CA2766586C - Nuclear reactor lattice tube plug insert and method - Google Patents
Nuclear reactor lattice tube plug insert and method Download PDFInfo
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- CA2766586C CA2766586C CA2766586A CA2766586A CA2766586C CA 2766586 C CA2766586 C CA 2766586C CA 2766586 A CA2766586 A CA 2766586A CA 2766586 A CA2766586 A CA 2766586A CA 2766586 C CA2766586 C CA 2766586C
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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Abstract
An apparatus and method of shielding radiation from a nuclear reactor having at least one fuel channel tube includes inserting a plug into an end of the fuel channel tube, providing a gas-tight seal with the plug in the fuel channel tube, and installing a flange about the plug and/or about the end of a sleeve also inserted within the fuel channel tube. In some embodiments, the sleeve receives the plug, and can protect the fuel channel tube and a wall aperture in which the fuel channel plug is received against damage. Also in some embodiments, radiation leakage can be reduced or prevented by the plug, the flange, and/or by a sealing arrangement between the sleeve and the plug and/or between the sleeve and the fuel channel tube.
Description
Attorney Docket No. 027813-9033-CA00 NUCLEAR REACTOR LATTICE TUBE PLUG INSERT AND METHOD
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional Application No.
61/433,325 of the same title, filed January 17, 2011.
FIELD OF THE INVENTION
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional Application No.
61/433,325 of the same title, filed January 17, 2011.
FIELD OF THE INVENTION
[0002] The present invention relates to methods, devices, and systems for retubing nuclear reactors.
SUMMARY
SUMMARY
[0003] A nuclear reactor has a limited life of operation. For example, second generation CANDUTm-type reactors ("CANada Deuterium Uranium") are designed to operate for approximately 25 to 30 years. After this time, the existing fuel channels can be removed and new fuel channels can be installed. Performing this "retubing" process can extend the life of a reactor. For example, retubing a CANDUTm-type reactor can extend the reactor's life by an additional 25 to 40 years. Without performing the retubing, a reactor that reaches the end of its useful life is typically decommissioned and replaced with a new reactor, which poses significant costs and time. Alternatively, replacement energy sources may be used to extend the life of a reactor. However, replacement energy sources are often more expensive than installing a new reactor, and can be difficult to acquire.
[0004] Nuclear reactor retubing processes include removal of a large number of reactor components, and include various other activities, such as shutting down the reactor, preparing the vault, and installing material handling equipment and various platforms and equipment supports.
In the process of removing reactor components, it is sometimes necessary to remove end fittings of the reactor fuel channels, and to insert sleeves, plugs, or other components in the unoccupied reactor lattice sites.
In the process of removing reactor components, it is sometimes necessary to remove end fittings of the reactor fuel channels, and to insert sleeves, plugs, or other components in the unoccupied reactor lattice sites.
[0005] During the removal process, particular procedures can be used to improve the efficiency of the process. For example, a stand-alone retube tooling platform can be installed on each face of the reactor, which is used to support operators and tools during the retubing process.
Attorney Docket No. 027813-9033-CA00 Also, when components are removed from the reactor, they must be transported and disposed of properly. In some embodiments, the components are volume reduced before being transported, such as by cutting the components into smaller pieces.
Attorney Docket No. 027813-9033-CA00 Also, when components are removed from the reactor, they must be transported and disposed of properly. In some embodiments, the components are volume reduced before being transported, such as by cutting the components into smaller pieces.
[0006] As mentioned above, it is often necessary in the process of retubing a nuclear reactor to insert components in lattice sites left unoccupied during the retubing process. In some cases, lattice shield plugs can be installed in such sites. Based at least in part upon the relatively large number of such lattice sites in a typical reactor and the collective time consumed in insertion and removal operations, new and improved lattice tube shield plugs and methods of inserting such plugs are welcome additions to the art.
[0007] Embodiments of the present invention provide lattice tube shield plug inserts and lattice tube shield plug insert and removal tools and methods which can be used to improve nuclear reactor retubing operations and nuclear reactors that have been retubed.
[0008] Some embodiments of the present invention provide a method of shielding radiation from a nuclear reactor having at least a portion of an open end of a tube of a fuel channel assembly, wherein the method comprises: inserting a plug into the open end of the tube; sealing the plug within the tube against passage of gas along the tube and past the plug; and installing a flange about at least one of the open end of the tube and the plug, wherein the flange substantially surrounds the at least one of the open end of the tube and the plug.
[0009] In some embodiments, a method of installing a shield on a nuclear reactor having a plurality of fuel channel tubes is provided, and comprises: inserting a first plug into an end of a first one of the fuel channel tubes; coupling a first flange to the first one of the fuel channel tubes; inserting a second plug into an end of a second one of the fuel channel tubes; coupling a second flange to the end of the second one of the fuel channel tubes;
positioning the first flange immediately adjacent the second flange; and shielding radiation from the nuclear reactor with the first and second plugs and with the first and second flanges.
positioning the first flange immediately adjacent the second flange; and shielding radiation from the nuclear reactor with the first and second plugs and with the first and second flanges.
[0010] Some embodiments of the present invention provide a modular shield assembly for shielding radiation from a nuclear reactor having a tube sheet defining a plurality of apertures and a plurality of fuel channel tubes each extending through a respective one of the plurality of Attorney Docket No. 027813-9033-CA00 apertures in the tube sheet, wherein the assembly comprises: a plurality of discrete shields, each shield including a sleeve insertable into an end of one of the plurality of fuel channel tubes, a plug insertable into the end of the one of the plurality of fuel channel tubes, and a flange couplable to the one of the plurality of fuel channel tubes; wherein at least one of the plug and the flange is removable from the corresponding fuel channel tube without requiring removal of adjacent shields; and wherein the shields collectively define a substantially continuous wall covering at least a portion of the tube sheet to shield radiation from the nuclear reactor.
[0011] In some embodiments, a modular shield assembly for shielding radiation from a nuclear reactor having a tube sheet defining a plurality of apertures and a plurality of fuel channel tubes each extending through a respective one of the plurality of apertures in the tube sheet is provided, and comprises: a sleeve insertable into an end of one of the plurality of fuel channel tubes, the sleeve extending through one of the apertures in the tube sheet; a plug insertable into the end of the one of the plurality of fuel channel tubes, the plug extending through the one of the apertures in the tube sheet and located within the sleeve, wherein the plug forms a shield to block radiation within the one of the plurality of fuel channel tubes from escaping to atmosphere; and a flange releasably couplable to the one of the plurality of fuel channel tubes to substantially surround at least one of the sleeve and the plug in a position shielding radiation from the nuclear reactor escaping to atmosphere.
[0012] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]rm Fig. 1 is a perspective view of a CANDU reactor.
[0014]
Fig. 2 is a cut away view of a CANDU m-type nuclear reactor fuel channel assembly.
Fig. 2 is a cut away view of a CANDU m-type nuclear reactor fuel channel assembly.
[0015] Fig. 3 is a close up perspective view of the connection between the tube sheet and the bellows, the bellows ferrules, and the end fitting of Fig. 2.
Attorney Docket No. 027813-9033-CA00 100161 Fig. 4 is a perspective view of a lattice site shield plug insert and removal tool in conjunction with other tools according to an embodiment of the present invention, shown installed before a reactor face.
[0017] Fig. 5 is a cross sectional view of lattice sleeve assemblies each having a lattice shield plug, according to an embodiment of the present invention.
[0018] Fig. 6 is a perspective view of a lattice site shield plug insert and removal tool according to an embodiment of the present invention.
[0019] Fig. 7 shows the lattice site shield plug insert and removal tool of Figs. 4 and 6 advancing with a lattice sleeve assembly attached thereto and in the process of installing the lattice sleeve assembly into a lattice site.
[0020] Fig. 8 shows the lattice site shield plug insert and removal tool of Figs. 4 and 6, fully advanced with the lattice sleeve assembly installed into a lattice site.
[0021] Fig. 9 is a close up perspective view of a reactor face with several lattice shield plug assemblies installed, according to an embodiment of the present invention.
[0022] Fig. 10 is a perspective view of a reactor face in which all lattice sleeve assemblies have been installed in lattice sites on the reactor face, according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0023] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
[0024] FIG. 1 is a perspective of a reactor core of a CANDUTm-type reactor 6. The reactor core is typically contained within a vault that is sealed with an air lock for radiation control and shielding. A generally cylindrical vessel, known as a calandria 10, contains a heavy-water Attorney Docket No. 027813-9033-CA00 moderator. The calandria 10 has an annular shell 14 and a tube sheet 18 at a first end 22 and a second end 24. The tube sheets 18 include a plurality of apertures that each accept a fuel channel assembly 28. As shown in FIG. 1, a number of fuel channel assemblies 28 pass through the tube sheets 18 of calandria 10 from the first end 22 to the second end 24.
[0025] As in the illustrated embodiment, in some embodiments the reactor core is provided with two walls at each end 22, 24 of the reactor core: an inner wall defined by the tube sheet 18 at each end 22. 24 of the reactor core, and an outer wall 64 (often referred to as a "end shield") located a distance outboard from the tube sheet 18 at each end 22, 24 of the reactor core. A
lattice tube 65 spans the distance between the tube sheet 18 and the end shield 64 at each pair of apertures (i.e., in the tube sheet 18 and the end shield 64, respectively).
[0026] FIG. 2 is a cut away view of the fuel channel assembly 28. As illustrated in FIG. 2, each fuel channel assembly 28 includes a calandria tube ("CT") 32 surrounding other components of the fuel channel assembly 28. The CTs 32 each span the distance between the tube sheets 18. Also, the opposite ends of each CT 32 are received within and sealed to respective apertures in the tube sheets 18. In some embodiments, a CT rolled joint insert 34 is used to secure the CT 32 to the tube sheet 18 within the bores, although other tube-to-sheet joining structures and methods can instead be used. In this manner, the CTs 32 each form a first boundary between the heavy water moderator of the calandria 10 and the interior of the fuel channels assemblies 28.
[0027] A pressure tube ("PT") 36 forms an inner wall of the fuel channel assembly 28. The PT 36 provides a conduit for reactor coolant and fuel bundles or assemblies 40. The PT 36, for example, generally holds two or more fuel assemblies 40 and acts as a conduit for reactor coolant that passes through each fuel assembly 40. An annulus space 44 is defined by a gap between each PT 36 and its corresponding CT 32. The annulus space 44 is normally filled with a circulating gas, such as dry carbon dioxide, helium, nitrogen, air, or mixtures thereof The annulus space 44 and gas are part of an annulus gas system typically having at least one of two primary functions. First, a gas boundary between the CT 32 and PT 36 provides thermal insulation between hot reactor coolant and fuel within the PTs 36 and the relatively cool CTs 32.
Attorney Docket No. 027813-9033-CA00 Second, the annulus gas system provides indication of a leaking calandria tube 32 or pressure tube 36 via the presence of moisture, deuterium, or both detected in the annulus gas.
[0028] An annulus spacer or garter spring 48 is disposed between the CT 32 and PT 36. The annulus spacer 48 maintains the gap between the PT 36 and the corresponding CT
32, while allowing passage of the annulus gas through and around the annulus spacer 48.
Maintaining the gap helps ensure safe and efficient, long-term operation of the reactor 6.
[0029] As also shown in FIG. 2, each end of each fuel channel assembly 28 is provided with an end fitting 50 located outside of the corresponding tube sheet 18. At the terminal end of each end fitting 50 is a closure plug 52. Each end fitting 50 also includes a feeder assembly 54. The feeder assemblies 54 feed reactor coolant into or remove reactor coolant from the PTs 36. In particular, for a single fuel channel assembly 28, the feeder assembly 54 on one end of the fuel channel assembly 28 acts as an inlet feeder, and the feeder assembly 54 on the opposite end of the fuel channel assembly 28 acts as an outlet feeder. As shown in FIG. 2, the feeder assemblies 54 can be attached to the end fittings 50 using a coupling assembly 56 including a number of screws, washers, seals, and/or other types of connectors.
[0030] The lattice tube 65 (described above) encases the connection between the end fitting 50 and the PT 36 containing the fuel assemblies 40. Shielding ball bearings 66 and cooling water surround the exterior the lattice tubes 65, which provides additional radiation shielding.
[0031] With continued reference to FIGS. 2 and 3, coolant from the inlet feeder assembly 54 flows along a perimeter channel of the end fitting 50 until it reaches a shield plug 58. The shield plug 58 is contained within the PT 36 and the lattice tube 65, and includes a number of openings that allow the coolant provided by the inlet feeder assembly to enter the end of the PT 36.
Another shield plug 58 is located within the PT 36 and the lattice tube 65 at the other end of the fuel channel assembly 28, and includes similar openings that allow coolant passing through the PT 36 to exit the PT 36 and flow to the outlet feeder assembly 54 through a perimeter channel of another end fitting 50 at the opposite face of the reactor 6. As shown in FIG.
1, feeder tubes 59 are connected to the feeder assemblies 54 that carry coolant to or away from the reactor 6.
Attorney Docket No. 027813-9033-CA00 [0032] Returning to FIGS. 2 and 3, a positioning hardware assembly 60 and bellows 62 are also coupled to each end fitting 50. The bellows 62 allows the fuel channel assemblies 28 to move axially ¨ a capability that can be important where fuel channel assemblies 28 experience changes in length over time, which is common in many reactors. The positioning hardware assemblies 60 can be used to set an end of a fuel channel assembly 28 in either a locked or an unlocked position. In the locked position, the end of the fuel channel assembly 28 is fixed in an axial position. In the unlocked position, the end of the fuel channel assembly 28 is allowed to move axially. A tool can be used with the positioning hardware assemblies 60 to switch the position of a particular fuel channel assembly 28.
100331 The positioning hardware assemblies 60 are also coupled to the end shield 64. The positioning hardware assemblies 60 each include a rod having an end that is received in a bore of the respective end shield 64. In some embodiments, the rod end and the bore in the end shield 64 are threaded.
[0034] It should be understood that although a CANDUT"-type reactor is illustrated in FIGS.
1-3, the methods and systems described below for retubing a reactor also apply to other types of reactors containing similar components as illustrated in FIGS. 1-3.
[0035] As shown in FIG. 4, the various tools utilized in the present invention can be installed and/or used adjacent the calandria 10 of the nuclear reactor 6 on a mobile table 70. The table 70 can carry and support tooling from lattice site to lattice site (i.e., those positions on each side of the reactor 6 defined by the locations of the fuel channel assemblies 28 described above) across the face of the calandria 10. In some embodiments, the table 70 is laterally movable in an x direction (e.g., upon rails, on a cart, and the like) at a common elevation across the face of the calandria 10, whereas in other embodiments, the table 70 is also vertically movable in a y direction and/or is movable toward and away from the reactor face in a z direction. By way of example, in some embodiments, the table 70 is movable in x and z directions, and is mounted upon a retube tooling platform 72 ("RTP") assembled in front of the calandria face and vertically movable (in the y direction) to different lattice sites. In some embodiments, the RTP 72 is an adjustable platform upon which much of the fuel channel component removal operations are performed. Also in some embodiments, the RTP 72 is a stand-alone machine that does not rely Attorney Docket No. 027813-9033-CA00 on existing plant structures for positioning or movement, and is adapted to adjustably support one or more tables.
100361 In some instances, it is desirable to insert a plug into an unoccupied lattice site resulting from nuclear reactor retubing operations. By way of example only, during re-tubing operations of CANDU I m reactors, all end fittings 50 are removed from the CANDU TM reactor.
The end fittings 50 are illustrated schematically in FIG. 4. Using end fitting removal tooling on platforms located on opposite ends 22, 24 of the reactor 6 (which can be identical, in some embodiments), the end fittings 50 can be removed from the same fuel channel assembly 28 from opposite reactor faces. In such cases, the end fittings 50 of the same fuel channel assembly 28 can be removed in a staggered fashion to accommodate end fitting flask trolley vault traffic.
After end fitting removal, it will be necessary in some cases to plug the lattice site.
[0037] After an end fitting 50 is removed from a fuel channel assembly 28, a lattice sleeve shield plug insertion and removal tool 74 (LS-SPIRT) can insert a lattice sleeve assembly 76 (LSA, also referred to as a "thumbtack") into the remainder of the fuel channel assembly 28 to attenuate radiation that could otherwise emit from the open channel and/or tube sheet face adjacent the open channel. As an additional valuable feature, once the LSA is installed in a lattice site, the LSA 76 can function as a portal through the end shield 64 through which tooling and reactor parts can be passed into and out of the reactor during re-tubing operations.
Accordingly, the LSA 76 can protect the aperture at the lattice site from damage while tooling and reactor parts are moved through the aperture. For example, it may be necessary to insert tooling through the end shield aperture and lattice tube 65 at a lattice site in order to remove portions of a fuel channel assembly 28 (e.g., split ring, PT, and/or CT of the fuel channel assembly 28, and the like). Also, and as will be discussed in greater detail below, the LSA 76 can provide a constant-diameter aperture by which proper tool and reactor part alignment and orientation are achieved. More particularly, an inner aperture through the LSA
76 can provide a bearing surface for tooling inserted into the end aperture of the lattice site.
100381 In some embodiments (and as will be described in greater detail below), the LSA 76 can also be used to plug the lattice site and form a seal to maintain a vacuum within the calandria Attorney Docket No. 027813-9033-CA00 10, and/or can providing a tooling interface between the LS-SPIRT 74 and the LSA 76 for LSA
installation and removal operations.
[0039] With reference back to FIGs. 2 and 3, an example of a LSA 76 application will now be described. In order to remove or service components of the fuel channel assembly 28 during a re-tubing operation, the outlet feeder assembly 54 and the positioning hardware assembly 60 are typically removed first, followed by removal of the closure plug 52. Removal of the closure plug 52 permits access to the inside of the end fitting 50 by appropriate tooling to sever the end fitting 50. Although the end fitting 50 can be severed at any desired location, in some embodiments (and with particular reference to FIG. 3), the end fitting 50 is severed at the ferrule on either end of the bellows 62 depending upon whether it is desirable to keep the bellows 62 intact after the retubing operations, to inspect the bellows 62 for damage or deterioration, or to replace the bellows 62. In the illustrated embodiment, the end fitting 50 has been severed at the inboard ferrule of the bellows 62, and so is not shown in FIG. 5. (Only the remainder of the inboard ferrule is visible between the flange 82 and the end shield 64 of each LSA 76 in FIG. 5, the rest of the bellows 62 of each LSA already having been removed).
[0040] After the end fitting 50 has been severed and removed (with the bellows 62 also removed as shown in the illustrated embodiment, or with the bellows 62 still intact at the lattice site), the open lattice site can be plugged with an LSA as described herein.
In some applications, LSAs 76 are inserted into each lattice tube 65 immediately after the end fitting 50 thereof has been severed and extracted.
[0041] As shown in FIG. 5, the LSA 76 of the illustrated embodiment includes three major components: a sleeve 78, a shield plug 80, and a flange 82. These components of the LSA 76 can all be made from steel with a smooth plated surface finish to inhibit corrosion and promote easy decontamination, although other materials are possible. In some embodiments, the outer diameter of the sleeve 78 can provide a clearance fit with the inner diameter of the lattice tube, and/or the inner diameter of the sleeve 78 can be the same as that of the inner diameter of the lattice tube 65 inboard of the fully-inserted LSA 76 (see FIG. 5) or of any component (e.g., split bearing ring) similarly located. Once installed as shown in FIG. 5, the sleeve 78 protects the Attorney Docket No. 027813-9033-CA00 aperture in the end shield 64 and the lattice tube 65 from contact and possible damage by tooling and reactor parts moving through the sleeve 78 and lattice tube 65.
[0042] In some embodiments, one or more seals are provided between the inside of the lattice tube 65 and the outside or end of the sleeve 78 when fully installed.
By way of example only, the inboard end of the sleeves 78 shown in FIG. 5 are provided with at least one annular seal 69 (e.g., 0-ring, labyrinth, and the like) carried by or otherwise located on the sleeve 78.
Alternatively or in addition, such seal(s) can be carried by or otherwise located on the lattice tube 65. With reference to the embodiment of FIG. 5, the seal(s) can match the inner diameter of that portion of the lattice tube 65 where the seals 69 are positioned when the LSA
76 is fully installed. For example, the inner diameter of the lattice tubes 65 in FIG. 5 are reduced at a shoulder located proximate the tube sheet 18, in which case the seals 69 are located on a similarly-reduced exterior diameter of the sleeve 78 to provide a seal between the sleeve 76 and the lattice tube 65. The seal generated by the seal(s) 69 are preferably gas-tight and do not permit gas or other fluid leakage despite a vacuum being maintained within the CT 32. It will be appreciated that any other suitable type of seal or sealing method can instead be utilized as desired.
[0043] With continued reference to the embodiment of FIG. 5, each of the LSAs 76 includes an internal shield plug 80. Although in some embodiments the sleeve 78 and shield plug 80 are integral (in which cases the sleeve 78 and shield plug 80 would have to be removed together for tooling and reactor part passage through the lattice tube in retubing operations), the shield plug 80 and sleeve 78 are separate parts in the illustrated embodiment.
Accordingly, the shield plug 80 can be removed from the sleeve 78 in order to access the interior of the fuel channel 28. In some embodiments, the shield plug 80 can comprise a removable core, such as a 2" removable core, or a core having any other shape with an exterior surface at least partially matching the interior surface of the sleeve 78 into which the shield plug 80 is inserted.
The shield plug 80 can be constructed of a single element or of multiple elements secured together to collectively perform the functions described here.
[0044] In some embodiments, a gas-tight seal is provided between the shield plug 80 and the sleeve 78 when the shield plug 80 is installed within the sleeve 78, such as to retain a vacuum Attorney Docket No. 027813-9033-CA00 within the CT 32. Such a seal can be provided in any of the manners described above in connection with the gas-tight seal(s) between the sleeve 78 and the lattice tube 65, such as by one or more annular seals located between an inside diameter of the sleeve 78 and an outside diameter of the shield plug 80. However, in the illustrated embodiment, the shield plug 80 of each LSA 76 includes an annular shoulder 85 that overlaps the end of the corresponding sleeve 78 to form a seal between the sleeve 78 and the shield plug 80, as well as compensate for tolerance variations. This seal can be rolled or formed in any other suitable manner.
[0045] By utilizing appropriate seals between the sleeve 78 and the lattice tube 65, and between the shield plug 80 and the sleeve 78 as described herein, the LSA can substantially seal the lattice tube 65 from atmosphere while maintaining a negative pressure in the calandria 10 to inhibit leakage of radioactive material from inside the calandria 10 to atmosphere.
[0046] Each of the shield plugs 80 illustrated in FIG. 5 include a recess 84 at an outboard end of the shield plug (i.e., proximate the flange 82 of the shield plug 80). The recess 84 defines a mating feature for engagement by the LS-SPIRT 74 in order to insert the shield plug 80 into the sleeve 78 and flange 82, to remove the shield plug 80 from the sleeve 78 and flange 82, or to insert or remove the entire LSA 76 with respect to a lattice site. The recess 84 can also have a deeper center hole for registration with a mating protrusion of the LS-SPIRT
74 for purposes of proper registration between the LS-SPIRT 74 and the shield plug 80 during such operations.
Although a recess 84 is provided in each of the shield plugs 80 of the illustrated embodiment, it should be noted that any other mating feature(s) can be utilized for releasably coupling the shield plug 80 (and therefore the entire LSA 76) to the LS-SPIRT 74, such as a protrusion of the shield plug 80 for releasable mating engagement in a recess at the end of the LS-SPIRT 75, mating bayonet fitting features on the shield plug 80 and LS-SPIRT 74, and the like.
[0047] As described above, each of the LSAs 76 in the illustrated embodiment has a flange 82. With reference to FIG. 5, when the LSAs are installed as described herein, the flanges 82 provide another layer of radiation protection by defining (with the shield plugs 80 and the ends of the sleeves 78 of the LSAs 76) a modular wall across the end shield 64. To this end, each of the flanges 78 has a shape matching the adjoining edges of adjacent flanges 78. As shown in FIG. 7 by way of example only, the flanges 78 in the illustrated embodiment are square.
Attorney Docket No. 027813-9033-CA00 However, depending at least in part upon the arrangement of fuel channel assemblies 28 across the reactor faces, other flange shapes are entirely possible, such as triangular, hexagonal, and other polygonal flanges 78. In still other embodiments, two or more different flange shapes can be used across the reactor faces to provide options for other polygonal, round, rotund, irregular, or other flange shapes. As with the illustrated embodiment, the alternative flange shapes can still cooperate to provide a substantially gapless wall across the end shield 64 for additional radiation protection. Furthermore, and in contrast to conventional radiation shields for nuclear reactors, the modularity provided by enabling removal and replacement of individual flanges corresponding to lattice sites is a significant advancement over designs in which only the entire end shield or similar wall can be removed and replaced or cut. In this regard, the use of LSAs 76 as disclosed herein enable service of particular fuel channel assemblies 28 without disturbing the rest of the radiation shielding wall provided by the flanges of other LSAs 76 already in place.
[0048] As shown in FIG. 5, the flange 82 of each LSA 76 includes three overlapping plates.
In other embodiments, any number of such plates (e.g., 1, 2, more the 4) can be used as desired.
By using multiple plates 82, service personnel can more easily remove the flanges 82 (which can have significant weight, in some embodiments). Also, a flange design permitting the installation of multiple plates enables service personnel to select the appropriate level of radiation shielding by installing the number of plates desired across the reactor face. In this regard, the plates 82 on any LSA 76 can each have the same thickness or have different thicknesses as desired.
[0049] In some embodiments, at least one (and in some cases, more than one or all) of the plates of each flange 82 are integral or otherwise permanently installed on the sleeve 78 and/or shield plug 80. Therefore, in such embodiments, removal of the entire flange 82 can require removal of the sleeve 78 and/or shield plug 80. However, in the illustrated embodiment, all plates of the LSA 76 are removable for maximum modularity, adjustability, and installation flexibility. By enabling removal of the plates of the flange 82, access to the tube sheet face 64 can be provided without having to remove the sleeve 78 or plug 80. In some embodiments, proper axial registration of the flange plates on the sleeve 78 is provided by an annular rib, collar, or other protrusion(s) formed on or attached to an exterior surface of the sleeve 78. With such features, the plates can be pushed into position on the sleeves 78 until they are stopped Attorney Docket No. 027813-9033-CA00 against such features, thereby preventing possible damage to the bellows 62, bellows ferrule, or other portion of the fuel channel assembly 28 behind the flange 82.
[0050] FIG. 6 illustrates an example of the LS-SPIRT 74 in greater detail.
The illustrated LS-SPIRT 74 includes a housing 86, grippers 88 and a drive mechanism 90. The drive mechanism 90 moves the housing 86 and the grippers 88 in the direction of arrow 92 with respect to the table 70 shown in HG. 4 (i.e. toward and away from the calandria 10). The grippers 88 are at least partially insertable into the bores 84 of the LSAs 76, and can include at least one axially adjustable shoe, pin, wedge, or other component that selectively engages the inside surface of the bores 84 of the LSAs 76 to grip the shield plug 80 of the LSAs. Suitable gripping tools are known in the art, and are not therefore described further herein.
[0051] By gripping the inside surface of a bore 84 of an LSA 76, the LS-SPIRT 74 can insert or remove the plug 80 of the LSA 76, can insert or remove the plug 80 and sleeve 78 of the LSA
with respect to a lattice tube 65 at a lattice site and/or can insert or remove the entire LSA (i.e., with the flange 82) with respect to a lattice tube 65 at a lattice site.
Operation of the LS-SPIRT
74 can be controlled by an operator either on the RTP 72 or in a remote location.
[0052] FIG. 7 illustrates the LS-SPIRT 74 engaging an LSA 76 with the LSA
76 spaced from the end shield 64 of the calandria 10. The position illustrated in FIG. 7 shows the LSA 76 prior to insertion into the lattice tube 65 or after removal of the LSA 76 from the lattice tube 65. The end fittings 50 shown in FIGS. 7-9 are shown schematically.
[0053] FIG. 8 illustrates the LS-SPIRT 74 engaging the LSA 76 with the LSA
76 fully inserted into the lattice tube 65 at a lattice site. The position illustrated in FIG. 8 shows the LSA
76 after insertion into the lattice tube 65 or prior to removal of the LSA 76 from the lattice tube 65.
[0054] FIG. 9 illustrates the tube sheet 64 after a number of end fittings 50 have been removed from the reactor face, and after a number of LSAs 76 have been installed. Some embodiments of the present invention utilize one or more fasteners 94 (e.g., bolts, in the illustrated embodiment) to secure the LSAs 76 to the fuelling machine tube sheet 64. This fastener installation process can be a manual face series operation in some embodiments, and can Attorney Docket No. 027813-9033-CA00 rely upon use of the RTP 72 (with optional front extensions 96) and various tooling to facilitate access to the LSAs 76. Commercial hand tools can be used for installing the fastener 94. In some embodiments, the fasteners 94 can facilitate separation of the components of the LSAs 76, such as to permit removal of the flange 82 without disturbing the sleeve 78 and/or plug 80 of an LSA 80, or (in non-illustrated embodiments), to permit removal of the sleeve 78 and/or the plug 80 while the flange 82 remains installed. The fasteners 94 can be inserted into the bore of the respective tube sheet 64 previously occupied by the rod of the respective positioning hardware assemblies 60. To this end, apertures in the flanges 82 can permit passage of the fasteners 94, which can be threaded into the bores of the tube sheet 64. The apertures in the flanges 82 of the illustrated embodiment are unthreaded, but can be threaded in other embodiments.
[0055] Once many of the LSAs 76 of the illustrated embodiment are installed on the reactor face, the flanges 82 together create thick shielding wall (e.g., of steel) that reduces exposure to radiation fields in front of the reactor face. By way of example only, in some embodiments the flanges 82 together create a 2" thick steel wall of shielding, thereby reducing exposure to radiation fields by a factor of eight. FIG. 10 shows all of the LSAs 76 installed on a reactor face.
One or more of the LSAs 76 can be removed to permit access to one or more of the lattice tubes 65 and/or the tube sheet face 64. For example, one of the plugs 80 or one of the flanges 82 can be removed while the remaining plugs 80 and flanges 82 (as well as sleeves 78) remain on the reactor 6. This permits an operator to access a specific portion of the calandria 10 without exposing the operator to an excessive amount of the radiation emitted from the calandria 10.
[0056] The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention as set forth in the appended claims.
Attorney Docket No. 027813-9033-CA00 100161 Fig. 4 is a perspective view of a lattice site shield plug insert and removal tool in conjunction with other tools according to an embodiment of the present invention, shown installed before a reactor face.
[0017] Fig. 5 is a cross sectional view of lattice sleeve assemblies each having a lattice shield plug, according to an embodiment of the present invention.
[0018] Fig. 6 is a perspective view of a lattice site shield plug insert and removal tool according to an embodiment of the present invention.
[0019] Fig. 7 shows the lattice site shield plug insert and removal tool of Figs. 4 and 6 advancing with a lattice sleeve assembly attached thereto and in the process of installing the lattice sleeve assembly into a lattice site.
[0020] Fig. 8 shows the lattice site shield plug insert and removal tool of Figs. 4 and 6, fully advanced with the lattice sleeve assembly installed into a lattice site.
[0021] Fig. 9 is a close up perspective view of a reactor face with several lattice shield plug assemblies installed, according to an embodiment of the present invention.
[0022] Fig. 10 is a perspective view of a reactor face in which all lattice sleeve assemblies have been installed in lattice sites on the reactor face, according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0023] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
[0024] FIG. 1 is a perspective of a reactor core of a CANDUTm-type reactor 6. The reactor core is typically contained within a vault that is sealed with an air lock for radiation control and shielding. A generally cylindrical vessel, known as a calandria 10, contains a heavy-water Attorney Docket No. 027813-9033-CA00 moderator. The calandria 10 has an annular shell 14 and a tube sheet 18 at a first end 22 and a second end 24. The tube sheets 18 include a plurality of apertures that each accept a fuel channel assembly 28. As shown in FIG. 1, a number of fuel channel assemblies 28 pass through the tube sheets 18 of calandria 10 from the first end 22 to the second end 24.
[0025] As in the illustrated embodiment, in some embodiments the reactor core is provided with two walls at each end 22, 24 of the reactor core: an inner wall defined by the tube sheet 18 at each end 22. 24 of the reactor core, and an outer wall 64 (often referred to as a "end shield") located a distance outboard from the tube sheet 18 at each end 22, 24 of the reactor core. A
lattice tube 65 spans the distance between the tube sheet 18 and the end shield 64 at each pair of apertures (i.e., in the tube sheet 18 and the end shield 64, respectively).
[0026] FIG. 2 is a cut away view of the fuel channel assembly 28. As illustrated in FIG. 2, each fuel channel assembly 28 includes a calandria tube ("CT") 32 surrounding other components of the fuel channel assembly 28. The CTs 32 each span the distance between the tube sheets 18. Also, the opposite ends of each CT 32 are received within and sealed to respective apertures in the tube sheets 18. In some embodiments, a CT rolled joint insert 34 is used to secure the CT 32 to the tube sheet 18 within the bores, although other tube-to-sheet joining structures and methods can instead be used. In this manner, the CTs 32 each form a first boundary between the heavy water moderator of the calandria 10 and the interior of the fuel channels assemblies 28.
[0027] A pressure tube ("PT") 36 forms an inner wall of the fuel channel assembly 28. The PT 36 provides a conduit for reactor coolant and fuel bundles or assemblies 40. The PT 36, for example, generally holds two or more fuel assemblies 40 and acts as a conduit for reactor coolant that passes through each fuel assembly 40. An annulus space 44 is defined by a gap between each PT 36 and its corresponding CT 32. The annulus space 44 is normally filled with a circulating gas, such as dry carbon dioxide, helium, nitrogen, air, or mixtures thereof The annulus space 44 and gas are part of an annulus gas system typically having at least one of two primary functions. First, a gas boundary between the CT 32 and PT 36 provides thermal insulation between hot reactor coolant and fuel within the PTs 36 and the relatively cool CTs 32.
Attorney Docket No. 027813-9033-CA00 Second, the annulus gas system provides indication of a leaking calandria tube 32 or pressure tube 36 via the presence of moisture, deuterium, or both detected in the annulus gas.
[0028] An annulus spacer or garter spring 48 is disposed between the CT 32 and PT 36. The annulus spacer 48 maintains the gap between the PT 36 and the corresponding CT
32, while allowing passage of the annulus gas through and around the annulus spacer 48.
Maintaining the gap helps ensure safe and efficient, long-term operation of the reactor 6.
[0029] As also shown in FIG. 2, each end of each fuel channel assembly 28 is provided with an end fitting 50 located outside of the corresponding tube sheet 18. At the terminal end of each end fitting 50 is a closure plug 52. Each end fitting 50 also includes a feeder assembly 54. The feeder assemblies 54 feed reactor coolant into or remove reactor coolant from the PTs 36. In particular, for a single fuel channel assembly 28, the feeder assembly 54 on one end of the fuel channel assembly 28 acts as an inlet feeder, and the feeder assembly 54 on the opposite end of the fuel channel assembly 28 acts as an outlet feeder. As shown in FIG. 2, the feeder assemblies 54 can be attached to the end fittings 50 using a coupling assembly 56 including a number of screws, washers, seals, and/or other types of connectors.
[0030] The lattice tube 65 (described above) encases the connection between the end fitting 50 and the PT 36 containing the fuel assemblies 40. Shielding ball bearings 66 and cooling water surround the exterior the lattice tubes 65, which provides additional radiation shielding.
[0031] With continued reference to FIGS. 2 and 3, coolant from the inlet feeder assembly 54 flows along a perimeter channel of the end fitting 50 until it reaches a shield plug 58. The shield plug 58 is contained within the PT 36 and the lattice tube 65, and includes a number of openings that allow the coolant provided by the inlet feeder assembly to enter the end of the PT 36.
Another shield plug 58 is located within the PT 36 and the lattice tube 65 at the other end of the fuel channel assembly 28, and includes similar openings that allow coolant passing through the PT 36 to exit the PT 36 and flow to the outlet feeder assembly 54 through a perimeter channel of another end fitting 50 at the opposite face of the reactor 6. As shown in FIG.
1, feeder tubes 59 are connected to the feeder assemblies 54 that carry coolant to or away from the reactor 6.
Attorney Docket No. 027813-9033-CA00 [0032] Returning to FIGS. 2 and 3, a positioning hardware assembly 60 and bellows 62 are also coupled to each end fitting 50. The bellows 62 allows the fuel channel assemblies 28 to move axially ¨ a capability that can be important where fuel channel assemblies 28 experience changes in length over time, which is common in many reactors. The positioning hardware assemblies 60 can be used to set an end of a fuel channel assembly 28 in either a locked or an unlocked position. In the locked position, the end of the fuel channel assembly 28 is fixed in an axial position. In the unlocked position, the end of the fuel channel assembly 28 is allowed to move axially. A tool can be used with the positioning hardware assemblies 60 to switch the position of a particular fuel channel assembly 28.
100331 The positioning hardware assemblies 60 are also coupled to the end shield 64. The positioning hardware assemblies 60 each include a rod having an end that is received in a bore of the respective end shield 64. In some embodiments, the rod end and the bore in the end shield 64 are threaded.
[0034] It should be understood that although a CANDUT"-type reactor is illustrated in FIGS.
1-3, the methods and systems described below for retubing a reactor also apply to other types of reactors containing similar components as illustrated in FIGS. 1-3.
[0035] As shown in FIG. 4, the various tools utilized in the present invention can be installed and/or used adjacent the calandria 10 of the nuclear reactor 6 on a mobile table 70. The table 70 can carry and support tooling from lattice site to lattice site (i.e., those positions on each side of the reactor 6 defined by the locations of the fuel channel assemblies 28 described above) across the face of the calandria 10. In some embodiments, the table 70 is laterally movable in an x direction (e.g., upon rails, on a cart, and the like) at a common elevation across the face of the calandria 10, whereas in other embodiments, the table 70 is also vertically movable in a y direction and/or is movable toward and away from the reactor face in a z direction. By way of example, in some embodiments, the table 70 is movable in x and z directions, and is mounted upon a retube tooling platform 72 ("RTP") assembled in front of the calandria face and vertically movable (in the y direction) to different lattice sites. In some embodiments, the RTP 72 is an adjustable platform upon which much of the fuel channel component removal operations are performed. Also in some embodiments, the RTP 72 is a stand-alone machine that does not rely Attorney Docket No. 027813-9033-CA00 on existing plant structures for positioning or movement, and is adapted to adjustably support one or more tables.
100361 In some instances, it is desirable to insert a plug into an unoccupied lattice site resulting from nuclear reactor retubing operations. By way of example only, during re-tubing operations of CANDU I m reactors, all end fittings 50 are removed from the CANDU TM reactor.
The end fittings 50 are illustrated schematically in FIG. 4. Using end fitting removal tooling on platforms located on opposite ends 22, 24 of the reactor 6 (which can be identical, in some embodiments), the end fittings 50 can be removed from the same fuel channel assembly 28 from opposite reactor faces. In such cases, the end fittings 50 of the same fuel channel assembly 28 can be removed in a staggered fashion to accommodate end fitting flask trolley vault traffic.
After end fitting removal, it will be necessary in some cases to plug the lattice site.
[0037] After an end fitting 50 is removed from a fuel channel assembly 28, a lattice sleeve shield plug insertion and removal tool 74 (LS-SPIRT) can insert a lattice sleeve assembly 76 (LSA, also referred to as a "thumbtack") into the remainder of the fuel channel assembly 28 to attenuate radiation that could otherwise emit from the open channel and/or tube sheet face adjacent the open channel. As an additional valuable feature, once the LSA is installed in a lattice site, the LSA 76 can function as a portal through the end shield 64 through which tooling and reactor parts can be passed into and out of the reactor during re-tubing operations.
Accordingly, the LSA 76 can protect the aperture at the lattice site from damage while tooling and reactor parts are moved through the aperture. For example, it may be necessary to insert tooling through the end shield aperture and lattice tube 65 at a lattice site in order to remove portions of a fuel channel assembly 28 (e.g., split ring, PT, and/or CT of the fuel channel assembly 28, and the like). Also, and as will be discussed in greater detail below, the LSA 76 can provide a constant-diameter aperture by which proper tool and reactor part alignment and orientation are achieved. More particularly, an inner aperture through the LSA
76 can provide a bearing surface for tooling inserted into the end aperture of the lattice site.
100381 In some embodiments (and as will be described in greater detail below), the LSA 76 can also be used to plug the lattice site and form a seal to maintain a vacuum within the calandria Attorney Docket No. 027813-9033-CA00 10, and/or can providing a tooling interface between the LS-SPIRT 74 and the LSA 76 for LSA
installation and removal operations.
[0039] With reference back to FIGs. 2 and 3, an example of a LSA 76 application will now be described. In order to remove or service components of the fuel channel assembly 28 during a re-tubing operation, the outlet feeder assembly 54 and the positioning hardware assembly 60 are typically removed first, followed by removal of the closure plug 52. Removal of the closure plug 52 permits access to the inside of the end fitting 50 by appropriate tooling to sever the end fitting 50. Although the end fitting 50 can be severed at any desired location, in some embodiments (and with particular reference to FIG. 3), the end fitting 50 is severed at the ferrule on either end of the bellows 62 depending upon whether it is desirable to keep the bellows 62 intact after the retubing operations, to inspect the bellows 62 for damage or deterioration, or to replace the bellows 62. In the illustrated embodiment, the end fitting 50 has been severed at the inboard ferrule of the bellows 62, and so is not shown in FIG. 5. (Only the remainder of the inboard ferrule is visible between the flange 82 and the end shield 64 of each LSA 76 in FIG. 5, the rest of the bellows 62 of each LSA already having been removed).
[0040] After the end fitting 50 has been severed and removed (with the bellows 62 also removed as shown in the illustrated embodiment, or with the bellows 62 still intact at the lattice site), the open lattice site can be plugged with an LSA as described herein.
In some applications, LSAs 76 are inserted into each lattice tube 65 immediately after the end fitting 50 thereof has been severed and extracted.
[0041] As shown in FIG. 5, the LSA 76 of the illustrated embodiment includes three major components: a sleeve 78, a shield plug 80, and a flange 82. These components of the LSA 76 can all be made from steel with a smooth plated surface finish to inhibit corrosion and promote easy decontamination, although other materials are possible. In some embodiments, the outer diameter of the sleeve 78 can provide a clearance fit with the inner diameter of the lattice tube, and/or the inner diameter of the sleeve 78 can be the same as that of the inner diameter of the lattice tube 65 inboard of the fully-inserted LSA 76 (see FIG. 5) or of any component (e.g., split bearing ring) similarly located. Once installed as shown in FIG. 5, the sleeve 78 protects the Attorney Docket No. 027813-9033-CA00 aperture in the end shield 64 and the lattice tube 65 from contact and possible damage by tooling and reactor parts moving through the sleeve 78 and lattice tube 65.
[0042] In some embodiments, one or more seals are provided between the inside of the lattice tube 65 and the outside or end of the sleeve 78 when fully installed.
By way of example only, the inboard end of the sleeves 78 shown in FIG. 5 are provided with at least one annular seal 69 (e.g., 0-ring, labyrinth, and the like) carried by or otherwise located on the sleeve 78.
Alternatively or in addition, such seal(s) can be carried by or otherwise located on the lattice tube 65. With reference to the embodiment of FIG. 5, the seal(s) can match the inner diameter of that portion of the lattice tube 65 where the seals 69 are positioned when the LSA
76 is fully installed. For example, the inner diameter of the lattice tubes 65 in FIG. 5 are reduced at a shoulder located proximate the tube sheet 18, in which case the seals 69 are located on a similarly-reduced exterior diameter of the sleeve 78 to provide a seal between the sleeve 76 and the lattice tube 65. The seal generated by the seal(s) 69 are preferably gas-tight and do not permit gas or other fluid leakage despite a vacuum being maintained within the CT 32. It will be appreciated that any other suitable type of seal or sealing method can instead be utilized as desired.
[0043] With continued reference to the embodiment of FIG. 5, each of the LSAs 76 includes an internal shield plug 80. Although in some embodiments the sleeve 78 and shield plug 80 are integral (in which cases the sleeve 78 and shield plug 80 would have to be removed together for tooling and reactor part passage through the lattice tube in retubing operations), the shield plug 80 and sleeve 78 are separate parts in the illustrated embodiment.
Accordingly, the shield plug 80 can be removed from the sleeve 78 in order to access the interior of the fuel channel 28. In some embodiments, the shield plug 80 can comprise a removable core, such as a 2" removable core, or a core having any other shape with an exterior surface at least partially matching the interior surface of the sleeve 78 into which the shield plug 80 is inserted.
The shield plug 80 can be constructed of a single element or of multiple elements secured together to collectively perform the functions described here.
[0044] In some embodiments, a gas-tight seal is provided between the shield plug 80 and the sleeve 78 when the shield plug 80 is installed within the sleeve 78, such as to retain a vacuum Attorney Docket No. 027813-9033-CA00 within the CT 32. Such a seal can be provided in any of the manners described above in connection with the gas-tight seal(s) between the sleeve 78 and the lattice tube 65, such as by one or more annular seals located between an inside diameter of the sleeve 78 and an outside diameter of the shield plug 80. However, in the illustrated embodiment, the shield plug 80 of each LSA 76 includes an annular shoulder 85 that overlaps the end of the corresponding sleeve 78 to form a seal between the sleeve 78 and the shield plug 80, as well as compensate for tolerance variations. This seal can be rolled or formed in any other suitable manner.
[0045] By utilizing appropriate seals between the sleeve 78 and the lattice tube 65, and between the shield plug 80 and the sleeve 78 as described herein, the LSA can substantially seal the lattice tube 65 from atmosphere while maintaining a negative pressure in the calandria 10 to inhibit leakage of radioactive material from inside the calandria 10 to atmosphere.
[0046] Each of the shield plugs 80 illustrated in FIG. 5 include a recess 84 at an outboard end of the shield plug (i.e., proximate the flange 82 of the shield plug 80). The recess 84 defines a mating feature for engagement by the LS-SPIRT 74 in order to insert the shield plug 80 into the sleeve 78 and flange 82, to remove the shield plug 80 from the sleeve 78 and flange 82, or to insert or remove the entire LSA 76 with respect to a lattice site. The recess 84 can also have a deeper center hole for registration with a mating protrusion of the LS-SPIRT
74 for purposes of proper registration between the LS-SPIRT 74 and the shield plug 80 during such operations.
Although a recess 84 is provided in each of the shield plugs 80 of the illustrated embodiment, it should be noted that any other mating feature(s) can be utilized for releasably coupling the shield plug 80 (and therefore the entire LSA 76) to the LS-SPIRT 74, such as a protrusion of the shield plug 80 for releasable mating engagement in a recess at the end of the LS-SPIRT 75, mating bayonet fitting features on the shield plug 80 and LS-SPIRT 74, and the like.
[0047] As described above, each of the LSAs 76 in the illustrated embodiment has a flange 82. With reference to FIG. 5, when the LSAs are installed as described herein, the flanges 82 provide another layer of radiation protection by defining (with the shield plugs 80 and the ends of the sleeves 78 of the LSAs 76) a modular wall across the end shield 64. To this end, each of the flanges 78 has a shape matching the adjoining edges of adjacent flanges 78. As shown in FIG. 7 by way of example only, the flanges 78 in the illustrated embodiment are square.
Attorney Docket No. 027813-9033-CA00 However, depending at least in part upon the arrangement of fuel channel assemblies 28 across the reactor faces, other flange shapes are entirely possible, such as triangular, hexagonal, and other polygonal flanges 78. In still other embodiments, two or more different flange shapes can be used across the reactor faces to provide options for other polygonal, round, rotund, irregular, or other flange shapes. As with the illustrated embodiment, the alternative flange shapes can still cooperate to provide a substantially gapless wall across the end shield 64 for additional radiation protection. Furthermore, and in contrast to conventional radiation shields for nuclear reactors, the modularity provided by enabling removal and replacement of individual flanges corresponding to lattice sites is a significant advancement over designs in which only the entire end shield or similar wall can be removed and replaced or cut. In this regard, the use of LSAs 76 as disclosed herein enable service of particular fuel channel assemblies 28 without disturbing the rest of the radiation shielding wall provided by the flanges of other LSAs 76 already in place.
[0048] As shown in FIG. 5, the flange 82 of each LSA 76 includes three overlapping plates.
In other embodiments, any number of such plates (e.g., 1, 2, more the 4) can be used as desired.
By using multiple plates 82, service personnel can more easily remove the flanges 82 (which can have significant weight, in some embodiments). Also, a flange design permitting the installation of multiple plates enables service personnel to select the appropriate level of radiation shielding by installing the number of plates desired across the reactor face. In this regard, the plates 82 on any LSA 76 can each have the same thickness or have different thicknesses as desired.
[0049] In some embodiments, at least one (and in some cases, more than one or all) of the plates of each flange 82 are integral or otherwise permanently installed on the sleeve 78 and/or shield plug 80. Therefore, in such embodiments, removal of the entire flange 82 can require removal of the sleeve 78 and/or shield plug 80. However, in the illustrated embodiment, all plates of the LSA 76 are removable for maximum modularity, adjustability, and installation flexibility. By enabling removal of the plates of the flange 82, access to the tube sheet face 64 can be provided without having to remove the sleeve 78 or plug 80. In some embodiments, proper axial registration of the flange plates on the sleeve 78 is provided by an annular rib, collar, or other protrusion(s) formed on or attached to an exterior surface of the sleeve 78. With such features, the plates can be pushed into position on the sleeves 78 until they are stopped Attorney Docket No. 027813-9033-CA00 against such features, thereby preventing possible damage to the bellows 62, bellows ferrule, or other portion of the fuel channel assembly 28 behind the flange 82.
[0050] FIG. 6 illustrates an example of the LS-SPIRT 74 in greater detail.
The illustrated LS-SPIRT 74 includes a housing 86, grippers 88 and a drive mechanism 90. The drive mechanism 90 moves the housing 86 and the grippers 88 in the direction of arrow 92 with respect to the table 70 shown in HG. 4 (i.e. toward and away from the calandria 10). The grippers 88 are at least partially insertable into the bores 84 of the LSAs 76, and can include at least one axially adjustable shoe, pin, wedge, or other component that selectively engages the inside surface of the bores 84 of the LSAs 76 to grip the shield plug 80 of the LSAs. Suitable gripping tools are known in the art, and are not therefore described further herein.
[0051] By gripping the inside surface of a bore 84 of an LSA 76, the LS-SPIRT 74 can insert or remove the plug 80 of the LSA 76, can insert or remove the plug 80 and sleeve 78 of the LSA
with respect to a lattice tube 65 at a lattice site and/or can insert or remove the entire LSA (i.e., with the flange 82) with respect to a lattice tube 65 at a lattice site.
Operation of the LS-SPIRT
74 can be controlled by an operator either on the RTP 72 or in a remote location.
[0052] FIG. 7 illustrates the LS-SPIRT 74 engaging an LSA 76 with the LSA
76 spaced from the end shield 64 of the calandria 10. The position illustrated in FIG. 7 shows the LSA 76 prior to insertion into the lattice tube 65 or after removal of the LSA 76 from the lattice tube 65. The end fittings 50 shown in FIGS. 7-9 are shown schematically.
[0053] FIG. 8 illustrates the LS-SPIRT 74 engaging the LSA 76 with the LSA
76 fully inserted into the lattice tube 65 at a lattice site. The position illustrated in FIG. 8 shows the LSA
76 after insertion into the lattice tube 65 or prior to removal of the LSA 76 from the lattice tube 65.
[0054] FIG. 9 illustrates the tube sheet 64 after a number of end fittings 50 have been removed from the reactor face, and after a number of LSAs 76 have been installed. Some embodiments of the present invention utilize one or more fasteners 94 (e.g., bolts, in the illustrated embodiment) to secure the LSAs 76 to the fuelling machine tube sheet 64. This fastener installation process can be a manual face series operation in some embodiments, and can Attorney Docket No. 027813-9033-CA00 rely upon use of the RTP 72 (with optional front extensions 96) and various tooling to facilitate access to the LSAs 76. Commercial hand tools can be used for installing the fastener 94. In some embodiments, the fasteners 94 can facilitate separation of the components of the LSAs 76, such as to permit removal of the flange 82 without disturbing the sleeve 78 and/or plug 80 of an LSA 80, or (in non-illustrated embodiments), to permit removal of the sleeve 78 and/or the plug 80 while the flange 82 remains installed. The fasteners 94 can be inserted into the bore of the respective tube sheet 64 previously occupied by the rod of the respective positioning hardware assemblies 60. To this end, apertures in the flanges 82 can permit passage of the fasteners 94, which can be threaded into the bores of the tube sheet 64. The apertures in the flanges 82 of the illustrated embodiment are unthreaded, but can be threaded in other embodiments.
[0055] Once many of the LSAs 76 of the illustrated embodiment are installed on the reactor face, the flanges 82 together create thick shielding wall (e.g., of steel) that reduces exposure to radiation fields in front of the reactor face. By way of example only, in some embodiments the flanges 82 together create a 2" thick steel wall of shielding, thereby reducing exposure to radiation fields by a factor of eight. FIG. 10 shows all of the LSAs 76 installed on a reactor face.
One or more of the LSAs 76 can be removed to permit access to one or more of the lattice tubes 65 and/or the tube sheet face 64. For example, one of the plugs 80 or one of the flanges 82 can be removed while the remaining plugs 80 and flanges 82 (as well as sleeves 78) remain on the reactor 6. This permits an operator to access a specific portion of the calandria 10 without exposing the operator to an excessive amount of the radiation emitted from the calandria 10.
[0056] The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention as set forth in the appended claims.
Claims (42)
1. A method of shielding radiation from a nuclear reactor having at least a portion of an open end of a tube of a fuel channel assembly, the method comprising:
inserting a plug into the open end of the tube;
sealing the plug within the tube against passage of gas along the tube and past the plug;
and installing a flange about at least one of the open end of the tube and the plug, wherein the flange substantially surrounds the at least one of the open end of the tube and the plug.
inserting a plug into the open end of the tube;
sealing the plug within the tube against passage of gas along the tube and past the plug;
and installing a flange about at least one of the open end of the tube and the plug, wherein the flange substantially surrounds the at least one of the open end of the tube and the plug.
2. The method of claim 1, further comprising installing a sleeve into the open end of the tube, wherein inserting the plug into the open end of the tube comprises inserting the plug into the sleeve.
3. The method of claim 2, further comprising fastening the flange to an end shield with at least one fastener.
4. The method of claim 2, wherein installing the flange comprises sliding the flange on the open end of the sleeve.
5. The method of claim 2, further comprising receiving the sleeve within a portion of the tube in axial alignment with an aperture in an end shield.
6. The method of claim 2, wherein sealing the plug comprises forming a seal between the plug and the sleeve.
7. The method of claim 2, further comprising forming a seal between the sleeve and the tube against passage of gas along the tube and past the sleeve.
8. The method of claim 1, further comprising removing the plug while keeping the flange in place after installing the flange.
9. The method of claim 1, further comprising removing the plug while keeping the sleeve in place after installing the flange.
10. The method of claim 1, wherein installing the flange comprises positioning the flange to cover and shield a portion of a face of the nuclear reactor.
11. The method of claim 10, further comprising repeating the inserting, sealing, and installing steps with multiple adjacent fuel channel assemblies, wherein installing the flange in at least some of the installing steps comprises orienting at least one side of the flange with at least one side of a flange corresponding to an adjacent fuel channel assembly.
12. The method of claim 1, further comprising maintaining a vacuum in the tube with the plug.
13. A method of installing a shield on a nuclear reactor having a plurality of fuel channel tubes, the method comprising:
inserting a first plug into an end of a first one of the fuel channel tubes;
coupling a first flange to the first one of the fuel channel tubes;
inserting a second plug into an end of a second one of the fuel channel tubes;
coupling a second flange to the end of the second one of the fuel channel tubes;
positioning the first flange immediately adjacent the second flange; and shielding radiation from the nuclear reactor with the first and second plugs and with the first and second flanges.
inserting a first plug into an end of a first one of the fuel channel tubes;
coupling a first flange to the first one of the fuel channel tubes;
inserting a second plug into an end of a second one of the fuel channel tubes;
coupling a second flange to the end of the second one of the fuel channel tubes;
positioning the first flange immediately adjacent the second flange; and shielding radiation from the nuclear reactor with the first and second plugs and with the first and second flanges.
14. The method of claim 13, further comprising coupling the first flange to a tube sheet with a first fastener.
15. The method of claim 13, further comprising removing the first plug without removal of the first flange to permit access to an interior of the first fuel channel tube.
16. The method of claim 13, further comprising removing the first flange without removal of the first plug to permit access to the tube sheet.
17. The method of claim 13, further comprising:
inserting a first sleeve into the first fuel channel tube; and positioning the first sleeve between the first plug and the first fuel channel tube.
inserting a first sleeve into the first fuel channel tube; and positioning the first sleeve between the first plug and the first fuel channel tube.
18. The method of claim 17, wherein coupling the first flange to the first fuel channel tube comprises coupling the first flange to the first sleeve.
19. The method of claim 17, further comprising forming a seal between the first sleeve and the first fuel channel tube.
20. The method of claim 17, further comprising forming a seal between the first sleeve and the first plug.
21. The method of claim 13, further comprising:
releasably mating an end of the first plug with an end of an insertion tool;
and inserting the first plug into the first tube with the insertion tool.
releasably mating an end of the first plug with an end of an insertion tool;
and inserting the first plug into the first tube with the insertion tool.
22. The method of claim 13, further comprising:
extending the first plug through an aperture in a tube sheet; and positioning the first plug to be simultaneously within the aperture in the tube sheet and within the first sleeve.
extending the first plug through an aperture in a tube sheet; and positioning the first plug to be simultaneously within the aperture in the tube sheet and within the first sleeve.
23. The method of claim 13, further comprising removing one plate of the first flange from at least one other plate of the first flange.
24. A modular shield assembly for shielding radiation from a nuclear reactor having a tube sheet defining a plurality of apertures and a plurality of fuel channel tubes each extending through a respective one of the plurality of apertures in the tube sheet, the assembly comprising:
a plurality of discrete shields, each shield including a sleeve insertable into an end of one of the plurality of fuel channel tubes, a plug insertable into the end of the one of the plurality of fuel channel tubes, and a flange couplable to the one of the plurality of fuel channel tubes;
wherein at least one of the plug and the flange is removable from the corresponding fuel channel tube without requiring removal of adjacent shields; and wherein the shields collectively define a substantially continuous wall covering at least a portion of the tube sheet to shield radiation from the nuclear reactor.
a plurality of discrete shields, each shield including a sleeve insertable into an end of one of the plurality of fuel channel tubes, a plug insertable into the end of the one of the plurality of fuel channel tubes, and a flange couplable to the one of the plurality of fuel channel tubes;
wherein at least one of the plug and the flange is removable from the corresponding fuel channel tube without requiring removal of adjacent shields; and wherein the shields collectively define a substantially continuous wall covering at least a portion of the tube sheet to shield radiation from the nuclear reactor.
25. The assembly of claim 24, wherein each of the plugs is separately removable from the respective one of the fuel channel tubes.
26. The assembly of claim 24, wherein each of the flanges is separately removable from the respective one of the fuel channel tubes.
27. The assembly of claim 24, further comprising a plurality of fasteners extending through respective apertures in the flanges and into respective holes in the tube sheet.
28. The assembly of claim 24, wherein each of the flanges is substantially square and includes an aperture through which a respective one of the sleeves extends.
29. The assembly of claim 24, wherein:
the flanges collectively form a wall spaced from the tube sheet;
the wall defines apertures extending therethrough; and the apertures in the wall are substantially aligned with the apertures in the tube sheet.
the flanges collectively form a wall spaced from the tube sheet;
the wall defines apertures extending therethrough; and the apertures in the wall are substantially aligned with the apertures in the tube sheet.
30. The assembly of claim 24, wherein each plug extends into a respective aperture in the tube sheet and into a respective sleeve.
31. The assembly of claim 24, wherein each sleeve forms a gas-tight seal within a respective fuel channel tube in which the sleeve is received.
32. The assembly of claim 24, wherein each plug forms a gas-tight seal within a respective sleeve in which the plug is received.
33. The assembly of claim 24, wherein the plurality of discrete shields seal the fuel channel tubes to maintain a substantial vacuum inside the fuel channel tubes.
34. The assembly of claim 33, wherein the substantial vacuum inhibits escape of radioactive particles from the fuel channel tubes when the discrete shields are removed from the fuel channel tubes.
35. A modular shield assembly for shielding radiation from a nuclear reactor having a tube sheet defining a plurality of apertures and a plurality of fuel channel tubes each extending through a respective one of the plurality of apertures in the tube sheet, the assembly comprising:
a sleeve insertable into an end of one of the plurality of fuel channel tubes, the sleeve extending through one of the apertures in the tube sheet;
a plug insertable into the end of the one of the plurality of fuel channel tubes, the plug extending through the one of the apertures in the tube sheet and located within the sleeve, wherein the plug forms a shield to block radiation within the one of the plurality of fuel channel tubes from escaping to atmosphere; and a flange releasably couplable to the one of the plurality of fuel channel tubes to substantially surround at least one of the sleeve and the plug in a position shielding radiation from the nuclear reactor escaping to atmosphere.
a sleeve insertable into an end of one of the plurality of fuel channel tubes, the sleeve extending through one of the apertures in the tube sheet;
a plug insertable into the end of the one of the plurality of fuel channel tubes, the plug extending through the one of the apertures in the tube sheet and located within the sleeve, wherein the plug forms a shield to block radiation within the one of the plurality of fuel channel tubes from escaping to atmosphere; and a flange releasably couplable to the one of the plurality of fuel channel tubes to substantially surround at least one of the sleeve and the plug in a position shielding radiation from the nuclear reactor escaping to atmosphere.
36. The assembly of claim 35, wherein the sleeve and the plug are located within the flange.
37. The assembly of claim 35, wherein the plug and flange are independently removable from the one of the plurality of fuel channel tubes.
38. The assembly of claim 37, wherein removal of the plug provides access into the one of the plurality of fuel channel tubes.
39. The assembly of claim 37, wherein removal of the flange provides access to the tube sheet.
40. The assembly of claim 35, further comprising a fastener adapted to extend through an aperture in the flange and into a hole in the tube sheet to couple the flange to the tube sheet.
41. The assembly of claim 35, wherein the flange is substantially square and defines a flange aperture substantially the same size as the one of the plurality of apertures in the tube sheet.
42. The assembly of claim 35, wherein in at least one position of the plug within the sleeve, the plug is provided with a gas-tight seal within the sleeve.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US201161433325P | 2011-01-17 | 2011-01-17 | |
| US61/433,325 | 2011-01-17 |
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| Publication Number | Publication Date |
|---|---|
| CA2766586A1 CA2766586A1 (en) | 2012-07-17 |
| CA2766586C true CA2766586C (en) | 2018-03-06 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2766586A Active CA2766586C (en) | 2011-01-17 | 2012-01-16 | Nuclear reactor lattice tube plug insert and method |
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| Country | Link |
|---|---|
| CA (1) | CA2766586C (en) |
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- 2012-01-16 CA CA2766586A patent/CA2766586C/en active Active
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| CA2766586A1 (en) | 2012-07-17 |
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