Abstract:
A method and apparatus for a deposition solution injector for a nuclear reactor that may inject an ambient temperature deposition solution into a high temperature, high pressure feed-water flow line. The method and the apparatus ensures that the deposition solution is delivered in a location within the feed-water that is beyond a boundary layer of flowing water, to prevent smearing of the solution and prevent clogging of the deposition solution within the injector. The axial cross-sectional profile of the injector, and the location of an injection slot on the injector, may reduce vortex eddy flow of the feed-water into the injector to further reduce injector blockage.

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 a high-temperature deposition solution injector to deliver an ambient temperature deposition solution to a high temperature, high pressure feed-water flow line. In particular, the method and the apparatus ensures that the deposition solution is delivered in a location within the feed-water that is beyond the boundary layer of the flowing water, to prevent excessive deposition of the solution on the feed-water pipe just downstream of the injection tap and to prevent deposition of the solution within the injection tap, causing blockage of the tap. 
         [0003]    2. Related Art 
         [0004]    In a nuclear reactor, deposition solutions are often injected into a high temperature/pressure feed-water line in order to deposit materials on reactor surfaces. In particular, as shown in  FIG. 1 , hydrogen injection  2  may be used to inject hydrogen in a feed-water suction line  4   b  (the suction line  4   b  is the inlet to feed-water pumps  10 ) to act as an oxygen scavenger for the water circulating in the reactor  8 . In conjunction with the hydrogen injection  2 , a noble metal (e.g., platinum) deposition solution injection system  6  may be used to inject a deposition solution into the feed-water discharge line  4   a  in order to deposit platinum ions on surfaces of the reactor  8 . While a Boiling Water Reactor (BWR)  8  configuration is depicted in  FIG. 1 , it should be understood that other types of nuclear reactors could also make use of deposition solution injections (such as the platinum deposition solution described herein). The platinum deposition solution may be, for example, a platinum salt solution of sodium hexahydroxyplatinate (Na 2 Pt(OH) 6 ). By injecting the solution into the feed-water discharge  4   a , platinum ions may deposit onto surfaces of the reactor  8  so that the platinum may act as a catalyst to react the injected hydrogen with oxygen molecules that may be present in the reactor. By causing hydrogen to react with oxygen molecules on surfaces of the reactor  8 , water (H 2 O) molecules may be produced. This reaction acts to reduce and potentially eliminate oxygen molecules present on surfaces of the reactor  8  that may otherwise promote corrosion of metal components, thereby extending the useful life of reactor components. 
         [0005]    As shown in  FIG. 2 , a conventional deposition solution injector configuration  12  may include a chemical feed skid  24  supplying a deposition solution to the feed-water discharge line  4   a . The chemical feed skid typically provides the chemical deposition solution at ambient temperatures with a flow-rate of around 50-120 cm 3 /minute and a pressure typically less than 1250 psi (via positive displacement pumps). A chemical feed line  26  may provide the deposition solution from the chemical feed skid  24  to the injection tap  20 . One or more injector valves  14  may be included in the chemical feed line  26  to provide shutoff for the deposition solution in the chemical feed line  26 . Typically, a pipe stub  16  is included at the valve  14  discharge. A weldment  18  may connect the injection tap  20  to the pipe stub  16  and feed-water discharge line  4   a.    
         [0006]    Because a distal end of a conventional injection tap  20  may extend only to an inner surface of the feed-water discharge line  4   a , deposited material  22  may form within the end of the injection tap  20 . The deposited material  22  may form at the injection point  6 , as the ambient (i.e., low) temperature deposition solution is mixed with intruding eddy flow of the high temperature, high velocity feed-water (ranging between 260 and 420° F. with a flow velocity of about 10-20 ft/sec) that may cause the deposition solution to break down into platinum ions which are then deposited within the inner distal end of the injection tap  20  (it is noted that sodium hexahydroxyplatinate, Na 2 Pt(OH) 6 , begins to break down at temperatures of 300-500° F.). Blockage of the injection tap  20  caused by the deposited material  22  may cause the positive displacement pumps to increase injection pressure to provide the specified injection flow rate. Pressure may increase to the design pressure of the injector configuration  12 , resulting in termination of an injection before all of the deposition solution is injected. This may cause a reduced amount of platinum to be deposited within the reactor  8 , itself. Furthermore, blockage of the injection tap  20  may prevent performance of the next scheduled injection (typically done once per year), or require an unplanned reactor shutdown to remove the blockage. 
         [0007]    In addition to blockage of the injection tap  20  by deposited material  22  within the injection points  6 , smearing of deposited material  22  may also occur along the inner surfaces of the feed-water line  4   a  as the slowly flowing deposition solution is unable to escape the boundary layer and enter the bulk flow of the feed-water. The smearing may cause significant amounts of platinum ions to deposit along the inside of the feed-water line where it is not needed or desired, which also may reduce the amount of platinum that reaches the reactor  8 . 
       SUMMARY OF INVENTION 
       [0008]    Example embodiments provide a method and an apparatus for injecting a deposition solution into a high pressure/temperature feed-water line. The method and apparatus ensure that the deposition solution is injected beyond a boundary layer of fluids traveling through the feed-water line and into the associated bulk flow of fluids. By injecting the deposition solution beyond the boundary layer, blockage of the injector and smearing of deposited material along the inner surfaces of the feed-water line may be mitigated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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. 
           [0010]      FIG. 1  is a perspective view of a conventional boiling water nuclear reactor (BWR) including deposition solution injection; 
           [0011]      FIG. 2  is a cross-sectional view of a conventional deposition solution injector configuration; 
           [0012]      FIG. 3  is a cross-sectional view of a deposition solution injector configuration, in accordance with an example embodiment; 
           [0013]      FIG. 4A  is a cross-sectional view of a distal end of an injector, in accordance with an example embodiment; and 
           [0014]      FIG. 4B  is an axial, cross-sectional view A-A of the injector of  FIG. 4A . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    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.). 
         [0019]    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. 
         [0020]    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. 
         [0021]      FIG. 3  is a cross-sectional view of a deposition solution injector configuration  32 , in accordance with an example embodiment. The injector configuration  32  includes a hollow injector tube  30  with a distal end  30   a  that extends beyond the inner surface of the feed-water line  4   a . In particular, the distal end  30   a  of the injector  30  may extend beyond a determined boundary layer of the bulk flow of fluids traveling through the feed-water line  4   a . The depth of the boundary layer (and, the required length X of the distal end  30   a  of the injector  30 ) may vary depending upon the temperature and velocity of the feed-water. The depth of the boundary layer may also vary depending on the type of fluid flowing in the feed-water line  4   a  (with potentially varying viscosity), the diameter and material of the feed-water line  4   a , as well as other parameters known to impact the Reynolds number (and resulting boundary layer depth) of fluid flowing in the feed-water line  4   a . It should therefore be understood that the length X should at least be long enough to extend beyond the boundary layer of the fluid flowing in the feed-water line  4   a.    
         [0022]    Deposition solution injector configuration  32  also includes a pipe stub  16   a  with an inner diameter that matches or slightly exceeds the outer diameter of injector  30 . This pipe stub  16   a  provides support to minimize vibration stresses in the injector  30  caused by feed-water flow forces. 
         [0023]    The inner diameter of the injector  30  may also contribute to potential blockage caused by deposited material, if the deposition material is heated to high temperatures as it flows to the distal end  30   a  of injector  30 . For this reason, the inside diameter of the injector  30  should be sized to be sufficiently small, ensuring that the deposition solution flows quickly through the hot region adjacent to the feed-water line  4   a . For a 50-120 cm 3 /minute flow rate of deposition solution through the injector  30 , a ⅛ inch inner diameter of the injector  30  would result in flow velocities of 3-9 inches/second. This would cause the deposition solution to be in the hot region for less than a second, ensuring that the deposition solution does not degrade during this short period. 
         [0024]      FIG. 4A  is a cross-sectional view of a distal end  30   a  of an injector  30 , in accordance with an example embodiment. The injector  30  is provided with an injection slot  30   b  located on a downstream side of the injector (specifically, the injector slot  30   b  is downstream of the feed-water flow passing across the distal end  30   a  of the injector  30 ). By locating the injection slot  30   b  on the downstream side of the injector  30 , the slot  30   b  is somewhat sheltered from the high pressure flow of the feed-water, thereby reducing the potential for the injector  30  to become clogged by deposited material. 
         [0025]    The injector should be sized to ensure that the entire injection slot  30   b  should extend beyond the boundary layer of flowing feed-water, just as the distal end  30   a  of the injector should extend beyond the boundary layer (as described in  FIG. 3 ). This ensures that the deposition solution may be fully injected into the bulk flow of feed-water in the feed-water line  4   a  without experiencing unnecessarily high deposition of platinum ions on the inside of the feed-water line  4   a . For this reason, length Y (the injector length from the inner surface of the feed-water line  4   a  to the opening of the injection slot  30   b ) must extend beyond the boundary layer of the feed-water. As described in  FIG. 3 , the boundary layer depth may vary depending on the temperature and velocity of the feed-water, the type of fluid flowing in the feed-water line, the diameter and material of the feed-water line, etc. As an example, for a 16 inch diameter feed-water line  4   a  with flowing water in a range of 15-20 feet/second at a temperature of 260-420° F., a length Y of 1 inch is adequate to ensure that the entire injection slot  30   b  extends beyond the boundary layer of fluids flowing in the feed-water line  4   a.    
         [0026]    The size of the injection slot  30   b  itself may also impact blockage of the injector  30 . Therefore, the cross-sectional area of the injection slot  30   b  should be sized to ensure that the exit velocity of the deposition solution approximately matches the feed-water flow velocity, ensuring that feed-water eddy flows do not enter the injection slot  30   b  and cause deposition and possible blockage. 
         [0027]    The injection slot  30   b  may be located a distance below the very distal end  30   a  of the injector  30 , to further shelter the injection slot  30   b  from the high pressures of the feed-water flow. However, the distal end  30   a  of the injector  30  should not extend too far beyond the depth of the feed-water boundary layer. By not extending the distal end  30   a  of the injector too far beyond the location of the boundary layer, bending and damage to the injector  30  by the high velocity feed-water flow may be avoided. Therefore, length X (the full length of the distal end  30   a  of the injector extending within the feed-water line  4   a ) should be no more than about 20% greater than the required length Y. 
         [0028]      FIG. 4B  is an axial, cross-sectional view A-A of the injector  30  of  FIG. 4A . As discussed in  FIG. 4A , the injection slot  30   b  may be located on a downstream side of the injector  30  (the downstream side, meaning downstream of the feed-water flow direction). The axial cross-sectional profile  30   c  of the injector may be a tapered, oval-shape with two acute ends (as shown in  FIG. 4B ), to hydrodynamically reduce feed-water fluid forces that may be experienced at the interface between the injection slot  30   b  and the bulk flow of the feed-water. The injection slot  30   b  may be located on the downstream-facing acute end of the injector  30  (as it is shown in  FIG. 4B ). The axial cross-sectional profile  30   c  may also be circular, square, or some other shape, so long as the injection slot  30   b  is located on the downstream side of the injector  30  to minimize eddy flow of incident feed-water that may enter into the injector  30 . 
         [0029]    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.