Abstract:
A shroud connection device for replacement core spray piping systems in a boiling water reactor includes replacement pipe, first and second coupling devices, and a rod. The pipe has a spherically shaped end, and includes a penetration extending through it from an inside portion to an outside portion. The first coupling device has first and second ends, the first end being dimensioned so as to receive the spherically shaped end of the pipe, and the second end abutting an outside portion of the shroud. The second coupling device has third and fourth ends, the third end abutting an inside portion of the shroud. The rod extends between the second coupling device and the penetration in the pipe.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an apparatus and method for connecting replacement core spray piping to the shroud of a boiling water reactor. More specifically, the invention relates to an apparatus and method for connecting core spray piping to a BWR shroud without having to weld or bolt the replacement piping to either the shroud or piping internal to the shroud. 
     2. Description of Related Art 
     Boiling water reactors include core spray piping to provide cooling water to the fuel in the event a highly unlikely casualty occurs resulting in a loss of core heat removal capability, such as a loss of coolant accident (LOCA). This core spray piping receives water pumped from a reservoir, such as a pressure suppression pool, and delivers it to the core. The piping from the reservoir enters the reactor vessel above the core shroud, via a safe end. The piping then goes into a tee that divides the flow into two pipes. Each of these two pipes then curve around the interior of the vessel and connect to a vertically oriented downcomer pipe section. The downcomer pipe section extends downward into the region between the core shroud and the reactor vessel. The downcomer pipe section then enters the core shroud through another safe end and terminates in another tee located near the top of the shroud. The tee located within the shroud divides the flow into two semicircular core spray spargers supported on the interior of the core shroud. Typically, there are two of these spray systems per reactor vessel, which serve four semicircular spray spargers in the shroud. 
     The piping in the core spray systems is stainless steel, typically 304 SS, that is welded at each connection point. These welded connections are susceptible to intergrantular stress corrosion cracking (IGSCC), which can result in cracks and subsequent leakage from the spray system pipes. In the BWR core spray system, the downcomer piping section, including that portion extending through the shroud, has been particularly prone to IGSCC. As a result various devices have been devised for repairing this portion of piping. 
     One such device, disclosed in U.S. Pat. No. 5,735,551 issued to Whitman et al., includes first and second L-shaped housings. The housings surround the faulty piping, and are bolted together. A first seal is mounted within each housing to seal the housings against the outer periphery of the downcomer piping. A second seal is mounted at an end of the each housing to seal each against the outer wall of the core shroud. The housing assembly is retained against the outer wall of the core shroud by a threaded rod extending through the shroud. The threaded rod reacts at one end against the housing assembly, and at the other end against a cap mounted on the inside of the shroud. 
     The above-described device has several drawbacks. First, the housings require a high degree of casting accuracy to ensure tight coupling around the core spray line piping elbow. Second, the device is extremely difficult to assemble in its intended use environment. The device is intended for effecting a repair to a pipe in the downcomer region between the reactor vessel and core shroud, while this region is full of water. The amount of assembly parts required and the fitting tolerances make this device nearly unworkable in an underwater environment. Third, the cap is mounted directly onto the core spray sparger. Thus, a portion of the reaction force from the threaded rod acts on the sparger and is also transmitted to the existing downcomer piping. This arrangement increases the likelihood of damage to the sparger piping within the shroud and the likelihood of further damage to the downcomer piping. 
     Another device, disclosed in U.S. Pat. No. 5,737,380 issued to Deaver et al., provides for the permanent repair of core spray piping by replacing damaged piping with new piping. The replacement downcomer piping includes articulating vertical pipe connectors. These articulating pipe connectors allow for quick and easy pipe coupling, and also provide for thermal expansion and contraction without undue stresses. This device also has drawbacks. First, the downcomer elbow portion is bolted to the shroud, thus this portion of piping remains subject to rotational stresses. Second, this device requires precision holes to be made in the shroud. Third, device is time consuming to implement in the underwater environment of the downcomer region. 
     Thus, there is a need to provide a device and method for providing the permanent repair of core spray piping, while alleviating the stresses in the piping connecting to the shroud. There is also a need to provide a device and method for achieving this goal without undue cost, complexity, and time. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an apparatus and method for connecting core spray piping to a BWR shroud without having to weld or bolt the replacement piping to either the shroud or piping internal to the shroud. 
     It is another object of the present invention to provide an inexpensive, quick, and easy-to-install apparatus and method for connecting core spray piping to a BWR shroud. 
     In one aspect of the present invention a shroud connection device for replacement core spray piping systems in a boiling water reactor comprises a pipe, a first coupling device, a second coupling device, and a rod. The pipe has a spherically shaped end and includes a penetration extending through it from an inside portion to an outside portion. The first coupling device has a first end dimensioned to receive the spherically shaped end and second ends, and a second end that abuts the outside portion of the shroud. The second coupling device has a third end that abuts the inside portion of the shroud, and a fourth end. The rod extends between the second coupling device and the penetration. 
     In another aspect of the present invention a device for connecting replacement core spray piping to a shroud in a boiling water reactor comprises flow directing means, interface means, force coupling means, and holding force transmitting means. The flow directing means directs core spray fluid flow within the reactor. The interface means receives an end of the flow directing means and transmits forces acting on the flow directing conduit to an outer wall of the shroud. The interface means completely surrounds a piping connection extending between inner and outer walls of the shroud. The coupling means provides a coupling force to couple the flow directing means to the interface means. The coupling force transmitting means transmits the coupling force to the inner wall of the shroud. 
     In yet another aspect of the present invention a method of connecting core spray piping to a shroud of a boiling water reactor includes an inserting step, two positioning steps, a connecting step, and an adjusting step. In the inserting step, a pipe having a spherically shaped end is inserted into a first end of a first coupling element. In the first positioning step, a second end of the first coupling element is positioned to completely surround at least a first end of a pipe connection extending through the shroud, and to abut an outside portion of the shroud. In the third positioning step, a third end of a second coupling element is positioned to completely surround a second end of the pipe connection, and to abut an inside portion of the shroud. In the connecting step, a tightening rod is connected between the second coupling element and a penetration extending from an inside portion of the pipe to an outside portion. In the adjusting step, the tightening rod is adjusted. 
     These and other objects, aspects, advantages and features of the present invention will become more apparent to those skilled in the art when the following detailed description is read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following detailed description, reference will be made to the attached drawings in which: 
     FIG. 1 is a cross sectional side view of the core spray piping replacement connection of the present invention. 
     FIG. 2 is an expanded cross sectional side view of the replacement piping/core shroud interface of the present invention. 
     FIG. 3 is a perspective view of a coupling device of the present invention. 
     FIG. 4 is a partial cut-away perspective view of the core spray piping replacement connection of the present invention. 
     FIG. 5 is yet another partial cut-away perspective view of the core spray piping replacement connection of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A cross sectional side view of the core spray system replacement piping shroud connection is depicted in FIG.  1 . As can be seen from this Figure, the connection  10  takes advantage of the so-called ball and socket type joint connection. Specifically, the connection  10  includes the replacement piping  12 , which has a spherically shaped ball  14  on the end that is to mate with the shroud  16 . This ball  14  may be a separate piece that is welded onto the pipe  12  end, the pipe  12  may be cast with this type of end, the ball  14  may be ground into the end, or provided in any other fashion known to the skilled artisan. In the preferred embodiment, the ball  14  is welded onto the end of the pipe. The ball  14  is received into a first coupling device  18 , known as an anchor socket. The anchor socket  18  includes an opening  22  extending through it and a seat  24  within the opening  22  dimensioned so that ball  14  fits snugly thereon. The anchor socket  18  abuts the outside wall  28  of shroud  16  when the connection  10  is established. 
     The anchor socket  18  provides the interface between the replacement pipe  12  and the existing core sparging system piping connection  26  which, in the preferred embodiment is a tee box. The tee box  26  extends from the outer wall  28  of the shroud  16  to the inner wall  32  of the shroud  16 , and is provided with a stabilizing bracket  34 . That portion of tee box  26  extending from the outer wall  28  includes an opening  36  that receives the core spray system fluid flow, and splits the flow into at least two additional pipes. One of the openings  38  receiving this split flow is shown in FIG.  1 . 
     As shown more particularly in FIG. 2, the anchor socket  18  includes first and second circumferential rings  21 ,  23 , respectively, to provide the seal between the pipe  12  and the tee box  26  by interference fit and baffle. First circumferential ring  21  is longer than second circumferential ring  23 , and abuts directly against the shroud outer wall  28 . Second circumferential ring  23  fits between that portion of the tee box  26  extending from the outer wall  28  and the pre-existing pipe safe end  25 . The pipe safe end  25  is cut, after removing the damaged piping, to a predetermined length to allow second circumferential ring  23  to be seated between the remaining safe end  25  and the tee box  26 . 
     The above-described ball and socket type joint lowers the load imparted to the shroud  16  by the replacement core spray pipe  12 . This arrangement also allows the pipe  12  to rotate relative to the shroud  16 , as a result of induced mechanical and thermal loads, without creating undue stresses in pipe  12 . Vertical shear is transmitted through second circumferential ring  23  directly to the pipe  12  and then to the shroud  16  without going through any welds. 
     Referring once again to FIG. 1, that portion of the tee box  26  extending from the shroud inner wall  32  includes a closed end  42 . However, for the instant invention, an opening  44  is introduced into the end to receive a rod  46 , discussed further below. Covering the end  42  of the tee box  26  is another coupling device  48 , known as a stool. The stool  48  receives, and provides an anchor point for, the rod  46  that provides the force for coupling the pipe  12  to the shroud  16 . 
     The stool  48 , shown more particularly in FIG. 3, straddles the existing tee box  26  and the stabilizing bracket  34 . Thus, the stool  48  is provided with at least two protuberant portions extending from its substantially cylindrical cover portion  52 . The first protuberant portion  54  includes a slot  56 , which receives the stabilizing bracket  34  therein. The first protuberant portion  54  abuts the inner wall  32  of the upper portion of the shroud  16 . The second protuberant portion  58 , is longer than the first protuberant portion  54 . This is because the second protuberant portion  58  abuts the inner wall  32  of the lower portion of the shroud  16 , which is not as thick as the upper portion. Of course, the ordinarily skilled artisan will recognize that this configuration is not limiting. For example, first and second protuberant portions  54 ,  58  could be of the same length when the stool  48  is used on the sparger below the one illustrated, where the upper portion of the shroud  16  does not exist. The substantially cylindrical cover  52  includes an opening  62  extending through it. This opening  62  receives the rod therein, and has a bottom  64  on which the head  47  of the rod abuts. 
     Referring now, once more, to FIG. 1, it can be seen that pipe  12  is fitted with a boss  13 . The boss  13  is depicted as including threads in its internal circumference, however, these threads are not necessary for practicing the invention. If boss  13  does include threads, the threads would have a pitch that match corresponding threads  49  on rod  46 . Additionally, a nut  15  is placed on the end of rod  46  to provide sufficient clamping force for the connection  10 . The nut  15  may be threaded with mating threads for the rod  46 . Thus, rotation of either the nut  15  or the rod  46 , or both, will draw the pipe  12  toward the shroud  16 , thereby providing the coupling force. Although the nut  15  and rod  46  are depicted as having mating threads, this is not a limiting arrangement. Any means of drawing the rod through boss  13 , known to the skilled artisan, could be used. In any case, because the rod  46  is located within the pipe  12 , the flow of fluid within the pipe will maintain the rod  46  and pipe  12  at the same temperature. This prevents differential thermal expansion from opening a gap in the joints between the pipe  12 , the anchor socket  18 , and the tee box  26 . 
     FIGS. 4 and 5 depict partial cut-away perspective views of the connection in its fully assembled condition. These figures are included to provide clear illustration of the connection  10  according to the preferred embodiment of the present invention. 
     The connection can be installed within the reactor vessel with relative ease. The existing downcomer pipe is cut away from the shroud  16  and tee box  26 , leaving the tee box  26  and a portion of the preexisting safe end  25 . A hole  44  is then made in the end  42  of tee box  26 . The replacement pipe  12 , including the ball  14 , is inserted into the anchor socket  18  and mated with the seat  24 . The pipe  12  and anchor socket  18  assembly are then positioned within the reactor vessel and against the outer wall  28  of the shroud  16 , such that the first and second circumferential rings  21 ,  23 , surround the safe end  25  and tee box  26 , respectively. The stool  48  is then inserted into the reactor vessel and against the inner wall  32  of the shroud  16 , such that the bracket  34  is received in the slot  56  of the first protuberant portion  54 . The rod  46  is then inserted through the hole  62  of the stool  48 , through the hole  44  in the tee box  26 , through the anchor socket  18  and pipe  12 , and into the boss  13 . The nut  15  is then inserted onto the threads  49  of rod  46 , and tightened to a predetermined torque for initial fit and then lowered to a specified load. The rod  46  may then be locked using a crimping process. 
     With the above-described connection, several technical, financial, and logistical advantages are obtained relative to known devices. The installation process is fast. A single hole and a single pipe cut are all that are needed for each tee box. The rod situated internal to the pipe allows for low leakage. No pre-measurements are required for installation. The ball and socket design reduces thermal and mechanical loads on existing parts. Vertical shear forces are transmitted to the shroud without going through a weld. And, finally, the connection is easily disassembled for maintenance and/or inspections. 
     While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art. However, it will be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.