Abstract:
A system and a method for injecting hydrogen into Boiling Water Reactor (BWR) reactor support systems in operation during reactor startup and/or shutdown to mitigate Inter-Granular Stress Corrosion Cracking (IGSCC). The system may provide hydrogen at variable pressures (including relatively higher pressures) that match changing operating pressures of the reactor supports systems as the reactor cycles through startup and shutdown modes.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Example embodiments relate generally to nuclear Boiling Water Reactors (BWRs), and more particularly to a system and a method for injecting hydrogen into reactor support systems during periods of reactor startup and shutdown. The system is capable of providing hydrogen at variable pressures (including high pressures of about 1,100 psig) in order to match the changing operating pressures of the support systems throughout the startup and shutdown modes. 
         [0003]    2. Related Art 
         [0004]    Conventionally, Hydrogen Water Chemistry (HWC) systems  1  (see  FIG. 1 ) inject hydrogen into feedwater systems at the suction of the condensate booster pumps or at the suction of the feedwater pumps (see injection point  2 ) of a Boiling Water Reactor (BWR). Injection of hydrogen into these locations helps mitigate Inter-Granular Stress Corrosion Cracking (IGSCC) in the recirculation piping and reactor internals. Specifically, the injected hydrogen causes a reduction in dissolved oxygen by lowering the radiolytic net production of hydrogen and oxygen in the core region of the reactor. 
         [0005]    The conventional HWC system  1  includes a hydrogen source  4  which may be a liquid storage tank (with compressors and vaporizers) or bottles of hydrogen. The hydrogen source may also be electrolytically generated. A hydrogen filter  6  may filter the hydrogen prior to the hydrogen passing through a series of valves, which may include a pressure control valve  8 , excess flow check valve  11 , shutoff valves  10  and bypass valves  12 . An air-operated control valve  14  may be used to isolate the hydrogen before entering a hydrogen injection module  16  that discharges hydrogen to conventional hydrogen injection points  2 . Purge connections  70  throughout the system  1  are generally used for maintenance and safety purposes. 
         [0006]    The conventional hydrogen injection points  2  are injection points located in lower-pressure systems (relative to the reactor), such as the suctions of the condensate booster pumps (85-160 psig) and the suctions of the feedwater pumps (400-650 psig). Because the pumps of these lower-pressure systems are not in service during the full reactor startup or shutdown (including emergency reactor shutdown, such as a reactor SCRAM), hydrogen therefore may not be injected at these conventional locations during startup and shutdown, as doing so would not allow hydrogen dissolution for efficient transport to the recirculation piping and/or reactor internals. Because IGSCC corrosion is more prevalent at lower operating temperatures (of about 200° F. to about 450° F., during reactor startup/heat-up to about 5% power), the reactor (and the reactor support systems) is at greater risk during startup and shutdown modes, thereby exacerbating the effects that are caused by an inability to inject hydrogen into the conventional injection points  2  during reactor startup and shutdown modes. 
       SUMMARY OF INVENTION 
       [0007]    Example embodiments provide a startup/shutdown hydrogen injection system (and associated method) for injecting hydrogen into BWR reactor support systems during periods of reactor startup and shutdown. Because the reactor (and the reactor support systems) experience temperatures and pressures that vary greatly as the reactor cycles through startup and shutdown modes (as a result of the reactor heat-up and cool-down), the hydrogen injection system provides hydrogen at a variable pressure that may match the operating pressures of these support systems at any period of time. Because the hydrogen injection system provides hydrogen to reactor support systems that also operate at potentially high pressures, the hydrogen injection system may boost the pressure of hydrogen beyond pressure levels normally associated with conventional HWC systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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. 
           [0009]      FIG. 1  is a piping and instrument (P&amp;ID) diagram of a conventional hydrogen water chemistry (HWC) system; 
           [0010]      FIG. 2  is a P&amp;ID diagram of a startup/ shutdown hydrogen injection system, in accordance with an example embodiment; and 
           [0011]      FIG. 3  is a flowchart of a method of making and using a startup/shutdown hydrogen injection system, in accordance with an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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.). 
         [0016]    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. 
         [0017]    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. 
         [0018]      FIG. 2  is a P&amp;ID diagram of a startup/shutdown hydrogen injection system  30 , in accordance with an example embodiment. The system may include one or more hydrogen sources. For instance, an optional dedicated hydrogen gas source  32  may be provided for the hydrogen injection system  30 . The dedicated hydrogen gas source  32  may be small hydrogen gas bottles, a hydrogen gas truck, or liquid storage containing hydrogen. Alternative to a dedicated hydrogen gas source  32  (or, in addition to a dedicated hydrogen gas source  32 ), a connection  20  may be provided which may connect to an existing HWC system  1  (see optional connection points  20  on  FIG. 1 , which may, for instance, connect to HWC system  1  either upstream or downstream of air-operated valve  14 , and inside or outside of the plant wall). 
         [0019]    If a connection  20  between an existing HWC system  1  and the startup/shutdown hydrogen injection system  30  is used to supply hydrogen, flow control equipment may be provided on the connection  20 . For instance, a pressure control valve  34 , a pressure transmitter  36 , a local flow indicator  38 , a flow control valve  40  and an air-operated valve  42  may be provided in the connection line  20  to control the flowrate and pressure of hydrogen coming from the existing HWC system  1  into the startup/shutdown hydrogen injection system  30 . A shutoff valve  44  may also be included to shut-off the flow of hydrogen into the hydrogen injection system  30 . 
         [0020]    Whether a connection between an existing HWC system  1  and the startup/shutdown hydrogen injection system  30  is used, or whether a dedicated hydrogen gas source  32  for the hydrogen injection system  30  is used, a hydrogen filter  46  may be provided to filter hydrogen gas prior to any pressurization of the hydrogen. 
         [0021]    The hydrogen injection system  30  may further include a hydrogen gas booster  48  that may significantly increase the pressure of hydrogen which is to be injected into hydrogen injection point  50 . The hydrogen gas booster  48  may be hydraulic or air-driven (pneumatic), and may be capable of increasing hydrogen pressure to any of a wide range of pressures, varying from about 0 psig to about 1,100 psig. By providing the hydrogen gas booster  48 , the hydrogen injection system  30  may provide hydrogen to reactor support systems that experience a reactor water flow (at potentially high operating pressures of about 1,100 psig, and operating temperatures as low as about 200° F. when oxygen concentration in the reactor water is relatively elevated) during reactor startup and/or shutdown conditions (reactor “shutdown” including reactor scrams, hot/standby and/or hot/shutdown modes). For instance, hydrogen injection point  50  may include injections points in reactor support systems such as the reactor water cleanup (RWCU) return line or the feedwater recirculation lines of the BWR. Because these example reactor support systems experience reactor water flow during reactor startup and/or shutdown, and because these systems experience a wide range of pressures as the reactor cycles through startup and/or shutdown, the hydrogen gas booster  48  is particularly well equipped in increasing hydrogen pressure that is appropriate for these example service points. 
         [0022]    The hydrogen gas booster  48  may be located downstream of the flow controls (including any one of the pressure control valve  34 , pressure transmitter  36 , flow indicator  38 , flow control valve  40  and air operated valve  42 ), as doing so allows the flow control equipment to be a lower pressure class (and thereby less expensive). The hydrogen gas booster  48  may be pneumatically operated via a plant service air  56  connection. A pressure control valve  58  may be used to control the pressure of service air entering the hydrogen gas booster  48 . An air filter may be used to filter the inlet air. Service air shutoff valves  62   a / 62   b  may be included in the air inlet line to close the air inlet line (to service the hydrogen gas booster  48 , for instance). The hydrogen gas booster  48  may include a air flow control valve  72  to throttle the air flow to the booster to subsequently increase the hydrogen pressure out of the booster  48 . The flow control valve  72  may be automatically or manually controlled. 
         [0023]    A number of system shut-off valves  54   a - 54   g  may be provided to manage hydrogen flow through desired portions of the system  30  for added flexibility. For instance, when hydrogen is being injected to systems requiring relatively lower pressure, the hydrogen gas booster  48  may not be required. In such a scenario, if the conventional hydrogen source  4  ( FIG. 1 ) is being used to supply hydrogen to injection point  50 , shutoff valves  54   c,    54   e  and  54   f  may be closed, while shutoff valves  54   d  and  54   g  may be opened. Alternatively, dedicated hydrogen gas source  32  may be used to supply lower-pressure hydrogen by closing shutoff valves  54   b,    54   e  and  54   f  (to bypass hydrogen gas booster  48 ), and opening shutoff valves  54   a,    54   c,    54   d  and  54   g  to hydrogen in injection point  50 . 
         [0024]    In scenarios where higher-pressure hydrogen service is desired, shutoff valve  54   b  may be opened, allowing hydrogen from hydrogen source  4  (through opened shutoff valve  54   c ) or hydrogen source  32  (through opened shutoff valve  54   a ) to enter the hydrogen gas booster  48 . Hydrogen leaving the hydrogen gas booster  48  may be directed to hydrogen injection point  50  through shutoff valves  54   e,    54   f  and  54   g.    
         [0025]    Local pressure indicators  64   a - 64   c  may be included to confirm the operating pressure of hydrogen and/or service air within the system. Especially in the case of high pressure hydrogen injection points  50 , a check valve  66  may be included in the hydrogen injection line  50  to ensure that fluids from the high pressure systems to not backup into the hydrogen injection system. 
         [0026]    The startup/ shutdown hydrogen injection system  30  may be provided on two separate skids  30   a / 30   b  for convenience, with the relatively lower pressure hydrogen equipment being predominantly included on one skid  30   a  and the relatively higher pressure hydrogen equipment being predominantly included on the other skid  30   b.    
         [0027]    A safety-relief valve  68  may be provided on the hydrogen gas booster  48  to vent hydrogen (to vent line  52 ) at times when the hydrogen gas booster  48  may become over-pressurized. Purge connections  70  throughout the system  30  may also be provided for maintenance and safety purposes. 
         [0028]      FIG. 3  is a flowchart of a method of making and using a startup/shutdown hydrogen injection system  30 , in accordance with an example embodiment. The method may include a step S 80  of fluidly connecting at least one hydrogen source to a BWR reactor support system in operation during periods of reactor startup and/or shutdown. This may be accomplished, for instance, by providing piping or tubing between the hydrogen source and the BWR reactor support system. It should be understood that a support system which is “in operation” during startup and/or shutdown relates to a system which provides a reactor water fluid flow through the system during periods when the reactor is starting up and shutting down (thereby offering a transport medium for the injected hydrogen to then be transported to the recirculation piping and/or reactor internals during startup and/or shutdown modes). 
         [0029]    The method may further include a step S 82  of directing a hydrogen flow from the at least one hydrogen source to the reactor support system. This may be accomplished, for instance, by opening valve connections in piping/tubing located between the hydrogen source and the reactor support system. The opening of the valve(s) may be accomplished via a controller, such as PLC  60  (see  FIG. 2 ). 
         [0030]    The method may further include a step S 84  of regulating a pressure of the hydrogen flow from the at least one hydrogen source to the reactor support system, based on an operating pressure of the reactor support system. Specifically, the pressure of the hydrogen flow may be regulated to match the operating pressure of the reactor support system, with the understanding that the operating pressure may change while the reactor cycles through the startup and/or shutdown modes. The regulating of the pressure of the hydrogen flow may be accomplished via a controller, such as PLC  60  (see  FIG. 2 ), which may compare a measured pressure at hydrogen injection point  50  against measured pressures at the pressure transmitter  36  or pressure indicator  64   c  (for instance) in order to regulate the pressure of the hydrogen being directed to the hydrogen injection point  50 . 
         [0031]    The hydrogen injection system  1  may include a programmable logic controller (PLC) and/or data acquisition system  60  that may be used to determine the rate and pressure for supplying hydrogen to injection point  50  (based upon a measure of the required injection point  50  pressure). Therefore, the PLC and/or data acquisition system  60  may be in communication with the control hardware shown in both the lower and higher pressure skids  30   a / 30   b  (not all connections shown in  FIG. 2 ). The PLC and/or data acquisition system  60  may also control the hydrogen gas booster  48  and any system valves within the hydrogen injection system  30 . 
         [0032]    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.