Abstract:
A method of repairing and inspecting a first nozzle penetrating a closed vessel. The method includes removing a portion of the first nozzle, and forming a weld between a replacement nozzle and a surface of the mid-wall of the vessel. The method further includes evaluating the integrity of the weld at the mid-wall of the vessel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a divisional of U.S. patent application Ser. No. 11/091,767, filed Mar. 29, 2005, the contents of which are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a method of providing a mid-wall repair, as well as a method of evaluating the mid-wall repair. 
       DISCUSSION OF THE RELATED ART 
       [0003]    In pressurized water (PWR) and boiling water (BWR) nuclear reactors, multiple penetrations are provided in a pressure vessel or piping. The penetrations consist of sleeves and/or nozzles that extend from the exterior of the pressure vessel through openings in a low alloy or carbon steel vessel wall and a nickel-chromium-iron (Ni—Cr—Fe) or stainless steel clad disposed on the interior surface of the pressure vessel. During initial fabrication (i.e., before access to the interior of the pressure vessel is limited, and before the pressure vessel is subjected to radiation and pressurized high temperature water as a result of operation of the nuclear reactor), a J-shaped groove is formed in the vessel interior clad and in some cases the low alloy steel or carbon steel vessel interior wall as well, and a weld material is deposited in the groove to weld the nozzle to the clad and vessel wall, where applicable. Thus, the nozzle is welded from the interior of the pressure vessel to connect the nozzle to the pressure vessel. 
         [0004]    As a result of operating and residual stresses in the J-groove weld and the primary water environment during operation, the welds, the sleeves or nozzles, and the Ni—Cr—Fe or stainless steel cladding are subject to stress corrosion cracking. Thus, it becomes necessary to repair the connection between the nozzle and the pressure vessel. 
         [0005]    In a known repair technique, the technician does not have access to the highly radioactive interior of the closed pressure vessel. Thus, repair of the connection between the pressure vessel and the nozzle is conducted from the exterior of the pressure vessel. 
         [0006]    In the known repair technique, the nozzle is severed at the mid-wall of the pressure vessel and a sacrificial plug installed to create a flush surface at the exterior of the pressure vessel. A welding pad of a material that is not susceptible to stress corrosion cracking, such as Alloy 52, is formed on the exterior of the pressure vessel. A hole is drilled in the welding pad, and a replacement nozzle formed of a material that is not susceptible to stress corrosion cracking, such as Alloy 690, is disposed in the hole. The replacement nozzle is then welded to the welding pad. Because it is not practical to provide postweld heat treatment stress relief of the weld and the adjacent areas, a temper bead welding technique is used to weld the welding pad to the pressure vessel or piping. 
         [0007]    The known repair technique suffers from a number of disadvantages, however. These disadvantages include that it is often difficult to precisely align the replacement nozzle with the openings in the pressure vessel wall and the new welding pad on the pressure vessel. Further, a relatively large amount of material is used to provide the welding pad of sufficient size (e.g., 6 inch by 6 inch by 0.5 inch) to permit testing and evaluation of the weld pad to the pressure vessel. Further, because formation of the temper bead must be precisely controlled, the weld pad requires a relatively large amount of time to produce, which may increase down time of the nuclear reactor and the amount of radiation to which the technician is exposed during the repair process. The severity of these problems is compounded by the fact that a typical pressure vessel includes multiple nozzles. 
       SUMMARY OF THE INVENTION 
       [0008]    Various illustrative embodiments provide a method of repairing and inspecting a first nozzle penetrating a closed vessel. In accordance with one aspect of an illustrative embodiment, the method may include removing a portion of the first nozzle, and forming a weld between a replacement nozzle and a surface of the mid-wall of the vessel. In accordance with another aspect of an illustrative embodiment, the method may further include evaluating the integrity of the weld at the mid-wall of the vessel. 
         [0009]    Various illustrative embodiments of evaluating the integrity of the weld at the mid-wall of the vessel may include performing a liquid penetrant test of the weld; comparing a characteristic of the weld to a characteristic of at least one of a known defective weld and a known defect-free weld; and comparing a characteristic of the weld obtained through ultrasonic inspection 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    An appreciation of the present invention, and many of the attendant advantages of the invention, can be readily ascertained and/or obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0011]      FIGS. 1-10  are detail views showing a method of providing and evaluating a mid-wall repair according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Examples of one or more embodiments of the present invention are described with reference to the drawings, wherein like reference numbers throughout the several views identify like or similar elements. 
         [0013]    The method of providing and evaluating a mid-wall repair, as shown in the drawings and as described herein, can be provided between a pressure vessel or piping  100  (referred to as pressure vessel in the following discussion) of a PWR or BWR nuclear reactor and at least one nozzle  10 . It is to be understood, however, that the method can be applied to various structures, including various nuclear reactor structures as well as structures that are not disposed in a nuclear reactor. 
         [0014]    As shown in  FIG. 1 , the pressure vessel  100  can include an interior surface  101  opposite an exterior surface  103 , and a mid-wall  105  extending between the interior and exterior surfaces  101  and  103 . The interior and exterior surfaces  101  and  103  can be curved or contoured, and the mid-wall  105  can be of a constant thickness, at least in the position through which the nozzle  10  is disposed. A clad material  107  can be disposed on the interior surface  101 . In a preferred embodiment, materials of the mid-wall  105  and the clad  107  can include steel, and more preferably can include a low alloy or carbon steel and an Ni—Cr—Fe or stainless steel material, respectively. 
         [0015]    As discussed above, the pressure vessel  100  can include at least one nozzle  10 . In a preferred embodiment, the pressure vessel  100  can include a plurality of nozzles  10 . It is to be understood, however, that the pressure vessel  100  can include any number of nozzles  10 . 
         [0016]    As shown in  FIG. 2  and  FIG. 1 , the nozzle  10  can be in the form of a sleeve or nozzle having an exterior surface  13  opposite an interior surface  15 , and a heater or other component  20  disposed within an interior defined by the interior surface  15  of the nozzle  10 . In a preferred embodiment, a material of the nozzle  10  can include an Alloy 600 or stainless steel material. 
         [0017]    A weld  109  can be used to connect the pressure vessel  100  and the nozzle  10 . In a preferred embodiment, a groove can be formed in the clad  107  or a combination of the clad and vessel wall with weld butter. More preferably, the clad  107  or combination of clad and vessel wall can include a J-shaped groove. The weld  109  can be formed in the groove to weld the pressure vessel  100  to the nozzle  10 . It is to be understood, however, that various welds can be used to weld the pressure vessel  100  to the nozzle  10 . 
         [0018]    As shown in  FIG. 2 , during an initial stage of the mid-wall repair process, a length of the nozzle  10  on an exterior side of the pressure vessel  100  can be removed. In a preferred embodiment, the nozzle  10  can be cut by an abrasive cutting operation commencing on the exterior surface  13  of the nozzle  10 . It is to be understood that the various material and component removal processes, including abrasive grinding and cutting, can be performed manually (i.e., by hand or with hand tools) or remotely (i.e., by automatic tools or processes, including those in use or those that are later developed). As shown in  FIG. 2 , the heater or other component  20  can then be removed from the interior of the nozzle  10 , decontaminated, and otherwise repaired or replaced, depending on its condition. 
         [0019]    As shown in  FIG. 3 , the length of the nozzle  10  extending from the exterior surface  103  of the pressure vessel  100  can be further reduced. Returning to  FIG. 2 , a spacer barrier can be disposed within a portion of the nozzle  10  extending above the clad  107  in the interior of the pressure vessel  100  prior to the further reduction of the length. This spacer barrier is a foreign materials exclusion (FME) device to prevent intrusion of foreign materials from the subsequent repair operations into the interior of the vessel. In a preferred embodiment, an abrasive cutting operation commencing on the exterior surface  13  of the nozzle  10  can be used to further reduce the length of the nozzle  10 . Preferably, the length of the nozzle is reduced to a predetermined length as close as practical to the curved exterior surface  103  of the pressure vessel  100 . 
         [0020]    As shown in  FIG. 4 , the nozzle  10  can be severed at a position adjacent the mid-wall  105  of the pressure vessel  100  (i.e., between the interior and exterior surfaces  101  and  103 ) to provide an upper nozzle portion  17 , which is welded to the pressure vessel  100  by the weld  109 , and a lower nozzle portion  19 , which is no longer connected to the pressure vessel  100 . In a preferred embodiment, the nozzle  10  can be severed by an abrasive cutting operation commencing on the interior surface  15  of the nozzle  10 . In the preferred embodiment, the nozzle  10  can be severed at a predetermined distance from the bottom of the nozzle  10  that maximizes the lower nozzle portion  19  that will subsequently be removed. 
         [0021]    As shown in  FIG. 5 , the lower nozzle portion  19  can be removed from the pressure vessel  100 . In a preferred embodiment, the lower nozzle portion  19  can be removed manually. The lower nozzle portion  19  can be removed from the pressure vessel  100  with a slide hammer or other means if it cannot be removed manually. 
         [0022]    As shown in  FIG. 6 , the upper nozzle portion  17  can remain welded to the pressure vessel  100 , and the FME device can be removed from the upper nozzle portion  17 . The upper nozzle portion  17 , as well as a portion of the mid-wall  105  exposed by removal of the lower nozzle portion  19  and defining a mid-wall void  113 , can be treated, cleaned, or otherwise prepared for subsequent attachment of a replacement nozzle and insertion of a heater or other implement after cleaning the upper nozzle portion  17 . In a preferred embodiment, scale or other sediment can be removed from the upper nozzle portion  17 , and a surface of the mid-wall void  113  can be cleaned by an abrasive operation. More preferably, an abrasive grinding wheel can be used to clean the upper nozzle portion  17  and the surface of the mid-wall void  113 . When access can be permitted to the upper nozzle portion  17  from the interior of the pressure vessel  100 , a cap (not shown) can be disposed to cover the upper nozzle portion  17 , such that scale or other sediment removed from the upper nozzle portion  17  or the mid-wall void  113  is prevented from contaminating the pressure vessel  100 . 
         [0023]    After cleaning the upper nozzle portion  17  and the mid-wall void  113 , the surface of the mid-wall void  113  can be evaluated after dye penetrant testing, to confirm that the surface of the mid-wall void  113 , such as a portion of the surface adjacent the upper nozzle portion  17 , is acceptable for subsequent installation of the replacement nozzle, as described below. 
         [0024]    As shown in  FIG. 7 , an alignment tool  40  can be disposed in the upper nozzle  17  to facilitate alignment and attachment of a replacement nozzle  30  with the pressure vessel  100 . The installation tool  43  can include a head portion  41  having an outer diameter corresponding to a diameter of the mid-wall void  113 , and having a flat surface configured to contact an end surface of the upper nozzle portion  17 . By this arrangement, the installation tool  43  can axially locate the alignment tool in the upper nozzle  17  and the self-centering feature of the alignment tool locates it radially relative the upper nozzle  17  with a high degree of precision. 
         [0025]    In an embodiment of the invention, the alignment tool  40  can include a sealing portion that seals against an interior surface of the upper nozzle portion  17 . Such an alignment tool  40  can permit reactor fuel off-load or refueling while the mid-wall repair is occurring, by permitting the pressure vessel  100  to be filled with water during the repair process of up to the removal of the alignment tool  40  and reinsertion of the heater or instrument. 
         [0026]    As shown in  FIG. 8 , the replacement nozzle  30  can be disposed on an alignment shaft  42  piloted in the alignment tool  40 , and can be precisely axially and radially located as described above. In a preferred embodiment, the material of the replacement nozzle  30  can be determined so as to resist stress corrosion cracking when the replacement nozzle  30  is welded to the mid-wall  105 , and more preferably a material of the replacement nozzle  30  can include Alloy 690 or stainless steel. 
         [0027]    As shown in  FIG. 9 , at least one clamping device  50  can be used to maintain the precise axial and radial position of the replacement nozzle  30  in the mid-wall void  113 . The clamping device  50  can include an end portion configured to retain the replacement nozzle  30 , and can include an opposite end portion configured to retain another one of the nozzles  10  or other available attachment point(s). By this arrangement, it is understood that the replacement nozzle  30  can be maintained at a desired position relative to other nozzles welded to the pressure vessel  100  or some other desired alignment. In a preferred embodiment, a plurality of clamping devices  50  are used to maintain the position of the replacement nozzle  30 , and more preferably at least three clamping devices  50  are used. 
         [0028]    The alignment tool  40  and alignment shaft  42  can be removed from the upper nozzle  17  and the replacement nozzle  30 , such that the clamping device maintains the position of the replacement nozzle  30  relative to the pressure vessel  100 . 
         [0029]    As shown in  FIG. 10 , the replacement nozzle  30  can be welded to the mid-wall  105  of the pressure vessel  100 , and more specifically a weld  115  having at least three weld layers can be formed between the surface of the mid-wall void  113  and the replacement nozzle  30 . In a preferred embodiment, the weld  115  can include a plurality of weld layers each having a predetermined deposit height, and more preferably can include at least three weld layers with a total predetermined deposit height of at least 0.125 inches, and the overall buildup of the weld  115  can be determined such that the weld  115  extends only minimally beyond an inner diameter of the replacement nozzle  30 . 
         [0030]    A welding tool  60  can be used to provide the weld  115  between the replacement nozzle  30  and the mid-wall  105 . The welding tool  60  can include a video camera such that a technician can monitor formation of the weld  115 , a wire feed through which the technician can deliver a material for the weld  115 , an inert gas delivery system to aid in formation of the weld  115 , and a water cooling system for cooling the welding tool  60 . 
         [0031]    A surface of the weld  115  can be prepared for subsequent testing and evaluation. After formation of the weld  115 , the weld surface can be prepared for subsequent testing and evaluation. An abrasive grinding operation can be used to remove an excess portion of the weld  115  (e.g., a portion of the weld extending beyond the inner diameter of the replacement nozzle  30 ). 
         [0032]    The weld  115  can be inspected to determine the sufficiency of the weld  115 . In a preferred embodiment, the weld  115  can be liquid penetrant inspected. 
         [0033]    In a preferred embodiment, the weld  115  can be ultrasonically inspected. More preferably, an ultrasonic map indicating properties of the weld  115  can be provided, the map including characteristics of portions of the weld  115  such as echodynamic signature including response amplitude and time of flight of the ultrasonic signal. By comparing the ultrasonic map of the weld  115  with a plurality of ultrasonic maps of known defect-free and defective welds, a technician can determine whether the weld  115  is substantially free of defects. The ultrasonic maps of known defect-free and defective welds can be determined by producing ultrasonic maps of various weld samples, and then by destructively evaluating the weld samples to determine the absence or existence of defects. It is understood that the term “defect-free” can include welds that meet or exceed the UT examination standards set forth in ASME Code, Section III, and specifically Paragraph NB-5330, which is hereby incorporated by reference. This is in contrast to the more forgiving UT examination requirements of ASME Code, Section XI, which is invoked for this repair by ASME Code Case N-638, which are also both hereby incorporated by reference. It is also to be understood that the above-described process can be performed to provide a weld that exceeds ASME Code, Section XI requirements. 
         [0034]    Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.