JP2017223563A - Filter vent device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter vent device that has an enhanced retention of radioactive iodine.SOLUTION: In a filter vent device 1, an iodine adsorption material 4 is immersed in a scrubber liquid 3. The iodine adsorption material 4 is one or more selected from a strong basicity anion exchange resin and a silver zeolite.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a filter vent device installed in a nuclear power plant.

  In the event of a severe accident at a nuclear power plant, in order to avoid the pressure inside the containment of the reactor from increasing and the inability to inject cooling water, or damage to the containment under pressure, A venting operation may be performed to discharge gas from the tank. In this venting operation, gas discharged from the containment vessel (hereinafter referred to as “vent gas”) is passed through the filter vent device connected to the containment vessel and the adsorption tower installed at the subsequent stage of the filter vent device to the atmosphere. (See, for example, Patent Documents 1 and 2).

  The radioactive iodine contained in the vent gas is removed from the vent gas by the combined use of the wet treatment in the filter vent device and the dry treatment in the adsorption tower. Specifically, the radioactive iodine contained in the vent gas is absorbed by the scrubber liquid in the filter vent device, and at the same time, an iodine adsorbent (for example, an inorganic carrier such as zeolite) in an adsorption tower installed at the subsequent stage of the filter vent device. Iodine adsorbent adsorbed with silver or silver salt). By these treatments, radioactive iodine contained in the vent gas can be held and confined in the filter vent device and the adsorption tower, and large-scale release of radioactive iodine into the atmosphere during severe accidents can be suppressed. .

Japanese Patent Laying-Open No. 2015-045518 Japanese Patent Laid-Open No. 2006-053488

  In nuclear power plants, further improvements in safety are always required. Therefore, the present inventors have intensively studied to further improve the performance of the filter vent device. As a result, it came to discover that the retention capability of the radioactive iodine of a filter vent apparatus can further be strengthened.

  The subject of this invention is providing the filter vent apparatus with which the retention strength of the radioactive iodine was strengthened.

  In order to solve this problem, the filter vent device of the present invention is characterized in that an iodine adsorbent is immersed in the scrubber liquid.

  Here, in the filter vent apparatus of the present invention, the iodine adsorbent is preferably at least one selected from strong basic anion exchange resins and silver zeolite. The “silver zeolite” is a zeolite to which silver or a silver salt is impregnated.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the filter vent apparatus with which the retention strength of radioactive iodine was strengthened. Therefore, the function of confining radioactive iodine in the filter vent device can be further enhanced, and the safety of the nuclear power plant can be further improved.

1 is a schematic configuration diagram of a filter vent device of the present invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  In FIG. 1, an example of embodiment of the filter vent apparatus of this invention is shown. The filter vent device 1 of the present embodiment includes a tank 2, a scrubber liquid 3 stored in the tank 2, an iodine adsorbent 4 immersed in the scrubber liquid 3, and a metal filter installed at the upper part in the tank 2. 5.

  The vent gas is first introduced into the scrubber liquid 3 stored in the tank 2. The vent gas introduced into the scrubber liquid 3 becomes bubbles and ascends the scrubber liquid 3. In this process, the scrubber liquid 3 and the vent gas come into gas-liquid contact, and radioactive iodine in the vent gas is dissolved in the scrubber liquid 3.

  Examples of the scrubber solution 3 include a liquid that can dissolve radioactive iodine, such as water, but it is preferable to use an alkaline chemical solution in which sodium thiosulfate and sodium hydroxide are dissolved in water. By using this alkaline chemical solution, radioactive iodine in the vent gas can be easily dissolved in the scrubber solution 3. Therefore, radioactive iodine in the vent gas can be effectively captured in the scrubber liquid 3.

  The concentration of sodium thiosulfate in the alkaline chemical solution is appropriately selected within the range in which the function of sodium thiosulfate that facilitates dissolving radioactive iodine in the alkaline chemical solution is exhibited. Further, the concentration of sodium hydroxide in the alkaline chemical solution is appropriately selected within a range in which the function of sodium hydroxide that prevents the decomposition of sodium thiosulfate is exhibited. Incidentally, sodium hydroxide also has a function of facilitating dissolution of radioactive iodine in an alkaline chemical solution.

  In the scrubber liquid 3, an iodine adsorbent 4 that adsorbs iodine (radioactive iodine) dissolved in the scrubber liquid 3 is immersed. In the present invention, an iodine adsorbent having heat resistance, alkali resistance and acid resistance is used in consideration of temperature fluctuation and pH fluctuation of the scrubber liquid 3 during the vent operation. Specifically, with respect to heat resistance, an iodine adsorbent that exhibits heat resistance even at 170 ° C. is used in view of the possibility that the temperature of the filter vent device will rise to a maximum of about 170 ° C. About alkali resistance, when using an alkaline chemical | medical solution as the scrubber liquid 3, the iodine adsorption material which has tolerance at high pH (for example, pH13) is used. In addition, regarding acid resistance, an iodine adsorbent having resistance even when the pH is lowered to 3 to 4 is used in consideration of the possibility that the scrubber liquid becomes weakly acidic when an extremely severe accident occurs. That is, when an alkaline chemical liquid is used as the scrubber liquid 3, an iodine adsorbent having resistance within the range of pH 13 to 4, preferably pH 13 to 3 is used. Examples of such an iodine adsorbent include various synthetic resins, zeolites, activated carbon, and substrates (for example, porous substrates such as zeolite and activated carbon) impregnated with metals or metal salts. Or in combination of two or more. However, the iodine adsorbent that can be used in the present invention is not limited to these.

  The adsorption form of radioactive iodine of the iodine adsorbing material 4 may be either physical adsorption or chemical adsorption, but is preferably chemical adsorption. In this case, radioactive iodine can be firmly adsorbed and retained by the iodine adsorbent, and the adsorbed radioactive iodine can be stably retained on the iodine adsorbent over a long period of time. As such an iodine adsorbent, for example, a synthetic resin having an ion exchange action with iodine (iodine ions) (for example, an anion in which an amino group, preferably a quaternary ammonium group is introduced as a functional group into a polymer matrix) Exchange resin). In addition, a substrate (preferably a porous substrate) in which a metal (for example, silver) that reacts with iodine (iodine ions) to generate metal iodide is added. However, the iodine adsorbent that chemically adsorbs radioactive iodine is not limited to these.

  Here, in the present invention, it is preferable to use silver zeolite as the iodine adsorbent 4. By using silver zeolite as the iodine adsorbing material 4, radioactive iodine dissolved in the scrubber liquid 3 can be adsorbed effectively. In order to exhibit the iodine adsorption ability of silver zeolite, it is known that the gas to be treated needs to be dehydrated and the silver zeolite itself needs to be heated to 150 ° C. (for example, paragraph of JP 2000-254446 A). 0005 etc.) and was not considered to exhibit iodine adsorption capacity in wet processing. However, according to the study by the present inventors, it was surprisingly found that the silver zeolite exhibits iodine adsorption performance even when immersed in the scrubber liquid 3. That is, according to the present invention, radioactive iodine can be adsorbed using silver zeolite in a form that has not been considered in the past. Moreover, silver adsorbed on the silver zeolite generates silver iodide by reaction with iodine and chemically adsorbs iodine, so that the adsorbed radioactive iodine can be stably maintained for a long period of time.

  In the present invention, it is particularly preferable to use a strongly basic anion exchange resin as the iodine adsorbent 4. By using a strongly basic anion exchange resin as the iodine adsorbing material 4, radioactive iodine dissolved in the scrubber liquid 3 can be adsorbed very effectively. In addition, the strongly basic anion exchange resin has a structure in which a quaternary ammonium group is introduced into a polymer base material (for example, styrene resin), and radioactive iodine is adsorbed by the ion exchange action of the quaternary ammonium group. Therefore, the adsorbed radioactive iodine can be stably held for a long time. The strongly basic anion exchange resin may be type I in which the quaternary ammonium group is a trimethylammonium group, or may be type II in which the quaternary ammonium group is a dimethylethanolammonium group. However, it is preferable to use type II. The strongly basic anion exchange resin is preferably a porous type having a large specific surface area. Thereby, the extremely excellent adsorption ability of radioactive iodine is exhibited. Examples of such strongly basic anion exchange resins include FAPS010 (Sumitomo Chemtex), Diaion PA series (Mitsubishi Chemical), Amberlite IRA series (organo), etc., but are not necessarily limited to these. is not.

  The size (particle diameter) of the iodine adsorbing material 4 is preferably small as long as the iodine adsorbing material 4 is not aerosolized. When the size (particle size) of the iodine adsorbent 4 becomes small enough to be aerosolized, an upward flow generated in the filter vent device 1 by introducing a vent gas into the scrubber liquid 3 (hereinafter referred to as “upward flow in the filter vent device 1”). This is because the iodine adsorbent 4 may leak to the outside of the filter vent device 1. Then, by making the iodine adsorbing material 4 small in a range where it does not aerosolize, it is possible to secure a sufficient specific surface area and easily secure the radioactive iodine adsorbing performance. In addition, the size (particle diameter) in which the iodine adsorbent 4 is not aerosolized is 0.1 mm or more. The shape of the iodine adsorbent 4 is not limited to a spherical shape, and may be a columnar shape, a disc shape, a cylindrical shape, a polygonal shape, or the like.

  The input amount of the iodine adsorbing material 4 to the scrubber liquid 3 is appropriately set in consideration of the specific surface area (for example, size (particle diameter)) of the iodine adsorbing material 4 and the radioactive iodine adsorption performance.

  The vent gas that has passed through the scrubber liquid 3 passes through the metal filter 5 installed between the scrubber liquid 3 and the exhaust port at the top of the tank 2, and is then discharged from the filter vent device 1. Splashes (droplets) 3 ′ generated by introducing the vent gas into the scrubber liquid 3 are captured by the metal filter 5 in the process of rising accompanying the upward flow in the filter vent device 1. As the metal filter 5, for example, a stainless steel mesh structure is used.

  In the present invention, since the iodine adsorbing material 4 is immersed in the scrubber liquid 3, the radioactive iodine concentration of the scrubber liquid 3 itself is that the radioactive iodine derived from the vent gas dissolved in the scrubber liquid 3 is adsorbed by the iodine adsorbing material 4. Is reduced. Thereby, the radioactive iodine density | concentration of the droplet (droplet) 3 'accompanying the upward flow in the filter vent apparatus 1 is also reduced. Therefore, even if the splashes 3 ′ accompanying the upward flow in the filter vent device 1 are discharged outside the filter vent device 1 without being captured by the metal filter 5, the discharge amount of radioactive iodine can be suppressed.

  Further, the iodine adsorbent 4 is not easily accompanied by the upward flow in the filter vent device 1 due to its weight, and even if it is accompanied, the iodine adsorbent 4 returns to the scrubber liquid 3 due to gravity sedimentation, so that it is discharged to the outside of the filter vent device 1. Not. Therefore, the radioactive iodine derived from the vent gas adsorbed on the iodine adsorbing material 4 is not discharged to the outside of the filter vent device 1.

  Moreover, since radioactive iodine self-heats (radioactive decay), the higher the radioactive iodine concentration in the droplet 3 ', the easier the moisture in the droplet 3' evaporates. In this case, the droplet 3 ′ tends to be small in the process accompanying the upward flow in the filter vent device 1, and the droplet 3 ′ becomes difficult to be captured by the metal filter 5 ′, and radioactive iodine is discharged outside the filter vent device 1. It may be done. In addition, moisture may evaporate from the droplets 3 ′ captured by the metal filter 5, and radioactive iodine may be discharged outside the filter vent device 1. On the other hand, in the present invention, since the iodine adsorbent 4 is immersed in the scrubber liquid 3, the radioactive iodine concentration of the droplet 3 'is reduced, and the heat generated per droplet 3' due to the self-heating of the radioactive iodine. Since the amount is small, the moisture in the splash 3 'is difficult to evaporate. Therefore, the splash 3 ′ is easily captured by the metal filter 5 in the process accompanying the upward flow in the filter vent device 1. In addition, evaporation of moisture from the droplet 3 ′ captured by the metal filter 5 is suppressed, and it is easy to suppress discharge of radioactive iodine contained in the droplet 3 ′ to the outside of the filter vent device 1.

  Moreover, by introducing a vent gas into the scrubber liquid 3, the scrubber liquid 3 may be heated and acidified, and radioactive iodine dissolved in the scrubber liquid 3 may volatilize. In the present invention, the radioactive iodine derived from the vent gas dissolved in the scrubber liquid 3 is adsorbed on the iodine adsorbing material 4 so as to reduce the radioactive iodine concentration of the scrubber liquid 3 itself. Even if this occurs, volatilization of radioactive iodine from the scrubber liquid 3 itself can be suppressed. Further, the radioactive iodine adsorbed on the iodine adsorbing material 4 is unlikely to be detached from the iodine adsorbing material 4 even when the scrubber liquid 3 is heated or acidified. Therefore, volatilization of radioactive iodine accompanying the high temperature and acidification of the scrubber liquid 3 can be suppressed extremely effectively.

  Therefore, in the filter vent apparatus of this invention, the retention strength of a radioactive iodine can be improved further conventionally. Therefore, the function of confining radioactive iodine in the filter vent device can be further enhanced to further improve safety.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the filter vent apparatus 1 shown in FIG. 1 has been described as an example, but the configuration of the filter vent apparatus other than the iodine adsorbent 4 is not limited to the above-described embodiment. In various known or new filter vent devices, the iodine adsorbent 4 is immersed in the scrubber liquid 3 to provide a filter vent device with enhanced retention of radioactive iodine. That is, the present invention can be easily applied to various known or new filter vent devices, and is extremely versatile.

  Moreover, an iodine adsorbent may be immersed in the scrubber liquid of the suppression chamber for the purpose of providing a suppression chamber with enhanced retention of radioactive iodine. Thereby, the radioactive iodine melt | dissolved in the scrubber liquid of a suppression chamber can be made to adsorb | suck to an iodine adsorption material, and the retention power of the radioactive iodine of a suppression chamber can also be strengthened.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Example 1]
The adsorption of iodine in the scrubber liquid was examined using various adsorbents.

  The scrubber solution was an aqueous solution in which sodium hydroxide and sodium thiosulfate were dissolved in distilled water. The sodium hydroxide concentration was 0.5 wt%. The sodium thiosulfate concentration was 0.2 wt%. A gas containing iodine was introduced into the scrubber solution for a certain period of time to prepare a dilute scrubber solution having an iodine concentration. In the following description, this scrubber liquid is referred to as “iodine-containing absorption liquid”.

  In a container containing 4 mL of an iodine-containing absorbing solution, 1 g of the adsorbent shown below was charged and sealed, left to stand by shaking for 1 minute at room temperature, and then the iodine concentration of the supernatant was analyzed.

<Investigated adsorbent>
(A) Synthetic adsorption resin A (Sumika Chemtex Co., Ltd., FAPS010)
(B) Synthetic adsorption resin B (Sumika Chemtex Co., Ltd., Duolite XAD761)
(C) Synthetic adsorption resin C (Sumika Chemtex Co., Ltd., Duolite S874)
(D) Synthetic adsorption resin D (Sumika Chemtex Co., Ltd., Duolite S876)
(E) Synthetic adsorption resin E (Sumika Chemtex Co., Ltd., Duolite S879)
(F) Zeolite Ag-X (Tosoh Corporation, model: ET-305G, binderless X-type zeolite)

  The particle size distribution of the synthetic adsorption resins A to E was 0.3 to 1.2 mm.

  The shape of zeolite Ag-X was a cylindrical pellet type (φ1.5 mm × 2.0 mm), and the silver loading rate was 18 wt%.

  The iodine concentration in the iodine-containing absorption liquid and the supernatant liquid before the adsorbent was added was analyzed by ICP (inductively coupled plasma) mass spectrometry (apparatus: Agilent 7700, manufactured by Agilent Technologies).

  The analysis results are shown in Table 1.

  Adsorption effect of iodine can be seen by using any adsorbent, and excellent iodine adsorption effect is exhibited by using (A) synthetic adsorption resin A and (F) zeolite Ag-X, especially (A) synthetic adsorption. It has been clarified that by using the resin A, an extremely excellent iodine adsorption effect is exhibited.

  (A) Synthetic adsorption resin A is a type II macroporous strongly basic anion exchange resin having a structure in which a dimethylethanolammonium group is introduced into a styrene resin that is a polymer matrix. Therefore, it is not limited to the synthetic adsorption resin A used in this example, but is a type II strong basic anion having a structure in which a dimethylethanolammonium group is introduced into a polymer base material such as a styrene resin as in the case of the synthetic adsorption resin A. Even when an exchange resin is used, it is considered that an excellent iodine adsorption effect is exhibited. Similar to the dimethylethanolammonium group, when a type I strongly basic anion exchange resin having a structure in which a trimethylammonium group classified as a quaternary ammonium group is introduced into a polymer matrix such as a styrene resin is used. It is also considered that an excellent iodine adsorption effect is exhibited. Further, even when a basic group such as an amino group is introduced into a polymer base material such as a styrene resin, it is considered that a certain iodine adsorption effect is exhibited.

  (F) Zeolite Ag-X is an iodine adsorbent in which silver is impregnated with zeolite. Considering that an excellent iodine adsorption effect was exhibited by zeolite Ag-X, not only zeolite, but also an iodine adsorbent in which silver (or silver salt) was impregnated on various porous inorganic carriers such as activated carbon was used. In some cases, it is considered that an excellent iodine adsorption effect can be achieved.

[Example 2]
Using the synthetic adsorption resin A that exhibited an extremely excellent iodine adsorption effect in Example 1, the required amount of adsorbent and the ability to retain iodine in the scrubber liquid were examined.

  In a container containing 4 mL of iodine absorbing solution, 0.01 g, 0.1 g, or 1 g of synthetic adsorption resin A is charged and sealed, shaken at room temperature for 1 minute, and then heated on a hot plate for 1 hour ( After allowing to stand at a liquid temperature of 100 ° C., the iodine concentration of the supernatant was analyzed.

  The iodine concentration of the iodine-containing absorbent and the supernatant before the adsorbent was added was analyzed in the same manner as in Example 1.

  The analysis results are shown in Table 2.

  When 1 g of iodine adsorbent was added, it became clear that about 96% of iodine in the liquid could be adsorbed. When 1 g of the iodine adsorbent was added, the weight ratio of the iodine adsorbent in the iodine absorbing solution was 20%. From this result, it was clarified that the iodine adsorbent used in this example can sufficiently adsorb iodine in the liquid by setting the weight ratio of the iodine adsorbent in the iodine absorbing liquid to 20%.

DESCRIPTION OF SYMBOLS 1 Filter vent apparatus 2 Tank 3 Scrubber liquid 3 'Spray 4 Iodine adsorbent 5 Metal filter

Claims (2)

  A filter vent device in which an iodine adsorbent is immersed in a scrubber liquid.   2. The filter vent device according to claim 1, wherein the iodine adsorbent is at least one selected from a strongly basic anion exchange resin and silver zeolite.

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