Radioactive substance removing apparatus

Abstract

To provide a radioactive substance removal device capable of enhancing efficiency of moisture removal as pretreatment of radioactive gas.SOLUTION: And a radioactive substance remover 3 that removes a radioactive substance from the gas from which moisture has been removed by the moisture remover 2, in which the moisture remover 2 has a flow path through which the gas flows, and removes moisture by cooling the gas in the flow path to frost moisture on a predetermined portion, and the flow path has a narrower flow path cross-sectional area or a shorter cooling wall surface distance on a downstream side than on an upstream side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Ra-226 (radium 226) is a radioactive nuclide that decays naturally with a half-life of 1600 years, and in recent years has been used as a raw material for radioactive materials used in cancer treatment. Although Ra-226 exists naturally, its production is extremely low, so previously manufactured sealed radiation sources and radium needles used in treatment are collected and reused. When such reuse is performed, the sealed container containing the Ra-226 is opened and chemically treated to extract and purify the Ra-226. This chemical treatment generates gas (exhaust) containing moisture, reagent components, and Rn-222 (radon-222), a daughter nuclide of Ra-226. Rn-222 is a rare gas and a radioactive nuclide with a half-life of 3.82 days. Before releasing gas containing such radioactive material into the atmosphere, the law requires that the radioactive material be thoroughly removed.

[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 drawn out 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 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, which comprises the following steps: a dehumidification step of cooling the mixed gas to remove moisture; a drying step of passing the mixed gas through a first adsorption tower packed with silica gel or acid-resistant zeolite to remove residual moisture; a separation step of passing the mixed gas through a second adsorption tower packed with nitrate-resistant zeolite to separate nitrogen oxides, liquefying the separated nitrogen dioxide by cooling and storing it; and a step of vaporizing the stored nitrogen dioxide by heating and supplying it (see Abstract). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-169252 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-266891 Summary of the Invention [Problem to be solved by the invention]

[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 desirable to improve the efficiency of removing moisture from gases containing radioactive substances, but the techniques of Patent Documents 1 and 2 have room for improvement in terms of improving the efficiency of removing moisture from gases containing such radioactive substances. Therefore, an object of the present invention is to provide a radioactive material removal device that can improve the efficiency of moisture removal as a pretreatment of radioactive gas. [Means for solving the problem]

[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. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a radioactive material removal apparatus 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 apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing the overall configuration of a radioactive material removal apparatus according to an embodiment of the present invention. [Figure 2A] FIG. 2 is a vertical cross-sectional view showing the basic configuration of a first moisture removal section and a second moisture removal section. [Figure 2B] FIG. 2 is a vertical cross-sectional view showing the basic configuration of a first moisture removal section and a second moisture removal section. [Figure 3A] FIG. 4 is a vertical cross-sectional view showing an example of the configuration of a second moisture removal section. [Figure 3B] FIG. 4 is a vertical cross-sectional view showing an example of the configuration of a second moisture removal section. [Figure 3C] FIG. 4 is a vertical cross-sectional view showing an example of the configuration of a second moisture removal section. [Figure 3D] FIG. 4 is a vertical cross-sectional view showing an example of the configuration of a second moisture removal section. [Figure 4] FIG. 10 is a block diagram showing the overall configuration of a radioactive substance removal apparatus that is a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a radioactive substance removal apparatus according to one 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 substance removal apparatus 1 includes a moisture removal unit 2 and a radioactive substance 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 substance removal unit 3 removes radioactive substances 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 substance 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 pipes 12 and 13, respectively, and discharge the gas into the gas transport flow path 11 via outlet pipes 14 and 15. The inlet pipes 12 and 13 and the outlet 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 walls 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 alloy is preferred, as it has 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 as 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 lead to radiation exposure and increased equipment contamination. Furthermore, the adsorbent may be deteriorated by radioactivity emitted by the radioactive material contained in the target gas or by chemical components (such as reagent components such as acids and alkalis generated during chemical processing). Therefore, the use of a cooling condenser in the moisture removal unit 2 is preferred for moisture removal from gases.

[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. However, Patent Documents 1 and 2 do not suggest any technical innovations in this regard. 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 to the cooled wall surface 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 section 2 will be described with reference to FIG. 1. The moisture removal section 2 has a first moisture removal section 21, which is a flow path forming the upstream side of the gas flow, and a second moisture removal section 22, which is a flow path forming the downstream side. The second moisture removal section 22 has a smaller flow path cross-sectional area or a shorter cooling wall distance than the first moisture removal section 21 (means for achieving this will be described later). The first moisture removal section 21 and the second moisture removal section 22 are housed in a cooling tank 23. The first moisture removal section 21 and the second moisture removal section 22 are cooled, and a preferred cooling means for this 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 means.

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

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

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

[0020] 2B, the gas introduced into the lower part 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 part of the container body 31 has had a considerable amount of moisture removed, and is discharged in this state from the pipe 25 and the outlet-side pipe 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 side piping 12 and piping 25 inside 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 piping 12 and piping 25 is below the melting point of water (0 degrees at normal pressure), the frost allows the first moisture removal unit 21 and the second moisture removal unit 22 to achieve 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 low 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 pipe 12 and the pipe 25, a temperature gradient occurs within the container body 31, with the temperature at the center of the container body 31 being higher and the temperature at the inner wall surface 31a being lower. The lower the temperature, the faster the gas cools, so cooling is possible even with a fast gas flow rate. However, if the inlet pipe 12 and the pipe 25 in the center of the container body 31 cool down, frost will form there, and because the inlet pipe 12 and the pipe 25 are narrow, they will easily become clogged. Therefore, to reduce the frequency of regeneration (melting frozen moisture) of the inlet pipe 12 and the pipe 25 and continuously operate the moisture removal section 2, an appropriate temperature setting is required.

[0022] Therefore, to regenerate the blocked inlet 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 inside the first moisture removal unit 21 and the second moisture removal unit 22. This heating 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 check valve or a means for easily attaching and detaching the first moisture removal unit 21 and the second moisture removal unit 22 can be used. In the example shown in FIG. 1 , a quick-connect 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 pipes 12 and 13 and the outlet pipes 14 and 15. As an example, by using the one-touch joint 45, the first moisture removal section 21, the second moisture removal section 22, the inlet pipes 12, 13, and the outlet pipes 14, 15 can be easily attached and detached.

[0023] Furthermore, to avoid the need to open the flow path, a drain pipe 42 for discharging moisture may be provided in the first moisture removal section 21 and the second moisture removal section 22. If complicated piping operations are required to remove liquefied moisture, this can lead to exposure to radioactive materials and the spread of contamination, so by using the drain pipe 42 to perform the regeneration in a short time, these can be reduced. A mechanism for adjusting the temperature inside the container body 31 may also be provided depending on the gas flow rate and the moisture content of the gas. For example, it is preferable to provide the first moisture removal unit 21 and the second moisture removal unit 22 with a heater or other heating unit 33 for heating frost and recovering condensed water. It is also preferable to provide the first moisture removal unit 21 and the second moisture removal unit 22 with a temperature sensor 34. This allows the temperature sensor 34 to monitor the temperatures inside the first moisture removal unit 21 and the second moisture removal unit 22, and to operate the heating unit 33 appropriately in accordance with the temperature to heat the first moisture removal unit 21 and the second moisture removal unit 22, thereby minimizing blockage of the inlet piping 12 and the piping 25. In this case, a control device using a microcomputer or the like may be provided to operate the heating unit 33 when the temperature detected by the temperature sensor 34 falls below a predetermined first temperature and to stop the heating unit 33 when the temperature detected by the temperature sensor 34 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 to be reduced (reduced in amount, increased in temperature) when the temperature detected by the temperature sensor 34 drops below a first temperature, and the reduction may be stopped 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 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 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 pipe 12, the pipe 25, and the outlet 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 sensor that detects the flow rate. By observing the difference in the pressure and flow rate detected by the blockage detection units 51 of the inlet pipe 12, the pipe 25, and the outlet pipe 14, the blockage status of each of the first moisture removal unit 21 and the second moisture removal unit 22 can be determined. Just before the first moisture removal unit 21 or the second moisture removal unit 22 becomes blocked, the pressure drop increases rapidly, and the gas flow rate becomes nearly zero. When a sudden change in the pressure drop 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 prevents static pressure from building up in the pipes by continuing to send gas in a blocked state, which could result in the leakage of radioactive material-containing gas.

[0027] The second moisture removal section 22 removes moisture from the gas when the amount of moisture in the gas is less than that in the first moisture removal section 21. This is because a certain amount of moisture has been removed from the gas by the first moisture removal section 21. Because the amount of moisture in the gas is less, the second moisture removal section 22 is less likely to be clogged with moisture even if its diameter is made smaller than that of the first moisture removal section 21, and furthermore, 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 section. In the second moisture removal section 22 of Fig. 3A, the diameter of the container body 31 is smaller than when the first moisture removal section 21 has the configuration shown in Figs. 2A and 2B. As a result, the second moisture removal section 22 has a smaller flow path cross-sectional area or a shorter cooling wall surface distance than the first moisture removal section 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 cross-sectional flow path area than the first moisture removal section 21. Note that the first moisture removal section 21 may also have the same configuration as in FIG. 3B, but by adjusting the spacing of the protruding members 53, the spacing of the protruding members 53 may 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 section 22, so that the second moisture removal section 22 has a narrower cross-sectional flow path area than the first moisture removal section 21. Note that the first moisture removal section 21 may also be configured in the same manner as in FIG. 3B, so that the particle size of the granular solids 56 in the second moisture removal section 22 is smaller than that in the first moisture removal section 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 cross-sectional flow path area than the first moisture removal section 21. Note that the first moisture removal section 21 may also have the same configuration as in 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 shows 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 of these may be provided and connected in series. These two or more moisture removal units may be a combination of multiple types of units having any of the configurations shown in FIGS. 3A to 3D. Two or more types of moisture removal units having 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 may include glass, metal, and resin. For cooling purposes, it is preferable that these members be 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 then the second moisture removal section 22, the gas has a lower temperature in the second moisture removal section 22 than in the first moisture removal section 21.

[0034] The radioactive substance removal section 3 will now be described. In FIG. 1 and other figures, components in the radioactive substance removal section 3 that are given the same reference numerals as those in the moisture removal section 2 described above are similar to those in the moisture removal section 2, and detailed description thereof will be omitted. The gas from which moisture has been removed to a certain extent in the moisture removal section 2 is introduced into the radioactive substance removal section 3, where the radioactive substances are removed. This removal of the radioactive substances is achieved by physical adsorption (adsorption due to van der Waals forces) in the adsorption section 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 section 72 is connected to the upstream side of the adsorption section 71 via a pipe 26. The cooling section 72 preliminarily cools the radioactive gas before it flows into the adsorption section 71. The adsorption section 71 and the cooling section 72 are housed in a cooling tank 23 having the same configuration as the moisture removal section 2. Therefore, the cooling mechanism of the cooling section 72 may be the same as that of the first moisture removal section 21, etc. As a result, by cooling the gas in the cooling section 72, it becomes possible to efficiently perform physical adsorption of the radioactive material by the adsorbent in the subsequent adsorption section 71. In this way, if the temperature of the gas is sufficiently cooled in advance, the adsorption section 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 -10Even if the amount of adsorbent is reduced, 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, its progeny nuclides, such as Bi-214 (bismuth 214) and Pb-214 (lead 214), emit a large amount of gamma rays, resulting in a high dose rate in the adsorbent that captures Rn-222. Since workers are required to operate the cooling tank 23 and valve 4 and remove the radioactive material removal unit 3 around the adsorbent, the area around the adsorbent must be shielded with lead or iron (shielding material) to prevent radiation exposure. If the volume of the adsorbent that captures Rn-222 is large, the required shielding material increases in size and weight. 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 must be shielded. However, if the adsorbent is small, the shielding material can also be made more compact. The shielding materials, lead and iron, are heavy, and therefore difficult to install in the cooling tank 23. 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 the 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 (cooling section 72), while the downstream side adsorbs the radioactive material in the gas using an adsorbent (adsorption section 71).

[0038] The temperature of the pre-cooling by the cooling unit 72 is preferably set to a temperature equal to or higher than the boiling point of the radioactive material, because if the temperature is too low, the radioactive material will liquefy and the area contaminated will increase, turning the cooling unit 72 into radioactive waste. Temperature adjustment may be performed using the heating unit 33 to adjust the local temperature of the cooling unit 72. The material of the container body 31 of the cooling unit 72 is preferably glass, metal, resin, or the like. The type of adsorbent mentioned above is preferably one with micropores 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 preferable as the adsorbent. If the pore size of the adsorbent is smaller than this, the molecules will not adsorb, but if the pore size is significantly larger than this, the molecules will easily desorb. Activated carbon as an adsorbent has a distribution of pore radius, but is preferable because it is inexpensive and easily available. Because it produces charcoal powder, installing a filter downstream of the adsorbent can reduce contamination by radioactive materials downstream and prevent malfunctions of downstream equipment 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 components of the reagent. Acid vapor deteriorates metal piping, and rust can cause clogging of the adsorbent. To prevent this, an acid removal device that uses a neutralizing agent can be installed upstream of the moisture removal section 2. If the distance from the moisture generating point where moisture is generated in the gas to the radioactive material removal device 1 is long, it is preferable to provide another moisture removal unit that uses liquefaction upstream of the moisture removal unit 2. This makes it possible to prevent moisture from condensing in the flow path of the moisture removal unit 2, etc., and causing blockage of the flow path. Furthermore, if the amount of moisture in this case is large, it is preferable to improve the efficiency of moisture removal by the frost formation.

[0041] Furthermore, since 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 modified example of the embodiment will be described. FIG. 4 is a block diagram of a radioactive material removal apparatus in which a moisture removal unit and a radioactive material removal unit 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 units 21 and second moisture removal units 22, as well as a cooling unit 72 and an adsorption unit 71, two units in this example, are provided, and these units of the same type are connected in parallel. These units of the same type can be switched to use either unit using a valve 4 as a switching unit. Note that components that are illustrated 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. It can be said that the first moisture removal unit 21 and the second moisture removal unit 22 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 wide flow path cross-sectional area or a long 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 narrow flow path cross-sectional area or a short 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 narrow flow path cross-sectional area or a short 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 contain 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, the moisture removal unit 2 and the radioactive material removal unit 3 are configured to be detachable by using a one-touch joint 41 or the like for the gas transport flow path 11. Therefore, even if the moisture removal unit 2 or the radioactive material removal unit 3 should become clogged, they can be easily detached and regenerated.

[0044] 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, with 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, as described above, have different functions) each equipped with a valve 4 (switching unit) for switching which of these devices is to be used. Therefore, even if one of these devices becomes clogged with moisture during use, the radioactive material removal apparatus 1 can continue operating without interruption by switching to another device of the same type. In the example of FIG. 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, with two units each.

[0045] At least one of the first moisture removal section 21, the second moisture removal section 22, the cooling section 72, and the adsorption section 71 has a heating section 33 for heating frost formed within the member and recovering condensed water. Therefore, frost formed within these devices can be melted and eliminated by heating with the heating section 33, thereby preventing blockage of these devices. The system also includes a blockage detection unit 51 that detects a blockage in 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. This allows for prompt detection of a blockage in the component, thereby enabling the blockage to be resolved promptly. Supplementally, in FIG. 4, the two moisture removal units 2 are connected in parallel, and the two radioactive substance 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 amount of moisture in the gas is less in the second moisture removal section 22 than in the first moisture removal section 21, the second moisture removal section 22 can sufficiently remove moisture from the gas, and even if the amount of moisture in the gas is less in the adsorption section 71 than in the cooling section 72, the radioactive material can be efficiently adsorbed by the adsorbent. It should be noted that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described examples have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations. [Explanation of symbols]

[0047] 1 Radioactive material removal equipment 2 Moisture removal section 3 Radioactive material removal section 4 Valve (switching unit) 11 Gas transport channel 21 1st moisture removal section 22 Second moisture removal section 33 Heating section 51 Blockage detection unit 56 Granular solids 71 Adsorption part 72 Cooling section

Claims

1. a moisture removal unit that removes moisture from the radioactive gas; a radioactive substance removal unit that removes radioactive substances from the gas after moisture has been removed by the moisture removal unit, 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 a predetermined location, 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, characterized in that

2. The radioactive material removal unit includes: a cooling unit that cools the gas after moisture has been removed by the moisture removing unit to a predetermined temperature; 2. The radioactive material removal apparatus according to claim 1, further comprising an adsorption section that adsorbs radioactive materials from the gas cooled by the cooling section using an adsorbent.

3. a gas transport flow path for transporting the radioactive gas; the moisture removal unit and the radioactive material removal unit are connected to the gas transport flow path, 2. The radioactive material removal device according to claim 1, wherein at least one of the moisture removal unit and the radioactive material removal unit is detachable from the gas transport flow path.

4. the moisture removal unit includes a first moisture removal unit on the upstream side and a second moisture removal unit on the downstream side, 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, 3. The radioactive material removal apparatus according to claim 2, wherein the parallel-connected ones have a switching unit for switching which one to use.

5. the moisture removal unit includes a first moisture removal unit on the upstream side and a second moisture removal unit on the downstream side, The radioactive material removal device according to claim 2, characterized in that 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 formed within the component and recovering condensed water.

6. the moisture removal unit includes a first moisture removal unit on the upstream side and a second moisture removal unit on the downstream side, 3. The radioactive material removal device according to claim 2, further comprising 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 moisture removal unit includes a first moisture removal unit on the upstream side and a second moisture removal unit on the downstream side, The radioactive material removal device according to claim 2, characterized in that 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. 2. The radioactive material removal device according to claim 1, wherein the flow path contains granular solids therein, and the cross-sectional area of ​​the flow path is narrower on the downstream side than on the upstream side due to differences in particle size of the granular solids.

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

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