Patent Publication Number: US-2022215971-A1

Title: Debris filtering skirt arrangement for nuclear fuel assembly bottom nozzle and bottom nozzle including same

Description:
CROSS-REFERENCE 
     This application claims priority to U.S. Provisional Patent Application No. 62/851,835, which was filed on May 23, 2019. The contents of which is incorporated by reference into this specification. 
    
    
     FIELD 
     The present invention relates generally to nuclear reactors and, more particularly, is concerned with debris filtering skirt arrangements for bottom nozzles for use in a nuclear fuel assembly such as employed in a pressurized water reactor (PWR). 
     BACKGROUND 
     During manufacture and subsequent installation and repair of components comprising a nuclear reactor coolant circulation system, diligent effort is made to assure removal of debris from the reactor vessel and its associated systems which circulate coolant through it under various operating conditions before it can reach the nuclear fuel assembly bundle region. Although elaborate procedures are carried out to help assure debris removal, experience shows that in spite of the safeguards used to affect such removal, some small amount of debris, such as metal chips and metal particles still remain hidden in the systems. Most of the debris consists of metal wires, chips and turnings which were probably left in the primary system after steam generator repair or replacement or similar types of plant modifications during the refueling process. Therefore, it is desirable to ensure that this type of debris does not make its way into the fuel assembly bundle region during plant operation. However, existing bottom nozzles and side skirts are not specifically configured to mitigate the introduction of debris into the reactor core. 
     For example, existing fuel assembly bottom nozzle side skirt designs have a large opening (˜5″×˜1″ per side) through which debris can easily pass and travel around the current fuel assembly bottom nozzle designs into the gap between fuel assemblies and into the fuel bundle region where debris-induced fuel fretting failures can occur. Altering the geometry of the fuel assembly to reduce the amount of debris that can pass through can increase the loss coefficient of the fuel assembly and obstruct the flow into the reactor vessel baffle-barrel region, adversely impacting the cooling of the reactor vessel former plates. 
     Accordingly, a need exists for improved solutions to the problem of debris filtering in nuclear reactors. New approaches must be compatible with the existing structure and operation of the components of the reactor, be effective throughout the operating cycle of the reactor, and at least provide overall benefits which outweigh any costs added. 
     SUMMARY 
     The following summary is provided to facilitate an understanding of some of the innovative features unique to the aspects disclosed herein, and is not intended to be a full description. A full appreciation of the various aspects can be gained by taking the entire specification, claims, and abstract as a whole. 
     In various aspects, a debris filtering skirt configured for use with a flow plate of a bottom nozzle configured to be positioned on the reactor vessel lower core plate in a nuclear reactor is disclosed. The debris filtering skirt includes a base portion including a first surface, a second surface, a bottom edge, and a plurality of sides, wherein the base portion defines an opening between the bottom edge and the reactor vessel lower core plate. The opening includes a dimension configured to position the bottom nozzle a predetermined distance away from the reactor vessel lower core plate, and a plurality of holes defined within at least one side of the plurality of sides of the base portion. Each hole of the plurality of holes includes an inlet proximal to the first surface of the base portion and an outlet proximal to the second surface of the base portion, and at least one hole of the plurality of holes includes a dimension determined based, at least in part, on a predetermined size of debris capable of traversing through the at least one hole. The dimension of the opening and the dimension of the at least one hole are determined based, at least in part, on a predetermined loss coefficient of the bottom nozzle. 
     In various aspects, a fuel assembly configured for selective engagement with the reactor vessel lower core plate of a nuclear reactor is disclosed. The fuel assembly includes a bottom nozzle including a flow plate. The flow plate includes a plurality of flow passages through which the majority of the reactor coolant can traverse towards the core region of the nuclear reactor, and a debris filtering skirt including a base portion including a plurality of holes and a bottom edge. The base portion further defines an opening between the bottom edge of the bottom nozzle and the reactor vessel lower core plate which the fuel assembly sits on, and the opening includes a dimension configured to position the bottom edge a predetermined distance away from the reactor vessel lower core plate when the fuel assembly is selectively engaged with the reactor vessel lower core plate. At least one hole of the plurality of holes includes a dimension determined based, at least in part, on a predetermined size of debris capable of traversing through from the inlet to the outlet. The dimension of the opening and the dimension of the at least one hole are determined based, at least in part, on a predetermined loss coefficient of the bottom nozzle. 
     In various aspects, a method of manufacturing a debris filtering skirt of a bottom nozzle configured for selective engagement with a reactor vessel lower core plate of a nuclear reactor is disclosed. The method includes determining a maximum loss coefficient of the bottom nozzle, determining a minimum filtration capability of the debris filtering skirt, calculating a first dimension based at least in part on the maximum loss coefficient and the minimum filtration capability, calculating a second dimension based at least in part on the maximum loss coefficient, producing the bottom nozzle, producing the debris filtering skirt including a bottom edge and a plurality of sides, and defining a plurality of holes in at least one side of the plurality of sides of the debris filtering skirt. At least one hole of the plurality of holes includes the first dimension, defining an opening within the debris filtering skirt, and the opening includes the second dimension such that, when the bottom nozzle is selectively coupled to the reactor vessel lower core plate, the bottom edge of debris filtering skirt is positioned the second dimension away from a surface of the reactor vessel lower core plate. 
     These and other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features of various aspects described herein, together with the advantages of such features, can be understood in accordance with the following description taken in conjunction with the accompanying drawings, as follows: 
         FIG. 1  illustrates a partial cross-section of a side view of a fuel assembly including a debris filter bottom nozzle. 
         FIG. 2  illustrates a isometric view of the debris filter bottom nozzle of the fuel assembly of  FIG. 1 . 
         FIG. 3  illustrates an isometric view of a debris filter bottom nozzle according to at least one aspect of the present disclosure. 
         FIG. 4  illustrates an isometric view of a filtering skirt arrangement of  FIG. 3 , wherein a top plate of the debris filter bottom nozzle has been removed to further illustrate its internal geometry. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. The drawings set out herein illustrate various aspects in one form and such aspects are not to be construed as limiting the scope of the disclosure in any manner. 
     DETAILED DESCRIPTION 
     Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the aspects as described in the disclosure and illustrated in the accompanying drawings. Well-known operations, components, and elements have not been described in detail so as not to obscure the aspects described in the specification. The reader will understand that the aspects described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and illustrative. Variations and changes thereto may be made without departing from the scope of the claims. Furthermore, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”. “upwardly”, “downwardly”, and the like are words of convenience and are not to be construed as limiting terms. 
     In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly”, and the like are words of convenience and are not to be construed as limiting terms. 
     Referring now to  FIG. 1 , a side view of a known fuel assembly  10 , in which various non-limiting aspects of the present disclosure can be employed, is illustrated in vertically foreshortened form. For example, the fuel assembly  10  can be used in a pressurized water reactor and has a structural skeleton which at its lower end includes a debris filter bottom nozzle  12  such as described in U.S. Pat. No. 4,900,507, the disclosure of which is herein incorporated by reference in its entirety. The bottom nozzle  12  can support the fuel assembly  10  on a reactor vessel lower core plate  14  in the core region of a reactor (not shown). The term “reactor vessel” is used broadly herein and can include for example, the fuel assembly of a nuclear reactor. In addition to the bottom nozzle  12 , the structural skeleton of the fuel assembly  10  can also include a top nozzle  16  at its upper end and a number of guide thimble tubes  18  which extend longitudinally between the bottom and top nozzles  12 , 16  and at opposite ends are attached thereto. Although the improved debris filter skit and bottom nozzle can be implemented in the fuel assembly  10  of  FIG. 1 , the present disclosure contemplates other non-limiting aspects involving alternate fuel assemblies. For example, the skirt can employ similar geometric features to be discussed herein, modified to accommodate any fuel assembly for which the reduction of debris is a priority. 
     The fuel assembly  10  can further include a plurality of transverse grids  20  that can be axially spaced along and/or mounted to the guide thimbles  18  and an organized array of elongated fuel rods  22  can be transversely spaced and/or supported by the grids  20 . Also, the assembly  10  can have an instrumentation tube  24  located in the center thereof and extending between and mounted to the bottom and top nozzles  12 , 16 . With such an arrangement of parts, the fuel assembly  10  can form an integral unit capable of being conveniently handled without damaging the assembly parts. 
     As mentioned above, the fuel rods  22  of  FIG. 1  of fuel assembly  10  can be held in spaced relationship with one another by the grids  20  spaced along the fuel assembly length. Each fuel rod  22  includes nuclear fuel pellets  26  and is closed at its opposite ends by an upper end plug  28  and a lower end plug  30 . For example, the pellets  26  can be maintained in a stack by a plenum spring  32  disposed between the upper end plug  28  and the top of the pellet stack. However, in other non-limiting aspects the pellets  26  can be otherwise configured via alternate mechanisms. In the non-limiting aspect of  FIG. 1 , the fuel pellets  26  can be composed of a fissile material capable of creating the reactive power of the reactor. However, in other non-limiting aspects of the present disclosure, the pellets  26  can include a variety of suitable materials capable of generating reactive power. Additionally, a liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through a plurality of flow openings in the lower core plate  14  to the fuel assembly. In still other non-limiting aspects, alternate coolants can be used to a similar effect. The bottom nozzle  12  of the fuel assembly  10  can pass the coolant flow along to the fuel rods  22  of the assembly in order to extract heat generated therein for the production of useful work. 
     In order to control the fission process, a number of control rods  34  can be reciprocally moved within the fuel assembly  10  of  FIG. 1 . For example, the rods  34  can be reciprocally moved in the guide thimble tubes  18  located at predetermined positions in the fuel assembly  10 . Accordingly, a rod cluster control mechanism  36  can be positioned above the top nozzle  16  to support the control rods  34 . In the fuel assembly  10  of  FIG. 1 , the control mechanism can include an internally threaded cylindrical member  37  with a plurality of radially extending flukes or arms  38 . Each arm  38  can be interconnected to a control rod  34  such that the control mechanism  36  can be operable to move the control rods vertically in the guide thimbles  18  to thereby control the fission process in the fuel assembly  10 , all in a well-known manner. 
     As mentioned above, a fuel assembly, such as the fuel assembly  10  of  FIG. 1 , can be damaged—by debris that gets trapped at or below the grids  20 . To prevent occurrence of such damage, it is highly desirable to prevent such debris from passing through the bottom nozzle flow holes or under the side skirts and between the fuel assemblies and reaching the fuel bundle region. 
     Referring now to  FIG. 2 , the bottom nozzle  12  can include support means, which can take the form of a plurality of corner legs  42  that can extend from a generally rectangular skirt portion  44 . The corner legs  42  can support the fuel assembly  10  on the reactor vessel lower core plate  14 . Bottom nozzle  12  can further include a generally rectangular planar plate  46  which is suitably attached to the skirt portion  44 . Although the rectangular planar plate  46  of the non-limiting aspect of  FIG. 2  is welded to the bottom nozzle  12 , other non-limiting aspects of the present disclosure contemplate alternate means of attaching the rectangular planar plate  46  to the bottom nozzle  12 . In still other non-limiting aspects, the rectangular planar plate  46  is integrally formed with the bottom nozzle  12  through procedures including but not limited to additive manufacturing. 
     The bottom nozzle  12  of  FIG. 2  can further include a plate  46  with a plurality of spaced flow holes  48 . The flow holes  48  can be sized to “filter out” debris of a damaging size. Such a design is intended to perform such filtering without appreciably affecting flow or pressure drop through the plate  46  and the fuel assembly  10 . However, as indicated in  FIG. 2 , and previously discussed in the Background section, such bottom nozzle  12  arrangements accommodate flow and pressure drop by including rather large openings through which debris may readily pass. Thus, it would be advantageous to implement a debris filter skirt and/or improved bottom nozzle  12  that can filter debris of a concerning size while preserving the flow of coolant and minimizing pressure drop through the plate  46 . 
     Having thus described an example of an arrangement in which aspects of the present disclosure can be implemented, a bottom nozzle having a side skirt design in accordance with at least one non-limiting aspect of the present disclosure will now be described. Referring now to  FIG. 3 , an improved bottom nozzle  50  can include an improved skirt  52 , which can be manufactured using existing manufacturing technologies, combined with a top plate  46  ( FIG. 2 ) to form a single, integral bottom nozzle  50 . However, in other non-limiting aspects, the improved bottom nozzle  50  and skirt  52  can be manufactured using less conventional procedures. For example, the bottom nozzle  50  and skirt  52  might be integrally formed using additive manufacturing processes. The skirt  52  can include a plurality of skirt flow holes  54  on one or more sides, which facilitates a lateral flow of coolant underneath the improved bottom nozzle  50  and through the plurality of the skirt flow holes. 
     According to the non-limiting aspect of  FIG. 3 , the improved bottom nozzle  50  and side skirt  52  includes an enhanced debris filtering capability due to a reduced gap between the reactor vessel lower core plate (not shown) and a bottom edge  56  of the skirt  52 , and a specifically configured plurality of flow holes  54  on the side skirt  52  of the bottom nozzle  50 . As depicted in the aspect of  FIG. 3 , the side skirts  52  have been lowered such that a gap or opening  58  between the bottom nozzle  50  and the reactor vessel lower core plate (not shown) is reduced to about 0.0″ to 0.150″ (instead of about 1″ such as previously discussed in reference to  FIG. 2 ). However, in other non-limiting aspects, the opening  58  and the configuration of flow holes  54  are configured to a variety of dimensions and designs to achieve the desired filtering capability. Notably, the opening  58  of the bottom nozzle  50  of  FIG. 3  has been substantially reduced in comparison to the opening  49  illustrated in the aspect of  FIG. 2 , because of the plurality of flow holes  54  of the side skirt  52 . In the aspect of  FIG. 3 , the side skirt flow holes  54  can include a diameter of about 0.020″ to 0.150″ defined within the side skirts  52 . However, it is to be appreciated that the side skirt  52  flow holes  54  may be a variety of different shapes (e.g., round, oval, etc.) and/or sizes without varying from the scope of the disclosed aspect of  FIG. 3 . It is also to be appreciated that one or more of the quantity, pattern, and/or pitch (e.g., square, triangular, etc.) of the side skirt flow holes may be varied without varying from the scope of the disclosed aspect of  FIG. 3 . 
     The reduction in the size of the skirt  52  opening  58  as compared to the prior art design of  FIG. 2  can be accomplished because the flow around the bottom nozzle  50  is largely defined by the gaps between adjacent bottom nozzles (not shown) which is smaller than the larger openings  49  in the side skirts of the prior art bottom nozzle  12  design of  FIG. 2 . Despite the opening  58  being configured to a smaller size and the introduction of the plurality of flow holes  54 , both of which enhance the filtering capability of the improved bottom nozzle  50 , the side skirt design  52  of  FIG. 3  does not adversely affect a pressure loss coefficient of the bottom nozzle  50 . This is due to the geometric features of the skirt  52  design being specifically configured to compensate for the reduction in size of the opening  58  and/or the introduction of the plurality of filtering flow holes  54 . Geometric features including but not limited to a length of each flow hole  54  and/or a diameter of each flow holes  54  can be specifically configured such that the bottom nozzle  50  maintains a predetermined loss coefficient (i.e., pressure loss) in spite of its improved filtering capabilities. For example, the Darcy-Weisbach equation can be used to calculate a pressure loss along the flow passage: 
     
       
         
           
             
               Δ 
               ⁢ 
               
                   
               
               ⁢ 
               p 
             
             = 
             
               L 
               · 
               
                 f 
                 d 
               
               · 
               
                 ρ 
                 2 
               
               · 
               
                 
                   v 
                   2 
                 
                 D 
               
             
           
         
       
     
     Where Δp is the pressure loss through the flow passage  12 , L is a length of the flow passage  12 , f D  is a darcy friction factor of the flow passage  12 , ρ is a density of the fluid traversing the flow passage  12 , ν is an average velocity of a fluid traversing the flow passage  12 , and D is a flow diameter of the flow passage  12 . The Darcy-Weisbach equation is merely illustrative, and other aspects employ a variety of fluid dynamics computations to optimize the bottom nozzle  50  and side skirt  52  design. However, according to some non-limiting aspects of the present disclosure, the specific geometry of the skirt  52  might not lend itself to the direct use of the Darcy-Weisbach equation, as the flow holes  48  and the top flow plate  46  through which the majority of the flow passes can remain unchanged. Since the present disclosure contemplates improvements to secondary flow paths, such as those through the bottom nozzle, Computational Fluid Dynamics (CFD) can be utilized to calculate and optimize the flow through the flow holes  54  of the side skirt  52 . This ensures that there is sufficient flow into the gaps between fuel assemblies as well as into the reactor vessel baffle-barrel region to ensure that the reactor vessel former plates are sufficiently cooled. 
     For example, in one non-limiting aspect of the present disclosure, the geometry and features of the skirt  52  can be specifically configured to achieve a predetermined loss coefficient of the bottom nozzle  50  that is greater than or equal to about 1.0 and less than or equal to about 2.5. However, in other non-limiting aspects, the skirt  52  can be further configured to achieve any desired loss coefficient through the bottom nozzle  50 . Alternatively and/or additionally, the skirt  52  can be configured to control the change in loss coefficient compared to those of conventional bottom nozzles. For example, in some non-limiting aspects, the geometry of the skirt  52  can be configured to achieve a loss coefficient no greater than 0-5% different than that of a conventional bottom nozzle. In still other non-limiting aspects, the skirt  52  can be specifically configured to achieve a loss coefficient that differs from the loss coefficient of a conventional bottom nozzle to varying degrees, depending on the intended application and/or preference of the user. Accordingly, the improved bottom nozzle  50  and side skirt  52  design of  FIG. 3  can achieve any desired flow characteristic of a lateral flow while filtering out debris of a predetermined size before it can reach the fuel bundle region and potentially cause damage. 
     According to other non-limiting aspects of the present disclosure, a variety of geometric features of the bottom nozzle  50  and skirt  52  can be specifically configured to effect other flow characteristics while filtering debris of varying sizes. For example, the dimensions of the opening  58  can be specifically tailored to achieve predetermined filtration and loss coefficient characteristics. In still other non-limiting aspects, the improved bottom nozzle  50  and debris filtering side skirt  52  can be particularly configured to improve the debris filtering efficiency of the bottom nozzle  12  of  FIG. 2  while maintaining existing design requirements, including but not limited to pressure drop, structural support, and the ability to ensure that sufficient flow reaches the baffle-barrel region for the purposes of cooling the reactor vessel former plates. 
     Furthermore, many nuclear reactor designs include bolts that are located on the reactor vessel lower core plate (not shown) in areas that can directly interfere with and prevent the lowering of the bottom nozzle  12  and side skirt  44  of  FIG. 2 . However, the improved bottom nozzle  50  and side skirt  52  can further include features that accommodate for such bolts. For example, the improved bottom nozzle  50  and side skirt  52  of  FIG. 3  include four pockets  60 , which are specifically positioned in the side skirt  52  to prevent the bottom nozzle  50  and side skirt  52  from directly interfering with the lower core plate bolts (not shown). This is accomplished while simultaneously providing the greatly improved debris protection and desirable flow characteristics, as previously discussed. In the non-limiting aspect of  FIG. 3 , the pocket width can be varied between about 1.5″ and 2.0″, the pocket height can be varied between about 0.50″ and 1.0″, and the pocket depth can be varied between about 0.80″ and 1.20″. However, the present disclosure further contemplates non-limiting aspects including pockets of varying dimensions configured to accommodate a wide variety of bolt configurations and lower core plate designs. Accordingly, the improved bottom nozzle  50  and side skirt  52  of  FIG. 3  can be further altered such that the improved filtration capabilities and flow characteristics can be implemented on a wide variety of reactor designs. 
     Referring now to  FIG. 4 , the improved bottom nozzle  50  of  FIG. 3  is illustrated without the top plate  46  of  FIG. 2  to further illustrate an internal geometry of the improved side skirt  52 . Specifically, the pockets  60  as depicted in  FIG. 3  are shown to include a recess  62  formed in a back wall thereof on the side opposite the pocket. Accordingly, the recesses  62  can provide a requisite clearance for guide thimble screws (not shown) to support the manufacture and/or maintenance of a fuel assembly, such as the fuel assembly  10  of  FIG. 1 . Furthermore, the pockets  60  of  FIGS. 3 and 4  can also allow one such fuel assembly  10  to be lifted off of the reactor vessel lower core plate (not shown) in situations where the fuel assembly  10  is stuck to the reactor vessel lower core plate ( FIG. 1 ). 
     In further reference of  FIGS. 3 and 4 , the improved bottom nozzle  50  can be manufactured using conventional manufacturing techniques such that the improved side skirt  52  is integral to the bottom nozzle  50 . Accordingly, the bottom nozzle  50  can be initially produced to include the aforementioned filtration and flow benefits. For example, in some non-limiting aspects of the present disclosure, the improved bottom nozzle  50  and side skirt  52  can be produced using additive manufacturing techniques. Such an approach can provide for even enhanced filtration benefits because the plurality of flow holes  54  can be produced with much smaller dimensions. Additionally, and/or alternatively, additive manufacturing techniques can enable non-line-of-sight flow holes  54  to be produced, thereby further enhancing the filtration capabilities of the bottom nozzle  50 . 
     However, the present disclosure contemplates other non-limiting aspects wherein the improved bottom nozzle  50  and side skirt  52  of  FIGS. 3 and 4  are independently manufactured and subsequently attached to one another. For example, an independently produced side skirt  52  can be attached to the bottom nozzle  12  of  FIG. 2 . Thus, even the known bottom nozzle  12  of  FIG. 2  can be retrofitted with the improved side skirt  52  to achieve the aforementioned benefits of filtration and flow. As an additional benefit, the improved side skirt  52  design of  FIGS. 3 and 4  does not require the alteration of conventional fuel assembly  10  ( FIG. 1 ) manufacturing processes, thereby further facilitating the ability to retrofit known bottom nozzles  12 . 
     Various aspects of the subject matter described herein are set out in the following numbered clauses: 
     Clause 1: A debris filtering side skirt configured for use with a flow plate of a bottom nozzle configured to be positioned on the reactor vessel lower core plate of a nuclear reactor, the debris filtering skirt including a base portion including a first surface, a second surface, a bottom edge, and a plurality of sides, wherein the base portion defines an opening between the bottom edge and the reactor vessel lower core plate of the nuclear reactor, wherein the opening includes a dimension configured to position the bottom nozzle a predetermined distance away from the reactor vessel lower core plate of the nuclear reactor, and a plurality of holes defined within at least one side of the plurality of sides of the base portion, wherein each hole of the plurality of holes includes an inlet proximal to the first surface of the base portion and an outlet proximal to the second surface of the base portion, and wherein at least one hole of the plurality of holes includes a dimension determined based, at least in part, on a predetermined size of debris capable of traversing through the inlet and the outlet, wherein the dimension of the opening and the dimension of the at least one hole are determined based, at least in part, on a predetermined loss coefficient of the bottom nozzle. 
     Clause 2: A debris filtering skirt according to clause 1, wherein the debris filtering skirt is integrally formed with the bottom nozzle, and wherein the debris filtering skirt and bottom nozzle constitute a single-piece unit. 
     Clause 3: A debris filtering skirt according to clauses 1 or 2, wherein the debris filtering skirt is a separately formed piece that is configured for selective engagement with the bottom nozzle. 
     Clause 4: A debris filtering skirt according to any of clauses 1-3, wherein the base portion is configured for selective engagement with the reactor vessel lower core plate. 
     Clause 5: A debris filtering skirt according to any of clauses 1-4, further including a pocket proximal to the first side of the base portion, wherein the pocket is configured to circumvent a bolt of the reactor vessel lower core plate, such that the bolt does not mechanically interfere with the selective engagement of the base portion and the reactor vessel lower core plate. 
     Clause 6: A debris filtering skirt according to any of clauses 1-5, wherein the pocket further includes a handle configured to allow a user to disengage the fuel assembly from the reactor vessel lower core plate. 
     Clause 7: A debris filtering skirt according to any of clauses 1-6, further including a recess proximal to the second surface, wherein the recess is configured to provide a predetermined clearance for a guide thimble screw of the fuel assembly. 
     Clause 8: A debris filtering skirt according to any of clauses 1-7, wherein the plurality of holes is defined in each side of the plurality of sides of the base portion. 
     Clause 9: A debris filtering skirt according to any of clauses 1-8, wherein the predetermined loss coefficient of the bottom nozzle is greater than or equal to 1.0 and less than or equal to 2.5. 
     Clause 10: A debris filtering skirt according to any of clauses 1-9, wherein the predetermined distance is less than or equal to 0.150 inches. 
     Clause 11: A debris filtering skirt according to any of clauses 1-10, wherein the dimension of the at least one hole of the plurality of holes is greater than or equal to 0.020 inches and less than or equal to 0.150 inches. 
     Clause 12: A fuel assembly configured for selective engagement with a reactor vessel lower core plate of a nuclear reactor, the fuel assembly including a bottom nozzle including a flow plate, wherein the flow plate includes a plurality of flow passages through which a coolant can traverse towards the core region of the nuclear reactor, and a debris filtering skirt including a base portion including a plurality of holes and a bottom edge, wherein the base portion defines an opening between the bottom edge and the reactor vessel lower core plate of the nuclear reactor, wherein the opening includes a dimension configured to position the bottom edge a predetermined distance away from the reactor vessel lower core plate when the fuel assembly is selectively engaged with the reactor vessel lower core plate, and wherein at least one hole of the plurality of holes includes a dimension determined based, at least in part, on a predetermined size of debris capable of traversing through the at least one hole, wherein the dimension of the opening and the dimension of the at least one hole are determined based, at least in part, on a predetermined loss coefficient of the bottom nozzle. 
     Clause 13: A fuel assembly according to clause 12, wherein the predetermined loss coefficient of the bottom nozzle is greater than or equal to 1.0 and less than or equal to 2.5. 
     Clause 14: A fuel assembly according to clause 12 or 13, wherein the predetermined distance is less than or equal to 0.150 inches. 
     Clause 15: A fuel assembly according to any of clauses 12-14, wherein the dimension of the at least one hole of the plurality of holes is greater than or equal to 0.020 inches and less than or equal to 0.150 inches. 
     Clause 16: A fuel assembly according to any of clauses 12-15, wherein the flow passage and plurality of filtering ligaments are co-formed with the debris filter bottom nozzle and constitute a single-piece unit. 
     Clause 17: A fuel assembly according to any of clauses 12-16, wherein the debris filtering skirt further includes a pocket configured to circumvent a bolt of the lower core plate, such that the bolt does not mechanically interfere with the selective engagement of the base portion and the lower core plate: and a recess positioned opposite the pocket, wherein the recess is configured to provide a predetermined clearance for a guide thimble screw of the fuel assembly. 
     Clause 18: A method of manufacturing a debris filtering skirt of a bottom nozzle configured for selective engagement with the reactor vessel lower core plate of a nuclear reactor, the method including determining a maximum loss coefficient of the bottom nozzle, determining a minimum filtration capability of the debris filtering skirt, calculating a first dimension based at least in part on the maximum loss coefficient and the minimum filtration capability, calculating a second dimension based at least in part on the maximum loss coefficient, producing the bottom nozzle, producing the debris filtering skirt including a bottom edge and a plurality of sides, defining a plurality of holes in at least one side of the plurality of sides of the debris filtering skirt, wherein at least one hole of the plurality of holes includes the first dimension, defining an opening within the debris filtering skirt, wherein the opening includes the second dimension such that, when the bottom nozzle is selectively coupled to the lower core plate, the bottom edge of debris filtering skirt is positioned the second dimension away from a surface of the reactor vessel lower core plate. 
     Clause 19: A method according to clause 18, wherein the first dimension is greater than or equal to 0.020 inches and less than or equal to 0.150 inches, and wherein the second dimension is less than or equal to 0.150 inches. 
     Clause 20: A method according to clause 18 or 19, wherein the bottom nozzle and debris filtering skirt are produced using additive manufacturing techniques such that the debris filtering skirt and bottom nozzle are co-formed and constitute a single-piece unit. 
     All patents, patent applications, publications, or other disclosure material mentioned herein, are hereby incorporated by reference in their entirety as if each individual reference was expressly incorporated by reference respectively. All references, and any material, or portion thereof, that are said to be incorporated by reference herein are incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as set forth herein supersedes any conflicting material incorporated herein by reference and the disclosure expressly set forth in the present application controls. 
     The present invention has been described with reference to various exemplary and illustrative aspects. The aspects described herein are understood as providing illustrative features of varying detail of various aspects of the disclosed invention; and therefore, unless otherwise specified, it is to be understood that, to the extent possible, one or more features, elements, components, constituents, ingredients, structures, modules, and/or aspects of the disclosed aspects may be combined, separated, interchanged, and/or rearranged with or relative to one or more other features, elements, components, constituents, ingredients, structures, modules, and/or aspects of the disclosed aspects without departing from the scope of the disclosed invention. Accordingly, it will be recognized by persons having ordinary skill in the art that various substitutions, modifications or combinations of any of the exemplary aspects may be made without departing from the scope of the invention. In addition, persons skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the various aspects of the invention described herein upon review of this specification. Thus, the invention is not limited by the description of the various aspects, but rather by the claims. 
     Those skilled in the art will recognize that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. 
     In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art w % ill recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A. B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A. B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A. B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B.” 
     With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although claim recitations are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are described, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise. 
     It is worthy to note that any reference to “one aspect.” “an aspect,” “an exemplification,” “one exemplification,” and the like means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, appearances of the phrases “in one aspect,” “in an aspect,” in an exemplification,” and “in one exemplification” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more aspects. 
     As used herein, the singular form of “a”, “an”, and “the” include the plural references unless the context clearly dictates otherwise. 
     Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, lower, upper, front, back, and variations thereof, shall relate to the orientation of the elements shown in the accompanying drawing and are not limiting upon the claims unless otherwise expressly stated. 
     The terms “about” or “approximately” as used in the present disclosure, unless otherwise specified, means an acceptable error for a particular value as determined by one of ordinary skill in the art, which depends in part on how the value is measured or determined. In certain aspects, the term “about” or “approximately” means within 1, 2, 3, or 4 standard deviations. In certain aspects, the term “about” or “approximately” means within 50%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.05% of a given value or range. 
     In this specification, unless otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term “about,” in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described herein should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Any numerical range recited herein includes all sub-ranges subsumed within the recited range. For example, a range of “1 to 10” includes all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Also, all ranges recited herein are inclusive of the end points of the recited ranges. For example, a range of “1 to 10” includes the end points 1 and 10. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited. All such ranges are inherently described in this specification. 
     Any patent application, patent, non-patent publication, or other disclosure material referred to in this specification and/or listed in any Application Data Sheet is incorporated by reference herein, to the extent that the incorporated materials is not inconsistent herewith. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material. 
     The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a system that “comprises,” “has,” “includes” or “contains” one or more elements possesses those one or more elements, but is not limited to possessing only those one or more elements. Likewise, an element of a system, device, or apparatus that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features.