JP3679823B6 - How to replace the core shroud - Google Patents

Description

0001
[Industrial application field]
The present invention relates to a method for replacing a core shroud installed in a nuclear reactor such as a boiling water light water cooled nuclear reactor.
0002
[Conventional technology]
Generally, the core shroud of this type of nuclear reactor is constructed by welding stainless steel members. If such a core shroud has a high carbon content, cracks may occur at or near welds during long-term operation due to stress corrosion cracking or the like. If such an event occurs, it may be necessary to repair or replace the core shroud to ensure reactor safety.
0003
However, core shrouds that have been used for a long time have become brittle due to neutron irradiation, and when welded, finer cracks may form around the weld metal, making it difficult to repair by welding. Another option is to connect the reinforcing members with bolts, but its use may be limited in nuclear reactors installed in high earthquake zones.
0004
Therefore, the most desirable method is considered to be to replace the core shroud, but the core shroud itself is welded to the support ring of the core shroud at the lower end, and there may be interference with the in-core stabilizer, in-core nuclear instrumentation guide pipe, etc. In addition, the difficulty of adjusting the position of the upper grid plate installed inside the core shroud and the core support plate, and theoutside the reactorDifficulty in handling and large amounts of waste generatedDifficulty in processing, etc.Until now, it was predicted that replacement would be extremely difficult due to various problems.
[0005]
However, in recent years, after a long period of time has passed after the practical operation of a nuclear reactor, replacement of the above-mentioned reactor core shroud has become an urgent necessity, and various techniques have been proposed (e.g., JP-A-63 -36195 etc.).
[0006]
However, the technologies proposed so far are too sensitive to high radioactivity within the reactor, and are still biased towards performing all operations, such as cutting and removing the core shroud and installing a new shroud, by remote control. Such technology that performs all operations remotely requires a huge amount of effort and time, and lacks specificity in detail, leaving many unclear points before it can be put to practical use.
[0007]
[Problem to be solved by the invention]
On the other hand, in recent years, technology for removing contaminants from nuclear reactor equipment (hereinafter referred to as "decontamination") has made significant progress. Proposals for cleaning have also been made (eg, Special Publication No. 3-10919, etc.). However, no particular proposal has been made so far regarding a technology for cleaning the reactor core by applying such technology for reducing the radiation dose equivalent rate inside the reactor and replacing the shroud by workers other than by remote work.
[0008]
In nuclear power plants, corrosion products from materials used in water supply/condensate systems, reactor primary systems, etc. are released into the primary system through dissolution or peeling (erosion), adhere to the reactor core region, and become radioactive. A part of it is released again as activated corrosion products and contaminates the reactor pressure vessel, structures, piping, etc. in the area outside the core.
[0009]
The forms of contamination are fixed contamination due to activated corrosion products trapped in the oxide film formed on the material surface, generally called the inner layer, and insoluble activated corrosion products floating in the primary coolant, called the outer layer. It is possible that the contamination is weakly attached to the inner layer.
0010
The chemical decontamination method is a method of removing contaminated radioactivity by dissolving the metal oxides constituting the inner and outer layers through the reduction reaction of a chemical decontamination agent. Mechanical decontamination methods such as high-pressure jet water are characterized by peeling off and removing the outer layer, which has relatively low adhesion, whereas chemical decontamination methods not only remove the outer layer but also the fixed oxide film on the inner layer. The feature is that high decontamination efficiency can be obtained by removing the contaminants. The decontamination factor (DF) obtained by chemical decontamination can usually range from several tens to several hundreds, and the higher the contamination level, the larger the value obtained.
[0011]
Regarding shroud replacement work, the present inventors focused on aerial work inside a nuclear reactor. In this case, beveling and manual welding, especially at the level of the shroud support ring, take time. If the atmospheric dose equivalent rate at this level is 1 mSv/h, it is possible to work for about 1 hour. By chemically decontaminating the reactor and then shielding the activation reactor internals with iron plates or the like, it is possible to reduce the air dose equivalent rate at the bottom of the reactor to 0.1 mSv/h or less. Therefore, radiation exposure during work inside the reactor can be kept low and work can be carried out for long periods of time. In addition, since radioactive corrosion products are removed, the problem of dust that dries and pollutes the atmosphere is alleviated, making it possible to improve safety in terms of protecting workers from internal radiation exposure.
0012
The present invention was made in view of the above circumstances, and when it becomes necessary to replace the core shroud in a nuclear reactor, it is possible to replace the core shroud in a short period of time without having to rely solely on remote control, and without causing radiation exposure problems. It is an object of the present invention to provide a method for replacing a core shroud, which allows time-efficient replacement of a core shroud with a structure that is almost the same as the original core shroud.
[0013]
[Means and actions for solving the problem]
In order to achieve the above object, in the core shroud replacement method according to the present invention, after removing the reactor pressure vessel top cover and the steam dryer, the steam separator is removed and the fuel, in-core nuclear instrumentation detector, Removal of control rods, fuel support fittings, control rod guide tubes, control rod drive mechanisms, and other shroud internal structures, as well as water supply spargers installed above the core shroud, core spray system piping, guide rods, and other equipment installed above the shroud. At the same time, the upper grid plate and core support plate were removed, and the in-core guide tube, stabilizer, and other lower structures at the bottom of the core were cut and removed to open the inside and outside of the core shroud, and in this state, the inside of the reactor was decontaminated. In addition to reducing the radiation level inside the reactor to below the standard value for human work, theA work platform is installed inside the core shroud where workers can work.The core shroud is then cut using cutting equipment at least near the welded part with the shroud support cylinder, removed as one body or multiple pieces, and the upper surface of the shroud support cylinder is shaped and the new core shroud is suspended and centered. and create a newreactor coreSecure the shroud onto the shroud support cylinderHowever, the decontamination inside the reactor will be chemical decontamination that removes surface oxides by injecting chemical agents, and a cylindrical shield will be placed in the core shroud at a position corresponding to the jet pump.It is characterized by

[0014]
According to the method of the present invention, it is possible for workers to enter the core shroud and carry out work, and the structure can be improved without causing damage to the structure compared to when relying only on remote control. Agents can be removed and installed. Additionally, work errors and measurement errors can be prevented, work can be done in a short time, and costs can be reduced compared to remote control.
[0015]
In addition, in the present invention, the upper grid plate and the core support plate are removed, and the in-core guide tube, stabilizer, and other lower structures at the bottom of the core are cut and removed to open the inside and outside of the core shroud, and the surface oxide is removed using chemical agents. In this process, chemical agents are injected into the reactor recirculation pump system and the reactor water is circulated by jet pumps to remove surface oxides inside the reactor pressure vessel. By doing so, the in-furnace dose equivalent rate is set to 1 mSv/h. Thereby, it is possible to reliably reduce the radiation exposure of the workers inside the furnace, and it is possible for the workers to access the inside of the furnace, so that the above-mentioned effects can be realized. In addition, in this chemical decontamination, by mainly using the existing reactor recirculation pump system and jet pumps, there is no need to install new pumps, and the entire reactor water can be easily circulated. As a result, work efficiency can be improved.
[0016]
Note that desirable aspects of the present invention are as follows.
[0017]
After decontaminating the reactor interior and before cutting the core shroud, the jet pump inlet mixer is removed to expand the space around the upper part of the core shroud. This expands the space needed to lift and remove the core shroud, making the shroud removal process easier, and also prevents the core shroud from shaking sideways and coming into contact with the jet pump inlet mixer, causing damage. can be avoided.
[0018]
After removing the jet pump inlet mixer, cover the upper end of the jet pump diffuser with a shield. This provides a shielding effect for the jet pump diffuser, which is the area with the highest radiation dose in the reactor. In addition, a cylindrical shield is placed in the core shroud at a position corresponding to the jet pump depending on the dose in the reactor. This further ensures that workers inside the reactor are prevented from being exposed to radiation.
[0019]
In the core shroud cutting process, the core shroud is removed while being cut into a plurality of short cylindrical segments sequentially from above by electric discharge machining, machining, or water jet machining. For example, if the core shroud is cut between the upper shell and the middle shell and only the upper shell is cut and removed, the lower part from the middle shell can be reused, reducing the replacement schedule. , it can also reduce waste. In addition, by cutting and removing the core shroud as short cylindrical segments, various choices can be made, such as dispersion in an equipment storage pool or storage in a stacked state, and storage becomes easy.
[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 with supporting blocks inserted into the plurality of cutting openings, the remaining non-metallic material is removed. The cut section is cut to prevent the core shroud from tilting. By carrying out such a cutting procedure, the cut core shroud can be held in a vertical state and removed safely while preventing contact or detachment.
[0021]
When cutting the core shroud, the cutting position near the weld between the core shroud and the shroud support cylinder is set at a height excluding the upper end portion of the shroud support ring, for example, 5 mm, which is affected by heat due to welding. As a result, it is possible to take into account the possibility that the vicinity of the welded portion of the shroud support cylinder has been altered due to thermal effects, and to obtain the 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 may occur in the heat affected zone (approximately 5 mm) of the welded part of the shroud support cylinder that remains without being removed due to welding of different materials. There is sex. By removing all parts where stress corrosion cracking may occur, for example, when a new shroud is welded and fixed, thermal effects due to reheating can be prevented, and the useful life of the new shroud can be extended.
[0022]
It is desirable to cut each instrumentation pipe in the furnace above the in-core stabilizer. This eliminates the need to reinstall the in-core stabilizer, effectively shortening the construction period and reducing radiation exposure.
[0023]
The removed steam dryer and steam/water separator/shroud head will be stored in a stacked state in the equipment storage pool. In addition, the cut core shroud segments are stored in an equipment storage pool in a stacked state with the removed reactor internals. As a result, the space within the equipment storage pool can be effectively utilized to efficiently store the steam dryer, steam separator, cut core shroud, and the like.
[0024]
If the steam dryer is stacked above the steam separator/shroud head, the support elements built into the equipment storage pool will allow for a height and concentric arrangement that is approximately similar to the assembly within the reactor. desirable. As a result, the steam dryer is placed in a supported state similar to that installed inside a nuclear reactor, and damage can be effectively prevented.
[0025]
The work frame shall have a guide on the upper surface that is parallel to the peripheral wall of the core shroud, and by moving core shroud cutting equipment, cutting surface shaping equipment, welding equipment for fixing the new core shroud, etc. along this guide, Cutting the core shroud, shaping the cut surface, welding, etc. Thereby, cutting of the core shroud, shaping of the cut surface, welding work for fixing the new core shroud, etc. can be performed efficiently, with high precision, reliably and safely.
[0026]
When welding and fixing the new shroud, it is necessary to strengthen the new shroud and/or the shroud support with a corrosion-resistant metal or other material in advance on the inner or outer surface of the area that will be affected by heat due to welding. Apply weld overlay made of material. If the core shroud is made of SUS304 material, for example, it is highly susceptible to stress corrosion cracking due to the high carbon content, so the new shroud can be replaced with one made of a material with less stress corrosion cracking, such as SUS316. However, if the new shroud is made of SUS304 material, or if the shroud support cylinder is made of SUS304 material that remains without replacement, weld build-up will be applied to the heat-affected areas to prevent stress corrosion cracking from the welds. It is possible to prevent damage caused by such things. Note that the lower end of the core shroud may be padded with Inconel if necessary.
[0027]
The new shroud shall be fixed to the shroud support cylinder by welding, or by bolting, pin connection, or other mechanical connection means in a removable manner. Usually, the core shroud and the shroud support cylinder are fixed by welding, but when considering later replacement, it is effective to adopt a removable fixing structure using mechanical joining means. Note that when welding the core shroud to the shroud support cylinder, the welding work is performed from the inner peripheral side of the shroud. Thereby, welding work can be performed more efficiently using a wider space than when welding is performed from the outer circumferential side.
[0028]
When replacing the reactor core shroud, a capsule that can be boarded by workers is prepared, and this capsule is raised and lowered from the refueling work floor or reactor pressure vessel flange to the work platform using an overhead crane or elevator in the reactor building. This ensures speed and safety of work.
[0029]
Furthermore, when replacing the core shroud, the jet pump is also replaced before or after the core shroud is removed. Even if you try to replace the jet pump alone with the core shroud installed, the space between the reactor wall of the reactor pressure vessel where the jet pump is installed and the core shroud is narrow, making it impossible to replace the jet pump. It is. Therefore, by replacing the jet pump in conjunction with replacing the shroud, both can be efficiently replaced.
[0030]
When replacing the reactor core shroud, workers inspect and repair equipment installed inside the reactor pressure vessel on a work platform installed inside the reactor during the shroud replacement process, or perform preventive maintenance against stress corrosion cracking, etc. I do. According to this method, the radiation level inside the reactor is lowered by the chemical decontamination mentioned above, and workers can enter the reactor in much the same way as when a new reactor is being built, allowing inspection, repair, and prevention that would be difficult with remote control. Maintenance processing, etc. can be performed effectively.
[0031]
The cut and removed core shroud will be transferred and stored in a lining tank located adjacent to the reactor building. This makes it possible to secure space on the operation floor and prevent workers from being exposed to radiation.
[0032]
When replacing the core shroud, the reactor core instrumentation piping and differential pressure/boric acid water injection piping should be temporarily cut and removed. Thereby, when removing the core shroud to be replaced, the core shroud can be easily replaced by excluding structures that obstruct movement. After the new shroud is installed, the newly created core instrumentation piping and differential pressure/boric acid water injection piping can be connected and restored. In this case, by providing a partial opening in the work platform to enable welding of each of the instrumentation guide tubes in the reactor that will be placed below it, exposure can be effectively prevented. It becomes possible for workers to perform welding work.
[0033]
In addition, mechanical pressure welding, seals, screws, and other connection methods are possible for joining differential pressure and boric acid water injection piping, but welding is recommended to prevent leakage and reduce flow resistance. desirable. In addition, since the in-core nuclear instrumentation piping and the differential pressure/boric acid water injection piping are small in diameter, if it is difficult to join them by welding, joints made of shape memory alloy can be used and joined by remote control. You can also do that. This makes it possible to significantly reduce the radiation exposure of workers.
[0034]
On the other hand, prepare an extension rod that protrudes upward, for example, by about 2 m from the scaffold provided on the flange of the reactor pressure vessel, and attach this extension rod to the tip of the differential pressure/boric acid water injection pipe or each instrumentation pipe in the reactor. If this is used as a guide to penetrate the core support plate and suspend the core support plate, the displacement of the core support plate in the circumferential direction and the core direction can be reduced, and the core support plate can be easily attached to the core shroud. Can be installed in a fixed position.
[0035]
In addition, if an evacuation room with a radiation shielding wall is prepared on the work platform where workers can retreat during automatic welding when replacing the core shroud or while waiting for inspection, it is possible to take an elevator, etc. to the operation floor between works. It is possible to further improve work efficiency compared to cases where radiation exposure increases, and it is also possible to reliably prevent workers from being exposed to radiation. In addition, it is more desirable that the evacuation room can be moved upward by lifting or the like if necessary.
[0036]
In addition, if the water level rise in the reactor water during core shroud replacement is limited to the annulus area, and the water level in the shroud is raised after the installation of the new upper grid plate and new core support plate is completed, the radiation radiation caused by water can be increased. The high shielding effect can effectively prevent radiation exposure from the reactor pressure vessel or jet pump to workers in the core shroud.
[0037]
For preventive maintenance treatment of the reactor pressure vessel or equipment installed at the bottom of the reactor, the reactor water at the bottom of the reactor pressure vessel is drained and shot peening is carried out through an opening made in a part of the work platform installed inside the reactor. By lowering the equipment to the bottom of the reactor and performing shot peening on the equipment installed at the bottom of the reactor, such as the stub tube, control rod drive mechanism housing, and in-core nuclear instrumentation housing, the surfaces of the materials and welds are transformed into compressive stress. Do it like this. This makes it possible to prevent cracks (stress corrosion cracking, etc.) occurring in the material or welded parts. In this case, as a preventive maintenance treatment method for the equipment, for example, stainless steel or Inconel steel containing platinum (Pt), palladium (Pb), etc., is sprayed onto the surface of the equipment installed at the bottom of the furnace. etc. act as a catalyst to recombine hydrogen and oxygen produced by radiolysis of water. Thereby, dissolved oxygen in the furnace is reduced and the corrosion potential is brought to a constant value, thereby making it possible to prevent stress corrosion cracking and the like.
[0038]
Note that if the integrity of the removed 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 one embodiment of the present invention. Figure 1 is an overall configuration diagram of the reactor building showing the state in which the core shroud has been cut and removed, Figures 2 to 4 are flowcharts showing a series of procedures according to this embodiment, and Figures 5 to 23 are sequential steps for replacing the core shroud. 24 to 42 are block diagrams showing the main points of the work in detail.
[0041]
In the boiling water reactor that is the target of the core shroud replacement method according to this embodiment, as shown in FIG. Supported by 3. The shroud support cylinder 3 is supported at the bottom of the reactor pressure vessel 1 by shroud support legs 4 . An upper grid plate 5 is provided at the top of the core shroud 2, and a core support plate 6 is provided at the bottom. A jet pump 7 is provided on the outer peripheral side of the core shroud 2, and this jet pump 7 is composed of 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]
Further, control rods 9 and fuel 10 are provided in the core shroud 2, and above the core shroud 2, a control rod guide pipe 11, a core spray pipe 12, a low pressure water injection pipe 13, a differential pressure detection/boric acid 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 for replacing the core shroud in the reactor pressure vessel 1 having such a configuration will first be described with reference to the flowcharts of FIGS. 2 to 4 and the configuration diagrams of FIGS. 5 to 23.
[0044]
(1) In the state shown in FIG. 5, the reactor pressure vessel upper cover 17 and steam dryer 15 are removed from the reactor pressure vessel 1 by the overhead crane 24 of the reactor building 23, as in a normal periodic inspection (step 101). . At this time, reactor water is maintained below the flange of the reactor pressure vessel 1.
[0045]
(2) The reactor well 18 is filled with water, and the steam/water separator/shroud head 16 is removed by the overhead crane 24 (step 102). After this, all the fuel 10 is moved from the reactor 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, resulting in the state shown in FIG.
[0046]
(3) Remove the dry tube/LPRM detector assembly 22 that passes through the core instrumentation guide pipe 25 and occupies the space between the upper grid plate 5 and the core support plate 6, and 6 (step 104). Note that the above steps are performed to ensure a space for removing the core shroud 2 upward after removal, and the order may be changed.
[0047]
(4) From this state, remove the fuel support fitting 10a, control rod 9, and control rod guide tube 11 (step 105). When removing the control rod guide tube 11, it is necessary to pull out the control rod drive mechanism 20 and the thermal sleeve (not shown) from the control rod drive mechanism housing 21 from the pedestal chamber 19. The removed control rod drive mechanism 20 and thermal sleeve are stored in a storage box, moved from the pedestal chamber 19 to a refueling work floor, etc., and stored there. Alternatively, the control rod guide tube 11 can be removed and then returned to the control rod drive mechanism housing 21.
[0048]
(5) Removal of the water supply 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 removing the core shroud. The guide rod 27 inserted into the hole of the bracket is cut and removed (step 108), and the coupling of the low pressure injection pipe 13 is removed (step 109). As a result, as shown in FIG. 7, the interior 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 up and removed (steps 110, 111). The removal of the upper grid plate 5 and the core support plate 6 will be described in detail later. Additionally, all or part of the upper part of the in-core instrumentation guide pipe 25 and the in-core stabilizer 28 are cut and removed (step 112), and the pipe is inserted through the bottom of the reactor pressure vessel 1 and installed along the inner wall of the core shroud 2. The rising differential pressure detection/boric acid water injection piping 14 will also be cut and removed. The cut pipe is caught on a 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, it is recommended to leave the existing in-core stabilizer 28 and cut the in-core instrumentation guide pipe 25. You can also do it.
[0050]
(7) A cylindrical seal container 29 with vertical openings is attached to the upper part of the reactor pressure vessel 1 in the reactor well 18, and is isolated from the surroundings in a liquid-tight manner (step 114). This is to isolate the inside of the furnace from the surroundings during chemical decontamination inside the furnace in the next step.
[0051]
(8) Decontaminate the inside of the reactor pressure vessel 1 with chemical agents (step 115).
[0052]
This process will be explained in detail later, but by injecting chemical agents into the reactor recirculation pump system and circulating them within the reactor using the jet pump 7, it is possible to reach a level where workers can enter the reactor. It reduces the radiation dose rate.
[0053]
(9) Remove the seal container 29 once (step 116) and remove the jet pump inlet mixer 7c (step 117). This is done in order to reduce the dose rate during work inside the reactor, since the contamination level of this part of the jet pump 7 is high. This chemical decontamination will also be explained in detail later.
[0054]
(10) After this, as shown in FIG. 9, the work platform 30 is installed at 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 this cutting process of the core shroud 2, the core shroud 2 is sequentially formed into a plurality of short cylindrical segments 2a, 2b, . Remove by cutting from the lower side of the weld. The detailed procedure will be described later.
[0055]
(11) As shown in FIG. 11, the aforementioned sealed container 29 is installed again in the reactor well 18 to isolate the inside of the reactor from the surroundings, and the reactor water level is lowered to below the work frame 30 (step 120). Then, the upper end of the jet pump diffuser 7a after the jet pump inlet mixer is removed is covered with a shielding body 31. Stellite containing cobalt is used as a wear-resistant material at the upper end of the jet pump diffuser 7a, and since the radiation dose is extremely high, this portion is covered with a shield 31 to reduce the radiation dose. Furthermore, a cylindrical shield 32 is arranged on the work stand 30 in the core shroud 2 according to the in-core dose rate. Further, an elevator 34 is installed inside the shield 32 (step 121), and the worker 33 is raised and lowered from above the furnace inside the capsule 35.
[0056]
(12) As shown in FIG. 12, a guide 36 is attached to the work platform 30, and the cutting surface forming device 37 is moved along this guide to process the upper surface of the shroud support cylinder 3 (step 122).
[0057]
(13) After this, as shown in FIG. 13, the new shroud 38 is suspended into the reactor core (step 123), a cylindrical shield (not shown) is installed inside (step 124), and as shown in FIG. The worker 35 enters the furnace and, as shown in FIG. 15, centers the new shroud 38 using 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 using the welding device 40 (step 126), and then, as shown in FIG. 28 and the differential pressure detection/boric acid water injection piping 14 are connected (step 127).
[0059]
(15) After removing the work platform 30 and the elevator 34 (step 127a) and setting the state as shown in FIG. 18, as shown in FIG. After performing core adjustment of the core support plate, it is fixed by bolting (step 129).
[0060]
(16) As shown in FIG. 20, the new upper lattice plate 43 is hung and the center position is adjusted (step 130). Thereafter, as shown in FIG. 21, the riser pipe of the core spray system piping 12 is welded (step 131), the water supply sparger 44 is installed (step 132), and the new guide rod 11 is installed (step 133).
[0061]
(17) As shown in Figure 22, raise the reactor water level to the bottom of the flange of the reactor pressure vessel 1 (step 134), restore the low-pressure water injection piping coupling (step 135), and fill the reactor well with water. (Step 136).
[0062]
(18) As shown in FIG. 23, return the dry tube/LPRM detector assembly 22 (step 137), return the fuel support fitting 10a, control rod 9, and control rod guide tube 11 (step 138), Load fuel (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 cover 17 are attached (step 141), and the work is completed.
[0064]
Next, the main steps among the above steps (step 1 to step 141) will be explained in detail with reference to FIGS. 24 to 42.
[0065]
FIG. 24 shows how the upper grid plate 5 is supported on the core shroud 2. The upper grid plate 5 is placed on the stepped portion of the upper end ring of the core shroud, and its periphery is fixed by brackets 51 and wedges 52. The L-shaped stopper 53 is fixed via a weld 56 to a bolt 55 screwed into a stud 54 fixed to the upper surface of the upper grid plate 5. Therefore, when removing the upper lattice plate 5, as shown in the figure, the wedges 52, stoppers 53, and bolts 55 fixed to the core shroud 2 are removed by remote control, and the upper lattice plate 5 is removed from the core shroud. Lift it above 2.
[0066]
FIG. 25 shows the state in which the core support plate 6 is supported on the core shroud 2. The core support plate 6 is fixed to the flange 57 of the lower stepped portion of the core shroud 2 via a bolt 58 and a nut 59, and a U-shaped cap 60 placed over the nut 59 is attached to the end of the bolt 58 via a block 61 at the welded portion. 62. Therefore, when removing this core support plate 6, as shown in FIG. 25, by removing the welded part 62 by remote control and removing the bolts 58 and nuts 59 fixed to the core shroud 2, It can be lifted above the core shroud 2.
[0067]
The upper grid plate 5 and core support plate 6 removed in this way are temporarily stored in the storage bit of the steam dryer 15 and steam/water separator/shroud head 16 in the reactor well 18 filled with water, or It will be moved and stored in a tank installed adjacent to the reactor building. As another method for removing the upper grid plate 5 and the core support plate 6, they may be removed while being cut into small segments by a method such as electrical discharge machining or plasma cutting.
[0068]
FIG. 26 shows an example of the configuration of a chemical decontamination device system. In this embodiment, as described above, in order to reduce radiation exposure when the core shroud 2 is removed and the reactor water level is lowered, This is to clean the bottom of the furnace. Chemical decontamination is performed with the core shroud 2 and jet pump 7 remaining after removing the upper grid plate 5 and the core support plate 6, as shown in FIG. With a shield attached to the top of the reactor pressure vessel 1 and filled with reactor water, a chemical agent is injected from the chemical agent injection device 65 connected to the inflow pipe 64 of the reactor recirculation pump 63, and then from the recirculation inlet nozzle. The jet pump 7 causes the chemical to flow into the furnace and circulate within the furnace. This liquid uses a permanganate nutrient solution, etc., and reduces and removes the activated oxides in the reactor pressure vessel 1, and is discharged from the recirculation outlet nozzle to the outflow pipe 66 outside the reactor. , is circulated by an externally mounted coolant purification device 67.
[0069]
Then, it is returned to the reactor through the reactor recirculation pump 63. By repeating this process several times, the radioactive materials attached to each device inside the reactor and the inner surface of the pressure vessel can be safely removed, thereby dramatically reducing the radiation dose inside the reactor. The waste gas is treated by a waste gas device 68. In addition to this, in order to reduce the dose in the radiation atmosphere inside the reactor, brush cleaning or cladding suction cleaning may be performed on the surface of the reactor internal structure as appropriate.
[0070]
For example, beveling and manual welding at the level of the shroud support ring 3 require more than a certain amount of time. If the atmospheric dose equivalent rate at this level is 1 mSv/h, it is possible to work for about 1 hour. By chemically decontaminating the reactor and then shielding the activation reactor internals with iron plates or the like, the air dose equivalent rate at the reactor bottom can be reduced to 0.1 mSv/h or less. Therefore, radiation exposure during work inside the reactor can be kept low and work can be carried out for long periods of time. Additionally, since radioactive corrosion products are removed, the problem of dust that dries and pollutes the atmosphere is reduced, increasing safety from the perspective of protecting workers from internal radiation exposure.be able to. In addition, in this chemical decontamination, by mainly using the existing reactor recirculation pump system and jet pumps, there is no need to install new pumps, and the entire reactor water can be easily circulated. As a result, work efficiency can be improved.
[0071]
27 to 32 show in detail the method of replacing the core shroud 2.
[0072]
FIG. 27 shows an example of a cutting process for 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 electrical discharge machining, machining, or water jet machining.
[0073]
FIG. 28 shows the shroud cutting device 70 and cutting operation for making the cut. A drive mechanism 72 that rotates and expands and contracts is provided on the lower surface of a liftable base 71 placed on the upper step of the core shroud 2, and a rotating claw 73 connected to the tip of the drive mechanism 72 is drilled into the core shroud 2. The core shroud 2 is lifted by inserting and locking into 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 hanging from the lower surface of the base 71, and this guide rail 77 is provided with electric discharge machining, machining, or high-pressure water jet method in which the guide rail 77 runs through wheels. A cutting device 78 is provided, and the core shroud 2 is cut by this cutting device 78. The shroud cutting device 30 is cut along the guide of the work platform 29.Let me runThe core shroud 2 may also be cut.
[0074]
29(A) to (D) show each cutting process of the core shroud 2. Note that although FIG. 29 shows the cutting of the core shroud 2 and the shroud support cylinder 3, the cutting of other parts is the same.
[0075]
First, from the state shown in FIG. 29(A), cutting openings 80 are formed at intervals along the circumferential direction of the core shroud 2, as shown in FIG. 29(B). Then, as shown in FIG. 3C, with support blocks 81 inserted into the plurality of cutting openings 80, the remaining uncut portions are cut to prevent the core shroud from tilting. do. By performing such a cutting procedure, the segments of the core shroud 2 are held vertically during cutting to prevent them from coming into contact with each other, or from being caught in the cutting device 70 by the core shroud 2, and to ensure safe removal. can do.
[0076]
Figures 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 how the cutting device 70 is suspended using the crane 24 installed in the reactor building 23 and the core shroud 2 is cut. When cutting of the upper segment 2a is completed in this state, for example, the cut upper segment 2a is lifted up by the crane 24 and removed, as shown in the upper side of FIG. Thereafter, as shown in the lower part of FIG. 31, cutting of the lower segment 2b is started. When the cutting of the lower segment 2b is completed, as shown in FIG. 32, it is similarly lifted up and removed by the crane 24.
[0077]
The removed segments 2a and 2b of the core shroud 2 are moved to the equipment storage pit 79 and stored there, as shown in FIG. In this case, for example, by installing one of the segments 2a and 2b above the upper lattice plate 5 and the core support plate 6, which were previously removed, via a support 80 such as a shelf, the space in the equipment storage pit 79 can be saved. can be used effectively.
[0078]
Note that the steam dryer 15 and the steam/water separator/shroud head 16 that were removed in the first stage are also removed from above via the support stand 81 that covers the steam/water separator/shroud head 16, as shown in FIG. By stacking the steam dryer 15 on the reactor, it is possible to efficiently store the reactor in a state similar to that in a nuclear reactor. In this case, if the steam dryer 15 protrudes above the water in the equipment storage pit 79, exposure to radiation can be reliably prevented by covering the air exposed portion with a cover 82 made of radiation shielding material.
[0079]
FIG. 33 shows in detail the cutting position when cutting and removing the core shroud 2 from the shroud support cylinder 3. Although this example shows a configuration 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, the same applies even when this shroud support ring 83 is not provided.
[0080]
That is, in this embodiment, the shroud support cylinder 3 is cut at a position below the welded portion 85 by a certain length h. This length h is set, for example, to 5 mm from the upper end side portion of the shroud support ring 3 which is affected by heat due to welding. Thereby, it is possible to take into consideration the possibility that the vicinity of the welded portion of the shroud support cylinder 3 has been altered due to thermal influence, and to obtain the strength reliability of the core shroud after replacement. For example, if 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 (approximately 5 mm) of the welded part of the shroud support cylinder 3 that remains without being removed due to welding of different materials. There is a possibility that By removing all the parts where stress corrosion cracking is likely to occur, for example, when fixing the new shroud 38 by welding, it is possible to prevent the heat effect caused by reheating, thereby extending the useful life of the new shroud 38. .
[0081]
Next, a case in which a new shroud is bonded and fixed onto the bonded shroud support cylinder 3 in place of the removed core shroud 2 will be explained in detail.
[0082]
FIG. 34 is an explanatory diagram of the new shroud 38 level adjustment, and FIGS. 35 and 36 are explanatory diagrams of the welding method. As described above, the cut surface of the shroud support cylinder 3 has been flattened in advance by running an electric discharge machining or machining type finishing device along the circumferential guide of the work platform 29.
[0083]
As shown in FIG. 34, a temporary bracket 86 is attached to the inner peripheral surface of the new shroud 38 in advance, and several jacks 87 are placed around the work platform 30 to support the temporary bracket 86 of the new shroud 38. Perform level adjustment. Then, the mounting jig 88 is temporarily attached and welded between the new shroud 38 and the shroud support cylinder 3. Note that a rail 89 for running the welding device is installed on the workbench 30, and a welding backing 90 is provided at the welding part.
[0084]
After adjusting the level of the new shroud 38 in this manner, welding is performed by a welding device 91, as shown in FIG. Welding of the new shroud 38 is performed from the inner circumferential side, but the outer annulus portion, which is the back side when viewed from the welding, is sufficiently dried and filled with inert gas to prevent oxidation during welding.
[0085]
A welder is lowered onto the work platform 30 and the new shroud 38 is welded to the upper end surface of the shroud support cylinder 3. The welder must wear airtight clothing or a mask to supply air until the new shroud 38 is welded to the upper end of the shroud support cylinder 3 in several passes and the inert gas in the annulus 19 no longer leaks into the new shroud 38. There is a need to. It is also possible to reduce radiation exposure by providing an atmospheric chamber in the center of the work frame 30, setting the welding device 91 outside the atmospheric chamber, and monitoring automatic welding in the atmospheric chamber.
[0086]
When welding the new shroud 38, an alignment scope or plumb bob is hung from the top of the reactor pressure vessel 1 to measure the deformation and positional deviation of the new shroud 38, and the welding start position for the next pass can be changed or the welding pass can be changed. Proceed with welding while making efforts to keep these values within the design specification values. After or during welding, the temporary bracket 86 and the temporary attachment jig 88 are removed from the new shroud 38.
[0087]
FIG. 36 shows that when the new shroud is welded and fixed, weld padding made of corrosion-resistant metal or other reinforcing material is applied in advance to the inner peripheral surface of the area that will be affected by heat due to welding between the new shroud 38 and the shroud support cylinder 3. 38b and 3b are shown. If the core shroud is made of SUS304 material, for example, it is highly susceptible to stress corrosion cracking due to the high carbon content, so the new shroud can be replaced with one made of a material with less stress corrosion cracking, such as SUS316. However, if the new shroud is made of SUS304 material, or if the shroud support cylinder made of SUS304 material remains without being replaced, weld build-up 38a, 3b is applied to the heat-affected parts to reduce the amount of heat from the welded part. Damage caused by stress corrosion cracking, etc. can be prevented. Note that the lower end of the core shroud may be padded with Inconel if necessary. Alternatively, it may be applied only to the shroud support cylinder 3.
[0088]
Note that these assumptions are such that the new shroud 38 is suspended from the upper end of the support cylinder 3. In this case, several guides are installed along the inner wall of the reactor pressure vessel 1 to prevent damage to other equipment such as the jet pump 7 when the new shroud 37 is lowered. The new shroud 38 serves as a shield to prevent high-level radiation irradiation from the stellite portion at the upper end of the jet pump diffuser 7a, but in order to further obtain a shielding effect, a shield may be installed along the inner wall of the new shroud 38. good. Further, in order to prevent radiation exposure from the annulus portion 19 when the reactor water level is lowered, a shield may be provided between the upper end of the new shroud 38 and the reactor pressure vessel 1. The reactor water level is lowered until the work platform 30 appears in the air.
[0089]
In addition, sheet curing is performed on the upper end of the new shroud 38 in order to prevent dust from flying up from the annulus section 19 between the new shroud 38 and the reactor pressure vessel 1 and to prepare the inert gas filling device.
[0090]
In addition, as shown in FIG. 37, the new shroud 38 may be fixed to the shroud support cylinder 3 by providing an overlapping part at both joint parts and joining with a connecting pin 91, or as shown in FIG. , brackets 92 and 93 may be provided on the new shroud 38 and the shroud support cylinder 3, and these may be connected with bolts 94 and 95 to fasten the new shroud 38.
[0091]
Note that the in-core stabilizer 28 can be installed by installing a scaffold on the legs installed on the control rod drive mechanism housing 21. It is desirable that the scaffolding be divided into several segments so that it can be removed while avoiding the in-core stabilizer 28, which is set up in a grid pattern.
[0092]
After replacing the core shroud, the work platform 30, scaffolding, etc. inside the core shroud are removed, and the reactor water level is raised to the upper part of the shroud middle section.
[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 onto the flange of the reactor pressure vessel 1, and the dozens of in-core core instrumentation guide pipes 25 and The extension rod attached to the tip of the differential pressure detection/boric acid water inflow pipe 14 is inserted into the corresponding through hole of the new core support plate 42. Once all of them are inserted, remove the temporary scaffolding on the flange of the reactor pressure vessel 1.
[0094]
39 to 42 show the centering work when installing the new core support plate 42 and the core upper grid plate 43.
[0095]
This centering work can be performed using an alignment measuring device 96, as shown in FIGS. 39 to 42. That is, as shown in FIG. 39, between the hole 97 for the control rod guide tube in the new core support plate 42 and the upper end of the control rod drive mechanism housing 21, or the rectangular opening in the new upper lattice plate 43 as shown in FIG. By fixing a 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 pendant 96b suspended in the cylindrical container 96a, Calculate the inclination of the cylindrical container 96a.Measureusing equipment. The plumb bob 96b is supported at its upper end by a universal joint 96c and is always vertical. Misalignment of the hole 97 for the control rod guide tube in the new core support plate 42 with respect to the upper end of the control rod drive mechanism housing 21, or the square shape of the new upper grid plate 43 with respect to the position of the hole 98 for the control rod guide tube in 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 checking the positional deviations of the openings at several points. After this, 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 bolts from rotating. Note that 99a and 99b are pins and brackets for locking the alignment measuring device 96 to the new core support plate 42.
[0096]
Other operations include, for example, draining the reactor water from the bottom of the reactor pressure vessel and lowering various inspection and repair equipment to the bottom of the reactor through an opening made in a part of the work platform 30 installed inside the reactor. , Welding repairs will be carried out around the control rod drive mechanism housing 21 and stub tube.
[0097]
In addition, as a method of converting the surface of the material into 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 equipment is lowered to the bottom of the reactor, and the stub tube and Shot peening can also be easily carried out around the welded parts of equipment installed at the bottom of the reactor, such as the control rod drive mechanism housing and each instrumentation housing in the reactor.
[0098]
Alternatively, as a method of performing preventive maintenance against stress corrosion cracking, etc. by reducing dissolved oxygen in the reactor and lowering the corrosion potential, the reactor water at the bottom of the reactor pressure vessel is drained and the thermal spray equipment is installed at the bottom of the reactor. It is also possible to easily thermally spray stainless steel or Inconel steel containing Pt or Pd onto the surfaces of equipment installed at the bottom of the furnace. When the reactor is restarted, Pt or Pd in the sprayed metal acts as a catalyst to recombine hydrogen and oxygen generated by water decomposition, reducing dissolved oxygen in the reactor and reducing corrosion potential. be.
0099
As described above, according to this embodiment, it is possible to restore almost the same structure as the original core shroud by remote control and in-core work. Utilizing the environment in which workers can enter the inside of the reactor pressure vessel 1, it is easy to carry out welding repairs on equipment installed on the inner surface of the reactor pressure vessel or the bottom of the reactor, or preventive maintenance treatment against stress corrosion cracking, etc. .
[0100]
Next, the present invention will be described with reference to FIGS. 43 to 67.As an example of disclosed technology related toexplain. thisDisclosure examplerelates to a method of replacing the jet pump 7 as well as the core shroud 2. Fig. 43 is an overall configuration diagram of the reactor building showing the state in which the core shroud has been cut and removed, Figs. 44 to 47 are flowcharts showing a series of procedures according to this embodiment, and Figs. 48 to 67 show the replacement work of the reactor shroud in sequence. FIG.
[0101]
BookDisclosure example, except for replacing the jet pump 7, is substantially the same as the previous embodiment. That is, in FIGS. 44 to 47 showing the process flow, the difference from the above embodiment among the steps shown in steps 201 to 247 is that the jet pump 7 is removed after cutting and removing the core shroud 2. This is an added point. i.e. bookDisclosure exampleAfter cutting and removing the core shroud 2, in steps 220 to 226 shown in FIG. 45, the jet pump 7 is cut, removed, processed, welded, and attached, and the reactor recirculation pump is cut and removed. .
[0102]
In this way, in the core shroud replacement method, by replacing the jet pump before or after removing the core shroud, if you try to replace only the jet pump alone with the core shroud installed, the jet pump will not be installed. Because the space between the reactor wall of the reactor pressure vessel and the reactor core shroud is narrow, it is impossible to replace the jet pump. Both can be exchanged.
[0103]
Further, FIG. 68 shows still another example of the present invention.Disclosure exampleIt shows. thisDisclosure exampleNow, the cut and removed core shroud 2 is transferred to a lining tank 23a provided in a location adjacent to the reactor building 23 and stored. In this case, transportation is possible by using a separately provided crane 24a or the like. In addition, a predetermined radiation shield will be provided around the area to prevent exposure to radiation. BookDisclosure exampleAccording to this method, the space in the equipment pit and the space on the operation floor of the reactor building 23 can be effectively utilized.
[0104]
【Effect of the invention】
As explained in the above embodiments, according to the core shroud replacement method according to the present invention, when it becomes necessary to replace the core shroud in a nuclear reactor, there is no need to rely solely on remote control, and there is no problem with radiation exposure. The core shroud can be replaced with a structure that is almost the same as the original core shroud in a short period of time and efficiently without causing any damage. In particular, during the process of decontamination inside the reactor, chemical agents are injected into the reactor recirculation pump system and the reactor water is circulated by jet pumps, which removes surface oxides inside the reactor pressure vessel and improves the core shroud. This makes it possible for workers to enter the interior of the structure and carry out the work, making it possible to remove and install structural agents without damaging the structure, compared to when relying solely on remote control. Additionally, work errors and measurement errors can be prevented, work can be done in a short time, and costs can be reduced compared to remote control.
[Brief explanation of drawings]
FIG. 1 is an explanatory view showing an embodiment of the core shroud replacement method according to the present invention, and is an overall view showing a state in which structural members are taken out and stored in the reactor.
FIG. 2 is a flowchart showing the operational procedure of the embodiment.
FIG. 3 is a flowchart showing the operational procedure of the embodiment.
FIG. 4 is a flowchart showing the operational procedure of the embodiment.
FIG. 5 is a diagram showing a nuclear reactor structure to which the above embodiment is applied.
FIG. 6 is a diagram showing the nuclear reactor shown in FIG. 5 in an open state.
7 is a diagram showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5. FIG.
8 is a diagram showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5. FIG.
9 is a diagram showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5. FIG.
FIG. 10 is a diagram showing a state in which the 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 how 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 illustrating the operation of the embodiment in detail, and is a diagram illustrating the mounting structure of the upper lattice plate.
FIG. 25 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating the attachment structure of the core support plate.
FIG. 26 is a diagram showing the operation of the embodiment in detail, and is a diagram showing a method of chemical decontamination.
FIG. 27 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating a method of cutting the core shroud.
FIG. 28 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating a method of cutting the core shroud.
FIGS. 29A to 29D are diagrams sequentially showing a procedure for cutting the core shroud.
FIG. 30 is a diagram showing the operation of the embodiment in detail, and is a diagram showing a method of cutting the core shroud.
FIG. 31 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating a method of cutting the core shroud.
FIG. 32 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating a method of cutting the core shroud.
FIG. 33 is a diagram showing the operation of the embodiment in detail, and is a diagram showing the cutting position of the core shroud.
FIG. 34 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating the joined state of the new core shroud.
FIG. 35 is a diagram showing the operation of the embodiment in detail, and is a diagram showing the welding state of the new core shroud.
FIG. 36 is a diagram showing the operation of the embodiment in detail, and is a diagram showing a state of overlay welding.
FIG. 37 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating a modification regarding attachment of a new core shroud.
FIG. 38 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating a modification regarding attachment of a new core shroud.
FIG. 39 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating the centering operation of the new core support plate.
FIG. 40 is a diagram showing the operation of the embodiment in detail, and is a diagram showing the centering operation of the new core support plate.
FIG. 41 is a diagram showing the operation of the above embodiment in detail, and is a diagram showing the centering operation of the new core support plate.
FIG. 42 is a diagram illustrating the operation of the embodiment in detail, and is a diagram illustrating the centering operation of the new core support plate.
FIG. 43: Core shroud replacement method according to the present inventionExamples of disclosures related toFIG. 2 is an explanatory view showing a state in which structural materials are taken out and stored from inside the furnace.
FIG. 42 is a flowchart showing the operational procedure of the embodiment.
FIG. 43: SaidDisclosure exampleFlowchart showing the operating procedure.
[Figure 44] SaidDisclosure exampleFlowchart showing the operating procedure.
FIG. 45: SaidDisclosure exampleFlowchart showing the operating procedure.
FIG. 46: SaidDisclosure exampleFlowchart showing the operating procedure.
[Figure 47] SaidDisclosure exampleFlowchart showing the operating procedure.
[Figure 48] SaidDisclosure exampleA diagram showing the structure of a nuclear reactor to which this is applied.
FIG. 49 is a diagram showing the nuclear reactor shown in FIG. 5 in an open state.
50 is a diagram showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5. FIG.
51 is a diagram showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5. FIG.
52 is a diagram showing a state in which parts are sequentially removed from the nuclear reactor shown in FIG. 5. FIG.
FIG. 53: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which the core shroud has been removed.
FIG. 54: According to the present inventionDisclosure exampleFIG. 3 is a diagram showing a state in which the jet pump is removed.
FIG. 55: SaidDisclosure exampleThe figure which shows the elevator installation state in .
FIG. 56: SaidDisclosure exampleFIG. 3 is a diagram showing how the upper end surface of the shroud support ring is shaped in FIG.
FIG. 57: SaidDisclosure exampleFIG. 3 is a diagram showing how the upper end surface of the shroud support ring is shaped in FIG.
FIG. 58: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 59: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 60: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 61: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
[Fig. 62] SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 63: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 64: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 65: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 66: SaidDisclosure exampleFIG. 3 is a diagram showing a state in which structural members are sequentially assembled in FIG.
FIG. 67: SaidDisclosure exampleThe figure which shows the completion state of exchange in .
FIG. 68: Still another example of the present invention.Disclosure exampleAn explanatory diagram showing.
[Explanation of symbols]
1 Reactor pressure vessel
2 Core shroud
2a, 2b... cylindrical segment
3 Shroud support cylinder
4 Shroud support leg
5 Upper grid 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 fitting
11 Control rod guide tube
12 Core spray piping
13 Low pressure water injection piping
14 Differential pressure detection/boric acid water injection piping
15 Steam dryer
16 Steam/water separator and shroud head
17 Reactor pressure vessel upper cover
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 pipe
26 Water supply sparger
27 Guide rod
28 Incore stabilizer
29 Seal container
30 Work platform
31, 32 Shielding body
33 Workers
34 Elevator
35 capsules
36 Guide
37 Cut 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 Welding part
57 Flange
58 volts
59 Nut
60 U-shaped cap
61 block
62 Welding part
63 Reactor recirculation pump
64 Inflow piping
65 Chemical agent 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 block
83 Shroud support ring
84,85 Welded part
87 Jack
86 Temporary bracket
88 Installation jig
89 Rail
90 Welding backing metal
91 Connecting pin
92,93 bracket
94,95 volts
96 Alignment measuring device
96a Container
97 holes
98 Opening
99a, 99b pins and brackets

Claims (1)

After removing the reactor pressure vessel top cover and steam dryer, remove the steam-water separator and inspect the inside of the shroud for fuel, in-core nuclear instrumentation detectors, control rods, fuel support fittings, control rod guide tubes, control rod drive mechanisms, and other components. The structures were removed, as well as the water supply sparger installed above the core shroud, core spray system piping, guide rods, and other equipment installed above the shroud, and the upper grid plate and core support plate were removed, and the in-core at the bottom of the core was removed. Guide pipes, stabilizers, and other lower structures will be cut and removed to open the inside and outside of the core shroud, and in this state, the inside of the reactor will be decontaminated to reduce the radiation level inside the reactor to below the standard value for human work. A work platform on which workers can work is installed inside the core shroud at approximately the height of the upper end of the shroud support cylinder, and the core shroud is cut using cutting equipment at least near the welded part with the shroud support cylinder. The shroud support cylinder was removed as a divided body, the upper surface of the shroud support cylinder was shaped, the new core shroud was suspended and centered, and the new core shroud was fixed on the shroud support cylinder. A method for replacing a reactor core shroud, characterized in that chemical decontamination is performed to remove surface oxides, and a cylindrical shield is placed at a position corresponding to a jet pump within the core shroud.

Images