JP2007024586A - Abrasive water jet cutting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasive water jet cutting method capable of solving various problems caused by rust and reducing the amount of secondary waste produced which is to be stored in a site bunker pool when an abrasive water jet cutting work is executed. <P>SOLUTION: Adhesion of radionuclides on equipment and a structural member is suppressed by using alumina not causing rust as abrasive 14. Waste is classified into high-level waste and low-level waste by using a separating/recovering device 24 utilizing difference in density between the alumina and high-level chips. A filter 25 collecting the alumina is incinerated as the low level waste to reduce the amount of the secondary waste produced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an abrasive water jet cutting method, and in particular, recovers abrasive (cutting aid) and cutting powder that are generated when a metal structural material activated by neutron irradiation in a nuclear power plant is cut with an abrasive water jet. It relates to the disposal method.

  When a nuclear power plant is operated, structural materials may deteriorate over time and may need to be replaced. In particular, when exchanging the shroud of the boiling water reactor, primary cutting for carrying out the old shroud from the inside of the furnace and secondary cutting for cutting the carried out shroud for disposal storage are required.

  Conventionally, as an underwater cutting technique, a roll cutter or electric discharge machining is used for primary cutting, and plasma cutting or abrasive water jet cutting is used for secondary cutting.

  Cutting with a roll cutter has an advantage that dust generated with cutting is small. However, there is a problem that the cutting speed is slow.

  In addition, in thermal cutting such as electric discharge machining cutting or plasma cutting, the cutting speed is increased. However, there is a concern about dust scattering into the gas due to local boiling due to heat and shielding gas.

  Abrasive water jet cutting has the advantage of less dust scattering and faster cutting speed. However, the secondary waste increases due to the abrasive used as the cutting aid. In addition, when cast steel is made abrasive, rust generated by corrosion adheres to the inner surfaces of the equipment and the pool and raises the radioactivity level, which increases the amount of work required for cleaning and decontamination after work.

  As a method for recovering the abrasive, a method of sucking the abrasive together with water and centrifuging it, and a filter filtration method are known.

  There is a method in which a dedicated container is installed in a pool for cutting work, and the work is performed in a limited space to increase the collection efficiency (see, for example, Patent Document 1).

  As a recovery method, a sedimentation separation method using a density difference has been proposed (see, for example, Patent Document 2). In addition, a method has been proposed in which the abrasive and the cutting powder are magnetically separated and a part of the abrasive is reused to reduce secondary waste (for example, see Patent Document 3).

Japanese Patent Application Laid-Open No. 07-084094 (pages 2 to 4, FIGS. 1, 4 and 6) Japanese Patent Laid-Open No. 10-260298 (pages 2 to 3 and FIGS. 1 to 3) Japanese Patent Laid-Open No. 2000-246644 (pages 2 to 3 and FIGS. 1 to 3)

  Abrasive water jet cutting is particularly attracting attention because of its high cutting speed and low risk of dust scattering.

  However, in the above prior art, iron-based materials such as cast steel were used for the abrasive, so the abrasive and cutting powder that were not taken into the recovery device accumulated at the bottom of the pool and solidified, or generated due to abrasive corrosion. There is a problem that the rust moves to the cutting device or the wall of the pool and accelerates the attachment of the radionuclide to the surface of the equipment or material in contact with the pool water.

  The cut retired material is stored in the site banker pool. The abrasive rust adhering to the removal material moves rust into the site banker pool, and cleaning work is also required in this pool.

  In addition, even when iron-based abrasives are reused by magnetic recovery to reduce secondary waste, the abrasives tend to harden due to the occurrence of rust, and the piping and hoses of the abrasive material supply system at the time of cutting are blocked. There is a fear.

  Furthermore, when the abrasive and the cut powder are simply collected and discarded, all of them are stored as high-level radioactive waste in the site bunker pool, which causes a pressure on the storage area.

  An object of the present invention is to eliminate the various problems caused by the occurrence of rust at the time of cutting work with an abrasive water jet and to reduce the amount of secondary waste to be stored in the site banker pool. Is to provide.

  In order to solve the above-mentioned problems, the present invention uses an oxide-based material such as alumina or garnet that does not generate rust due to corrosion as an abrasive, and uses a difference in specific gravity from stainless steel to be cut. In this way, it is divided into recovered components centered on cutting powder with a high radioactivity level and components centered on abrasives that contain almost no cutting powder, greatly reducing decontamination and cleaning work caused by rust, Abrasive water jet that reduces the amount of secondary waste to be stored in the site bunker pool, reduces the amount of replacement work such as shrouds, shortens the construction period, and reduces the cost and exposure dose of workers. A cutting method is proposed.

  According to the present invention, since rust is not generated in alumina as an abrasive, the cleaning work accompanying the cutting work can be greatly reduced, and the exposure dose of the worker can be reduced. Moreover, separation using the density difference from the cut powder becomes possible, the amount of high-level waste generated can be suppressed, and the amount of secondary waste stored and discarded in the site banker pool can be suppressed.

  Next, an abrasive water jet cutting method according to the present invention will be described with reference to FIGS. The cutting target is a shroud in a reactor pressure vessel.

  FIG. 1 is a flowchart showing a schematic process of shroud replacement work in a boiling water nuclear power plant.

  FIG. 2 is a diagram schematically showing the relationship between the primary cutting work place of the shroud 1 and the secondary cutting work place of the shroud 2 after unloading in a boiling water nuclear power plant.

  In FIG. 1, after the reactor is shut down, the pressure vessel is opened, equipment inside the reactor such as a dryer and a separator, and fuel are taken out, a cutting device for primary cutting is installed, and the shroud is primarily cut.

  The cut shroud 1 is installed on a gantry 12 installed in a dryer separator pool (DSP) 7 from the reactor pressure vessel 3 through the reactor well using the overhead crane 9.

  The dryer separator pool 7 is isolated from the reactor well 5 by closing the gate after receiving the carry-out shroud 2. In the dryer / separator pool 7, the shroud is secondarily cut using the abrasive water jet cutting device of the present invention. The shroud that has been finely cut is stored in a transport container having a shielding ability, lifted from the dryer / separator pool 7, loaded on a truck, and stored in a site bunker pool.

  On the other hand, in the furnace in which the old shroud has been carried out, the cutting device 20 used for the primary cutting is removed after surface cleaning for removing attached radioactivity, rust and the like. In addition, after cleaning the furnace, a new shroud is installed. Thereafter, the fuel is reloaded, the removed in-reactor equipment is reinstalled, the pressure vessel is sealed, and the reactor is started.

  The abrasive water jet cutting method of the present invention is a cutting method related to a process surrounded by a thick frame in FIG.

  FIG. 3 is a diagram showing a detailed apparatus configuration and arrangement for secondary cutting work of the shroud 2 after unloading in the dryer / separator pool 7.

  A state in which the shroud 1 installed in the reactor pressure vessel 3 is cut and carried out and installed on the mount 12 of the dryer / separator pool 7 is shown. After carrying out, the shroud 2 is secondarily cut by the high-pressure water flow including the abrasive 14 ejected from the cutting nozzle 13 on the gantry 12. The abrasive 14 and the cutting powder used for cutting are processed by a separation and recovery device 8 installed in the dryer / separator pool 7.

  When the shroud 1 is moved from the reactor to the dryer / separator pool 7, other operations can be performed in parallel in the reactor, so that the entire repair and replacement process can be shortened.

  Further, since the dryer / separator pool 7 has a shallower water depth than that in the nuclear reactor, it is easy to scan the cutting device 20, and it is possible to cut using a plurality of cutting devices 20.

  The unloaded shroud 2 divided by the primary cutting is moved from the inside of the nuclear reactor and fixed on the processing platform 12. A water supply pipe 27 and an abrasive material supply pipe 28 are connected to the cutting device 20, and high pressure water and abrasive 14 are supplied from an ultrahigh pressure pump 36 and an abrasive material supply device 35.

  After the operator 30 determines the cutting position with the cutting device operating mechanism 26, the high-pressure water and the abrasive 14 are supplied. The cutting device 20 and the collector 21 are installed at positions facing each other with the shroud 2 being sandwiched after being carried out. However, the arrangement of the cutting device 20 and the collector 21 may be reversed or adjacent to each other.

  Most of the abrasive 14 used is sucked together with the cut powder and water from the collector 21 by the suction pump 22 and removed by the steam separator 23, the separator 24 and the filter 25, and clean water is removed from the filter 25. Drained.

  The steam / water separator 23 separates the gas sucked by the suction pump 22 simultaneously with the suction of the abrasive 14. The separation device 24 separates the abrasive 14 from the cut powder and water. Gas-water separation and solid-liquid separation utilize the density difference with respect to water. For example, using a centrifuge, it is possible to perform air-water separation in which a gas having a weight lower than that of water is exhausted from above, and abrasive 14 having a large specific gravity relative to water and cutting powder can be discharged from below.

  When alumina is used as the abrasive 14, a density difference is generated between the cut powder of stainless steel. By utilizing this difference in density, the cut powder and the abrasive 14 can be separated. That is, a small amount of cutting powder having a high radioactivity level can be selectively collected, and the amount of secondary waste to be stored in the site bunker pool can be reduced.

  Further, since the filter 25 that collects the abrasive 14 from which the cut powder has been removed becomes a low-level waste, when a filter material that can be incinerated is used, the volume can be reduced by incineration after drying.

  Examples of the abrasive 14 in which rust is unlikely to occur include garnet, stainless wire, zirconia beads, silicon carbide, and titanium oxide.

Garnet made from sea sand has many chlorine impurities and cannot be brought into the reactors of reusable reactors.
In silicon carbide, a lot of very fine crushed powder is generated and the turbidity of water is remarkable.
Stainless wire, zirconia beads, and titanium oxide are expensive.

  After all, alumina is most suitable.

  A work carriage 31 is installed on the dryer / separator pool 7. The operator 30 can work while operating the underwater camera 32 and the illumination 33 and checking the camera image on the monitor 34. At this time, the cutting powder and the abrasive 14 that have not been sucked into the collector 21 are accumulated and settled at the bottom of the pool when the particle size is large. A small particle diameter floats in the water, causing turbidity of the pool water, which becomes an obstacle when the operator 30 operates the equipment installed in the water.

  However, since alumina is used as the abrasive 14 in the present invention, the load on the filter 25 is small due to its physical characteristics and the amount of secondary waste generated is small. Transparency can be recovered easily.

  Furthermore, since alumina does not rust like cast steel, the mixture of the cutting powder deposited on the bottom of the dryer / separator pool 7 and the abrasive 14 is hardened and difficult to remove. Rust and radioactivity do not adhere to the surface.

  Therefore, the deposit accumulated on the bottom can be easily recovered by suction cleaning, and the labor of cleaning when the equipment in contact with the water in the dryer / separator pool 7 is pulled up from the water can be greatly reduced. Moreover, the cleaning operation in the dryer / separator pool 7 when the secondary cutting operation is completed is facilitated.

  Shredded shroud is housed in a shielded transport container, lifted into the air from the dryer / separator pool 7, transported to the building with the site bunker pool 7 using a truck, and shielded in the site bunker pool 7. It is removed from the container and stored in the pool in an orderly stacked manner with the storage container. Even in the work in the site bunker pool 7, the use of alumina as an abrasive does not spread the contamination caused by rust, and the cleaning work in the site bunker pool 7 after the removal work is greatly reduced. .

  FIG. 4 is a diagram illustrating a system configuration of a recovery apparatus including a two-stage cyclone separator according to the second embodiment of the present invention.

  In the first embodiment, most of the used abrasive 14 is sucked together with the cutting powder and water from the collector 21 by the suction pump 22, and after the cutting powder is selectively removed by the separation device 24, it is separated from the water by the filter 25. It was.

  In this case, since a large amount of the abrasive 14 becomes a load on the filter 25, the amount of use of the filter 25 increases, and it is necessary to increase the installation space of the filter 25 or to frequently replace the filter element.

  Therefore, in the second embodiment, as shown in FIG. 4, the separation device 24 is arranged in series, and the upstream separation device 24 separates and collects cutting powder having a high dose rate, and the downstream separation device 24 uses the abrasive 14. Of these, particles that were not crushed were separated and recovered from water, and the system was changed to a method in which only the abrasive 14 that was crushed and became fine and difficult to separate due to the density difference was collected by the filter 25.

  The waste container 29 is divided so that the cutting powder and the abrasive 14 are stored separately. In this way, the load on the filter 25 is greatly reduced, and the secondary waste to be incinerated is greatly reduced.

  Moreover, the particle | grains which were not crushed among the abrasives 14 can be reused as an abrasive. Although not shown here, a system may be provided in which particles that have not been crushed are sent back to the abrasive material supply device 35 and reused.

  In the first and second embodiments, it is assumed that the shroud that has been primarily cut is cut by the dryer / separator pool 7.

  The fuel pool 6 may be used as the location where the structural material is cut by the abrasive water jet cutting method of the present invention.

  Further, the abrasive water jet cutting method of the present invention can be applied not only to the secondary cutting but also to the primary cutting performed in the reactor pressure vessel 3.

It is a flowchart which shows the schematic process of shroud replacement | exchange construction in a boiling water nuclear power plant. It is a figure which shows roughly the relationship between the primary cutting construction place of the shroud 1 and the secondary cutting construction place of the shroud 2 after carrying out in a boiling water nuclear power plant. It is a figure which shows the detailed apparatus structure and arrangement | positioning of the secondary cutting construction of the shroud 2 after carrying out in the dryer separator pool 7. FIG. It is a figure which shows the system | strain structure of the collection | recovery apparatus provided with the two-stage cyclone separator in Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shroud 2 Shroud after unloading 3 Reactor pressure vessel 4 Jet pump 5 Reactor well 6 Fuel pool 7 Dryer / separator pool 8 Separation and recovery device 9 Overhead crane 12 Mount 13 Cutting nozzle 14 Abrasive 20 Cutting device 21 Recovery vessel 22 Suction pump Reference Signs List 23 Air-water separator 24 Separator 25 Filter 26 Cutting device operation mechanism 27 Water supply pipe 28 Abrasive material supply pipe 29 Waste container 30 Worker 31 Work carriage 32 Underwater camera 33 Illumination 34 Monitor 35 Abrasive material supply device 36 Ultra high pressure pump

Claims (10)

In an abrasive water jet cutting method in which a high-pressure water stream mixed with abrasive is collided with an activated structural material used in a nuclear reactor to cut the structural material,
Cutting the structural material using oxide particles as the abrasive,
The abrasive used for cutting and the cutting powder of the structural material are sucked and collected together with water,
Sorting the abrasive, cutting powder and water based on density difference,
Abrasive water jet cutting method, wherein the disposal method of secondary waste is changed according to the dose rate level. The abrasive water jet cutting method according to claim 1,
An abrasive water jet cutting method, wherein the abrasive is alumina. The abrasive water jet cutting method according to claim 1 or 2,
An abrasive water jet cutting method, wherein a cyclone separator is used when the abrasive, cutting powder, and water are separated based on a density difference. The abrasive water jet cutting method according to claim 3,
Abrasive water jet cutting method characterized in that a cyclone separator for separating abrasive, cutting powder, and water based on density difference is arranged in two stages in series to separate the abrasive that has not been crushed from the crushed abrasive and the cutting powder. . In the abrasive water jet cutting method according to any one of claims 1 to 4,
Store and dispose of high dose rate level waste in the water of the site bunker pool,
An abrasive water jet cutting method characterized by storing and discarding low dose rate level waste in a solid waste storage. In an abrasive water jet cutting method in which a high-pressure water stream mixed with abrasive is collided with an activated structural material used in a nuclear reactor to cut the structural material,
Cutting the structural material using oxide particles as the abrasive,
The abrasive used for cutting and the cutting powder of the structural material are sucked and collected together with water,
Separating the cutting powder from abrasive and water based on density difference;
After that, the abrasive and water are separated with a filter,
Abrasive water jet cutting method, wherein the disposal method of secondary waste is changed according to the dose rate level. In the abrasive water jet cutting method according to claim 6,
A method for cutting an abrasive water jet, wherein a cyclone separator is used when separating the abrasive from the abrasive and water based on a density difference. The abrasive water jet cutting method according to claim 6 or 7,
A method for cutting an abrasive water jet, wherein the filter that collects the abrasive is incinerated. In an abrasive water jet cutting device that provides an abrasive water jet nozzle at the tip of a positioning mechanism and cuts a cutting object in water,
A suction pump that sucks and collects abrasives generated by cutting and cutting powder;
An abrasive water jet cutting device characterized in that a separating device for separating the collected abrasive and the cutting powder by a density difference is provided. In the abrasive water jet cutting device according to claim 9,
Separation device that separates abrasives that have not been crushed and those that have been crushed with respect to the abrasives that have been separated from the cut powder, and means for reusing the abrasives with the same particle size separated by the separation device into the abrasive supply system An abrasive water jet cutting device characterized by comprising:

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