Nuclear reactor internal piping structure

Abstract

The present invention addresses the problem of reducing the working time required to change the fuel assembly or inspect an in-reactor structure to which in-reactor piping is connected, the inside of a nuclear reactor pressure vessel, and other in-reactor structures in normal periodic inspection of a nuclear reactor facility. In order to solve the abovementioned problem, the in-reactor piping structure for a nuclear reactor according to the present invention is characterized in that a pipe connected to a nuclear reactor pressure vessel and a pipe connected to an in-reactor structure are connected in a detachable insertion structure, and specifically, by comprising a first pipe connected to the nuclear reactor pressure vessel, a second pipe connected to the in-reactor structure, and a third pipe for connecting the first pipe and the second pipe, the first pipe and the third pipe being connected, and the second pipe and the third pipe being connected in a detachable insertion structure.

Description

[Technical field]

[0001] The present invention relates to an in-reactor piping structure of a nuclear reactor, and more particularly to an in-reactor piping structure of a nuclear reactor suitable for connecting in-reactor piping provided between a reactor pressure vessel and an in-reactor structure of a boiling water reactor, for example. [Background technology]

[0002] In general, in a boiling water reactor, reactor cooling water is injected into an annulus consisting of a reactor pressure vessel and reactor internals, and the reactor cooling water injected into the annulus is heated by a nuclear reaction in a reactor core consisting of a plurality of fuel assemblies, and a part of the reactor cooling water becomes steam. A gas-liquid two-phase flow containing the reactor cooling water and the steam is separated into reactor cooling water and steam by a steam separator installed above the reactor core.

[0003] On the other hand, in a boiling water reactor, in order to directly cool the reactor core when the normal operating state is deviated from, reactor cooling water is injected directly into the reactor internals from outside the reactor pressure vessel through the internal piping installed between the reactor pressure vessel and the internals. The above-mentioned internal piping is usually attached to the reactor pressure vessel and the internals by welding.

[0004] An example of the structure of such in-reactor piping in a boiling water reactor is described in Patent Document 1.

[0005] Patent Document 1 describes a boiling water reactor in which fuel assemblies, a steam separator, and a steam dryer are provided inside the reactor pressure vessel, a reactor internal pump is inserted from the bottom of the reactor pressure vessel, the fuel assemblies are surrounded by a shroud, a core support, and an upper lattice plate, and a high-pressure core spray system is provided which has the functions of injecting cooling water when the pressure inside the reactor pressure vessel is high and low, and of spraying cooling water directly onto the fuel assemblies.

[0006] Furthermore, Patent Document 1 describes that the high pressure core spray system includes high pressure core injection system piping connected between a pressure vessel nozzle provided in the reactor pressure vessel and a high pressure core injection sparger arranged on the inner wall of an upper lattice plate, and that the high pressure core injection system piping is configured such that a thermal sleeve and a pipe (reactor pressure vessel side piping) are welded on the pressure vessel nozzle side, and a pipe (high pressure core injection sparger side piping), a 90° elbow, and a pipe (connecting piping) are welded on the upper lattice plate side, and that the pipe (connecting piping) is welded and fixed to the upper lattice plate by a support member. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2004-333251 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, since the in-reactor piping described in the above-mentioned Patent Document 1 is attached to the reactor pressure vessel and the in-reactor structures by welding, the in-reactor structures to which the in-reactor piping is connected cannot be detached during normal periodic inspections of nuclear reactor facilities. This poses the problem that the inspection time of the in-reactor structures to which the in-reactor piping is connected, the inside of the reactor pressure vessel, and other in-reactor structures, as well as the replacement of fuel assemblies, is lengthened.

[0009] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide an in-core piping structure of a nuclear reactor that can shorten the work time required for inspecting in-core structures to which in-core piping is connected, the inside of a reactor pressure vessel, and other in-core structures, and for replacing fuel assemblies, during normal periodic inspections of nuclear reactor facilities. [Means for solving the problem]

[0010] In order to achieve the above object, the in-core piping structure of the present invention is a reactor pressure vessel, and a pipe connected to an in-core structure are connected by a detachable plug-in structure. a first tube connected to the reactor pressure vessel, a second tube connected to the reactor internals, and a third tube connecting the first tube and the second tube, the first tube and the third tube being connected to each other, and the second tube and the third tube being connected to each other by a detachable insertion structure, and a pull-out assist mechanism is provided at an insertion portion of the third tube into the second tube, the pull-out assist mechanism comprising a screw hole ring having a plurality of ring female thread portions fixed to the second tube, a ring fixed to the third tube, and a pull-out bolt, and when the third tube is pulled out from the second tube, the pull-out bolt is inserted into the plurality of ring female thread portions provided in the screw hole ring, and the pull-out bolt is rotated to push down the ring, thereby pulling out the third tube from the second tube; Alternatively, a tube connected to a reactor pressure vessel and a tube connected to a reactor internal structure are connected by a detachable insertion structure, the apparatus comprising: a first tube connected to the reactor pressure vessel, a second tube connected to the reactor internal structure, and a third tube connecting the first tube and the second tube, the first tube and the third tube being connected, and the second tube and the third tube being connected by a detachable insertion structure, and an extraction assist device is provided at an insertion portion of the third tube into the second tube, the extraction assist device comprising a vibration propagation ring installed in contact with the insertion portion of the third tube into the second tube, and an oscillator unit that oscillates vibration, and when the third tube is extracted from the second tube, vibration generated by the oscillator unit is propagated to the insertion portion of the third tube into the second tube via the vibration propagation ring, thereby extracting the third tube from the second tube. It is characterized by: Effect of the Invention

[0012] According to the present invention, it is possible to obtain an in-reactor piping structure for a boiling water reactor, which enables the attachment and detachment of in-reactor structures to which in-reactor piping is connected during normal periodic inspections of nuclear reactor equipment, and which can shorten the work time required for inspecting the in-reactor structures to which the in-reactor piping is connected, the inside of the reactor pressure vessel, and other in-reactor structures, as well as for replacing fuel assemblies. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram showing an overall configuration of a boiling water reactor in which the in-reactor piping structure of a nuclear reactor of the present invention is adopted; [Diagram 2] FIG. 1 is a diagram showing a first embodiment of the in-core piping structure of a nuclear reactor according to the present invention, in which a first pipe connected to a reactor pressure vessel is inserted into a second pipe connected to an upper lattice plate to be connected to the first pipe. [Diagram 3] FIG. 3 is a view taken along the line AA in FIG. 2. [Figure 4] FIG. 4 is a diagram showing a third embodiment of the in-core piping structure of a nuclear reactor according to the present invention, illustrating an insertion portion of one of the pipes in FIG. [Diagram 5] FIG. 4 is a diagram showing a fourth embodiment of the in-core piping structure of a nuclear reactor according to the present invention, illustrating an insertion portion of one of the pipes in FIG. [Figure 6] FIG. 5 is a diagram showing a fifth embodiment of the in-core piping structure of a nuclear reactor according to the present invention, illustrating an insertion portion of one of the pipes in FIG. [Figure 7] FIG. 10 is a diagram showing a sixth embodiment of the in-core piping structure of a nuclear reactor according to the present invention, illustrating an insertion portion of one of the pipes in FIG. [Figure 8] FIG. 7 is a diagram showing a seventh embodiment of the in-core piping structure of a nuclear reactor according to the present invention, illustrating an insertion portion of one of the pipes in FIG. [Figure 9]FIG. 8 is a diagram showing an eighth embodiment of the in-core piping structure of a nuclear reactor according to the present invention, in which a first pipe connected to a reactor pressure vessel is connected by being inserted into a second pipe connected to an upper lattice plate. [Figure 10] FIG. 10 is a view taken along the arrow BB in FIG. [Figure 11] 11 is a diagram showing a ninth embodiment of the in-core piping structure of a nuclear reactor according to the present invention, and corresponds to FIG. [Figure 12] FIG. 17 is a perspective view showing a portion where a third pipe of the in-core piping is inserted into a second pipe according to a tenth embodiment of the in-core piping structure of a nuclear reactor of the present invention. [Figure 13(a)] FIG. 11 is a diagram showing an eleventh embodiment of the in-core piping structure of a nuclear reactor according to the present invention, illustrating a partly cross-sectional view of an insertion portion of a third pipe of the in-core piping into a second pipe. [Figure 13(b)] FIG. 13(b) is a cross-sectional view of the insertion portion of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an in-core piping structure of a nuclear reactor according to the present invention will be described based on the illustrated embodiment. In each drawing, the same reference numerals are used for the same components.

[0015] Furthermore, the following is merely an example, and is not intended to limit the contents of the invention to the specific embodiments described below. EXAMPLES

[0016] FIG. 1 shows the overall configuration of a boiling water reactor in which the in-reactor piping structure of the present invention is adopted.

[0017] As shown in FIG. 1, a boiling water reactor 1 is roughly constructed by arranging at least a shroud head 11, an upper lattice plate 7, a core shroud 5, control rod guide tubes 9, and a core support plate 6 inside a reactor pressure vessel 2.

[0018] The above-mentioned core shroud 5 surrounds the reactor core 3 in which a plurality of fuel assemblies 4 are loaded, and a core support plate 6 is attached to the core shroud 5 at the lower end of the reactor core 3.

[0019] An upper grid plate 7 attached to the core shroud 5 is disposed at the upper end of the reactor core 3, and the upper ends of the fuel assemblies 4 are supported by this upper grid plate 7. A plurality of control rods 8 that are moved in and out between the fuel assemblies 4 are each connected to a control rod drive mechanism (not shown) installed in each control rod drive mechanism housing 10.

[0020] Further, a plurality of control rod guide tubes 9 are installed below the reactor core 3 inside the reactor pressure vessel 2, and the control rods 8 withdrawn from the reactor core 3 are guided by the control rod guide tubes 9.

[0021] Meanwhile, a shroud head 11 is attached to the upper end of the upper lattice plate 7, a steam-water separator 12 is attached above the shroud head 11, and a steam dryer 13 is disposed above the steam-water separator 12.

[0022] Next, a first embodiment of the in-reactor piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 2 and Fig. 3. Fig. 2 shows a state in which a first pipe 14a connected to a reactor pressure vessel 2 is connected by being inserted into a second pipe 14d connected to an upper lattice plate 7, and Fig. 3 is a view taken along the line AA in Fig. 2.

[0023] As shown in Figures 2 and 3, the in-core piping 14 comprises a first pipe 14a connected to the reactor pressure vessel 2, a second pipe 14d connected to the upper lattice plate 7 which is an in-core structure, and a third pipe 14c connecting the first pipe 14a and the second pipe 14d, and the first pipe 14a and the third pipe 14c are connected via a sleeve 14b, and the second pipe 14d and the third pipe 14c are connected by a detachable plug-in structure.

[0024] In addition, the third pipe 14c is supported in the vertical direction (perpendicular to the paper surface in Figure 2, and up and down in Figure 3) by a bracket 15, and the bracket 15 is composed of a lower bracket 15a attached to the reactor pressure vessel 2 and an upper bracket 15b attached to this lower bracket 15a by bracket bolts 15c.

[0025] In addition, the first tube 14a, the sleeve 14b and the third tube 14c of the in-core piping 14 are attached inside the reactor pressure vessel 2 before the upper lattice plate 7 is installed at the upper end of the core shroud 5, and are further supported in the vertical direction by brackets 15.

[0026] In addition, the second pipe 14d of the in-core piping 14 is pre-attached to the upper lattice plate 7, and when the upper lattice plate 7 to which the second pipe 14d of the in-core piping 14 is attached is attached to the upper end of the core shroud 5, the third pipe 14c of the in-core piping 14 is inserted into and connected to the second pipe 14d.

[0027] That is, the diameter of the tip of the third tube 14c is smaller than the diameter of the second tube 14d, and the tip of the third tube 14c tapers in a tapered shape (part indicated by symbol 14c1) such that the diameter gradually decreases toward the tip, so that the third tube 14c can be inserted into the second tube 14d.

[0028] The reactor cooling water flows from a nozzle (not shown) provided in the reactor pressure vessel 2 through the in-reactor piping 14 toward the upper grid plate 7, and leakage from the insertion portion of the third pipe 14c of the in-reactor piping 14 into the second pipe 14d is prevented by the ejector principle. This also applies to other embodiments described below.

[0029] By using the in-core piping 14 with such a structure, it is possible to remove the upper lattice plate 7 without cutting the in-core piping 14 (the upper lattice plate 7 can be removed simply by unplugging the third tube 14c and the second tube 14d). This makes it easy to inspect the upper lattice plate 7, the inside of the reactor pressure vessel 2 corresponding to the installation position of the upper lattice plate 7, and the in-core structures such as the core shroud 5 located below the upper lattice plate 7, and to replace the fuel assemblies 4, and therefore reduces the time required for these operations.

[0030] Furthermore, by providing the sleeve 14b, the third tube 14c can rotate in the circumferential direction independently of the first tube 14a, and it is also possible to absorb the displacement difference between the reactor pressure vessel 2 and the upper grid plate 7 due to the difference in thermal expansion during the operation of the reactor.

[0031] That is, the third tube 14c can rotate circumferentially independently of the first tube 14a via the sleeve 14b. Therefore, even if there is a difference in displacement between the reactor pressure vessel 2 and the upper lattice plate 7 due to the difference in thermal expansion during reactor operation, the third tube 14c can absorb the difference in displacement by displacing with the rotation.

[0032] In addition, the bracket 15 shown in Figures 2 and 3 has the upper bracket 15b attached to the lower bracket 15a with bracket bolts 15c, but since there is no need to remove the upper bracket 15b when removing the upper lattice plate 7, other attachment methods such as welding can also be used.

[0033] In this embodiment, the upper lattice plate 7 is taken as an example of the in-reactor structure to which the in-reactor piping 14 is connected, but the structure of the in-reactor piping 14 is not limited to the connection between the reactor pressure vessel 2 and the upper lattice plate 7, but can be applied to any in-reactor piping that connects the reactor pressure vessel 2 to other in-reactor structures. This also applies to other embodiments described below.

[0034] Furthermore, in this embodiment, the first tube 14a and the third tube 14c are connected via the sleeve 14b, but it is also possible to increase the diameter of the end of the first tube 14a and directly insert and connect the third tube 14c into the end of the first tube 14a with the increased diameter, in which case the sleeve 14b will not be necessary. EXAMPLES

[0035] A second embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described.

[0036] In Example 2, although not specifically shown, in the insertion portion between the third tube 14c and the second tube 14d of the configuration described in Example 1, materials with different thermal expansion coefficients are used for the third tube 14c and the second tube 14d.

[0037] In this embodiment, by using materials with different thermal expansion coefficients for the third tube 14c and the second tube 14d, the difference in thermal expansion of each material during reactor operation can be utilized to reduce the gap at the insertion portion between the third tube 14c and the second tube 14d, and the leak path can be reduced, thereby reducing the leak flow rate.

[0038] For example, by using an austenitic stainless steel as the material for the third tube 14c and a high-nickel alloy as the material for the second tube 14d, the leak path at the insertion portion between the third tube 14c and the second tube 14d can be reduced.

[0039] That is, since austenitic stainless steel has a larger thermal expansion coefficient than high-nickel alloys, the austenitic stainless steel expands during reactor operation, thereby reducing the gap between the third tube 14c and the second tube 14d at their insertion portions, thereby making it possible to reduce the leak path.

[0040] With this configuration of the present embodiment, it is possible to obtain the same effects as in the first embodiment, and by using materials with different thermal expansion for the third tube 14c and the second tube 14d and utilizing the difference in thermal expansion during reactor operation, it is possible to reduce the leak path at the insertion portion between the third tube 14c and the second tube 14d, thereby reducing the leak flow rate. EXAMPLES

[0041] A third embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 4. Fig. 4 shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d.

[0042] In the third embodiment shown in FIG. 4, a bellows tube 14e is provided on the second tube 14d. By providing this bellows tube 14e, it becomes easier to insert the third tube 14c into the second tube 14d, and the time required for this operation can be shortened.

[0043] That is, normally, when inserting the third tube 14c into the second tube 14d, an axial misalignment occurs between the two, making the insertion operation difficult and time-consuming; however, in this embodiment, the axial misalignment between the third tube 14c and the second tube 14d can be absorbed by the bellows tube 14e, making it easier to insert the third tube 14c into the second tube 14d and shortening the time required for the insertion operation.

[0044] With this configuration of the present embodiment, it goes without saying that the same effects as in embodiment 1 can be obtained, and by providing the bellows tube 14e on the second tube 14d, it becomes easier to insert the third tube 14c into the second tube 14d, and the time required for the insertion work can be further shortened.

[0045] The attachment position of the bellows tube 14e is not limited to the second tube 14d shown in FIG. 4, but the bellows tube 14e may be provided in a part of the third tube 14c, or may be provided in both the second tube 14d and the third tube 14c. EXAMPLES

[0046] A fourth embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 5. Fig. 5 shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d.

[0047] Example 4 shown in FIG. 5 has a plurality of circumferential groove shapes (uneven shapes) 14f provided on the surface (surface excluding the tapered portion indicated by reference symbol 14c1) of the insertion portion of the third tube 14c into the second tube 14d. By providing these plurality of circumferential groove shapes (uneven shapes) 14f, the pressure loss for the leak flow from the insertion portion of the third tube 14c into the second tube 14d can be increased and the leak flow rate can be reduced.

[0048] That is, when a groove shape (uneven shape) 14f is provided on the surface of the insertion portion of the third tube 14c into the second tube 14d, the pressure loss for the leak flow from the insertion portion becomes larger than in a straight shape without the groove shape (uneven shape) 14f on the surface, and the leak flow rate can be reduced.

[0049] With such a configuration of this embodiment, it is possible to obtain the same effect as in embodiment 1, and by providing a plurality of circumferential groove shapes (uneven shapes) 14f on the surface of the insertion portion of the third tube 14c into the second tube 14d, the leakage flow rate can be further reduced.

[0050] The same effect can be obtained by providing the above-mentioned multiple circumferential groove shapes (concave and convex shapes) 14f on the inner surface of the second tube 14d. EXAMPLES

[0051] A fifth embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 6. Fig. 6 shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d.

[0052] In the fifth embodiment shown in FIG. 6, a seal ring 16 is provided at the insertion portion of the third pipe 14c of the furnace piping 14 into the second pipe 14d. By providing this seal ring 16, the leak path from the insertion portion of the third pipe 14c into the second pipe 14d can be made smaller, and the leak flow rate can be reduced.

[0053] Even with such a configuration of the present embodiment, it goes without saying that the same effects as those of the first embodiment can be obtained, and by providing the seal ring 16, the leakage flow rate can be further reduced. EXAMPLES

[0054] A sixth embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 7. Fig. 7 shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d.

[0055] Example 6 shown in Figure 7 has a structure in which a flange 17 is provided at the insertion portion of the third pipe 14c of the furnace piping 14 into the second pipe 14d. An upper flange 17a is attached to the second pipe 14d by welding, and a lower flange 17b is attached to the third pipe 14c by welding. The upper flange 17a and the lower flange 17b are fixed with flange bolts 17c, thereby making it possible to firmly fix the insertion portion of the third pipe 14c into the second pipe 14d.

[0056] This allows the upper flange 17a and the lower flange 17b to be in surface contact with each other, and the sealing provided by the surface contact between the upper flange 17a and the lower flange 17b reduces the leakage flow rate from the insertion portion of the third pipe 14c into the second pipe 14d.

[0057] Even with such a structure of this embodiment, it goes without saying that the same effects as those of the first embodiment can be obtained, and by providing the flange 17, the leakage flow rate can be further reduced. EXAMPLES

[0058] A seventh embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 8. Fig. 8 shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d.

[0059] In the seventh embodiment shown in FIG. 8, a fastening sleeve 18 consisting of a fastening pipe 18a and a fastening pipe female thread 18b is provided at the insertion portion of the third pipe 14c of the furnace piping 14 into the second pipe 14d. The fastening pipe 18a is attached to the second pipe 14d by fitting, and the fastening pipe female thread 18b is provided at the interface between the fastening pipe 18a and the third pipe 14c, and a pipe male thread 14g is provided at the interface between the fastening pipe female thread 18b of the fastening pipe 18a of the third pipe 14c, and this fastening pipe female thread 18b and the pipe male thread 14g are screwed together.

[0060] This makes it possible to fix the insertion portion of the third pipe 14c into the second pipe 14d, and since there is a large pressure loss at the interface between the fastening sleeve 18 provided at the insertion portion of the third pipe 14c into the second pipe 14d and the third pipe 14c and the second pipe 14d, it is possible to reduce the leakage flow rate from the insertion portion of the third pipe 14c into the second pipe 14d.

[0061] In addition, since the fastening tube 18a is attached to the second tube 14d by fitting, the attachment portion of the fastening tube 18a to the second tube 14d is free, and the second tube 14d is provided with a protrusion portion 14h to prevent the fastening sleeve 18 from falling off when the screw fastening between the fastening sleeve 18 and the third tube 14c is released.

[0062] Even with such a structure of this embodiment, it goes without saying that the same effects as those of the first embodiment can be obtained, and by providing the fastening sleeve 18, the leakage flow rate can be further reduced. EXAMPLES

[0063] An eighth embodiment of the in-core piping structure of a nuclear reactor of the present invention will be described with reference to Fig. 9 and Fig. 10. Fig. 9 shows a state in which a first pipe 14a connected to a reactor pressure vessel 2 is connected by being inserted into a second pipe 14d connected to an upper lattice plate 7, and Fig. 10 is a view taken along the line BB in Fig. 9.

[0064] As shown in Figures 9 and 10, the in-core piping 14 of this embodiment is configured by inserting the tip of a third pipe 14i into each of a first sleeve 14j installed at the tip of a first pipe 14a connected to the reactor pressure vessel 2 and a second sleeve 14k installed at the tip of a second pipe 14d connected to the upper lattice plate 7, so as to be detachably connected thereto.

[0065] In the in-furnace piping 14 of this embodiment, the third pipe 14i has its tip inserted into the first sleeve 14j and the second sleeve 14k, respectively, and is then fixed by a nut 14m using a male threaded rod 14n provided on the inside of the first pipe 14a and the second pipe 14d, respectively, so that it will not come off during operation. The third pipe 14i is lifted and lowered using a lifting bracket 14p.

[0066] When removing the third pipe 14i, the nut 14m is removed from the tip (upper side) of the male threaded rod 14n, thereby removing the third pipe 14i. That is, the third pipe 14i is detachably connected to the first sleeve 14j and the second sleeve 14k.

[0067] Furthermore, by providing the first sleeve 14j and the second sleeve 14k, the third tube 14i can rotate in the circumferential direction independently of the first tube 14a and the second tube 14d, and it is also possible to absorb the displacement difference caused by the thermal expansion difference between the reactor pressure vessel 2 and the upper lattice plate 7 during reactor operation.

[0068] That is, the third tube 14i can rotate in the circumferential direction independently of the first tube 14a and the second tube 14d via the first sleeve 14j and the second sleeve 14k. Therefore, even if there is a displacement difference due to the difference in thermal expansion between the reactor pressure vessel 2 and the upper lattice plate 7 during reactor operation, the third tube 14i can absorb the displacement difference by displacing with the rotation.

[0069] With this structure of the present embodiment, it is possible to obtain the same effects as in the first embodiment, and by connecting the first pipe 14a and the second pipe 14d via the independent third pipe 14i, the time required for attaching and detaching the in-furnace piping 14 can be further reduced. EXAMPLES

[0070] A ninth embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 11. Fig. 11 is a view corresponding to Fig. 10 of the eighth embodiment.

[0071] Example 9 shown in FIG. 11 is the same as Example 8 in that a bellows tube 14q is provided near the center of the third tube 14i of the in-furnace piping 14, which makes it easier to connect the first tube 14a and the second tube 14d of the third tube 14i and can shorten the time required for connecting the first tube 14a and the second tube 14d of the third tube 14i.

[0072] In other words, the bellows tube 14q can absorb the axial misalignment between the first tube 14a and the second tube 14d, making it easier to connect the first tube 14a and the second tube 14d of the third tube 14i, and shortening the time required for the connection work.

[0073] Furthermore, by expanding and contracting the bellows tube 14q, it is possible to more easily absorb displacement caused by the difference in thermal expansion between the reactor pressure vessel 2 and the upper grid plate 7 during operation of the reactor.

[0074] With the structure of this embodiment, it goes without saying that the same effects as those of the eighth embodiment can be obtained, and by providing the bellows pipe 14q near the center of the third pipe 14i, the time required for connecting the in-reactor piping 14 can be further reduced, and the displacement caused by the difference in thermal expansion between the reactor pressure vessel 2 and the upper lattice plate 7 during the operation of the reactor can be more easily absorbed. EXAMPLES

[0075] A tenth embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 12. Fig. 12 shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d.

[0076] In the tenth embodiment shown in FIG. 12, as an example of an insertion portion of the in-furnace piping 14, a structure is provided in which a withdrawal assist mechanism 19 is provided at the insertion portion of the third pipe 14c of the in-furnace piping 14 into the second pipe 14d.

[0077] For example, when the portion of the third tube 14c inserted into the second tube 14d becomes stuck and difficult to remove, it is advantageous to provide a removal assistance mechanism 19 shown in FIG.

[0078] That is, the extraction assistance mechanism 19 of this embodiment comprises a ring 19a with a threaded hole having a plurality of ring threaded portions 19b attached to the second pipe 14d by welding, a ring 19c attached to the third pipe 14c by welding, and an extraction bolt 19d. When extracting the third pipe 14c from the second pipe 14d, the extraction bolt 19d is inserted into the plurality of ring threaded portions 19b provided on the ring 19a with a threaded hole, the extraction bolt 19d is rotated, and the ring 19c is pushed down, thereby allowing the third pipe 14c to be extracted from the second pipe 14d. This makes it easier to extract the third pipe 14c from the second pipe 14d and makes it possible to shorten the time required for the extraction of the third pipe 14c from the second pipe 14d.

[0079] Even with such a structure of the present embodiment, it is possible to obtain the same effects as those of the first embodiment, and it is also possible to reduce the time required for the operation of pulling out the third pipe 14c from the second pipe 14d.

[0080] In this embodiment, the pull-out assist mechanism 19 using the pull-out bolt 19d is shown as an example, but it goes without saying that the pull-out assist mechanism 19 is not limited to the shape shown in FIG.

[0081] Moreover, the tenth embodiment can be applied to the first to ninth embodiments described above. EXAMPLES

[0082] An eleventh embodiment of the in-core piping structure of a nuclear reactor according to the present invention will be described with reference to Fig. 13(a) and Fig. 13(b). Fig. 13(a) shows an insertion portion of the third pipe 14c of the in-core piping 14 into the second pipe 14d, and Fig. 13(b) shows a cross section of the insertion portion of Fig. 13(a).

[0083] As shown in Figures 13(a) and 13(b), in this embodiment, as an example of an insertion portion of the in-furnace piping 14, an extraction assistance device 20 is installed at the insertion portion of the third pipe 14c of the in-furnace piping 14 into the second pipe 14d, during the operation of extracting the third pipe 14c from the second pipe 14d.

[0084] The extraction auxiliary device 20 of this embodiment is composed of a vibration transmission ring 20a that is placed in contact with the furnace piping 14, and an oscillator 20b, and the vibration generated by the oscillator 20b during the extraction operation is transmitted via the vibration transmission ring 20a to the insertion portion of the third tube 14c into the second tube 14d.

[0085] This makes it possible to facilitate the operation of pulling out the third tube 14c from the second tube 14d, and thus makes it possible to shorten the time required for the operation of pulling out the third tube 14c from the second tube 14d.

[0086] That is, by transmitting the vibration generated by the oscillator 20b via the vibration transmission ring 20a to the insertion portion of the third tube 14c into the second tube 14d, the vibration can break the adhesion of the insertion portion of the third tube 14c into the second tube 14d, and further, can remove dust and other foreign matter present between the third tube 14c and the second tube 14d. This makes it easier to pull out the third tube 14c from the second tube 14d, and therefore makes it possible to shorten the time required to pull out the third tube 14c from the second tube 14d.

[0087] Even with such a structure of the present embodiment, it is possible to obtain the same effects as those of the first embodiment, and it is also possible to reduce the time required for the operation of pulling out the third pipe 14c from the second pipe 14d.

[0088] In this embodiment, the pulling-out assist device 20 is shown as an example by vibrating the insertion portion of the third tube 14c into the second tube 14d, but it goes without saying that the pulling-out assist device 20 is not limited to the shape shown in Figures 13(a) and 13(b).

[0089] Moreover, the eleventh embodiment can be applied to the first to tenth embodiments described above.

[0090] The present invention is not limited to the above-described embodiments, and includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0091] 1... boiling water reactor, 2... reactor pressure vessel, 3... reactor core, 4... fuel assembly, 5... core shroud, 6... core support plate, 7... upper grid plate, 8... control rod, 9... control rod guide tube, 10... control rod drive mechanism housing, 11... shroud head, 12... steam separator, 13... steam dryer, 14... reactor internal piping, 14a... first tube, 14b... sleeve, 14c, 14i... third tube, 14c1... tapered portion, 14d... second tube, 14e, 14q... bellows tube, 14f... groove shape, 14g... pipe male thread portion, 14h... protrusion portion, 14j... first sleeve, 14k... second sleeve, 14m... na , 14n...rod with male thread, 14p...lifting bracket, 15...bracket, 15a...lower bracket, 15b...upper bracket, 15c...bracket bolt, 16...seal ring, 17...flange, 17a...upper flange, 17b...lower flange, 17c...flange bolt, 18...fastening sleeve, 18a...fastening tube, 18b...fastening tube female thread, 19...pulling-out assist mechanism, 19a...ring with threaded hole, 19b...ring female thread, 19c...ring, 19d...pulling bolt, 20...pulling-out assist device, 20a...vibration transmission ring, 20b...oscillating portion.

Claims

1. The pipe connected to the reactor pressure vessel and the pipe connected to the reactor internals are connected by a detachable plug-in structure, a first pipe connected to the reactor pressure vessel, a second pipe connected to the reactor internals, and a third pipe connecting the first pipe and the second pipe; the first tube and the third tube are connected to each other, and the second tube and the third tube are connected to each other by a detachable plug structure; a withdrawal assist mechanism is provided at an insertion portion of the third tube into the second tube; the extraction assist mechanism includes a ring with a screw hole having a plurality of ring female threads fixed to the second pipe, a ring fixed to the third pipe, and an extraction bolt; an extraction bolt for extracting the third pipe from the second pipe, the extraction bolt being inserted into a plurality of female threads of the ring with a screw hole, and the ring being pressed down by rotating the extraction bolt, thereby extracting the third pipe from the second pipe.

2. A pipe connected to a reactor pressure vessel and a pipe connected to a reactor internal structure are connected by a detachable plug-in structure, a first pipe connected to the reactor pressure vessel, a second pipe connected to the reactor internals, and a third pipe connecting the first pipe and the second pipe; the first tube and the third tube are connected to each other, and the second tube and the third tube are connected to each other by a detachable plug structure; a withdrawal assist device is provided at an insertion portion of the third tube into the second tube; The pulling-out assisting device includes a vibration transmission ring that is in contact with an insertion portion of the third tube into the second tube, and an oscillator that generates vibrations; an oscillator for generating vibrations generated by the oscillator and transmitting the vibrations to the portion of the third tube inserted into the second tube via the vibration transmission ring, thereby removing the third tube from the second tube.

3. The reactor piping structure of a nuclear reactor according to claim 1 or 2, The diameter of the tip of one of the second and third tubes is smaller than the diameter of the other tube, 13. An internal piping structure for a nuclear reactor, wherein the small-diameter tube has an end tapered so that the diameter of the end portion gradually decreases toward the tip portion.

4. The reactor piping structure of a nuclear reactor according to claim 1 or 2, 13. An internal piping structure for a nuclear reactor, wherein the second pipe and the third pipe are made of materials having different thermal expansion coefficients.

5. The reactor piping structure of a nuclear reactor according to claim 1 or 2, 13. An internal piping structure for a nuclear reactor, wherein either or both of the second pipe and the third pipe are provided with a bellows pipe.

6. The reactor piping structure of a nuclear reactor according to claim 1 or 2, 13. An in-core piping structure for a nuclear reactor, characterized in that a plurality of circumferential grooves (concave and convex portions) are formed on the surface of the insertion portion of either the second pipe or the third pipe.

7. The reactor piping structure of a nuclear reactor according to claim 1 or 2, 13. An internal piping structure for a nuclear reactor, comprising: a seal ring provided at an insertion portion between said second pipe and said third pipe.

8. The reactor piping structure of a nuclear reactor according to claim 1 or 2, 13. An in-core piping structure of a nuclear reactor, comprising: a flange provided at each insertion portion of the second pipe and the third pipe; and the insertion portions of the second pipe and the third pipe are fixed via the flanges.

9. The reactor piping structure of a nuclear reactor according to claim 1 or 2, an internal piping structure for a nuclear reactor, characterized in that a fastening sleeve consisting of a fastening pipe and a fastening pipe female thread portion is provided at an insertion portion of the third pipe into the second pipe, the fastening pipe is attached to the second pipe by a fitting type, a fastening pipe female thread portion is provided at a joint portion of the fastening pipe with the third pipe, and a pipe male thread portion is provided at a joint portion of the third pipe with the fastening pipe female thread portion of the fastening pipe, and the fastening pipe female thread portion and the pipe male thread portion are screwed together, thereby fixing the insertion portion of the third pipe into the second pipe.

10. The in-reactor piping structure of a nuclear reactor according to any one of claims 1 to 9, An in-core piping structure of a nuclear reactor, characterized in that the insertion structure of the second pipe and the third pipe uses an ejector principle using a fluid in the in-core piping to prevent leakage flow from the insertion structure.

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