Exhaust cleaning filter and exhaust cleaning device

Abstract

To provide an exhaust cleaning filter which is unlikely to deteriorate by radiation from radioactive dusts.SOLUTION: An exhaust cleaning filter 7 is cylindrical, wherein radioactive dusts in exhaust air EH are captured by the exhaust cleaning filter 7 and purified exhaust air PEH is exhausted outside the exhaust cleaning filter 7 through a cylinder of the exhaust cleaning filter 7 in a process that the exhaust air EH passes from the outside of the exhaust cleaning filter 7 to the inside. The exhaust cleaning filter 7 has a main filter. The main filter includes a sheet of metal fiber. The exhaust cleaning filter 7 can be washed. In a step of washing the exhaust cleaning filter 7, compressed air jetted into the cylinder of the exhaust cleaning filter 7 passes from the inside of the exhaust cleaning filter 7 to the outside. In that process, the radioactive dusts captured by the exhaust cleaning filter 7 are blown off outside the exhaust cleaning 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 gas to obtain purified exhaust gas, 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] During decommissioning work at nuclear power plants and nuclear facilities, large amounts of radioactive dust (dust containing radioactivity or dust carrying radiation; the same applies below) are generated. Large amounts of radioactive dust can lead to exposure of decommissioning workers and the risk of radioactive contamination spreading outside the decommissioning work area. For this reason, 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 a site, 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, this high-performance filter is prone to clogging as it processes dust particles of various sizes, and must be replaced frequently. This ultimately results in an increase in radioactive waste. Since it is problematic from the standpoint of radiation exposure for people to approach a high-performance filter that has captured a large amount of radioactive dust, it is desirable to minimize the frequency of filter replacement.

[0004] Techniques for removing radioactive dust from exhaust gas are disclosed in Patent Documents 1 and 2 below.

[0005] The secondary product recovery and processing 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-shaped pre-filter to increase the filtering area and extend the life of the filter. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2003-185794 A [Patent Document 2] JP 2000-300926 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the secondary product recovery processing system of Patent Document 1, it is not clear what type of filter is used as the filter installed in the upstream of the circulation line. If a general filter made of polyester resin or the like is used as this filter, it has low resistance to radiation and is easily deteriorated.

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

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

[0011] In the dust cartridge filter of Patent Document 2, a filter in the hollow cylindrical filter body is made of glass fiber filter paper sandwiched between supporting media (polyester resin) on both sides, and a nonwoven fabric is used as a plate-shaped prefilter portion.

[0012] However, the filter using polyester resin or the like as in Patent Document 2 has 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 gas 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 for removing radioactive dust from exhaust 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 an interior 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 is injected into a cylinder of the exhaust purification filter, passes from the inside to the outside of the exhaust purification filter, and in the process, blows off radioactive dust captured by the exhaust purification filter 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 contains a metal fiber sheet, the exhaust purification filter is less susceptible to deterioration due to radiation emitted from radioactive dust in the exhaust.

[0017] In addition, since there is a risk of exposure during the replacement of an exhaust purification filter to which radioactive dust has adhered, it is preferable to avoid replacing the exhaust purification filter as much as possible, but 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 ability of the exhaust purification filter decreases, the exhaust purification filter can be regenerated by backwashing with compressed gas, so that it is not necessary to replace the exhaust purification filter every time a large amount of radioactive dust or the like adheres to the exhaust purification filter, and it is not necessary to replace the exhaust purification filter for a long period of time. Therefore, it is possible to prevent exposure of workers involved in the replacement of the exhaust purification filter and the generation of a large amount of radioactive waste (used exhaust purification filters). In addition, it is also possible to reduce the cost of stopping the purification process of the exhaust gas due to the replacement of the filter and the cost of replacing and disposing of the exhaust purification filter.

[0018] It has been found that when cleaning the exhaust purification filter, applying compressed gas to the inside of the exhaust purification filter for cleaning is more effective at removing radioactive waste adhering to the exhaust purification filter than applying compressed gas to the outside of the exhaust purification filter for cleaning. Therefore, by so-called backwashing of the exhaust purification filter as in the first embodiment, 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 fine particles are contained in the exhaust from the work area, the exhaust purification filter is unlikely to be damaged by the fine particles because the main fill of the exhaust purification filter contains a metal fiber sheet. Also, even if sparks that could cause a fire are contained in the exhaust from the work area, a fire is unlikely to break out because the main fill of the exhaust purification filter contains a metal fiber sheet.

[0020] (Second Aspect) The exhaust purification filter has a shape retaining means for retaining the shape of the main filter, The shape retention means includes a metal mesh member, The exhaust purification filter of the first aspect is obtained 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 the second aspect, the exhaust purification filter is configured such that shape retention means including a metal mesh member is laminated on the front and back sides of the 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 retain its shape. That is, since it is difficult to retain the shape with only the metal fiber sheet, it is preferable to laminate the shape retention means including the metal mesh member as in the second aspect. Furthermore, by providing the shape retention means including the metal mesh member, the strength of the exhaust purification filter can be increased, and as a result, it becomes easier to withstand the pressure (pressure due to compressed gas) applied to the exhaust purification filter when backwashing the exhaust purification filter.

[0022] Furthermore, if a shape retention means including a metal mesh member is not provided, it is difficult to form the 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 retention 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 is increased, which has the advantage that the amount of exhaust purification processing per unit time can be increased without increasing the size of the container that houses the exhaust purification filter (the container of the exhaust purification device).

[0024] (Third Aspect) The main filter comprises: The exhaust purification filter has a laminated structure including a surface layer located on the outside of the exhaust purification filter, a back layer located on the inside of the exhaust purification filter, and an intermediate layer located 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, and the fiber diameter of the metal fibers of the surface layer and the back layer is larger than that of the metal fibers of the intermediate layer. In this case, the metal fibers of the intermediate layer, which have a small fiber diameter, can best remove radioactive dust, etc., but have the disadvantage of being weak in strength due to their small fiber diameter. Therefore, by providing a surface layer and a back layer made of metal fibers with a larger fiber diameter than the metal fibers of the intermediate layer, the weakness of the fibers of the intermediate layer can be compensated for by the strength of the fibers of the surface layer and the back layer. As a result, compared to a case in which the main filter is made into a single layer (the fiber diameter of the metal fibers constituting this single layer is assumed to be the same as that of the metal fibers of the intermediate layer), the strength of the main filter can be increased, the shape stability of the main filter can be improved, and the exhaust purification filter can be easily withstood the pressure (pressure due to compressed gas) applied to the exhaust purification filter during backwashing of the exhaust purification filter. In particular, the back layer of the main filter is subjected to the most compressed gas pressure during backwashing, and by increasing the pressure resistance of the back layer, damage to the main filter caused by compressed gas can be prevented.

[0026] In addition, when the metal fiber diameter of the layer located on the outside of the main filter is large, radioactive dust and the like captured 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. Therefore, there is also the advantage that the cleaning effect during backwashing is improved.

[0027] Furthermore, by forming the main filter in a laminated structure, it is possible to reduce variations in performance between main filters when a plurality of main filters are manufactured, and it is possible to stabilize the performance of the main filter.

[0028] As in the second embodiment, a 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 the compressed gas during backwashing.

[0029] (Fourth aspect) The main filter is made of multiple layers, The exhaust purification filter according to the first aspect, wherein a fiber diameter of the metal fibers in a layer positioned on an outer side of the exhaust purification filter is larger than a fiber diameter of the metal fibers in a layer positioned on an inner side 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 and the like captured in the voids of the layer located on the outside of the main filter can be 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. Therefore, there is an advantage in that the cleaning effect during backwashing is improved.

[0031] (Fifth aspect) An exhaust purification device having an exhaust purification filter for removing radioactive dust from exhaust 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 an interior 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, 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 includes: 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 an axial direction of the injection nozzle is the same as an 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 (the 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 high cleaning effect for 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 includes: Partition walls that divide the internal 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, 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 arranged inside some of the small spaces from directly colliding with the exhaust purification filter arranged inside another adjacent small space.

[0036] (Action and effect) In a seventh aspect, a partition wall is provided in the exhaust gas purification device. This partition wall can prevent compressed gas injected from the injection part toward an exhaust gas purification filter arranged inside one of the small spaces from directly colliding with an exhaust gas purification filter arranged inside another adjacent small space. As a result, it is possible to prevent compressed gas used when backwashing an exhaust gas purification filter arranged in one of the small spaces from colliding with an exhaust gas purification filter arranged in another small space, thereby preventing a negative effect on the purification process of exhaust gas by the exhaust gas purification filter arranged in the other small space.

[0037] (Eighth aspect) The exhaust purification device is provided with a mounting plate, A housing for supporting the exhaust purification filter is provided. 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 a side plate portion connecting sides of the front plate portion and the rear plate portion, and has a box shape with an open bottom, in which an upper end edge of the front plate portion, an upper end edge of the rear plate portion, and an upper end edge of the side plate portion 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) In the backwashing stage, the radioactive dust adhering to the outer surface of the exhaust purification filter is blown out of the exhaust purification filter by the pressure of the injected compressed gas, but since the housing is provided, most of the blown out radioactive dust scatters within the inner wall of the housing and falls as it is. Therefore, the radioactive dust 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 end edge of the front plate portion, the lower end edge of the rear plate portion, and the lower end 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 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 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 walls 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 type structure and is fixed to the mounting plate so as to be attachable and detachable, The housing is capable of being inserted and removed from a casing of the exhaust purification device.

[0042] (Action and effect) Since the exhaust purification filter has a cartridge structure, when dust trapped in the exhaust purification filter of the exhaust purification device accumulates inside the exhaust purification filter and the pressure loss of the exhaust purification filter becomes large, the exhaust purification 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 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 an interior 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 step of cleaning the exhaust purification filter, in which compressed air is injected into a cylinder of the exhaust purification filter and passes from the inside to the outside of the exhaust purification filter, and radioactive dust captured by the exhaust purification filter is blown off to the outside of the exhaust purification filter, The residual dust removal device includes: The purified exhaust gas has a residual dust removal filter having a particle collection rate of 99.97% or more for dust particles having a particle size of 0.3 μm remaining in the purified exhaust gas. A radioactive dust removal system comprising:

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

[0045] In addition, by using a 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 remaining 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 dust removal filter.

[0046] Furthermore, by installing an exhaust purification filter in front of 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, the machines in the work area may break down or workers working in the work area may be exposed to radiation due to radiation emitted from the radioactive dust remaining in the returned purified exhaust gas. 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. Effect 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 susceptible to deterioration due to radiation from the radioactive dust. [Brief description of the drawings]

[0049] [Figure 1] 1 is a schematic diagram showing a radioactive dust removal system according to the present invention. [Diagram 2]An enlarged view of the exhaust purification filter of the radioactive dust removal system, showing the state during filtration. [Diagram 3] An enlarged view of the exhaust purification filter of the radioactive dust removal system, showing the state during cleaning. [Figure 4] 3 is a cross-sectional view taken along line AA in FIG. 2. [Diagram 5] 5 is an enlarged view of a portion X of the exhaust purification filter in FIG. 4. [Figure 6] FIG. 4 is a perspective view for explaining an upper seal portion. [Figure 7] FIG. 4 is a perspective view for explaining 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 having gaps between the metal fibers. [Figure 9] FIG. 2 is a cross-sectional view showing an example of lamination of a metal fiber sheet and a metal mesh sheet. [Figure 10] FIG. 11 is a cross-sectional view showing another example of lamination of a metal fiber sheet and a metal mesh sheet. [Figure 11] 4 is a side view of the exhaust purification device, showing a state in which small spaces are formed by partition walls. FIG. [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 having a cartridge-type housing that supports an exhaust purification filter. [Figure 15] FIG. 13 is a diagram illustrating a state in which the housing is fixed to the mounting plate. [Figure 16] XX cross-sectional view of Figure 15. [Figure 17] 16 is a cross-sectional view of FIG. 15 taken along the line YY. [Figure 18] XX cross-sectional view of Figure 15. [Figure 19] 16 is a cross-sectional view of FIG. 15 taken along the line YY. [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] 11 is a schematic diagram showing a state in which the housing is attached to the mounting plate. FIG.

[0050] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that the following description and the drawings merely show 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 that contains 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) The work area 2 refers to a place where radioactive dust is present, such as a place where decommissioning work is carried out at a nuclear power plant, or a room for cutting and reducing the volume of radioactive metals. As shown in FIG. 1, it is preferable to provide an exhaust hood 6 in a place where there is a lot of radioactive dust in the work area 2, and it is preferable to actively suck in the radioactive dust generated by dismantling work carried out in the work area 2 using this exhaust hood 6. This suction creates a negative pressure in the work area 2, and prevents the radioactive dust in the work area 2 from being released to the outside from unintended places. Suction from the exhaust hood 6 can be performed, for example, by a suction fan 5 provided at the rear.

[0053] (Exhaust gas purification device 3) The exhaust EH discharged from the working 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. Although Figs. 2 to 5 show an example of the exhaust purification filter 7 having a perfect circular cross-sectional shape, the cross-sectional shape is not limited to this example, and any shape such as an elliptical, rectangular, or hexagonal cross-sectional shape may be used. The configuration of the exhaust purification filter 7 is not particularly limited, but it is preferable to use a metal fiber sheet (called a metal fiber sheet, constituting the main filter 14 described later) formed by collecting a plurality of metal fibers into a sheet shape, and a metal mesh member (called a metal mesh member, constituting the shape retention means 15 described later) sandwiched on the upper and lower surfaces of the metal fiber sheet. Note that, as the metal fibers of the metal fiber sheet, stainless steel fibers, tungsten steel fibers, aluminum fibers, nickel fibers, titanium fibers, etc. can be used. 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 the stainless steel fiber sheet is shown below. The metal fiber sheet is not limited to the stainless steel fiber sheet, and may be a sheet containing tungsten steel fiber, aluminum fiber, nickel fiber, or titanium fiber. The stainless steel fiber sheet may be a sheet formed by bending one long stainless steel fiber many times. A conceptual diagram of the stainless steel fiber sheet is shown in FIG. 8. The diameter (fiber diameter) of the stainless steel fiber is preferably about 2 to 4 μm, and the fiber diameter may be selected based on the particle size distribution of the generated dust and the radiation intensity of the dust. In addition, in order 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%. 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 more 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 not easily deteriorated by radiation emitted from radioactive dust, and therefore the frequency of filter replacement can be reduced. In particular, it is excellent for collecting high-dose radioactive dust generated during decommissioning work at nuclear power plants. In addition, even if sharp fine powder is contained in the exhaust EH from the demolition environment area, there is little risk of the filter being damaged by the fine powder, and from this point of view, the frequency of filter replacement can also be reduced. 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, but it is preferable to use a flat stainless steel fiber sheet folded into a bellows shape and formed into a cylindrical shape as shown in FIG. 5 in order to increase the filtration area. As shown in FIG. 5, it is most preferable that the exhaust purification filter 7 is provided with a shape retention means 15 for protecting the main filter 14 on both sides (front and back) of the main filter 14, but the shape retention means 15 may be provided on one side (front or back) of the main filter 14. By providing this shape retention means 15, the exhaust purification filter 7 can be maintained in the above-mentioned bellows shape. That is, since the stainless steel fiber sheet constituting the main filter 14 has low shape stability, it is difficult to maintain the bellows shape without the net sheet constituting the shape retention means 15, but by providing the shape retention means 15, the shape stability of the exhaust purification filter 7 is increased and the bellows shape can be maintained. In addition, by providing the shape retention means 15, the strength of the exhaust purification filter 7 is increased, so that the exhaust purification filter 7 is more likely to withstand the pressure of compressed gas applied to the main filter 14 when cleaning the main filter 14.

[0057] It is preferable that the shape retention means 15 is a mesh sheet so that the exhaust EH can reach the main filter 14. Furthermore, if the mesh gaps 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 gaps of the shape retention means 15 is larger than the size of the gaps 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, it is preferable to use stainless steel or the like.

[0058] 9 and 10 show an example of lamination of the main filter 14 and the shape retention means 15 constituting the exhaust purification filter 7. In addition, in FIG. 9 and FIG. 10, the front side and the upper side mean 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 back side and the lower side mean 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. Since the main filter 14 includes a metal fiber sheet and the shape retention means 15 includes a metal mesh member, it can be said that the exhaust purification filter 7 is a laminate of a metal fiber sheet and a metal mesh member. In addition, the main filter 14 may include a material other than the metal fiber sheet, and the shape retention means 15 may also include a material other than the metal mesh member. It is preferable to use a metal fiber sheet (especially a stainless steel fiber sheet) as the main material of the main filter 14, and it is preferable to use a metal mesh member as the main material of the shape retention means 15. The main filter 14 may be composed of only a metal fiber sheet, and the shape retention means 15 may be composed of only a metal mesh member. In addition, in order to facilitate understanding, the thickness of each layer constituting the exhaust purification filter 7 is exaggerated and shown as being thick in Figures 9 and 10, 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 the shape-retaining means 15 is laminated on the front side US (outside) of the main filter 14 and the shape-retaining means 15 is also laminated on the back side DS (inside) of the main filter 14. From the viewpoint of protecting the main filter 14 and from the viewpoint of forming the main filter 14 into a bellows shape and maintaining the bellows shape, it is most preferable to provide the shape-retaining means 15 on both sides (front side US and back side DS) of the main filter 14 as shown in FIG. 9, but a form in which the shape-retaining means 15 is provided on either one side (front side US or back side DS) of the main filter 14 may also be used. When 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, the shape-retaining means 15 may not be provided at all. If the shape-retaining means 15 is thin, the function of protecting the main filter 14 may be reduced, and if the shape-retaining means 15 is thick, the ventilation resistance may increase and the exhaust purification processing amount per unit time may be reduced. 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 may not be sufficiently removed, and if the thickness of the main filter 14 is thick, there is a risk that the airflow resistance increases and the amount of exhaust purification treatment per unit time decreases. Note that the thickness of the front side shape retaining means 15U and the thickness of the back side shape retaining means 15B may be the same thickness or different thicknesses.

[0060] The basic structure of the exhaust purification filter 7 shown in Fig. 10 is the same as that in Fig. 9, but differs in 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, can best remove radioactive dust and the like, but have the disadvantage of being weak due to their small fiber diameter. Therefore, by providing the upper-layer main filter 14U and the lower-layer main filter 14D, which are made of metal fibers with a larger fiber diameter than the metal fibers of the middle-layer main filter 14M, the weakness of the 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 when the main filter 14 is made into a single layer (the fiber diameter of the metal fibers constituting this single layer is assumed to be 2 to 4 μm, the same as the metal fibers of the middle-layer main filter 14M), 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 be more easily withstood the pressure (pressure due to compressed gas) applied to the exhaust purification filter 7 during backwashing of the exhaust purification filter 7. In particular, since the rear side of the main filter 14 is subjected to the greatest pressure of the compressed gas during backwashing, 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 layer main filter 14U located on the outside of the main filter 14 is large, radioactive dust and the like captured in the gaps of the upper layer main filter 14U located on the outside of the main filter 14 is more easily blown out to the outside of the main filter 14 during backwashing, compared to when the metal fiber diameter of the upper layer main filter 14U located on the outside of the main filter 14 is small. Therefore, there is also the advantage that the cleaning effect during backwashing is improved.

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

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

[0065] [Formula 1] P(%) = Main filter layer weight (g / m 2 ) / specific gravity of metal fibers that make 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 the above formula 1 is 798 when the metal fiber is stainless steel (SUS316L), for example. In addition, in the case where the main filter is made of a single layer, the "layer of the main filter" in formula 1 refers to that single layer. When the main filter is made of multiple layers and it is desired to find the porosity of each layer of the main filter, it is sufficient to use the basis weight, metal fiber, and thickness of each layer of the main filter. When the main filter is made of multiple layers and it is desired to find the porosity of the entire main filter in a stacked state, it is sufficient to use the basis weight, metal fiber, and thickness of the entire main filter.

[0067] When manufacturing the main filter 14 made of multiple layers, it is preferable to uniformly stack the metal fibers as raw materials and 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, and any shape such as a perfect circle as shown in Fig. 4, an ellipse, a rectangle, or a hexagon can 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 cylindrical as shown in FIG. 4 and FIG. 5, the imaginary line IL connecting the multiple valleys 7Y of the exhaust purification filter 7 becomes a circle in cross section. It is preferable to make the shape of the inner tube 8 the same shape (circular) as this imaginary line IL, and to make the back surface of the multiple valleys 7Y of the exhaust purification filter 7 contact the surface of the inner tube 8, and it is more preferable to make the back surface of all the valleys 7Y of the exhaust purification filter 7 contact the surface of the inner tube 8. By making the multiple valleys 7Y, 7Y contact the inner tube 8 in advance, it is possible to prevent the exhaust purification filter 7 from colliding with the inner tube 8 every time the exhaust EH passes through the exhaust purification filter 7, and therefore the life of the exhaust purification filter 7 can be extended.

[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 respectively 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 where the exhaust purification filter 7 and the inner cylinder 8 are sealed is called a seal part 9, and in the embodiment of Fig. 3 and Fig. 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 a size substantially the same as the inner diameter of the inner tube 8) of 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 downward, and the upper end of the exhaust purification filter 7 and the upper end of the inner tube 8 are inserted into the inside of this groove, and then the inside of the groove is filled with adhesive to fix 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 in a form integrated with the flange portion 7Z. Similarly, the lower seal portion 9B is formed by fixing a disk 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 periphery, and the cross section of the upright wall 22 has a U-shaped groove 23 with an opening at the top. Then, after 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, 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, to improve 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, and the inside of the casing 50 is divided into a pre-purification chamber and a post-purification chamber, and the pre-purification chamber and the post-purification chamber are divided by an attachment plate 10 and the exhaust gas purification filter 7 provided in the casing 50. The attachment plate 10 is provided with a through hole of the same shape as the through hole 19 of the flange portion 7Z, and the through hole 19 of the flange portion 7Z and the through hole of the attachment plate 10 face each other, and the flange portion 7Z is fixed in contact with the attachment plate 10 or with a gasket interposed therebetween. The attachment plate 10 has an exhaust gas supply port 16 through which the exhaust gas EH flows into the casing 50 on the wall of the casing 50 on the pre-purification chamber side, and a purified exhaust gas discharge port 18 through which the purified exhaust gas PEH flows out of the casing 50 on the wall of the casing 50 on the post-purification chamber side. 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 EH passes through the exhaust purification filter 7 from the outside to the inside, radioactive dust and the like in the exhaust EH are captured by the exhaust purification filter 7. The purified exhaust gas PEH, which has been purified by passing through the exhaust purification filter 7, passes through the openings of the inner cylinder 8 from the outside to the inside and reaches the purified exhaust passage 13. Thereafter, in the embodiment of FIG. 2, the purified exhaust gas PEH moves from the lower side to the upper side of the purified exhaust passage 13, passes through the hole portion of the annular ring 20 of the upper seal portion 9A, the through hole 19 of the flange portion 7Z, and the through hole of the mounting plate 10, and reaches the upper part of the exhaust purification device 3. Then, it is discharged from the exhaust purification device 3 and sent to the residual dust removal device 4 through the purified exhaust vent pipe L2.

[0073] On the other hand, in the process in which 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 of the exhaust EH decreases, so it is preferable to backwash the exhaust purification filter 7 at a specified 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 (the purified exhaust passage 13), and then flows in the opposite direction to that in FIG. 2. That is, after passing through the opening of the inner cylinder 8 from the inside to the outside, it 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, falls below the exhaust purification device 3, and accumulates there. 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 prescribed timing, the pressure loss and collection efficiency can be returned to near their initial values, so that the exhaust purification filter 7 does not need to be disposed of as a disposable item, thereby making effective use of global environmental resources and reducing the costs associated with replacing and disposing of the exhaust purification filter 7.

[0076] In addition, while the exhaust EH is being purified by the exhaust purification filter 7, backwashing can be performed without stopping the purification process. This is because backwashing is completed in a short time of a few seconds, so there is no need to bother stopping the purification process. In addition, because the lumps of foreign matter such as radioactive dust that peel off from the exhaust purification filter 7 during backwashing have a certain weight, even if the exhaust EH is flowing toward the exhaust purification filter 7, the lumps of foreign matter such as radioactive dust that peel off from the exhaust purification filter 7 are unlikely to reattach to the exhaust purification filter 7 due to the influence of the flow of the exhaust EH. If it is desired to reliably prevent the lumps of foreign matter such as radioactive dust that peel off from the exhaust purification filter 7 from reattaching to the exhaust purification filter 7, the purification process of the exhaust EH may be temporarily stopped before backwashing, and the purification process of the exhaust EH may be resumed after the backwashing is completed. However, when such a process is performed, it takes a certain amount of time to switch between the purification process of the exhaust EH and the cleaning (backwashing) process, which is inconvenient in that the purification process amount of the exhaust EH is slightly reduced.

[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 Fig. 11 and 12, a partition wall 29 is provided that divides 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] Specifically, as shown in FIG. 11, the upper end of the 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 from there, and the lower end of the partition wall 29 is located near the lower end of the exhaust purification filter 7. In order to prevent the compressed gas PA during backwash from directly colliding with the exhaust purification filter 7 arranged in another small space 27, it is preferable to position the lower end of the partition wall 29 near the lower end of the exhaust purification filter 7. Also, as shown in FIG. 12, this partition wall 29 is attached so as to separate the adjacent exhaust purification filters 7. In addition, as shown in FIG. 12, it is preferable that the partition wall 29 is not abutted against the inner wall of the container 28 of the exhaust purification device 3, and a predetermined gap is 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 is not extended further below the lower end of the exhaust purification filter 7, and a predetermined gap is provided below the partition wall 29. This is because, during the exhaust purification process, the exhaust gas EH that has entered the container 28 of the exhaust purification device 3 passes through the gaps and easily enters each of the small spaces 27A, 27B.

[0079] By the partition wall 29 thus attached, the internal space 26 of the exhaust purification device 3 is divided almost equally into two, 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 by the partition wall 29 in this way, it is possible to prevent the compressed gas PA injected from the injection part (nozzle 11) to the exhaust gas purification filter 7 arranged inside one small space 27 from directly colliding with the exhaust gas purification filter 7 arranged in the other adjacent small space 27. As a result, the influence of the compressed gas PA used when backwashing the exhaust gas purification filter 7 arranged in one small space 27 is less likely to reach the exhaust gas purification filter 7 arranged in the other small space 27. In other words, when the exhaust gas purification filter 7 arranged in some small spaces 27 is backwashed and the exhaust gas EH is purified using the exhaust gas purification filter 7 arranged in the other small space 27, the compressed gas PA is less likely to have an adverse effect on the exhaust gas purification filter 7 during the purification process. Therefore, even while some exhaust gas purification filters 7 are being washed, the other exhaust gas purification filters 7 can perform the exhaust gas purification process as usual, which has the advantage that the efficiency of the exhaust gas purification process in the entire exhaust gas purification device 3 is less likely to decrease.

[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 backwashed. Of course, contrary to the illustrated example, exhaust purification processing may be performed by the second exhaust purification filter 7B while the first exhaust purification filter 7A is backwashed.

[0082] 11 and 12 show an example 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 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 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, the exhaust purification device 3 is provided with a mounting plate 110 and has a housing 34 supporting the exhaust purification filter 7, the housing 34 has an upper plate portion 34u to which the exhaust purification filter 7 is fixed, a front plate portion 34f, a rear plate portion 34b arranged at an interval from the front plate portion 34f, and side plate portions 34s, 34s ​​(the side plate portions are, for example, two plates that face each other at an interval) connecting the sides of the front plate portion 34f and the rear plate portion 34b, and has a box shape with an open bottom, in which the upper end edge of the front plate portion 34f, the upper end edge of the rear plate portion 34b, and the upper end edges of the side plate portions 34s, 34s ​​are each connected to the upper plate portion 34u, and the housing 34 is fixed to the mounting plate 110. In the exhaust purification device 3 to which the housing 34 is fixed, the exhaust EH flows into the exhaust purification device 3 from the exhaust supply port 16 provided in the casing 50 of the exhaust purification device 3, enters the internal space 39 of the housing 34 from below the housing 34, passes through the exhaust purification filter 7, becomes purified exhaust PEH, and is discharged to the outside of the exhaust purification device 3 from the purified exhaust exhaust outlet 18. The housing 34 is fixed to a mounting plate 110 provided on the casing 50, and the inside of the casing 50 is divided into a pre-purification chamber and a post-purification chamber by this mounting plate 110 and the exhaust purification filter 7. The exhaust EH passes from the pre-purification chamber to the post-purification chamber through the exhaust purification filter 7, 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 inside of a box surrounded by the upper plate portion 34u, the front plate portion 34f, the rear plate portion 34b, and the side plate portions 34s, 34s ​​that constitute 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 when the internal space 39 is formed into a truncated cone as described below, it is preferable that the surfaces 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 portion of the exhaust purification filter 7, and the flange portion is fixed to the periphery of the through hole of the upper plate portion 34u. The flange portion of the exhaust purification filter 7 and the upper plate portion 34u of the housing 34 may 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 appropriately adjusted depending on the volume of the work area in which the exhaust purification device 3 is installed, the amount of floating dust, and the like, and is not particularly limited.

[0090] As shown in Figs. 16 to 19, the shape of the internal space 39 formed by the members constituting the housing 34 may be a rectangular parallelepiped shape, but it may also be a truncated cone shape as described below. 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 rectangular shape) 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 rectangular shape) (e.g., a rectangular pyramid), that is, 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 (surfaces on the side of the internal space 39) of the front plate 34f, the rear plate 34b, and the side plate portions 34s, 34s ​​facing the internal space 39 are disposed at an angle to the vertical line, so that radioactive dust is less likely to adhere to the surfaces on the side of the internal space 39, and even if it does adhere, it is likely to fall off in the continuing flow of radioactive dust. This makes it possible to prevent the housing 34 from being highly contaminated by radioactive dust.

[0091] In the case where 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 the normal line Lf5 extending from the surface facing the internal space 39 in the front plate portion 34f constituting the internal space 39 (i.e., the inner surface 34f1 of the front plate portion 34f) and the vertical line L6 intersecting the normal line Lf5 is, for example, preferably less than 90° and 80° or more, more preferably 87° or less and 85° or more, and particularly preferably 87°. Similarly, the acute angle θ formed by the normal line Lb5 extending from the inner surface 34b1 of the rear plate portion 34b and the vertical line L6 intersecting the normal line Lf5 is, for example, preferably less than 90° and 80° or more, more preferably 87° or less and 85° or more, 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] Specifically, the truncated cone may be a truncated cone, a truncated polygonal pyramid, or a truncated square pyramid. 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, and is particularly preferably stainless steel. If the material is a metal, it is preferable because of its strength resistance and radiation resistance.

[0094] The housing 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 in an attachable and detachable manner. 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 housing 34 has a cartridge type structure and is attachable and detachable, in the replacement work, the worker only needs to replace the entire housing, 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 preferable shape is, for example, a square tube formed by connecting 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 a member 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 (if the housing-side receiving portion 41 is a rectangular cylindrical shape, the plate-side receiving portion 110a may also be cylindrical) is provided on the lower surface of the mounting plate 110 and faces the housing-side receiving portion 41. The housing-side receiving portion 41 and the plate-side receiving portion 110a form a pair, and are removably fixed in a state in which the upper edge of the housing-side receiving portion 41 and the lower edge of the plate-side receiving portion 110a are in contact with each other. In order to improve the sealing performance, a gasket 33 may be interposed between the housing-side receiving portion 41 and the plate-side receiving portion 110a. In this case, the gasket 33 may be provided on the lower edge of the plate-side receiving portion 110a.

[0097] A through hole 110b is provided in a portion surrounded by the plate-side receiving portion 110a in the mounting plate 110. This through hole 110b is provided so that the purified exhaust gas PEH that has passed through the exhaust gas 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 for supporting the housing 34 is provided below the housing 34 so that the housing side receiving portion 41 and the plate side receiving portion 110a are maintained in a state of facing each other and in 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 a 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 of the height adjustment means 37 include an eccentric cam mechanism and 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 part 41 and the plate side receiving part 110a are paired, and it is desirable that they have the same shape to maintain airtightness. However, as shown in Figs. 18 and 19, since the shape of the internal space 39 of the housing 34 is a truncated cone, the perimeter of the upper plate part 34u of the housing 34 may be shorter than the perimeter of the plate side receiving part 110a. In this case, it is preferable to extend the entire edge of the upper plate part 34u in the radial direction, expand the upper plate part 34u so that the edge of the upper plate part 34u is a surface that protrudes outward from the upper edge of the front plate part 34f, the upper edge of the rear plate part 34b, and the upper edges of the side plate parts 34s and 34s, and provide the housing side receiving part 41 on the outer surface of the expanded upper plate part 34u. Of course, the degree of expansion of the upper plate part 34u may be such that the housing side receiving part 41 can be provided on the outer surface of the upper plate part 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 purification front chamber side. The door 38 is kept closed while the exhaust purification device 3 is in operation.

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

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

[0105] (Appendix 1) An exhaust purification device having an exhaust purification filter for removing radioactive dust from exhaust 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 an interior 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 is provided. 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 a side plate portion connecting sides of the front plate portion and the rear plate portion, and has a box shape with an open bottom, in which an upper end edge of the front plate portion, an upper end edge of the rear plate portion, and an upper end edge of the side plate portion 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 end edge of the front plate portion, the lower end edge of the rear plate portion, and the lower end 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 type structure and is fixed to the mounting plate so as to be attachable and detachable, The housing is capable of being inserted and removed from 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 tube, 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 layer main filter (upper layer main filter), 14M: middle layer main filter, 14D: back layer main filter (lower layer main filter), 15: shape retention means, 15U: surface side shape retention means (upper side shape retention means), 15D: back side shape retention means (lower side 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 part, 50: casing, 110: mounting plate, 110a: plate side receiving part, 110b: through hole, IL: virtual line, EH: exhaust, Lf5: (virtual) normal line extending from the inner surface of the front plate part, inner surface of the rear plate part, Lb5: (virtual) normal line extending from the inner surface of the rear plate part, Ls15, Ls25: (virtual) normal lines extending from the inner surfaces of the side plate parts 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 for removing radioactive dust from exhaust containing radioactive dust generated in a work area, the exhaust purification filter has a cylindrical shape, and in the process in which the exhaust gas passes from the outside to the inside of the exhaust purification filter, radioactive dust in the exhaust gas is captured by the exhaust purification filter, and the purified exhaust gas passes through an interior 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 located as a layer on at least one side of the stainless steel metal fiber sheet, 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 purification device having an exhaust purification filter and a backwashing means for removing radioactive dust from exhaust containing radioactive dust generated in a work area, the exhaust purification filter has a cylindrical shape, 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 an interior 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 located as a layer on at least one side of the stainless steel metal fiber sheet, These are laminated and compressed, 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 having an injection nozzle for injecting 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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