Abstract:
Systems passively eliminate noncondensable gasses from facilities susceptible to damage from combustion of built-up noncondensable gasses, such as H2 and O2 in nuclear power plants, without the need for external power and/or moving parts. Systems include catalyst plates installed in a lower header of the Passive Containment Cooling System (PCCS) condenser, a catalyst packing member, and/or a catalyst coating on an interior surface of a condensation tube of the PCCS condenser or an annular outlet of the PCCS condenser. Structures may have surfaces or hydrophobic elements that inhibit water formation and promote contact with the noncondensable gas. Noncondensable gasses in a nuclear power plant are eliminated by installing and using the systems individually or in combination. An operating pressure of the PCCS condenser may be increased to facilitate recombination of noncondensable gasses therein.

Description:
GOVERNMENT SUPPORT 
     This invention was made with Government support under contract number DE-FC07-07ID14778, awarded by the U.S. Department of Energy. The Government has certain rights in the invention. 
    
    
     BACKGROUND 
       FIG. 1  is a cross-section schematic of a conventional containment building  10  cross section. Although containment  10  is shown in  FIG. 1  having components and characteristics of an Economic Simplified Boiling Water Reactor (ESBWR), it is understood that components described therein are usable with other plant configurations. As shown in  FIG. 1 , containment  10  may include a gravity-driven coolant system (GDCS)  15 , which may be a large, water-filled tank used to cool a reactor vessel in the event of a loss of primary coolant. A suppression pool  16  may be within containment  10  and used to condense steam from the reactor vessel and relieve pressure in the event of an accident. Several Passive Containment Cooling System (PCCS) condensers  50  are arranged in a PCCS pool  20 , outside of containment  10 . The PCCS condensers  50  remove additional heat and condense steam within containment  10  during a loss of coolant accident within the containment  10 . 
     PCCS condensers  50  include an inlet  51  within containment  10  that receives steam and noncondensable gasses that may be released into containment  10  during a severe accident. The steam is formed from boiling coolant in the reactor, and the noncondensable gasses, such as O 2  and H 2 , accumulate within the reactor and containment  10  during operation of the nuclear plant from radiation and chemical release. The steam and noncondensable gasses pass through inlet  51  of PCCS condenser  50  into branched pipes and vertical tubes  52 , which are submerged in the PCCS pool  20 . Heat from the steam and noncondensable gasses is transferred from vertical tubes  52  to PCCS pool  20 , and steam within vertical tubes  52  condenses into water. Lower headers  53  collect the condensed water and noncondensable gasses in the PCCS condenser  50 . 
     From lower header  53 , the condensed water is driven by gravity and a pressure differential downward through an annular duct  54 , which includes two concentric pipes that provide an inner and outer passage in annular duct  54 . Condensed water flows through the outer pipe of annular duct  54  into a shared drain line  57 , which drains the condensed water into GDCS pool  15 . From the lower header  53 , noncondensable gasses flow downward through the inner passage  54   a  ( FIG. 2 ) in annular duct  54  into vent line  58 , which terminates at a sparger  59  in suppression pool  16 . A fan  30  may be connected to the vent line  58  to enhance noncondensable flow out of PCCS condensers  50 . 
     The lower header  53  includes a drain manifold  55  that separates condensed water and noncondensable gasses into the outer and inner passages, respectively, of the annular duct  54 .  FIG. 2  is an illustration of conventional drain manifold  55 . As shown in  FIG. 2 , drain manifold  55  includes a vent hood/drip hood  75  that diverts condensed water flowing downward onto the drip hood  75  to either side of drain manifold  55 . Several compression wave baffles  65  brace and secure drain manifold  55  in lower header  53 . Noncondensable gasses are permitted to flow up into drip hood  75  and into inner passage  54   a  of annular duct  54 , while the diverted condensed water flows into the outer passage about the edges of annular duct  54 . In this way, the water may flow back into GDCS pool  15  for use as reactor coolant without any noncondensable gasses causing blocked or reverse flow. 
     SUMMARY 
     Example embodiments are directed to systems for passively eliminating noncondensable gasses from facilities susceptible to damage from combustion of built-up noncondensable gasses, such as H 2  and O 2  in nuclear power plants, without the need for external power and/or moving parts. Example systems include catalyst materials installed in areas subject to noncondensable gas exposure, where the catalyst material catalyzes a reaction in the noncondensable gas to an inert byproduct. Example systems may include catalyst plates installed in a lower header of the Passive Containment Cooling System (PCCS) condenser, a catalyst packing member, and/or a catalyst coating on an interior surface of a condensation tube of the PCCS condenser or an annular outlet of the PCCS condenser. Example systems may include structures with surfaces or hydrophobic elements that inhibit water formation and promote contact with the noncondensable gas. 
     Example methods are directed to passively eliminating noncondensable gasses in a nuclear power plant by installing and using example embodiment catalyst systems individually or in combination. Example methods may further include increasing an operating pressure of the PCCS condenser to facilitate recombination of noncondensable gasses therein. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic of a conventional ESBWR containment. 
         FIG. 2  is an illustration of a conventional drain manifold. 
         FIG. 3  is an illustration of an example embodiment catalyst system. 
         FIG. 4  is an illustration of another example embodiment catalyst system. 
         FIG. 4A  is an illustration of a tabbed surface of a catalyst system, in accordance with an example embodiment. 
         FIG. 4B  is an illustration of a ridged surface of a catalyst system, in accordance with an example embodiment. 
         FIG. 5  is an illustration of a yet further example embodiment catalyst system. 
         FIG. 6A  is an illustration of an additional example embodiment catalyst system for use in a vent line. 
         FIG. 6B  is a top view of the example embodiment catalyst system of  FIG. 6A  with a cap removed for clarity. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, example embodiments will be described in detail with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein. 
     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. 
     It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can 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.). 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the language explicitly 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. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures or described in the specification. For example, two figures or steps shown in succession may in fact be executed substantially and concurrently or may sometimes be executed in the reverse order or repetitively, depending upon the functionality/acts involved. 
     The inventors of the present application have identified that large amounts of noncondensable gasses may directly enter passive coolant features in nuclear power plants during an accident involving a loss of coolant. Such noncondensable gasses may be reactive, especially in high-temperature, high-pressure settings. Ignition of noncondensable gasses in an enclosed structure, such as those found in passive coolant features, may be especially damaging to those and surrounding structures. This damage may further compound an accident scenario. Example embodiments and methods discussed below uniquely address these previously-unidentified dangers recognized in passive coolant features and provide several advantages, including increased risk mitigation during accident scenarios, for example. 
     Example embodiments include catalyst materials positioned/installed within structures that are likely to be exposed to or contain noncondensable gasses and features susceptible to damage from noncondensable gas ignition. The catalyst materials may permit reaction of noncondensable gasses in a continuous and nondestructive manner into inert or useful products, thereby reducing risk of explosion and reducing gas pressure within an air-tight containment structure. Catalysts may be placed and configured to especially address areas most susceptible to explosive damage, most exposed to noncondensable gasses during normal operations or accident scenarios, and/or most accessible to passive heat transfer to eliminate heat energy from recombination of noncondensable gasses. 
       FIG. 3  is an illustration of an example embodiment catalyst system  100  useable in a drain manifold  55  conventionally found in a PCCS condenser  50  ( FIG. 1 ). Example embodiment system  100  may include one or more support meshes  110  installed at a bottom of drip hood  75 . Support meshes  110  may be any supporting structure that permits fluid flow through support meshes  110 , including gridded wire, perforated plates, a solid filter, etc. Each support mesh  110  may sit between two compression wave baffles  65  so as to form partial or full compartments within drip hood  75 . 
     One or more catalyst plates  105  are positioned within drip hood  75  of drain manifold  55 . The catalyst plates  105  may sit on one or more support meshes  110  or may be otherwise affixed within drip hood  75 . Catalyst plates are sized to fit within drain manifold  55  and may, for example, extend an entire length of drain manifold  55  or may be sized to fit within an individual compartment between two compression wave baffles  65 . As shown in  FIG. 3 , if catalyst plates  105  fit within a single compartment between compression wave baffles  65 , one or more sets of catalyst plates  105  may be in different compartments. Catalyst plates  105  may be thin so as to accommodate multiple catalyst plates  105  within drip hood  75  and increase surface area of catalyst plates  105 . Catalyst plates  105  may be separated or intersecting. Catalyst plates  105  may include a wavy or corrugated surface that increases surface area and promotes liquid drainage off of catalyst plates  105  and promotes noncondensable gas contact and interaction with a catalyst material therein. Or, for example, catalyst plates  105  may have flat, perforated, bumpy, spiky, tabbed, veined, and/or any other type of desired surface. 
     Catalyst plates  105  and potentially support mesh  110  include catalyst materials that encourage the non-explosive reaction or recombination of noncondensable gasses. For example, catalyst materials may be palladium (Pd) or a palladium alloy that promotes reaction of combustible noncondensable gasses, such as hydrogen (H 2 ) and/or oxygen (O 2 ), into water or other harmless oxides and/or hydrides. Other known catalysts, including platinum (Pt), rhodium (Rh), organic compounds, etc. are useable as the catalyst material in example system  100 . Catalyst plates  105  and/or support meshes  110  may be fabricated entirely of the catalyst material or may be coated, matrixed, embedded, etc. with the catalyst material so as to conserve an amount of catalyst material required while maximizing catalyst material surface area. 
       FIG. 4  is an illustration of another example embodiment catalyst system  200 . As shown in  FIG. 4 , one or more catalyst packing members  205  are placed within pipes/tubes in a PCCS condenser  50  ( FIG. 1 ). For example, catalyst packing members  205  may be placed in condenser inlet  51 , branches and vertical tubes  52 , and/or annular duct  54 , each receiving and transmitting noncondensable gasses within the condenser  50  ( FIG. 1 ). Catalyst packing members  205  may be retained in PCCS condenser structures by fastening, welding, friction, etc. 
     Catalyst packing members  205  may be cruciform, as shown in  FIG. 4 , with two or more intersecting plates that fill a cross-section of the structure into which catalyst packing members  205  are placed. Alternately, catalyst packing members  205  may be separated and parallel in any orientation within structure  51 ,  52 ,  54 , etc. Catalyst packing members  205  may be thin so as to accommodate multiple catalyst packing members  205  within structure  51 ,  52 ,  54 , etc. and increase surface area of catalyst packing members  205 . 
     As shown in Details A and B of  FIG. 4 , catalyst packing members  205  may include several different surfaces that increase surface area and/or promote liquid drainage off of catalyst packing members  205 , especially in the instance that catalyst packing members  205  are placed in inlet  51  or tubes  52  in direct contact with steam and condensate flowing into PCCS condenser  50  ( FIG. 1 ). Detail A illustrates a tabbed surface  206  that may promote liquid drainage off of tabs and away from a surface of the catalyst packing member  205 . Detail B illustrates a veined or ridged surface  207  that increases surface area and promotes liquid flow in channels off of catalyst packing member  205  and promotes noncondensable gas contact and interaction with a catalyst material therein. Or, for example, catalyst packing members  205  may have flat, perforated, bumpy, spiky and/or any other type of desired surface, with the understanding that some flow path within structures  51 ,  52 ,  54  is maintained and not completely blocked by a surface of catalyst packing members  205 . 
     Catalyst packing members  205  include catalyst materials that encourage the non-explosive reaction of noncondensable gasses. For example, catalyst materials may be palladium (Pd) or a palladium alloy that promotes reaction of combustible noncondensable gasses, such as hydrogen (H 2 ) and/or oxygen (O 2 ), into water or other harmless oxides and/or hydrides. Other known catalysts, including platinum (Pt), rhodium (Rh), organic compounds, etc. are useable as the catalyst material in example system  200 . Catalyst packing members  205  may be fabricated entirely of the catalyst material or may be coated, matrixed, embedded, etc. with the catalyst material so as to conserve an amount of catalyst material required while maximizing catalyst material surface area. 
       FIG. 5  is an illustration of another example embodiment catalyst system  300 . As shown in  FIG. 5 , a catalyst coating or liner  305  is coated/placed on a surface of pipes/tubes in a PCCS condenser  50  ( FIG. 1 ). For example, catalyst coating  305  may be placed in condenser inlet  51 , branches and vertical tubes  52 , and/or annular duct  54 , each receiving and transmitting noncondensable gasses within the condenser  50  ( FIG. 1 ). Catalyst coating  305  may additionally be placed on interior surfaces of other PCCS structures, such as lower headers  53  ( FIG. 1 ) or in other reactor structures receiving noncondensable gas flow and/or particularly vulnerable to noncondensable gas explosive damage. 
     Catalyst coating  305  may be in the form of a liner attached or frictionally sitting in structure  51 ,  52 ,  54 , etc. or, for example, may be a chemical coating deposited on a surface of structure  51 ,  52 ,  54 , etc. Catalyst coating  305  may be thin so as to accommodate flow through structures  51 ,  52 ,  54 , etc. Catalyst coating  305  may include several different surfaces that increase surface area and/or promote liquid drainage off of catalyst coating  305 , especially in the instance that catalyst coating  305  is placed in inlet  51  or tubes  52  in direct contact with steam and condensate flowing into PCCS condenser  50  ( FIG. 1 ). For example, catalyst packing members  205  may have flat, perforated, bumpy, spiky, tabbed, veined, and/or any other type of desired surface, with the understanding that some flow path within structures  51 ,  52 ,  54  is maintained and not completely blocked by catalyst coating  305 . Catalyst coating  305  may also include a hydrophobic element that repels steam and/or facilitates the removal of condensed water from catalyst coating  305  and promotes noncondensable gas contact and interaction with a catalyst material therein. For example, an electrostatically-applied fluoropolymer such as Teflon may be applied to areas with catalyst coating  305 . 
     Catalyst coating  305  includes catalyst materials that encourage the non-explosive reaction of noncondensable gasses. For example, catalyst materials may be palladium (Pd) or a palladium alloy that promotes reaction of combustible noncondensable gasses, such as hydrogen (H 2 ) and/or oxygen (O 2 ), into water or other harmless oxides and/or hydrides. Other known catalysts, including platinum (Pt), rhodium (Rh), organic compounds, etc. are useable as the catalyst material in example system  300 . Catalyst coating  305  may be fabricated entirely of the catalyst material or may be coated, matrixed, embedded, etc. with the catalyst material so as to conserve an amount of catalyst material required while maximizing catalyst material surface area. 
       FIGS. 6A and 6B  are illustrations of an additional example embodiment catalyst system  400  adapted for use in vent line  54 . Positioning catalyst system  400  within a vent line may be provide direct contact between catalyst materials and noncondensable gasses with minimum risk of condensate presence or blocking within vent line  54 . Further, positioning within vent line  45  provides example embodiment system  400  with stable access to noncondensable gasses without risk of damage to catalyst system  400  if noncondensable gas ignition occurs in lower header  53 . 
     As shown in  FIGS. 6A and 6B  example embodiment catalyst system  400  includes a plurality of catalyst plates  405  spaced at an inlet of vent line  54 , above a flange  404  where the vent line  54  extends outside of lower header  53 . Catalyst plates  405  may be spaced at regular intervals and held in constant position within a frame  406  so that catalyst plates are readily inserted into a top portion of vent line  54 . Catalyst plates  405  may be thin so as to accommodate multiple catalyst plates  405  within vent line  54  and increase surface area of catalyst plates  405 . Catalyst plates  405  may include a wavy or corrugated surface that increases surface area and promotes liquid drainage off of catalyst plates  405  and promotes noncondensable gas contact and interaction with a catalyst material therein. Or, for example, catalyst plates  405  may have flat, perforated, bumpy, spiky, tabbed, veined, and/or any other type of desired surface. 
     Catalyst plates  405  include catalyst materials that encourage the non-explosive reaction or recombination of noncondensable gasses. For example, catalyst materials may be palladium (Pd) or a palladium alloy that promotes reaction of combustible noncondensable gasses, such as hydrogen (H 2 ) and/or oxygen (O 2 ), into water or other harmless oxides and/or hydrides. Other known catalysts, including platinum (Pt), rhodium (Rh), organic compounds, etc. are useable as the catalyst material in example system  100 . Catalyst plates  405  may be fabricated entirely of the catalyst material or may be coated, matrixed, embedded, etc. with the catalyst material so as to conserve an amount of catalyst material required while maximizing catalyst material surface area. 
     Example embodiment catalyst system  400  may further include a hood or cap  410  that aids in preventing liquid or condensate from entering example embodiment system  400  from the lower header  53 , such that catalyst plates  405  will remain substantially dry and in contact with noncondensable gasses flowing over the plates. Cap  410  may join to a top of vent line  54  but permit gas flow into the vent line, as shown in  FIG. 6A . Cap  410  may further prevent damage to catalyst plates  405  aligned within vent line  54  in the instance of gas ignition within lower header  53  or other part of PCCS condenser  50  ( FIG. 1 ). Cap  410  and catalyst plates  405  within modular frame  406  may be easily removable together from vent line  54  for installation/repair/inspection/etc. For example, cap  410  may screw onto flange  404  and catalyst plates  405  and any frame  406  may sit within a top portion of vent line  54  under cap  410 . 
     While example embodiment systems position catalyst materials within a PCCS condenser  50  ( FIG. 1 ) of a nuclear plant, it is understood that other locations in conventional plants or in future-developed plants are useable with example systems. Such locations, including a PCCS condenser, may be especially likely to be damaged by uncontrolled noncondensable gas reaction, uniquely exposed to noncondensable gas flow or buildup, and/or positioned to safely eliminate heat energy from recombination of noncondensable gasses. The PCCS condenser  50  may possess several of these characteristics because of its position and function in receiving released noncondensable gasses in a nuclear power plant, such that example embodiment catalyst systems within a PCCS condenser may recombine a large portion of noncondensable gasses released in a nuclear plant, reducing explosion potential and gas pressure within containment. Heat released through recombination in example embodiment systems may be readily transferred from PCCS condenser  50  to the PCCS pools  20 . Additionally, example embodiment systems may receive and recombine large proportions of released noncondensable gasses without any additional outside power source or forced gas flow. 
     Example methods include installing one or more example embodiment catalyst systems in a PCCS condenser or other eligible piece of equipment in known or future facilities that may benefit from passive noncondensable recombination and elimination, such as an ESBWR. Example embodiments  100 ,  200 , and/or  300  may be installed individually and in various combinations based on a particular plant&#39;s design needs. Such installation may occur during plant construction, during equipment construction or delivery, and/or following construction during operations, such as during a fuel outage. 
     Because example embodiment systems and methods of using the same enhance elimination of noncondensable gasses, plant operation may be modified to take advantage of the enhanced elimination. Example methods include operating a PCCS condenser  50  having one or more example embodiment catalyst systems  100 ,  200 , and/or  300  installed therein at an increased pressure. The increased pressure in combination with example embodiments may further encourage noncondensable recombination and heat transfer from PCCS condenser  50 . Increased pressure may be achieved by increasing containment  10  pressure and/or narrowing pipes  52 ,  54 , etc. within PCCS condenser  50 , for example. 
     Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. Variations are not to be regarded as departure from the spirit and scope of the 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.