Abstract:
A flow limiter may include a head and a fin extending from a bottom of the head. The head may include a side surface having at least one first hole and the side surface may be symmetric about a first axis. The fin may include at least one second hole and the at least one second hole may have an axis substantially perpendicular to the first axis. The flow limiter may be inserted into a support casting that may interface with a nuclear fuel bundle to reduce the flow of water to the nuclear fuel bundle thereby reducing a moisture carry over (MCO) level at an exit of a fuel bundle of a nuclear reactor.

Description:
BACKGROUND 
     1. Field 
     Example embodiments relate to a flow limiter that may reduce a moisture carry over (MCO) level at an exit of a fuel bundle of a nuclear reactor. Example embodiments also relate to a system that includes the flow limiter. 
     2. Description of Related Art 
     In conventional boiling water reactors, fuel assemblies including nuclear fuel rods are used to convert water to steam. The steam may be used for various purposes, for example, as a reheating medium or as a force to drive a turbine. In conventional nuclear reactor plants, the fuel assemblies interface with a fuel support casting. 
     During the operation of a boiling water reactor, water is supplied to a fuel bundle through a fuel support casting. Ideally, the water exits the fuel bundle as pure steam. However, after a certain number of cycles, a fuel bundle will inevitably become a low power bundle and will be moved to one of the outer, peripheral rows along with the other low power bundles. Nevertheless, even if a low power bundle is arranged in one of the outer, peripheral rows, the steam exiting the low power bundle may still contain an increased amount of water droplets if the amount of incoming water exceeds the ability of the low power bundle to convert all of the water to steam. 
     The amount of water droplets in the steam exiting a fuel bundle may be referred to as a moisture carry over (MCO) level. A high moisture carry over level may be detrimental to the operation of a boiling water reactor for at least two reasons. First, a high moisture carry over level may increase the amount of radiation exposure to plant operators. Second, a high moisture carry over level may cause damage to the blades of the steam turbine. Consequently, nuclear power plants typically opt to reduce core flow in order to decrease moisture carry over levels. However, a reduction in core flow results in a reduction in reactor power which ultimately results in decreased revenues. 
     SUMMARY 
     In accordance with example embodiments, a flow limiter may include a head and a fin extending from a bottom of the head. The head may include a side surface having at least one first hole and the side surface may be symmetric about a first axis. In example embodiments, the fin may include at least one second hole and the at least one second hole may have an axis substantially perpendicular to the first axis. 
     In accordance with example embodiments, a system may include a fuel support casting having at least one channel and a flow limiter in the at least one channel. In example embodiments, the flow limiter may include a head and a fin extending from a bottom of the head. The head may include a side surface having at least one first hole and the side surface may be symmetric about a first axis which is parallel to an axis of the at least one channel. In example embodiments the fin may include at least one second hole and the second hole may have an axis substantially perpendicular to the first axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of non-limiting example embodiments herein may become more apparent upon review of the detailed description in conjunction with the accompanying drawings. The accompanying drawings are merely provided for illustrative purposes and should not be interpreted to limit the scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. For purposes of clarity, various dimensions of the drawings may have been exaggerated. 
         FIG. 1  is a perspective view of a fuel support casting in accordance with example embodiments. 
         FIG. 2  is a top view of the fuel support casting in accordance with example embodiments. 
         FIG. 3  is a section view along line of  FIG. 2  of the fuel support casting in accordance with example embodiments. 
         FIG. 4 . is a perspective view of a flow limiter in accordance with example embodiments. 
         FIG. 5 . is another perspective view of a flow limiter in accordance with example embodiments. 
         FIG. 6 . is a side view of a flow limiter in accordance with example embodiments. 
         FIG. 7 . is another side view of a flow limiter in accordance with example embodiments. 
         FIG. 8 . is a plan view of a flow limiter in accordance with example embodiments. 
         FIG. 9 . is view of the flow limiter installed in a fuel support casting in accordance with example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It should be understood that, although the tee ins first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments. 
     Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing various 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 “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, 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. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and inter mediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1  is a perspective view of a fuel support casting  10  according to example embodiments. The fuel support casting  10  may include a lower barrel section  40  attached to an interface plate  20 . In operation, the interface plate  20  may interface with four nuclear fuel bundles at orifices  25   a ,  25   b ,  25   c , and  25   d.    
       FIG. 2  is a plan view of the fuel support casting  10 . As shown in  FIG. 2 , the fuel support casting  10  includes a cruciform space  30  which penetrates the fuel support casting  10 . In example embodiments, the cruciform space  30  may be configured to allow a cruciform shaped control rod to pass there through to regulate the nuclear activity of control rods that may be housed in the aforementioned fuel assemblies. 
       FIG. 3  is a cross-section of the fuel support casting  10  illustrated in  FIGS. 1 and 2 . As shown in  FIG. 3 , the fuel support casting  10  may include four channels  45  (two of which are illustrated in  FIG. 3 ) which guide water to the fuel bundles via the orifices  25   a ,  25   b ,  25   c , and  25   d . The four channels  45  are formed by internal surfaces of the fuel support casting  10 . Because each of the four channels  45  may be identical, only one of channels will be explained in detail for the sake of brevity. 
     As shown in  FIG. 3 , water may enter the fuel support casting  10  via a lower orifice  50  which may resemble a circular hole in a lower part of the barrel portion  40  of the fuel support casting  10 . In example embodiments, water may enter a channel  45  via the lower orifice  50  and may initially enter into a lower portion of the channel  45 . The lower portion of the channel may be formed by internal surfaces of the support casting  10 . For example, as shown in  FIG. 3 , a bottom of the channel  45  may be defined by an internal surface  75  of the fuel support casting  10 . As shown in  FIG. 3 , the internal surface  75  may be inclined. For example, the bottom surface  75  may be inclined at an angle of approximately 45 degrees with respect to the flow of water entering the fuel support casting  10  from the lower orifice  50 . Because the internal surface  75  may be inclined with respect to a flow of water entering the fuel support casting  10 , the water entering the fuel support casting  10  may be redirected by the internal surface  75  to the fuel assemblies that may be interfaced with the interface plate  20 . 
     As shown in  FIG. 3 , cross-sections of a channel  45  may change from a bottom of the fuel support casting  10  to a top of the fuel support casting. For example, H 1  represents a height of a first portion  90  of the channel  45  as measured from a bottom of the fuel support casting  10 . As shown in the figures, the internal surface  75  defines a bottom of the channel  45  and thus defines a bottom of the first portion  90 . The first portion  90 , however, may be further defined by two other surfaces. The first surface, which is arranged to face a center of the fuel support casting  10 , may form a semicircular surface, as shown in  FIG. 2 , while a second surface defining the first portion  90 , may be formed away from a center of the fuel support casting  10  and may be formed to be substantially flat. This latter surface may include the orifice  50  which may allow water to enter the channel  45 . Thus, the first portion  90  of the channel  45  may include a flat inclined bottom  45 , a back semicircular wall arranged near the center of the fuel support casting  45 , and a third flat surface arranged away from the center of the fuel support casting  45 . As described earlier, the third flat surface may include the orifice  50  to allow water to enter the fuel support casting  10 . 
     The channel  45  may also include a second portion  93  on the first portion  90  and the second portion  93  may occupy that portion of the channel  45  between H 1  and H 2  as shown in  FIG. 3 . The second portion may include a back surface which may be arranged near the center of the fuel support casting  10  and a front surface arranged away from the center of the fuel support casting  10 . The front surface may be inclined thus allowing a cross-section of the second region to increase from H 1  to H 2 . As shown in  FIG. 2 , the latter surface may transition the channel  45  from having a flat straight wall at H 1  to an arcuate shaped wall at H 2 . 
     The channel  45  may also include a third portion  96  on the second portion  93  and the third portion  96  may occupy a region of the channel  45  between H 2  and H 3  as shown in  FIG. 3 . The third portion  96  may include a back surface which may be arranged near the center of the fuel support casting  10  and a front surface arranged away from the center of the fuel support casting  10 . The front surface, as shown in  FIGS. 2 and 3 , may be arc shaped and may be constant from heights H 2  to H 3 . Thus, a cross-section of the third portion  96  may be constant. 
     The channel  45  may also include a fourth portion  99  on the third portion  96  and the fourth portion  99  may occupy a region of the channel between H 3  and H 4  as shown in  FIG. 3 . The fourth portion  99  may include a back surface which may be arranged near the center of the fuel support casting  10  and a front surface arranged away from the center of the fuel support casting  10 . The front surface may be arc-shaped along a length of the channel  45  thus allowing a cross-section of the fourth portion  99  to increase from H 3  to H 4 . As shown in  FIG. 2 , the latter surface may transition from an arc shape at H 3  to a semi-circular shape at H 4 . In example embodiments, the top of the fourth portion  99  may have a diameter D 1  as shown in  FIG. 3 . 
     As explained previously, water may enter channel  45  via the orifice  50  and may be directed upwards by the surface  75  to a top of the channel  45 . In order to control the flow of water passing through a channel  45 , example embodiments further includes a flow limiter that may be configured to be placed in at least one of the channels  45 . 
       FIGS. 4-5  are perspective views of a flow limiter  100  according to example embodiments.  FIG. 6  is a side view of the flow limiter  100  according to example embodiments.  FIG. 7  is a front view of the flow limiter  100  according to example embodiments.  FIG. 8  is a top view of the flow limiter  100  according to example embodiments. 
     As shown in  FIGS. 4-8 , the flow limiter  100 , according to example embodiments, may include a head  120  and a fin  140 . The head  120  may have a funnel shape wherein the sides of the head  120  have an arcuate profile and a top of the head  120  may be circular as shown in  FIG. 8  and may have a diameter of D 2 . In example embodiments, the diameter D 2  of the head may be smaller than the diameter D 1  of the fuel support casting. The head  120  may also include a plurality of openings  125  as shown in  FIGS. 4-8 . For example,  FIGS. 4-8  illustrate the head  120  as including six triangular shaped openings  125 . Although  FIGS. 4-8  show six triangular shaped openings  125 , example embodiments are not limited thereto. For example, there may be more or less than six openings. In addition, the openings may have shapes other than triangular. For example, openings  125  could be circular, oval, square, triangular, polygonal, or a combination thereof. In addition, the openings  125  may form a pattern other than that illustrated in the figures. For example, there may be a first plurality of openings formed near a top of the head  120  and a second plurality of openings formed below the first plurality of openings. In addition, the openings  125  may be provided at an equal spacing around a circumference of the head  120 , however, example embodiments are not limited thereto as the openings  125  may be provided irregularly around the circumference of the head  120 . 
     As shown in  FIG. 6 , the profile of the head  120  may include sides having an arcuate shape. A bottom of the head  120 , therefore, may terminate in a point. In example embodiments, the head may be formed to be symmetric about a first axis  1000 . However, example embodiments are not limited to a head having sides with an arcuate shape nor is it limited to a head being symmetric as shown in  FIG. 6 . For example, the head could have the shape of a hemisphere or may be elliptical, thus, the head  120  may be formed without a point on a bottom of the head  120 . As another example, the sides of the head  120  may be flat and inclined thus forming a funnel. As yet another example, the flow limiter may also include protrusions or depressions which may render the limiter asymmetric about the axis  1000  or may be formed, in general, to be asymmetric. 
     In example embodiments, the flow limiter  100  may also include a fin  140 . The fin  140  may extend from a bottom (or near bottom) of the head  120  and may include an opening  145  extending along a length of the fin  140  and having an axis  2000  which may be substantially perpendicular to the axis  1000  of the head  120 . Although the flow limiter  100  according to example embodiments illustrates a fin  140  with only a single opening  145 , example embodiments are not limited thereto. For example, rather than having a single opening  145 , the fin could include a plurality of openings formed along a length of the fin  140 . 
     In example embodiments the fin may have a cross-section having an arcuate profile, however, example embodiments are not limited thereto. For example, the fin may be relatively flat or may have a polygonal cross-section. 
     In example embodiments, the head  120  and the fin  140  may be made from stainless steel. For example, the head  120  and the fin  140  may be made from 316 stainless steel. 
     In example embodiments, the flow limiter  100  may be configured to reside within a channel  45  of the fuel support casting  10 .  FIG. 9 , for example, illustrates the flow limiter  100  residing within a channel  45  of the fuel support casting  10 . As shown in  FIG. 9 , the head  120  of the flow limiter  100  may be configured to fit mostly within the fourth portion  99  of the channel  45 , however, example embodiments are not limited thereto as the head  120  of the flow limiter  100  may be configured to reside completely within the fourth portion  99  or may be configured to extend to a region below the fourth portion  99 . In addition, as shown in  FIG. 9 , a bottom  150  of the fin  140  may be configured to contact the inclined surface  75  within the fuel support casting  10 . Thus, the bottom  150  of the fin may also include an inclined surface  155  configured to engage the inclined surface  75  of the fuel support casting  10 . Thus, the fin  140  may be configured to support the flow limiter  100  in the channel  45 . 
     Once installed, the flow limiter  100  may limit flow of water to a fuel assembly. For example, as water enters the channel  45 , the flow of water may be restricted due to the presence of the flow limiter  100 . In example embodiments, the flow may be controlled by the sizes of the openings  125  and  145 . For example, if the holes  125  and  145  are relatively small, the flow of water passing through the channel  45  is relatively small, whereas, the greater the size of the openings  125  and  145 , the greater the flow of water passing through the channel  45  and to a fuel bundle. Thus, the flow limiter  100  may be configured to limit the flow of water passing through a channel by limiting the sizes of holes  125  and  145  in the flow limiter  100 . 
     While example embodiments have been disclosed herein, it should be understood that other variations may be possible. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure, 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.