Radioactive substance removal device

Abstract

The present invention is provided with a moisture removal unit (2) that removes moisture from a radioactive gas, and a radioactive substance removal unit (3) that removes a radioactive substance from the gas from which moisture has been removed by the moisture removal unit (2), the moisture removal unit (2) having a flow path through which the gas flows, cooling the gas in the flow path, and removing moisture by causing the moisture to form frost at a prescribed site, and the flow path having a narrower flow path cross-sectional area or a smaller cooling wall surface distance on the downstream side than on the upstream side.

Description

Radioactive material removal equipment

[0001] The present invention relates to a radioactive material removal device.

[0002] Ra-226 (radium-226) is a radioactive nuclide that decays naturally with a half-life of 1,600 years. In recent years, it has been used as a source of radioactive materials for cancer treatment. While Ra-226 exists naturally, its production volume is extremely low. Therefore, previously manufactured sealed radiation sources and radium needles for treatment are often recovered and reused. For such reuse, sealed containers containing Ra-226 are opened and subjected to chemical treatment to extract and purify the Ra-226. This chemical treatment generates gas (exhaust) containing moisture, reagent components, and Rn-222 (radon-222), the daughter nuclide of Ra-226. Rn-222 is a rare gas and a radioactive nuclide with a half-life of 3.82 days. Laws and regulations require that radioactive materials be thoroughly removed before releasing such gases into the atmosphere.

[0003] JP 2018-169252 A (Patent Document 1) is a background art in this technical field. This publication states that "a containment vessel includes a filter unit that removes radioactive materials from gas inside the containment vessel that hermetically houses the reactor pressure vessel that houses the reactor core, an exhaust pipe that is connected to the filter unit and extended to the outside of the containment vessel, a first storage section that is connected to the end of the exhaust pipe outside the containment vessel, a first cooling section that condenses steam in the gas supplied to the first storage section, and an adsorption section that is connected independently to the first storage section and introduces the gas stored in the first storage section and adsorbs radioactive rare gases in the gas" (see Abstract).

[0004] Another example of background art is Japanese Patent Laid-Open Publication No. 2000-266891 (Patent Document 2), which describes a method for recycling nitrogen oxides contained in off-gas from a uranium denitration process in a spent nuclear fuel reprocessing process, the method comprising the steps of: a dehumidification step in which the mixed gas is cooled to remove moisture; a drying step in which the remaining moisture is removed by passing the mixed gas through a first adsorption tower filled with silica gel or acid-resistant zeolite; a second adsorption tower filled with nitrate-resistant zeolite; a cooling and liquefying step in which the separated nitrogen dioxide is stored; and a heating and vaporizing step in which the stored nitrogen dioxide is supplied. (See Abstract.)

[0005] JP 2018-169252 A JP 2000-266891 A

[0006] As described above, when attempting to remove radioactive substances from a gas containing radioactive substances, a pretreatment step of removing moisture from the gas is required. Therefore, it is preferable to increase the efficiency of removing moisture from the gas containing radioactive substances. However, the techniques of Patent Documents 1 and 2 have room for improvement in terms of increasing the efficiency of removing moisture from such a gas containing radioactive substances. Therefore, an object of the present invention is to provide a radioactive substance removal device that can increase the efficiency of moisture removal as a pretreatment step for radioactive gas.

[0007] In order to solve the above problems, the present invention comprises a moisture removal section that removes moisture from radioactive gas, and a radioactive substance removal section that removes radioactive substances from the gas after the moisture has been removed by the moisture removal section, wherein the moisture removal section has a flow path through which the gas flows, and removes moisture by cooling the gas in the flow path and causing moisture to frost at predetermined locations, and the flow path has a narrower cross-sectional area or a shorter cooling wall distance on the downstream side than on the upstream side.

[0008] According to the present invention, it is possible to provide a radioactive material removal device that can improve the efficiency of moisture removal as a pretreatment of radioactive gas. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments.

[0009] FIG. 1 is a block diagram showing the overall configuration of a radioactive substance removal apparatus according to one embodiment of the present invention. FIG. 1 is a longitudinal sectional view showing the basic configuration of a first moisture removal section and a second moisture removal section. FIG. 2 is a longitudinal sectional view showing the basic configuration of a first moisture removal section and a second moisture removal section. FIG. 3 is a longitudinal sectional view showing an example configuration of the second moisture removal section. FIG. 4 is a longitudinal sectional view showing an example configuration of the second moisture removal section. FIG. 5 is a block diagram showing the overall configuration of a radioactive substance removal apparatus which is a modified example of the embodiment.

[0010] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a radioactive material removal apparatus according to an embodiment of the present invention. A gas transport flow path 11 is a pipe or the like that transports a radioactive gas in the direction of the arrow in the figure. The radioactive material removal apparatus 1 includes a moisture removal unit 2 and a radioactive material removal unit 3, which are each connected to the gas transport flow path 11 with the former on the upstream side. The moisture removal unit 2 removes moisture from the radioactive gas. The radioactive material removal unit 3 removes radioactive material from the gas after moisture removal in the moisture removal unit 2. The process of removing moisture from the radioactive gas in the moisture removal unit 2 is a pre-processing before the process in the radioactive material removal unit 3.

[0011] The moisture removal unit 2 and the radioactive material removal unit 3 take in gas from the gas transport flow path 11 via inlet-side pipes 12 and 13, respectively, and discharge the gas into the gas transport flow path 11 via outlet-side pipes 14 and 15. The inlet-side pipes 12 and 13 and the outlet-side pipes 14 and 15 are opened and closed by a valve 4. In the case of gas that does not contain much moisture, the gas from the gas transport flow path 11 is passed only through the radioactive material removal unit 3, and the moisture removal unit 2 is not used, thereby reducing the spread of contamination and the operating costs of the device. Furthermore, in the case of gas that contains a very large amount of moisture, the gas is passed only through the moisture removal unit 2 repeatedly to sufficiently reduce the moisture, and then the gas after the moisture removal is passed through the radioactive material removal unit 3. This prevents the radioactive material removal unit 3 from being clogged with moisture, and enables continuous operation of the radioactive material removal device 1.

[0012] The moisture removal unit 2 will now be described. The moisture removal unit 2 is a cooling condenser that cools the gas in its flow path and causes moisture to frost on the wall surfaces of the flow path, etc., thereby recovering moisture. The cooling condenser can be made of glass, metal, resin, etc. In this case, metal has better thermal conductivity and cooling performance, but is not preferred if the gas to be treated contains chemical components such as acid, as this can cause deterioration of the metal. If the chemical components are removed by passing the gas through an alkali removal device before passing it through the moisture removal unit 2, there is no problem with using metal inside the condenser. If metal is used, aluminum or aluminum alloys are preferred, as they have better thermal conductivity than stainless steel.

[0013] Generally, adsorbents such as silica gel, activated carbon, and zeolite are used to remove moisture. However, if the gas to be treated contains moisture close to its saturated vapor pressure, a large amount of adsorbent is required to adsorb the moisture, resulting in increased radioactive waste. This is because the large amount of adsorbent also adsorbs a certain amount of radioactive material. Furthermore, adsorbent performance deteriorates when it adsorbs moisture. In such cases, the adsorbent must be regenerated by heating or replaced with a new one, which disrupts the continuous operation of the moisture removal unit. Furthermore, replacing adsorbents containing radioactive material (including gas) can cause radiation exposure and increased equipment contamination. Furthermore, the adsorbent may be deteriorated by radioactivity emitted by radioactive materials contained in the target gas or by chemical components (such as reagent components such as acids and alkalis generated during chemical processing). Therefore, applying the above-mentioned cooling condenser to the moisture removal unit 2 is preferred for removing moisture from gas.

[0014] However, when a cooling condenser is applied to the moisture removal unit 2, it is desirable to increase the moisture removal efficiency by preventing the moisture removal unit 2 from being clogged with a large amount of moisture, etc. However, in this regard, Patent Documents 1 and 2 do not suggest any technical innovations. Therefore, the following describes a radioactive material removal device 1 equipped with a moisture removal unit 2 with high moisture removal efficiency.

[0015] That is, the moisture removal unit 2 has a flow path through which gas flows, and removes moisture by cooling the gas in the flow path and causing moisture to frost on predetermined locations such as the inner wall surface. The flow path has a narrower cross-sectional area or a shorter distance between the cooling walls on the downstream side than on the upstream side. Moisture can also be removed by condensing the moisture. Incidentally, when comparing frost formation with condensation, frost formation can be said to be preferable because it can lower the dew point of the gas.

[0016] An example of the configuration of the moisture removal unit 2 will be described with reference to FIG. 1 . The moisture removal unit 2 has a first moisture removal unit 21, which is a flow path forming the upstream side of the gas flow, and a second moisture removal unit 22, which is a flow path forming the downstream side. The second moisture removal unit 22 has a narrower flow path cross-sectional area or a shorter cooling wall distance than the first moisture removal unit 21 (means for achieving this will be described later). The first moisture removal unit 21 and the second moisture removal unit 22 are housed in a cooling tank 23. The first moisture removal unit 21 and the second moisture removal unit 22 are cooled, and a preferred cooling method is, for example, placing a cooling medium such as chilled ethanol or liquid nitrogen, or dry ice, in the cooling tank 23, as this is a simple method.

[0017] Gas is introduced into the first moisture removal section 21 from the inlet-side pipe 12. The first moisture removal section 21 and the second moisture removal section 22 are connected by a pipe 25, and the gas in the first moisture removal section 21 is sent via the pipe 25. The gas in the second moisture removal section 22 is sent to the gas transport flow path 11 via the outlet-side pipe 14.

[0018] 2A and 2B are longitudinal cross-sectional views showing the basic configurations of the first moisture removal unit and the second moisture removal unit. As described below, FIGS. 2A and 2B show a typical configuration example of the first moisture removal unit 21, and FIGS. 3A to 3D show a typical configuration example of the second moisture removal unit 22. However, because the principles of removing moisture from gas in the first moisture removal unit 21 and the second moisture removal unit 22 are similar, both the first moisture removal unit 21 and the second moisture removal unit 22 will be described here using FIGS. 2A and 2B.

[0019] 2, the first moisture removal unit 21 and the second moisture removal unit 22 are configured such that, for example, an inlet pipe 12 (in the case of the first moisture removal unit 21) and a pipe 25 (in the case of the second moisture removal unit 22) are inserted deep into a bottle-shaped container body 31. Then, the pipe 25 (in the case of the first moisture removal unit 21) and the outlet pipe 14 (in the case of the second moisture removal unit 22) are connected to the container body 31, for example, from the upper side.

[0020] As shown in FIG. 2B , within the cooled container body 31, the gas introduced into the lower portion of the container body 31 is cooled and frosts on the inner wall surface 31a of the container body 31 (the inner wall surface 31a as the predetermined portion). Reference numeral 32 denotes the ice that forms at this time. The gas that returns to the upper portion of the container body 31 has had a significant amount of moisture removed, and is discharged in this state from the piping 25 and the outlet piping 14. Frost formation begins on the inner wall surface 31a of the container body 31, which is in contact with the cooling medium and has a low temperature, and increases toward the inside of the container body 31. When the frost reaches the inlet piping 12 and piping 25 within the container body 31 and blocks the gas flow path, the inside of the container body 31 becomes clogged, and the first moisture removal unit 21 and the second moisture removal unit 22 are no longer able to cool the gas. If the cooling temperature of the inlet side pipe 12 and pipe 25 is below the melting point of water (0 degrees at normal pressure), frosting will cause the first moisture removal section 21 and the second moisture removal section 22 to exhibit a moisture recovery effect.

[0021] The first moisture removal section 21 and the second moisture removal section 22 can cool the gas more efficiently at lower temperatures. When the gas temperature is room temperature, the cooling temperature is preferably approximately -50 to -40°C. Because the gas is introduced into the container body 31 through the inlet-side piping 12 and piping 25, a temperature gradient is created within the container body 31, with a higher temperature at the center of the container body 31 and a lower temperature at the inner wall surface 31a. Because the lower the temperature, the faster the gas cools, allowing for cooling even with a fast gas flow rate. However, if the inlet-side piping 12 and piping 25 in the center of the container body 31 cools, frost forms there, and the narrow piping of the inlet-side piping 12 and piping 25 quickly becomes clogged. Therefore, to reduce the frequency of regeneration (melting frozen moisture) of the inlet-side piping 12 and piping 25 and continuously operate the moisture removal section 2, an appropriate temperature setting is required.

[0022] Therefore, to regenerate the blocked inlet-side pipe 12 and pipe 25, the first moisture removal unit 21 and the second moisture removal unit 22 are heated to liquefy the frost and remove moisture from the inside of the first moisture removal unit 21 and the second moisture removal unit 22. Heating in this case can be performed by stopping the cooling tank 23 and waiting for the tank to return to room temperature, or by stopping the cooling tank 23 or removing the first moisture removal unit 21 and the second moisture removal unit 22 from the cooling tank 23 and then heating the tank. Removing the first moisture removal unit 21 and the second moisture removal unit 22 from the cooling tank 23 may result in the spread of contamination due to the leakage of radioactive gas. To prevent this, a means for easily attaching and detaching the first moisture removal unit 21 and the second moisture removal unit 22 or a check valve may be used. In the example shown in FIG. 1 , a one-touch joint 41, for example, is used to easily attach and detach the first moisture removal unit 21 and the second moisture removal unit 22 from the inlet-side pipes 12 and 13 and the outlet-side pipes 14 and 15. As an example, by using a one-touch joint 45, the first moisture removal section 21, the second moisture removal section 22, the inlet side pipes 12, 13 and the outlet side pipes 14, 15 can be easily attached and detached.

[0023] Furthermore, drain pipes 42 for discharging moisture may be provided in the first moisture removal unit 21 and the second moisture removal unit 22 so that the flow path does not need to be opened. Removing liquefied moisture requires complicated piping operations, which can lead to exposure to radioactive materials and the spread of contamination. Therefore, the drain pipes 42 enable the regeneration process to be performed in a short time, thereby reducing these risks. A mechanism for adjusting the temperature inside the vessel body 31 according to the gas flow rate and the moisture content in the gas may also be provided. For example, the first moisture removal unit 21 and the second moisture removal unit 22 may preferably be provided with a heater or other heating unit 33 for heating frost and recovering condensate. It is also preferable to provide a temperature sensor 34 in the first moisture removal unit 21 and the second moisture removal unit 22. As a result, the temperature sensor 34 monitors the temperatures inside the first moisture removal section 21 and the second moisture removal section 22, and the heating section 33 is operated appropriately according to the temperature to heat the inside of the first moisture removal section 21 and the second moisture removal section 22, thereby minimizing blockage of the inlet side pipe 12 and the pipe 25. In this case, a control device using a microcomputer or the like may be provided, which operates the heating section 33 when the temperature detected by the temperature sensor 34 falls below a predetermined first temperature, and stops the heating section 33 when the temperature rises to or exceeds a predetermined second temperature higher than the first temperature.

[0024] Alternatively, the amount and temperature of the cooling medium in the cooling tank 23 may be controlled to prevent blockage of the inlet pipe 12 and the pipe 25, as described above. In this case, the amount and temperature of the cooling medium in the cooling tank 23 may be controlled (reduced in amount, increased in temperature) by monitoring the temperature detected by the temperature sensor 34 and controlling the amount and temperature of the cooling medium in the cooling tank 23 to reduce or increase the amount when the temperature drops below a first temperature, and to stop the reduction when the temperature rises above a preset second temperature higher than the first temperature.

[0025] Furthermore, if the gas is cooled below the boiling point of the radioactive material, the radioactive material will be liquefied in the moisture removal unit 2. If the gas contains Rn-222, progeny nuclides of radon, such as Bi-214 (bismuth 214) and Pb-214 (lead 214), which emit a large number of gamma rays, will be present, resulting in a high radiation dose. Therefore, if Rn-222 is collected in the moisture removal unit 2, the amount of radioactive waste will increase. If the moisture removal is performed above the dew point of the gas, no alpha-ray-emitting nuclides will be contained in the moisture removal unit 2, and the radiation dose will not increase, thereby reducing the amount of radioactive waste. If only the hollow first moisture removal unit 21 and second moisture removal unit 22 are used, without any adsorbent inside, the amount of Rn-222 liquefied and recovered can be ignored.

[0026] Additionally, the inlet-side pipe 12, the pipe 25, and the outlet-side pipe 14 are provided with a blockage detection unit 51. The blockage detection unit 51 can be configured with a pressure sensor that detects the pressure of the gas in these pipes or a flow rate sensor that detects the flow rate. By observing the difference in the pressures and flow rates detected by the blockage detection units 51 of the inlet-side pipe 12, the pipe 25, and the outlet-side pipe 14, the blockage status of each of the first moisture removal unit 21 and the second moisture removal unit 22 can be determined. Immediately before the first moisture removal unit 21 or the second moisture removal unit 22 becomes blocked, the pressure loss increases rapidly, and the gas flow rate becomes nearly zero. When such a sudden change in the pressure loss or flow rate is detected, a control device using a microcomputer or the like can take measures such as notifying the user, switching to another parallel device as described below, or stopping the processing of the radioactive material removal device 1. This allows gas to continue to be sent in a blocked state, creating static pressure in the pipe, preventing leakage of gas containing radioactive materials.

[0027] The second moisture removal unit 22 removes moisture from the gas when the amount of moisture in the gas is less than that in the first moisture removal unit 21. This is because a certain amount of moisture has been removed from the gas by the first moisture removal unit 21. Because the amount of moisture in the gas is less, the second moisture removal unit 22 is less likely to be clogged with moisture even if its diameter is made smaller than that of the first moisture removal unit 21, and the cooling efficiency of the gas can be improved.

[0028] 3A to 3D are longitudinal cross-sectional views showing examples of the configuration of the second moisture removal unit. The second moisture removal unit 22 in Fig. 3A has a smaller diameter of the container body 31 than the first moisture removal unit 21 having the configuration shown in Figs. 2A and 2B. This results in the second moisture removal unit 22 having a smaller flow path cross-sectional area or a shorter cooling wall distance than the first moisture removal unit 21.

[0029] 3B, a plurality of protruding members (plates or the like) 53 are protruded to the left and right from the piping 25 inside the container body 31 of the second moisture removal section 22 toward the inner wall surface 31a of the container body 31, so that the second moisture removal section 22 has a narrower flow path cross-sectional area than the first moisture removal section 21. Note that the first moisture removal section 21 may also have the same configuration as that shown in FIG. 3B, and by adjusting the spacing of the protruding members 53, the spacing of the protruding members 53 may be configured to be shorter in the second moisture removal section 22 than in the first moisture removal section 21.

[0030] 3C , a plurality of granular solids 56 are placed in the container body 31 of the second moisture removal unit 22, thereby making the second moisture removal unit 22 have a narrower cross-sectional flow path area than the first moisture removal unit 21. Note that the first moisture removal unit 21 may also have the same configuration as that of FIG. 3B , and may be configured so that the particle size of the granular solids 56 is smaller in the second moisture removal unit 22 than in the first moisture removal unit 21.

[0031] 3D , one or more partition plates 59 with their longitudinal direction aligned in the depth direction of the container body 31 are inserted into the container body 31 of the second moisture removal section 22, thereby shortening the distance between the wall surfaces within the container body 31 and making the second moisture removal section 22 have a smaller flow path cross-sectional area than the first moisture removal section 21. Note that the first moisture removal section 21 may also have the same configuration as that of FIG. 3B , and by adjusting the distance between the wall surfaces within the container body 31, the spacing between the partition plates 59 may be closer in the second moisture removal section 22 than in the first moisture removal section 21.

[0032] 1 illustrates an example in which only two moisture removal units, the first and second moisture removal units 21 and 22, are provided, but three or more units may be provided and connected in series. These two or more moisture removal units may combine multiple types of units having any of the configurations shown in FIGS. 3A to 3D. Two or more types of moisture removal units with different flow path cross-sectional areas may be used, and the moisture removal unit to be used may be selected by valve control or the like depending on the amount of moisture in the gas.

[0033] The protruding member 53, the granular solid 56, and the partition plate 59 may have through-holes formed therein to serve as flow paths for the gas to pass through. Materials for these members can include glass, metal, and resin. To cool these members, they are preferably in thermal contact with the inner wall surface 31a of the container body 31. From the viewpoint of ensuring thermal conductivity, metal is preferred as the material for these members. Furthermore, since the same gas flows through the first moisture removal section 21 and the second moisture removal section 22 in that order, the gas is at a lower temperature in the second moisture removal section 22 than in the first moisture removal section 21.

[0034] The radioactive substance removal unit 3 will now be described. In FIG. 1 and other figures, components in the radioactive substance removal unit 3 that are designated by the same reference numerals as those in the moisture removal unit 2 are similar to those in the moisture removal unit 2, and detailed description thereof will be omitted. The gas from which moisture has been removed to a certain extent in the moisture removal unit 2 is introduced into the radioactive substance removal unit 3, where radioactive substances are removed. This removal of radioactive substances is achieved by physical adsorption (adsorption due to van der Waals forces) within the adsorption unit 71 by an adsorbent (not shown). As the adsorbent, for example, a microporous material such as activated carbon, molecular sieve, or silica can be used.

[0035] A cooling unit 72 is connected to the upstream side of the adsorption unit 71 via a pipe 26. The cooling unit 72 preliminarily cools the radioactive gas before it flows into the adsorption unit 71. The adsorption unit 71 and the cooling unit 72 are housed in a cooling tank 23 having the same configuration as the moisture removal unit 2. Therefore, the cooling mechanism of the cooling unit 72 may be the same as that of the first moisture removal unit 21, etc. As a result, by cooling the gas in the cooling unit 72, it becomes possible to efficiently perform physical adsorption of the radioactive material by the adsorbent in the subsequent adsorption unit 71. In this way, if the temperature of the gas is sufficiently cooled in advance, the adsorption unit 71 can adsorb the radioactive material with a small amount of adsorbent, and the amount of radioactive waste can be reduced to, for example, about several grams. Generally, the amount of radioactive material is very small (for 1 MBq of gaseous radioactive material, 1 －１６ ~1 －１０ Even if the amount of the adsorbent is reduced (approximately 100 mol), it is possible to prevent the adsorption capacity from becoming insufficient.

[0036] In this case, if the radioactive material contained in the gas is Rn-222, the daughter nuclides, such as Bi-214 (bismuth 214) and Pb-214 (lead 214), which emit a large number of gamma rays, are present, resulting in a high dose rate in the adsorbent that captures Rn-222. Around the radioactive material removal unit 3, workers are required to operate the cooling tank 23 and valve 4, remove the radioactive material removal unit 3, and perform other tasks. Therefore, the area around the adsorbent must be shielded with lead or iron (shielding material) to prevent radiation exposure. If the volume of the adsorbent portion capturing Rn-222 is large, the size and weight of the required shielding material increases. If the radiation source is small, localized shielding can be used, reducing the manufacturing cost of the shielding equipment. In other words, if a large amount of adsorbent is used, a large volume of the adsorbent will emit radiation, and the entire large volume will need to be shielded. However, if the adsorbent is small, the shielding material can also be made more compact. Since the shielding materials, lead and iron, are heavy, it is difficult to install them in the cooling tank 23, etc. Therefore, the use of a small amount of adsorbent as in this embodiment has the advantage of avoiding these problems.

[0037] The cooling section 72 may have the configuration described above with reference to Figures 2A to 3D. Alternatively, the cooling section 72 may simply pass gas through a cooled hollow tube, as shown in Figures 2A and 2B. Alternatively, the cooling section 72 may have a structure in which the hollow tube is spiraled to increase the path length and enhance the cooling effect. The cooling section 72 may be integrated with the adsorption section 71 using an adsorbent, and a pipe of the same diameter may be provided as the cooling section 72. The upstream side of the cooling section 72 only cools the gas without an adsorbent, while the downstream side adsorbs radioactive materials in the gas using an adsorbent (adsorption section 71).

[0038] The pre-cooling temperature of the cooling unit 72 is preferably set above the boiling point of the radioactive material, since excessive cooling can liquefy the radioactive material, increasing the area of ​​contamination and turning the cooling unit 72 into radioactive waste. Temperature control using the heating unit 33 may be performed to adjust the local temperature of the cooling unit 72. The container body 31 of the cooling unit 72 is preferably made of glass, metal, resin, or other suitable material. The adsorbent is preferably one with fine pores and a large surface area. In the case of radon, the size of the radon molecule is 4 to 5 Å, so a material with pores larger than this is preferred. Smaller pore sizes in the adsorbent do not adsorb the molecules, while pores significantly larger than this size facilitate desorption. Activated carbon, although having a distribution of pore radius, is preferred as an adsorbent because it is inexpensive and readily available. Because charcoal powder is produced, installing a filter downstream of the adsorbent can reduce downstream contamination by radioactive materials and prevent equipment installed downstream from malfunctioning due to the powder being mixed in.

[0039] It is preferable to provide removable and airtight plugs at the inlet and outlet ends of the radioactive material removal unit 3 or adsorption unit 71. This is because, after radon is captured by the adsorbent, it must be allowed to decay for a period of time before it can be released into the atmosphere, and the radioactive material removal unit 3 or adsorption unit 71 must be safely stored during this period. Because the half-life of radon-222 is 3.8 days, if a large amount of radon is captured, the radioactive material removal unit 3 or adsorption unit 71 must be stored for up to several dozen months before being released into the atmosphere. Because moisture can also be adsorbed into the adsorption unit 71, its internal pressure increases when stored at room temperature. Therefore, it is preferable that the plugs be pressure-resistant sealing means. Furthermore, the radioactive material removal unit 3 or adsorption unit 71 may be continuously cooled while waiting for the decay.

[0040] The gas to be treated may contain reagent components. Acid vapor deteriorates metal piping, and rust causes clogging of the adsorbent. To prevent this, an acid removal device using a neutralizing agent can be installed upstream of the moisture removal section 2. If the distance from the moisture generation point where moisture is generated in the gas to the radioactive material removal device 1 is long, it is preferable to install another moisture removal section using liquefaction upstream of the moisture removal section 2. This can prevent moisture from condensing in the flow path of the moisture removal section 2, etc., and causing blockage of the flow path. Furthermore, if the amount of moisture is large in this case, it is preferable to improve the efficiency of moisture removal by frost formation.

[0041] Furthermore, because the adsorption section 71 is located downstream of the cooling section 72, the gas passing through them is at a lower temperature in the adsorption section 71 than in the cooling section 72. A modification of the above embodiment will be described. FIG. 4 is a block diagram of a radioactive material removal apparatus in which a moisture removal section and a radioactive material removal section are connected in parallel. This radioactive material removal apparatus 1a differs from the radioactive material removal apparatus 1 in the following respects. That is, a plurality of first moisture removal sections 21 and second moisture removal sections 22, as well as cooling sections 72 and adsorption sections 71, are provided, two in this example, and these same types of units are connected in parallel. These same types of units can be switched to use either unit using a valve 4 as a switching unit. Note that components shown in FIG. 1 but not in FIG. 4 are omitted for convenience, and these components are also provided in the configuration of FIG. 4. Note that "same type" means having the same function. The first moisture removal section 21 and the second moisture removal section 22 can be said to have the same function. On the other hand, the cooling unit 72 and the adsorption unit 71 have different functions in this embodiment.

[0042] Next, the effects of this embodiment will be described. The moisture removal unit 2 is configured such that the second moisture removal unit 22 has a narrower flow path cross-sectional area or a shorter cooling wall distance than the first moisture removal unit 21. Therefore, the first moisture removal unit 21, which has a wider flow path cross-sectional area or a longer cooling wall distance, is less likely to be clogged by moisture removed from the gas. Furthermore, the second moisture removal unit 22, which has a narrower flow path cross-sectional area or a shorter cooling wall distance, has high cooling efficiency and can sufficiently remove moisture. Furthermore, because the first moisture removal unit 21 removes a certain amount of moisture, the second moisture removal unit 22 is less likely to be clogged by moisture removed from the gas (frost), even if it has a narrower flow path cross-sectional area or a shorter cooling wall distance. Since the moisture removal unit 2 can efficiently remove moisture from the gas in this way, it is possible to prevent the radioactive material removal unit 3 from being clogged by moisture.

[0043] Furthermore, the radioactive material removal unit 3 can further remove moisture from the gas by cooling the gas in the cooling unit 72 as a pretreatment for the adsorption unit 71. This allows the gas to be in a state where it contains almost no moisture, improving the adsorption efficiency of the adsorbent in the adsorption unit 71, reducing the amount of adsorbent, and reducing the amount of adsorbent generated as radioactive waste. Furthermore, by using a one-touch joint 41 or the like for the gas transport flow path 11, the moisture removal unit 2 and the radioactive material removal unit 3 are configured to be detachable. Therefore, even if the moisture removal unit 2 or the radioactive material removal unit 3 becomes clogged, they can be easily detached and regenerated.

[0044] In addition, in the configuration of Figure 4, at least one of the first moisture removal unit 21, the second moisture removal unit 22, the cooling unit 72, and the adsorption unit 71 is connected in parallel in multiple units (two units in this example). These parallel-connected devices with the same functions (the first moisture removal unit 21, the second moisture removal unit 22, the cooling unit 72, and the adsorption unit 71 are devices with different functions, as described above) have a valve 4 (switching unit) that switches which one to use. Therefore, even if one of these devices of the same type becomes clogged with moisture during use, operation of the radioactive material removal apparatus 1 can be continued without interruption by switching to another device of the same type. Note that in the example of Figure 4, each of the first moisture removal unit 21, the second moisture removal unit 22, the cooling unit 72, and the adsorption unit 71 is connected in parallel in two units.

[0045] At least one of the first moisture removal unit 21, the second moisture removal unit 22, the cooling unit 72, and the adsorption unit 71 includes a heating unit 33 for heating frost formed within the unit and recovering condensate. Therefore, frost formed within these devices can be melted and eliminated by heating with the heating unit 33, thereby preventing blockage of these devices. At least one of the first moisture removal unit 21, the second moisture removal unit 22, the cooling unit 72, and the adsorption unit 71 includes a blockage detection unit 51 for detecting a blockage within the unit. This allows for prompt notification of a blockage in the unit, thereby enabling prompt resolution of the blockage. Additionally, in FIG. 4 , the two moisture removal units 2 are connected in parallel, and the two radioactive material removal units 3 are also connected in parallel. Furthermore, the two first moisture removal units 21 are also connected in parallel, and the two second moisture removal units 22 are also connected in parallel. Also, in Fig. 4, the two adsorption units 72 are also connected in parallel, and the two cooling units 72 are also connected in parallel.

[0046] Furthermore, the second moisture removal section 22 can lower the temperature of the internal gas than the first moisture removal section 21, and the adsorption section 71 can lower the temperature than the cooling section 72. Therefore, even if the second moisture removal section 22 has a lower moisture content in the gas than the first moisture removal section 21, it can sufficiently remove moisture from the gas, and even if the adsorption section 71 has a lower moisture content in the gas than the cooling section 72, it can efficiently adsorb radioactive materials with the adsorbent. Note that the present invention is not limited to the above-described embodiment and includes various modifications. For example, the above-described example has been described in detail to clearly explain the present invention, and is not necessarily limited to an embodiment having all of the described configurations.

[0047] REFERENCE SIGNS LIST 1 Radioactive material removal device 2 Moisture removal section 3 Radioactive material removal section 4 Valve (switching section) 11 Gas transport flow path 21 First moisture removal section 22 Second moisture removal section 33 Heating section 51 Blockage detection section 56 Granular solid 71 Adsorption section 72 Cooling section

Claims

1. A radioactive material removal device comprising: a moisture removal unit that removes moisture from radioactive gas; and a radioactive material removal unit that removes radioactive material from the gas after the moisture has been removed by the moisture removal unit, wherein the moisture removal unit has a flow path through which the gas flows, and removes moisture by cooling the gas in the flow path and causing the moisture to frost at predetermined locations, and wherein the flow path has a narrower cross-sectional area or a shorter cooling wall distance on the downstream side than on the upstream side.

2. The radioactive material removal device according to claim 1, characterized in that the radioactive material removal unit has a cooling unit that cools the gas after moisture has been removed by the moisture removal unit to a predetermined temperature, and an adsorption unit that adsorbs radioactive materials from the gas after cooling by the cooling unit using an adsorbent.

3. A radioactive material removal device as described in claim 1, characterized in that it comprises a gas transport flow path that transports the radioactive gas, the moisture removal unit and the radioactive material removal unit are connected to the gas transport flow path, and at least one of the moisture removal unit and the radioactive material removal unit is detachable from the gas transport flow path.

4. The radioactive material removal device according to claim 2, wherein the moisture removal unit has a first moisture removal unit that forms the upstream side and a second moisture removal unit that forms the downstream side, and at least one of the first moisture removal unit, the second moisture removal unit, the cooling unit, and the adsorption unit is connected in parallel in plurality, and the parallel-connected units have a switching unit that switches which of them to use.

5. The radioactive material removal device described in claim 2, characterized in that the moisture removal unit has a first moisture removal unit that forms the upstream side and a second moisture removal unit that forms the downstream side, and at least one of the first moisture removal unit, the second moisture removal unit, the cooling unit, and the adsorption unit has a heating unit for heating frost that has formed within the component and recovering condensate.

6. The radioactive material removal device described in claim 2, characterized in that the moisture removal unit has a first moisture removal unit that forms the upstream side and a second moisture removal unit that forms the downstream side, and has a blockage detection unit that detects a blockage state within at least one of the first moisture removal unit, the second moisture removal unit, the cooling unit, and the adsorption unit.

7. The radioactive material removal device described in claim 2, characterized in that the moisture removal section has a first moisture removal section that forms the upstream side and a second moisture removal section that forms the downstream side, and the second moisture removal section lowers the temperature of the gas more than the first moisture removal section, or the adsorption section lowers the temperature more than the cooling section.

8. A radioactive material removal device as described in claim 1, characterized in that the flow path contains granular solids inside, and the cross-sectional area of ​​the flow path is narrower on the downstream side than on the upstream side due to differences in the particle size of the granular solids.

9. A radioactive material removal device according to claim 8, wherein the granular solid is an inorganic material such as metal or glass.

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