JP4393011B2 - Replacement method of core spray system equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of replacing an in-reactor structure installed in a reactor pressure vessel of a boiling water reactor during a service period, and particularly for injecting cooling water into a reactor at the time of a reactor cooling water loss accident. The present invention relates to a replacement method suitable for replacing a core spray system device installed in a reactor pressure vessel.
[0002]
[Prior art]
Among the reactor pressure vessel internal structures in boiling water reactors, the core spray system equipment penetrates the core spray system piping that connects the reactor pressure vessel nozzle and the core shroud, and the upper shell of the core shroud. The core spray system pipe is connected to the core spray system pipe, and the core shroud is installed on the inner surface of the upper shell of the core shroud over the entire circumference. For example, if the core is exposed due to a loss of coolant, such as a recirculation system pipe break, to prevent melting of the fuel cladding due to overheating of the fuel, the core spray system pipes the water in the suppression pool from the external pipe to the core place purger. Then, water is injected into the core from this core spare purger.
[0003]
The core spray system piping is composed of pipes in a range of approximately 180 degrees, and two systems are installed at positions symmetrical to 180 degrees. The core spray system piping is connected to the thermal sleeve welded to the safe end of the core spray nozzle of the reactor pressure vessel, branches to the left and right via the junction box, and runs along the inner wall of the pressure vessel in the direction of about 90 degrees. Are arranged in a semi-annular shape. The end of this semi-annular portion has a vertical pipe that folds vertically and hangs down. The inlet pipe, which is the lower part of this vertical pipe, bends further horizontally through a sleeve, and is attached to the upper outer wall of the core shroud. It is connected to the protruding core spur purger pipe.
[0004]
A ring bracket is attached to the pipe of the core sparger protruding from the upper outer wall of the core shroud to prevent leakage of the reactor water flowing inside the shroud. It has the role of relieving thermal stress between the core place purger when sprayed and the core spray system piping and the shroud mounting portion.
[0005]
By the way, the reactor internal structure of a reactor pressure vessel is comprised by welding the member made from stainless steel. Stainless steel with a high carbon content is known to cause stress corrosion cracking in the weld heat-affected zone near the weld in a high-temperature water environment, and the core spray used in contact with the high-temperature reactor coolant. There are concerns about the occurrence of this in system piping. When such an event occurs, it is necessary to repair or replace the reactor internal structure in order to ensure reactor safety.
[0006]
However, in-furnace structures that have been used for a long period of time are embrittled due to neutron irradiation, and when welded, defects may occur in the deposited metal, making repairs by welding difficult. Therefore, replacement of the in-furnace structure can be considered as a desirable solution when a crack is generated due to stress corrosion cracking or the like in the irradiated portion.
[0007]
Various methods have been considered in the past as methods for replacing the core spray system equipment, which is an in-reactor structure installed in such a reactor pressure vessel, during the service period, but most of them are in the reactor pressure vessel. However, there is no known example assuming replacement of the core spray system equipment itself.
[0008]
[Problems to be solved by the invention]
As described above, the reactor internal structure is constituted by welding stainless steel members. Stainless steel with a high carbon content is known to cause stress corrosion cracking in the weld heat-affected zone near the weld in a high-temperature water environment, and the core spray used in contact with the high-temperature reactor coolant. There are concerns about the occurrence of this in system equipment. When such an event occurs, it is necessary to repair or replace the reactor internal structure in order to ensure reactor safety.
[0009]
However, in the conventional replacement method, since almost all of the reactor internal structure is removed and replaced with a new structure, the entire reactor interior is cleaned with nothing after the internal reactor structure is removed. After laying a shield inside the reactor pressure vessel, it was possible for workers to enter the reactor and perform work.
[0010]
Such a full replacement method for the structure inside the reactor requires a long construction period and a large amount of cost because of the large construction, and there is a problem that the structure located above the core shroud of the core spray system equipment, etc. The application of this method was not appropriate for single replacement of goods. As a problem in the partial replacement of core spray system equipment, etc., because existing structures with high radiation levels are installed, it is difficult for workers to approach and perform construction, replacement equipment It was mentioned that it was impossible to attach to existing structures by welding.
[0011]
Therefore, it has been necessary to consider a construction method and a structure of a new structure so that such an environment can be improved so that workers can enter the furnace and perform construction, and work can be performed easily in a short time.
[0012]
An object of the present invention is to solve the problems as described above and to provide a construction method and structure for replacing a core spray system device in a reactor internal structure that can be replaced even under a high radiation environment.
[0013]
[Means for Solving the Problems]
  In order to achieve the above object, in the invention according to claim 1, a reactor core spray provided in the reactor pressure vessel is installed to inject cooling water into the reactor pressure vessel in the event of a reactor coolant loss accident. A core spray system pipe that connects the nozzle and the core shroud, and a header that penetrates the upper shell of the core shroud, is connected to the core spray system pipe, and almost entirely around the inner surface of the upper shell of the core shroud. The existing core spray system equipment equipped with the installed core sparger is cut and removed while the core shroud and the upper lattice plate remain, during the operation period of the nuclear reactor,A split ring-shaped pipe portion of a new core space purger with a spray nozzle attached in advance by welding is carried into the core shroud, and a header for connecting the pipe portion is inserted into a hole formed in the upper shell of the core shroud, Place a new core place purgerA method of replacing a core spray system device is provided.
[0014]
In the invention according to claim 2, in the method for replacing the core spray system equipment according to claim 1, the existing core spray system equipment is cut in the air or underwater by a remote cutting device or diver and removed. A method for replacing the core spray system equipment is provided.
[0015]
In the invention according to claim 3, in the method for replacing the core spray system device according to claim 1 or 2, the reactor core is chemically cleaned or mechanically cleaned after the existing core spray system device is cut and removed. A core spray system equipment replacement method is provided, in which a new core spray system equipment is installed by decontamination in accordance with an entry into the reactor pressure vessel by an operator.
[0016]
  In the invention according to claim 4, in the method for replacing the core spray system equipment according to any one of claims 1 to 3, mechanical fastening means is provided as means for fixing the new core spray system equipment to the core shroud. Method of replacing core spray system equipment characterized by being appliedTheprovide.
[0017]
  According to a fifth aspect of the present invention, in the method for replacing a core spray system device according to any one of the first to fourth aspects, the new core spray purger is completed as a device in which a spray nozzle is attached in advance by welding. In addition, the split ring-shaped pipe part of the core sparger is inserted into the core shroud while being elastically deformed to the inner diameter side of the core by the sparger restraining device, and the pipe connection header is formed on the upper shell of the core shroud A method of replacing a core spray system device, wherein after inserting into an existing hole, a new core sparger is placed by releasing the restraint of the pipe portion by the restraining device.Theprovide.
[0018]
  In the invention which concerns on Claim 6, in the replacement method of the core spray system apparatus in any one of Claim 1-5, the inlet pipe of new core spray system piping has the flange part formed in the edge part. A core spray system device characterized in that it is fastened to an existing core shroud via a stud, and a pin provided in the flange portion is fitted into a pin hole provided in the core shroud to be connected to a core space sparger. Replacement methodTheprovide.
[0019]
  In the invention which concerns on Claim 7, in the replacement method of the core spray system apparatus in any one of Claim 1-6, the material which gave the stress core crack countermeasure and the crevice corrosion countermeasure to the new core spray system apparatus And method of replacing core spray system equipment characterized by applying structureTheprovide.
[0020]
  According to an eighth aspect of the present invention, in the method for replacing a core spray system device according to any one of the first to seventh aspects, a core shroud and a core that are not stress corrosion cracking countermeasure materials after cutting an existing core sparger Peening or desensitizing heat treatment to remove residual stress or improve material as a preventive maintenance for the welded portion with the bracket for mounting the sparger.ReasonA method for replacing core spray system equipment, characterized by performing construction and maintaining equipment integrity.Theprovide.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a method for replacing a core spray system device according to the present invention will be described with reference to the drawings. FIG. 1 is a process diagram illustrating a procedure for replacing a core spray system device according to the present embodiment, and FIG. 2 is an overall cross-sectional view illustrating an in-furnace structure to which the present embodiment is applied. 3 is an enlarged perspective view showing the core spray system equipment portion of the in-core structure shown in FIG. 2, and FIGS. 4 to 6 show in detail the existing core spray system equipment to be replaced. It is explanatory drawing. 7-10 is explanatory drawing which shows in detail the new core spray system apparatus after replacement | exchange. FIGS. 11-14 is explanatory drawing of replacement work.
[0022]
(A) Description of existing core spray system equipment (FIGS. 2 to 6)
First, the configuration of the reactor pressure vessel will be described with reference to FIG. The reactor pressure vessel 1 has a core shroud 2 disposed therein, and the core shroud 2 is supported by a shroud support cylinder 3. The shroud support cylinder 3 is supported on the bottom of the reactor pressure vessel 1 by a shroud support leg 4. An upper lattice plate 5 is provided on the upper portion of the core shroud 2, and a core support plate 6 is provided on the lower portion. A jet pump 7 is provided on the outer peripheral side of the core shroud 2. The jet pump 7 is roughly composed of a jet pump diffuser 7a, a jet pump riser pipe 7b, a jet pump inlet mixer 7c, and the like. A baffle plate 8 is provided below the jet pump 7.
[0023]
A control rod 9 and fuel 10 are provided in the core shroud 2. Above the core shroud 2, a control rod guide tube 11, a core spray system pipe 12, a core spare purger 13, differential pressure detection / boric acid Equipment such as a water injection pipe 14, a steam dryer 15 and a steam / water separator / shroud head 16 is provided. Of the in-core structures, the core spray system equipment 17 is connected to the core spray nozzle 18 provided on the furnace wall, and the fuel 10 is overheated when the core is exposed due to a loss of coolant such as a breakage of the recirculation system equipment. In order to prevent the melting of the fuel cladding tube due to the water, it is installed as a device that guides and spreads the water of the suppression pool from the external piping to the upper part of the core.
[0024]
Next, the existing core spray system equipment will be described with reference to FIGS. As shown in FIG. 3, the core spray system device 17 is installed in two systems at symmetrical positions of 180 degrees, and includes a core spray system pipe 12 and a core spare purger 13. The core spray system pipe 12 is connected to the core spray nozzle 18 of the reactor pressure vessel 1 through a safe end 19 and a thermal sleeve 19a, and includes a junction box 20, a bent pipe 21, a rising pipe 22, an inlet pipe 23, and a connecting pipe 24. And is connected to the upper shell 25 of the core shroud 2 and the header 26 of the core spare purger 13. Further, the core spray system pipe 12 is supported by the reactor pressure vessel 1 by a clamp 27 at the position of the bent pipe 21. The core place purger 13 is installed inside the upper body 25 and includes a header 26, a pipe portion 28 branched to the left and right, and a plurality of spray nozzles 29 attached to the pipe portion 28.
[0025]
FIG. 4 is a side view showing a state in which the existing core sparger 13 is fixed to the core shroud 2, and FIG. 5 is a cross-sectional view taken along line AA in FIG. As shown in these drawings, the pipe portion 28 of the core place purger 13 is held by a bracket 30. In this case, the bracket 30 is welded and fixed to the core shroud 2 so as to hold the core sparger 13. The movement of the core spare purger 13 in the tube axis direction is not restricted.
[0026]
FIG. 6 shows a lower connection structure of the core spray system pipe 12 to the existing core place purge 13. As shown in FIG. 6, the inlet pipe 23 of the core spray system pipe 12 and the header 26 of the core spray purger 13 are connected by a connecting pipe 24, and a ring bracket attached to the outside of the connecting pipe 24 by welding. 31 is fixed to the outer wall of the upper shell 25 of the core shroud 2 by welding. Thus, by making the joint part with the core shroud 2 into a double tube structure, leakage of the reactor water flowing inside the core shroud 2 is prevented, and the pump of the emergency core spray system is activated and sprayed. It is assumed that it has a function to alleviate the difference in thermal expansion between the core sparger 13 and the core spray system pipe 12 and the core shroud 2 that are sometimes generated.
[0027]
(B) Description of new core spray system equipment (FIGS. 7 to 10)
Next, a new core spray system device for replacement according to the present embodiment will be described.
[0028]
FIGS. 7 and 8 show a configuration in which a new core spare purger 13 is attached to the core shroud 2. That is, after the existing core sparger 13 shown in FIGS. 4 and 5 is cut and removed by a method described later, a fixing bracket 30 for the core sparger 13 is installed and placed on the upper shell 25 of the core shroud 2. A through hole 37a is provided, and a U-shaped clamp 37 is inserted and installed in the through hole 37a. One end of the clamp 37 is fastened from the outside of the upper shell 25 of the core shroud 2 with a fixing sleeve 38, a washer 39 and a nut 40, and a new core sparger 13 is fixed to the core shroud 2. Further, in order to ensure the fixing by the clamp 37, in the configuration shown in the figure, the block 41 holds it from the outside and the nut 42 fixes it. As described above, in this embodiment, the new core spare purger 13 is fixed by the mechanical fastening structure without performing welding.
[0029]
FIGS. 9 and 10 show a structure for fixing a new core place purge 13 to the core shroud 2 and a structure for connecting the inlet pipe 23 of the core spray system pipe 12.
[0030]
The joining portion between the end of the new inlet pipe 23 and the header 26 of the new core spare purger 13 is also performed by a mechanical fastening structure. That is, the header 26 of the new core sparger 13 is inserted into the hole 64 of the upper shell 25 of the core shroud and is fastened to the core shroud 2 by the nut 32 inserted from the outside into the hole 64. The inlet pipe 23 has a flange portion 33 at an end, and the flange portion 33 is fastened from the outside of the core shroud 2 by a stud 34 and a nut 35 screwed to the stud 34. Further, pins 36 are installed at diagonal positions on the pitch circumference of the stud 34, and the flange portion 33 is positioned on the core shroud 2 by the pins 36. The flange portion 33 has a double cylindrical structure, and the inner cylinder portion 65 is fitted to the inner surface of the header fastening nut 32. During normal operation or during an earthquake, a load acts on the flange portion 33 of the inlet tube 23 in the tube axis direction, and this load is supported by the flange fastening stud 34 and the nut 35.
[0031]
On the other hand, at the time of the nuclear reactor coolant loss accident, the core spray system pipe 12 contracts as the cold water is injected into the core spray system equipment. As a result, an excessive torsional moment, shear load, and Works. However, these loads are received by the positioning pins 36 installed on the flange portion 33, so that an excessive moment does not act on the stud 34. Furthermore, the flange part 33 is made into a double pipe structure, and the fitting with the header 26 side is made into a fitting structure that can slide in the axial direction, so that the inlet pipe 23 when cold water is injected into the core spray system equipment. It is possible to alleviate the rapid temperature fluctuation of the flange portion 33 and reduce the thermal stress of the portion.
[0032]
(C) Replacement process (Figure 1)
Next, the procedure for replacing the core spray system device 17 including the core spray system pipe 12 and the core sparger 13 having the above-described structure will be described in order along steps (S101) to (S114).
[0033]
(1) Removal process such as dryer (S101)
In this step, the steam dryer 15 and the steam / water separator / shroud head 16 shown in FIG. 2 are removed and transferred to a dryer / separator pool (not shown). Further, all the fuel assemblies 10 are transferred and stored in a fuel pool (not shown). Thus, preparation for cutting the core spray system device 17 is performed.
[0034]
(2) Removal of guide rods (S102)
Next, a guide rod (not shown) that interferes with the removal and installation of the core spray system piping 12 is cut and removed from the reactor pressure vessel 1 that has been in the upper opening state in the previous step, for example, by an underwater diver, and is shown in FIG. The clamp 27 of the core spray system pipe 12 is cut and removed, and the core spray system pipe rise pipe 22 is cut. Further, a diver is attached to a ring portion of the core spray system pipe 12 to be removed and a part of the rising pipe 22 by a diver.
[0035]
Then, an EDM (electric discharge machining) device (not shown) is attached to the lid of the junction box 20 by a diver and the lid is removed, and then the thermal sleeve 19a of the core spray nozzle 18 is cut by the EDM (electric discharge machining) device, and the core spray nozzle 18 and the core spray system pipe 12 are separated, and the core spray system pipe 12 is removed outside the furnace.
[0036]
(3) Core space purger cutting and removal (S103)
In this step, a hanger is remotely attached to the pipe portion 28 that sandwiches the header 20 of the core sparger 13 and the pipe portion 28 is cut outside thereof to divide the core sparger 13 into, for example, three parts.
[0037]
And a hanging tool is attached to the inlet pipe 23, the root part of the inlet pipe 23 is cut | disconnected by an EDM (electric discharge machining) apparatus, and the inlet pipe 23 and the center part of the core spare purger 13 are removed out of the furnace. After that, hanging tools are attached to the remaining pipe portions (two places) of the core sparger 13 and the bracket 30 provided for fixing the core sparger 13 to the core shroud 2 is cut by EDM (electric discharge machining). Remove the part outside the furnace.
[0038]
(4) Clamp mounting hole processing (S104)
After completely removing the core place purger 13 in the previous step, as shown in FIGS. 7 and 8, a clamp 37 for supporting the new core place purger 13 at a position near the existing bracket 30 of the core shroud 2. The mounting through-hole 37 is processed. These holes are formed, for example, as a pair of through holes between the upper and lower core spacers 13 near the clamp 30 shown in FIG. 3 (see the hole 37a in FIG. 8). Processing of the through hole 37a into the upper shell 25 of the core shroud 2 is performed by EDM (electric discharge machining).
[0039]
(5) Shroud seal surface processing, hole processing (S105)
Simultaneously with the machining of the through hole 37a for mounting the clamp, the flange seal surface 43 for mounting the new inlet pipe 23 shown in FIGS. 7 and 8 is formed on the outer surface of the core shroud 2 by EDM (electric discharge machining). Process by machine.
[0040]
Further, as shown in FIGS. 9 and 10, the screw hole 44 for fixing the stud 35 and the pin hole 45 are processed on the outer surface of the core shroud 2 by an EDM (electric discharge machining) machine. The stud 34 is attached to the front.
[0041]
(6) Chemical cleaning in the reactor (S106)
Next, local chemical decontamination is performed on the RPV (reactor pressure vessel) 1 wall surface in the range above the upper surface of the shroud, which is a range where work is performed on the platform installed on the upper portion of the shroud, by the CORD method or the like.
[0042]
FIG. 11 is an explanatory diagram showing a decontamination situation by the local chemical decontamination apparatus. As shown in FIG. 11, the reactor water level 61 is lowered to the normal operating water level, and decontamination is performed on the upper part of the core shroud 2 (a range approximately 5 meters above the upper surface of the core shroud 2, which is a range in which work is performed). The tank 47 is installed on the upper surface of the upper ring of the core shroud 2. As shown in FIG. 11, a flow pump 46 and a pipe 62 are provided inside the decontamination tank 47 so that the reactor water can circulate inside and outside the decontamination tank 47.
[0043]
The reactor water below the upper ring 2a of the core shroud 2 and the reactor water above are separated from each other by a double seal mechanism 48 and purge water (seal water) provided at the lower outer peripheral side of the decontamination tank 47. The upper furnace water is circulated between the decontamination tank 47 and the decontamination apparatus 63, thereby performing chemical decontamination of the upper part of the furnace.
[0044]
After completion of chemical decontamination, the decontamination tank 47 is carried out of the furnace, and mechanical decontamination such as partially jetting jet water into the furnace is performed to complete the cleaning. As a result, the radiation level in the reactor pressure vessel 1 is lowered, and air work is possible.
[0045]
(7) Suspension of new core spare purger (S107)
After completion of the chemical decontamination, the decontamination tank 47 is carried out of the furnace, and then mechanical decontamination such as partially jetting jet water into the furnace is performed to complete the cleaning. After the cleaning is completed, a new core spare purger 13 is suspended in the furnace by a crane (not shown).
[0046]
7 and 8 is narrowed down by a sparger restraining device (not shown) so that the diameter of the pipe portion 28 is equal to or smaller than the inner diameter of the upper shell 25 of the core shroud 2, and is suspended in the upper shell 25. The header 26 shown in FIGS. 9 and 10 is inserted into the hole 64 of the core shroud 2. After insertion, the restraint by the restraining device is released.
[0047]
(8) Mounting of sparger installation stand (S108)
Next, as shown in FIG. 12, the upper grid plate shield 49 is carried into the furnace, and after the upper grid plate shield 49 is installed on the upper grid plate 5, it is newly added to the upper surface flange portion of the core shroud 2. A work platform 50 is installed for installing a new core spare purger, and a worker enters the area. Then, the horizontal level of the core sparger 13 is adjusted from the work platform 50 for a new core sparger installation.
[0048]
After completion of leveling, the pipe-fixing clamp 37 shown in FIGS. 7 and 8 is moved from the core side, and the end of the clamp 37 is inserted into the through-hole 37 a formed in the core shroud 2. In this state, the fixing sleeve 38, the washer 39 and the nut 40 are inserted from the furnace wall side, and the clamp 37 is fastened. Further, the clamp 37 is fixed by the block 41 and the nut 42.
[0049]
(9) Tightening the new core place purger (S109)
After all the new clamps 37 are fastened, as shown in FIGS. 7 and 8, the nut 43 is inserted into the header 26 from the furnace wall side and fastened, and the installation of the core spare purger 13 is finished.
[0050]
(10) Mounting of mounting base for piping installation (S110)
FIG. 13 is an explanatory diagram illustrating a pipe installation gantry mounting step. In this step, the above-described work base 50 for installing the sparger and the upper grid plate shield 49 are carried out of the furnace, and the work base 51 for installing the pipe is installed at the site. Thereafter, the remaining thermal sleeve 19 in the core spray nozzle 18 shown in FIG. 3 and the remaining portion of the clamp to which the pipe is attached are cut and removed, and a safe end groove processing machine is inserted into the core spray nozzle 18. Safe end beveling is performed for the new core spray system piping 12. Further, in order to restore the core spray system piping 12, the dimensions are measured from the core spray nozzle 18 to the flange processing portion of the core shroud 2 using a template, while the core spray system piping 12 is engaged outside the reactor building. Align parts and bend pipes.
[0051]
(11) Install new inlet pipe (S111)
While the core spray system pipe 12 is bent outside the reactor building, as shown in FIG. 10, the flange portion of the inlet pipe 13 of the new core spray system pipe 12 is provided in the reactor pressure vessel 1. A positioning pin 36 is set on 33, the inlet 34 is installed using the stud 34 attached to the core shroud 2 and the inner surface of the header mounting nut 32 as a guide, and the nut 35 is fastened and fixed.
[0052]
Here, a stress corrosion cracking (SCC) countermeasure material is adopted as a constituent material of the replacement core spray system equipment.
[0053]
(12) Piping installation of new core spray system (S112)
FIG. 14 is an explanatory diagram showing a new core spray system piping installation process. As shown in FIG. 14, a new core spray system pipe 12 with a new thermal sleeve 52 is tilted and suspended in the nuclear reactor while avoiding interference with the water supply sparger, and this thermal sleeve 52 is inserted into the core spray nozzle 18. The groove portion of the safe end 19 and the groove portion of the thermal sleeve 52 are welded together.
[0054]
The rising pipe 54 of the new core spray system pipe 12 is connected to the new inlet pipe 23 via a sleeve 56, and the rising pipe 54 and the sleeve 56 and the new inlet pipe 23 and the sleeve 56 are welded to each other.
[0055]
In this way, after the new core spray system device 17 is connected as a system, a clamp for pressing the new core spray system piping 53 is attached, and finally a lid 58 is attached to the tee 57 of the new core spray system device 17.
[0056]
(13) Guide rod restoration, work platform removal (S113)
After the restoration of the new core spray system piping 12 is completed, a guide rod (not shown) is attached to the guide pin bracket of the core shroud 2, and then the work platform 51 is removed.
[0057]
In addition, with respect to the heat-affected range of the welded portion of the core sparger fixing bracket 30 provided on the inner surface of the upper shell 25 of the core shroud 2, which was not accessible when the existing core sparger 13 was installed. Then, after the core spare purger 13 is completely removed, it is possible to carry out construction such as peening for removing residual stress and desensitization heat treatment for the purpose of material improvement as preventive maintenance work.
[0058]
(14) Fuel loading, dryer, separator recovery (S114)
In this step, the above-described fuel assembly 10 is returned from a fuel pool (not shown), and the steam dryer 15 and the steam / water separator / shroud head 16 are returned to the reactor pressure vessel 1 from the dryer / separator pool. As shown, the installation and restoration work is completed again.
[0059]
According to the above embodiment, the structure on the upper part of the core shroud, which has been considered difficult to replace alone due to problems such as interference with surrounding structures, high radiation environment, bonding to neutron irradiation materials, etc. It becomes possible.
[0060]
That is, the core spray system pipe 12 connecting the nozzle 18 of the reactor pressure vessel 1 and the core shroud 2 and the header 26 penetrating the upper shell of the core shroud 2 are provided, and the core shroud 2 is connected via the connection pipe 24. Then, the core spray system device 17 composed of the core spray system 13 connected to the core spray system pipe 12 is cut and removed without removing the upper lattice plate 5, and the new core spray system device 17 is remotely attached to the core shroud 2. By doing so, the core spray system equipment 17 can be easily replaced in a short period of time as compared with the conventional whole reactor internal replacement method. Further, by using a mechanical fastening structure as a mounting structure for the new core spray system equipment 17, the core spray system is subjected to the core shroud 2 subjected to neutron irradiation in the same restraint condition as before replacement without using welding. The equipment 17 can be attached and restored.
[0061]
  In addition, after cutting and removing the existing core spray system equipment 17, the inside of the reactor pressure vessel 1 is decontaminated by chemical or mechanical cleaning locally, and the water level in the reactor pressure vessel 1 is lowered. Installation of replacement equipment is easy by installing work platforms 50 and 51 on the core shroud 2 and an operator entering the reactor pressure vessel 1 and installing a new core spray system device 17. Thus, the construction period can be shortened. In addition, the core spray system device 17 arranged in the reactor pressure vessel 1 includes an EDM device that is mechanically cut by an underwater diver and underwater remotely operated.Cut withBy removing them, it is possible to cut the work with a diver at a low radiation level, and to apply remote cutting with an EDM device at a high level, thereby improving work efficiency.
[0062]
Furthermore, the new core spare purger 13 is preliminarily attached by welding the spray nozzle 29 to a completed state, and the new core spare purger 13 is formed by a sparger restraining device that restrains the pipe portion 28 by elastically deforming it inside. Is inserted into the core shroud 2, the header 26 is inserted into the existing hole 64 formed in the upper shell of the core shroud 2, the restraint of the pipe portion 28 is released, and the core spare purger 13 is installed at a predetermined position. This makes it possible to install a replacement core spare purger by remote control from above the reactor pressure vessel 1. Further, the inlet pipe 23 of the new core spray system pipe 12 has a flange portion 33 at the end, and is fastened by the core shroud 2 and the stud 34, and a pin 36 installed on the flange portion 33 is provided in the core shroud 2. By fitting into the pin hole 45, the load acting in the tube axis direction at the joint portion of the inlet tube 23 with the core shroud 2 is received by the stud 34 and the nut 35 for fastening the flange portion 33. Since the torsional load of the flange portion 33 generated by the thermal contraction of the core spray system pipe 12 at the time of water loss accident can be handled by the pin 36, the flange fastening structure can be made compact.
[0063]
Furthermore, the new core spray system equipment 17 applies a material and a structure that have been subjected to stress corrosion cracking (SCC) and crevice corrosion (clevis) countermeasures, and after cutting the core spare purger 13, stress corrosion cracking ( For the welded part between the core shroud 2 and the bracket 30, which is not a countermeasure material of SCC), residual stress is removed as preventive maintenance, and peening and desensitization heat treatment are performed to improve the quality of the equipment. By maintaining the above, improvement work can be carried out on the part where the preventive maintenance work could not be performed due to the interference of the core spare purger 13.
[0064]
【The invention's effect】
As described above in detail, according to the present invention, when a failure occurs in the core spray system equipment in the reactor pressure vessel or when a failure may occur, the failure is caused by replacing the target part. Therefore, the reliability of the plant can be improved and the life of the plant can be extended.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a core spray system piping replacement procedure according to an embodiment of the present invention.
FIG. 2 is an overall cross-sectional view showing an in-furnace structure to which an embodiment of the present invention is applied.
FIG. 3 is an installation diagram of a core spray system device to which an embodiment of the present invention is applied.
FIG. 4 is a side view showing a configuration of an existing core spare purger according to an embodiment of the present invention.
5 is a cross-sectional view taken along line AA in FIG.
FIG. 6 is a partial cross-sectional view showing a configuration of existing core spray system piping in an embodiment of the present invention.
FIG. 7 is a side view showing an installation configuration of a new core spare purger according to an embodiment of the present invention.
8 is a sectional view taken along line BB in FIG.
FIG. 9 is a side view showing an installation configuration of a new core spray system pipe in one embodiment of the present invention.
10 is a cross-sectional view taken along the line CC in FIG. 9;
FIG. 11 is an explanatory diagram of a decontamination process in one embodiment of the present invention.
FIG. 12 is an explanatory diagram of a work platform installation process according to an embodiment of the present invention.
FIG. 13 is an explanatory diagram of a work platform installation process according to an embodiment of the present invention.
FIG. 14 is an explanatory diagram of an installation process of core spray system piping in one embodiment of the present invention.
[Explanation of symbols]
1 Reactor pressure vessel
2 Core shroud
5 Upper lattice plate
12 Core spray system piping
13 Core Spare Purger
17 Core spray system equipment
18 Core spray nozzle
24 Connection pipe
26 Header
30 Bracket
31 Ring bracket
33 Flange
34 Stud
36 pins

Claims (8)

A core spray system pipe installed to inject cooling water into a reactor pressure vessel in the event of a reactor water loss accident and connecting a core spray nozzle and a core shroud provided in the reactor pressure vessel; and the core An existing core spray system device comprising a core spur purger which is connected to the core spray system piping through a header penetrating the upper shell of the shroud and is installed on the inner surface of the upper shell of the core shroud almost entirely. The core shroud and the upper grid plate are cut and removed while the reactor is in service, and a split ring-shaped pipe portion of a new core sparger, to which a spray nozzle is attached by welding in advance, Into the hole formed in the upper shell of the core shroud, and a new furnace The method replacement of the core spray line equipment characterized by placing the spray sparger.   2. The method for replacing a core spray system device according to claim 1, wherein the existing core spray system device is cut and removed by a remote cutting device or diver in the air or in water. Replacement method.   3. The method for replacing a core spray system device according to claim 1 or 2, wherein after the existing core spray system device is cut and removed, the inside of the reactor pressure vessel is decontaminated by chemical cleaning or mechanical cleaning, A method of replacing a core spray system device, wherein a new core spray system device is installed by entering the reactor pressure vessel.   The core spray system equipment replacement method according to any one of claims 1 to 3, wherein a mechanical fastening means is applied as means for fixing a new core spray system equipment to the core shroud. Replacement method for spray system equipment.   5. The method of replacing a core spray system device according to claim 1, wherein the new core spray purger is completed in advance as a device having a spray nozzle attached thereto by welding, and the core spray purger is divided. The ring-shaped pipe portion is inserted into the core shroud while being elastically deformed toward the core inner diameter side by a sparger restraining device, and the pipe connection header is inserted into an existing hole formed in the upper shell of the core shroud. After that, the core spray system equipment replacement method is characterized in that a new core spray purger is placed by releasing the restraint of the pipe portion by the restraining device.   6. The method of replacing a core spray system device according to claim 1, wherein an inlet pipe of a new core spray system pipe has a flange portion formed at an end portion of the core pipe through an existing core shroud via a stud. The core spray system equipment replacement method is characterized in that a pin provided on the flange portion is engaged with a pin hole provided in the core shroud and connected to a core sparger.   The method for replacing core spray system equipment according to any one of claims 1 to 6, wherein a new core spray system equipment is applied with a material and a structure subjected to stress corrosion cracking countermeasures and crevice corrosion countermeasures. Replacement method for core spray system equipment. 8. The method for replacing a core spray system device according to claim 1, wherein after welding an existing core sparger, welding between a core shroud that is not a material for stress corrosion cracking and a bracket for mounting the core sparger for part performs construction of peening or de-sensitization Kanetsu treatment for the removal or material improves, the residual stress as preventive maintenance, preparative the core spray system equipment and maintains the integrity of the equipment Replacement method.

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