Filter Vent Device

Abstract

To provide a filter vent device that can prevent decomposition of an organic iodine removing agent and decomposition of a compound reducing and removing inorganic iodine under high temperature and high dose.SOLUTION: A filter vent device 30 according to the present invention comprises a filter vent container 1 having an organic iodine removing agent 2 for collecting organic iodine, scrubbing water 13 for collecting inorganic iodine, and an alkali supply material 3 for providing a pH buffering function to the scrubbing water 13.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a filter vent device.

Background Art

[0002] In a nuclear power plant facility, a filter vent device is installed to prevent radioactive substances released from the nuclear reactor from leaking into the environment. When a core damage occurs in a nuclear reactor accident and the pressure in the containment vessel abnormally increases, the containment vessel may be damaged and lead to a large-scale leak. Therefore, the filter vent device vents the steam in the containment vessel in advance to prevent overpressure damage of the containment vessel. When high-temperature and high-pressure steam is released from the nuclear reactor into the containment vessel, it passes through the filter vent device, and major radioactive substances are collected before being released into the atmosphere.

[0003] Radioactive substances generated during a nuclear reactor accident include noble gases, aerosols, inorganic iodine, organic iodine, etc. In the filter vent device, these radioactive substances except noble gases are captured, and the release into the environment is suppressed. Generally, as described in Patent Document 1, the filter vent device holds scrubbing water that acts as a wet filter in a filter vent container, and further incorporates a fiber filter that is a dry filter.

[0004] The scrubbing water may have a chemical solution added to the water, and the vented steam is released into the scrubbing water. By reacting with the chemical solution, ionized inorganic iodine (elemental iodine) and aerosols are collected by dissolving in the scrubbing water. Also, some aerosols released into the gas phase after passing through the scrubbing water adhere to and collide with the fiber filter and are collected.

[0005] On the one hand, organic iodine, such as methyl iodide, is poorly soluble in water. Even if it is introduced into the pool water or scrubbing water in the pressure suppression chamber during venting, it cannot be sufficiently collected. In addition, organic iodine such as methyl iodide may be newly generated by the reaction of elemental iodine during the exhaust process from the reactor. For these reasons, a filter vent device capable of efficiently collecting organic iodine is required. For example, in Patent Document 2, a dry filter such as silver zeolite or activated carbon is installed on the vent path in the filter vent device to collect organic iodine.

[0006] Since organic iodine removal materials such as silver zeolite and activated carbon may have a reduced collection efficiency when water adheres to them, a mechanism for removing water is required when there is concern about the influence of moisture, which complicates the structure of the filter vent device. In addition, since these organic iodine removal materials are solids, a special device design or a complex device structure is required as in Patent Document 2.

[0007] A technique for solving this problem is disclosed, for example, in Patent Document 3. Patent Document 3 describes that an ionic liquid is disposed as a non-volatile liquid (organic iodine removal material) capable of collecting organic iodine in the filter vent container of the filter vent device. The invention described in Patent Document 3 can capture radioactive substances excluding noble gases with only the filter vent container without requiring a complex device structure by this organic iodine removal material, and can suppress the release to the environment.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] Conventional filter vent devices contain a compound (reducing agent) that reduces and removes inorganic iodine from scrubbing water to reduce and remove inorganic iodine, and physically removes aerosol (particles). On the other hand, for the organic iodine removing material described in Patent Document 3, decomposition can be suppressed when the pH of the scrubbing water is lower under high temperature and high dose during venting. During venting, due to the inflow of radioactive substances into the filter vent container, the scrubbing water containing the organic iodine removing material and the reducing agent is exposed to high temperature and high dose, and the pH of the scrubbing water decreases. When the pH of the scrubbing water becomes 6.5 or less, the decomposition of the reducing agent is promoted. Also, the lower the pH, the lower the function of collecting inorganic iodine in the scrubbing water. If the initial pH is increased to suppress these, the decomposition of the organic iodine removing material (ionic liquid) is promoted, and the removal performance of organic iodine cannot be maintained high.

[0010] The present invention has been made in view of the above situation. An object of the present invention is to provide a filter vent device capable of suppressing the decomposition of an organic iodine removing material and a compound that reduces and removes inorganic iodine under high temperature and high dose.

Means for Solving the Problems

[0011] The filter vent device according to the present invention that solves the above problems has a filter vent container having an organic iodine removing material that collects organic iodine and a scrubbing In water alkali supply material that imparts a pH buffering function. and in the filter vent container, there are the organic iodine removing material and the alkali supply material, and the alkali supply material is installed in a mesh container installed at a position higher than the liquid level of the organic iodine removing material It was decided as follows.

Effects of the Invention

[0012] According to the present invention, it is possible to provide a filter vent device capable of suppressing the decomposition of an organic iodine removing material and a compound that reduces and removes inorganic iodine under high temperature and high dose. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 11

Embodiments for Carrying Out the Invention

[0014] Hereinafter, a filter vent device according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the description of the embodiments, substantially the same or similar configurations are denoted by the same reference numerals, and the description may be omitted when the description is redundant.

[0015] <First Embodiment> Figure 1 is a schematic diagram showing the configuration of a filter vent device 30 according to a first embodiment of the present invention. In Figure 1, the filter vent device 30 is configured to remove radioactive substances contained in the gas as much as possible when the dry well 31 and the wet well 32 release the gas in the containment vessel 33 to reduce the pressure in the containment vessel 33 in the event of a severe accident such as damage to the reactor pressure vessel 34.

[0016] As shown in Figure 1, the filter vent device 30 according to the present embodiment has a filter vent container 1. The filter vent container 1 has an organic iodine removal material 2, scrubbing water 13, and an alkali supply material 3.

[0017] The organic iodine removal material 2 collects and removes organic iodine. The organic iodine removal material 2 has the function of dissolving and decomposing organic iodine, which is a radioactive substance, and retaining the organic iodine as iodide ions. The substance constituting the organic iodine removal material 2 will be described later. The organic iodine removal material 2 is hydrophobic and immiscible with the scrubbing water 13.

[0018] The scrubbing water 13 dissolves and collects inorganic iodine. Although the filter vent device 30 shown in Figure 1 illustrates a state where the scrubbing water 13 is accommodated in the filter vent container 1, the scrubbing water 13 only needs to be accommodated in the filter vent container 1 during venting. It does not necessarily need to be accommodated in the filter vent container 1 during normal operation of the reactor. That is, the scrubbing water 13 in the filter vent container 1 may already be filled before venting, or may be generated by the condensation of steam flowing into the filter vent container 1 during venting. If the scrubbing water 13 is pre-accommodated in the filter vent container 1, it is possible to immediately collect inorganic iodine in the event of an accident. When the scrubbing water 13 is accommodated in the filter vent container 1 during venting, the organic iodine removal material 2, the alkali supply material 3, etc. are less likely to deteriorate.

[0019] The alkali supply material 3 imparts a pH buffering function to the scrubbing water 13. The alkali supply material 3 is a compound that reduces and removes inorganic iodine, and by including this in the scrubbing water 13, the scrubbing water 13 can be given the function of collecting inorganic iodine. The compound constituting the alkali supply material 3 will be described later.

[0020] The filter vent device 30 has a dry well vent pipe 7 and a wet well vent pipe 8 connected to a storage container 33, and an inlet pipe 9 with one end connected to the dry well vent pipe 7 and the wet well vent pipe 8 and the other end disposed below in the filter vent container 1. An isolation valve 5 is provided in the dry well vent pipe 7. An isolation valve 6 is provided in the wet well vent pipe 8. Further, the filter vent device 30 has a fiber filter 10 above in the filter vent container 1 and an outlet pipe 11 with one end disposed downstream of the fiber filter 10, that is, above the fiber filter 10, and the other end connected to an exhaust cylinder 12 outside the filter vent container 1. The filter vent container 1 configured as described above is used for collecting radioactive aerosols, inorganic iodine, and organic iodine.

[0021] Although it varies depending on the individual plant output and accident scenario, among the radioactive substances generated during an accident, in a severe accident involving fuel damage where the reactor pressure vessel 34 is damaged, it is estimated that about 1 kg of organic iodine and about 20 kg of inorganic iodine are generated. It is estimated that mainly methyl iodide (CH3I) is generated as the organic iodine. Also, it is estimated that mainly iodine molecules (I2) are generated as the inorganic iodine.

[0022] Therefore, in this embodiment, a hydrophobic organic iodine-removing material 2 having the property of collecting organic iodine is a substance composed only of cations and anions. As the organic iodine-removing material 2, a liquid that does not substantially volatilize at a temperature lower than about 160°C is used. During a nuclear reactor accident, venting of steam at about 100 to 160°C is assumed. If the liquid acting as the wet filter is non-volatile, even if high-temperature and high-pressure gas is introduced during venting, it is possible to avoid the liquid itself from volatilizing. As the organic iodine-removing material 2, those that do not substantially volatilize at a temperature lower than 200°C are more preferable. Since the organic iodine-removing material 2 only needs to be a liquid at the temperature during venting, it may be a solid at room temperature, but it is more preferably a liquid. Further, the organic iodine-removing material 2 is preferably a liquid (X + ) composed only of a combination of a cation (X - ) and an anion (Y + -Y - ). With such an organic iodine-removing material 2, high collection performance of organic iodine can be achieved by the three-step mechanism ((1) dissolution, (2) decomposition, (3) retention) described later.

[0023] Furthermore, the alkali supply material 3 may be a solid or a liquid at room temperature and atmospheric pressure before venting and at high temperature and high pressure during venting. By having the alkali supply material 3, fluctuations in the pH of the scrubbing water 13 can be suppressed in the high-temperature irradiation environment inside the filter vent container 1, and it is possible to prevent it from becoming extremely acidic (for example, pH 4 or lower) or alkaline (pH 12.5 or higher). Therefore, decomposition of the organic iodine-removing material 2 is suppressed during the main venting period, and high organic iodine collection performance can be obtained. In addition, the alkali supply material 3 has the effect of supplying hydroxide ions (OH - ) to the scrubbing water 13 and interacting with acidic substances such as protons (H + ) in the scrubbing water 13 to buffer the pH, enabling high collection performance of inorganic iodine.

[0024] In addition, as the above-described organic iodine removing material 2, for example, a room temperature molten salt, an ionic liquid, a quaternary salt, a surfactant, a phase transfer catalyst, or a mixture of these can be used. Further, as the above-described alkali supply material 3, for example, an oxide, a hydroxide, a carbonate, a borate, a phosphate, an organic acid salt, an Mg / Al-based layered compound, or a mixture of these can be used.

[0025] During an accident, a gas with a relatively high temperature flows into the filter vent container 1, so it is presumed that organic iodine and inorganic iodine are in a gaseous state. In order to collect gaseous iodine, diffusion electrophoresis, thermophoresis, Brownian diffusion, and convection of iodine in bubbles in a liquid are utilized. In the present embodiment, in order to bring the organic iodine removing material 2 and the scrubbing water 13 into contact with gaseous iodine, it is desirable to provide the organic iodine removing material 2 and the scrubbing water 13 so that the residence time (contact time between the bubbles and the liquid) of the bubbles in the liquid becomes long. The longer the residence time (contact time) is, the easier the reaction between the organic iodine removing material 2 and the organic iodine occurs and can be removed. To embody this, in the present embodiment, for example, a dispersion pipe such as a sparger may be provided at the other end of the inlet pipe 9 disposed below the filter vent container 1 to generate fine and numerous bubbles.

[0026] Next, with reference to FIG. 1, the operating principle of the filter vent device 30 according to the first embodiment will be described. During an accident, the radioactive substances released from the reactor pressure vessel 34 to the containment vessel 33 are introduced into the dry well vent pipe 7 or the wet well vent pipe 8 connected to the containment vessel 33 by opening the isolation valve 5 or the isolation valve 6. Thereafter, the radioactive substances flow into the scrubbing water 13 in the filter vent container 1 via the inlet pipe 9. Alternatively, due to the condensation of steam, scrubbing water 13 is generated in the filter vent container 1, and the radioactive substances flow therein via the inlet pipe 9. Thereby, inorganic iodine is collected in the scrubbing water 13.

[0027] At this time, since the alkali supply material 3 in the filter vent container 1 imparts a pH buffering function to the scrubbing water 13, it is possible to suppress fluctuations in the pH of the scrubbing water 13 and prevent it from becoming extremely acidic (e.g., pH 4 or lower) or alkaline (pH 12.5 or higher). Therefore, the filter vent device 30 can suppress the decomposition of the organic iodine removing material 2 that comes into contact with the scrubbing water 13 during the main vent period. Further, the alkali supply material 3 is a compound that reduces and removes inorganic iodine, and as described above, it is possible to give the scrubbing water 13 a function of collecting inorganic iodine. The organic iodine that was not collected by the scrubbing water 13 flows into the hydrophobic organic iodine removing material 2, is decomposed into iodide ions, and is collected. Aerosols, which are radioactive substances other than iodine, are also collected by the scrubbing water 13 in the filter vent container 1. The gas after iodine collection passes through the fiber filter 10 and the outlet pipe 11 and is discharged to the outside through the exhaust stack 12 in a state where radioactive substances have been sufficiently removed.

[0028] The collection of inorganic iodine is carried out by decomposing radioactive inorganic iodine (I2) into radioactive iodide ions (I - ) or iodate ions (IO3 - ) by the alkali supply material 3 or the scrubbing water 13 or both of them (the above-mentioned (2) decomposition). This is also carried out in the same manner when the chemical solution 4 described later is included. 3I2 + 6OH - → 5I - + IO3 - + 3H2O

[0029] Also, the collection of organic iodine is carried out by decomposing radioactive organic iodine (RI) into radioactive iodide ions (I - ) by the organic iodine removing material 2 as shown in the following formula. In the following formula, R represents an organic substance (hydrocarbon group) such as an alkyl group (the same applies hereinafter). X + -Y - + RI → X + -Y - + I - + R +

[0030] Iodide ions are more stable in the liquid phase compared to organoiodine and interact with the cations of the organoiodine remover 2, being stably retained in the state of iodide ions. Therefore, radioactive organoiodine can be retained in the liquid phase to reliably prevent leakage into the environment (the above-mentioned (3) retention). Although organoiodine can be sufficiently collected only by the organoiodine remover 2, the decomposition of the organoiodine remover 2 can be suppressed by using the organoiodine remover 2 and the alkali supply material 3 in combination, and a high collection performance of organoiodine can be maintained during the vent period.

[0031] Examples of the cation constituting the organoiodine remover 2 include organic cations such as phosphonium, sulfonium, ammonium, pyrrolidinium, piperidinium, and morpholinium. As the cation constituting the organoiodine remover 2, it is only necessary that the structure of the cation is mainly bonded to substituents such as carbon around a phosphorus element, a sulfur element, or a nitrogen element. Preferably, in order to maintain high solubility of iodine, it is preferably mainly composed of a single-bond carbon chain, but a part thereof may be cross-linked by a double bond, a triple bond, or an oxygen element. For example, methyl iodide, which is organoiodine, does not dissolve in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide and separates, but dissolves in trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)amide having the same anion structure but a different cation structure and is uniformly mixed. Substances such as a methyl group having 1 carbon chain number decompose and volatilize at a high temperature of 160°C, so the carbon chain number is preferably 2 or more. For example, it has been found that 1-butyl-3-methylimidazolium iodide causes the methyl group of the cation to desorb and self-decompose at 160°C. From such a viewpoint, it can be said that it is preferable that the organic cation has a long carbon chain and is bulky because the solubility of organoiodine (the above-mentioned (1) dissolution) and the heat resistance of the organic cation are increased, so that organoiodine can be collected with high collection efficiency.

[0032] Examples of anions constituting the organic iodine removing material 2 include inorganic anions such as H3C having an anionic charge on the carbon element - and organic anions such as H2RC - , HR2C - , R3C - , NC - , RCC - . Also included are organic anions such as RS - having an anionic charge on the sulfur element. Also included are inorganic anions such as N3 - , H2N - and organic anions such as HRN - , R2N - having an anionic charge on the nitrogen element. Also included are organic anions such as RO - , RCO2 - , RPO3 - , RSO3 - , RPO4 - , R2PO2 - , R3CO - and inorganic anions such as HO - , NO2 - , FO3 - , ClO3 - , BrO3 - , IO3 - , FO4 - , ClO4 - , BrO4 - , IO4 - . Also included are inorganic anions such as F - , Cl - , Br - , I - , F3 - , Cl3 - , Br3 - , I3 - having an anionic charge on the halogen element. As anions constituting the organic iodine removing material 2, ions with high nucleophilicity are preferred in terms of having a strong action of decomposing organic iodine, and in particular, those in which the charged element, excluding the hydrogen element, is present at the terminal are preferred. For example, compared with H2N - , R2N - (R-N -An anion molecule composed of elements other than hydrogen, centered around a charged nitrogen element such as (-R), has a low nucleophilicity and a reduced decomposition performance with respect to methyl iodide. As an anion, due to its high nucleophilicity, its difficulty in undergoing hydrolysis, and its difficulty in changing the pH of the scrubbing water 13 when injected into the filter vent container 1, H3C - 、H2RC - 、HR2C - 、R3C - 、NC - 、RCC - 、RS - 、N3 - 、H2N - 、HRN - 、R2N - 、RO - 、RCO2 - 、RPO3 - 、RSO3 - 、RPO4 - 、R2PO2 - 、R3CO - 、HO - 、NO2 - 、FO3 - 、ClO3 - 、BrO3 - 、IO3 - 、FO4 - 、ClO4 - 、BrO4 - 、IO4 - 、F - 、Cl - 、Br - 、I - 、F3 - 、Cl3 - 、Br3 - 、I3 - etc. are preferred. In order to collect organic iodine with high performance, not only the dissolution of iodine by the cation of the organic iodine removing material 2 (the above-mentioned (1) dissolution), but also the decomposition of iodine caused by the nucleophilic attack of the anion on iodine is required. Taking an example of the organic iodine removing material 2, there is trihexyl (tetradecyl) phosphonium chloride and the like.

[0033] Examples of the compound constituting the alkali supply material 3 include MgO, CaO, SrO, Mg(OH)2, Fe(OH)2, CaMg(CO3)2, Na2CO3, NaHCO3, Na2B4O7, Na2B 10 O 16 , Na2HPO4, KH2PO4, C8H5KO4, Mg6Al2(OH) 16 CO3·mH2O, and the like. When the alkali supply material 3 is a solid such as MgO, MgO reacts with H2O as shown in the following formula to generate OH - , thereby increasing the pH. However, when OH - reacts with H + , the pH decreases. The reaction between MgO and H2O reaches equilibrium at a pH of 10 to 11, and the reaction between MgO and H2O no longer occurs, so the pH no longer increases. Therefore, it is possible to suppress the pH of the scrubbing water 13 from becoming extremely alkaline (pH 12.5 or higher). MgO(s) + H2O → Mg 2+ + 2OH - 2OH - + 2H + → 2H2O

[0034] The content of the alkali supply material 3 is preferably 400 ppm or more with respect to the scrubbing water 13. Further, the alkali supply material 3 may be a pH buffer solution in which the content of the alkali supply material 3 is 400 ppm or more with respect to the scrubbing water 13. In either case, the filter vent device 30 can suppress the decomposition of the organic iodine removing material 2 and the decomposition of the compound for reducing and removing inorganic iodine during the main vent period, and high organic iodine collection performance and inorganic iodine collection performance can be obtained.

[0035] Next, the effects of the present embodiment will be described. The filter vent device 30 according to the first embodiment described above includes a filter vent container 1, a dry well vent pipe 7 and a wet well vent pipe 8 connected to a storage container 33, an inlet pipe 9 having one end connected to the dry well vent pipe 7 and the wet well vent pipe 8 and the other end introduced into the filter vent container 1, and an outlet pipe 11 connected to a fiber filter 10. The filter vent device 30 has a hydrophobic organic iodine removing material 2 for collecting organic iodine in the filter vent container 1. The filter vent device 30 also has scrubbing water 13 for collecting inorganic iodine in the filter vent container 1. Further, the filter vent device 30 has an alkali supply material 3 that imparts a pH buffering function to the scrubbing water 13. This alkali supply material 3 can suppress the decomposition of the organic iodine removing material 2, and can also suppress the decomposition of a compound (including not only the alkali supply material 3 itself but also a chemical solution 4 described later) that reduces and removes inorganic iodine contained in the scrubbing water 13 by the pH buffering function. Thus, the filter vent device 30 according to the first embodiment has only the organic iodine removing material 2, the scrubbing water 13, and the alkali supply material 3 in the filter vent container 1 (that is, without installing a dry filter such as silver zeolite or activated carbon on the vent path in the filter vent device as in the prior art), and can suppress the decomposition of the organic iodine removing material 2 during the main vent period and maintain high organic iodine collection performance. Further, the filter vent device 30 according to the first embodiment can give the scrubbing water 13 a function of collecting inorganic iodine by the alkali supply material 3 containing a compound that reduces and removes inorganic iodine, while suppressing the decomposition of the compound. Furthermore, the organic iodine removing material 2 is a liquid containing at least one of a room temperature molten salt, an ionic liquid, a surfactant, a quaternary salt, and a phase transfer catalyst. Among these organic iodine removing materials 2, the ionic liquid has been put into practical use for general industry. These organic iodine removing materials 2 are characterized by being non-volatile and having sufficient heat resistance even under the condition of about 200°C, which is the gas temperature that is supposed to flow into the filter vent device 30 during an accident. The ionic liquid also has the property of collecting substrates such as radioactive substances at a high concentration in the ionic liquid.In particular, since organic iodine is poorly soluble in water and highly volatile, by using an ionic liquid as a powerful non-volatile liquid for collecting it, organic iodine can be collected with an efficiency of 98% or more. Similarly, a room-temperature molten salt, a surfactant, a quaternary salt, and a phase-transfer catalyst can also be suitably applied to the organic iodine removing material 2, and the same effect as that of the ionic liquid can be obtained. Further, since the organic iodine removing material 2 is a liquid that remains in the liquid phase even at 200°C or higher, even in the event of an accident, the organic iodine removing material 2 can be stably present in the liquid phase, and organic iodine can be sufficiently collected.

[0036] In this embodiment, the type of the nuclear reactor is not particularly limited. Examples of the nuclear reactor include various types such as a boiling water reactor (BWR), an advanced boiling water reactor (ABWR), and a pressurized water reactor (PWR). Ionic liquids contaminated with radioactive substances can be treated and regenerated, for example, by the method described in Japanese Patent Application Laid-Open No. 2003-507185.

[0037] <Second Embodiment> FIG. 2 is a schematic diagram showing the configuration of a filter vent device 30 according to the second embodiment of the present invention. As shown in FIG. 2, the filter vent device 30 according to the present embodiment is different from the filter vent device 30 according to the first embodiment shown in FIG. 1 in that the alkali supply material 3 is a liquid. Other configurations and operations are the same as those of the filter vent device 30 according to the first embodiment described above. Although the scrubbing water 13 is not shown in FIG. 2, the scrubbing water 13 is generated by condensation of the vapor introduced into the filter vent container 1 during venting. With such a configuration, it is possible to suppress the decomposition of the alkali supply material 3 due to the contact between the alkali supply material 3 and the scrubbing water 13 before venting.

[0038] <Third Embodiment> FIG. 3 is a schematic diagram showing a configuration example of a filter vent device 30 according to a third embodiment of the present invention. FIG. 4 is a schematic diagram showing another configuration example of the filter vent device 30 according to the third embodiment of the present invention. As shown in FIGS. 3 and 4, the filter vent device 30 according to the present embodiment is different from the filter vent device 30 according to the first embodiment shown in FIG. 1 in that it includes a first storage container 14a connected to the filter vent container 1 via an injection valve 16 (specifically, a first injection valve 16a). That is, the filter vent device 30 according to the present embodiment is different from the filter vent device 30 according to the first embodiment in that the first storage container 14a is installed outside the filter vent container 1. Further, as shown in FIGS. 3 and 4, the filter vent device 30 according to the present embodiment is different from the filter vent device 30 according to the first embodiment in that the filter vent container 1 does not contain scrubbing water 13. Other configurations and operations are the same as those of the filter vent device 30 according to the first embodiment described above. Therefore, the scrubbing water 13 is stored in the filter vent container 1 during venting. The filter vent container 1 and the first storage container 14a are connected by a first injection pipe 15a. The first injection valve 16a is provided in the first injection pipe 15a.

[0039] And in the third embodiment, as shown in FIG. 3, the filter vent container 1 can have an organic iodine removing material 2 therein and the first storage container 14a can have an alkali supply material 3 therein. Or, in the third embodiment, as shown in FIG. 4, the filter vent container 1 can have an alkali supply material 3 therein and the first storage container 14a can have an organic iodine removing material 2 therein. In the aspect of the filter vent device 30 according to the third embodiment shown in FIGS. 3 and 4, the organic iodine removing material 2 and the alkali supply material 3 are stored in different containers. Therefore, the possibility of decomposition of the organic iodine removing material 2 and the alkali supply material 3 can be eliminated during long-term storage until the filter vent device 30 is used in the event of an accident.

[0040] In the third embodiment, at the time of venting, the first injection valve 16a is opened at a timing earlier than the isolation valves 5 and 6. By doing so, immediately before the vapor is introduced from the storage container 33 into the filter venting device 30, the organic iodine removing material 2 and the alkali supply material 3 will be present in the filter venting container 1. Then, in this state, the vapor containing radioactive substances is introduced into the filter venting container 1, where it condenses to generate scrubbing water 13 (not shown in FIGS. 3 and 4) for treatment. Therefore, the filter venting device 30 can more surely remove organic iodine by the organic iodine removing material 2 and collect inorganic iodine by the scrubbing water 13.

[0041] <Fourth Embodiment> FIG. 5 is a schematic diagram showing a configuration example of a filter venting device 30 according to the fourth embodiment of the present invention. As shown in FIG. 5, the filter venting device 30 according to the present embodiment is different from the filter venting device 30 according to the second embodiment shown in FIG. 2 in that it includes a first storage container 14a connected to the filter venting container 1 via an injection valve 16 (specifically, the first injection valve 16a). Further, the filter venting device 30 according to the present embodiment is different from the filter venting device 30 according to the second embodiment shown in FIG. 2 in that the first storage container 14a is installed outside the filter venting container 1. Furthermore, the filter venting device 30 according to the present embodiment is different from the filter venting device 30 according to the second embodiment in that the filter venting container 1 has a chemical solution 4 for enhancing the function of collecting inorganic iodine. The chemical solution 4 will be described in the fifth embodiment. Other configurations and operations are the same as those of the filter venting device 30 according to the second embodiment described above. The filter venting container 1 and the first storage container 14a are connected by a first injection pipe 15a. The first injection valve 16a is provided on the first injection pipe 15a.

[0042] And in the fourth embodiment, (i) the filter vent container 1 can have the organic iodine removing material 2 and the alkali supply material 3 therein, and the chemical solution 4 can be provided in the first storage container 14a. In this case, the alkali supply material 3 can be either solid or liquid (FIG. 5 illustrates the liquid alkali supply material 3). Alternatively, in the fourth embodiment, (ii) the filter vent container 1 can have the alkali supply material 3 and the chemical solution 4 therein, and the organic iodine removing material 2 can be provided in the first storage container 14a. Also in this case, the alkali supply material 3 can be either solid or liquid. Alternatively, in the fourth embodiment, (iii) the filter vent container 1 can have the organic iodine removing material 2 and the chemical solution 4 therein, and the alkali supply material 3 can be provided in the first storage container 14a. Also in this case, the alkali supply material 3 can be either solid or liquid. Note that FIG. 5 illustrates the mode (i) as a representative of these (the modes (ii) and (iii) are not illustrated). In the mode of the filter vent device 30 according to the fourth embodiment shown in FIG. 5, one of the organic iodine removing material 2, the alkali supply material 3, and the chemical solution 4 is stored in a different container. Therefore, the possibility of decomposition of these elements can be eliminated during long-term storage until the filter vent device 30 is used in the event of an accident.

[0043] Similar to the third embodiment, in the fourth embodiment, at the time of venting, the first injection valve 16a is opened at a timing earlier than the isolation valves 5 and 6. By doing so, immediately before the vapor is introduced from the storage container 33 into the filter vent device 30, the organic iodine removing material 2, the chemical solution 4, and the alkali supply material 3 are accommodated in the filter vent container 1. Then, in this state, the vapor containing radioactive substances is introduced into the filter vent container 1, and the vapor condenses to generate the scrubbing water 13 (not shown in FIGS. 3 and 4) for treatment. Therefore, the filter vent device 30 can surely remove the organic iodine by the organic iodine removing material 2 and collect the inorganic iodine by the scrubbing water 13 and the chemical solution 4.

[0044] <Fifth Embodiment> FIG. 6 is a schematic diagram showing the configuration of a filter vent device 30 according to the fifth embodiment of the present invention. As shown in FIG. 6, the filter vent device 30 according to the present embodiment is different from the filter vent device 30 according to the first embodiment shown in FIG. 1 in that a chemical solution 4 is filled in the filter vent container 1 instead of the scrubbing water 13. Other configurations and operations are the same as those of the filter vent device 30 according to the first embodiment described above.

[0045] The chemical solution 4 is a basic compound having no pH buffering function and functions as a reducing agent. As the chemical solution 4, a mixture of the chemical solution 4 and the alkali supply material 3 can also be used. Examples of the chemical solution 4 include hydroxides such as NaOH, KOH, NH2OH, and N2H5OH, and nitrogen-sulfur compounds such as (NH4)2S and H2NC2H4SH, which have an effect of enhancing the iodine trapping function. Here, FIG. 7 is a graph showing the decomposition behavior of the organic iodine removing material 2 and the chemical solution 4. When the pH exceeds 12 in a high-temperature irradiation environment, the decomposition of the organic iodine removing material 2 is promoted, and when it is below near neutral pH of 6, the decomposition of the chemical solution 4 is promoted. In order to suppress the decomposition of both the organic iodine removing material 2 and the chemical solution 4, it is preferable to keep the equilibrium pH of the alkali supply material 3 between 4 and 12.5 (pH fluctuation allowable range) as shown in FIG. 7 during the main vent period under high temperature and high dose. By the alkali supply material 3 assuming the function of keeping the pH between 4 and 12.5, the inorganic iodine trapping function by the chemical solution 4 can be maintained high, and the organic iodine removing function by the organic iodine removing material 2 can be maintained high. Note that when exposed to high temperature and high dose without the alkali supply material 3, the pH of each of the chemical solution 4, the scrubbing water 13, and the organic iodine removing material 2 decreases as shown by the arrow A in FIG. 7.

[0046] <Sixth Embodiment> FIG. 8 is a schematic diagram showing a configuration example of a filter vent device 30 according to the sixth embodiment of the present invention. As shown in FIG. 8, in the filter vent device 30 according to the present embodiment, the first storage container 14a and the second storage container 14b are installed outside the filter vent container 1. Specifically, the filter vent device 30 according to the present embodiment includes a first storage container 14a connected to the filter vent container 1 via an injection valve 16 (first injection valve 16a), and a second storage container 14b connected to the filter vent container 1 via an injection valve 16 (second injection valve 16b). That is, the filter vent device 30 according to the present embodiment is different from the filter vent device 30 according to the third embodiment shown in FIG. 3 in that it includes a second storage container 14b connected to the filter vent container 1 via the second injection valve 16b. Other configurations and operations are the same as those of the filter vent device 30 according to the third embodiment described above.

[0047] Note that the filter vent container 1 and the first storage container 14a are connected by a first injection pipe 15a, similar to the third embodiment. The first injection valve 16a is provided in the first injection pipe 15a. The filter vent container 1 and the second storage container 14b are connected by a second injection pipe 15b. The second injection valve 16b is provided in the second injection pipe 15b. That is, in the sixth embodiment, the first storage container 14a and the second storage container 14b are each individually connected to the filter vent container 1 via an injection valve 16 (specifically, the first injection valve 16a and the second injection valve 16b, respectively). In this way, by appropriately opening the first injection valve 16a and the second injection valve 16b during venting, the alkali supply material 3 stored in the first storage container 14a and the chemical solution 4 stored in the second storage container 14b can be individually injected into the filter vent container 1.

[0048] In the sixth embodiment, one kind is selected from the group consisting of the organic iodine removing material 2, the alkali supply material 3, and the chemical solution 4 and stored in each of the filter vent container 1, the first storage container 14a, and the second storage container 14b. FIG. 8 typically shows a state in which the organic iodine removing material 2 is stored in the filter vent container 1, the alkali supply material 3 is stored in the first storage container 14a, and the chemical solution 4 is stored in the second storage container 14b among such aspects. In the aspect of the sixth embodiment, the organic iodine removing material 2, the alkali supply material 3, and the chemical solution 4 are stored in different containers, and the possibility of decomposition of the organic iodine removing material 2, the alkali supply material 3, and the chemical solution 4 can be eliminated during long-term storage until the use (venting) of the filter vent device 30 in the event of an accident.

[0049] FIG. 9 is a schematic diagram showing another configuration example of the filter vent device 30 according to the sixth embodiment of the present invention. The filter vent device 30 shown in FIG. 9 is different from the filter vent device 30 shown in FIG. 8 in that the second storage container 14b and the first storage container 14a are connected via an injection valve 16 (specifically, the second injection valve 16b), and the first storage container 14a and the filter vent container 1 are connected via an injection valve 16 (specifically, the first injection valve 16a). That is, in the filter vent device 30 shown in FIG. 9, the first storage container 14a and the second storage container 14b are connected in series. Other configurations and operations are the same as those of the filter vent device 30 shown in FIG. 8 described above. Since the filter vent device 30 shown in FIG. 9 has the above-described configuration, for example, the chemical solution 4 can be made to flow into the solid alkali supply material 3 and easily injected into the filter vent container 1.

[0050] <Seventh Embodiment> FIG. 10 is a schematic diagram showing the configuration of the filter vent device 30 according to the seventh embodiment of the present invention. As shown in Fig. 10, the filter vent device 30 according to the seventh embodiment is different from the filter vent device 30 according to the third embodiment shown in Fig. 3 in that a mesh container 17 is installed in the filter vent container 1 instead of the first storage container 14a, and an alkali supply material 3 is installed in this mesh container 17. The mesh container 17 is installed at a position higher than the liquid level of the organic iodine removing material 2 in the filter vent container 1. Other configurations and operations are the same as those of the filter vent device 30 according to the third embodiment described above.

[0051] The filter vent device 30 according to the seventh embodiment has a simpler configuration compared to the mode in which, like the filter vent device 30 according to the third embodiment, it has a first storage container 14a outside the filter vent container 1 and has an alkali supply material 3 in this first storage container 14a. Also, during venting, steam is introduced into the filter vent container 1 and condensed to become scrubbing water 13, and the liquid level rises, so that the alkali supply material 3 dissolves in the liquid. Therefore, compared to the filter vent device 30 according to the third embodiment, the filter vent device 30 according to the seventh embodiment does not need to perform the operation of opening the first injection valve 16a (injection operation). Therefore, the filter vent device 30 according to the seventh embodiment can easily perform the removal of organic iodine by the organic iodine removing material 2 and the collection of inorganic iodine by the scrubbing water 13 while being easy to operate.

[0052] Next, with reference to Fig. 10, the operating principle of the filter vent device 30 according to the seventh embodiment will be described. During an accident, the radioactive substances released from the reactor pressure vessel 34 to the containment vessel 33 are introduced into the dry well vent pipe 7 or the wet well vent pipe 8 connected to the containment vessel 33 by opening the isolation valve 5 or the isolation valve 6. Thereafter, the radioactive substances are introduced into the filter vent container 1 via the inlet pipe 9. Scrubbing water 13 (not shown in FIG. 10) is generated by the condensation of steam, and as the liquid level of the scrubbing water 13 rises, the alkali supply material 3 comes into contact with the scrubbing water 13. By the contact between the alkali supply material 3 and the scrubbing water 13, the scrubbing water 13 reaches the equilibrium pH of the alkali supply material 3 without an excessive increase in pH. Also, inorganic iodine is trapped by the scrubbing water 13. Since the alkali supply material 3 in the filter vent container 1 has a pH buffering action, it can suppress fluctuations in the pH of the scrubbing water 13 and prevent it from becoming extremely acidic (for example, pH 4 or less) or alkaline (pH 12.5 or more), and can suppress the decomposition of the organic iodine removing material 2 that comes into contact with the scrubbing water 13 during the main vent period.

[0053] Also, in this embodiment, the chemical solution 4 can be installed in the mesh container 17, and a mixture of the alkali supply material 3 and the chemical solution 4 can also be installed in the mesh container 17 (neither is shown in FIG. 10). In the case of these embodiments, for example, the lid portion has a mesh structure, and the bottom portion and the side wall portion do not adopt a mesh structure. Even in these embodiments, the collection functions of organic iodine and inorganic iodine can be enhanced.

[0054] As described above, the filter vent device according to the present invention has been described in detail according to the embodiments. However, the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Also, for a part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

[0055] For example, FIG. 11 is a schematic diagram showing a modified example of the filter vent device 30 according to the present invention. As shown in FIG. 11, the filter vent device 30 may have an organic iodine removing material 2, an alkali supply material 3, scrubbing water 13, and a chemical solution 4 in the filter vent container 1. Specifically, as shown in FIG. 11, the filter vent container 1 may have the organic iodine removing material 2 and the scrubbing water 13 therein, the alkali supply material 3 may be stored in the first storage container 14a, and the chemical solution 4 may be stored in the second storage container 14b. In the embodiment shown in FIG. 11, the first storage container 14a is connected to the filter vent container 1 by the first injection pipe 15a via an injection valve 16 (specifically, the first injection valve 16a). The second storage container 14b is connected to the filter vent container 1 by the second injection pipe 15b via an injection valve 16 (specifically, the second injection valve 16b). In this modified example, the alkali supply material 3 and the chemical solution 4 are stored in containers different from the filter vent container 1, respectively. Therefore, the filter vent device 30 according to this modified example can suppress the decomposition of the alkali supply material 3 and the chemical solution 4 during long-term storage until the filter vent device 30 is used (vented) during an accident.

[0056] Also, in the present embodiment, the filter vent device 30 may include a scrubbing water storage container (not shown in any figure) connected to the filter vent container 1 via an injection pipe and a valve provided in this injection pipe, and the scrubbing water 13 can be stored in this scrubbing water storage container. By doing so, the filter vent device 30 can quickly inject the scrubbing water 13 into the filter vent container 1 during venting and be prepared for collecting inorganic iodine.

Description of Reference Numerals

[0057] 1 Filter vent container 2 Organic iodine removing material 3 Alkali supply material 4 Chemical solution 5 Isolation valve 6 Isolation valve 7 Dry well vent pipe 8 Wet well vent pipe 9 Inlet pipe 10 Fiber filter 11 Outlet pipe 12 Exhaust stack 13 Scrubbing water 14a First storage container 14b Second storage container 15a First injection pipe 15b Second injection pipe 16 Injection valve 16a First injection valve 16b Second injection valve 17 Mesh container 30 Filter vent device 31 Dry well 32 Wet well 33 Storage container 34 Reactor pressure vessel

Claims

1. The filter vent container has an organic iodine removing material for collecting organic iodine, and an alkali supply material for imparting a pH buffering function to the scrubbing water for collecting inorganic iodine, and has inside the filter vent container, the organic iodine removing material and the alkali supply material, wherein the alkali supply material is installed inside a mesh container installed at a position higher than the liquid level of the organic iodine removing material A filter vent device characterized by the above.

2. In the filter vent device according to Claim 1, the filter vent container further has a chemical solution having a function of enhancing the collection function of the inorganic iodine. A filter vent device characterized by the above.

3. In the filter vent device according to Claim 2, inside a mesh container having a lid portion with a mesh structure, there is the chemical solution, or a mixture of the alkali supply material and the chemical solution. A filter vent device characterized by the above.

4. In the filter vent device according to Claim 2 or Claim 3, the chemical solution is a basic compound having no pH buffering function. A filter vent device characterized by the above.

5. In the filter vent device according to Claim 1, the content of the alkali supply material is 400 ppm or more with respect to the scrubbing water. A filter vent device characterized by the above.

6. In the filter vent device according to Claim 1, Claim 2, Claim 3 or Claim 5, the equilibrium pH of the alkali supply material is 4 to 12.

5. A filter vent device characterized by the above.

7. In the filter vent device according to Claim 4, the equilibrium pH of the alkali supply material is 4 to 12.

5. A filter vent device characterized by the above.

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