Abstract:
Disclosed is a containment filtered venting system (CFVS) for a nuclear power plant, which may include a filtering and venting container which is configured to store the components of the filtered venting system; an inlet pipe which is connected to the filtering and venting container and a reactor building; combined nozzles which are connected to the inlet pipe and are submerged under a filtering solution filled in part of the filtering and venting container; a cyclone separator which is configured to remove larger size substances in droplets and aerosols mixed with the filtering solution from the combined nozzles and guide to a metal filter; a metal filter which is connected to the top of the cyclone separator and is configured to filer impurities mixed in the residual droplets and aerosols; a molecular sieve which is configured to remove organic iodine from exhaust gas filtered by the metal filter; and an outlet pipe which serves to connect the filtering and venting container and a stack.

Description:
FIELD 
       [0001]    The present invention relates to a containment filtered venting system (CFVS) for a nuclear power plant. 
       BACKGROUND 
       [0002]    A filtered venting system for a containment building is directed to a system wherein substances, when the pressure in a containment building is over a predetermined level, may be vented from a reactor building in order to prevent any danger of damage to a containment building due to over-pressure in the containment building when a postulated accident occurs in a nuclear power plant. Since the reactor building has plenty of radioactive aerosol and radioactive gas during the ventilation, a proper filtering with respect to the radioactive substances is necessary. The filtered venting systems for a nuclear building have been developed by AREVA, WH, IMI, etc. and have been applied to many power plants. 
         [0003]    The AREVA corporation (the old name is the Siemens corporation) has disclosed a Korean Patent “Nuclear engineering system and method for nuclear engineering system” wherein the publication number is 10-2006-0015761, the publication date is Feb. 20, 2006, and the international publication number is WO 2004/114322).  FIGS. 1 ˜ 3  are illustrating the above nuclear engineering system. 
         [0004]    The IMI corporation (the old name is the SULZER corporation) has disclosed “an apparatus for removing aerosols from the air of a nuclear reactor containment, wherein the patent number is U.S. Pat. No. 5,406,603, and the date of the patent is Apr. 1, 1995. 
         [0005]    The Westinghouse corporation has disclosed “filtered venting and decay heat removing apparatus and system for containment structures, and method of operation, wherein the patent number is U.S. Pat. No. 4,859,405, and the date of the patent is Aug. 22, 1989. 
         [0006]    The CFVS of the ARVA corporation has features in that the droplet which has passed through nozzles is physically absorbed by a pre-filter and re-circulates as a scrubber solution with the aid of gravity. At this time, when a plenty of droplets are inputted into the pre-filter, the droplets may disturb the flow or may be inputted into a metal fiber filter of the next stage, thus causing problems, for example, a clogging, etc. In addition, since the number of nozzles is relatively smaller, if an individual nozzle is damaged, it might affect other nozzles. 
         [0007]    The CFVS of the IMI corporation has features in that a chemical substance named Aliquat336 is added to the scrubber solution so as to remove organic iodine. Such a substance may explode at a room temperature and may cause a forming phenomenon, and the performance of such a substance has not been verified at an early stage of venting. The efficiency of the CFVS is not proved when it is at a high temperature which is an actual operation condition of the CFVS. There may be a plenty of difficulties in the manufacturing and installing due to the uses of hundreds of impact nozzles. 
         [0008]    The Westinghouse corporation has supplied two kinds of CFVSs of DFM and FILTRA-MWSS. In case of the DFM, there may be a hot spot due to clogging and residual heat. In case of zeolite which is a filler of an iodine filter generally used so as to remove organic iodine, since the filtering efficiency is high at a high temperature rather than at a room temperature, the filtering efficiency of the iodine filter may be low when a pre-heating is not provided at an initial stage of CFVS operation. In case of the FILTRA-MVSS, since there is not any means for removing an organic iodine except for the scrubber solution, the removing efficiency of such a substance is low, and the manufacturing and installing may be hard because of the uses of hundreds of long Venturi nozzles. 
       SUMMARY 
     Disclosure of the Invention 
       [0009]    Accordingly, the present invention is made in an effort to overcome the above-mentioned problems. It is an object of the present invention to provide a containment filtered venting system (CFVS) for a nuclear power plant, wherein aerosols and gas iodine may be removed at a high efficiency, and a driven operation time may increase, and a filtering technique with respect to a filtered substance may be surely diversified, and any possibility of failures in performance may be prevented. The inert gas, which has not been considered in the past, may be eliminated. 
         [0010]    To achieve the above objects, there is provided a containment filtered venting system (CFVS) for a nuclear power plant, which may include a filtering and venting container which is configured to store the components of the filtered venting system; an inlet pipe which is connected to the filtering and venting container and a reactor building; combined nozzles which are connected to the inlet pipe and are submerged under a filtering solution filled in part of the filtering and venting container; a cyclone separator which is configured to remove larger size substances in droplets and aerosols mixed with the filtering solution from the combined nozzles and guide to a metal filter; a metal filter which is connected to the top of the cyclone separator and is configured to filer impurities mixed in the residual droplets and aerosols; a molecular sieve which is configured to remove organic iodine from exhaust gas filtered by the metal filter; and an outlet pipe which serves to connect the filtering and venting container and a stack. 
         [0011]    A radiation fin is formed on an outer surface of the filtering and venting container. 
         [0012]    A rupture plate is formed at the outlet pipe of the filtering and venting container, thus preventing any venting into the atmosphere if the pressure inside of the filtering and venting container does not rise over a predetermined level. 
         [0013]    The filtering and venting container is installed outside of the filtering and venting container and higher than the height of the filtering and venting container and includes a water filling tank which stores filtering solution and is connected to a lower side of the filtering and venting container and is configured to increase a passive operation time and a filtering efficiency maintaining time with the aid of the passive water filling if the water level lowers below a predetermined level. 
         [0014]    A pre-filter or a strainer is disposed at an entrance pipe of the filtering and venting container. In the normal state or during the operation of the filtering and venting container, the inputs of impurities into the filtering and venting container may be prevented, and larger size aerosols can be previously removed, thus increasing the efficiency of the filtering and venting container while lowering the chance of any physical failure. 
         [0015]    The combined nozzles are configured in such a way that a distribution pipe of each combined nozzle is connected from the inlet pipe, and a contraction pipe the cross section of which gradually decreases extends from the distribution pipe and in a vertical direction, and a neck part the cross section of which is smallest is formed near the contraction part, and a plurality of holes for sucking the filtering solution are formed at the neck part, and an inner diffuser the cross section of which gradually increases in the upward direction is formed at the top of the neck part, and an upper cover is formed upward at an end portion of the diffuser, and the flowing direction of the exhaust gas from the diffuser is changed to the outward direction, and a side cover is formed at an end portion of the upper cover, thus changing the flowing direction of the exhaust gas to the downward direction. 
         [0016]    An entrance is formed at a side of the cyclone separator, and a main outlet port of the cyclone separator is formed in a shape of a circular pillar and at an inner side of a cyclone and is formed at the ends of both sides of a concave part concavely formed up to a predetermined height of the body of the cyclone separator and has a circular cross section, and the larger size substances of aerosols inputted through at least one inlet port formed at a side and droplets flow back into a scrubber solution through a scrubber solution collection pipe which is a sub-outlet port connected to the lower side of the cyclone separator with the aid of gravity and centrifugal force while such larger size substances flow down along the concave part, and the smaller size substances push up toward the main outlet port while the smaller size substances flow down along the concave part. 
         [0017]    The metal filter is formed of a pre-filter with larger size pores and a fine metal filter with smaller size pores, wherein the pre-filter serves to previously remove the residual droplets which have passed through the cyclone separator and larger size aerosols, and the fine metal filter serves to remove the residual fine aerosols. 
         [0018]    An active carbon filter is disposed at a front end of the rupture plate and serves to delay in a physical adsorption way the discharge of an inert gas including Xenon and Krypton. 
       Industrial Effects 
       [0019]    According to the present invention, it is possible to provide a filtered venting system having a good radioactive aerosol and gas removing effect as compared with the conventional art. 
     
    
     
       DRAWINGS 
         [0020]    The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein; 
           [0021]      FIGS. 1 to 3  are views illustrating conventional filtered venting systems; and 
           [0022]      FIGS. 4 to 17  are views illustrating filtered venting systems according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The present invention will be described with reference to the accompanying drawings.  FIGS. 4 to 8  are views of an exemplary embodiment of the present invention, of which  FIG. 4  is a view illustrating a basic concept of the present invention. The product of the present invention may include an inlet pipe and a filtering and venting container which are connected to a reactor building, a throttling orifice, a molecular sieve, and an outlet pipe. At least two isolation pipes are provided at the inlet pipe. 
         [0024]    The filtering and venting container may include combined nozzles, a cyclone separator, and a metal fiber filter including a pre-filter. The throttling orifice and the molecular sieve, which are disposed outside, may be provided inside of the filtering and venting container, and all the metal fiber filter including a pre-filter and the molecular sieve may be provided outside. In addition, an outlet isolation valve is provided at the output pipe, and a rupture disc may be provided. 
         [0025]      FIG. 9  is a view illustrating the cross sections of the combined nozzles according to the present invention. As illustrated in  FIG. 9 , the combined nozzles of the present invention are configured in such a way that distribution pipes from inlet pipes are connected, and a contraction part is provided, in which the cross section decreases in a vertical direction from the distribution pipes, and a next part with the smallest cross section is formed next to the contraction part, and a plurality of holes are formed at the neck part so as to absorb filtering solution. An inner diffuser the cross section of which gradually increases is formed at the top of the neck part. An upper cover is formed at the top of the end of the diffuser, thus changing to the outward direction the flowing direction of exhaust gas from the diffuser, and a side cover is formed at an end portion of the upper cover, thus changing to the downward direction the flowing direction of the exhaust gas. 
         [0026]    Therefore, the length of the diffuser may be made as long as possible, and the height of the outlet port may be maximally lowered. Compared with the conventional art, it is possible to prevent any impact-based loads and vibrations of the side wall of the filtering water tank which occur because of the locally erupting air bubbles due to the non-uniform dispersion of small air bubbles in a filtering water tank and the fluctuations at the surface of water. 
         [0027]    The conventional Venturi scrubber is configured to atomize the filtering solution into droplets while allowing the exhaust gas inputted through the distribution pipe to pass. Since the Venturi scrubber is disposed, with the Venturi standing from bottom to top, the level of the water surface of the filtering solution should be always higher than the height of the Venturi scrubber, for which the diffuser extending from the Venturi should be longer than a predetermined length so as to enhance the filtering performance along with the formation of droplets, so the Venturi scrubber may become bulky inevitably. In the conventional Venturi scrubber, air bubbles intensively gather at the side of the surface of the water tank where the outlet port is formed, so air bubbles may locally erupt from the surface of water, for which impacts may apply to the side wall of the filtering water tank or vibrations may occur at the side wall thereof. 
         [0028]    The present invention has disclosed a combined nozzle concept instead of the above-described conventional Venturi scrubber structure, in which combined nozzle structure the height of the surface of the water of the filtering solution may be adjustable irrespective of the length of a diffusing pipe, and air bubbles are guided not to intensively gather at the side of the surface of the water tank. In the combined nozzle of the present invention, there is not any difference between the inlet port through which filtering solution enters and the outlet port through which the filtering solution exits in the form of air bubbles. In this case, mechanical instability near the neck part may be externally supported by the side cover  107  and the lower side cover  117 , and the portion near the neck part may be separated by a separation plate  108 , which may be substituted with the conventional Venturi scrubber.  FIG. 16  is a view illustrating the above configuration. 
         [0029]    In the conventional Venturi scrubber, it is hard for the air bubbles from the outlet port to ascend up the water surface and to flow back in through the neck part, but in the combined nozzles of the present invention, it is possible for the air bubbles from the outlet port to flow back into the combined nozzles through the neck part, so securing a re-circulation, for which the nozzles of the present invention are different from the conventional Venturi scrubber. The above mentioned re-circulation may contribute to gathering the dusts contained in the exhaust gas into a lump, and the staying time in the filtering water tank may increase, thus enhancing the filtering efficiency as compared with the conventional Venturi scrubber. 
         [0030]      FIG. 5  is a view illustrating a configuration wherein there is provided a water filling tank in which scrubber solution is passively filled.  FIG. 6  is a view illustrating a configuration wherein a radiation fin is attached inside of a filtered venting container.  FIG. 7  is a view illustrating a configuration wherein it is possible to preheat a molecular sieve by detouring part of the flux at a mouth.  FIG. 8  is a view illustrating a configuration wherein an active carbon is engaged at a rear end of the molecular sieve.  FIG. 15  is a view illustrating a pre-filter or a strainer which is installed at the mouth of a passing-through pipe installed inside of the containment building, thus previously preventing any clogging of the pipe due to impurities which may input into the inside of the filtered venting system during the operation of the filtered venting system. 
         [0031]    An isolation valve is formed between the entrance pipe and the filtered venting container. Two isolation valves are provided, and the exhaust to the filtering and venting container may be blocked during the normal operation. The isolation valve may open when the pressure of the reactor building reaches at a previously set CFVS opening pressure and may be closed at the closing pressure. 
         [0032]    The rupture plate at the outlet pipe serves to prevent the exhaust into the air if the pressure of the filtering and venting container does not increase over a predetermined pressure level when the filtering and venting container first operates. An outlet isolation valve of the outlet pipe serves to prevent the input of gas from the atmosphere into the filtering and venting container in the standby state and opens when the CFVS operates and keeps being open. 
         [0033]    The combined nozzles are submerged under the filtering solution (scrubber solution) and serve to efficiently remove the radioactive aerosols contained in the exhaust gas. A chemical substance, which may efficiently eliminate elements and organic iodine, is resolved in the filtering solution. In a state where a predetermined water level is maintained, the aerosols contained the flux which has passed through the combined nozzles can be additionally eliminated. 
         [0034]    The droplets of over predetermined sizes among a plurality of droplets forming while passing through the surface of the filtering solution are filtered by a cyclone separator which uses centrifugal force. The droplets filtered by the cyclone separator are combined back with the filtering solution. 
         [0035]    The exhaust gas which has passed through the cyclone separator passes through the pre-filter, so the residual fine droplets are removed, and the droplets filtered while they pass through the pre-filter are combined back with the droplets or the filtering solution. 
         [0036]    The exhaust gas which has passed through the pre-filter passes through the metal fiber filter, so most of the residual aerosols can be removed, and the exhaust gas which has passed through the metal fiber filter flows into the molecular sieve in a state where mist, etc. is removed thanks to the flashing phenomenon while the exhaust gas flows through the throttling orifice. In the molecular sieve, a silver ion exchange zeolite is filled so as to remove the element/organic iodine. Most of the residual elements and organic iodine are removed over enough staying time. The external water filling tank is filled with water since the external filling water tank valve is opened in a state where the CFVS operation is stopped or during the CFVS operation in case where the water level drops below a predetermined set value after the water level of the filtering solution is monitored. The radiation fin of the filtering and venting container serves to lower the temperature of the filtering and venting container, thus increasing the condensing degree of the exhaust gas. 
         [0037]    Part of the flux from the reactor building detours and preheats the molecular sieve, thus optimizing the efficiency of removing the element and organic iodine, and the active carbon filter serves to delay the discharge of the inert gas, for example, xenon, krypton, etc. in a physical adsorption way. 
         [0038]    In addition, compared with the conventional filtered venting system, the condensing effect may be enhanced by forming the radiation fin at the filtering and venting container, thus less lowering the water level of the scrubber solution during the operation, which may increase the whole passive filtering operation time. Since the scrubber solution may be passively filled into the filtering and venting container through the scrubber solution water filing tank based on gravity, the whole passive filtering operation time may be increased, and the cyclone separator using a hydroscopic moisture separator for generating centrifugal force may be used, and the pre-filter may be used as a backup tool, so it is possible to lower any chance of the problems, for example, a clogging, etc. even when a lot of droplets are formed. 
         [0039]      FIG. 10  is a view of an exemplary embodiment of the cyclone filtering device. The present invention does not use a single filter. The present invention is characterized in that the droplets and aerosols are processed through the cyclone before the droplets and aerosols are processed through the filter, thus increasing lifespan and enhancing reliability with respect to the filtering system based on any change of the flow rate. The cyclone is configured in such a way that the droplets and aerosols enter past the side surface of the cyclone and flow down along a concave portion formed at the center and then flow back upward. At this time, since the droplets and aerosols flow down circulating around the concave portion, as illustrated in the drawings, when the droplets and aerosols flow down along the concave portion, it is called a cyclone. At this time, radioactive substances in the droplets and aerosols are filtered, and are further filtered by the filter installed inside of the cyclone.  FIG. 11  is a view illustrating a configuration wherein the cyclone filtering device is engaged to the filter. 
         [0040]    In addition, since at least two filtering techniques are used so as to remove aerosols and elements/organic iodine, even though one filtering way has a problem, it is possible to secure minimal filtering efficiency for each substance. 
         [0041]    In addition, each nozzle may have a uniform flux distribution in such a way to change the arranged interval between the nozzles, the vertical height based on the inner diameter and the position of the arm where the nozzles are disposed, the sizes of the position-based nozzles and the arranging way of the nozzles. The degradation ratio of the performance due to the problem of each individual nozzle may be lowered through the optimization of the number of the nozzles, and the manufacturing and installation time may be optimized. 
         [0042]      FIG. 12  is a view illustrating an example of an arrangement of combined nozzles disposed at the branched arm using a common head of an inlet pipe. 
         [0043]    In addition, the combined nozzles may be directly divided from a lower cavity connected to the inlet pipe so as to secure the uniform flux distribution and productivity and economic performance.  FIG. 13  is a view of an example of the above arrangement, and  FIG. 14  is a view illustrating an arrangement at a side surface. 
         [0044]    Since the metal fiber filter and the molecular sieve may be selectively installed inside or outside of the filtering and venting container, the filtering and venting container may be designed based on the installation space of each power plant. In order to enhance the filtering performance of the molecular sieve, part of the flux from the reactor building may be detoured to preheat the molecular sieve, thus maintaining the optimum organic iodine removing efficiency and optimizing the amount of zeolite. In addition, the emission time of the inert gas may increase by selectively installing the active carbon filter at the rear end of the molecular sieve, thus reducing the level of radioactivity in the surrounding environment. 
         [0045]      FIG. 17  is a cross sectional view and a plane view of the cyclone filtering device. The cyclone filtering device is formed in a cone shape wherein the cross section when viewing from the above looks like a circular pillar shape the cross section of which becomes gradually smaller in the downward direction. An inlet port is formed at a lower side and in the side surface, and an outlet port is formed at an upper side for the sake of discharge. 
         [0046]    Therefore, the droplets and aerosols inputted through the inlet port of the side surface meet the outlet port of the lower side while circulating around along the concave portion and discharge through the separator, and the residual gas discharges upward. 
         [0047]    As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described examples are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.