Abstract:
A strainer wall structure includes curved sections, a method of manufacturing the same, and a filtering method using the strainer wall structure to provide a substantially larger effective filtering area in the same length and width, substantially reducing foreign substances covering a suction surface and flow resistance of the foreign substances, and reducing pressure drop at a cooling water pass corresponding thereto. The strainer wall structure includes an inlet side through which cooling water is introduced and an outlet side through which the filtered cooling water is discharged, includes a body having openings in directions of the inlet side and the outlet side, and a first filter plate inserted into the body and including curved sections formed by alternately bending a first punched plate having filtering holes in opposite directions and at a predetermined interval.

Description:
TECHNICAL FIELD 
     The present invention relates to a strainer wall structure (referred to as a passive filtering apparatus) for filtering foreign substances, settlings, etc., generated upon occurrence of failures or accidents of an apparatus requiring a water circulation system, and more particularly, to a strainer wall structure including a plurality of curved sections, a method of manufacturing the same, and a filtering method using the same, that are used to remove foreign substances from a fluid suctioned into a pipe and a re-circulation pump when the re-circulation pump goes through an operation of an emergency core cooling system (ECCS) when a pipe failure occurs in a nuclear power plant. 
     BACKGROUND ART 
     A nuclear reactor of a nuclear power plant is surrounded by a safety vessel formed of concrete and steel, which is referred to as a containment, in which a coolant circulates to maintain a proper temperature. In addition, the nuclear reactor includes an ECCS for cooling the nuclear reactor upon occurrence of failures or accidents. 
     The ECCS must be operated upon occurrence of accidents such as coolant leakage, etc., to cool the nuclear reactor for 30 days with no external interference. 
     The ECCS is a system for collecting coolant discharged and water sprinkled upon a pipe failure into a sump disposed at the lowermost part in the containment, sprinkling the water from an upper part of the containment using the re-circulation pump to cool the containment, and circulating some of the water through a nuclear reactor cooling system to remove remaining heat of the nuclear reactor using a remaining heat removing pump. 
     When coolant leakage occurs due to damage to a pipe, etc., in a primary system of the nuclear power plant, foreign substances such as lagging materials, coating materials, latent foreign substances, etc., are generated due to discharge of a coolant. In addition, the discharged coolant and water sprinkled from a sprinkler system of the containment move all foreign substances to a re-circulation sump disposed at a lower end of the containment of the nuclear reactor. Therefore, in order for the foreign substances not to decrease performance of the ECCS, a filtering apparatus is provided in front of an introduction part of a suction pipe guided to an emergency cooling pump. 
     When a high temperature and high pressure pipe is broken, foreign substances such as fragments of lagging materials, coating materials, etc., are generated and moved toward the sump, and the filtering apparatus functions to filter the foreign substances moved to the sump and supply the filtered water into the re-circulation pump, without interfering with the operation of the re-circulation pump. 
     The filtering apparatus ensures that the foreign substances generated due to accidents can be filtered and the water can appropriately pass therethrough. In this case, a pressure drop due to the foreign substances must be guaranteed not to exceed an allowable critical value. 
     A conventional filter screen used in a pressurized water reactor type nuclear power plant has a small screen surface only, and the screen surface is mainly formed of flat grid segments. Thus, when the screen surface is contaminated with fiber settlings, a pressure drop at the screen may be largely increased to an unallowable level. 
     However, the filtering apparatus having a single surface may be easily deformed by a high pressure, and a small effective filtering area per a unit volume may decrease filtering efficiency. In order to solve the problem, while the number of filtering apparatus may be increased, their installation cost is high, which causes economical problems. Therefore, a filtering apparatus capable of increasing a filtering area per unit volume is still needed. 
     SUMMARY OF THE INVENTION 
     In order to solve the foregoing and/or other problems, it is an aspect of the present invention to provide a strainer wall structure including a plurality of curved sections, a method of manufacturing the same, and a filtering method using the same that are capable of providing a substantially larger effective filtering area in the same length and width, substantially reducing foreign substances covering a suction surface and a flow resistance of the foreign substances, and reducing a pressure drop at a cooling water pass corresponding thereto. 
     It is another aspect of the present invention to provide a strainer wall structure including a plurality of curved sections, a method of manufacturing the same, and a filtering method using the same in which manufacturing and installation costs can be reduced to solve economical problems in exchange and installation thereof. 
     The foregoing and/or other aspects of the present invention may be achieved by providing a strainer wall structure including an inlet side through which cooling water is introduced and an outlet side through which the filtered cooling water is discharged, including a body having openings in directions of the inlet side and the outlet side; and a first filter plate inserted into the body and including a plurality of curved sections formed by alternately bending a first punched plate having a plurality of filtering holes in opposite directions at predetermined intervals. 
     The first filter plate may include the curved sections convex toward the inlet side and the curved sections convex toward the outlet side, which are alternately bent in a zigzag shape in opposite directions at predetermined intervals, and introduction spaces into which the cooling water is introduced and discharge spaces through which the cooling water is discharged, which are alternately disposed. 
     The first filter plate may be provided in plural. 
     The strainer wall structure may further include second filter plates coupled between the first filter plates and formed by bending a second punched plate having a plurality of filtering holes in a two-stage shape. 
     A space surrounded by the first filter plates and the second filter plates forms a suction pocket into which the cooling water is introduced and a discharge pocket through which the cooling water is discharged. 
     The second filter plate may have a dual wall structure to form a discharge cam therein. 
     When the cooling water is suctioned into the suction pocket, the cooling water may be surrounded by five surfaces. 
     The filtering holes may have a diameter of 1 to 3 mm. 
     The body may include closed surfaces disposed at side surfaces, an upper plate assembled to an upper part, and a lower plate assembled to a lower part. 
     The upper plate may include projections to be press-fitted to upper ends of the second filter plates and assembled to an upper part, and the lower plate may include projections to be press-fitted to lower ends of the second filter plates and assembled to a lower part. 
     The strainer wall structure may further include coupling members for coupling the upper plate and the lower plate to the closed surfaces to fix the first filter plates and the second filter plates into the body. 
     Another aspect of the present invention may be accomplished by providing a method of manufacturing a strainer wall structure, including forming a first punched plate having a predetermined width and a predetermined length and including a plurality of filtering holes, and alternately bending the first punched plate in opposite directions at predetermined intervals to form a first filter plate having a plurality of curved sections; inserting the first filter plate into a body including openings in directions of an inlet side and an outlet side of cooling water; and fixing the first filter plate into the body using coupling members. 
     In forming the first filter plate, bending the first filter plate in 180° opposite directions at predetermined intervals to alternately form the curved sections convex toward the inlet side and the curved sections convex toward the outlet side; and, in inserting the first filter plate, the first filter plate is inserted into the body such that introduction spaces into which the cooling water is introduced and discharge spaces through which the cooling water is discharged are alternately disposed. 
     The method may further include, in forming the first filter plate, forming a plurality of first filter plates; simultaneously with forming the first filter plate or before or after forming the first filter plate, bending a second punched plate having a plurality of filtering holes in a two-stage shape to form a second filter plate having a dual wall structure including a discharge cam formed therein; and coupling the second filter plate between the plurality of first filter plates, in inserting the first filter plate, inserting the first filter plates and the second filter plate, which are coupled to each other, and in fixing the first filter plate, fixing the inserted first filter plates and second filter plate into the body. 
     Fixing the first and second filter plates may further include coupling closed surfaces to side surfaces of the first filter plates coupled to the second filter plates, press-fitting the upper plate to upper ends of the second filter plates to assemble the upper plate to an upper part, and press-fitting the lower plate to lower ends of the second filter plates to assemble the lower plate to a lower part; and coupling the upper plate and the lower plate to the closed surfaces using the coupling members to fix the first filter plates and the second filter plates into the body. 
     Another aspect of the present invention may be accomplished by providing a cooling water filtering method using a strainer wall structure, including installing the strainer wall structure at a passage through which cooling water flows; introducing the cooling water into an inlet side; introducing the cooling water into a suction pocket of a first filter plate, contacting the cooling water with curved sections convex toward the inlet side, and contacting the cooling water with a bent surface of the second filter plate; and filtering the cooling water through a punched surface of the first filter plate and a dual wall of the second filter plate to discharge the cooling water to an outlet side. 
     In contacting the cooling water, the cooling water introduced into the suction pocket of the first filter plate may contact the punched plate of the first filter plate and the dual wall of the second filter plate. 
     In discharging the cooling water, the cooling water contacting the punched surface of the first filter plate may be filtered to be discharged to the outlet side, the cooling water contacting the dual wall of the second filter plate may be filtered in a discharge cam of the second filter plate to be discharged to the outlet side, the cooling water contacting the curved sections convex toward the inlet side may be filtered in the discharge pocket to be discharged to the outlet side, and the cooling water contacting the bent surface of the second filter plate may be filtered in the discharge cam to be discharged to the outlet side. 
     According to a strainer wall structure of the present invention, it is possible to provide a substantially larger effective filtering area in the same length and width. Therefore, a flow resistance of settlings and foreign substances covering a suction surface can be substantially reduced. In addition, a pressure drop generated along the strainer wall structure can be reduced depending on reduction in flow resistance. 
     Further, since the strainer wall structure of the present invention is fabricated by assembling a first filter plate and a second filter plate, which are formed of a punched plate, an upper plate, a lower plate and closed surfaces, without welding, it is possible to easily perform maintenance and installation thereof. 
     Furthermore, since a plurality of first filter plates having curved sections convex in opposite directions and second filter plates having a dual wall structure are coupled to each other, a load pressure can be distributed to increase structural integrity. 
     In addition, it is possible to provide the strainer wall structure having a relatively simple structure and capable of simultaneously and economically producing a plurality of first filter plates through one process, and increasing an effective filtering area per unit time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view of a strainer wall structure in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a front view of the strainer wall structure in accordance with an exemplary embodiment of the present invention; 
         FIG. 3  is an exploded perspective view of the strainer wall structure in accordance with an exemplary embodiment of the present invention; 
         FIG. 4  is an exploded perspective view of a first filter plate in accordance with an exemplary embodiment of the present invention; 
         FIG. 5  is a side view of the first filter plate in accordance with an exemplary embodiment of the present invention; 
         FIG. 6  is a perspective view of a second filter plate in accordance with an exemplary embodiment of the present invention; 
         FIG. 7  is a perspective view of a strainer filtering apparatus, to which two first filter plates and one second filter plate are coupled, in accordance with an exemplary embodiment of the present invention; 
         FIG. 8  is a flowchart showing a method of manufacturing a strainer wall structure in accordance with an exemplary embodiment of the present invention; and 
         FIG. 9  is a flowchart showing a filtering method using a strainer wall structure in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will now be described more fully with reference to the accompanying drawings in which some embodiments are shown. These inventive concepts may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough and complete and fully conveys the inventive concept to those skilled in the art. 
     In the drawings, like reference numerals designate like elements throughout the invention. 
     Constitution and Structure of Strainer Wall Structure 
     Hereinafter, a constitution and structure of a strainer wall structure  10  in accordance with an exemplary embodiment of the present invention will be described. 
       FIG. 1  is a perspective view of a strainer wall structure in accordance with an exemplary embodiment of the present invention,  FIG. 2  is a front view of the strainer wall structure in accordance with an exemplary embodiment of the present invention, and  FIG. 3  is an exploded perspective view of the strainer wall structure in accordance with an exemplary embodiment of the present invention. 
     The strainer wall structure  10  in accordance with an exemplary embodiment of the present invention is installed at a passage through which cooling water flows. 
     As shown in  FIGS. 1 to 3 , the strainer wall structure  10  in accordance with an exemplary embodiment of the present invention includes a body having an inlet side  100  through which cooling water is introduced, an outlet side  200  through which the cooling water is filtered and discharged, closed surfaces  320  coupled to side surfaces, an upper plate  330  disposed at an upper side, and a lower plate  340  disposed at a lower side. 
     In addition, the body includes a first filter plate  400  and a second filter plate  500  disposed therein. 
     The upper plate  330  includes projections  350  projecting upward therefrom. The projections  350  have a width equal to a width of the second filter plate  500 . In addition, the number of projections  350  formed on the upper plate  330  is equal to the number of the second filter plates  500 . Therefore, the upper plate  330  has a structure to be press-fitted to the second filter plate  500  of a strainer filtering apparatus  600 . 
     The lower plate  340  also has the same structure as the upper plate  330  to be press-fitted to the second filter plate  500 . 
     In addition, coupling members  700  couple the upper plate  330  to the closed surfaces  320  installed at the side surfaces, and couple the lower plate  340  to the closed surfaces  320 . In the specific embodiment, the coupling members  700  may include fixing pins  710  having threads formed at both ends, and fastening members  720  such as nuts, etc. 
       FIG. 4  is an exploded perspective view of a first filter plate in accordance with an exemplary embodiment of the present invention, and  FIG. 5  is a side view of the first filter plate in accordance with an exemplary embodiment of the present invention. 
     The first filter plate  400  is formed by curvedly bending a first punched plate having a plurality of filtering holes  20 . Specifically, the first filter plate  400  is formed by alternately and curvedly bending the first punched plate having a predetermined width (in this embodiment, 80 mm) at predetermined intervals (in this embodiment, 300 mm). 
     The filtering holes  20  formed in the first filtering plate  400  have a diameter of about 1 to 3 mm, preferably, 2 to 2.5 mm (in this embodiment, 2.5 mm). As shown in  FIG. 5 , the first filter plate  400  is alternately bent in a zigzag shape at predetermined intervals to form a plurality of curved sections  430  and  440 . Arrows shown in  FIGS. 4 and 5  represent a flow direction of cooling water. 
     The first filter plate  400  may include curved sections  430  convex in an inlet direction and curved sections  440  convex in an outlet direction, which are opposite to each other. 
     Cooling water introduced into the inlet side  100  enters an introduction space  410  to be filtered, and then, discharged to the outlet side  200 . 
     Next, the cooling water contacting the curved sections  430  convex toward the inlet side  100  is filtered by the first filter plate  400  to be introduced into a discharge space  420  and then discharged to the outlet side  200 . That is, the introduction spaces  410  and the discharge spaces  420  are alternately disposed. 
       FIG. 6  is a perspective view of a second filter plate in accordance with an exemplary embodiment of the present invention. 
     As shown in  FIG. 6 , a second punched plate having a predetermined width (in this embodiment, 680 mm) and a predetermined height (in this embodiment, 1060 mm) and including a plurality of filtering holes  20  is bent in a two-stage manner to form a bent surface  530  and a dual wall  520 . That is, the second filter plate  500  has a dual wall  520  structure. 
     The cooling water contacts the bent surface  530  of the second filter plate  500  to be filtered by the filtering holes  20 , introduced into a discharge cam  510 , and then, discharged to the outlet side  200 . The filtering holes  20  formed in the second filter plate  500  have a diameter of about 1 to 3 mm, preferably, 2 to 2.5 mm (in this embodiment, 2.5 mm). 
       FIG. 7  is a perspective view of a strainer filtering apparatus, to which two first filter plates and one second filter plate are coupled, in accordance with an exemplary embodiment of the present invention. 
     As shown in  FIG. 7 , the first filter plates  400  are coupled to side surfaces of the dual wall  520  of the second filter plate  500 . The first filter plates  400  and the second filter plate  500  are coupled by welding, bonding, press-fitting, or the like. 
     It will be appreciated that in the structure, in which the first filter plates  400  and the second filter plate  500  are coupled to each other, suction pockets  610  into which cooling water is introduced and discharge pockets  620  through which the filtered cooling water is discharged are alternately disposed at both sides of the second filter plate  500 . The suction pockets  610  are surrounded by the introduction spaces  410  of the first filter plates  400  and the dual wall  520  of the second filter plate  500 . 
     As shown in  FIGS. 1 and 3 , the strainer filtering apparatus  600  to which the first filter plates  400  and the second filter plate  500  are coupled is inserted into the body. The number of the first filter plates  400  and the second filter plates  500  constituting the strainer filtering apparatus  600  is not limited. However, when the number of the first filter plates  400  of the strainer filtering apparatus  600  is n, the number of the second filter plates  500  is n−1. 
     As shown in  FIG. 1 , in this embodiment, four first filter plates  400  and three second filter plates  500  are provided. The strainer wall structure  10  includes the suction pockets  610  into which cooling water is introduced and the discharge pockets through which the filtered cooling water is discharged, which are alternately disposed. As shown in  FIGS. 1 and 7 , the suction pockets  610  are surrounded by the introduction spaces  410  of the first filter plates  400  and the dual walls  520  of the second filter plates  500  to form a structure in which the introduced cooling water contacts five surfaces. In addition, the discharge pockets  620  has a structure surrounded by the discharge spaces  420  of the first filter plates  400  and the dual walls  520  of the second filter plates  500 . 
     Method of Manufacturing Strainer Wall Structure 
     Hereinafter, a method of manufacturing a strainer wall structure  10  in accordance with an exemplary embodiment of the present invention will be described.  FIG. 8  is a flowchart showing a method of manufacturing a strainer wall structure in accordance with an exemplary embodiment of the present invention. 
     A base plate (in this embodiment, having a thickness of 3.2 mm) is punched using a laser beam, a drill, etc., to fabricate a first punched plate having a plurality of filtering holes  20  (having a diameter of about 2 to 2.5 mm) (S 10 ). The first punched plate is cut at predetermined intervals to fabricate a plurality of first punched plates having a predetermined width (in this embodiment, 80 mm) and a predetermined length larger than the width. 
     Next, the first punched plate is alternately bent in a zigzag shape at predetermined intervals (in this embodiment, 300 mm) to form a first filter plate  400  having a plurality of curved sections  430  and  440  (S 20 ). As described above, the fabricated first filter plate  400  has curved sections  430  convex toward an inlet side  100  and curved sections  440  convex toward an outlet side  200 . In addition, introduction spaces  410  into which cooling water is introduced and discharge spaces  420  through which the cooling water is discharged are alternately disposed. 
     Further, a base plate having the same height as the formed first filter plate  400  is prepared, and the base plate is punched to fabricate a second punched plate having a plurality of filtering holes  20  (having a diameter of about 2 to 2.5 mm). The second punched plate is bent in a two-stage shape to form a second filter plate  500  having a dual wall  520  and a bent surface  530  (S 30 ). 
     Next, the second filter plates  500  and the first filter plates  400  are coupled to each other to fabricate a strainer filtering apparatus  600  by bonding, welding or press-fitting (S 40 ). The strainer filtering apparatus  600  includes the first filter plates  400  and the second filter plates  500  alternately coupled to each other. The fabricated strainer filtering apparatus  600  is inserted into a body to complete a strainer wall structure  10  in accordance with an exemplary embodiment of the present invention. 
     The body includes closed surfaces  320  disposed at side surfaces, an upper plate  330  and a lower plate  340 , which are assembled to each other. Specifically, the upper plate  330  includes projections  350  to be press-fitted to upper ends of the second filter plates  500  of the strainer filtering apparatus  600  and coupled to an upper part of the body. In addition, the lower plate  340  also includes projections  350  to be press-fitted to lower ends of the second filter plates  500  of the strainer filtering apparatus  600  and coupled to a lower end of the body. 
     Therefore, the projections  350  have the same width as the second plates  500 , and the number of the projections  350  formed at the upper end and the lower end is the same as the number of the second filter plates  500  installed in the strainer filtering apparatus  600 . 
     Next, the closed surfaces  320  are coupled to both side surfaces of the body. The closed surfaces coupled to both side surfaces are coupled to the upper plate  330  and the lower plate  340  by coupling members  700 . As the closed surfaces  320  are coupled to the upper plate  330  and the lower plate  340  by the coupling members  700 , the strainer filtering apparatus  600  is fixed into the body (S 50 ). That is, fixing pins  710  having threads formed at both ends are inserted into fixing holes formed at one sides of the closed surfaces  320  and one sides of the upper plates  330 , and coupled by fastening members  720  such as nuts, etc. In addition, the fixing pins  710  are inserted into fixing holes formed at one sides of the closed surfaces  320  and one sides of the lower plate  340  to be coupled by fastening members  720 . 
     &lt;Cooling Water Filtering Method using Strainer Wall Structure&gt; 
     Hereinafter, a cooling water filtering method using a strainer wall structure  10  in accordance with an exemplary embodiment of the present invention will be described.  FIG. 9  is a flowchart showing a filtering method using a strainer wall structure in accordance with an exemplary embodiment of the present invention. 
     First, the strainer wall structure  10  having the above constitution and fabricated through the method as described above is installed at a passage through which cooling water flows (S 100 ). 
     The cooling water is introduced from an inlet side  100  into the strainer wall structure  10  in accordance with an exemplary embodiment of the present invention (S 200 ). 
     Next, the introduced cooling water is introduced in to suction pockets  610  of the strainer filtering apparatus  600 . The suction pockets  610  are surrounded by introduction spaces  410  of first filter plates  400  and a dual wall  520  of second filter plates  500 . The cooling water introduced into the suction pockets  610  contacts five surfaces (S 300 ). 
     Next, the cooling water is filtered by the punched surfaces of the first filter plates  400  to be discharged to an outlet side  200 . Or, the cooling water may be filtered by the dual walls  520  of the second filter plates  500  installed at side surfaces of the suction pockets  610  to be introduced into discharge cams  510  of the second filter plates  500  to be discharged (S 400 ). 
     Otherwise, the cooling water introduced into the inlet side  100  contacts curved sections  430  convex toward the inlet side of the first filter plate  400 . The cooling water contacting the curved sections  430  convex toward the inlet side is filtered by the punched surfaces to be introduced into the discharge spaces  420  and discharged to the outlet side  200 . 
     Otherwise, the cooling water introduced into the inlet side  100  contacts the bent surface  530  of the second filter plate  500 . The cooling water contacting the bent surface  530  of the second filter plate  500  is filtered by the filtering holes  20  to be introduced into the discharge cam  510  of the second filter plate  500  and discharged to the outlet side. 
     The foregoing description concerns an exemplary embodiment of the invention, is intended to be illustrative, and should not be construed as limiting the invention. The present teachings can be readily applied to other types of devices and apparatus. Many alternatives, modifications, and variations within the scope and spirit of the present invention will be apparent to those skilled in the art.