Abstract:
In one embodiment, the heat removal system includes a storage tank configured to store a heat transfer medium, a transfer system configured to selectively transfer the heat transfer medium from the storage tank to the nuclear reactor, and a delivery system operationally connected to the transfer system. The delivery system is configured to deliver the heat transfer medium to a suppression pool room of the nuclear reactor. The suppression pool room houses a suppression pool.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for an alternative cooling system for the suppression pool of a Boiling Water Reactor (BWR) nuclear reactor. The cooling system may be particularly beneficial in the event a plant emergency that causes plant electrical power to be disrupted, or normal cooling of the suppression pool to otherwise become impaired. The cooling system may also be used to supplement a conventional residual heat removal system. 
         [0003]    2. Related Art 
         [0004]      FIG. 1  is a cut-away view of a conventional boiling water nuclear reactor (BWR) reactor building. The reactor building  5  includes a suppression pool room  10  in which a suppression pool  15  is disposed. The suppression pool  15  is a torus shaped housing that forms part of the reactor building primary containment. Specifically, the suppression pool  15  is an extension of the steel primary containment vessel  20 , which is located within the shell  25  of the reactor building  5 . The suppression pool  15  is positioned below the reactor  30  and spent fuel pool  35 , and is used to limit containment pressure increases during certain accidents. In particular, the suppression pool  15  is used to cool and condense steam released during plant accidents. For instance, the plant safety/relief valves are designed to discharge steam into the suppression pool  15 , to condense the steam and mitigate undesired pressure increases. Conventionally, a BWR suppression pool  15  is approximately 140 feet in total diameter (i.e., plot plan diameter), with a 30 foot diameter torus shaped shell. During normal operation, the suppression pool  15  usually has water in the pool at a depth of about 15 feet (with approximately 1,000,000 gallons of suppression pool water in the suppression pool  15 , during normal operation). 
         [0005]    The pool  15  is conventionally cleaned and cooled by the residual heat removal (RHR) system of the BWR plant. During normal (non-accident) plant conditions, the RHR system can remove water from the suppression pool  15  (using conventional RHR pumps) and send the water through a demineralizer (not shown) to remove impurities and some radioactive isotopes that may be contained in the water. During a plant accident, the RHR system is also designed to remove some of the suppression pool water from the suppression pool  15  and send the water to a heat exchanger (within the RHR system) for cooling. 
         [0006]    During a serious plant accident, normal plant electrical power may be disrupted. In particular, the plant may be without normal electrical power to run the conventional RHR system and pumps. If electrical power is disrupted for a lengthy period of time, water in the suppression pool  15  may eventually boil and impair the ability of the suppression pool  15  to condense plant steam and reduce containment pressure. 
         [0007]    In a plant emergency, use of the RHR system may cause highly radioactive water (above acceptable design limits) to be transferred between the suppression pool  15  and RHR systems (located outside of primary containment). The transfer of the highly radioactive water between the suppression pool  15  and RHR system may, in and of itself, cause a potential escalation in leakage of harmful radioactive isotopes that may escape the suppression pool  15 . Additionally, radiation dosage rates in areas of the RHR system could be excessively high during an accident, making it difficult for plant personnel to access and control the system. 
       SUMMARY OF INVENTION 
       [0008]    At least one embodiment is directed to a heat removal system for a nuclear reactor. 
         [0009]    In one embodiment, the heat removal system includes a storage tank configured to store a heat transfer medium, a transfer system configured to selectively transfer the heat transfer medium from the storage tank to the nuclear reactor, and a delivery system operationally connected to the transfer system. The delivery system is configured to deliver the heat transfer medium to a suppression pool room of the nuclear reactor. The suppression pool room houses a suppression pool. 
         [0010]    In one embodiment, the transfer system includes at least one valve configured to control a flow of the heat transfer medium. 
         [0011]    In one embodiment, the delivery system defines at least one opening into the suppression pool room. For example, the opening may be disposed above a mid-point of the suppression pool room. 
         [0012]    In one embodiment, the delivery system is configured to deliver the heat transfer medium onto a housing of the suppression pool to remove heat. 
         [0013]    In one embodiment, the heat removal system further includes a vent configured to vent gas from the suppression pool room. 
         [0014]    At least one embodiment is directed to a method of removing heat from a nuclear reactor. 
         [0015]    In one embodiment, the method includes activating at least one flow control valve of a transfer system to permit flow of a heat transfer medium from a storage tank to a delivery system via the heat transfer system. The delivery system is configured to supply the heat transfer medium to a suppression pool room of the nuclear reactor, and the suppression pool room houses a suppression pool. 
         [0016]    At least one embodiment is directed to a method of providing a heat removal system for a nuclear reactor. 
         [0017]    In one embodiment, the method includes installing a delivery system in the nuclear reactor. The delivery system is configured to deliver a heat transfer medium to a suppression pool room, and the suppression pool room includes a suppression pool. The method further includes installing at least one vent in the suppression pool room. The vent is configured to vent gas from the suppression pool room. 
         [0018]    The method may further include connecting a transfer system between the delivery system and a storage tank. The storage tank stores the heat transfer medium, and the transfer system is configured to selectively transfer the heat transfer medium from the storage tank to the delivery system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
           [0020]      FIG. 1  is a cut-away view of a conventional boiling water nuclear reactor (BWR) reactor building; 
           [0021]      FIG. 2  is a cut-away view of a BWR building and heat removal system according to an embodiment; 
           [0022]      FIG. 3A  illustrates another example embodiment of a transfer system. 
           [0023]      FIG. 3B  illustrates a further example embodiment of a transfer system. 
           [0024]      FIG. 4  illustrates yet another embodiment of a delivery system  120 . 
           [0025]      FIG. 5  illustrates a method a method of installing the heat removal system. 
           [0026]      FIG. 6  illustrates a method of heat removal according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
         [0028]    Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. 
         [0029]    It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0030]    It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). 
         [0031]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0032]    It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
         [0033]      FIG. 2  is a cut-away view of a boiling water nuclear reactor (BWR) reactor building and heat removal system according to an example embodiment. The reactor building  5  includes a suppression pool room  10  in which a suppression pool  15  is disposed. The suppression pool  15  is a torus shaped housing, which forms part of the reactor building primary containment, and includes suppression pool water. Specifically, the suppression pool  15  is an extension of the steel primary containment vessel  20 , which is located within the shell  25  of the reactor building  5 . The suppression pool  15  is positioned below the reactor  30  and spent fuel pool  35 , and is used to limit containment pressure increases during certain accidents. In particular, the suppression pool  15  is used to cool and condense steam released from the plant safety valves during normal and off normal conditions. For instance, many plant safety/relief valves are designed to discharge steam into the suppression pool  15 , to condense the steam and mitigate undesired pressure increases inside the containment. In this example, the BWR suppression pool  15  may be approximately 140 feet in total diameter (i.e., plot plan diameter), with a 30 foot diameter torus shaped housing or shell. During normal operation, the suppression pool  15  may have suppression pool water in the pool at a depth of about 15 feet (with approximately 1,000,000 gallons of suppression pool water in the suppression pool  15 , during normal operation). 
         [0034]    The pool  15  may be cleaned and cooled by the residual heat removal (RHR) system of the BWR plant. During normal (non-accident) plant conditions, the RHR system can remove water from the suppression pool  15  (using conventional RHR pumps) and send the water through a demineralizer (not shown) to remove impurities and some radioactive isotopes that may be contained in the water. During a plant accident, the RHR system is also designed to remove heat from the suppression pool water with a heat exchanger (within the RHR system) for cooling. 
         [0035]    According to an embodiment, a heat removal system is further provided. The heat removal system includes a storage tank  105 , transfer system  110 , and a delivery system  120 . The storage tank  105  stores a heat transfer medium  107 . The heat transfer medium  107  may be water, sea water, etc. In one embodiment, the storage tank  105  is disposed at a height greater than a mid-point M of the suppression pool  15 . 
         [0036]    The transfer system  110  is configured to provide one or more fluid communication paths from the storage tank  105  to the BWR building  5 . For example, the transfer system  110  may include a first pipe  113 , a flow control valve  115  and a second pipe  117 . The first pipe  113  receives the heat transfer medium  107  from the storage tank  105 . The flow control valve  115  controls the flow of the heat transfer medium  107  from the first pipe  113  to the second pipe  117 . The second pipe  117  supplies the heat transfer medium  107  to a delivery system  120  at the BWR building  5 . It will be appreciated that transfer system  110  may include one or more pipes receiving the heat transfer medium  107  from the storage tank  105 . It will be further appreciated that the transfer system  110  may include one or more pipes supplying the heat transfer medium  107  to the delivery system  120 . Still further, it will be appreciated that the transfer system  110  may include one or more flow control valves controlling the flow of the heat transfer medium  107  from the storage tank  105  to the delivery system  120 . 
         [0037]    For example,  FIG. 3A  illustrates another example embodiment of a transfer system  110 . In this embodiment, the transfer system  110  includes a plurality of second pipes  117 - 1  to  117 -N, where N is an integer greater than 1.  FIG. 3B  illustrates a further example embodiment of a transfer system  110 . In this embodiment, the transfer system  110  includes a plurality of first pipes  113 - 1  to  113 -N, a one-to-one corresponding plurality of flow control valves  115 - 1  to  115 -N, and a one-to-one corresponding plurality of second pipes  117 - 1  to  117 -N, where N is an integer greater than 1. 
         [0038]    Returning to  FIG. 2 , the delivery system  120  includes at least one pipe  123  connected to the transfer system  110  and penetrating into the suppression pool room  10 . The pipe  123  defines at least one opening  125  into the suppression pool room  10  for delivery of the heat transfer medium  107  into the suppression pool room  10 . In one embodiment, the opening  125  is at least above a mid-point M of the suppression pool  15 . Furthermore, as shown in  FIG. 2 , the opening  125  may be disposed over the suppression pool  15  such that the heat transfer medium  107  flowing into the suppression pool room  10  flows over the housing of the suppression pool  15 . 
         [0039]    It will be appreciated that the delivery system  120  may include one or more pipes  123  connected to the transfer system  110  and defining one or more openings  125  into the suppression pool room  10 . Furthermore, if a plurality of pipes  123  are provided, the plurality of pipes  123  may be disposed at different positions around the suppression pool room  10 . In one embodiment, one or more of the plurality of pipes  123  is disposed at least above a mid-point M of the suppression pool  15 . Furthermore, in one embodiment, at least one of the openings  125  of the plurality of pipes  123  may be disposed over the suppression pool  15  such that the heat transfer medium  107  flowing into the suppression pool room  10  flows over the housing of the suppression pool  15 . 
         [0040]      FIG. 4  illustrates yet another embodiment of a delivery system  120 . In this embodiment, the delivery system  120  includes an inlet pipe  140  and a manifold  145 . The inlet pipe  140  is connected to the transfer system  110  and penetrates into the suppression pool room  10 . The manifold  145  is connected to the inlet pipe  140  such that the heat transfer medium  107  flowing through the inlet pipe  140  from the transfer system  110  flows into the manifold  145 . The manifold  145  may be a circular pipe that includes a plurality of openings  147  from which the heat transfer medium  107  flows into the suppression pool room  10 . As shown in  FIG. 4 , the manifold  145  is disposed over the suppression pool  15  such that the heat transfer medium  107  supplied by the manifold  145  flows over the housing of the suppression pool  15 . In the embodiment of  FIG. 4 , struts  150  may be anchored to walls of the suppression pool room  10  and attached to the manifold  145  to support the manifold  145  above the suppression pool  15 . 
         [0041]    In the embodiment of  FIG. 4  the manifold  145  is shown to have a circular shape matching a shape of the suppression pool  15 . However, the manifold is not limited to this shape. For example, the manifold  145  may have a polygonal shape, and still be substantially disposed over the suppression pool  15 . 
         [0042]    It will further be understood that the example embodiments are not limited to a delivery system having a singled inlet pipe connected to the manifold  145 . It will further be understood that the example embodiments are not limited to a delivery system having a singled manifold. 
         [0043]    In another embodiment, instead of a manifold, a sprinkler system may be provided to spray the heat transfer medium  107  onto the suppression pool  15 . 
         [0044]    Additionally, the embodiments are not limited to a single storage tank and/or a single transfer system and/or a single delivery system. 
         [0045]    As further shown in  FIG. 2 , the heat removal system may also include one or more vents  130 . Each vent  130  is configured to allow gas to escape from the suppression pool room  10 . As will be appreciated, sufficiently high temperatures may cause the heat transfer medium  107  to convert to a gaseous state and build pressure within the suppression pool room  10 . The vent or vents  130  reduce this pressure to provide an added measure of safety. 
         [0046]    Next, installation and operation of the heat removal system will be described with respect to  FIGS. 5 and 6 .  FIG. 5  illustrates a method a method of installing the heat removal system. As shown, the method includes installing the delivery system  120  and vents  130  in the BWR building  5  in step S 510 . Next, the delivery system  120  is connected to the transfer system  120  in step S 520 . The transfer system  120  may have already been connected to the storage tank  105 , or may be connected to the storage tank after being connected to the delivery system  120 . 
         [0047]      FIG. 6  illustrates a method of heat removal according to an example embodiment. As shown, the method includes, in step S 610 , activating at least one flow control valve  115  of the transfer system  110  to permit flow of the heat transfer medium  107  from the storage tank  105  to the delivery system  120  via the transfer system  110 . Because the storage tank  105  is disposed above a mid-point M of the suppression pool  15 , gravity will cause the heat transfer medium  107  to fill the suppression pool room  10  such that at least half the suppression pool  15  becomes submerged in the heat transfer medium  107 . The flow control valve  115  may be activated by an electrical signal, may be activated by physically engaging part of the valve, etc. As another example, the flow control valve  115  may be an explosive control valve where detonating a charge associated with the flow control valve activates the flow control valve. 
         [0048]    It will also be appreciated, that the transfer system  110  and/or storage tank  105  may include a pump to pump the heat transfer medium  107  through the transfer system  110 . 
         [0049]    In one embodiment, the storage tank  105 , the flow control valve  115  and controls associated therewith may be positioned in a remote location that is remote from the suppression pool  15 , for the safety of plant personnel. That is to say, locations of these elements may be at a distance from the suppression pool  15  that permits human operation with a decreased risk of radiation exposure. 
         [0050]    The heat removal system according to the example embodiments may be installed prior to BWR plant operation, or may be installed as a retro-fitted system. 
         [0051]    It should be understood that the heat removal system may be used during periods of time other than plant accident conditions. For instance, the heat removal system may be used simply to supplement the normal cooling of the suppression pool via the RHR system, to provide the suppression pool system with extra temperature design margins. 
         [0052]    Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.