JP4491381B2 - Structure cutting method and apparatus - Google Patents

Description

  The present invention relates to a method of cutting a structure with a water jet mixed with a cutting aid, and more particularly to a method of cutting a structure suitable for cutting a activated in-furnace structure.

  For nuclear power plants, the construction of reactor internals is being considered for replacement with new materials and disposal after the end of their useful lives. When replacing or dismantling the reactor internal structure, it is necessary to cut it. One of the cutting methods is a water jet method in which a cutting aid is mixed in a water stream (see Patent Document 1). Here, in order to cut the structure by the water jet method in which a cutting aid is mixed, it is necessary to make a large amount of the cutting aid collide with the structure, and the cutting aid pulverized by the collision floats in water. As a result of studying the application of the water jet method mixed with cutting aid to the reactor internal structure, the cutting aid activated by the construction of the reactor internal structure adheres to the injection nozzle and peripheral equipment. It was found that there is a possibility of causing secondary contamination.

JP 2000-135679 A

  It is an object of the present invention to provide a method for preventing secondary contamination by a cutting aid activated by the construction of the reactor internal structure when the water jet method mixed with the cutting assistant is applied to the reactor internal structure. .

  A liquid, mixed with a cutting aid and pressurized, is jetted from a nozzle to cut the activated structure. Aluminum oxide is used as a cutting aid.

Aluminum oxide (alumina) does not undergo an oxidation reaction that is essential for a corrosion reaction, and does not produce a hydroxide. Therefore, even when the water jet method mixed with cutting aid is applied to the reactor internal structure, it is possible to prevent the activated aluminum oxide from adhering to the peripheral equipment as rust. Adhesion, that is, secondary contamination can be prevented. Furthermore, it becomes easy to ensure the transparency of water, and workability can be improved.

  Since the inventor also examined the filtration performance of aluminum oxide, the examination results are shown below. In the water jet method in which a cutting aid is mixed, a large amount of cutting aid is collided during cutting or processing of a structure. For this reason, the lifetime of the recovery filter for purifying the fragments of the cutting aid is shortened. In addition, the pulverized cutting aid floats in water, causing a problem of turbidity. When pool water becomes cloudy, it causes a drop in visibility when an operator operates equipment installed in the water. Therefore, it is necessary to maintain the transparency of water by sucking the cutting aid sprayed at the time of cutting as much as possible and filtering it. However, the crushed cutting aid has a wide range of particle diameters, but if it is 5 μm or less, the filtration resistance of the filter is large, and the filtration performance deteriorates. Furthermore, since such a crushed cutting aid is difficult to remove even by centrifugation, the life of the filter is shortened when there are many small pieces. Further, when the chemical form of the crushed cutting aid is changed to hydroxide, the filtration resistance is further increased, and the filter life is greatly shortened. The use of a large amount of filter causes an increase in cost and replacement work, and also increases the amount of waste containing radioactivity because the cut pieces of the structure are filtered. If there are few particles having a particle size of less than 5 μm, which makes centrifugal separation difficult and the filtration resistance of the filter is large, the life of the filter can be extended, and the amount of discarded filter can be reduced. As a result of investigation by the inventor, it was obtained as a new finding that aluminum oxide is suitable as a cutting aid from the viewpoint of reducing the amount of waste of such a filter, and the contents thereof will be described below.

  FIG. 2 shows the particle size distribution of crushed pieces floating in water when stainless steel is cut by a water jet method using aluminum oxide as a cutting aid. Fig. 2 shows the sampled pool water, filtered the collected pool water through a filter with an opening of 10 µm, passed the filtrate through a 5 µm filter, and passed the filtrate through a 3 µm filter. When the water was passed through and the filtrate was passed through a filter having a small mesh, the change in the weight of each filter before and after the water flow was measured. FIG. 2 also shows the measurement results when cast steel is used as a cutting aid under the same cutting conditions. The material to be cut is stainless steel, the thickness of the material to be cut is 10 mm, the cutting speed is 10 mm / min, and the supply amount of cutting aid is 400 g / min. When aluminum oxide is used as a cutting aid, almost the entire amount is collected by a 5 μm filter, and it can be seen that there are many particles of 5 μm or more. On the other hand, when cast steel is used as the cutting aid, it can be seen that small fragments of 0.45 μm to 3 μm exist. The proportion by weight of aluminum oxide of 5 μm or less was 0.05% of the total suspended matter weight, whereas that of cast steel was 1.78%.

  FIG. 3 is a graph in which the weight of each cutting aid is converted into the number of the experimental results of FIG. The number of particles was calculated on the assumption that all the weights collected by each filter were spherical particles having a diameter of each opening diameter (formula (1)). Furthermore, FIG. 3 also adds results when garnet, silicon carbide, or cast iron is used as a general cutting aid.

Number of particles = Filter collected weight ÷ Density ÷ (4 / 3π (filter opening / 2) ³ )
... (1)
Here, “5 μm or more” is the sum of the number of particles collected by the 5 μm and 10 μm filters, and “less than 5 μm” is the sum of the number of particles collected by the 3 μm, 1.2 μm and 0.45 μm filters. It is. The number of aluminum oxides is less than 5 μm compared with 5 μm or more, but cast steel and other cutting aids are less than 5 μm.

FIG. 4 is a graph in which the weight of each cutting aid is converted into a number in the same manner as in FIG. “10 μm or more” is the number of particles collected by a 10 μm filter, and “less than 10 μm” is the sum of the numbers of particles collected by a 5 μm, 3 μm, 1.2 μm, and 0.45 μm filter. When the numbers of particles collected at 10 μm or more and less than 10 μm were compared, the same tendency as the experimental result of FIG. 3 was obtained. In other words, the number of aluminum oxides is less than 10 μm compared to 10 μm or more, but the cutting aid such as cast steel has more results of less than 10 μm.

From the above experimental results, it became clear that even if the cutting was performed under the same conditions, the size of the fragments was different depending on the cutting aid. FIG. 5 is a diagram showing the relationship between the subject of filtration and the average resistivity, and is cited from [Taiji Sugimoto, “New Edition Filtration Mechanism”, Jinshokan, 1982]. According to FIG. 5, when the particle size of a crushing piece is large, it turns out that the filtration resistance at the time of filter filtration is small. For example, the filtration resistance of 10 μm spherical particles is 6 × 10 ⁹ m / kg, but the filtration resistance of 1 μm spherical particles is two orders of magnitude greater than 10 μm spherical particles. When filtering the cutting aid, the smaller the filtration resistance, the smaller the pressure loss of the filter. Therefore, the larger the particle size, the more weight can be collected. Moreover, since cast iron contains ferric hydroxide, the filtration resistance can be estimated to be about 1.5 × 10 ¹³ m / kg.

From the above examination results, it became clear that aluminum oxide is a substance with high filtration performance, although the turbidity after crushing was severely avoided in the past. When aluminum oxide is used as a cutting aid, particles of 5 μm or more are 0.1% or less of the total suspended solids, and the filtration resistance during filter filtration is 6 × 10 ⁹ m / kg even if conservatively estimated. Therefore, it is thought that the weight of the crushed pieces that can be collected is large and the amount of filter waste can be greatly reduced. Furthermore, since filtration is easy, it becomes easy to ensure transparency of water, and workability can be improved. That is, by using aluminum oxide having a large amount of crushed pieces of 5 μm or more as a cutting aid, the filterable weight increases and the amount of filter waste can be reduced.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In this embodiment, the core shroud 1 which is a structure inside the nuclear reactor is cut using a water jet method in which aluminum oxide is mixed as a cutting aid.

FIG. 1 is a flowchart showing the work procedure of the present embodiment. First, the reactor is stopped (S1), and the pressure vessel is opened (S2). Next, in-furnace equipment and fuel that interfere with the cutting operation are taken out (S3). The extracted in-furnace equipment and fuel are stored in the equipment pool and the fuel pool, respectively. Thereafter, the cutting device 20 for cutting the core shroud is installed in the reactor pressure vessel (S4).

  Thereafter, the shroud is cut with a water jet mixed with a cutting aid using a cutting device (S5). The shroud cutting operation (S5) will be described. FIG. 6 is a schematic view showing a cutting work situation of the shroud 1 in the present embodiment. A reactor pressure vessel filled with water is used as the working pool 11. Since the in-reactor structure is irradiated with neutrons during operation, it contains activated cobalt in the structural material. Moreover, the radioactive oxide has adhered to the surface of the structural material. For this reason, it is desirable to perform the cutting work in water from the viewpoint of preventing the exposure of the worker.

The cutting device 20 is attached to a cutting device operation mechanism 26 that can arbitrarily set a cutting place. The cutting device operating mechanism 26 is connected to the cutting frame 12 so as to be rotatable in the inner circumferential direction of the shroud. A water supply pipe 27 and a cutting aid supply pipe 28 are connected to the cutting device 20, and water and cutting aid 14 are supplied from the water supply device 36 and the cutting aid supply device 35, respectively. After the cutting position is determined by the cutting device operating mechanism 26, water and the cutting aid 14 are supplied to the cutting device 20. On the other hand, the collection container 21 is installed at a position facing the cutting device 20 with the shroud 1 interposed therebetween. With this recovery device, water, bubbles, and cutting aid 14 after cutting the structure are sucked by the suction pump 22. The water, bubbles, and cutting aid 14 sucked by the suction pump 22 are passed through the air / water separator 23, the solid-liquid separator 24, and the filter 25, and the bubbles and the cutting aid 14 are removed. The steam separator 23 separates the gas sucked by the suction pump 22. The solid-liquid separator 24 separates the cutting aid 14 and water. The steam-water separator 23 and the solid-liquid separator 24 utilize the density difference with respect to water, and for example, a centrifuge can be used. The centrifuge exhausts a gas having a weight smaller than that of water from the upper portion, and discharges a cutting aid 14 having a weight higher than that of water from the lower portion. Since the cutting aid 14 and the like are removed by the steam separator 23 and the like, clean water is drained from the filter 25.

  FIG. 7 shows a cross section of the cut portion when the core shroud 1 is cut using a water jet method in which a cutting aid is mixed. The cutting aid 14 sprayed together with water from the nozzle 13 collides with the shroud 1 which is a reactor internal structure and grinds the shroud 1. The cutting aid 14 is crushed at the time of collision and becomes a crushed piece 15 having a wide particle size distribution. Although this crushed piece 15 is sucked into the collection container 21 together with the uncrushed cutting aid, it floats in water when it is scattered to the nozzle 13 side due to a collision with the shroud 1 or leaks from the collection container 21. It becomes.

  The cutting aid 14 and the crushed pieces 15 floating in the water adhere to the surfaces of peripheral devices such as the inner wall surface of the pool and the cutting device 20. When the cutting aid contains Fe or the like, the cutting aid adhering to the surface is dissolved by a corrosion reaction in the pool water, or changes with time such as a shape change to a hydroxide proceed. For example, when Fe is contained in the cutting aid, Fe is dissolved in water by the oxidation reaction of formula (2).

Fe → Fe ²⁺ + 2e ⁻ (2)
Electrons e ⁻ generated by the oxidation reaction are consumed by the reduction reactions of the formulas (3) and (4), and hydrogen gas H ₂ and hydroxide ions OH ⁻ are generated.

2H ⁺ + 2e ⁻ → H ₂ (3)
O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (4)
Since equations (2) to (4) proceed simultaneously, they can be expressed as equations (5) and (6).

Fe + 2H ⁺ → Fe ²⁺ + H ₂ (5)
Fe + _1/2 O ₂ + H ₂ O → Fe ²⁺ + 2OH ⁻ (6)
Fe ²⁺ and OH ⁻ produced by the corrosion reaction become ferrous hydroxide as shown in formula (7), and change into ferric hydroxide by the reaction shown in formula (8) by oxygen dissolved in water. And so-called red rust is generated.

Fe ²⁺ + 2OH ⁻ → Fe (OH) ₂ (7)
2Fe (OH) ₂ + H ₂ O + 1 / 2O ₂ → 2Fe (OH) ₃ (8)
That is, a substance that dissolves in water, such as iron, changes its chemical form over time due to a corrosion reaction, and becomes rust and adheres to the surface of the inner wall surface of the pool. On the other hand, when the structure to be cut (the shroud 1) is activated, the cutting aid 14 and the fragment 15 are also activated by the activated structure. When the reactor internal structure is a cutting work target, the cutting aid 14 and the shredded pieces 15 that are activated when the cutting work is performed are the surfaces of peripheral equipment such as the inner wall surface of the pool and the cutting device 20. It may adhere to and cause secondary contamination.

  Here, in the present invention, aluminum oxide is used as the cutting aid 14. As described above, the cutting aid 14 and the crushed pieces 15 that could not be sucked float in water, but aluminum oxide is insoluble in water (insoluble) and is electrically insulated, so it is indispensable for the corrosion reaction. No oxidation reaction occurs and no hydroxide is produced. Therefore, it can prevent that the activated cutting aid 14 and the crushing piece 15 generate | occur | produce as rust on a pool inner wall surface etc., and can suppress secondary contamination.

  In parallel with the cutting operation of the shroud 1 or collectively after the cutting operation is completed, the cut shroud is taken out of the reactor pressure vessel and transferred to the equipment pool (S5).

After the shroud cutting and unloading work (S5) is completed, the surface of the cutting device 20, the processing platform 12, the air / water separator 23 and the like is cleaned (S6). After the surface cleaning, the cutting device 20 and the like are removed (S7). Next, the inside of the pool is washed (S8). In addition, you may abbreviate | omit washing | cleaning (S6) of the cutting processing apparatus 20 grade | etc., And (S8) of a pool as needed.

  After removing all the structures in the shroud, the new shroud is carried into the reactor vessel and installed at a predetermined position (S10). By replacing the shroud with a new one, the reliability of the shroud can be improved and the life of the shroud can be increased, and the nuclear plant can be operated for a long time. Thereafter, the fuel and in-reactor equipment are reinstalled (S10), the pressure vessel is closed (S11), and the nuclear reactor is activated (S12).

  In this embodiment, the activated structure (shroud 1) is cut by spraying a pressurized liquid mixed with a cutting aid from a nozzle, and aluminum oxide is used as the cutting aid. Aluminum oxide does not undergo an oxidation reaction that is essential for a corrosion reaction, and does not produce a hydroxide. Therefore, even when the water jet method mixed with cutting aid is applied to the reactor internal structure, it is possible to prevent the activated aluminum oxide from adhering to the peripheral equipment as rust. That is, secondary contamination can be suppressed.

  FIG. 8 is a schematic view showing a cutting operation situation of the structure in the present embodiment. In this embodiment, the work for cutting the structure is performed in the work pool 11. The work pool 11 can be used by partitioning a part of a dryer separator pool or a fuel storage pool. In this embodiment, the shroud 1 that has already been cut in the reactor pressure vessel is used as the structure to be cut. When the shroud 1 that has already been cut is further cut and subdivided, the work pool 11 can be used. The structure (shroud) 1 is moved from the inside of the nuclear reactor and fixed on the processing platform 12. By moving the structure 1 from the reactor to the work pool 11, it is possible to perform other work in the reactor and shorten the entire repair and replacement process. Moreover, since the dryer separator pool has a shallower water depth than in the nuclear reactor, the cutting device 20 can be easily scanned. It is also possible to carry out the work by using a plurality of cutting devices 20.

  In the present embodiment, the cutting device 20 and the collection container 21 are installed at positions facing each other with the structure (shroud) 1 in between. The arrangement of the cutting device 20 and the collection container 21 may be reversed. The cutting aid is sucked by the suction pump 22 and removed by the steam / water separator 23, the solid / liquid separator 24 and the filter 25. The cutting process and the recovery of the cutting aid are the same as in the first embodiment. A work carriage 31 is installed on the work pool 11, and an operator can operate while operating the underwater camera 32 and the illumination 33 and confirming with the monitor 34. At this time, when a suction leak of the crushed pieces occurs, the crushed pieces 15 of the cutting aid 14 float in the water, causing turbidity of the pool water, which becomes an obstacle when the operator operates the equipment installed in the water. . However, as described in the description of FIGS. 2 to 4, since the load on the filter can be reduced by using aluminum oxide as the cutting aid 14, rapid filtration is possible and water transparency is restored. Easy to do.

  FIG. 9 is a schematic view showing a state of cutting the structure in the present embodiment. In this embodiment, the recovery system is simplified, and the steam / water separator 23 and the filter 25 used in Embodiments 1 and 2 are not equipped. The present invention can be applied to a case where a device for filtering with the filter 25 or the like is separately prepared, or a case where a filtering device provided in the work pool 11 is used. The solid-liquid separation device 24 uses a density difference between substances, and a heavy one can be selectively collected in the waste container 29. Since the density is determined by the weight and particle size of the substance, when aluminum oxide is used, since there are many large particles of 5 μm or more, the ratio that can be removed by centrifugation is high. Therefore, if the solid-liquid separation device 24 is used as a pretreatment, the amount collected by a separately prepared filter or a built-in filtration device can be reduced. At this time, in the solid-liquid separator 24, the small-diameter particles that pass slightly float in the work pool 11, but do not generate rust, so that adhesion of radioactivity can be suppressed.

  FIG. 10 is a schematic view showing a state of cutting the structure in this embodiment. FIG. 10 is similar to the third embodiment in that the recovery system is simplified and the steam / water separator 23 and the filter 25 are not provided, but the recovery system is different from the third embodiment in that the recovery system is installed outside the work pool 11. Thus, the present invention can be applied even when a sufficient space for installing the collection system in the work pool 11 cannot be secured.

  In each of the above-described embodiments, alumina oxide is used as a cutting aid in consideration of secondary contamination suppression and filter waste reduction, but other cutting aids may be used. FIG. 11 shows the material and density, altitude, fracture toughness value and electrical conductivity of the cutting aid. The “judgment applicability determination result” in the rightmost column is a result of the inventor's applicability to a cutting aid taking into account hardness, electrical conductivity, and the like. As described above, it is preferable to select the cutting aid 14 having a low electrical conductivity in consideration of secondary contamination of the work pool 11 and the like. Specifically, silicon carbide or zirconium oxide (zirconia) can be used in addition to aluminum oxide (alumina). Moreover, since the cutting method using the water jet mixed with the cutting aid uses the characteristic of cutting the structure when the cutting aid 14 collides, the cutting aid 14 having a higher hardness than the structure is selected. It is preferable to do this. Specifically, silicon carbide, zirconium oxide, and titanium oxide (titania) can be used in addition to aluminum oxide.

The flowchart which shows the operation | movement procedure of a 1st Example. The figure which shows the particle size distribution of the reorganization of a cutting aid. The figure which shows the particle number of the fragment of a cutting aid when 5 micrometers is made into a threshold value. The figure which shows the particle number of the fragment of a cutting aid when 10 micrometers is made into a threshold value. The figure which shows the relationship between filtration object and average specific resistance. Schematic which shows the structure cutting work situation in a 1st Example. The figure which shows the cutting | disconnection outline | summary of the structure by a cutting aid. Schematic which shows the structure cutting work condition in 2nd Example. Schematic which shows the structure cutting work condition in a 3rd Example. Schematic which shows the structure cutting work condition in a 4th Example. The figure which shows the relationship between the material of a cutting aid, and electrical conductivity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Structure, 13 ... Nozzle, 14 ... Cutting aid, 20 ... Cutting processing device, 21 ... Recovery container, 22 ... Suction pump, 23 ... Gas-water separator, 24 ... Solid-liquid separator, 25 ... Filter, 35 ... cutting auxiliary agent supply device, 36 ... water supply device.

Claims (8)

A structure cutting method for cutting a structure activated by spraying a liquid mixed with a cutting aid and pressurized from a nozzle, wherein the cutting aid contains aluminum oxide. A method for cutting a structure. After shutting down the reactor, the fuel in the reactor pressure vessel is taken out of the reactor pressure vessel,
A cutting device is installed in the reactor pressure vessel,
By injecting a pressurized liquid mixed with a cutting aid containing aluminum oxide into the activated structure in the reactor pressure vessel from a nozzle provided in the cutting processing apparatus, the structure Cut and
Unloading the cut structure out of the reactor pressure vessel;
A method for cutting a structure, wherein the cutting device is carried out of the reactor pressure vessel. In Claim 2, after carrying out the cut structure out of the reactor pressure vessel, the cut structure is transferred to a dryer separator pool,
Wherein in said dryer separator pool, the cutting aid containing aluminum oxide was pressurized and pressurized mixed fluid, by injecting the truncated structure, further cutting the cut structure A method for cutting a structure. After shutting down the reactor, the fuel in the reactor pressure vessel is taken out of the reactor pressure vessel,
Cutting the activated structure in the reactor pressure vessel;
Carrying the cut structure out of the reactor pressure vessel and transferring it to a dryer separator pool;
Wherein in said dryer separator pool, the cutting aid containing aluminum oxide was pressurized and pressurized mixed fluid, by injecting the truncated structure, further cutting the cut structure A method for cutting a structure.   2. The method for cutting a structure according to claim 1, wherein the structure is a core shroud. In Claim 1, when cutting the structure, the cutting aid used for cutting from a suction device installed at a position opposite to the position where the cutting aid is sprayed across the structure, and A method for cutting a structure, wherein the liquid is sucked, and then the cutting aid and the liquid are removed from the sucked cutting aid and liquid by a solid-liquid separator or a filter. A nozzle that mixes a cutting aid and pressurizes the structure against the activated structure to cut the activated structure;
A cutting aid supply device for supplying the cutting aid to the nozzle;
A liquid supply device for supplying the pressurized liquid to the nozzle,
The structure cutting apparatus, wherein the cutting aid contains aluminum oxide . 8. The cutting aid and the liquid used for cutting according to claim 7 , wherein the cutting aid and the liquid used for the cutting are sucked when the structure is cut, which is installed at a position opposite to a position where the cutting aid is sprayed across the structure. A suction device to
A structure-cutting apparatus comprising a solid-liquid separation device or a filter for removing the cutting aid from the sucked cutting aid and liquid.

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