 22. Since the RPV 10 is surrounded by the RSW 30, it is not possible to make a cut in the side of the RPV 10 from the outside of the RPV 10. In the work of step S12, a cutting machine is inserted into the inside of the RPV 10 from the +Z side of the RPV 10, and the RPV 10 is cut from the inside. When cutting the RPV 10, care is taken not to cut the RPV thermal insulation 40.

As shown in FIG. 6, the length L1 in the X-axis direction of the gap after removing the cut piece 11 is set to be longer than the length L2 in the X-axis direction of the remaining cut portion 21 of the RPV nozzle 20 and the connecting pipe 22 that remain around the RPV 10. As shown in FIG. 5, the cut piece 11 is cut into two pieces at opposing positions that pass through the center of the cylindrical RPV 10. The length L3 shown in FIG. 5 is determined taking into consideration the transportable size and weight.

Next, the cut pieces 11 that do not have the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipe 22 are removed from the reactor containment vessel 2 (step S13). Specifically, as shown in FIG. 7, the cut pieces 11 are lifted in the +Z direction by a crane. The RPV thermal insulation material 40 that covers the periphery of the RPV 10 is connected as a whole. Therefore, when the cut pieces 11 are lifted, they are separated from the RPV thermal insulation material 40. The cut pieces 11 are transported from the reactor containment vessel 2 to a predetermined location and stored in a predetermined disposal container. The process of removing the cut pieces 11 that do not have the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipe 22 is referred to as the first removal process. As shown in FIG. 6, the length L1 of the gap in the X-axis direction after the cut pieces 11 are removed is the length of the cut pieces. The length L2 in the X-axis direction of the remaining cut portion 21 of the RPV nozzle 20 and the connecting pipe 22 left around the RPV 10 is the length of the remaining cut portion protruding from the reactor pressure vessel. Therefore, the length of the cut piece removed in the first removal process is longer than the length of the remaining cut portion protruding from the reactor pressure vessel.

Next, as shown by line C in Figure 8, a cut is made in the side of the RPV 10, and the cut portion is cut to form a cut piece 12 (step S14). This cut piece 12 includes the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipes 22. In the work of step S14, a cutting machine is inserted into the inside of the RPV 10 from the +Z side of the RPV 10, and the RPV 10 is cut from the inside. When cutting the RPV 10, care is taken not to cut the RPV thermal insulation material 40.

Next, the cut piece 12 having the remaining cut portion 21 of the RPV nozzle 20 and the connection pipe 22 is moved in the direction of the gap after the cut piece 11 is removed, thereby pulling out the remaining cut portion 21 from the RSW 30 (step S15). Specifically, as shown in FIG. 9 and FIG. 10, the cut piece 12 is moved in the +X direction by a crane. The length L1 of the cut piece 11 in the X-axis direction is longer than the length L2 of the remaining cut portion 21 of the connection pipe 22 left in the cut piece 12 in the X-axis direction. Therefore, by moving the cut piece 12 in the +X direction, the remaining cut portion 21 can be pulled out from the RSW 30. The RPV heat insulating material 40 covering the periphery of the RPV 10 is connected as a single unit. Therefore, by moving the cut piece 12 in the +X direction, the cut piece 12 having the remaining cut portion 21 of the RPV nozzle 20 and the connection pipe 22 is separated from the RPV heat insulating material 40.

Next, the cut piece 12 having the remaining cut portion 21 of the RPV nozzle 20 and the connecting pipe 22 is removed from the reactor containment vessel 2 (step S16). Specifically, as shown in FIG. 9, the cut piece 12 is lifted in the +Z direction by a crane. The cut piece 12 is transported from the reactor containment vessel 2 to a predetermined location and stored in a predetermined containment vessel. The process of removing the cut piece 12 having the remaining cut portion 21 of the RPV nozzle 20 and the connecting pipe 22 is referred to as the second removal process.

Next, the work from step S13 to step S16 is performed on the portion of the RPV 10 facing the cut piece 12 removed in step S16 (step S17). Specifically, the cut piece 13 shown in FIG. 10 is formed in the same manner as the cut piece 12. The cut piece 13 is moved in the -X direction by a crane, and the remaining portion 21 of the connection pipe 22 is pulled out from the RSW 30. Then, the cut piece 13 is lifted in the +Z direction by the crane. The cut piece 13 is transported from the reactor containment vessel 2 to a predetermined location and stored in a predetermined disposal container.

The RPV 10 is then dismantled by repeating steps S11 to S17.

After the RPV 10 is dismantled, the RPV thermal insulation material 40 remaining inside the RSW 30 is cut into pieces of a specified size and removed (step S18). The RPV thermal insulation material 40 is transported from the reactor containment vessel 2 to a specified location and stored in a specified disposal container.

As described above, the method for dismantling a reactor pressure vessel according to this embodiment includes a first removal step of removing the cut pieces 11 that do not have the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipes 22 around them from the reactor containment vessel 2, a step of moving the cut pieces 12 that have the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipes 22 around them in the direction of the gap after removing the cut pieces 11 that do not have the remaining cut portions 21, thereby pulling out the remaining cut portions 21 from the thermal shield wall (RSW) 30, and a second removal step of lifting the cut pieces 12 that have the remaining cut portions 21 and removing them from the reactor containment vessel 2. Since the length L1 in the X-axis direction of the cut pieces 11 removed in the first removal step shown in FIG. 6 is longer than the length L2 in the X-axis direction of the remaining cut portions 21, the remaining cut portions 21 can be easily pulled out from the thermal shield wall (RSW) 30. Therefore, the reactor pressure vessel (RPV) 10 can be dismantled while the RPV 10 is covered with the thermal shield wall (RSW) 30. This reduces the amount of radiation exposure to workers.

In a typical method for dismantling a reactor pressure vessel (RPV) 10, the RPV 10 is sliced into pieces of transportable size. The RPV 10 is then dismantled by sequentially removing the cut pieces with a crane. However, uncut portions 21 of the RPV nozzle 20 and connecting pipes 22 remain around the RPV 10. When attempting to pull up the cut pieces with the uncut portions 21, the uncut portions 21 get caught on the RSW 30 and RPV thermal insulation 40 and cannot be removed. If the uncut portions 21 are removed first, workers will be working near the vessel without a thermal shield wall, increasing their radiation exposure.

In addition, in the method for dismantling a reactor pressure vessel according to this embodiment, the RPV thermal insulation material 40 is dismantled and removed after the reactor pressure vessel 10 is removed from inside the reactor containment vessel 2. The RPV thermal insulation material 40 is made of a material different from that of the reactor pressure vessel 10. By separating the process for removing the reactor pressure vessel 10 from the process for removing the RPV thermal insulation material 40, it is possible to prevent cutting chips of different materials from being mixed together. This makes it possible to shorten the work time of the subsequent waste sorting process.

In the above description, a case has been described in which cut piece 12 is formed by making the cut shown by line C in FIG. 8 after removing cut piece 11. However, the dismantling method does not need to be limited to this. For example, the order of steps S13 and S14 may be reversed. Specifically, after cutting RPV 10 into a ring with length L3 as shown in FIG. 5, a cut may be made in the Z-axis direction to form two cut pieces 11, 12, and 13, and cut piece 11 may be removed, followed by removal of cut piece 12 and cut piece 13.

In the above description, the RPV 10 is cut into four pieces, namely, two pieces 11, 12, and 13. However, the number of pieces into which the sliced RPV 10 is divided does not need to be limited. For example, the number of pieces may be three, five, six, etc. In this case, the pieces that do not have the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipe 22 are removed first, and the pieces that have the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipe 22 are moved in the direction of the gap after removal, so that the remaining cut portions 21 of the RPV nozzle 20 and the connecting pipe 22 are pulled out from the RSW 30. This makes it possible to prevent the remaining cut portions 21 from getting caught on the RSW 30, and shortens the dismantling work time. In addition, the reactor pressure vessel (RPV) 10 can be dismantled while covered with the thermal shield wall (RSW) 30, thereby reducing the amount of radiation exposure of workers.

In the above explanation, the case where the connection pipe 22 connected to the RPV nozzle 20 before dismantling is passed through the RSW 30 has been described. However, there are also cases where the RPV nozzle 20 passes through the RSW 30 and the connection pipe 22 is connected to the RPV nozzle 20 outside the RSW 30. In this case, the RPV nozzle 20 remains uncut around the RPV 10. There are also cases where the connection pipe 22 is pulled out from the RPV nozzle 20 without cutting the connection pipe 22. In this case, a short RPV nozzle 20 remains around the RPV 10. In the conventional dismantling method, the uncut part of the pipe or the RPV nozzle 20 gets caught on the RSW 30, so it is difficult to pull out the uncut part of the pipe or the RPV nozzle 20 from the RSW 30 by operating a crane. Therefore, the RPV 10 is dismantled while the RSW 30 is being dismantled. Or, the dismantling time of the RPV 10 is prolonged. However, according to the dismantling method of the embodiment, the remaining portion of the connection pipe 22 or the RPV nozzle 20 can be pulled out of the RSW 30 by operating a crane, so the RPV 10 can be dismantled while the RPV 10 is surrounded by the RSW 30. In addition, the dismantling work time for the reactor pressure vessel can be shortened.

In the above explanation, the RPV insulation material 40 is removed after the RPV 10 is removed without dismantling the RSW 30. If the gap between the RSW 30 and the RPV insulation material 40 is large, a cutting tool may be inserted into the gap to cut and remove the RPV insulation material 40 without dismantling the RSW 30, and then the RPV 10 may be removed. Also, the RPV 10 and the RPV insulation material 40 may be dismantled and removed alternately without dismantling the RSW 30. However, care must be taken not to mix the cut pieces of the RPV 10 and the cut pieces of the RPV insulation material 40.

Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

1... Reactor building 2... Reactor containment vessel 10... Reactor pressure vessel (RPV)
11, 12, 13... Cut pieces 15... Upper end portion 20... RPV nozzle 21... Remaining cut portion 22... Connection pipe 30... Thermal shield wall (RSW)
40...RPV insulation material

Claims (5)

A method for dismantling a reactor pressure vessel, in which a reactor pressure vessel having a nozzle to which a connection pipe is connected is dismantled in a state in which the vessel is surrounded by a thermal shield wall, comprising the steps of:
cutting the connecting pipe along an outer periphery of the heat shield wall;
forming a cut piece having a size allowing the reactor pressure vessel to be transported, the cut piece having no remaining portion of the connection pipe, and a cut piece having the remaining portion of the connection pipe;
a first removal step of removing a cut piece of the connection pipe that does not have an uncut portion from the reactor containment vessel;
a step of pulling out the remaining portion of the connection pipe from the heat shielding wall by moving the remaining portion of the connection pipe in a direction toward a gap left after removing the remaining portion of the connection pipe;
a second removal step of removing the cut piece having an uncut portion of the connection pipe from the reactor containment vessel;
A method for dismantling a reactor pressure vessel, comprising: the reactor pressure vessel is cylindrical;
a length of the cut piece removed in the first removal step in a circumferential direction of the reactor pressure vessel being cut into a ring is longer than a length of the remaining cut portion protruding from the reactor pressure vessel;
The method for dismantling a reactor pressure vessel according to claim 1. the reactor pressure vessel and the nozzle are covered with a thermal insulation material;
In the step of forming the cut piece, the thermal insulation material is not cut, and only the reactor pressure vessel is cut;
The first removal step and the second removal step include a step of separating the thermal insulation material from the reactor pressure vessel and the remaining cut portions of the connecting piping.
3. The method for dismantling a reactor pressure vessel according to claim 1 or 2. cutting the heat-insulating material while the heat-shielding wall is surrounding the heat-insulating material;
A step of removing the cut heat insulating material;
including,
The method for dismantling a reactor pressure vessel according to claim 3. The step of removing the heat-insulating material is performed after the second removal step in a state in which the periphery is covered with the heat shielding wall.
The method for dismantling a reactor pressure vessel according to claim 4.

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