Exhaust purification filter and exhaust purification device

Abstract

To provide a radioactive dust exhaust cleaning filter which is hardly deteriorated by radiation from radioactive dust.SOLUTION: An exhaust gas purification filter (7) for removing radioactive dust from exhaust gas (EH) containing the radioactive dust generated in a work area (2), the exhaust gas purification filter (7) having a cylindrical shape and being configured such that the radioactive dust in the exhaust gas (EH) is captured by the exhaust gas purification filter (7) in a process in which the exhaust gas (EH) passes from an outside to an inside of the exhaust gas purification filter (7), and purified exhaust gas (PEH) is discharged to an outside of the exhaust gas purification filter (7) through an inside of a cylinder of the exhaust gas purification filter (7), the exhaust purification filter 7 includes a metal fiber sheet and is washable, and in a stage of washing the exhaust purification filter 7, the compressed air injected into the cylinder of the exhaust purification filter 7 passes from the inside to the outside of the exhaust purification filter 7, and in the process, the radioactive dust captured by the exhaust purification filter 7 is blown off to the outside of the exhaust purification filter 7.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust purification filter used to remove radioactive dust from exhaust gases to obtain purified exhaust gases, an exhaust purification device equipped with the exhaust purification filter, and a radioactive dust removal system equipped with the exhaust purification device. [Background technology]

[0002] Decommissioning work at nuclear power plants and nuclear facilities generates large amounts of radioactive dust (dust containing radioactivity or dust carrying radiation; the same applies below). Large amounts of radioactive dust can lead to exposure of decommissioning workers and the risk of radioactive contamination spreading outside the decommissioning work area. Therefore, it is necessary to reduce the concentration of radioactive dust within the work area. At the same time, it is also necessary to maintain negative pressure within the work area to prevent radioactive materials from leaking from within the work area to outside the work area.

[0003] In such sites, it is preferable to use a filtration device equipped with a high-performance filter (e.g., a HEPA filter) that removes fine radioactive dust. However, these high-performance filters process dust particles of various sizes, so they tend to clog easily and must be replaced frequently. This ultimately increases the amount of radioactive waste. Since having people approach a high-performance filter that has captured a large amount of radioactive dust is problematic from the perspective of radiation exposure, it is desirable to minimize the frequency of filter replacement.

[0004] Techniques for removing radioactive dust from exhaust gases include those disclosed in Patent Documents 1 and 2 below.

[0005] The secondary product recovery and treatment system disclosed in Patent Document 1 is characterized by comprising a local exhaust enclosure installed in the demolition environment area, a filter that filters and recovers the secondary products recovered in the local exhaust enclosure, an exhaust fan connected to the outlet side of the filter, and a circulation line that circulates the exhaust from the exhaust fan back to the demolition environment area. The effects of this system include the efficient recovery of secondary products generated from the demolition site, and improved safety by treating the exhaust in a closed recovery system without releasing the exhaust to the outside.

[0006] The dust cartridge filter disclosed in Patent Document 2 combines a hollow cylindrical filter body with a plate-like pre-filter to increase the filtering area and extend the life of the filter. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-185794 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-300926 Summary of the Invention [Problem to be solved by the invention]

[0008] The secondary product recovery processing system in Patent Document 1 does not clarify what type of filter is used as the filter installed upstream of the circulation line. If a general filter made of polyester resin or the like were used as this filter, it would have low resistance to radiation and would be prone to deterioration.

[0009] Furthermore, if the exhaust gas from the demolition environment area contains sharp particles, the filter may be damaged by these particles, which also poses the problem of requiring more frequent filter replacement.

[0010] Furthermore, depending on the type of dust contained in the exhaust from the demolition environment area (for example, if the exhaust contains sparks from cutting with a fusion or grinder, etc.), there is a risk that the filter may catch fire and cause a fire.

[0011] The dust cartridge filter of Patent Document 2 uses a hollow cylindrical filter body made of glass fiber filter paper sandwiched between support media (polyester resin) on both sides, and a plate-shaped pre-filter made of nonwoven fabric.

[0012] However, filters using polyester resins such as those in Patent Document 2 have the same problems as those in Patent Document 1. That is, there are various problems such as the risk of deterioration due to radiation, the risk of damage due to sharp fine powder, and the risk of fire.

[0013] Therefore, an object of the present invention is to provide an exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, and that is less likely to be deteriorated by radiation from the radioactive dust. [Means for solving the problem]

[0014] The present invention, which has solved the above problems, is as follows.

[0015] (First aspect) An exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, the exhaust purification filter is cylindrical, and radioactive dust in the exhaust gas is captured by the exhaust purification filter as the exhaust gas passes from the outside to the inside of the exhaust purification filter, and the purified exhaust gas passes through the inside of the cylinder of the exhaust purification filter and is discharged to the outside of the exhaust purification filter, The exhaust purification filter has a main filter, the main filter includes a sheet of metal fibers; The exhaust purification filter is washable, In the step of cleaning the exhaust purification filter, compressed air injected into the cylinder of the exhaust purification filter passes from the inside to the outside of the exhaust purification filter, and in the process, radioactive dust captured by the exhaust purification filter is blown down to the outside of the exhaust purification filter. An exhaust purification filter characterized by:

[0016] (Action and effect) Since the main filter of the exhaust purification filter includes a metal fiber sheet, the exhaust purification filter is less likely to deteriorate due to radiation emitted from radioactive dust in the exhaust.

[0017] Furthermore, because replacing an exhaust purification filter contaminated with radioactive dust poses a risk of radiation exposure, it is preferable to avoid replacing the exhaust purification filter whenever possible. However, the exhaust purification filter of the first embodiment can reduce the frequency of replacement. That is, with the exhaust purification filter of the first embodiment, even if a large amount of radioactive dust or the like adheres to the exhaust purification filter and the purification capacity of the exhaust purification filter decreases, the exhaust purification filter can be regenerated by backwashing with compressed gas. This eliminates the need to replace the exhaust purification filter every time a large amount of radioactive dust or the like adheres to the exhaust purification filter, eliminating the need to replace the exhaust purification filter over a long period of time. This prevents worker exposure during the exhaust purification filter replacement work and the generation of large amounts of radioactive waste (used exhaust purification filters). It also reduces the cost of halting exhaust purification processing due to filter replacement and the cost of replacing and disposing of exhaust purification filters.

[0018] It has been found that when cleaning the exhaust purification filter, cleaning by directing compressed gas against the inside of the exhaust purification filter is more effective in removing radioactive waste adhering to the exhaust purification filter than cleaning by directing compressed gas against the outside of the exhaust purification filter. Therefore, by so-called backwashing the exhaust purification filter as in the first aspect, there is an advantage that the exhaust purification filter does not need to be replaced for a longer period of time.

[0019] Furthermore, even if sharp particles or fine particles are contained in the exhaust gas from the work area, the exhaust gas purification filter is unlikely to be damaged by the particles because the main fill of the exhaust gas purification filter contains a metal fiber sheet. Also, even if sparks or the like that could cause a fire are contained in the exhaust gas from the work area, a fire is unlikely to occur because the main fill of the exhaust gas purification filter contains a metal fiber sheet.

[0020] (Second aspect) The exhaust purification filter has a shape retention means for retaining the shape of the main filter, the shape-retaining means includes a metal mesh member; The exhaust purification filter of the first aspect is formed by laminating a flat shape-retaining means on the front and back sides of the flat main filter, or on the front or back side of the flat main filter, and folding the laminate into an accordion-like shape to form a cylindrical shape.

[0021] (Action and effect) In a second aspect, the exhaust purification filter is configured such that shape-retaining means including a metal mesh member is laminated on the front and back sides of a flat main filter, or on the front or back side of the flat main filter. This configuration makes it easier for the main filter, including the metal fiber sheet, to maintain its shape. That is, since it is difficult to maintain the shape with a metal fiber sheet alone, it is preferable to laminate a shape-retaining means including a metal mesh member, as in the second aspect. Furthermore, by providing a shape-retaining means including a metal mesh member, the strength of the exhaust purification filter can be increased, which results in the filter being more likely to withstand the pressure (pressure from compressed gas) applied to the exhaust purification filter when it is backwashed.

[0022] Furthermore, if a shape-retaining means including a metal mesh member is not provided, it is difficult to form a metal fiber sheet into a bellows shape. Even if the metal fiber sheet can be formed into a bellows shape, it has poor shape stability and is difficult to maintain the bellows shape. By using a shape-retaining means including a metal mesh member in the exhaust purification filter, it is possible to form the metal fiber sheet into a bellows shape and maintain the bellows shape.

[0023] Furthermore, by making the exhaust purification filter bellows-shaped, the filtering area increases, which has the advantage of allowing the amount of exhaust purification processing per unit time to be increased without having to increase the size of the container that houses the exhaust purification filter (the container of the exhaust purification device).

[0024] (Third Aspect) The main filter is The exhaust purification filter has a laminated structure including a surface layer positioned on the outside of the exhaust purification filter, a back layer positioned on the inside of the exhaust purification filter, and an intermediate layer positioned between the surface layer and the back layer, The exhaust gas purification filter according to the first aspect, wherein the fiber diameter of the metal fibers in the surface layer and the back layer is larger than the fiber diameter of the metal fibers in the intermediate layer.

[0025] (Action and effect) The main filter has a laminated structure of a surface layer, an intermediate layer, and a back layer, with the fiber diameter of the metal fibers in the surface layer and the back layer being larger than that of the metal fibers in the intermediate layer. In this case, the metal fibers in the intermediate layer, which have a smaller fiber diameter, are best able to remove radioactive dust and the like, but have the disadvantage of being weaker due to their smaller fiber diameter. Therefore, by providing the surface and back layers with metal fibers having a larger fiber diameter than the metal fibers in the intermediate layer, the weakness of the fibers in the intermediate layer can be compensated for by the strength of the fibers in the surface and back layers. As a result, compared to a single-layer main filter (assuming the fiber diameter of the metal fibers constituting this single layer is the same as that of the metal fibers in the intermediate layer), the main filter is stronger, improving its shape stability and making it more resistant to the pressure (pressure due to compressed gas) applied to the exhaust purification filter during backwashing. In particular, the back layer of the main filter is subjected to the greatest compressed gas pressure during backwashing, so by increasing the pressure resistance of this back layer, damage to the main filter by compressed gas can be prevented.

[0026] Furthermore, when the metal fiber diameter of the layer located on the outside of the main filter is large, radioactive dust particles and the like trapped in the voids of the layer located on the outside of the main filter can be more easily blown out to the outside of the main filter during backwashing compared to when the metal fiber diameter of the layer located on the outside of the main filter is small, which has the advantage of improving the cleaning effect during backwashing.

[0027] Furthermore, by forming the main filter into a laminated structure, it is possible to reduce variations in performance among the main filters when manufacturing a plurality of main filters, thereby stabilizing the performance of the main filters.

[0028] As in the second embodiment, shape-retaining means may be provided on the outside or inside of the main filter, thereby further increasing the pressure resistance of the exhaust purification filter so that it can withstand the pressure of compressed gas during backwashing.

[0029] (Fourth aspect) The main filter is made up of multiple layers, The exhaust purification filter of the first aspect, wherein the fiber diameter of the metal fibers in the layer located on the outside of the exhaust purification filter is larger than the fiber diameter of the layer located on the inside of the exhaust purification filter.

[0030] (Action and effect) When the metal fiber diameter of the layer located on the outside of the main filter is large, radioactive dust particles and the like trapped in the voids of the layer located on the outside of the main filter can be more easily blown out to the outside of the main filter during backwashing than when the metal fiber diameter of the layer located on the outside of the main filter is small, which has the advantage of improving the cleaning effect during backwashing.

[0031] (Fifth aspect) An exhaust purification device equipped with an exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, the exhaust purification filter is cylindrical, and radioactive dust in the exhaust gas is captured by the exhaust purification filter as the exhaust gas passes from the outside to the inside of the exhaust purification filter, and the purified exhaust gas passes through the inside of the cylinder of the exhaust purification filter and is discharged to the outside of the exhaust purification filter, The exhaust purification filter has a main filter, the main filter includes a sheet of metal fibers; The exhaust purification filter is washable, a configuration in which, in the stage of cleaning the exhaust purification filter, the compressed air injected into the cylinder of the exhaust purification filter passes from the inside to the outside of the exhaust purification filter, and the radioactive dust captured by the exhaust purification filter is blown off to the outside of the exhaust purification filter. An exhaust gas purification device characterized by:

[0032] (Action and effect) According to the fifth aspect, the same effects as those of the first aspect are achieved.

[0033] (Sixth aspect) The exhaust purification device is an injection unit that injects compressed air into a cylinder of the exhaust purification filter; The injection unit has an injection nozzle, The exhaust purification device according to the fifth aspect, wherein the axial direction of the injection nozzle is the same as the axial direction of the exhaust purification filter.

[0034] (Action and effect) By aligning the axial direction of the injection nozzle with the axial direction of the exhaust purification filter (height direction of the tube), the gas injected from the injection nozzle reaches the inside of the exhaust purification filter with almost no loss of momentum, which has the advantage of providing a higher cleaning effect on the exhaust purification filter.The cleaning effect (the effect of brushing off radioactive dust adhering to the outer surface of the exhaust purification filter) is higher than when the axial direction of the injection nozzle is perpendicular to the axial direction of the exhaust purification filter.

[0035] (Seventh aspect) The exhaust purification device is Partition walls divide the interior space into multiple small spaces, an injection unit that injects compressed air into a cylinder of the exhaust purification filter, the exhaust purification filters are disposed in the plurality of small spaces formed by the partition walls, respectively; The partition wall is An exhaust purification device of the fifth aspect, which prevents the compressed gas injected from the injection section toward the exhaust purification filter located inside some of the small spaces from directly colliding with the exhaust purification filter located inside other adjacent small spaces.

[0036] (Action and effect) In a seventh aspect, a partition wall is provided within the exhaust gas purification device. This partition wall can prevent compressed gas injected from the injection unit toward an exhaust gas purification filter arranged inside one of the small spaces from directly impinging on an exhaust gas purification filter arranged inside another adjacent small space. As a result, it can be prevented that compressed gas used to backwash an exhaust gas purification filter arranged in one of the small spaces impinges on an exhaust gas purification filter arranged in another small space and adversely affects the exhaust gas purification process by the exhaust gas purification filter arranged in that other small space.

[0037] (Eighth aspect) The exhaust purification device is provided with a mounting plate, a housing for supporting the exhaust purification filter; The housing has an upper plate portion to which the exhaust purification filter is fixed, a front plate portion, a rear plate portion disposed at a distance from the front plate portion, and side plate portions connecting the sides of the front plate portion and the rear plate portion, and is a box-shaped housing with an open bottom, in which the upper edge of the front plate portion, the upper edge of the rear plate portion, and the upper edges of the side plate portions are each connected to the upper plate portion, The exhaust purification device according to the fifth aspect, wherein the housing is fixed to the mounting plate.

[0038] (Action and effect) During the backwashing stage, the pressure of the injected compressed gas blows the radioactive dust adhering to the outer surface of the exhaust purification filter out of the filter, but the presence of a housing means that much of the blown-out radioactive dust scatters within the inner wall of the housing and falls down. Therefore, the radioactive dust that has accumulated in the lower part of the exhaust cleaning device can be easily collected.

[0039] (Ninth aspect) The internal space of the housing is When the shape of the truncated cone is such that the perimeter defined by the lower edge of the front plate portion, the lower edge of the rear plate portion, and the lower edge of the side plate portion is the perimeter of the lower surface of the truncated cone, and the perimeter of the upper plate portion is the perimeter of the upper surface of the truncated cone, The exhaust purification device of the eighth aspect, wherein the perimeter formed by the lower edge of the front plate portion, the lower edge of the rear plate portion, and the lower edge of the side plate portion is longer than the perimeter of the upper plate portion.

[0040] (Action and effect) When the internal space of the casing has the above-mentioned shape, radioactive dust is less likely to adhere to the inner wall of the casing and falls easily, making it easy to collect and contributing to long-term operation.

[0041] (Tenth aspect) The housing in which the exhaust purification filter is supported has a cartridge structure and is fixed to the mounting plate so as to be attachable and detachable, The housing is removably mounted in a casing of the exhaust purification device.

[0042] (Action and effect) Since the exhaust purification filter has a cartridge structure, dust trapped in the exhaust purification filter of the exhaust purification device accumulates inside the exhaust purification filter, and when the pressure loss of the exhaust purification filter becomes large, the filter can be replaced.

[0043] (Eleventh aspect) an exhaust purification device having an exhaust purification filter that removes radioactive dust from exhaust gas containing radioactive dust generated in the work area; a residual dust removal device that removes radioactive dust remaining in the purified exhaust gas discharged from the exhaust gas purification device, the exhaust purification filter is cylindrical, and radioactive dust in the exhaust gas is captured by the exhaust purification filter as the exhaust gas passes from the outside to the inside of the exhaust purification filter, and the purified exhaust gas passes through the inside of the cylinder of the exhaust purification filter and is discharged to the outside of the exhaust purification filter, The exhaust purification filter has a main filter, the main filter includes a sheet of metal fibers; The exhaust purification filter is washable, a configuration in which, in the stage of cleaning the exhaust purification filter, radioactive dust captured by the exhaust purification filter is blown off to the outside of the exhaust purification filter as the compressed air injected into the cylinder of the exhaust purification filter passes from the inside to the outside of the exhaust purification filter, The residual dust removal device is A residual dust removal filter having a particle collection rate of 99.97% or more for dust particles with a particle size of 0.3 μm remaining in the purified exhaust gas, A radioactive dust removal system characterized by:

[0044] (Action and effect) The radioactive dust removal system of the twelfth aspect has the same effects as the first aspect.

[0045] In addition, by using a residual dust removal filter that has a particle collection rate of 99.97% or more for dust particles with a particle size of 0.3 μm that remain in the purified exhaust gas, there is an advantage that almost no radioactive dust is found in the purified exhaust gas after it passes through the residual dust removal filter.

[0046] Furthermore, by installing an exhaust purification filter before the residual dust removal filter and using this exhaust purification filter to capture most of the radioactive dust present in the exhaust, the frequency of replacing the residual dust removal filter can be reduced, which in turn reduces the costs associated with replacing and disposing of the residual dust removal filter.

[0047] It is preferable not to return the purified exhaust gas discharged from the exhaust gas purification filter to the work area. If the purified exhaust gas is returned to the work area, there is a risk that the radiation emitted from the radioactive dust remaining in the returned purified exhaust gas may cause malfunctions in the machinery in the work area or expose workers working in the work area to radiation. By not returning the purified exhaust gas to the work area, such inconveniences can be prevented. However, since the purified exhaust gas that has passed through the residual dust removal filter is clean air and contains almost no radioactive dust, there is no problem in returning the purified exhaust gas to the work area. [Effects of the Invention]

[0048] According to the present invention, it is possible to provide an exhaust purification filter that removes radioactive dust from exhaust gas containing radioactive dust generated in a work area, and that is less likely to be deteriorated by radiation from the radioactive dust. [Brief explanation of the drawings]

[0049] [Figure 1] 1 is a schematic diagram showing a radioactive dust removal system according to the present invention. [Figure 2]This is an enlarged view of the exhaust purification filter of the radioactive dust removal system, showing the state during filtration. [Figure 3] This is an enlarged view of the exhaust purification filter of the radioactive dust removal system, showing the filter being cleaned. [Figure 4] 3 is a cross-sectional view taken along the line AA in FIG. 2. [Figure 5] 5 is an enlarged view of a portion X of the exhaust purification filter in FIG. 4. [Figure 6] FIG. 2 is a perspective view illustrating an upper seal portion. [Figure 7] FIG. 4 is a perspective view illustrating a lower seal portion. [Figure 8] FIG. 1 is an image diagram showing an example of a main filter made of a plurality of metal fibers with gaps between the metal fibers. [Figure 9] FIG. 1 is a cross-sectional view showing an example of lamination of a metal fiber sheet and a metal mesh sheet. [Figure 10] FIG. 10 is a cross-sectional view showing another example of lamination of a metal fiber sheet and a metal mesh sheet. [Figure 11] 1 is a side view of the exhaust gas purification device, showing a state in which small spaces are formed by partition walls. [Figure 12] 12 is a cross-sectional view of FIG. 11 taken along line B-B. [Figure 13] 13 is a cross-sectional view similar to FIG. 12 showing another embodiment of the present invention. [Figure 14] 1 is a schematic front view of an exhaust purification device provided with a cartridge-type housing that supports an exhaust purification filter. [Figure 15] FIG. 10 is a diagram illustrating a state in which the housing is fixed to the mounting plate. [Figure 16] 16 is a cross-sectional view taken along the line XX in FIG. 15. [Figure 17] 16 is a cross-sectional view of FIG. 15 taken along the line Y-Y. [Figure 18] 16 is a cross-sectional view taken along the line XX in FIG. 15. [Figure 19] 16 is a cross-sectional view of FIG. 15 taken along the line Y-Y. [Figure 20]1 is a schematic side view of an exhaust purification device having a cartridge-type housing that supports an exhaust purification filter. [Figure 21] FIG. 10 is a schematic diagram illustrating a state in which the housing is attached to the mounting plate.

[0050] A preferred embodiment of the present invention will be described below with reference to the drawings. Note that the following description and drawings merely illustrate one embodiment of the present invention, and the contents of the present invention should not be interpreted as being limited to this embodiment.

[0051] (Radioactive Dust Removal System 1) 1 shows an example of a radioactive dust removal system 1. This removal system 1 includes an exhaust purification device 3 that removes radioactive dust from exhaust air EH containing radioactive dust generated in a work area 2, and a residual dust removal device 4 that removes radioactive dust remaining in the purified exhaust air PEH discharged from the exhaust purification device 3.

[0052] (Work Area 2) Work area 2 refers to a location where radioactive dust is present, such as a place where decommissioning work is carried out at a nuclear power plant or a room where radioactive metals are cut and reduced in volume. As shown in Figure 1, it is preferable to install an exhaust hood 6 in a location in work area 2 where there is a lot of radioactive dust, and it is preferable to use this exhaust hood 6 to actively suck in radioactive dust generated by demolition work carried out in work area 2. This suction creates a negative pressure within work area 2, preventing radioactive dust within work area 2 from being released to the outside from unintended locations. Note that suction from exhaust hood 6 can be performed, for example, by a suction fan 5 installed downstream.

[0053] (Exhaust gas purification device 3) The exhaust gas EH discharged from the work area 2 is supplied to the exhaust purification device 3 through the exhaust ventilation pipe L1. An exhaust purification filter 7 is housed inside the exhaust purification device 3. As shown in FIGS. 2 to 5, this exhaust purification filter 7 is formed in a cylindrical shape. While FIGS. 2 to 5 illustrate an example of the exhaust purification filter 7 having a circular cross-sectional shape, this is not limited to this example, and any cross-sectional shape, such as an oval, square, or hexagon, may also be used. The configuration of the exhaust purification filter 7 is not particularly limited, but it is preferable to use a metal fiber sheet (referred to as a metal fiber sheet and constituting the main filter 14 described below) formed by gathering multiple metal fibers into a sheet shape, with the metal fiber sheet sandwiched between metal mesh members (referred to as a metal mesh member and constituting the shape retention means 15 described below) on the top and bottom surfaces. The metal fibers of the metal fiber sheet may be stainless steel fibers, tungsten steel fibers, aluminum fibers, nickel fibers, titanium fibers, or the like. Of these metal fibers, it is most preferable to use stainless steel fibers (i.e., stainless steel fibers), and the following description will be given taking as an example a stainless steel fiber sheet using stainless steel fibers as the metal fibers. That is, in the following description, the term "stainless steel fiber sheet" can be read as "metal fiber sheet."

[0054] An embodiment of a stainless steel fiber sheet is shown below. The metal fiber sheet is not limited to a stainless steel fiber sheet, and may, of course, be a sheet containing tungsten steel fibers, aluminum fibers, nickel fibers, or titanium fibers. The stainless steel fiber sheet may also be a sheet formed by bending a single long stainless steel fiber multiple times. A conceptual diagram of a stainless steel fiber sheet is shown in FIG. 8. The diameter (fiber diameter) of the stainless steel fiber is preferably a nominal fiber diameter of approximately 2 to 4 μm. The fiber diameter should be selected based on the particle size distribution of the generated dust and the radiation intensity of the dust. Furthermore, to increase the removal rate of radioactive dust in the exhaust EH, the porosity of the stainless steel fiber sheet is preferably 65 to 80%. Furthermore, the performance of the exhaust purification filter 7 is preferably such that it has a particle collection rate of 90% or more for dust particles with a particle size of 0.3 μm or larger remaining in the exhaust EH.

[0055] As described above, by using stainless steel fiber as the material for the exhaust purification filter 7, it is possible to make it less susceptible to degradation due to radiation emitted from radioactive dust, thereby reducing the frequency of filter replacement. It is particularly effective at capturing high-dose radioactive dust generated during decommissioning work at nuclear power plants. Furthermore, even if sharp particles are contained in the exhaust EH from the demolition environment area, there is little risk of the filter being damaged by these particles, which also reduces the frequency of filter replacement. Furthermore, it is possible to prevent the exhaust purification filter 7 from burning and causing a fire.

[0056] The exhaust purification filter 7 may be a flat stainless steel fiber sheet simply formed into a cylindrical shape. However, to increase the filtration area, it is preferable to use a flat stainless steel fiber sheet folded into a bellows shape and then formed into a cylindrical shape, as shown in FIG. 5 . As shown in FIG. 5 , the exhaust purification filter 7 is most preferably configured with shape-retaining means 15 for protecting the main filter 14 on both sides (front and back) of the main filter 14. However, the shape-retaining means 15 may be provided on one side (front or back) of the main filter 14. The provision of this shape-retaining means 15 allows the exhaust purification filter 7 to maintain the aforementioned bellows shape. Specifically, the stainless steel fiber sheet that constitutes the main filter 14 has low shape stability, making it difficult to maintain the bellows shape without the mesh sheet that constitutes the shape-retaining means 15. However, the provision of the shape-retaining means 15 increases the shape stability of the exhaust purification filter 7, allowing it to maintain its bellows shape. Furthermore, the provision of the shape-retaining means 15 increases the strength of the exhaust purification filter 7, making it easier to withstand the pressure of compressed gas applied to the main filter 14 when cleaning it.

[0057] To enable the exhaust EH to reach the main filter 14, the shape retention means 15 is preferably a mesh sheet. Furthermore, if the mesh pores of the shape retention means 15 are small, the amount of exhaust filtration per unit time decreases and the shape retention means 15 is more likely to become clogged. Therefore, it is preferable that the size of the mesh pores of the shape retention means 15 be larger than the size of the pores of the main filter 14. Furthermore, it is preferable to use a material for the shape retention means 15 that is not easily deteriorated by radiation emitted from radioactive dust, and specifically, stainless steel or the like is preferably used.

[0058] 9 and 10 show examples of stacking the main filter 14 and shape-retaining means 15 that constitute the exhaust purification filter 7. In FIGS. 9 and 10, the terms "front side" and "upper side" refer to the outside (the side where the container 28 of the exhaust purification device 3 is located) when the exhaust purification filter 7 is attached to the exhaust purification device 3, and the terms "back side" and "lower side" refer to the inside (the side where the inner tube 8 is located) when the exhaust purification filter 7 is attached to the exhaust purification device 3. Because the main filter 14 includes a metal fiber sheet and the shape-retaining means 15 includes a metal mesh member, the exhaust purification filter 7 can also be considered a laminate of a metal fiber sheet and a metal mesh member. The main filter 14 may include a material other than a metal fiber sheet, and the shape-retaining means 15 may also include a material other than a metal mesh member. It is preferable to use a metal fiber sheet (particularly a stainless steel fiber sheet) as the main material for the main filter 14, and it is preferable to use a metal mesh member as the main material for the shape-retaining means 15. The main filter 14 may be composed solely of a metal fiber sheet, and the shape-retaining means 15 may be composed solely of a metal mesh member. In addition, in Figures 9 and 10, the thickness of each layer constituting the exhaust purification filter 7 is exaggerated and shown as thick for ease of understanding, but the actual thickness of each layer is not limited to these thicknesses.

[0059] In FIG. 9 , a three-layer structure is formed in which a shape-retaining means 15 is laminated on the front side US (outside) of the main filter 14 and also on the back side DS (inside) of the main filter 14. From the perspective of protecting the main filter 14 and from the perspective of forming the main filter 14 into a bellows shape and maintaining that bellows shape, it is most preferable to provide the shape-retaining means 15 on both sides of the main filter 14 (front side US and back side DS) as shown in FIG. 9 . However, a configuration in which the shape-retaining means 15 is provided on only one side of the main filter 14 (front side US or back side DS) may also be used. If it is not necessary to protect the main filter 14 and it is not necessary to form the main filter 14 into a bellows shape, it is possible to not provide any shape-retaining means 15 at all. If the shape-retaining means 15 is too thin, its function of protecting the main filter 14 may be reduced, while if the shape-retaining means 15 is too thick, it may increase airflow resistance and reduce the amount of exhaust purification treatment per unit time. On the other hand, if the thickness of the main filter 14 is thin, there is a risk that the radioactive dust in the exhaust EH will not be sufficiently removed, and if the thickness of the main filter 14 is thick, there is a risk that the airflow resistance will increase and the amount of exhaust purification treatment per unit time will decrease. Note that the thickness of the front-side shape retaining means 15U and the back-side shape retaining means 15B may be the same thickness, or may be different thicknesses.

[0060] The basic structure of the exhaust purification filter 7 shown in Figure 10 is the same as that shown in Figure 9, except that the main filter 14 has a three-layer structure made up of an upper main filter 14U, a middle main filter 14M, and a lower main filter 14D. When using such a three-layer structure, the fiber diameter of the stainless steel fibers in the upper main filter 14U is preferably 6 to 10 μm, the fiber diameter of the stainless steel fibers in the middle main filter 14M is preferably 2 to 4 μm, and the fiber diameter of the stainless steel fibers in the lower main filter 14D is preferably 6 to 10 μm.

[0061] When the main filter 14 has such a layered structure, the metal fibers of the middle-layer main filter 14M, which have a small fiber diameter, are most effective at removing radioactive dust and the like, but have the disadvantage of being weak due to their small fiber diameter. Therefore, by providing an upper-layer main filter 14U and a lower-layer main filter 14D made of metal fibers with a larger fiber diameter than the metal fibers of the middle-layer main filter 14M, the weak fibers of the middle-layer main filter 14M can be compensated for by the strength of the fibers of the upper-layer main filter 14U and the lower-layer main filter 14D. As a result, compared to a single-layer main filter 14 (assuming the diameter of the metal fibers constituting this single layer is the same as the metal fibers of the middle-layer main filter 14M, 2 to 4 μm), the strength of the main filter 14 can be increased, the shape stability of the main filter 14 can be improved, and the main filter 14 can more easily withstand the pressure (pressure from compressed gas) applied to the exhaust purification filter 7 during backwashing of the exhaust purification filter 7. In particular, the rear side of the main filter 14 is subjected to the greatest pressure of compressed gas during backwashing, so by increasing the pressure resistance of the lower main filter 14D, damage to the main filter 14 by the compressed gas PA can be prevented.

[0062] Furthermore, when the metal fiber diameter of the upper main filter 14U located outside the main filter 14 is large, radioactive dust and the like captured in the gaps of the upper main filter 14U located outside the main filter 14 can be more easily blown out to the outside of the main filter 14 during backwashing compared to when the metal fiber diameter of the upper main filter 14U located outside the main filter 14 is small. This has the advantage of improving the cleaning effect during backwashing.

[0063] 10 shows an example in which the main filter 14 has a three-layer structure, but it may have a four-layer or more layer structure. When using a four-layer or more layer structure, it is preferable to make the fiber diameter of the stainless steel fibers smaller toward the center of the thickness direction TD of the main filter 14, from the perspective of protecting the metal fiber layers with small fiber diameters.

[0064] It is preferable that the porosity of the single layer of main filter 14 is 65 to 80%, and that of each layer of multi-layer main filter 14 is 65 to 80%. This porosity can be calculated from the following formulas 1 and 2.

[0065] [Formula 1] P (%) = Basis weight of the main filter layer (g / m 2 ) / specific gravity of metal fiber that makes up the main filter layer × T (thickness of the main filter layer (cm)) [Formula 2] Porosity (%)=100-P(%)

[0066] The specific gravity of the metal fiber in Equation 1 is 798 when the metal fiber is stainless steel (SUS316L), for example. Furthermore, the "layer of the main filter" in Equation 1 refers to the single layer when the main filter is composed of a single layer. When the main filter is composed of multiple layers and the porosity of each layer of the main filter is to be calculated, the basis weight, metal fiber, and thickness of each layer of the main filter can be used. When the main filter is composed of multiple layers and the porosity of the entire stacked main filter is to be calculated, the basis weight, metal fiber, and thickness of the entire main filter can be used.

[0067] When manufacturing the main filter 14 made up of multiple layers, it is preferable to uniformly stack the metal fibers as raw materials and then sinter (compress and fix) the stack.

[0068] It is preferable to provide a cylindrical inner tube 8 inside the exhaust purification filter 7. A punched sheet having a plurality of openings of a predetermined size formed into a cylindrical shape can be used as this inner tube 8. The cross-sectional shape of this inner tube 8 is not particularly limited either, and any shape such as a perfect circle as shown in FIG. 4, an oval, a square, or a hexagon may be used.

[0069] When the exhaust purification filter 7 is shaped like a bellows as shown in Fig. 5, peaks 7X and valleys 7Y are generated. When the exhaust purification filter 7 is shaped like a bellows and then cylindrical as shown in Figs. 4 and 5, an imaginary line IL connecting the multiple valleys 7Y of the exhaust purification filter 7 becomes circular in cross section. It is preferable to shape the inner tube 8 in the same shape (circular) as this imaginary line IL so that the back surfaces of the multiple valleys 7Y of the exhaust purification filter 7 come into contact with the surface of the inner tube 8, and it is more preferable to shape the inner tube 8 so that the back surfaces of all the valleys 7Y of the exhaust purification filter 7 come into contact with the surface of the inner tube 8. By previously bringing the multiple valleys 7Y, 7Y into contact with the inner tube 8, it is possible to prevent the exhaust purification filter 7 and the inner tube 8 from colliding each time exhaust EH passes through the exhaust purification filter 7, thereby extending the life of the exhaust purification filter 7.

[0070] 3 and 4, the upper and lower ends of the exhaust purification filter 7 and the upper and lower ends of the inner cylinder 8 are sealed, preventing exhaust gas containing radioactive dust from taking a shortcut and entering the purified exhaust passage 13 without passing through the exhaust purification filter 7. The part that seals the exhaust purification filter 7 and the inner cylinder 8 is called a seal part 9, and in the embodiment of FIGS. 3 and 4, there is an upper seal part 9A that seals the upper end of the exhaust purification filter 7 and the upper end of the inner cylinder 8, and a lower seal part 9B that seals the lower end of the exhaust purification filter 7 and the lower end of the inner cylinder 8.

[0071] As shown in FIG. 6 , the upper seal portion 9A is formed by fixing the upper end of the exhaust purification filter 7 and the upper end of the inner tube 8 to an annular ring 20 fixed to the edge of a through-hole 19 (a hole having approximately the same size as the inner diameter of the inner tube 8) in a flange portion 7Z. Specifically, the cross section of the annular ring 20 fixed to the flange portion 7Z has a U-shaped groove with an opening at the bottom. After the upper end of the exhaust purification filter 7 and the upper end of the inner tube 8 are inserted into this groove, an adhesive is filled into the groove, thereby fixing the upper end of the exhaust purification filter 7 and the upper end of the inner tube 8 to the annular ring. In this way, the upper end of the exhaust purification filter 7 is formed integrally with the flange portion 7Z. Similarly, the lower seal portion 9B is formed by fixing a circular plate 21 to the lower end of the exhaust purification filter 7 and the lower end of the inner tube 8, as shown in FIG. 7 . Specifically, the disk 21 has an upright wall 22 that stands upward from its peripheral edge, and the cross section of the upright wall 22 has a U-shaped groove 23 that has an opening at the top. The lower end of the exhaust purification filter 7 and the lower end of the inner tube 8 are inserted into the inside of this groove 23, and then the inside of the groove 23 is filled with adhesive, thereby fixing the lower end of the exhaust purification filter 7 and the lower end of the inner tube 8 to the disk 21. Also, for the sake of visibility, the exhaust purification filter 7 and the inner tube 8 are shown as being integrated in Figures 6 and 7, but in reality they are made of separate members.

[0072] The exhaust gas purification device 3 of the present invention has a casing 50 with an exhaust gas purification filter 7 therein. The interior of the casing 50 is divided into a pre-purification chamber and a post-purification chamber, which are separated by a mounting plate 10 and the exhaust gas purification filter 7 provided on the casing 50. The mounting plate 10 has a through-hole of the same shape as the through-hole 19 in the flange portion 7Z, and the through-hole 19 in the flange portion 7Z faces the through-hole in the mounting plate 10. The flange portion 7Z is fixed to the mounting plate 10 in contact with the mounting plate 10 or via a gasket. The mounting plate 10 has an exhaust gas supply port 16 in the wall of the casing 50 facing the pre-purification chamber, through which the exhaust gas EH flows into the casing 50, and a purified exhaust gas outlet 18 in the wall of the casing 50 facing the post-purification chamber, through which the purified exhaust gas PEH flows out of the casing 50. The exhaust gas EH is configured to flow from the outside to the inside of the cylindrical exhaust gas purification filter 7. As the exhaust gas EH passes through the exhaust gas purification filter 7 from the outside to the inside, radioactive dust particles and the like in the exhaust gas EH are captured by the exhaust gas purification filter 7. The purified exhaust gas PEH, which has been purified by passing through the exhaust gas purification filter 7, passes through the openings in the inner cylinder 8 from the outside to the inside and reaches the purified exhaust passage 13. Then, in the embodiment of FIG. 2 , the purified exhaust gas PEH moves from the bottom to the top of the purified exhaust passage 13, passing through the hole in the annular ring 20 of the upper seal portion 9A, the through-hole 19 in the flange portion 7Z, and the through-hole in the mounting plate 10, and reaches the top of the exhaust gas purification device 3. The purified exhaust gas PEH is then discharged from the exhaust gas purification device 3 and sent to the residual dust removal device 4 through the purified exhaust vent pipe L2.

[0073] On the other hand, as the exhaust EH passes through the exhaust purification filter 7 from the outside to the inside, foreign matter such as radioactive dust captured by the exhaust purification filter 7 accumulates on the outer surface of the exhaust purification filter 7. If the layer of foreign matter such as radioactive dust accumulated on the outer surface becomes thick, the efficiency of the purification process for the exhaust EH decreases, so it is preferable to backwash the exhaust purification filter 7 at a predetermined timing.

[0074] For example, as shown in FIG. 3 , compressed gas PA (e.g., compressed air) is injected into the exhaust purification filter 7 from an injection nozzle 11 provided above the exhaust purification filter 7. The compressed gas PA injected from the injection nozzle 11 moves downward, enters the inside of the exhaust purification filter 7 (purified exhaust passage 13), and then flows in the opposite direction to that shown in FIG. 2 . That is, after passing through the openings of the inner cylinder 8 from the inside to the outside, the compressed gas PA passes through the exhaust purification filter 7 from the inside to the outside. As the compressed gas PA passes through the exhaust purification filter 7 in this way, a layer of foreign matter (foreign matter layer) such as radioactive dust that has accumulated on the outer surface of the exhaust purification filter 7 is peeled off, and falls and accumulates below the exhaust purification device 3. The deposits SD accumulated below the exhaust purification device 3 are periodically discharged to the outside of the exhaust purification device 3.

[0075] As described above, by backwashing the exhaust purification filter 7 at a predetermined timing, the pressure loss and collection efficiency can be returned to near their initial values, so the exhaust purification filter 7 does not need to be disposed of as a disposable item, which makes it possible to make effective use of global environmental resources and reduce the costs associated with replacing and disposing of the exhaust purification filter 7.

[0076] It is also possible to perform backwashing while the exhaust gas purification filter 7 is purifying the exhaust EH without stopping the purification process. This is because backwashing takes only a few seconds, so there is no need to stop the purification process. Furthermore, because clumps of radioactive dust and other foreign matter that detach from the exhaust gas purification filter 7 during backwashing have a certain weight, even if the exhaust gas EH is flowing toward the exhaust gas purification filter 7, the clumps of radioactive dust and other foreign matter that detach from the exhaust gas purification filter 7 are unlikely to reattach to the exhaust gas purification filter 7 due to the influence of the exhaust gas EH flow. To reliably prevent clumps of radioactive dust and other foreign matter that detach from the exhaust gas purification filter 7 from reattaching to the exhaust gas purification filter 7, it is possible to temporarily stop the exhaust gas purification process before backwashing and then resume the exhaust gas purification process after the backwashing is completed. However, performing such a process has the disadvantage of slightly reducing the amount of exhaust gas purified because it takes some time to switch between the exhaust gas purification process and the cleaning (backwashing) process.

[0077] 11 and 12, it is preferable to provide a plurality of exhaust purification filters 7 inside the exhaust purification device 3, and while one exhaust purification filter 7 is being backwashed, the exhaust EH is filtered by the other exhaust purification filter 7. For example, in the embodiment of FIGS. 11 and 12, partition walls 29 are provided that separate the internal space 26 of the exhaust purification device 3 into a plurality of small spaces, and an exhaust purification filter 7 is provided in each small space.

[0078] More specifically, as shown in FIG. 11 , the upper end of a partition wall 29 is fixed to the lower surface of the mounting plate 10 of the exhaust purification device 3, and the partition wall 29 extends downward therefrom, with the lower end of the partition wall 29 positioned near the lower end of the exhaust purification filter 7. It is preferable that the lower end of the partition wall 29 be positioned near the lower end of the exhaust purification filter 7 to prevent the compressed gas PA from directly colliding with the exhaust purification filter 7 disposed in another small space 27 during backwashing. As shown in FIG. 12 , the partition wall 29 is attached so as to separate adjacent exhaust purification filters 7. It is preferable that the partition wall 29 not abut against the inner wall of the container 28 of the exhaust purification device 3, but rather that a predetermined gap be provided between the inner wall of the container 28 and the partition wall 29. Similarly, as shown in FIG. 11 , it is preferable that the partition wall 29 not extend further below the lower end of the exhaust purification filter 7, but rather that a predetermined gap be provided below the partition wall 29. This is because, during the exhaust gas purification process, the exhaust gas EH that has entered the container 28 of the exhaust gas purification device 3 can easily pass through the gaps and enter the small spaces 27A, 27B.

[0079] The partition wall 29 attached in this manner divides the internal space 26 of the exhaust purification device 3 into two almost equal parts, forming a first small space 27A and a second small space 27B. A first exhaust purification filter 7A is provided in the first small space 27A, and a second exhaust purification filter 7B is provided in the second small space 27B.

[0080] By dividing the internal space 26 of the exhaust gas purification device 3 with the partition wall 29 in this way, it is possible to prevent the compressed gas PA injected from the injection unit (nozzle 11) toward the exhaust gas purification filter 7 arranged inside one small space 27 from directly colliding with the exhaust gas purification filter 7 arranged in another adjacent small space 27. As a result, the compressed gas PA used when backwashing the exhaust gas purification filter 7 arranged in one small space 27 is less likely to affect the exhaust gas purification filter 7 arranged in the other small space 27. In other words, when the exhaust gas EH is purified using the exhaust gas purification filter 7 arranged in one small space 27 while the exhaust gas purification filter 7 arranged in the other small space 27 is being backwashed, the compressed gas PA is less likely to have an adverse effect on the exhaust gas purification filter 7 that is undergoing purification processing. Therefore, even while some of the exhaust gas purification filters 7 are being washed, the other exhaust gas purification filters 7 can perform exhaust gas purification processing as usual, which has the advantage of less reduction in the efficiency of exhaust gas purification processing in the entire exhaust gas purification device 3.

[0081] 11 and 12 show a state in which exhaust purification processing is performed by the first exhaust purification filter 7A arranged in the first small space 27A while the second exhaust purification filter 7B arranged in the second small space 27B is being backwashed. Of course, contrary to the example shown, exhaust purification processing may also be performed by the second exhaust purification filter 7B while the first exhaust purification filter 7A is being backwashed.

[0082] 11 and 12 show examples in which only one partition wall 29 is provided, but it is also possible to provide a plurality of partition walls 29. For example, as shown in Fig. 13, by providing partition walls 29 in a cross shape in the internal space 26 of the exhaust purification device 3, four small spaces 27, a first small space 27A to a fourth small space 27D, may be formed, and a first exhaust purification filter 7A to a fourth exhaust purification filter 7D may be arranged in each of the small spaces 27A to 27D, respectively.

[0083] (Residual dust removal device 4) The residual dust removal device 4 has a residual dust removal filter that removes radioactive dust remaining in the purified exhaust gas PEH. The performance of this residual dust removal filter preferably has a particle collection rate of 99.97% or more for dust particles with a particle size of 0.3 μm remaining in the purified exhaust gas PEH.

[0084] Specifically, the residual dust removal filter may be, for example, a HEPA filter (an air filter with a particle collection rate of 99.97% or more for particles with a particle diameter of 0.3 μm at the rated air flow rate and an initial pressure loss of 245 Pa or less), or a ULPA filter (an air filter with a particle collection rate of 99.9995% or more for particles with a particle diameter of 0.15 μm at the rated air flow rate and an initial pressure loss of 245 Pa or less).

[0085] If a dust removal filter is used that does not have a particle collection efficiency of 99.97% or more for dust particles with a particle size of 0.3 μm in the purified exhaust PEH, there is a problem that a large amount of radioactive dust may be mixed into the purified exhaust PEH discharged from the dust removal device 4.

[0086] (Alternative filter 7) The following embodiment is also preferable as the exhaust purification device 3 according to the present invention. Specifically, in this embodiment, the exhaust purification device 3 is provided with a mounting plate 110 and has a housing 34 that supports the exhaust purification filter 7, the housing 34 having an upper plate 34u to which the exhaust purification filter 7 is fixed, a front plate 34f, a rear plate 34b that is disposed at an interval relative to the front plate 34f, and side plate portions 34s, 34s ​​(for example, two side plate portions that face each other at an interval) that connect the sides of the front plate 34f and the rear plate 34b, and the upper edge of the front plate 34f, the upper edge of the rear plate 34b, and the upper edges of the side plate portions 34s, 34s ​​are each connected to the upper plate portion 34u, forming a box shape that is open at the bottom, and the housing 34 is fixed to the mounting plate 110. In the exhaust gas purification device 3 to which the housing 34 is fixed, exhaust gas EH flows into the exhaust gas purification device 3 through an exhaust gas supply port 16 provided in the casing 50 of the exhaust gas purification device 3, enters the internal space 39 of the housing 34 from below, passes through the exhaust gas purification filter 7, becomes purified exhaust gas PEH, and is discharged to the outside of the exhaust gas purification device 3 through the purified exhaust gas outlet 18. The housing 34 is fixed to a mounting plate 110 provided on the casing 50, and this mounting plate 110 and the exhaust gas purification filter 7 divide the interior of the casing 50 into a pre-purification chamber and a post-purification chamber. The exhaust gas EH passes from the pre-purification chamber through the exhaust gas purification filter 7 to reach the post-purification chamber, but there is no other flow path from the pre-purification chamber to the post-purification chamber. The internal space 39 of the housing 34 refers to the box-shaped interior surrounded by the top plate 34u, front plate 34f, rear plate 34b, and side plate portions 34s, 34s ​​that make up the housing 34.

[0087] The shape of the surfaces of the front plate portion 34f, rear plate portion 34b, and side plate portions 34s, 34s ​​that form the housing 34, facing the internal space 39, may be curved or flat, but if the internal space 39 is a truncated cone as described below, it is preferable that it be flat.

[0088] The exhaust purification filter 7 can be fixed to the upper plate portion 34u of the housing 34 in the following manner: A flange portion is provided at the upper end of the exhaust purification filter 7, and the flange portion is fixed to the periphery of the through-hole in the upper plate portion 34u. The flange portion of the exhaust purification filter 7 and the upper plate portion 34u of the housing 34 can be fixed and sealed with an adhesive or welding to prevent gas from passing between them.

[0089] The number of exhaust purification filters 7 supported by the housing 34 may be adjusted appropriately depending on the volume of the work area where the exhaust purification device 3 is installed, the amount of floating dust, etc., and is not particularly limited.

[0090] As shown in FIGS. 16 to 19, the shape of the internal space 39 formed by the members that make up the housing 34 may be a rectangular parallelepiped, but may also be a truncated cone as follows. For example, the internal space 39 of the housing 34 has the shape of a truncated cone, and when the perimeter formed by the lower edge of the front plate portion 34f, the lower edge of the rear plate portion 34b, and the lower edges of the side plate portions 34s, 34s ​​(e.g., the perimeter of an approximately square) is defined as the perimeter of the lower surface of the truncated cone, and the perimeter of the upper plate portion 34u is defined as the perimeter of the upper surface of the truncated cone, the perimeter formed by the lower edge of the front plate portion 34f, the lower edge of the rear plate portion 34b, and the lower edges of the side plate portions 34s, 34s ​​is longer than the perimeter of the upper plate portion (e.g., the perimeter of an approximately square) (e.g., a square pyramid), that is, a form in which the upper plate portion side of the internal space 39 of the housing 34 becomes the upper surface of the truncated cone, and the lower edge side of the internal space 39 becomes the lower surface of the truncated cone. In this configuration, the surfaces of the front plate 34f, the rear plate 34b, and the side plate portions 34s, 34s ​​that face the internal space 39 (the surfaces on the internal space 39 side) are arranged at an angle with respect to the vertical line, so that radioactive dust is less likely to adhere to the surfaces on the internal space 39 side, and even if it does adhere, it is easily detached in the continuing flow of radioactive dust. This makes it possible to prevent the housing 34 from being highly contaminated with radioactive dust.

[0091] In a configuration in which the upper plate side of the internal space 39 of the housing 34 is the upper surface of the truncated cone and the lower edge side of the internal space 39 is the lower surface of the truncated cone, the acute angle θ formed by a normal line Lf5 extending from a surface of the front plate 34f that forms the internal space 39 and faces the internal space 39 (i.e., the inner surface 34f1 of the front plate 34f) and a vertical line L6 that intersects with the normal line Lf5 is, for example, preferably less than 90° and not less than 80°, more preferably not more than 87° and not less than 85°, and particularly preferably 87°. Similarly, the acute angle θ formed by a normal line Lb5 extending from the inner surface 34b1 of the rear plate 34b and a vertical line L6 that intersects with the normal line Lf5 is, for example, preferably less than 90° and not less than 80°, more preferably not more than 87° and not less than 85°, and particularly preferably 87°. Similarly, the acute angle θ formed by a normal line Ls15 extending from the inner surface 34s1 of the first side plate portion 34s and a vertical line L6 intersecting the normal line Ls15 is, for example, preferably less than 90° and not less than 80°, more preferably not more than 87° and not less than 85°, and particularly preferably 87°. Similarly, the acute angle θ formed by a normal line Ls25 extending from the inner surface 34s2 of the second side plate portion 34s and a vertical line L6 intersecting the normal line Ls25 is, for example, preferably less than 90° and not less than 80°, more preferably not more than 87° and not less than 85°, and particularly preferably 87°.

[0092] The truncated cone may be a truncated cone, a truncated polygonal pyramid, or a truncated square pyramid, but in consideration of the ease of attachment and detachment of the housing 34, a truncated square pyramid is particularly preferable.

[0093] The material of the housing 34 is not particularly limited, but is preferably a metal, such as stainless steel, tungsten, aluminum, nickel, or titanium, with stainless steel being particularly suitable. Metals are preferred because they have strength and radiation resistance.

[0094] The casing 34 supporting the exhaust purification filter 7 has a cartridge-type structure, and can be fixed to the mounting plate 110 of the exhaust purification device 3 so as to be attachable and detachable. If the exhaust purification device 3 is operated and decommissioning work or the like is continued, radioactive materials may gradually adhere to the exhaust purification filter 7, or the exhaust purification filter 7 may become clogged, even if the exhaust purification device 3 is periodically backwashed. In this case, the exhaust purification filter 7 will need to be replaced, but if the casing 34 has a cartridge-type structure and is attachable and detachable, then in the replacement work, the worker only needs to replace the entire casing, which is easy to work with and reduces exposure to radioactive materials.

[0095] 15 and 21, the housing 34 may be provided with, for example, a housing-side receiving portion 41 extending upward from the upper plate portion 34u so that the housing 34 can be fixed to the mounting plate 110. The shape of the housing-side receiving portion 41 is not particularly limited, but a preferred shape is a square tube formed by connecting, for example, a member extending further upward from the upper end of the front plate portion 34f of the housing 34, a member extending further upward from the upper end of the rear plate portion 34b, and members extending further upward from the upper ends of the side plate portions 34s, 34s.

[0096] On the other hand, a plate-side receiving portion 110a of substantially the same shape as the housing-side receiving portion 41 is provided on the underside of the mounting plate 110, facing the housing-side receiving portion 41 (if the housing-side receiving portion 41 is rectangular cylindrical, the plate-side receiving portion 110a should also be cylindrical). The housing-side receiving portion 41 and the plate-side receiving portion 110a form a pair, and are removably fixed together with the upper edge of the housing-side receiving portion 41 and the lower edge of the plate-side receiving portion 110a in contact. In addition, a gasket 33 may be interposed between the housing-side receiving portion 41 and the plate-side receiving portion 110a to improve sealing performance. In this case, the gasket 33 is preferably provided on the lower edge of the plate-side receiving portion 110a.

[0097] A through-hole 110b is provided in the portion of the mounting plate 110 surrounded by the plate-side receiving portion 110a. This through-hole 110b is provided so that the purified exhaust gas PEH that has passed through the exhaust purification filter 7 from the internal space of the housing 34 and flowed into the purified exhaust passage 13 flows into the space above the mounting plate 110.

[0098] On the other hand, a support member 36 is provided below the housing 34 to support the housing 34 so that the housing-side receiving portion 41 and the plate-side receiving portion 110a are maintained in opposing contact with each other. The support member 36 is movable up and down, and the height of the support member 36 itself is adjustable, providing a mechanism for adjusting the height of the housing 34 placed on the support member 36. The height of the support member 36 can be adjusted by height adjustment means 37 connected to the support member 36. The height adjustment means 37 is not particularly limited as long as it can adjust the height of the support member 36, but examples include a means equipped with an eccentric cam mechanism or a jack mechanism such as a floor jack or a pantograph jack. The height adjustment means 37 may be provided in the casing 50.

[0099] When attaching the housing 34 to the mounting plate 110, the housing 34 is placed on the support member 36, and the support member 36 is then moved upward until the housing side receiving portion 41 contacts the plate side receiving portion 110a.On the other hand, when removing the housing 34 from the mounting plate 110, the support member 36 is moved downward.

[0100] The housing-side receiving portion 41 and the plate-side receiving portion 110a are paired, and it is desirable that they have the same shape to maintain airtightness. However, as shown in Figures 18 and 19, the shape of the internal space 39 of the housing 34 is a truncated cone, and therefore the perimeter of the upper plate portion 34u of the housing 34 may be shorter than the perimeter of the plate-side receiving portion 110a. In this case, it is preferable to extend the entire edge of the upper plate portion 34u radially so that the edge of the upper plate portion 34u extends outward beyond the upper edge of the front plate portion 34f, the upper edge of the rear plate portion 34b, and the upper edges of the side plate portions 34s and 34s, and then provide the housing-side receiving portion 41 on the outer surface of the expanded upper plate portion 34u. Of course, the degree of expansion of the upper plate portion 34u need only be such that the housing-side receiving portion 41 can be provided on the outer surface of the upper plate portion 34u.

[0101] The used housing 34 removed from the mounting plate 110 is removed from the casing 50 of the exhaust purification device 3, a new housing 34 is placed inside the casing 50, and attached to the mounting plate 110, and then operation of the exhaust purification device 3 can be resumed.

[0102] An opening 35 for inserting and removing the housing 34 and a door 38 for closing the opening 35 are provided in the wall of the casing 50 on the side of the purification front chamber. The door 38 is kept closed while the exhaust gas purification device 3 is operating.

[0103] A bag 31 for storing the used casing 34 removed from the casing 50 is provided in the opening 35. The opening of the bag 31 is provided contiguous with the opening 35, and the inside of the casing 50 and the inside of the bag 31 form a single, sealed space, so that the atmosphere inside the casing 50 does not leak out of the bag 31. The work of removing the casing 34 with the used exhaust purification filter 7 fixed thereto from the casing 50 and the work of putting the casing 34 with a new exhaust purification filter 7 fixed thereto into the casing 50 is preferably performed using the so-called bag-in / bag-out method, as this avoids worker exposure.

[0104] Preferred embodiments of the present invention will be described below.

[0105] (Appendix 1) An exhaust purification device equipped with an exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, the exhaust purification filter is cylindrical, and radioactive dust in the exhaust gas is captured by the exhaust purification filter as the exhaust gas passes from the outside to the inside of the exhaust purification filter, and the purified exhaust gas passes through the inside of the cylinder of the exhaust purification filter and is discharged to the outside of the exhaust purification filter, The exhaust purification device is provided with a mounting plate, a housing for supporting the exhaust purification filter; The housing has an upper plate portion to which the exhaust purification filter is fixed, a front plate portion, a rear plate portion disposed at a distance from the front plate portion, and side plate portions connecting the sides of the front plate portion and the rear plate portion, and is a box-shaped housing with an open bottom, in which the upper edge of the front plate portion, the upper edge of the rear plate portion, and the upper edges of the side plate portions are each connected to the upper plate portion, The housing is fixed to the mounting plate. An exhaust gas purification device characterized by:

[0106] (Appendix 2) The internal space of the housing is When the shape of the truncated cone is such that the perimeter defined by the lower edge of the front plate portion, the lower edge of the rear plate portion, and the lower edge of the side plate portion is the perimeter of the lower surface of the truncated cone, and the perimeter of the upper plate portion is the perimeter of the upper surface of the truncated cone, The perimeter defined by the lower end edge of the front plate portion, the lower end edge of the rear plate portion, and the lower end edges of the side plate portions is longer than the perimeter of the upper plate portion. 2. The exhaust purification device according to claim 1.

[0107] (Appendix 3) The housing in which the exhaust purification filter is supported has a cartridge structure and is fixed to the mounting plate so as to be attachable and detachable, The housing is removably mounted in a casing of the exhaust purification device. 2. The exhaust purification device according to claim 1. [Explanation of symbols]

[0108] 1: Radioactive dust removal system, 2: Work area, 3: Exhaust purification device, 4: Residual dust removal device, 5: Suction fan, 6: Exhaust hood, 7: Exhaust purification filter, 7A: First exhaust purification filter, 7B: Second exhaust purification filter, 7C: Third exhaust purification filter, 7D: Fourth exhaust purification filter, 7X: Peak portion, 7Y: Valley portion, 7Z: Flange portion, 8: Inner cylinder, 9: Seal portion, 9A: Upper seal portion, 9B: Lower seal portion, 10: Mounting plate, 11: Injection nozzle, 12: Compressed gas supply pipe, 13: Purified exhaust passage, 14: Mesh In-filter, 14U: surface main filter (upper main filter), 14M: middle main filter, 14D: back main filter (lower main filter), 15: shape retention means, 15U: surface shape retention means (upper shape retention means), 15D: back shape retention means (lower shape retention means), 16: exhaust supply port, 17: metal fiber, 18: purified exhaust outlet, 19: through hole, 20: annular ring, 21: disk, 22: standing wall, 23: groove, 24: deposit outlet, 25: residual dust removal filter, 26: internal space, 27: small space, 27A: first small space, 27B: second small space, 27C: third small space, 27D: fourth small space, 28: container of exhaust purification device, 29: partition wall, 31: bag, 33: gasket, 34: housing, 34u: upper plate portion of housing, 34f: front plate portion of housing, 34f1: inner surface of front plate portion of housing, 34b: rear plate portion of housing, 34b1: inner surface of side plate portion of housing, 34s: side plate portion of housing, 34s1, 34s2: inner surfaces of side plate portions of housing, 35: opening, 36: support member, 37: height adjustment means, 38: door, 39: housing Internal space, 40: through hole, 41: housing side receiving portion, 50: casing, 110: mounting plate, 110a: plate side receiving portion, 110b: through hole, IL: imaginary line, EH: exhaust, Lf5: (imaginary) normal line extending from the inner surface of the front plate portion, inner surface of the rear plate portion, Lb5: (imaginary) normal line extending from the inner surface of the rear plate portion, Ls15, Ls25: (imaginary) normal lines extending from the inner surfaces of the side plate portions 34s, 34s, respectively, L6: vertical line, PEH: purified exhaust, PA: compressed gas, SD: deposits, US: front side (upper side), DS: back side (lower side), TD: thickness direction

Claims

1. An exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, the exhaust purification filter has a cylindrical shape, and radioactive dust in the exhaust gas is captured by the exhaust purification filter as the exhaust gas passes from the outside to the inside of the exhaust purification filter, and the purified exhaust gas passes through the inside of the cylinder of the exhaust purification filter and is discharged to the outside of the exhaust purification filter, The exhaust purification filter has a stainless steel metal fiber sheet having voids and a metal mesh sheet positioned as a layer on at least one side of the stainless steel metal fiber sheet, and These are laminated and compressed and fixed, and then folded in an accordion-like shape to form the cylindrical shape. the voids of the mesh of the metal mesh sheet are larger than the voids of the metal fiber sheet, The metal mesh sheet constitutes a shape retention means for the metal fiber sheet. An exhaust purification filter characterized by:

2. 2. The exhaust gas purification filter according to claim 1, wherein the metal fiber sheet comprises a surface layer sheet, an intermediate layer sheet, and a back layer sheet, which are laminated and fixed by pressure bonding.

3. The back layer sheet of the metal fiber sheet is located on the inner side of the exhaust purification filter, and the fiber diameter of the back layer sheet is larger than the fiber diameter of the intermediate layer sheet. The exhaust gas purification filter according to claim 2.

4. An exhaust gas purification device equipped with an exhaust gas purification filter and backwashing means for removing radioactive dust from exhaust gas containing radioactive dust generated in a work area, the exhaust purification filter is cylindrical, and in the process of the exhaust passing from the outside to the inside of the exhaust purification filter, radioactive dust in the exhaust is captured by the exhaust purification filter, and the purified exhaust passes through the inside of the cylinder of the exhaust purification filter and is discharged to the outside of the exhaust purification filter, The exhaust purification filter has a stainless steel metal fiber sheet having voids and a metal mesh sheet positioned as a layer on at least one side of the stainless steel metal fiber sheet, and These are laminated, compressed and fixed, and then folded into a bellows shape to form a cylindrical shape. the voids of the mesh of the metal mesh sheet are larger than the voids of the metal fiber sheet, The metal mesh sheet constitutes a shape retention means for the metal fiber sheet. An exhaust gas purification device characterized by:

5. The backwashing means is an injection unit provided with an injection nozzle that injects compressed air into a cylinder of the exhaust purification filter, 5. The exhaust purification device according to claim 4, wherein an axial direction of the injection nozzle is the same as an axial direction of the exhaust purification filter.

6. 5. The exhaust gas purification device according to claim 4, wherein the metal fiber sheet comprises a surface layer sheet, an intermediate layer sheet, and a back layer sheet, which are laminated and fixed by pressure bonding.

7. The back layer sheet of the metal fiber sheet is located on the inner side of the exhaust purification filter, and the fiber diameter of the back layer sheet is larger than the fiber diameter of the intermediate layer sheet. The exhaust gas purification filter according to claim 6.

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