JP2016186427A - Filter vent method, filter vent device, and nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter vent device capable of holding radioactive iodine underwater in a scrubbing container for a long time.SOLUTION: Scrubbing water 12 containing many platinum oxide nanoparticles 33 is filled into a vent tank 11 of a filter vent device 10. A filter 13 is disposed above the water level of the scrubbing water 12 in the vent tank 11. One end of an inlet pipe 14 including a separation valve 15 is dipped into the scrubbing water 12, and the other end of the inlet pipe 14 is made to communicate with a wet well of a containment vessel. When a severe accident occurs, gas containing radioactive iodine Iand hydrogen is discharged from the wet well to the scrubbing water 12 through the inlet pipe 14. The radioactive iodine Iis converted into Iby an action of the hydrogen and the platinum of the platinum oxide nanoparticles 33. The generated Iis stably held in the scrubbing water 12 for a long time.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a filter vent method, a filter vent apparatus, and a nuclear power plant, and more particularly, suppresses release of radioactive substances (particularly, radioactive iodine) from a reactor containment vessel during venting after a severe accident in a nuclear power plant. The present invention relates to a filter vent method, a filter vent apparatus, and a nuclear power plant suitable for the above.

  In a boiling water nuclear power plant (BWR plant), a reactor pressure vessel is disposed in a reactor containment vessel, and the atmosphere of the dry well in the reactor containment vessel is replaced with nitrogen gas during operation of the BWR plant. Furthermore, an emergency gas treatment system and a combustible gas concentration control system are communicated to the dry well in the reactor containment vessel in case of an accident of loss of coolant. The combustible gas concentration control system has a recombiner that contains a catalyst for reacting hydrogen and oxygen.

  For example, if a coolant loss accident occurs in which piping connected to the reactor pressure vessel breaks in the containment vessel, high-temperature and high-pressure cooling water in the reactor pressure vessel is Is discharged into the dry well in the containment vessel as high-temperature steam. The water level of the cooling water in the reactor pressure vessel is lowered, and a water-zirconium reaction occurs in the fuel rod that has become high temperature to generate a large amount of hydrogen gas. In addition, oxygen gas is generated together with hydrogen gas by radiolysis of water generated by the released radioactive material. Hydrogen gas and oxygen gas flow into the combustible gas concentration control system together with gases such as nitrogen gas and water vapor in the dry well. Hydrogen gas and oxygen gas are recombined by a chemical reaction caused by the action of the catalyst in the recombiner of the combustible gas concentration control system to be water (steam). Moreover, the emergency core cooling system is activated by the lowering of the coolant level in the reactor pressure vessel, and the coolant is injected into the core in the reactor pressure vessel. Thus, even when a coolant loss accident occurs, the safety of the BWR plant is maintained.

  On the other hand, if the emergency gas treatment system and combustible gas concentration control system installed for hydrogen treatment do not function due to a severe accident and the hydrogen generation continues, The internal pressure increases and approaches the limit value of internal pressure. A filter vent device, which is a technique for suppressing the pressure increase in the reactor containment vessel under such a severe accident situation, is provided in the BWR plant. Examples of filter vent devices are described in JP-A-3-209193, JP-A-9-101393, JP-A-2014-44118, JP-A-7-209488, and the like.

  In JP-A-3-209193, in two BWR plants, a pressure suppression pool of a pressure suppression chamber formed in a reactor containment vessel of the other BWR plant is used as a filter vent device. When a severe accident occurs in a BWR plant among a plurality of BWR plants installed in a nuclear power plant, the gas containing the radionuclide of the dry well in the reactor containment vessel of this BWR plant is The cooling water of the pressure suppression pool formed in the pressure suppression chamber in the reactor containment vessel is raised through, and after some radionuclides are removed in the cooling water, it is formed above the pool in the pressure suppression chamber Reach the wet well. The gas containing the radionuclide is further discharged into the cooling water of the pressure suppression pool in the pressure suppression chamber of another BWR plant, and after removing the radionuclide with this cooling water, the gas passes through the wet well in the latter pressure suppression chamber. Is discharged from the exhaust stack to the outside environment.

  In Japanese Patent Laid-Open No. 9-101393, in a severe accident, a gas containing a radionuclide reaching a wet well above a pressure suppression pool in a pressure suppression chamber in a reactor containment vessel of a BWR plant is stored in a condensate storage tank. The radionuclide is removed in water. The gas from which the radionuclide has been removed is released to the outside environment through the vent pipe.

  The filter vent device described in Japanese Patent Application Laid-Open No. 2014-44118 is connected to each of a dry well in a reactor containment vessel of a BWR plant and a wet well formed above a pressure suppression pool in a pressure suppression chamber. A filter container (vent tank) is provided, and the filter container is filled with pool water, and a filter for collecting radionuclides is installed in the gas phase portion above the pool water in the filter container. In a severe accident, the gas containing the radionuclide in the dry well and wet well is released into the pool water in the filter container, and a part of the radionuclide is removed by the pool water, and then in the gas phase part in the filter container. The radionuclide contained in the reached gas is removed by the filter in the filter container.

  Similar to the filter vent device described in Japanese Patent Laid-Open No. 2014-44118, the filter vent device described in Japanese Patent Laid-Open No. 7-209488 is a scrubber tank (vented with a filter disposed therein and filled with water. Tank). In JP-A-7-209488, a collection tank having a moisture removal layer and an activated carbon filter is disposed downstream of the scrubber tank and connected to the scrubber tank.

  Non-Patent Document 1 and Non-Patent Document 2 also describe filter vent devices.

  Japanese Patent Laid-Open No. Hei 4-194791 discloses water containing sodium thiosulfate in a reactor containment vessel in order to remove radioactive iodine released from the reactor pressure vessel into the reactor containment vessel in the event of a reactor accident. It describes that it is sprayed.

  Japanese Laid-Open Patent Publication Nos. 2014-101240 and 2014-163811 describe colloidal particles that are nanoparticles containing a noble metal oxide. Japanese Patent Application Laid-Open No. 2005-10160 describes catalyst nanoparticles containing one or more of platinum, palladium, osmium, rhodium, ruthenium, iridium, oxides, nitrides, borides, phosphides, and mixtures of these metals. doing.

JP-A-3-209193 JP-A-9-101393 JP 2014-44118 A JP-A-7-209488 JP-A-4-194791 JP 2014-101240 A JP 2014-163811 A Japanese Patent Laid-Open No. 2005-10160

18th Power and Energy Technology Symposium OS8-2 “Light Water Reactor / New Reactor / Nuclear Safety” of the Japan Society of Mechanical Engineers

The OECD Nuclear Energy Agency, “Specialist meeting on filtered containment venting systems”, CSNI report 148 (1988). NUREG / CR-5950 (Iodine evolution and pH control)

  In the filter vent apparatus described in Japanese Patent Application Laid-Open No. 2014-44118 and Japanese Patent Application Laid-Open No. 7-209488, water (scrubbing water) for removing radionuclides contained in the supplied gas is provided inside the vent tank; Contains a filter. The gas flowing into the vent tank is first released into the scrubbing water, and the aerosol contained in the gas and the components dissolved in the water are removed in the scrubbing water. Particulates and gas components not captured by the scrubbing water contained in the gas flowing out of the scrubbing water in the vent tank are removed by a filter in the vent tank. This filter is classified into a type that physically removes the aforementioned substance, a type that removes the substance by a chemical reaction, and a type that has the performance of both.

  An alkaline substance is added to the scrubbing water to remove radioactive iodine. A representative example of this alkaline substance is sodium hydroxide.

In NUREG / CR-5950 (Iodine evolution and pH control), iodine in water under irradiation has an equilibrium between I ₂ and I ⁻ , and when the pH of the water is on the acidic side, I It states that the ratio of ₂ will increase. In this equilibrium, the equilibrium reaction between iodine compounds of I ₂ , I ⁻ , HOI and IO ⁻ is taken into consideration as in the formulas (1) and (2), and the distribution ratio of each component is determined by the component ratio. Depends on the pH of the water present.

I ₂ + OH ⁻ = I ⁻ + HOI (1)
^{HOI = IO - + H + ...} (2)
When the pH of water is made alkaline by adding sodium hydroxide or the like, the abundance ratio of I ₂ in water decreases, and iodine is stably dissolved in water as an ionic component of I ⁻ and IO ⁻ . Based on these equilibrium relationships, the results of calculating the ratio of molecular iodine I ₂ concentration in water to the initial concentration of I ⁻ concentration added to water using the equilibrium constant under irradiation are shown in FIG. . The calculation results shown in FIG. 3 show that the initial I ⁻ concentration in water is 1 × 10 ⁻⁷ mol / L, 1 × 10 ⁻⁶ mol / L and 1 × 10 ⁻⁵ mol / L, and the pH is 1 It was obtained by changing to 7. The lower the pH of water in which iodine dissolves, and the higher the initial I ⁻ concentration, the higher the proportion of I ₂ . However, when the pH of water in which iodine is dissolved is about 7, the ratio of I ₂ is almost close to zero.

Once I ^{− in} water becomes molecular I ₂ , this I ₂ is volatile and moves to the gas phase formed above the water. The I _{2 that} has entered the gas phase is released to the outside environment as it is vented, or reacts with organic matter such as paint painted on the inner surfaces of the vent tank and the vent pipe connected to the vent tank to form organic iodine. It changes into form and is released to the external environment at the time of venting. For this reason, it is necessary to take measures to reduce the ratio of I ₂ produced or to install another means for capturing gas phase iodine.

  Therefore, iodine can be stably retained in the scrubbing water under conditions where the pH of the water is alkaline in the presence of radiation. In order to prevent the scrubbing water from becoming acidic and reducing the removal rate of radioactive iodine in the vent tank, a large excess of sodium hydroxide is usually dissolved in the scrubbing water and managed with sufficient tolerance. ing.

  Further, sodium thiosulfate is added to the scrubbing water in order to stably capture iodine. Sodium thiosulfate reacts efficiently with iodine in the reaction of formula (3), as used for iodine titration.

I ₂ + 2S ₂ O ₃ ^2- → 2I ⁻ + S ₄ O ₆ ²⁻ (3)
However, since sodium thiosulfate is a reducing agent, in the environment of heat and radiation, the oxidation of sodium thiosulfate itself is promoted, and sodium thiosulfate in the scrubbing water is consumed. For this reason, a large excess of sodium thiosulfate is dissolved in the scrubbing water, but sodium thiosulfate is consumed in the long term and needs to be replenished.

  The objective of this invention is providing the filter vent method, filter vent apparatus, and nuclear power plant which can hold | maintain radioactive iodine for longer time in the water in a scrubbing container.

The feature of the present invention that achieves the above-described object is to discharge a gas containing radioactive iodine in a severe accident of a nuclear power plant into water containing nanoparticles containing platinum group metal in a scrubbing vessel,
In the water, radioactive iodine is reduced by the platinum group metal contained in the nanoparticles containing the platinum group metal,
The purpose is to keep the water-soluble iodine produced by the reduction in the water in the scrubbing container.

  In order to discharge the gas containing radioactive iodine during the severe accident of a nuclear power plant into the water containing the platinum group metal nanoparticles in the scrubbing vessel, the inflowing radioactive iodine contains nanoparticles containing the platinum group metal. Is converted to water-soluble radioactive iodine by being reduced by the platinum group metal contained therein. For this reason, water-soluble radioactive iodine can be retained in the water in the scrubbing container for a longer time. Therefore, the amount of radioactive iodine exhausted to the external environment during severe accidents can be significantly reduced.

  When the reducing agent is present in the water in the scrubbing container, the conversion to the water-soluble radioactive iodine by the platinum group metal contained in the nanoparticles containing the metal group metal is promoted. It is desirable to use hydrogen generated during a severe accident as the reducing agent.

  Further, platinum formed by supporting a platinum group metal (platinum, palladium or rhodium) on the surface of a kind of oxide particle selected from silica, titania and zirconia, which is a carrier as a platinum group metal-containing nanoparticle. It is desirable to use nanoparticles containing group metals.

  According to the present invention, radioactive iodine can be retained in water in the scrubbing container for a longer time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a boiling water nuclear power plant to which a filter vent apparatus according to a first embodiment which is a preferred embodiment of the present invention is applied. It is a detailed block diagram of the filter vent apparatus shown by FIG. It is explanatory drawing which shows the pH dependence of the chemical form of iodine in the presence of radiation. It is a detailed block diagram of the filter vent apparatus of Example 2 applied to the boiling water nuclear power plant which is another suitable Example of this invention. It is a block diagram of the boiling water nuclear power plant to which the filter vent apparatus of Example 3 which is another suitable Example of this invention is applied. It is a detailed block diagram of the filter vent apparatus shown by FIG. It is a block diagram of the boiling water nuclear power plant to which the filter vent apparatus of Example 4 which is another suitable Example of this invention is applied. It is a detailed block diagram of the filter vent apparatus shown by FIG. It is a block diagram of the pressurized water nuclear power plant to which the filter vent apparatus of Example 5 which is another suitable Example of this invention is applied.

  The inventors examined a filter vent method that can retain radioactive iodine in the water in the scrubbing container for a longer time. The knowledge obtained from this study will be described below.

When nanoparticles containing platinum group precious metals exist in the water in the scrubbing vessel, the radioactive iodine I ₂ contained in the gas released into the water in the scrubbing vessel through the piping from the reactor containment vessel in the event of a severe accident is platinum. It is converted to radioactive I ⁻ (water-soluble radioactive iodine) which is stable in water by the action of a platinum group metal (for example, platinum, palladium or rhodium) of nanoparticles containing a group noble metal. A part of the radioactive iodine contained in the gas released into the water is adsorbed by the platinum group metal of the nanoparticles containing the platinum group metal present in the water. For this reason, the radioactive iodine I ₂ released into the water in the scrubbing vessel is trapped in the water in the scrubbing vessel in the chemical form of I ⁻ and held for a longer time, and the platinum group metal present in the water is also removed. It is adsorbed by the platinum group metal of the nanoparticles containing and retained in water for a longer time. The amount of radioactive iodine released from the water in the scrubbing container to the external environment is significantly reduced over a long period of time. Platinum group metals that act as catalysts are unlikely to be consumed in the water and do not require replenishment as nanoparticles into the water in the scrubbing vessel.

  The nanoparticle containing the platinum group metal may be a nanoparticle of the platinum group metal itself, and the platinum group metal (on the surface of a kind of oxide particles selected from silica, titania and zirconia as the carrier) Nanoparticles formed by attaching platinum, palladium or rhodium) may also be used.

If a reducing agent is present in the water in the scrubbing vessel, the radioactive iodine released in the water is quickly brought into a stable chemical form in water by the action of the platinum group metal of the nanoparticles containing the reducing agent and the platinum group noble metal. It is converted to ^- certain I. As the reducing agent, hydrogen that is generated in a severe accident and released into the reactor containment vessel is used. The hydrogen released into the reactor containment vessel is supplied into the water in the scrubbing vessel together with the gas containing radioactive iodine I ₂ . By using hydrogen released into the reactor containment vessel in the event of a severe accident as a reducing agent, there is no need to separately supply reducing agent into the water in the scrubbing vessel. Even under conditions where it is difficult to replenish, the reducing agent can be easily supplied into the water in the scrubbing container.

Platinum group metals are known as hydrogen oxidation catalysts. When hydrogen generated in a reactor pressure vessel during a severe accident flows into the water in the scrubbing vessel together with radioactive iodine I ₂ , the reaction expressed by the equation (4) occurs. It is generated in the water by the action of the platinum group metal to produce I ⁻ .

I ₂ + H ₂ → 2I ⁻ + 2H ⁺ (4)
When hydrogen contained in the gas discharged from the reactor containment vessel flows into the water in the scrubbing vessel, the platinum group metal (platinum, palladium or rhodium) of the platinum group metal present in the water is a catalyst for hydrogen. When hydrogen discharges to generate protons and electrons, the generated electrons reduce the radioactive iodine discharged into the water together with the gas to I ⁻ .

  As described above, the nanoparticle containing a platinum group metal is a particle having a nanometer size particle size or a support of at least one substance selected from platinum, palladium and rhodium of the platinum group metal. These are particles having a particle size of nanometer size formed by supporting a platinum group metal (platinum, palladium or rhodium) on the surface of a kind of oxide particles selected from silica, titania and zirconia. Nanoparticles containing a platinum group metal having a particle size of nanometer size are stably dispersed in the water in the scrubbing container and are difficult to precipitate in the water. The particle diameter of the nanoparticles containing the platinum group metal is preferably in the range of 1 nm to 5 nm.

Nanoparticles containing a platinum group metal having a particle size of nanometer size are stably dispersed in the water in the scrubbing container. Therefore, the above-mentioned radioactive iodine I ₂ supplied to the water is quickly dispersed evenly in the water. It can be reduced, and stable I ⁻ can be efficiently produced in water. Since the nanoparticles containing platinum group metal are nanoparticulate, the surface area increases in proportion to the reciprocal of the radius of the particles with the same weight of catalyst, and the efficiency of the reduction reaction of radioactive iodine I ₂ becomes high. .

  As described above, nanoparticles including a noble metal oxide, which is an example of a nanoparticle including a platinum group metal, are described in JP-A Nos. 2014-101240 and 2014-163811. Nanoparticles (colloidal particles) containing a noble metal oxide are prepared, for example, by preparing an aqueous solution of hexahydroxoplatinate and passing the aqueous solution of hexahydroxoplatinate through a hydrogen ion type cation exchange resin layer. The cation contained in is substituted with hydrogen ions, thereby producing a hexahydroxoplatinic acid suspension and irradiating the resulting suspension with gamma rays.

Silver may be used in place of the platinum group metal. It has been known for a long time that silver reacts with iodine I ⁻ to form hardly soluble AgI by the reaction represented by the formula (5).

I ⁻ + Ag ⁺ → AgI (5)
Therefore, if silver is present in the water in the scrubbing container, when radioactive iodine flows into the water by exhaust in a severe accident, the salt in the water and the radioactive iodine react quickly and are not easily dissolved in water. AgI is produced, and radioactive iodine can be retained in the water in the scrubbing vessel. The produced AgI precipitates in water in the scrubbing vessel. Preferably, the silver is dispersed in water in a scrubbing vessel as silver-containing nanoparticles having a nanometer size particle size. When nanoparticles containing silver are stably dispersed in the water in the scrubbing container and a gas containing radioactive iodine flows into the water in a severe accident, the silver of the nanoparticles containing silver reacts rapidly with iodine and AgI And it is possible to retain radioactive iodine in the water. By using silver-containing nanoparticles, which are fine particles, the surface area for silver of the same weight increases in proportion to the reciprocal of the radius, so that the reaction efficiency between silver and iodine increases. The particle size of the nanoparticles containing silver is preferably in the range of 1 nm to 5 nm.

Moreover, since platinum group metals are expensive, it is desirable to reduce the amount used. Thus, as described above, platinum is obtained by using a kind of oxide particles selected from silica, titania and zirconia as a carrier and attaching a platinum group metal (platinum, palladium or rhodium) to the surface of this carrier. Constitutes nanoparticles containing group metals. The amount of platinum group metal used in the nanoparticles containing platinum group metal can be reduced by dispersing nanoparticles in which platinum group metal is added to the surface of the support in water in the scrubbing container, and thus a small amount of platinum group The metal can efficiently change radioactive iodine in water to I ⁻ .

Furthermore, when high-temperature gas containing radioactive iodine in severe accidents flows into the water in the scrubbing vessel, the temperature of the water rises, and the radiation dose rate in the water rises due to the radioactive iodine trapped in the water. . At this time, silica, titania or zirconia, which is a carrier of nanoparticles containing platinum group metal present in the water, is excited by heat from water and radiation from radioactive iodine, and the added platinum group metal acts as a promoter. By doing so, it acts as a photocatalyst. At this time, radioactive iodine in water is reduced by the electrons generated on the photocatalyst, and can be changed to stable I ⁻ . The above-mentioned nanoparticles containing silver may also be constituted by attaching silver to the surface of a support of silica, titania or zirconia.

Preferably, the water in the scrubbing vessel to which nanoparticles containing a platinum group metal or nanoparticles containing silver are added is preferably alkaline. In particular, it is desirable that the pH of the water be adjusted within the range of 7-15. If the pH of the water in the scrubbing container is adjusted within the range of 7 to 15, the nanoparticles containing platinum group metal and the nanoparticles containing silver are likely to be dispersed in the water and further difficult to precipitate. The effect that can be obtained. In order to adjust the pH of the water in the scrubbing container within the range of 7 to 15, an aqueous alkali solution such as sodium hydroxide is poured into the water in the scrubbing container. In addition, by injection of a sodium thiosulfate aqueous solution as a reducing agent, hydrogen gas was supplied into the water by the reducing power of sodium thiosulfate contained in the water in the scrubbing container at the initial stage when hydrogen gas was supplied into the water in the event of a severe accident. Radioactive iodine can be reduced to I ⁻ .

  In order to adjust the pH of the water in the scrubbing container within the range of 7 to 15, a pH meter is installed in the scrubbing container. The pH meter measures the pH of the water in the scrubbing container, adjusts the amount of the aqueous alkaline solution injected into the water in the scrubbing container based on the measured pH value, and adjusts the pH of the water in the scrubbing container to 7-15. Adjust within range.

Furthermore, if the pH of the water in the scrubbing container is maintained within the range of 7 to 15, the nanoparticles containing platinum group metal or silver in the water in the scrubbing container are, as described above, It becomes easier to disperse in water and more difficult to precipitate. For this reason, a severe accident occurred, and while the gas containing radioactive iodine was discharged from the reactor containment vessel into the water in the scrubbing vessel, the pH of the water in the scrubbing vessel was measured with a pH meter, and this pH was It is confirmed that it is maintained within the range of 7-15. When the pH was confirmed to have been maintained in the range of 7 to 15, I of radioactive iodine by nanoparticles comprising nanoparticles or silver containing a platinum group metal of the water ^- you can see the reduction or HgI of it can.

  Examples of the present invention reflecting the above examination results will be described below.

  A filter vent device according to a first embodiment which is a preferred embodiment of the present invention will be described with reference to FIGS. 1 and 2. The filter vent apparatus of the present embodiment is applied to a boiling water nuclear plant (BWR plant).

  In the BWR plant 1 to which the filter vent device 10 of the present embodiment is applied, the reactor pressure vessel 3 is arranged in the reactor containment vessel 2. The reactor pressure vessel 3 is installed at the upper end of a pedestal 4 that is a cylindrical support member installed in the reactor containment vessel 2. In the reactor containment vessel 2, a dry well 5 and a pressure suppression chamber 6 that are isolated from each other are formed. The pressure suppression chamber 6 is annular and surrounds the pedestal 4. A pressure suppression pool 7 filled with cooling water is formed in the pressure suppression chamber 6 and surrounds the pedestal 4. A wet well 8 that is a gas phase space is formed in the pressure suppression chamber 6 above the surface of the cooling water in the pressure suppression pool 7. A plurality of vent pipes 9 are arranged in the pressure suppression chamber 6, the upper ends of the vent pipes 9 are opened to the dry well 5, and the lower ends of the vent pipes 9 are immersed in the cooling water of the pressure suppression pool 7. The lower end of each vent pipe 9 is opened in the cooling water of the pressure suppression pool 7. During the operation of the BWR plant 1, the atmospheres of the dry well 5 and the wet well 8 are replaced with nitrogen gas.

  The filter vent apparatus 10 includes a vent tank (scrubbing container) 11, inlet pipes 14 and 35, and an outlet pipe 16. The vent tank 11 is filled with scrubbing water 12. The filter 13 is disposed in the gas phase portion formed above the water surface of the scrubbing water 12 in the vent tank 11. The inlet pipe 14 is connected to the reactor containment vessel 2 and communicates with the wet well 8 in the pressure suppression chamber 6. An isolation valve 15 is installed in the inlet pipe 14 outside the vent tank 11. The inlet pipe 14 passes through the side wall of the vent tank 11 and is attached to the vent tank 11. The other end of the inlet pipe 14 is immersed in the scrubbing water 12 in the vent tank 11. One end of the inlet pipe 35 provided with the isolation valve 36 is connected to the reactor containment vessel 2 and communicated with the dry well 5. The other end of the inlet pipe 35 is connected to the inlet pipe 14 between the vent tank 11 and the isolation valve 15.

  The scrubbing water 12 includes a large number of added platinum oxide nanoparticles 33 which are nanoparticles containing a platinum group metal. The particle diameter of the platinum oxide nanoparticles 33 is in the range of 1 nm to 5 nm, and the average particle diameter of the platinum oxide nanoparticles 33 is, for example, 2.5 nm. In FIG. 2, the platinum oxide nanoparticles 33 are represented by circles that are much larger than actual circles for easy viewing. The scrubbing water 12 does not contain alkalis such as sodium thiosulfate and sodium hydroxide. One end of the outlet pipe 16 is connected to the upper end of the vent tank 11 above the filter 13. The other end of the outlet pipe 16 is connected to the exhaust pipe 17.

  Normally, the isolation valve 15 is closed, and the wet well 8 and the vent tank 11 are not in communication. Further, the isolation valve 36 is also closed, and the dry well 5 and the vent tank 11 are not in communication. When a severe accident occurs in the BWR plant 1, hydrogen and radioactive iodine generated in the reactor pressure vessel 3 are released into the dry well 5 in the reactor containment vessel 2. A gas containing hydrogen and radioactive iodine in the dry well 5 is released into the cooling water of the pressure suppression pool 7 through each vent pipe 9.

  The isolation valves 15 and 36 are opened before the pressure inside the containment vessel 2 rises due to a severe accident and the reactor containment vessel 2 is damaged. By opening the isolation valve 15, the gas containing hydrogen and radioactive iodine in the wet well 8 is discharged into the vent tank 11 through the inlet pipe 14. By opening the isolation valve 15, the gas containing hydrogen and radioactive iodine in the wet well 8 is released into the scrubbing water 12 in the vent tank 11 by the differential pressure between the reactor containment vessel 2 and the vent tank 11. When the isolation valve 36 is opened, the gas containing hydrogen and radioactive iodine in the dry well 5 is released into the scrubbing water 12 in the vent tank 11 through the inlet pipes 35 and 14.

The hydrogen released into the scrubbing water 12 acts as a reducing agent. The radioactive iodine I ₂ released to the scrubbing water 12 is converted to stable radioactive I ⁻ in the scrubbing water 12 by the action of hydrogen in the scrubbing water 12 and platinum contained in the platinum oxide nanoparticles 33. The Part of the radioactive iodine I ₂ is adsorbed on the platinum. In this way, radioactive iodine I ₂ contained in the gas discharged from the reactor containment vessel 2 into the vent tank 11 is converted into radioactive I ⁻ , and further, the platinum contained in the platinum oxide nanoparticles 33 is converted into platinum. It is adsorbed and removed from the gas. The radioactive I ⁻ is held in a stable state for a long time in the scrubbing water 12 in the vent tank 11. The radioactive iodine I ₂ adsorbed on platinum in the scrubbing water 12 is also held in a stable state in the scrubbing water 12 for a long time. Therefore, the radioactive I ⁻ held in the scrubbing water 12 and the radioactive iodine I ₂ adsorbed on the platinum can be prevented from being released from the scrubbing water 12 to the gas phase portion in the vent tank 11. For this reason, the radioactive iodine I ₂ released from the scrubbing water 12 into the gas phase portion thereof is remarkably reduced.

  Aerosol-like radioactive substances (aerosols containing radionuclides) and soluble radioactive substances contained in the gas released into the scrubbing water 12 in the vent tank 11 are dissolved in the scrubbing water 12 and removed. Of the radionuclides contained in the gas released into the scrubbing water 12, the gaseous radioactive material that has not been trapped in the scrubbing water and some of the aerosol-like radioactive material are released into the gas phase in the vent tank 11. The aerosol-like radioactive substance is removed by the filter 13 disposed in the gas phase portion in the vent tank 11. The filter 13 is formed of a material (metal, molecular sieve, etc.) that can withstand the flow of high-temperature and high-pressure gas discharged from the reactor containment vessel 2 to the vent tank 11 in a severe accident. The gas from which the radionuclide has been removed and passed through the filter 13 is discharged from the vent tank 11 to the outlet pipe 16 and exhausted from the exhaust pipe 17 to the outside environment.

The platinum oxide nanoparticles 33 added to the scrubbing water 12 are produced by irradiating a hexahydroxoplatinic acid suspension with gamma rays and contain a large amount of PtO ₂ . The platinum oxide nanoparticles 33 not only have a very high catalytic activity for hydrogen oxidation, but also have a high dispersibility that does not cause precipitation for more than one year. Furthermore, the platinum oxide nanoparticles 33 are suitable for addition to the scrubbing water 12 in the vent tank 11 because of high dispersibility in an alkaline environment. The amount of radioactive iodine I ₂ released into the reactor containment vessel 2 at the time of a severe accident is 200 to 300 mol in most BWR plants. Among these, the amount of radioactive iodine I ₂ transferred into the scrubbing water 12 in the vent tank 11 is about 1 mol. When these radioactive iodines are removed by chemical adsorption with platinum, at least equimolar platinum is required. Therefore, when the amount of radioactive iodine I ₂ transferred into the vent tank 11 is 1 mol, the necessary platinum The amount of is about 200 g. If the amount of scrubbing water 12 in one vent tank 11 is about 10 m ³ , the platinum concentration may be about 20 ppm. This platinum concentration is a value in the case of removing 1 mol of radioactive iodine I ₂ by directly adsorbing it to platinum, but using hydrogen flowing into the scrubbing water 12 in the vent tank 11 from the reactor containment vessel 2. When reducing radioactive iodine I ₂ , platinum acts as a catalyst and is not consumed, so the concentration of platinum added to the scrubbing water 12 may be less than 20 ppm. In the case where platinum is used in a large excess in excess of the amount of radioactive iodine I ₂ flowing into the scrubbing water 12 in order to efficiently advance the reduction reaction of the radioactive iodine I ₂ in the scrubbing water 12, the amount of radioactive iodine 10 times the amount of platinum. In this case, the platinum concentration in the scrubbing water 12 is about 200 ppm, and platinum oxide nanoparticles 33 in an amount satisfying this platinum concentration are added to the scrubbing water 12.

According to the present embodiment, since the platinum oxide nanoparticles 33 are added to the scrubbing water 12 in the vent tank 11, the radioactive material that has flowed into the scrubbing water 12 in the vent tank 11 from the reactor containment vessel 2 in the event of a severe accident. it can be converted to radioactive I ^{- -} iodine I ₂ easily soluble radioactive I in water can be made to hold over a stable long in scrubbing water 12. A part of the radioactive iodine I ₂ that has flowed into the scrubbing water 12 is adsorbed on the platinum contained in the platinum oxide nanoparticles 33, and the radioactive iodine I ₂ adsorbed on the platinum is also stable in the scrubbing water 12 over a long period of time. Can be held. For this reason, the amount of radioactive iodine I ₂ released to the external environment in a severe accident is significantly reduced.

Since most of platinum contained in the platinum oxide nanoparticles 33 added to the scrubbing water 12 functions as a catalyst for promoting the reduction reaction of radioactive iodine I ₂ , scrubbing for a long time without being consumed. Present in water 12. For this reason, the replenishment of the platinum oxide nanoparticles 33 to the scrubbing water 12 in the vent tank 11 after a severe accident has occurred by adding a necessary amount of platinum oxide nanoparticles 33 to the scrubbing water 12 in advance. Is unnecessary.

  In this embodiment, hydrogen generated during a severe accident is used as the reducing agent added to the scrubbing water 12, so that it is not necessary to add a reducing agent separately to the scrubbing water 12, and it is difficult for a person to approach after a severe accident or reduction. Even under conditions where it is difficult to replenish the water into the water, hydrogen as a reducing agent can be easily supplied into the scrubbing water 12 in the vent tank 11.

Since the nanoparticles containing the platinum group metal added to the scrubbing water 12 are present in a range of 1 nm to 5 nm in size, the nanoparticles containing the platinum group metal are easily dispersed in the scrubbing water 12. For this reason, radioactive iodine I ₂ discharged into the scrubbing water 12 at the time of a severe accident can be quickly reduced, and stable I ⁻ can be efficiently generated in the scrubbing water 12. In particular, since the platinum oxide nanoparticles 33 are used as the nanoparticles containing the platinum group metal, the dispersibility of the platinum oxide nanoparticles 33 in the scrubbing water 12 is further improved, ^and the production efficiency of I ⁻ is further improved. To do.

  In this embodiment, the scrubbing water 12 in the vent tank 11 does not contain sodium thiosulfate and sodium hydroxide. For this reason, addition of these chemical | medical agents to the scrubbing water 12 is unnecessary.

However, sodium thiosulfate as a reducing agent may be added to the scrubbing water 12 in advance. When sodium thiosulfate is added to the scrubbing water 12 in advance, the scrubbing water 12 is generated by the reducing power of sodium thiosulfate contained in the scrubbing water 12 at the initial stage when hydrogen gas is supplied into the scrubbing water 12 in a severe accident. The radioactive iodine I ₂ flowing into it can be reduced to I ⁻ . For this reason, even when hydrogen gas is supplied into the scrubbing water 12, the amount of radioactive iodine released to the outside environment can be significantly reduced. Sodium hydroxide may be added to the scrubbing water 12, and the sodium hydroxide is added so that the pH of the scrubbing water 12 is in the range of 7-15. When the pH of the scrubbing water 12 is in the range of 7 to 15, the dispersibility of the nanoparticles containing the platinum group metal in the scrubbing water 12 is improved, and the nanoparticles containing the platinum group metal are difficult to precipitate.

  A filter vent apparatus according to embodiment 2, which is another preferred embodiment of the present invention, will be described with reference to FIG. The filter vent apparatus of the present embodiment is applied to a BWR plant.

  The BWR plant to which the filter vent apparatus of the present embodiment is applied has a configuration in which the filter vent apparatus 10 is replaced with the filter vent apparatus 10A in the BWR plant 1 of the first embodiment. Other configurations of the BWR plant to which the filter vent device 10A of the present embodiment is applied are the same as those of the BWR plant 1.

  Furthermore, the filter vent apparatus 10A has a configuration in which a pH meter 18 and a sampling pipe 19 are added to the filter vent apparatus 10. Other configurations of the filter vent device 10A are the same as those of the filter vent device 10. Both ends of the sampling pipe 19 are connected to the vent tank 11, and the pH meter 18 is provided in the sampling pipe 19.

In the present embodiment, when a severe accident occurs, also in this embodiment, the gas containing radioactive iodine I ₂ and hydrogen passes through the inlet pipe 14 from the wet well 8 of the reactor containment vessel 2 into the vent tank 11. Guided into scrubbing water 12. At this time, the isolation valve 15 provided in the inlet pipe 14 is open. As described in Example 1, the radioactive iodine I ₂ is converted into stable radioactive I ⁻ in the scrubbing water 12 by the action of hydrogen present in the scrubbing water 12 and platinum contained in the platinum oxide nanoparticles 33. Converted. Further, a part of the radioactive iodine I ₂ introduced into the scrubbing water 12 is adsorbed by platinum contained in the platinum oxide nanoparticles 33.

While the gas containing radioactive iodine I ₂ is introduced into the scrubbing water 12, the scrubbing water 12 in the vent tank 11 is sampled from one end of the sampling pipe 19 and flows into the sampling pipe 19. It returns to the vent tank 11 from the end. The pH meter 18 measures the pH of the scrubbing water 12 flowing in the sampling tube 19. Since the pH meter 18 is not a pH meter that can measure the pH of the high-temperature scrubbing water 12, a cooler (not shown) is installed upstream of the pH meter in the sampling tube 19.

The scrubbing water 12 flowing in the sampling pipe 19 is cooled by a cooler until it reaches room temperature, for example. The pH of the cooled scrubbing water 12 is measured by a pH meter 18. Based on the measured pH value, it is confirmed whether the scrubbing water 12 in the vent tank 11 has a pH of 7 or higher. If the pH of the scrubbing water 12 is maintained within the range of 7 to 15, the platinum oxide nanoparticles 33 in the scrubbing water 12 are not precipitated in the scrubbing water 12 but are dispersed in the scrubbing water 12. It has become. For this reason, it can be confirmed that in the scrubbing water 12, the change of radioactive iodine I ₂ to I ⁻ is favorably continued by the platinum contained in the platinum oxide nanoparticles 33.

  A pH meter that can measure the pH of the high-temperature scrubbing water 12 may be installed in the sampling tube 19 as the pH meter 18. By using a pH meter that can measure the pH of the high-temperature scrubbing water 12, it is not necessary to cool the scrubbing water 12 flowing in the sampling tube 19, and the installation of a cooler in the sampling tube 19 becomes unnecessary. A pH meter that can measure the pH of the hot scrubbing water 12 can directly measure the pH of the hot scrubbing water 12. However, if a gas containing radioactive iodine is blown into the scrubbing water 12 when a severe accident occurs, the pH meter that can measure the pH of the high-temperature scrubbing water 12 may be damaged due to a rapid temperature rise of the scrubbing water 12.

  The pH value measured by the pH meter 18 can also be used to adjust the pH of the scrubbing water in the vent tank 11 before the occurrence of a severe accident. Before the occurrence of a severe accident, a sodium hydroxide aqueous solution is added to the scrubbing water 12 in the vent tank 11 and an injection pipe (not shown) connecting the tank and the vent tank 11 from a tank (not shown) filled with the aqueous solution. ) Through the scrubbing water 12 in the vent tank 11. The sodium hydroxide aqueous solution is injected into the scrubbing water 12 so that the pH of the scrubbing water 12 is in the range of 7-15. That is, when the pH value measured by the pH meter 18 reaches a certain value within the range of 7 to 15, for example, 8, a valve (not shown) provided in the injection pipe is closed and hydroxylated. The injection of the aqueous sodium hydroxide solution into the scrubbing water 12 from the tank filled with the aqueous sodium solution is stopped. As a result, the pH of the scrubbing water 12 in the vent tank 11 is maintained at 8, and the dispersibility of the platinum oxide nanoparticles 33 in the scrubbing water 12 can be ensured.

  This embodiment can also obtain each effect produced in the first embodiment.

  A filter vent device according to embodiment 3, which is another preferred embodiment of the present invention, will be described with reference to FIGS. The filter vent apparatus of the present embodiment is applied to a BWR plant.

  The BWR plant 1A to which the filter vent apparatus 10B of the present embodiment is applied has a configuration in which the filter vent apparatus 10 is replaced with the filter vent apparatus 10B in the BWR plant 1 of the first embodiment. The other configuration of the BWR plant 1A is the same as that of the BWR plant 1.

  The filter vent device 10B has a configuration in which the scrubbing water 12 in the filter vent device 10 is replaced with scrubbing water 12A to which silver nanoparticles 34 are added. The scrubbing water 12 </ b> A itself is the same water as the scrubbing water 12. The silver nanoparticles 34 have a particle diameter in the range of 1 nm to 5 nm, and the average particle diameter of the silver nanoparticles 34 is, for example, 2.5 nm.

As in the first embodiment, when a severe accident occurs, a gas containing radioactive iodine I ₂ and hydrogen is discharged from the wet well 8 of the reactor containment vessel 2 into the scrubbing water 12 in the vent tank 11 through the inlet pipe 14. The At this time, the isolation valve 15 provided in the inlet pipe 14 is open. The radioactive iodine I ₂ discharged to the scrubbing water 12 causes a reaction represented by the formula (4) with hydrogen in the scrubbing water 12 to generate I ⁻ and H ⁺ . The produced I ⁻ causes a reaction represented by the formula (5) with silver contained in the silver nanoparticles 34 present in the scrubbing water 12 to produce hardly soluble AgI. The produced AgI precipitates in the scrubbing water 12 and accumulates at the bottom of the vent tank 11. For this reason, the amount of radioactive iodine exhausted from the exhaust pipe 17 to the outside environment is significantly reduced.

As described in Example 1, the amount of radioactive iodine I ₂ transferred into the scrubbing water 12 in the vent tank 11 at the time of a severe accident is about 1 mol. When these radioactive iodine I ₂ is removed by chemisorption with silver, at least equimolar silver is required. For this reason, when the amount of radioactive iodine I ₂ is 1 mol, the amount of silver required in the scrubbing water 12 is about 110 g. If the amount of scrubbing water 12 in one vent tank 11 is about 10 m ³ , the silver concentration in the scrubbing water 12 may be a silver particle concentration of about 11 ppm. When silver is used in a large excess in excess of the amount of radioactive iodine I ₂ flowing into the scrubbing water 12, the amount of silver that is 10 times the amount of radioactive iodine is used. In this case, the concentration of silver in the scrubbing water 12 is about 110 ppm.

According to the present embodiment, radioactive iodine I ₂ contained in the gas discharged into the scrubbing water 12 in the vent tank 11 during a severe accident changes to I ⁻ due to the action of hydrogen contained in the scrubbing water 12. ^- reacts with silver contained in the silver nano-particles 34 generate a AgI sparingly soluble. For this reason, the amount of radioactive iodine exhausted to the external environment is significantly reduced.

When alkali (sodium thiosulfate, sodium hydroxide, etc.) is added to the scrubbing water 12 in the vent tank 11, the vent tank 11 of the filter vent apparatus 10B of the present embodiment is similar to the second embodiment. You may connect the both ends of the sampling pipe | tube 19 in which the pH meter 18 was provided. By adopting such a configuration, the pH of the scrubbing water 12 in the vent tank 11 can be measured with the pH meter 18 as in the second embodiment. For this reason, the dispersion state of the silver nanoparticles 34 in the scrubbing water 12 can be confirmed based on the measured pH, and the reaction between silver contained in the silver nanoparticles 34 and I ⁻ in the scrubbing water 12 is good. You can check if it is continued.

  A filter vent device according to a fourth embodiment which is another preferred embodiment of the present invention will be described with reference to FIGS. The filter vent device 10C of the present embodiment is applied to a BWR plant.

  The BWR plant 1B to which the filter vent device 10C of the present embodiment is applied has a configuration in which the filter vent device 10 is replaced with the filter vent device 10C in the BWR plant 1 of the first embodiment. The other structure of the BWR plant 1B is the same as that of the BWR plant 1.

  10 C of filter vent apparatuses have the structure which replaced the scrubbing water 12 which added the platinum oxide nanoparticle 33 in the filter vent apparatus 10 with the scrubbing water 12B which added the nanoparticle 33A containing a platinum group metal. The scrubbing water 12B itself is the same water as the scrubbing water 12. The particle size of the nanoparticles 33A containing a platinum group metal is in the range of 1 nm to 5 nm, and the average particle size of the silver nanoparticles 34 is, for example, 2.5 nm.

  The nanoparticles 33A containing a platinum group metal use a kind of oxide particles selected from silica, titania and zirconia as a carrier, and a platinum group metal (platinum, palladium or rhodium) is attached to the surface of the carrier. It is the nanoparticle containing the platinum group metal obtained by this. In this embodiment, the nanoparticles 33A containing platinum group metal added to the scrubbing water 12B in the vent tank 11 are nanoparticles containing platinum adhering to the surface of silica as a carrier.

In the present embodiment, when a severe accident occurs, also in this embodiment, the gas containing radioactive iodine I ₂ and hydrogen passes through the inlet pipe 14 from the wet well 8 of the reactor containment vessel 2 into the vent tank 11. Guided into scrubbing water 12. At this time, the isolation valve 15 provided in the inlet pipe 14 is open. As described in Example 1, the radioactive iodine I ₂ is stable in the scrubbing water 12 due to the action of platinum contained in the nanoparticles 33A containing hydrogen and platinum group metals present in the scrubbing water 12. ^- is converted to. Furthermore, a part of the radioactive iodine I ₂ introduced into the scrubbing water 12 is adsorbed by platinum contained in the nanoparticles 33A containing a platinum group metal. For this reason, the present embodiment can remarkably reduce the amount of radioactive iodine exhausted to the external environment as in the first embodiment.

  In the present embodiment, each effect produced in the first embodiment can be obtained. Since the present embodiment uses the nanoparticles 33A containing platinum group metal using oxide particles as a carrier, the amount of expensive platinum group metal used can be reduced, and the same effect as in the first embodiment can be obtained. be able to.

Further, when high-temperature gas containing radioactive iodine in a severe accident flows into the scrubbing water 12 in the vent tank 11, the temperature of the scrubbing water 12 rises, and radioactive I trapped in the scrubbing water 12. ^- radiation dose rate in the scrubbing water 12 by radionuclides such increases. At this time, the silica which is the carrier of the nanoparticles 33A containing the platinum group metal present in the scrubbing water 12 is excited by heat in the scrubbing water 12 and radiation from the radionuclide, and is attached to the surface of the silica. Acts as a cocatalyst, thereby acting as a photocatalyst. At this time, radioactive iodine I ₂ in the scrubbing water 12 is further reduced by the electrons generated on the photocatalyst, and can be changed to stable I ⁻ . For this reason, in this embodiment, the generation efficiency of I ⁻ is improved.

  Moreover, you may connect the both ends of the sampling pipe | tube 19 which provided the pH meter 18 to the vent tank 11 of 10 C of filter vent apparatuses similarly to Example 2. FIG.

  A filter vent apparatus according to embodiment 5, which is another preferred embodiment of the present invention, will be described with reference to FIG. In the present embodiment, the filter vent device 10 of the first embodiment is used, and this filter vent device 10 is applied to a pressurized water nuclear plant (PWR plant) unlike the first to fourth embodiments.

  Since the configuration of the filter vent device 10 has been described in the first embodiment, the description of the configuration is omitted here. An outline of the configuration of the PWR plant 1C to which the filter vent device 10 is applied will be described with reference to FIG. The PWR plant 1C includes a reactor containment vessel 20, a reactor pressure vessel 21 that is a reactor vessel, a steam generator 22, a turbine 27, and a condenser 29. Is arranged. The reactor pressure vessel 21 and the steam generator 22 are disposed in the reactor containment vessel 20. The reactor pressure vessel 21 and the steam generator 22 are connected by a primary system pipe 26 on the high temperature side, and one end of the primary system pipe 26 is connected to one end of a plurality of heat transfer tubes disposed in the steam generator 22. The The A pressurizer 23 is connected to the primary system pipe 26. In addition, the reactor pressure vessel 21 and the steam generator 22 are also connected by a primary system pipe 25 on the low temperature side, and one end of the primary system pipe 25 is the other end of the plurality of heat transfer tubes disposed in the steam generator 22. Contacted the department. A primary coolant pump 24 is provided in the primary piping 25.

  The turbine 27 and the condenser 29 are installed outside the reactor containment vessel 20. A main steam pipe 30 connected to the shell side of the steam generator 22 is connected to the turbine 27. A generator 28 is connected to the turbine 27. A condenser 29 to which steam exhausted from the turbine 27 is guided is connected to the shell side of the steam generator 22 by a water supply pipe 31.

When a severe accident occurs in the PWR plant 1C, as in the BWR plant 1, hydrogen and radioactive iodine generated in the reactor pressure vessel 21 are removed from the space in the reactor containment vessel 20 (the reactor containment vessel 2 of the BWR plant 1). To the dry well 5). Since the inlet pipe 14 of the filter vent device 10 is connected to the reactor containment vessel 20 and communicates with the space in the reactor containment vessel 20, the isolation containment valve 15 is opened in the event of a severe accident so that the reactor containment vessel is opened. A gas containing hydrogen and radioactive iodine I ₂ existing in the space in 20 is discharged into the scrubbing water 12 in the vent tank 11 through the inlet pipe 14.

In this scrubbing water 12, as in Example 1, the radioactive iodine I ₂ released to the scrubbing water 12 is contained in hydrogen and platinum oxide nanoparticles 33 (average particle size 2.5 nm) in the scrubbing water 12. Is converted to stable radioactive I ⁻ in the scrubbing water 12 by the action of platinum. Part of the radioactive iodine I ₂ is adsorbed on the platinum.

  For this reason, each effect which arises in Example 1 can be acquired also by the filter vent apparatus 10 contained in PWR plant 1C of a present Example.

  DESCRIPTION OF SYMBOLS 1,1A, 1B ... Boiling water type nuclear power plant, 1C ... Pressurized water type nuclear power plant, 2,20 ... Reactor containment vessel, 3,21 ... Reactor pressure vessel, 5 ... Dry well, 8 ... Wet well, 10, 10A , 10B, 10C ... filter vent device, 11 ... vent tank, 12, 12A, 12B ... scrubbing water, 13 ... filter, 14, 35 ... inlet piping, 18 ... pH meter, 19 ... sampling tube, 33 ... platinum oxide nano Particles, 33A ... nanoparticles containing platinum group metal, 34 ... silver nanoparticles.

Claims (14)

At the time of a severe accident in a nuclear power plant, a gas containing radioactive iodine is discharged into water containing nanoparticles containing platinum group metals in a scrubbing vessel,
In the water, the radioactive iodine is reduced by the platinum group metal contained in the nanoparticles containing the platinum group metal,
A filter vent method, wherein water-soluble iodine produced by the reduction is retained in the water in the scrubbing container.   The production of the water-soluble iodine is performed by the radioactive iodine in the water, the platinum group metal contained in the nanoparticles containing the platinum group metal present in the water, and the reducing agent contained in the water. Item 2. The filter vent method according to Item 1.   The filter vent method according to claim 2, wherein hydrogen contained in the gas that is generated in the severe accident and discharged into the water is used as the reducing agent.   The filter vent method according to claim 1 or 2, wherein the pH of the water in the scrubbing container is in the range of 7 to 15.   The filter vent method according to claim 2, wherein the pH of the water is measured.   3. The filter according to claim 1, wherein the nanoparticles containing a platinum group metal are nanoparticles containing a platinum group metal in which a platinum group metal is attached to a kind of surface selected from silica, titania and zirconia. Vent method.   The filter vent method according to claim 1, wherein a particle size of the nanoparticles containing the platinum group metal is in a range of 1 nm to 5 nm. At the time of a severe accident in a nuclear power plant, a gas containing radioactive iodine is discharged into the water containing silver nanoparticles in the scrubbing vessel,
In the said water, the said radioactive iodine reacts with the silver contained in the said silver nanoparticle, and silver iodide is produced | generated, The filter vent method characterized by the above-mentioned.   One end of the scrubbing vessel is immersed in the water containing the platinum group metal nanoparticles contained in the scrubbing vessel and the platinum group metal inserted in the scrubbing vessel. A filter vent device comprising: a first pipe that guides radioactive iodine.   The filter vent device according to claim 9, wherein the nanoparticles containing the platinum group metal are nanoparticles containing a platinum group metal in which a platinum group metal is attached to a kind of surface selected from silica, titania and zirconia. .   The filter vent apparatus according to claim 9 or 10, wherein a particle size of the nanoparticles containing the platinum group metal is in a range of 1 nm to 5 nm.   The filter vent device according to claim 9, wherein a filter is disposed above the water surface in the scrubbing container.   The filter vent device according to claim 9, wherein a pH meter is provided and a second pipe into which the water flows is connected to the scrubbing container. A reactor containment vessel, and a filter vent device according to any one of claims 9 to 13,
The nuclear power plant, wherein the first pipe of the filter vent device is connected to the reactor containment vessel and communicates with a space in the reactor containment vessel.

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