Patent Publication Number: US-9839925-B2

Title: Methods of cleaning a submerged surface using a fluid jet discharging a liquid/gas combination

Description:
BACKGROUND 
     Field 
     The present disclosure relates to methods of cleaning a submerged surface. 
     Description of Related Art 
     To ensure safe operation, submerged reactor surfaces are periodically inspected for cracks that may jeopardize the integrity of the structure. That being said, the submerged reactor surfaces must be cleaned of unwanted buildup and deposits (also referred to as “dust”) before the periodically required inspections can be conducted. The “dust” layer created by the high temperature, high radiation reactor environment adheres rather tightly to the affected surfaces and is relatively difficult to remove. Conventionally, the submerged reactor surfaces are mechanically cleaned using brush-type tools. However, this mechanical cleaning approach involving brush-type tools is not completely effective in removing the unwanted buildup and deposits from the submerged reactor surfaces. Additionally, this mechanical cleaning approach tends to leave behind brush debris (bristles, tufts, staples, and/or other broken-off components) in the reactor. 
     SUMMARY 
     Example embodiments herein relate to a method of cleaning a submerged surface covered by a liquid medium. The method includes injecting a cleaning liquid with a submerged fluid jet through the liquid medium at the submerged surface. The method may also include introducing at least one of a non-reactive gas and a reactive gas with the cleaning liquid through the submerged fluid jet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the non-limiting 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 schematic view of a method and an apparatus for cleaning a submerged surface. 
         FIG. 2  is a cross-sectional view of the fluid jet of  FIG. 1 . 
         FIG. 3  is a front view of the fluid jet of  FIG. 2 . 
         FIG. 4  is a graph showing the relationship between the pH of the liquid medium and the quantity of ammonia injected as the reactive gas. 
     
    
    
     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 terms 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 intermediate 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. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. 
     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 schematic view of a method and an apparatus for cleaning a submerged surface. Referring to  FIG. 1 , an apparatus for cleaning a submerged surface includes a cleaning liquid supply  100 , a non-reactive gas supply  102 , and a reactive gas supply  104  connected to a fluid jet  126 . The cleaning liquid supply  100  is configured to supply a cleaning liquid  100 ′ ( FIG. 2 ) to the fluid jet  126  through a cleaning liquid line  114  via a pump  106 . The flow opening in the cleaning liquid line  114  may be regulated with a first valve  108 . Similarly, the non-reactive gas supply  102  and the reactive gas supply  104  are configured to supply a non-reactive gas  102 ′ and a reactive gas  104 ′ ( FIG. 2 ) to the fluid jet  126  through a non-reactive gas line  116  and a reactive gas line  118 , respectively. The flow openings in the non-reactive gas line  116  and the reactive gas line  118  may be regulated with a second valve  110  and a third valve  112 , respectively. Although not shown, it should be understood that one or more pumps may be provided to drive the non-reactive gas  102 ′ and the reactive gas  104 ′ from the non-reactive gas supply  102  and the reactive gas supply  104 , respectively. 
     The fluid jet  126  may be arranged within a vessel  122  containing a liquid medium  120  so as to face a submerged surface  124  of the vessel  122 . The liquid medium  120  may be water, although example embodiments are not limited thereto. During the operation of the fluid jet  126 , the force generated by the fluids expelled therefrom may repel the fluid jet  126  and, thus, cause the fluid jet  126  to depart from an ideal or desired position relative to the submerged surface  124  of the vessel  122 . To counter this repulsive force, the fluid jet  126  may be stabilized with a balancing jet  128 . In particular, the balancing jet  128  may expel a secondary fluid in a direction opposite to the direction that the primary fluids are being expelled from the fluid jet  126 . Although  FIG. 1  illustrates a fluid jet  126  being used to clean an interior surface of the vessel  122 , it should be understood that the fluid jet  126  may be used on a variety of other submerged surfaces (whether in a reactor facility or in other environments). 
       FIG. 2  is a cross-sectional view of the fluid jet of  FIG. 1 . Referring to  FIG. 2 , the fluid jet  126  is configured to include a first passage  200 , a second passage  202 , and a third passage  204 . During operation of the fluid jet  126 , the cleaning liquid  100 ′ travels through the first passage  200 , the non-reactive gas  102 ′ travels through the second passage  202 , and the reactive gas  104 ′ travels through the third passage  204 . The first passage  200 , second passage  202 , and third passage  204  are designed such that the cleaning liquid  100 ′, non-reactive gas  102 ′, and reactive gas  104 ′ are isolated from each other while en route to and while within the fluid jet  126  and mix with each other when expelled from the fluid jet  126  into the liquid medium  120 . 
       FIG. 3  is a front view of the fluid jet of  FIG. 2 . Referring to  FIG. 3 , the fluid jet  126  may be configured such that the third passage  204  is concentrically arranged within the second passage  202 . The second passage  202  may also be concentrically arranged within the first passage  200 . The fluid jet  126  may be formed of a large cylinder structure, a medium cylinder structure arranged within the large cylinder structure, and a small cylinder structure arranged within the medium cylinder structure. The inner surface of the large cylinder structure and the outer surface of the medium cylinder structure define the first passage  200 . The inner surface of the medium cylinder structure and the outer surface of the small cylinder structure define the second passage  202 . The inner surface of the small cylinder structure defines the third passage  204 . Additional details regarding the fluid jet  126  will be provided below in connection with methods of cleaning using the fluid jet  126 . 
     A method of cleaning a submerged surface  124  covered by a liquid medium  120  includes injecting a cleaning liquid  100 ′ with a submerged fluid jet  126  through the liquid medium  120  at the submerged surface  124 . The method additionally includes introducing at least one of a non-reactive gas  102 ′ and a reactive gas  104 ′ with the cleaning liquid  100 ′ through the submerged fluid jet  126 . The “flame” of the fluid jet  126  facilitates the removal of “dust” and other unwanted materials from the submerged surface  124 . 
     The injecting step may include directing the cleaning liquid  100 ′ at an interior surface of a vessel  122  covered by the liquid medium  120 . Alternatively, the injecting step may include directing the cleaning liquid  100 ′ at a component immersed in the liquid medium  120  (e.g., a mechanical part within the vessel  122 ). However, it should be understood that the cleaning liquid  100 ′ may be directed at any surface in need of cleaning. Furthermore, the injecting step may include using water as the cleaning liquid  100 ′. 
     The injecting and introducing steps may include configuring the submerged fluid jet  126  such that the cleaning liquid  100 ′ and the at least one of the non-reactive gas  102 ′ and the reactive gas  104 ′ exit the submerged fluid jet  126  prior to mixing with each other. For example, the injecting and introducing step may be performed with a triple concentric tuyere as the submerged fluid jet  126 . In such a situation, the cleaning liquid  100 ′ may be injected through a first passage  200  of the triple concentric tuyere, the non-reactive gas  102 ′ may be introduced through a second passage  202  of the triple concentric tuyere, and the reactive gas  104 ′ may be introduced through a third passage  204  of the triple concentric tuyere. However, example embodiments are not limited thereto, and it should be understood that each of the cleaning liquid  100 ′, the non-reactive gas  102 ′, and the reactive gas  104 ′ may be supplied through any of the first passage  200 , the second passage  202 , and the third passage  204 . For instance, the non-reactive gas  102 ′ may be supplied through the third passage  204 , and the reactive gas  104 ′ may be supplied through the second passage  202 . 
     The injecting and introducing steps may include configuring the triple concentric tuyere such that the first passage  200  surrounds the second passage  202  and the third passage  204 . With this configuration, supplying the cleaning liquid  100 ′ through the outer first passage  200  will help focus the inner-supplied non-reactive gas  102 ′ and/or reactive gas  104 ′ during their path toward the submerged surface  124 , thereby reducing their premature diffusion into the liquid medium  120  and enhancing the cleaning of the submerged surface  124 . The injecting and introducing may also include configuring the triple concentric tuyere such that the second passage  202  and/or the third passage  204  extends further from the submerged fluid jet  126  than the first passage  200 . Such a configuration may help to further reduce the premature diffusion of the non-reactive gas  102 ′ and/or reactive gas  104 ′ into the liquid medium  120  during their path toward the submerged surface  124 . 
     The introducing step may include supplying the at least one of the non-reactive gas  102 ′ and the reactive gas  104 ′ as voids  206  (e.g., bubbles) that cavitate at an interface with the submerged surface  124  so as to facilitate a removal of deposits from the submerged surface  124 . The introducing step may also include generating heat at an interface with the submerged surface  124  as a result of an absorption of the reactive gas  104 ′ by at least one of the liquid medium  120  and the cleaning liquid  100 ′. The introducing step may further include increasing a pH at an interface with the submerged surface  124  as a result of an absorption of the reactive gas  104 ′ by at least one of the liquid medium  120  and the cleaning liquid  100 ′ so as to facilitate passivation of the submerged surface  124 . As a result, a passive corrosion layer may be formed on the submerged surface  124 . 
     During the cleaning of the submerged surface  124 , the non-reactive gas  102 ′ and the reactive gas  104 ′ may be co-injected so as to be simultaneously introduced with the cleaning liquid  100 ′. At least one of atmospheric air, nitrogen, and a noble gas may be used as the non-reactive gas  102 ′. Additionally, at least one of ammonia and hydrazine may be used as the reactive gas  104 ′. However, it should be understood that example embodiments are not limited thereto and that other suitable gases may also be used as the non-reactive gas  102 ′ and the reactive gas  104 ′. For instance, the introducing step may include the use of hydrogen chloride as the reactive gas  104 ′. 
     The use of water as the cleaning liquid  100 ′ will result in the cleaning of the submerged surface  124  due to local fluid velocity. The local fluid velocity depends on the smoothness of the submerged surface  124 , the impurities in the cleaning liquid  100 ′ and the liquid medium  120 , and the oxygen content of the cleaning liquid  100 ′ and the liquid medium  120 . The force acting on the submerged surface  124  of the vessel  122  is given by the following equation:
 
 F=ρqV/g  sin θ
 
     wherein 
     F is the force, 
     ρ is the density of the cleaning liquid  100 ′, 
     q is the volumetric flow rate of the cleaning liquid  100 ′, 
     V is the velocity of the cleaning liquid  100 ′, 
     g is a dimensionless conversion constant, and 
     θ is the angle of inclination between the fluid jet  126  and the submerged surface  124 . 
     When the cleaning liquid  100 ′ is augmented with the non-reactive gas  102 ′, a relatively high frequency vibration is generated, thereby enhancing the mechanical removal of “dust” from the submerged surface  124 . In particular, the entrained bubbles of the non-reactive gas  102 ′ collapse at the liquid-solid interface of the liquid medium  120  and the submerged surface  124  via a phenomenon called cavitation to cause the relatively high frequency vibration. Generally, the bubble radius of the non-reactive gas  102 ′ exiting the nozzle of the fluid jet  126  will be about five times that of the nozzle diameter. The dynamic pulsating mode of the oscillation is given by the following equation: 
     
       
         
           
             
               
                 
                   f 
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       R 
                     
                   
                 
               
               
                 
                   
                     
                       3 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       γ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P 
                     
                     _ 
                   
                   ρ 
                 
               
             
           
         
       
     
     wherein 
     f is the fundamental mode natural frequency, 
     R is the bubble radius (m) of the non-reactive gas  102 ′, 
     γ is the gas specific heat ratio (e.g., 1.4 for N 2 ), 
     P is the mean static pressure (Pa), and 
     ρ is the density (kg/m 3 ) of the liquid medium  120 . 
     When nitrogen (N 2 ) is used as the non-reactive gas  102 ′ and assuming a nozzle diameter of 1 mm and a bubble radius of 5 mm, the frequency is about 600 Hz, although example embodiments are not limited thereto. 
     When the cleaning liquid  100 ′ is augmented with the reactive gas  104 ′ (with or without the non-reactive gas  102 ′), relatively high frequency vibrations with a larger magnitude acoustic pulse (acoustical pressure waves) are generated. Additionally, the absorption of the reactive gas  104 ′ by the cleaning liquid  100 ′ and/or liquid medium  120  causes a local temperature increase (heat of dissolution) while also causing dissolved gas to come out of solution. The resulting cavitation and heat increases the removal of “dust” from the submerged surface  124 . Furthermore, the reactive gas  104 ′ will cause a localized pH increase. The increased alkalinity decreases the corrosion rate by making the cleaned submerged surface  124  more passive. 
     In a non-limiting embodiment where ammonia (NH 3 ) is used as the reactive gas  104 ′, the chemical reaction for the dissolution of ammonia (NH 3 ) in water (H 2 O) is expressed below.
 
NH 3 +H 2 O NH 4   + +OH − 
 
After the cleaning is complete and the reactor is started up, the resulting ammonium ions (NH 4   − ) in the vessel  122  will undergo a radiological decomposition according to the following formula.
 
2NH 4 → γ 2N 2 +4H 2  
 
       FIG. 4  is a graph showing the relationship between the pH of the liquid medium and the quantity of ammonia injected as the reactive gas. The chemistry control in a typical boiling water reactor (BWR) is to maintain pure water with a conductivity of 0.10-0.15 μS/cm with a pH between 6.5-8.0. The effect of the introduction of ammonia as the reactive gas  104 ′ during cleaning will likely be minimal in view of the relatively large volume of the liquid medium  120  in the vessel  122 . 
     The method of cleaning the submerged surface  124  may further include stabilizing the submerged fluid jet  126  with a balancing jet  128 . In such a case, a first force generated by a first jet exiting the submerged fluid jet  126  is countered by a second force generated by a second jet exiting the balancing jet  128 . The magnitude of the first force may be about equal to that of the second force. Furthermore, the direction of the first force may be opposite that of the second force. As a result, the fluid jet  126  may be maintained in a desired position relative to the submerged surface  124 . 
     While a number of 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.