JP3679823B2 - How to replace the core shroud - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for replacing a core shroud installed in a nuclear reactor such as a boiling water type light water cooled nuclear reactor.
[0002]
[Prior art]
Generally, a reactor core shroud of this type is constructed by welding stainless steel members. When such a core shroud has a high carbon content, cracks may occur due to stress corrosion cracking or the like at or near the weld during long-term operation. When such an event occurs, it may be necessary to repair or replace the core shroud to ensure the safety of the nuclear reactor.
[0003]
However, the core shroud that has been used for a long time has become brittle due to neutron irradiation, and when it is welded, finer cracks may occur around the deposited metal, making repair by welding difficult. In addition, a method of bolting the reinforcing member is conceivable, but its adoption may be limited in a nuclear reactor installed in a high earthquake zone.
[0004]
Therefore, the most desirable method is considered to be the replacement of the core shroud, but the core shroud itself is welded to the support ring of the core shroud at the lower end, and it interferes with the in-core stabilizer, the core instrumentation guide tube, etc. High radiation dose, difficulty in adjusting the position of the upper grid plate and the core support plate installed inside the core shroud, and removal of the core shroudOutside the reactorDifficulty in handling and waste generated in large quantitiesProcessing difficulties, etc.Due to various problems, replacement has been predicted to be extremely difficult until now.
[0005]
However, in recent years when a long period of time has passed after the practical operation of a nuclear reactor, the replacement of the above-described core shroud is becoming an urgent task, and various techniques have been proposed (eg, JP-A-63). -36195).
[0006]
However, in the proposed technology so far, since it is sensitive to high activation inside the reactor, all operations such as cutting and removal of the core shroud and installation of the new shroud are still biased toward remote operation. The technology for performing all such operations remotely requires a great deal of time and effort, and lacks the details in detail, and there are many unclear points for practical use.
[0007]
[Problems to be solved by the invention]
On the other hand, in recent years, the technology for removing pollutants (hereinafter referred to as “decontamination”) in nuclear reactor facilities has advanced remarkably and, for example, using chemical agents such as permanganate solutions, radiation contamination sites have become extremely effective. Proposals for cleaning have also been made (eg, Japanese Patent Publication No. 3-10919). However, there has been no particular proposal for a shroud replacement technique by a worker other than remote work by applying such a technique for reducing the radiation dose equivalent rate in the reactor to clean the core.
[0008]
In nuclear power plants, corrosion products from materials used in water supply / condensation systems, reactor primary systems, etc. are released into the primary system by melting or peeling (erosion), and adhere to the core region for activation. A part of it is released again as a radioactive corrosion product and contaminates the reactor pressure vessel, structure, piping, etc. in the region outside the core.
[0009]
Contamination forms include fixed contamination caused by activated corrosion products incorporated into the oxide film formed on the surface of the material, commonly referred to as the inner layer, and insoluble activated corrosion products floating in the primary coolant, referred to as the outer layer. Contamination is weakly deposited on the inner layer.
[0010]
The chemical decontamination method is a method of removing contaminated radioactivity by dissolving the metal oxides constituting the inner layer and the outer layer by a reduction reaction of the chemical decontamination agent. The mechanical decontamination method such as high-pressure jet water is characterized by peeling and removing the outer layer part with relatively low adhesion, but the chemical decontamination method extends not only to the outer layer but also to the fixed inner layer oxide film. Since it is removed, a high decontamination efficiency is obtained. The decontamination factor (DF) obtained by chemical decontamination can usually be several tens to several hundreds, and a higher value is obtained as the contamination level is higher.
[0011]
The present inventors paid attention to the aerial work in the nuclear reactor for the shroud replacement work. In this case, it takes time for the groove processing and manual welding particularly at the level of the shroud support ring. When the atmospheric dose equivalent rate at this level is 1 mSv / h, work for about 1 hour is possible. In-furnace chemical decontamination, and then the activation furnace internal structure is shielded with an iron plate or the like, whereby the air dose equivalent rate at the bottom of the furnace can be reduced to 0.1 mSv / h or less. Therefore, it is possible to keep work exposure in the nuclear reactor low and work for a long time. In addition, since the activated corrosion products are removed, the problem of dust that dries and pollutes the atmosphere is reduced, and it is possible to improve safety from the viewpoint of protecting internal exposure of workers.
[0012]
The present invention has been made in view of the above circumstances, and when it becomes necessary to replace the core shroud in the nuclear reactor, it is not necessary to rely only on remote operation, and it is short without causing the problem of exposure. An object of the present invention is to provide a core shroud replacement method capable of replacing a structure substantially similar to the original core shroud in a time efficient manner.
[0013]
[Means and Actions for Solving the Problems]
  In order to achieve the above object, a core shroud replacement method according to the present invention includes a reactor pressure vessel top cover.,Steam dryerAnd fuelAfter removingA chemical agent that removes surface oxides is injected into the reactor using an existing reactor recirculation pump and an existing jet pump, circulated, and then decontaminated.Core shroudTheWelded part with the fluid support cylinderThan a certain length downward positionCut withRemoved,Inward of the core shroud at the height of the upper end of the shroud support cylinderWorkers entered the furnace with a work platform where people could work, and remainedTop surface of shroud support cylinderTheShapingThe new core shroud is fixed above the shroud support cylinder and welded.It is characterized by that.
[0014]
According to such a method of the present invention, it becomes possible for an operator to enter the core shroud and perform work, and the structure is not damaged as compared with the case where only the remote operation is relied on. The agent can be removed and installed. In addition, work errors and measurement errors can be prevented, work can be performed in a short time, and costs can be reduced as compared with remote operation.
[0015]
  Also furnaceIn-reactor decontamination that removes surface oxides with chemical agents while the inside and outside of the core shroud are open. In this process, chemical agents are injected into the reactor recirculation pump system, and reactor water circulation by the jet pump is performed. Removing surface oxides in the reactor pressure vessel byso,It is possible to reliably reduce the exposure of workers in the furnace, and it is possible for the workers to access the furnace, thereby realizing the above-described action. In this chemical decontamination, the existing reactor recirculation pump system and jet pump are mainly used, so there is no need to install new pumps and the entire reactor water can be easily circulated. Therefore, work efficiency can be improved.
[0016]
Desirable embodiments of the present invention are as follows.
[0017]
After in-core decontamination and before core shroud cutting, the jet pump inlet mixer is removed to enlarge the space around the upper part of the core shroud. This increases the space for lifting and removing the core shroud, facilitating the removal work of the shroud, and inconveniences such as the core shroud rolling and contacting the jet pump inlet mixer when it is lifted. Can be avoided.
[0018]
After removing the jet pump inlet mixer, the upper end of the jet pump diffuser is covered with a shield. Thereby, the shielding effect of the jet pump diffuser which is a part with the highest radiation dose in the furnace can be obtained. Further, a cylindrical shield is disposed at a position corresponding to the jet pump in the core shroud according to the in-core dose. This further ensures prevention of radiation exposure to workers in the furnace.
[0019]
In the core shroud cutting step, the core shroud is removed while being cut into a plurality of short cylindrical segments in order from above by electric discharge machining, machining, or water jet machining. For example, when cutting between the upper shell and the middle shell of the core shroud and cutting and removing only the upper shell, the lower part can be reused from the middle shell, so the replacement schedule is reduced. , You can also reduce waste. Further, by cutting and removing the core shroud as a short cylindrical segment, various types of storage in a device storage pool or the like can be selected, and storage can be easily performed.
[0020]
In each cutting process of the core shroud, first, cutting openings are formed at intervals along the circumferential direction of the core shroud, and the remaining non-removed portions are inserted in a state where supporting blocks are inserted into the plurality of cutting openings. The cutting portion is cut to prevent tilting of the core shroud. By performing such a cutting procedure, the cut core shroud can be held in a vertical state, and can be safely removed while preventing contact and disconnection.
[0021]
When cutting the core shroud, the cutting position in the vicinity of the welded portion between the core shroud and the shroud support cylinder is set to a height position excluding the upper portion of the shroud support ring that is affected by heat due to welding, for example, 5 mm. Thereby, in consideration of the possibility that the vicinity of the welded portion of the shroud support cylinder has been altered due to thermal influence, it is possible to obtain strength reliability of the core shroud after replacement. For example, if the core shroud is made of SUS304 steel and the shroud support cylinder is made of Inconel, stress corrosion cracking is possible in the heat affected zone (about 5 mm) of the welded portion of the shroud support cylinder that remains without being removed by welding of different materials. There is sex. By removing all the parts that may cause the stress corrosion cracking, for example, when the new shroud is fixed by welding, the thermal effect due to reheating can be prevented, and the useful life of the new shroud can be extended.
[0022]
It is desirable to cut the instrumentation pipes in the furnace above the in-core stabilizer. Thereby, it becomes unnecessary to attach an in-core stabilizer again, and shortening of a construction period and exposure reduction can be achieved effectively.
[0023]
The removed steam dryer and steam / water separator / shroud head are housed in a stack in the equipment storage pool. Further, the segment of the core shroud that has been cut is accommodated in the equipment storage pool in a state of being stacked with the removed internal structure. Thereby, the steam dryer, the steam separator, the cut | disconnected core shroud, etc. can be efficiently stored using the space in an equipment storage pool effectively.
[0024]
When the steam dryer is stacked above the steam / water shroud head, the height and concentricity of the assembly in the reactor storage pool may be approximately the same as the assembly in the reactor by the support member incorporated in the equipment storage pool. desirable. As a result, the steam dryer is in a support state similar to the installation state in the reactor, and damage prevention and the like can be effectively achieved.
[0025]
The work platform has a guide parallel to the peripheral wall of the core shroud on the upper surface, and by moving a cutting device for the core shroud, a cut surface shaping device, or a welding device for fixing the new core shroud along the guide, Cutting the core shroud, shaping the cut surface or fixing by welding. As a result, the core shroud cutting, cutting of the cut surface, welding work for fixing the new core shroud, and the like can be performed efficiently, accurately and reliably.
[0026]
At the time of welding and fixing the new shroud, at least one of the new shroud and the shroud support, in advance, corrosion-resistant metal and other reinforcements on the inner peripheral surface side or outer peripheral surface side of the part that will be affected by the welding. A weld overlay made of material is applied. When the core shroud is, for example, SUS304 material, it is highly susceptible to stress corrosion cracking because of the high carbon content, etc., so the new shroud can be replaced with a material made of material such as SUS316 that has less stress corrosion cracking. However, when the new shroud is made of SUS304 material, and for the shroud support cylinder made of SUS304 material that remains without being replaced, stress corrosion cracking from the welded portion is applied by applying a weld overlay to the part that is affected by heat. It is possible to prevent damage caused by the above. Inconel may be built up on the lower end of the core shroud as needed.
[0027]
The new shroud is fixed to the shroud support cylinder by welding, or by detachable joint fixing by bolting, pin coupling or other mechanical joining means. Usually, the core shroud and the shroud support cylinder are fixed by welding in many cases. However, when a later replacement is taken into consideration, the use of a detachable fixing structure by mechanical joining means is effective. When welding the core shroud to the shroud support cylinder, the welding operation is performed from the inner side of the shroud. Thereby, compared with the case where it carries out from an outer peripheral side, a welding operation can be efficiently performed using a wide space.
[0028]
When exchanging the core shroud, a capsule in which an operator can enter is prepared, and this capsule is moved up and down from the fuel exchange work floor or the reactor pressure vessel flange to the work platform by an overhead crane or an elevator in the reactor building. Thereby, quickness and safety of work can be secured.
[0029]
In addition, when replacing the core shroud, the jet pump is also replaced before or after removing the core shroud. Even if only the jet pump is replaced with the core shroud installed, the space between the reactor pressure vessel wall where the jet pump is installed and the core shroud is narrow, and it is not possible to replace the jet pump. It is. Therefore, by exchanging the jet pump in connection with the shroud exchange, both can be exchanged efficiently.
[0030]
When replacing the core shroud, on the work platform installed in the reactor during the shroud replacement process, inspection and repair of equipment installed in the reactor pressure vessel by workers, or preventive maintenance treatment against stress corrosion cracking, etc. I do. According to such a method, the radiation level in the reactor is lowered by the chemical decontamination described above, and workers can enter almost the same as when a new reactor is installed. Therefore, inspection, repair, and prevention that are difficult by remote operation are possible. Maintenance processing and the like can be performed effectively.
[0031]
The core shroud that has been cut and removed is transferred to and stored in a lining tank provided at a location adjacent to the reactor building. As a result, a space on the operation floor can be ensured and workers can be prevented from being exposed.
[0032]
When replacing the core shroud, the core instrumentation pipe and the differential pressure / borate water injection pipe are once cut and removed. As a result, when removing the core shroud to be replaced, the core shroud can be easily replaced without the structure that obstructs the movement. After the installation of the new shroud, the newly produced in-core nuclear instrumentation piping and differential pressure / borate water injection piping may be connected and restored. In this case, the work platform is provided with a partial opening that enables welding of each in-furnace instrumentation guide tube to be placed below it, so that exposure can be effectively prevented. The welding work by the worker becomes possible.
[0033]
In addition, for the connection of the differential pressure and boric acid water injection pipes, mechanical pressure welding or connection methods such as seals and screws are conceivable, but welding is used to prevent leakage and reduce flow resistance. Is desirable. In addition, the core instrumentation pipe in the reactor and the differential pressure / borate water injection pipe have a small diameter, so if jointing by welding is difficult, joints made by shape memory alloy are used for remote operation. You can also. Thereby, it becomes possible to significantly reduce the exposure of the worker.
[0034]
On the other hand, prepare an extension rod that protrudes, for example, about 2 m upward from the scaffolding provided on the flange of the reactor pressure vessel, and attach this extension rod to the tip of the differential pressure / borate water injection pipe or each instrumentation pipe in the reactor, If this core is passed through the core support plate as a guide and the core support plate is suspended, the core support plate can be easily attached to the core shroud by reducing the circumferential shift and the core direction shift of the core support plate. Can be installed in a fixed position.
[0035]
In addition, if an evacuation chamber with a radiation shielding wall that can be evacuated by an operator is prepared on the work platform during automatic welding or inspection waiting for the replacement of the core shroud, it is possible to reach the operation floor with an elevator or the like between work. The working efficiency can be further improved as compared with the case where it goes up, and the exposure of workers can be reliably prevented. In addition, it is more desirable that the evacuation chamber can be moved upward by lifting or the like when necessary.
[0036]
In addition, if the reactor water level rise in the core shroud exchange is limited to the annulus, and after the installation of the new upper lattice plate and the new core support plate is completed, the water level in the shroud is raised, the radiation of water The high shielding effect can effectively prevent radiation exposure from the reactor pressure vessel or the jet pump to the workers in the core shroud.
[0037]
For preventive maintenance of the reactor pressure vessel or equipment installed at the bottom of the reactor, drain the reactor water at the bottom of the reactor pressure vessel and perform shot peening from an opening in a part of the work base installed in the reactor. The equipment is lowered to the bottom of the furnace, and the equipment installed on the bottom of the furnace, such as the stub tube, control rod drive mechanism housing, and in-core nuclear instrumentation housing, is shot peened to change the surface of the material and welds to compressive stress. Like that. Thereby, the crack (stress corrosion cracking etc.) which generate | occur | produces in a material and a welding part can be prevented. As a preventive maintenance processing method for equipment in this case, for example, stainless steel or Inconel steel containing platinum (Pt), palladium (Pb) or the like is sprayed on the surface of equipment installed at the bottom of the furnace, and platinum or palladium To act as a catalyst for recombining hydrogen and oxygen produced by radiolysis of water. Thereby, the stress corrosion cracking etc. can be prevented by reducing the dissolved oxygen in the furnace and making the corrosion potential constant.
[0038]
In addition, when the soundness of the taken-out upper lattice plate and core support plate is maintained, cost reduction and waste reduction can be achieved by using these upper lattice plate and core support plate again.
[0039]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0040]
1 to 42 show an embodiment of the present invention. FIG. 1 is an overall configuration diagram of a reactor building showing a state in which a core shroud is cut and removed, FIGS. 2 to 4 are flowcharts showing a series of procedures according to this embodiment, and FIGS. FIG. 24 to FIG. 42 are configuration diagrams showing in detail the main points of the work.
[0041]
In the boiling water reactor to which the core shroud replacement method according to this embodiment is applied, as shown in FIG. 5, a core shroud 2 is disposed in a reactor pressure vessel 1, and the core shroud 2 is a shroud support cylinder. 3 is supported. 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, and the jet pump 7 includes a jet pump diffuser 7a, a jet pump riser pipe 7b, and a jet pump inlet mixer 7c. A baffle plate 8 is provided below the jet pump 7.
[0042]
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 pipe 12, a low-pressure water injection pipe 13, a differential pressure detection / borate water Equipment such as an injection pipe 14, a steam dryer 15, and a steam / water separator / shroud head 16 are provided.
[0043]
A method of replacing the core shroud in the reactor pressure vessel 1 having such a configuration will be described first with reference to the flowcharts of FIGS. 2 to 4 and the configuration diagrams of FIGS.
[0044]
(1) In the state shown in FIG. 5, the reactor pressure vessel upper lid 17 and the steam dryer 15 are removed from the reactor pressure vessel 1 by the overhead crane 24 of the reactor building 23 in the state shown in FIG. 5 (step 101). . At this time, the reactor water is maintained under the flange of the reactor pressure vessel 1.
[0045]
(2) The reactor well 18 is filled with water, the steam separator / shroud head 16 is removed from the overhead crane 24 (step 102), and then all fuel 10 is transferred from the core to the fuel pool (step 103). ), The reactor water level is returned to the lower part of the flange of the reactor pressure vessel 1, and the state shown in FIG.
[0046]
(3) The dry tube / LPRM detector assembly 22 occupying the space between the upper lattice plate 5 and the core support plate 6 through the in-core nuclear instrumentation guide tube 25 is removed, and the upper lattice plate 5 and the core support plate are removed. 6 is emptied (step 104). In addition, the above procedure is performed in order to ensure the space removed after removing the core shroud 2, and the order may be changed.
[0047]
(4) From this state, the fuel support fitting 10a, the control rod 9 and the control rod guide tube 11 are removed (step 105). When removing the control rod guide tube 11, the control rod drive mechanism 20 and a thermal sleeve (not shown) need to be pulled out from the control rod drive mechanism housing 21 from the pedestal chamber 19. The removed control rod drive mechanism 20 and the thermal sleeve are stored in a storage box, moved from the pedestal chamber 19 to a fuel change work floor or the like, and stored. Alternatively, after the control rod guide tube 11 is removed, it can be returned to the control rod drive mechanism housing 21.
[0048]
(5) Removal of feed water sparger 26 installed above the core shroud 2 (step 106), cutting and removal of the core spray system piping 12 (step 107), hanging from the bracket on the inner wall of the reactor pressure vessel 1, and the core shroud The guide rod 27 inserted into the bracket hole is cut and removed (step 108), and the coupling of the low-pressure injection pipe 13 is removed (step 109). Thereby, as shown in FIG. 7, the inside of the core shroud 2 becomes empty.
[0049]
(6) From this state, as shown in FIG. 8, the upper lattice plate 5 and the core support plate 6 are sequentially lifted and removed (steps 110 and 111). The removal of the upper lattice plate 5 and the core support plate 6 will be described in detail later. Further, the upper part of the in-core nuclear instrumentation guide tube 25 and all or a part of the in-core stabilizer 28 are cut and removed (step 112), and the bottom of the reactor pressure vessel 1 is penetrated to stand along the inner wall of the core shroud 2. The rising differential pressure detection / boric acid water injection pipe 14 is also cut and removed. The cut pipe is caught by the metal fitting attached to the inner wall of the core shroud 2 and remains in the core shroud 2. In a plant where the position of the weld line between the core shroud 2 and the shroud support cylinder 3 is higher than the position of the in-core stabilizer 28, the in-core nuclear instrumentation guide tube 25 is cut while leaving the existing in-core stabilizer 28. You can also.
[0050]
(7) A cylindrical seal vessel 29 having an upper and lower opening is attached to the upper portion of the reactor pressure vessel 1 in the reactor well 18 and is liquid-tightly isolated from the surroundings (step 114). This is in order to isolate the inside of the furnace from the surroundings during chemical decontamination in the furnace in the next step.
[0051]
(8) The inside of the reactor pressure vessel 1 is decontaminated with a chemical agent (step 115).
[0052]
Although this process will be described in detail later, a chemical agent is injected into the reactor recirculation pump system and circulated in the reactor using the jet pump 7 to a level at which workers can enter the reactor. The radiation dose rate is reduced.
[0053]
(9) The seal container 29 is once removed (step 116), and the jet pump inlet mixer 7c is removed (step 117). This is performed in order to reduce the dose rate during the operation in the furnace because the contamination degree of the same part in the jet pump 7 is high. This chemical decontamination will also be described in detail later.
[0054]
(10) After that, as shown in FIG. 9, the work platform 30 is installed on the inner lower part of the core shroud 2 (step 118). Then, as shown in FIGS. 9 and 10, the core shroud 2 is cut and removed (step 119). In the cutting process of the core shroud 2, the core shroud 2 is made into a plurality of short cylindrical segments 2a, 2b... Remove while cutting from the lower part of the weld. Detailed procedures will be described later.
[0055]
(11) As shown in FIG. 11, the above-described seal vessel 29 is again installed in the reactor well 18 to isolate the inside of the reactor from the surroundings, and the reactor water level is lowered below the work platform 30 (step 120). The upper end of the jet pump diffuser 7a after the jet pump inlet mixer is removed is covered with a shield 31. At the upper end of the jet pump diffuser 7a, stellite containing cobalt is used as a wear-resistant material, and the amount of radiation irradiation is extremely high. Therefore, this portion is covered with a shield 31 to reduce the amount of exposure. Further, a cylindrical shield 32 is disposed on the work platform 30 in the core shroud 2 in accordance with the in-core dose rate. Moreover, the elevator 34 is installed in the shield 32 (step 121), and the worker 33 is moved up and down from the furnace in the capsule 35.
[0056]
(12) As shown in FIG. 12, a guide 36 is mounted on the work platform 30, and the cut surface forming device 37 is moved along the guide to perform upper surface processing of the shroud support cylinder 3 (step 122).
[0057]
(13) Thereafter, as shown in FIG. 13, the new shroud 38 is suspended in the core (step 123), and a cylindrical shield (not shown) is installed inside (step 124), as shown in FIG. Then, the worker 35 enters the furnace, and as shown in FIG. 15, the new shroud 38 is centered by the centering device 39 mounted on the work platform 30 (step 125).
[0058]
(14) Next, as shown in FIG. 16, the new shroud 38 is welded to the shroud support cylinder 3 by the welding device 40 (step 126), and then, as shown in FIG. 17, the in-core nuclear instrumentation guide tube 25, the in-core stabilizer. 28 and the differential pressure detection / borate water injection pipe 14 are connected (step 127).
[0059]
(15) After removing the work platform 30 and the elevator 34 (step 127a) to obtain the state shown in FIG. 18, the new core support plate 42 is suspended on the new shroud 38 (step 128) as shown in FIG. After the core of the core support plate is adjusted, it is fixed by bolting (step 129).
[0060]
(16) As shown in FIG. 20, the new upper lattice plate 43 is suspended and the lead position is adjusted (step 130). Thereafter, as shown in FIG. 21, the rising pipe of the core spray system pipe 12 is welded (step 131), the feed water sparger 44 is installed (step 132), and the new guide rod 11 is attached (step 133).
[0061]
(17) As shown in FIG. 22, the reactor water level is raised to the bottom of the flange of the reactor pressure vessel 1 (step 134), the low-pressure water injection pipe coupling is restored (step 135), and the reactor well is full. (Step 136).
[0062]
(18) As shown in FIG. 23, the dry tube / LPRM detector assembly 22 is returned (step 137), the fuel support fitting 10a, the control rod 9 and the control rod guide tube 11 are returned (step 138). The fuel is loaded (step 139).
[0063]
Then, the steam / water separator / shroud head 16 is attached (step 140), the steam dryer 15 and the reactor pressure vessel upper lid 17 are attached (step 141), and the operation is completed.
[0064]
Next, a main process among the above processes (step 1 to step 141) will be described in detail with reference to FIGS.
[0065]
FIG. 24 shows a state in which the upper grid plate 5 is supported on the core shroud 2. The upper lattice plate 5 is placed on a step portion of the core shroud upper end ring, and the periphery thereof is fixed by a bracket 51 and a wedge 52. The L-shaped stopper 53 is fixed to a bolt 55 screwed to a stud 54 fixed to the upper surface of the upper grid plate 5 via a welded portion 56. Therefore, when the upper grid plate 5 is removed, the wedge 52, the stopper 53 and the bolt 55 fixed to the core shroud 2 are removed by remote control as shown in the figure, whereby the upper grid plate 5 is removed from the core shroud. Suspend above 2.
[0066]
FIG. 25 shows a state in which the core support plate 6 is supported on the core shroud 2. The core support plate 6 is fixed to a flange 57 at a lower step portion of the core shroud 2 via a bolt 58 and a nut 59, and a U-shaped cap 60 placed on the nut 59 is welded to a bolt 58 end portion via a block 61. 62 is fixed. Therefore, when removing the core support plate 6, as shown in FIG. 25, the welding portion 62 is removed by remote operation, and the bolts 58 and nuts 59 fixed to the core shroud 2 are removed, It can be suspended above the core shroud 2.
[0067]
The upper lattice plate 5 and the core support plate 6 thus removed are temporarily stored in the reactor well 18 that is full of water, in the storage bits of the steam dryer 15 and the steam / water separator / shroud head 16, or Move to a tank installed adjacent to the reactor building for storage. As another method for removing the upper lattice plate 5 and the core support plate 6, the upper lattice plate 5 and the core support plate 6 may be removed while being cut into small segments by a method such as electric discharge machining or plasma cutting.
[0068]
FIG. 26 shows a configuration example of the chemical decontamination apparatus system. In this embodiment, as described above, in order to reduce the radiation exposure when the reactor shroud 2 is removed and the reactor water level is lowered, the inside and outside of the reactor core shroud 2 and the inner surface of the reactor pressure vessel 1, the reactor pressure vessel 1 The bottom of the furnace is cleaned. As shown in FIG. 26, the chemical decontamination is performed with the core shroud 2 and the jet pump 7 left after the upper lattice plate 5 and the core support plate 6 are removed. In the state where the shield is attached to the upper part of the reactor pressure vessel 1 and the reactor water is full, the chemical agent is injected from the chemical agent injection device 65 connected to the inflow pipe 64 of the reactor recirculation pump 63, and from the recirculation inlet nozzle. A chemical is introduced into the furnace by the jet pump 7 and circulated in the furnace. This solution uses a permanganate nutrient solution or the like, which reduces and removes the activated oxide in the reactor pressure vessel 1, and is discharged from the recirculation outlet nozzle to the outflow piping 66 outside the reactor. It is circulated by a coolant purification device 67 attached to the outside.
[0069]
Then, it is returned to the reactor again through the reactor recirculation pump 63. By repeating this process several times, the radioactive material attached to each device in the furnace and the inner surface of the pressure vessel can be safely removed, and thereby the radiation dose in the furnace can be drastically reduced. Waste gas is processed by the waste gas device 68. In addition to this, brush cleaning or clad suction cleaning of the surface of the in-furnace structure may be performed as appropriate in order to reduce the dose of the radiation atmosphere in the furnace.
[0070]
For example, groove processing and manual welding at the level of the shroud support ring 3 require a certain time or more. When the atmospheric dose equivalent rate at this level is 1 mSv / h, work for about 1 hour is possible. By shielding the in-furnace chemical decontamination and then the activation furnace internal structure with an iron plate or the like, the air dose equivalent rate at the bottom of the furnace can be made 0.1 mSv / h or less. Therefore, it is possible to keep work exposure in the nuclear reactor low and work for a long time. Also, since activated corrosion products are removed, the problem of dust that dries and pollutes the atmosphere is reduced, and safety is also improved in terms of protecting internal exposure of workers.be able to. In this chemical decontamination, the existing reactor recirculation pump system and jet pump are mainly used, so there is no need to install new pumps and the entire reactor water can be easily circulated. Therefore, work efficiency can be improved.
[0071]
27 to 32 show the method for replacing the core shroud 2 in detail.
[0072]
FIG. 27 shows an example of the cutting process of the core shroud 2. The core shroud 2 is removed while being cut into, for example, two short cylindrical segments 2a and 2b in order from above by electric discharge machining, machining, or water jet machining.
[0073]
FIG. 28 shows the shroud cutting device 70 for performing the cutting and the cutting action. A drive mechanism 72 that rotates and expands and contracts is provided on the lower surface of a liftable base 71 that is placed on the upper end step of the core shroud 2, and a rotating claw 73 connected to the tip of the drive mechanism 72 is drilled in the core shroud 2. The core shroud 2 is lifted by being inserted and locked in the provided locking hole 74. Further, a guide rail 76 is provided along the circumferential direction at the lower end of the cylindrical support 75 that hangs down from the lower surface of the base 71, and electric discharge machining, machining, or high-pressure water jet system that travels through the wheels on the guide rail 77. The cutting device 78 is provided, and the core shroud 2 is cut by the cutting device 78. The shroud cutting device 30 extends along the guide of the work platform 29.RunThe core shroud 2 may be cut.
[0074]
29A to 29D show each cutting process of the core shroud 2. Although FIG. 29 shows the cutting of the core shroud 2 and the shroud support cylinder 3, the cutting of other portions is the same.
[0075]
First, from the state of FIG. 29A, as shown in FIG. 29B, the cut openings 80 are formed at intervals along the circumferential direction of the core shroud 2. Then, as shown in FIG. 3C, the remaining non-cutting portion is cut in a state where the supporting block 81 is inserted into the plurality of cutting openings 80 so as to prevent the tilting of the core shroud. To do. By carrying out such a cutting procedure, the segments of the core shroud 2 are kept in a vertical state during the cutting, and are safely removed by preventing contact or disconnection or the cutting device 70 being pinched by the core shroud 2. can do.
[0076]
30, 31, and 32 show the state of removal of the core shroud. FIG. 30 is an overall view corresponding to the state shown in FIG. 28, and shows a state in which the cutting device 70 is suspended using the crane 24 installed in the reactor building 23 and the core shroud 2 is cut. For example, when the cutting of the upper segment 2a is completed in this state, the cut upper segment 2a is lifted by the crane 24 and removed as shown in the upper side of FIG. Thereafter, as shown in the lower side of FIG. 31, the process proceeds to cutting of the lower segment 2b. When the cutting of the lower segment 2b is completed, as shown in FIG. 32, it is similarly lifted by the crane 24 and removed.
[0077]
As shown in FIG. 1, the removed segments 2a and 2b of the core shroud 2 are moved to the equipment storage pit 79 and stored. In this case, for example, one of the segments 2a and 2b is installed above the previously removed upper lattice plate 5 and core support plate 6 via a support member 80 such as a shelf plate, whereby the space in the equipment storage pit 79 is obtained. Can be used effectively.
[0078]
Similarly, the steam dryer 15 and the steam / water separator / shroud head 16 removed in the first stage are also moved upward via a support base 81 covering the steam / water separator / shroud head 16 as shown in FIG. By stacking the steam dryer 15 on the inside, it can be efficiently stored in the same state as in the nuclear reactor. In this case, when the steam dryer 15 protrudes on the water of the equipment storage pit 79, the exposed portion of the air is covered with the cover 82 made of a radiation shielding material, so that it is possible to reliably prevent the explosion.
[0079]
FIG. 33 shows in detail the cutting position when the core shroud 2 is cut and removed from the shroud support cylinder 3. In this example, a configuration is shown in which a shroud support ring 83 is connected between the core shroud 2 and the shroud support cylinder 3 via welded portions 84 and 85, but the same applies even when the shroud support ring 83 is not provided.
[0080]
That is, in this embodiment, cutting is performed at a position below the welded portion 85 of the shroud support cylinder 3 by a predetermined length h. This length h is set to 5 mm from the upper end side part of the shroud support ring 3 which receives the heat influence by welding, for example. Thereby, in consideration of the possibility that the vicinity of the welded portion of the shroud support cylinder 3 is deteriorated due to thermal influence, it is possible to obtain the strength reliability of the core shroud after replacement. For example, when the core shroud is made of 2SUS304 steel and the shroud support cylinder 3 is made of Inconel, stress corrosion cracking occurs in the heat affected zone (about 5 mm) of the welded portion of the shroud support cylinder 3 that remains without being removed by welding of different materials. There is a possibility. By removing all the parts that may cause stress corrosion cracking, for example, when the new shroud 38 is fixed by welding, the thermal effect due to reheating can be prevented, and the useful life of the new shroud 38 can be extended. .
[0081]
Next, a case where a new shroud is joined and fixed on the joining shroud support cylinder 3 in place of the removed core shroud 2 will be described in detail.
[0082]
FIG. 34 is an explanatory diagram for level adjustment of the new shroud 38, and FIGS. 35 and 36 are explanatory diagrams for the welding method. As described above, the cut surface of the shroud support cylinder 3 is flattened by running a finish processing apparatus of an electric discharge machining or machining method along the circumferential guide of the work base 29 in advance.
[0083]
As shown in FIG. 34, temporary brackets 86 are attached in advance to the inner peripheral surface side of the new shroud 38, and several jacks 87 are placed around the work platform 30 to support the temporary brackets 86 of the new shroud 38. Adjust the level. Then, the attachment jig 88 is temporarily attached between the new shroud 38 and the shroud support cylinder 3 and welded. A rail 89 for traveling the welding apparatus is attached on the work table 30, and a welding backing metal 90 is provided in the welded portion.
[0084]
After adjusting the level of the new shroud 38 in this way, welding is performed by a welding device 91 as shown in FIG. Welding of the new shroud 38 is performed from the inner peripheral side, but the outer annulus portion corresponding to the back side as viewed from the welding is sufficiently dried, and an inert gas is enclosed to prevent oxidation during welding.
[0085]
The welder is lowered onto the work platform 30 and a new shroud 38 is welded to the upper end surface of the shroud support cylinder 3. Until the new shroud 38 is welded to the upper end of the shroud support cylinder 3 several times and the inert gas in the annulus 19 no longer leaks into the new shroud 38, the welder wears an airtight suit or mask and supplies air. There is a need to. It is also possible to reduce the radiation exposure by providing an atmospheric chamber in the center of the work platform 30, setting the welding apparatus 91 out of the atmospheric chamber, and monitoring automatic welding in the atmospheric chamber.
[0086]
At the time of welding the new shroud 38, the alignment scope or the lowering swing is suspended from the upper part of the reactor pressure vessel 1, thereby measuring the deformation and displacement of the new shroud 38, changing the welding start position of the next pass, or the cosmetic fill pass. Welding is carried out by devising them so that they are within the design specification values, such as by welding. The temporary bracket 86 and the temporary attachment jig 88 are removed from the new shroud 38 after or during welding.
[0087]
FIG. 36 shows a weld overlay made of a corrosion-resistant metal or other reinforcing material on the inner peripheral surface side of a part that will be thermally affected by the welding of the new shroud 38 and the shroud support cylinder 3 in advance when the new shroud is fixed by welding. The case where 38b and 3b are applied is shown. When the core shroud is, for example, SUS304 material, it is highly susceptible to stress corrosion cracking due to a large amount of carbon material contained. Therefore, the new shroud can be replaced with a material made of a material with less stress corrosion cracking such as SUS316. However, when the new shroud is made of SUS304 material, and for the shroud support cylinder made of SUS304 material that remains without being replaced, by applying weld overlays 38a and 3b to the portions affected by heat, Damage due to stress corrosion cracking can be prevented. Inconel may be built up on the lower end of the core shroud as needed. Further, it may be applied only to the shroud support cylinder 3.
[0088]
Note that the new shroud 38 is suspended from the upper end of the support cylinder 3 as these preconditions. In this case, several guides are attached along the inner wall of the reactor pressure vessel 1 so that the jet pump 7 and other devices are not damaged when the new shroud 37 is suspended. The new shroud 38 serves as a shield that prevents high-level radiation from the stellite portion at the upper end of the jet pump diffuser 7a. However, in order to obtain a further shielding effect, a shield may be attached along the inner wall of the new shroud 38. Good. Further, a shield may be provided between the upper end of the new shroud 38 and the reactor pressure vessel 1 to prevent radiation from the annulus portion 19 when the reactor water level is lowered. The reactor water level is lowered until the work platform 30 appears in the air.
[0089]
Further, in order to prevent dust from rising from the annulus portion 19 between the new shroud 38 and the reactor pressure vessel 1 and to prepare an inert gas sealing device, sheet curing is performed on the upper end of the new shroud 38.
[0090]
As shown in FIG. 37, the new shroud 38 may be fixed to the shroud support cylinder 3 by providing overlapping portions at both joint portions and joining them with a connecting pin 91, as shown in FIG. The new shroud 38 and the shroud support cylinder 3 may be provided with brackets 92 and 93, which are coupled by bolts 94 and 95, and the new shroud 38 may be fastened.
[0091]
The in-core stabilizer 28 can be attached by installing a scaffold on a leg installed on the control rod drive mechanism housing 21. It is desirable to divide the scaffold into several segments so that the in-core stabilizer 28 assembled in a cross beam shape can be avoided and removed.
[0092]
After the core shroud replacement, the work platform 30 and the scaffolding in the core shroud are removed, and the reactor water level is raised to the upper part of the shroud middle shell.
[0093]
Then, as described above, a temporary scaffold is installed on the flange of the reactor pressure vessel 1, the new core support plate 42 is lifted on the flange of the reactor pressure vessel 1, and dozens of in-core nuclear instrumentation guide tubes 25 and The extension rod attached to the tip of the differential pressure detection / boric acid water inflow pipe 14 is inserted into a through hole at a corresponding position of the new core support plate 42. After all the plugs are inserted, the temporary scaffold on the flange of the reactor pressure vessel 1 is removed.
[0094]
39 to 42 show a centering operation when the new core support plate 42 and the core upper lattice plate 43 are attached.
[0095]
This centering operation can be performed using an alignment measuring device 96 as shown in FIGS. That is, as shown in FIG. 39, between the control rod guide tube hole 97 of the new core support plate 42 and the upper end portion of the control rod drive mechanism housing 21, or the rectangular opening of the new upper lattice plate 43 shown in FIG. By fixing the cylindrical container 96a between the portion 98 and the hole 97 for the control rod guide tube of the core support plate 42, and measuring the deviation of the downward swing 96b suspended in the cylindrical container 96a, Calculate the inclination of the cylindrical container 96ataking measurementUse the device. The lower swing 96b is supported at its upper end by a universal joint portion 96c and is always vertical. The position of the hole 97 for the control rod guide tube of the new core support plate 42 with respect to the upper end of the control rod drive mechanism housing 21 or the square of the new upper grid plate 43 with respect to the position 98 of the hole for the control rod guide tube of the new core support plate 42 The position of the new core support plate 42 or the new upper lattice plate 43 can be known by examining several points of the position shift of the opening. Thereafter, the new core support plate 42 and the new upper lattice plate 43 are bolted to the new shroud 38. Tack welding can also be performed remotely to prevent the bolt from rotating. Reference numerals 99a and 99b denote pins and brackets for locking the alignment measuring device 96 to the new core support plate 42.
[0096]
As other operations, for example, the reactor water at the bottom of the reactor pressure vessel is drained, and various inspection and repair devices are lowered to the bottom of the reactor from an opening in a part of the work platform 30 installed in the reactor. Then, welding repair around the control rod drive mechanism housing 21 and the stub tube is performed.
[0097]
Moreover, as a method of changing the surface portion of the material to compressive stress and performing preventive maintenance treatment against stress corrosion cracking, etc., the reactor water at the bottom of the reactor pressure vessel is drained, the shot peening device is lowered to the bottom of the reactor, a stub tube, It is also possible to easily perform shot peening around the welded portion of equipment installed on the bottom of the furnace, such as the control rod drive mechanism housing and each instrument housing in the furnace.
[0098]
Alternatively, by reducing the dissolved oxygen in the reactor and lowering the corrosion potential, a preventive maintenance process against stress corrosion cracking, etc., is performed by draining the reactor water at the bottom of the reactor pressure vessel and placing the thermal spraying device at the bottom of the reactor. It is also possible to easily spray and apply stainless steel or Inconel steel containing Pt or Pd on the surface of the equipment installed at the bottom of the furnace. When the reactor is restarted, Pt or Pd in the sprayed metal works as a catalyst to recombine hydrogen and oxygen generated by the decomposition of water, and it has the effect of reducing dissolved oxygen in the reactor and lowering the corrosion potential. is there.
[0099]
As described above, according to the present embodiment, it is possible to restore almost the same structure as that of the original core shroud by remote operation and in-core work. Using an environment in which workers can enter the reactor pressure vessel 1, it is easy to perform preventive maintenance treatments such as welding repair or stress corrosion cracking of equipment installed on the inner surface or bottom of the reactor pressure vessel. .
[0100]
Next, the present invention will be described with reference to FIGS.As a disclosure exampleexplain. thisDisclosure exampleThese relate to a method of replacing the jet pump 7 together with the replacement of the core shroud 2. FIG. 43 is an overall configuration diagram of the reactor building showing a state in which the core shroud has been cut and removed, FIGS. 44 to 47 are flowcharts showing a series of procedures according to the present embodiment, and FIGS. 48 to 67 sequentially show replacement work of the core shroud. It is a block diagram shown in FIG.
[0101]
BookDisclosure exampleIs substantially the same as the above embodiment except for replacement of the jet pump 7. That is, in FIG. 44 to FIG. 47 showing the flow of processing, the difference from the above embodiment among the steps shown in Step 201 to Step 247 is that the step of removing the jet pump 7 after cutting and removing the core shroud 2. This is an added point. Ie bookDisclosure exampleThen, after cutting and removing the core shroud 2, the jet pump 7 is cut, removed, processed, welded, attached, and the reactor recirculation pump is cut and removed in steps 220 to 226 shown in FIG. 45. .
[0102]
In this way, in the core shroud replacement method, the jet pump is installed when only the jet pump is replaced alone with the core shroud installed by replacing the jet pump before or after removing the core shroud. Since the space between the reactor pressure vessel wall and the core shroud is narrow, it is impossible to replace and install the jet pump. On the other hand, it is possible to replace the jet pump efficiently. Both can be exchanged.
[0103]
FIG. 68 shows still another embodiment of the present invention.Disclosure exampleIs shown. thisDisclosure exampleThen, the core shroud 2 that has been cut and removed is transferred to and stored in a lining tank 23 a provided at a location adjacent to the reactor building 23. In this case, transportation is possible by using a crane 24a provided separately. It should be noted that a predetermined radiation shield is provided around to prevent exposure. BookDisclosure exampleAccordingly, the space in the equipment pit and the space on the operation floor of the reactor building 23 can be effectively used.
[0104]
【The invention's effect】
As described in the above embodiments, according to the core shroud replacement method according to the present invention, when it is necessary to replace the core shroud in the nuclear reactor, it is not necessary to rely only on remote operation and the problem of exposure. Therefore, it is possible to efficiently replace the original core shroud with a structure that is almost the same in a short time. In particular, in the decontamination process of the reactor, the chemical agent is injected into the reactor recirculation pump system and the reactor water is circulated by the jet pump, thereby removing the surface oxides in the reactor pressure vessel, thereby reducing the core shroud. An operator can enter and work inside, and the structural agent can be removed and attached without damaging the structure as compared with the case where it depends only on remote operation. In addition, work errors and measurement errors can be prevented, work can be performed in a short time, and costs can be reduced as compared with remote operation.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of a method for replacing a core shroud according to the present invention, and is an overall view showing a state in which a structural material is taken out from the furnace and stored.
FIG. 2 is a flowchart showing an operation procedure of the embodiment.
FIG. 3 is a flowchart showing an operation procedure of the embodiment.
FIG. 4 is a flowchart showing an operation procedure of the embodiment.
FIG. 5 is a diagram showing a nuclear reactor structure to which the one embodiment is applied.
6 is a view showing a state where the nuclear reactor shown in FIG. 5 is opened.
7 is a view showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5;
FIG. 8 is a view showing a state where parts are sequentially removed from the nuclear reactor shown in FIG. 5;
FIG. 9 is a view showing a state where parts are sequentially removed from the nuclear reactor shown in FIG. 5;
FIG. 10 is a view showing a state where a core shroud is removed in the embodiment.
FIG. 11 is a diagram showing an elevator installation state in the embodiment.
FIG. 12 is a diagram showing how the upper end surface of the shroud support ring is shaped in the embodiment.
FIG. 13 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 14 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 15 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 16 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 17 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 18 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 19 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 20 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 21 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 22 is a diagram showing a state in which structural members are sequentially assembled in the embodiment.
FIG. 23 is a diagram showing a replacement completion state in the embodiment.
FIG. 24 is a diagram showing the operation of the embodiment in detail, and shows the mounting structure of the upper grid plate.
FIG. 25 is a diagram showing in detail the operation of the embodiment, and shows a structure for attaching a core support plate.
FIG. 26 is a diagram showing in detail the operation of the embodiment, showing a method of chemical decontamination.
FIG. 27 is a diagram showing in detail the operation of the embodiment, and shows a method for cutting the core shroud.
FIG. 28 is a diagram showing in detail the operation of the embodiment, and shows a method for cutting the core shroud.
FIGS. 29A to 29D are diagrams sequentially showing a cutting procedure of a core shroud.
FIG. 30 is a diagram showing in detail the operation of the embodiment, and shows a method for cutting the core shroud.
FIG. 31 is a diagram showing in detail the operation of the embodiment, and shows a method for cutting the core shroud.
FIG. 32 is a diagram showing in detail the operation of the embodiment, and shows a method for cutting the core shroud.
FIG. 33 is a diagram showing in detail the operation of the embodiment, and showing the cutting position of the core shroud.
FIG. 34 is a diagram showing in detail the operation of the embodiment, and showing the joined state of the new core shroud.
FIG. 35 is a diagram showing in detail the operation of the embodiment, showing a welded state of the new core shroud.
FIG. 36 is a diagram showing in detail the operation of the embodiment, and shows a state of overlay welding.
FIG. 37 is a view showing the operation of the embodiment in detail, and showing a modification regarding the attachment of a new core shroud.
FIG. 38 is a diagram showing in detail the operation of the embodiment, and showing a modified example related to the attachment of a new core shroud.
FIG. 39 is a diagram showing the operation of the embodiment in detail, and showing the centering operation of the new core support plate.
FIG. 40 is a diagram showing the operation of the embodiment in detail, and showing the centering operation of the new core support plate.
41 is a diagram showing in detail the operation of the embodiment, and showing the centering operation of the new core support plate. FIG.
42 is a diagram showing in detail the operation of the embodiment, and showing the centering operation of the new core support plate. FIG.
FIG. 43 shows a core shroud replacement method according to the present invention.Disclosure examples related toFIG. 3 is an explanatory view showing the overall state of the structural material taken out from the furnace and stored.
FIG. 42 is a flowchart showing an operation procedure of the embodiment.
FIG. 43Disclosure exampleThe flowchart which shows the operation | movement procedure.
FIG. 44Disclosure exampleThe flowchart which shows the operation | movement procedure.
FIG. 45Disclosure exampleThe flowchart which shows the operation | movement procedure.
FIG. 46Disclosure exampleThe flowchart which shows the operation | movement procedure.
FIG. 47Disclosure exampleThe flowchart which shows the operation | movement procedure.
FIG. 48Disclosure exampleOf a nuclear reactor structure to which is applied.
49 is a view showing a state where the nuclear reactor shown in FIG. 5 is opened.
50 is a view showing a state where parts are sequentially removed from the nuclear reactor shown in FIG. 5;
51 is a view showing a state where parts are sequentially removed from the nuclear reactor shown in FIG. 5;
52 is a view showing a state where parts are sequentially removed from the nuclear reactor shown in FIG. 5;
FIG. 53Disclosure exampleThe figure which shows the state which removed the core shroud in FIG.
Fig. 54 of the present inventionDisclosure exampleThe figure which shows the state which removed the jet pump in.
FIG. 55Disclosure exampleThe figure which shows an elevator installation state.
Fig. 56Disclosure exampleFIG. 3 is a diagram showing a state of shaping of the upper end surface of the shroud support ring.
Fig. 57Disclosure exampleFIG. 3 is a diagram showing a state of shaping of the upper end surface of the shroud support ring.
Fig. 58Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 59Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 60Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 61Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 62Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 63Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 64Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 65Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 66Disclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled.
Fig. 67Disclosure exampleFIG. 9 is a diagram showing a replacement completion state.
FIG. 68 shows still another embodiment of the present invention.Disclosure exampleFIG.
[Explanation of symbols]
1 Reactor pressure vessel
2 Core shroud
2a, 2b ... cylindrical segment
3 Shroud support cylinder
4 Shroud support leg
5 Upper lattice plate
6 Core support plate
7 Jet pump
7a Jet pump diffuser
7b Jet pump riser pipe
7c Jet pump inlet mixer
8 Baffle plate
9 Control rod
10 Fuel
10a Fuel support bracket
11 Control rod guide tube
12 Core spray piping
13 Low pressure water injection pipe
14 Differential pressure detection / Boric acid water injection piping
15 Steam dryer
16 Air / water separator and shroud head
17 Reactor pressure vessel top lid
18 Reactor well
19 Pedestal room
20 Control rod drive mechanism
21 Control rod drive mechanism housing
22 Dry tube / LPRM detector assembly
23 Reactor building
24 overhead crane
25 In-core nuclear instrumentation guide tube
26 Water supply sparger
27 Guide rod
28 In-core stabilizer
29 Seal container
30 Working platform
31, 32 Shield
33 workers
34 Elevator
35 capsules
36 Guide
37 Cutting surface forming equipment
38 New Shroud
39 Centering device
40 Welding equipment
42 New core support plate
43 New upper lattice plate
44 Water supply sparger
51 Bracket
52 wedge
53 Stopper
54 Stud
55 volts
56 welds
57 Flange
58 volts
59 nuts
60 U-shaped cap
61 blocks
62 Welded part
63 Reactor recirculation pump
64 Inflow piping
65 Chemical drug injection device
66 Outflow piping
67 Coolant purification device
68 Waste gas equipment
70 shroud cutting device
71 base
72 Drive mechanism
73 Rotating claw
74 Locking hole
75 Cylindrical support
76 Guide rail
77 Guide rail
78 Cutting device
80 cutting opening
81 blocks
83 Shroud support ring
84,85 welds
87 Jack
86 Temporary bracket
88 Mounting jig
89 rails
90 Welding backing
91 Connecting pin
92, 93 Bracket
94,95 volts
96 Alignment measuring device
96a container
97 holes
98 opening
99a, 99b Pin and bracket

Claims (1)

After removing the reactor pressure vessel top , steam dryer, and fuel , the existing reactor recirculation pump and existing jet pump are used to inject and circulate chemical agents that remove surface oxides into the reactor for decontamination. and then the core shroud than welded portion between the push from the loud support cylinder and removed by cutting with constant length lower position, work a person can work on the core shroud side of the substantially upper end height position of the shroud support cylinder A core shroud replacement method characterized in that an operator enters the furnace with the gantry installed , shapes the upper surface of the remaining shroud support cylinder , and welds the new core shroud fixed above the shroud support cylinder. .

Images