Abstract:
An apparatus for cooling a spent fuel pool having a heat exchanger includes a cooling water pool positioned above the spent fuel pool; a floating device configured to be elevated according to a water level of a cooling water in the spent fuel pool; and an emergency cooling water supply pipe configured to form a path through which the cooling water of the cooling water pool is moved to the spent fuel pool and configured to include a floating valve that opens or closes a flow passage of the cooling water in connection with the elevation of the floating device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority benefits under 35 U.S.C. §119 to Korean Patent Application No. 10-2011-0091156, filed Sep. 08, 2011. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an apparatus for providing a cooling water to a spent fuel pool, and more particularly to a passive cooling apparatus of a spent fuel pool in which, when a power is disconnected to a pump for supplying the cooling water due to an accident and thus the spent fuel pool&#39;s cooling capacity is disrupted to deplete the cooling water, the cooling water is supplied to the spent fuel pool, without a separate power supply, according to a water level of the cooling water in the spent fuel pool, thereby preventing or delaying a damage to the spent fuel pool. 
         [0004]    2. Description of the Related Art 
         [0005]    When storing nuclear fuel, especially in case of storing a spent nuclear fuel prior to final disposal, it is essential to store the nuclear fuel in a manner such that a criticality safety is maintained, decay heat is removed, radioactive materials are sealed, and human beings and the environment are sufficiently protected from radiation. 
         [0006]    A wet storage method in which spent nuclear fuel is stored in a storage tank has been widely operated in various countries up to the current time, and is a well established technology for storing the spent fuel. 
         [0007]    Generally, an aggregate of the spent fuel is stored in a storage rack within the storage tank composed of concrete materials, and the storage tank is usually lined with stainless steel or epoxy paint. 
         [0008]    Typically, in a conventional method of cooling a spent fuel storage tank, radioactive decay heat generated in the spent fuel is removed by forced cooling using a heat exchanger and a temperature of cladding is maintained at 30˜40° C. during an operation, and therefore, it is advantageous in that a storage density is higher than in case of a dry storage method. However, the conventional forced cooling method using the heat exchanger has a serious problem such that, when a power supply is stopped due to an accident, a cooling function becomes disabled and the nuclear fuel is exposed by depletion of the cooling water. 
         [0009]    In addition, with respect to the storage of the spent fuel, U.S. Pat. No. 5,488,642, titled “COOLING SYSTEM FOR SPENT FUEL,” published on Jan. 30, 1996 discloses a cooling system of the spent fuel pool; however, this system requires an operation of, for example, a heat exchanger or a pump, and thus, a supply of electric power is still required. Thus, this system fails to teach a cooling apparatus according to the present invention for supplying a cooling water without power supply in the event of an emergency situation where the power supply is disrupted. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, the present invention has been made keeping in mind the above mentioned problems occurring in the related art, and an object of the present invention is to provide a cooling apparatus of a spent fuel pool in which, when a power supply is stopped and a heat exchanger for cooling the spent fuel pool is disabled, a cooling water is supplied to the spent fuel pool, without a separate power supply, thereby delaying or preventing a leakage of a radioactive material due to a damage to a coating material of a nuclear fuel caused by depletion of the cooling water. 
         [0011]    Also, another object of the present invention is to provide a multipurpose cooling apparatus of a spent fuel pool, which can perform a cooling function for the spent fuel pool in a normal state in which power supply is functional, and can provide a cooling water to the spent fuel pool without requiring separate power when the power supply is interrupted. 
         [0012]    According to an aspect of the present invention, provided is an apparatus for cooling a spent fuel pool having a heat exchanger, the apparatus comprising: a cooling water pool positioned above the spent fuel pool; a floating device configured to be elevated according to a water level of a cooling water in the spent fuel pool; and an emergency cooling water supply pipe configured to form a path through which the cooling water of the cooling water pool is moved to the spent fuel pool and configured to include a floating valve that opens or closes a flow passage of the cooling water in connection with the elevation of the floating device. 
         [0013]    According to another aspect of the present invention, provided is an apparatus for cooling a spent fuel pool, the apparatus comprising: the spent fuel pool; a cooling water pool positioned above the spent fuel pool and having a heat exchanger; a cooling water recovery pipe configured to recover a cooling water of the spent fuel pool into the cooling water pool and having a cooling water circulation pump; and a cooling water supply pipe configured to move a cooling water of the cooling water pool to the spent fuel pool. 
         [0014]    In one embodiment, the apparatus for cooling a spent fuel pool can further comprises a floating device configured to be elevated according to a water level of the cooling water of the spent fuel pool; and an emergency cooling water supply pipe configured to include a floating valve that opens or closes a flow passage of the cooling water in connection with the elevation of the floating device. 
         [0015]    In one embodiment, the apparatus for cooling a spent fuel pool may further comprise a movable cooling water circulation pipe including a movable pump for connecting the cooling water recovery pipe with the cooling water supply pipe, a movable heat exchanger, and valves. 
         [0016]    In one embodiment, the apparatus for cooling a spent fuel pool may further comprise an emergency cooling water circulation pipe configured to circulate the cooling water of the spent fuel pool and the cooling of the cooling water pool. 
         [0017]    In one embodiment, the cooling water pool may comprise an air cooling pipe. 
         [0018]    In one embodiment, the cooling water pool may comprise a cooling water supplementing pipe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a configuration view illustrating a detailed configuration of a cooling apparatus  1  of a spent fuel pool; 
           [0021]      FIG. 2  is a configuration view illustrating a cooling water pool, a cooling water recovery pipe, and a cooling water supply pipe that replaces a function of a heat exchanger provided in a conventional spent fuel pool; 
           [0022]      FIG. 3  is a configuration view illustrating a detailed configuration of a cooling apparatus  2  of a spent fuel pool according to another exemplary embodiment of the present invention; 
           [0023]      FIG. 4  is a configuration view illustrating the cooling apparatus  2  of the spent fuel pool equipped with a movable cooling water circulation pipe according to another exemplary embodiment of the present invention; 
           [0024]      FIG. 5  is a configuration view illustrating the cooling apparatus  2  of the spent fuel pool equipped with an emergency cooling water circulation pipe and an air cooling pipe according to another exemplary embodiment of the present invention; and 
           [0025]      FIG. 6  is a configuration view illustrating the cooling apparatus  2  of the spent fuel pool equipped with a movable cooling water circulation pipe, an emergency cooling water circulation pipe, and an air cooling pipe according to another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the attached drawings. 
         [0027]    Exemplary embodiments of the present invention will be described herein below with reference to the accompanying drawings. Throughout the drawings, like reference numbers are used to identify like elements. Also, in the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
         [0028]    As shown in  FIGS. 1 through 3 , spent fuel cooling apparatuses  1  and  2  according to the present invention includes spent fuel pools  100  and  100 ′, cooling water pools  200  and  200 ′, emergency cooling water supply pipes  300  and  300 ′, which are respectively equipped with floating valves  310  and  310 ′ that open or close in connection with floating devices  320  and  320 ′, a cooling water recovery pipe  400 , which is equipped with a cooling water circulation pump  410 , and a cooling water supply pipe  500 . 
         [0029]    As shown in  FIG. 1  in detail, in the cooling apparatus  1  of the spent fuel pool according to the present invention, the cooling water pool  200  is positioned above the spent fuel pool  100 , which is equipped with a heat exchanger  20 . In addition, the floating device  320 , which is elevated according to a water level of the cooling water filled within the spent fuel pool  100 , is provided and the emergency cooling water supply pipe  300 , which is equipped with the floating valve  310  that opens or closes in connection with the floating device  320 , is included. 
         [0030]    In a normal state, i.e., when a power supply is functional, a cooling function of the spent fuel pool  100  using the heat exchanger  20  according to a forced cooling method is maintained. However, when an accident occurs such that the power supply is stopped and an operator can not take an additional measure, the cooling function of the spent fuel pool  100  using the heat exchanger  20  is stopped, and a temperature of the cooling water stored in the spent fuel pool  100  is increased due to decay heat generated in the spent fuel  10  stored in the spent fuel pool  100 . Eventually the cooling water becomes depleted. In this case, when the water level of the cooling water filled in the spent fuel pool  100  is lowered below a certain level, the floating device  320  descends according to the water level of the cooling water, and the floating valve  310 , which is mounted on the emergency cooling water supply pipe  300  to be associated with the floating device  320 , is opened such that the cooling water stored in the cooling water pool  200  is supplied to the spent fuel pool  100  by a gravity force. Therefore, even when there exists no power supply and no further action by the operator, the cooling water can be supplied to the spent fuel pool  100  during a certain period of time, thereby preventing damage to cladding of the spent fuel  10  due to depletion of the cooling water. 
         [0031]    In addition, as shown in  FIGS. 2 and 3  in detail, according to another embodiment of the present invention, in the spent fuel cooling apparatus  2 , the spent fuel pool  200 ′ equipped with the heat exchanger  30  is located lower than the spent fuel pool  100 ′. The spent fuel pool  100 ′ and the spent fuel pool  200 ′, which is equipped with the heat exchanger  30 , are connected to the cooling water recovery pipe  400 , which includes a cooling water circulation pump  410  mounted thereon, and the cooling water supply pipe  500 . Meanwhile, the floating device  320 ′, which is elevated according to the water level of the cooling water filled in the spent fuel pool  100 ′, can be provided and the emergency cooling water supply pipe  300 ′, which is equipped with the floating valve  310 ′ that opens or closes in connection with the floating device  320 ′, can be included. 
         [0032]    In a normal state in which a cooling function is functionally operated for storing the spent fuel  10 , i.e., when a power supply is effective to perform a cooling function, a valve  420  provided on the cooling water circulation pipe  400  is opened and the cooling water circulation pump  410  mounted on the cooling water recovery pipe  400  is operated such that the cooling water of which temperature is raised in the spent fuel pool  100 ′ is moved to the cooling water pool  200 ′ that includes the heat exchanger  30  to lower the temperature of the cooling water, and the cooling water is supplied to the spent fuel pool  100 ′ when the valve  510  equipped on the cooling water supply pipe  500  is opened. Also, the heat exchanger  30  is provided in the cooling water pool  200 ′ so that, when the temperature of the cooling water is raised or the water level of the cooling water pool  200 ′ is lowered due to the supply of the cooling water, a cooling water at a lower temperature is circulated through valves  240 ,  250  equipped on the cooling water pool  200 ′ so that the temperature of the cooling water stored in the cooling water pool  200 ′ can be lowered as well as supplementing the spent cooling water. 
         [0033]    On the other hand, when an accident occurs such that the power supply is stopped and an operator cannot take an additional measure, the cooling function of the spent fuel pool  200 ′ equipped with the heat exchanger  30  is stopped, and a temperature of the cooling water filled in the spent fuel pool  100  is increased due to the decay heat generated in the spent fuel  10  stored in the spent fuel pool  100 ′ and eventually the cooling water becomes depleted. In this case, when the water level of the cooling water filled in the spent fuel pool  100 ′ is lowered below a certain level, the floating device  320 ′ descends according to the water level of the cooling water, and the floating valve  310 ′, which is mounted on the emergency cooling water supply pipe  300 ′ to be associated with the floating device  320 ′, is opened such that the cooling water stored in the cooling water pool  200 ′ is supplied to the spent fuel pool  100 ′ by a gravity force. Therefore, even when there is no power supply and no further action by the operator, the cooling water can be supplied to the spent fuel pool  100 ′ during a certain period of time, thereby preventing damage to a coating material of the spent fuel  10  due to depletion of the cooling water. 
         [0034]    In addition, as shown in  FIG. 4  in detail, the spent fuel cooling apparatus  2  according to another embodiment of the present invention can include a movable cooling water circulation pipe  600  that connects the cooling water recovery pipe  400  and the cooling water supply pipe  500 . 
         [0035]    When the heat exchanger  30  or the cooling water circulation pump  410  cannot function due to a power failure caused by an accident but can be accessible by the operator, the movable cooling water circulation pipe  600 , which is equipped with a movable pump  610  for connecting the cooling water recovery pipe  400  and the cooling water supply pipe  500 , a movable heat exchanger  620 , and valves  630 ,  640 ,  650 , and  660  can be installed. When the function of the heat exchanger  30  is maintained but the cooling water circulation pump  410  does not function, the valve  640  in  FIG. 4  is closed and the valves  630 ,  650  and  660  are opened. Next, both the movable pump  610  and the movable heat exchanger  620  are operated to perform a normal cooling function. 
         [0036]    In addition, as shown in  FIG. 5  in detail, the spent fuel cooling apparatus  2  according to another embodiment of the present invention can include an emergency cooling water circulation pipe  700  or an air cooling pipe  800 . 
         [0037]    When the cooling function is normally performed due to a smooth power supply, the temperature of the cooling water  110 ′ stored in the spent fuel pool  100 ′ is maintained lower, and therefore, the circulation of the cooling water through the emergency cooling water circulation pipe  700  does not occur. However, when an accident occurs such as a power failure occurs, the cooling apparatus cannot function normally and the temperature of the cooling water  110 ′ stored in the spent fuel pool  100 ′ is increased to heat the emergency cooling water circulation pipe  700 , thereby generating a natural convection. Therefore, by circulating the lower-temperature cooling water  230 ′, which has been supplied to the cooling water pool  200 ′, through the emergency cooling water circulation pipe  700 , a temperature rise of the cooling water  110 ′ stored in the spent fuel pool  100 ′ can be prevented or delayed. Meanwhile, in order to provide a maximum heat transfer area, a portion of the emergency cooling water circulation pipe  700  that is included in the spent fuel pool  100 ′ can be formed in a spiral structure. 
         [0038]    Meanwhile, the cooling water pool  200 ′ can include one or more air cooling pipe  800 . The air cooling pipe  800  is used to air cool the cooling water  230 ′ stored in the cooling water pool  200 ′. When an air inside the air cooling pipe  800  is heated and rises, an internal pressure therein is decreased and a cool air from outside is introduced to a lower portion of the air cooling pipe  800 . The air cooling pipes  800  are connected to each other at a bottom portion, and when an emergency power or portable power is available, a fan is operated to increase an air cooling effect and a cooling pin can be mounted on the air cooling pipe  800  to maximize a cooling efficiency. 
         [0039]    In addition, the cooling water pool  200 ,  200 ′ can be equipped with cooling water supplementing pipes  210 ,  210 ′ for supplementing a depleted cooling water and cooling water level gauges  220 ,  220 ′ for identifying the cooling water  230 ,  230 ′ that is remaining in the cooling water pools  200 ,  200 ′. The cooling water supplementing pipes  210 ,  210 ′ are connected to an outside of a nuclear reactor so that, when the cooling water stored in the cooling water pools  200 ,  200 ′ is supplied to the spent fuel pool  100 ,  100 ′ through the emergency cooling water supply pipe  300 ,  300 ′ due to an accident such as power failure and is thus depleted, the cooling water can be supplied to the cooling water pool  200 ,  200 ′ in a convenient and safe way through the cooling water supplementing pipe  210 ,  210 ′ that is connected to the external of the nuclear reactor, thus obviating the need for an individual to enter into the nuclear reactor in which the accident occurs. Meanwhile, when the operator can access the spent fuel pool  100 ,  100 ′, the cooling water  230 ,  230 ′ that is remaining in the cooling water pools  200 ,  200 ′ is identified through the cooling water level gauge equipped within the cooling water pools  200 ,  200 ′, thereby being capable of supplying the cooling water to the cooling water pools  200 ,  200 ′ in a timely manner to maintain an effective cooling function of the cooling apparatuses  1 ,  2  of the spent fuel pool. 
         [0040]    According to the present invention, a cooling apparatus is provided in which, when an accident such as a power failure occurs so that the cooling apparatus cannot normally function, a cooling water can be provided to the spent fuel pool without requiring a separate power supply or an additional action by an operator so that a damage to the nuclear fuel caused when the cooling water is depleted can be prevented or delayed. 
         [0041]    In addition, according to the present invention, a multi-purpose cooling apparatus of a spent fuel pool, which can perform a cooling function of a spent fuel pool in a normal state where a power supply is functional and can provide a cooling water to the spent fuel pool in the event of an accident such as a power failure without requiring a separate power supply, thereby preventing or delaying a release of a radioactive material. 
         [0042]    Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.