Tool for cutting and removing thimbles from nuclear reactor and method of using same

Abstract

A method and cutting tool for cutting and removing a thimble from a nuclear reactor are provided. The method comprises providing a cutting tool having a cutting member and at least one radiation shield configured to overlap with an aperture defined by the thimble. The radiation shield defines an area greater than or equal to a cross-sectional area of the aperture. The cutting tool is inserted through a containment wall and the radiation shield is overlapped with the aperture of the thimble such that the radiation shield overlaps the entire cross-sectional area of the aperture when viewed along a longitudinal axis of the thimble. The thimble is cut at a first location adjacent to the calandria shell to decouple the thimble from the calandria shell; and at a second location to decouple the thimble from the containment wall. The thimble is removed through a penetration in the containment wall.

Description

TOOL FOR CUTTING AND REMOVING THIMBLES FROM NUCLEAR REACTOR AND METHOD OF USING SAMECROSS REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

[0001] The present application claims priority to U.S. provisional patent application no. 63 / 623,950 filed on January 23, 2024, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The disclosure relates generally to decommissioning a nuclear reactor, and more particularly to removing thimbles of a calandria at end of life.BACKGROUND

[0003] A nuclear reactor has a limited operational life. For example, second generation CANDUTM-type reactors (“CANada Deuterium Uranium”) are designed to operate for approximately 25 to 30 years. After this time, the nuclear reactor may in some instances be decommissioned. Nuclear reactor decommissioning 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. The removal process can also include removing closure plugs and positioning hardware assemblies, disconnecting feeder assemblies, severing bellows, removing end fittings, releasing and removing calandria tube inserts, severing and removing pressure tubes, removing calandria tube, and removing the calandria. Many of the components that are removed may be radioactive and require special handling.SUMMARY

[0004] In one aspect, the disclosure describes a method of cutting and removing a thimble from a nuclear reactor, the thimble coupled to a calandria shell and a containment wall of the nuclear reactor, the method comprising: providing a cutting tool having a cutting member and at least one radiation shield configured to overlap with an aperture defined by the thimble, the radiation shield defining a plane, the radiation shield having an area greater than or equal to a cross-sectional area of the aperture; inserting a cutting tool through the containment wall; overlapping the at least one radiation shieldwith the aperture of the thimble, the at least one radiation shield overlapping the entire cross-sectional area of the aperture when viewed along a longitudinal axis of the thimble; cutting the thimble at a first location adjacent to the calandria shell to decouple the thimble from the calandria shell; cutting the thimble at a second location to decouple the thimble from the containment wall; removing the thimble through a penetration in the containment wall.

[0005] In an embodiment, the containment wall is an reactivity mechanism deck or an outer wall of the nuclear reactor.

[0006] In an embodiment, the cutting tool is inserted through the inner diameter of the thimble.

[0007] In an embodiment, the cutting tool is inserted through a gap defined between an external diameter of the thimble and the containment wall.

[0008] In an embodiment, the cutting tool is inserted through lattice tube of the nuclear reactor.

[0009] In an embodiment, the at least one radiation shield comprises a proximal radiation shield and at least one distal radiation shield, the proximal radiation shield configured to overlap with the aperture defined by the thimble, and the at least one distal radiation shield configured for insertion through the aperture. In another embodiment, the at least one distal radiation shield about equal to the inner diameter of the thimble. In another embodiment, the at least one distal radiation shield is configured to insertion into the inner diameter of the thimble.

[0010] In an embodiment, the thimble is an ion chamber thimble, an liquid injection shutdown unit thimble, an horizontal flux detector thimble, viewing port assembly thimble, shut-off unit thimble, vertical flux detector thimble, liquid zone control unit thimble, control absorber units thimble, or an adjuster unit thimble.

[0011] In an embodiment, the containment wall defines an inner volume of the nuclear reactor, and the method comprises maintaining the inner volume at vacuum pressure to mitigate against dust and debris from cutting to migrate outside calandria shell.

[0012] In an embodiment, the at least one radiation shield sealable couples to the containment wall or the thimble.

[0013] Embodiments may include combinations of the above features.

[0014] In another aspect, the disclosure describes a cutting tool for cutting a thimble of a nuclear reactor, the cutting tool comprising: a support member; a cutting member coupled to the support member; and at least one radiation shield coupled to the support member, the at least one radiation shield configured to overlap with an aperture defined by a thimble, the radiation shield defining a plane and having an area greater than or equal to a cross-sectional area of the aperture defined by the thimble.

[0015] In an embodiment, the cutting tool comprises at least one camera coupled to the support member for recording visual image data of the cutting member and / or the thimble.

[0016] In an embodiment, the at least one radiation shield is configured to sealable couple to the thimble.

[0017] In an embodiment, the support member and the cutting member are configured to be inserted into the inner diameter of the thimble.

[0018] In an embodiment, the support member and the cutting member are configured to be inserted in a penetration between the thimble and a vault or reactivity mechanisms deck of the nuclear reactor.

[0019] In an embodiment, the cutting member is an internal diameter saw, an outer diameter tubing cutter, or a cutting blade.

[0020] In an embodiment, the the at least one radiation shield comprises a proximal radiation shield and at least one distal radiation shield, the proximal radiation shield configured to overlap with the aperture defined by the thimble, and the at least one distal radiation shield configured for insertion through the aperture.

[0021] Embodiments may include combinations of the above features.

[0022] Further details of these and other aspects of the subject matter of this application will be apparent from the detailed description included below and the drawings.DESCRIPTION OF THE DRAWINGS

[0023] Reference is now made to the accompanying drawings, in which:

[0024] FIG. 1 is a perspective view of a CANDU™-type reactor.

[0025] FIG. 2A is a cutaway view of a CANDUTM-type nuclear reactor fuel channel assembly.

[0026] FIG. 2B is a perspective view of a work table and a calandria tube insert removal tool adjacent a face of the CANDU™-type reactor, according to an embodiment.

[0027] FIG. 2C is a cut away elevation view CANDUTM-type reactor, according to an embodiment.

[0028] FIG. 3 is a side cut away view of an example ion chamber thimble.

[0029] FIG. 4 is a side cut away view of an example liquid injection shutdown unit thimble.

[0030] FIG. 5 is an enlarged side cut away view of an example horizontal flux detector thimble coupled to a calandria shell.

[0031] FIG. 6 is a side cut away view of an example horizontal flux detector thimble.

[0032] FIG. 7 is a side cut away view of an example viewing port assembly thimble.

[0033] FIG. 8 is a side cut away view of an example shut-off unit thimble.

[0034] FIG. 9 is a side cut away view of an example vertical flux detector thimble.

[0035] FIG. 10 is a side cut away view of an example liquid zone control unit thimble.

[0036] FIG. 11 is a side cut away view of an example control absorber unit thimble.

[0037] FIG. 12 is a side cut away view of an example adjuster unit thimble.

[0038] FIG. 13A and 13B are side cut away views of example cutting tool inserted into a thimble according to an embodiment. FIG. 13C is a plan view of the cutting tools of FIG. 13A and 13B along the line R-R.

[0039] FIG. 14 is a schematic diagram of an example method of cutting and removing a thimble from a nuclear reactor.DETAILED DESCRIPTION

[0040] Before any embodiments are explained in detail, it is to be understood that the disclosure 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 disclosure is capable of other embodiments and of being practiced or of being carried out in various ways.

[0041] DEFINITIONS

[0042] Although terms such as “maximize”, “minimize” and “optimize” may be used in the present disclosure, it should be understood that such term may be used to refer to improvements, tuning and refinements which may not be strictly limited to maximal, minimal or optimal.

[0043] The term “connected” or "coupled to" may include both direct coupling (in which two elements that are coupled to each other and contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0044] The term “substantially” as used herein may be applied to modify any quantitative representation which could permissibly vary without resulting in a change in the basic function to which it is related.

[0045] Terms such as "up to", "at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

[0046] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and / or" means any one of the items, any combination of the items, or all of the items with which this term is associated.

[0047] The term "about" can refer to a variation of± 5%, ± 10%, ± 20%, or± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" can include one or two integers greater than and / or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term "about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0048] The term “penetration” refers to an opening defined by a vault wall of a nuclear reactor, or reactivity mechanisms deck, through which a thimble extends.

[0049] Aspects of various embodiments are described through reference to the drawings.

[0050] 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. Although aspects are described with particular reference to the CANDUTM-type reactor 6 for convenience, the disclosure is not limited to CANDU™- type reactors, and may be useful outside this particular field as well. A generally cylindrical vessel, known as the calandria vessel 10 of the CANDUTM-type reactor 6, contains a heavy-water moderator. The calandria vessel 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 (referred to herein as bores 19) 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 vessel 10 from the first end 22 to the second end 24.

[0051] As in the illustrated embodiment of Figs. 1 and 2A, 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 bores 19 (i.e., in the tube sheet 18 and the end shield 64, respectively).

[0052] FIG. 2A is a cutaway view of one fuel channel assembly 28 of the reactor core illustrated in FIG. 1. As illustrated in FIG. 2A, each fuel channel assembly 28includes 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 bores 19 in the tube sheets 18. In some embodiments, a rolled joint insert, for example calandria tube insert 34, is used to secure the CT 32 to the tube sheet 18 within the bores 19. 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. One or more annulus spacers or garter springs 48 are disposed between the CT 32 and PT 36. The annulus spacers 48 maintain the gap between the PT 36 and the corresponding CT 32, while allowing passage of annulus gas through and around the annulus spacers 48.

[0053] As also shown in FIG. 2A, each end of each fuel channel assembly 28 is provided with an end fitting assembly 50 located outside of the corresponding tube sheet 18. Each end fitting assembly 50 includes an end fitting body 57 and an end fitting liner 58. At the terminal end of each end fitting assembly 50 is a closure plug 52. Each end fitting assembly 50 also includes a feeder assembly 54. The feeder assemblies 54 feed reactor coolant into or remove reactor coolant from the PTs 36 via feeder tubes 59 (FIG. 1). 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. 2A, the feeder assemblies 54 can be attached to the end fitting assemblies 50 using a coupling assembly 56 including a number of screws, washers, seals, and / or other types of connectors. The lattice tube 65 (described above) encases the connection between the end fitting assembly 50 and the PT 36 containing the fuel assemblies 40. Shielding ball bearings 66 and cooling water surround the exterior of the lattice tubes 65, which provides additional radiation shielding.

[0054] A positioning hardware assembly 60 and bellows 62 are also coupled to each end fitting assembly 50. The bellows 62 allows the fuel channel assemblies 28 tomove 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 configuration that fixes the axial position, or an unlocked configuration. The positioning hardware assemblies 60 are also coupled to the end shield 64. The illustrated 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. Again, it should be understood that although a CANDUTM-type reactor is illustrated in FIGS. 1-2A, the invention may also apply to other types of reactors, including reactors having components that are similar to those illustrated in FIGS. 1-2A.

[0055] FIG. 2B illustrates one embodiment of a heavy work table (“HWT”) 96 installed on a tooling platform (“RTP”) 95 adjacent the end 24 of the nuclear reactor. A similar HWT can be installed adjacent the end 22 of the nuclear reactor. The HWT 96 and any tools mounted on the HWT are controlled by a control station (not shown).

[0056] FIG. 2C illustrates a cross-sectional view of a calandria vessel 10 inside calandria vault 11. There are several pipes that are connected to Calandria vessel 10 on the outside, including: ion chambers 300, horizontal thimbles 88 (e.g. thimbles for horizontal flux detector units), vertical thimbles 77 (e.g. thimbles of control absorber units, and control / vertical flux detector units), main moderator pipes 20, and moderator discharge pipes 21.

[0057] Vertical thimbles 77 may extend from the top calandria vessel 10 up through reactivity mechanism deck 30 and may be surrounded by the vault light water during operation. Vertical thimbles 77 may be welded in precise locations to nozzles of calandria shell 14 and may be vertically free to slide in bearings positioning them in the reactivity mechanism deck. Metal bellows 31a are welded to thimbles 77 and reactivity mechanism deck 30 in to maintain a seal while permitting free vertical movement to accommodate differential thermal expansion between thimbles 77 and deck 30.

[0058] Horizontal thimbles 88 may extend from through a wall of vault 11 to the nozzles of calandria shell 14. Like their vertical counterparts, horizontal thimbles 88 are supported by bearings in openings defined by the vault wall and are sealed by flexiblemetallic bellows 31 b. An opening defined by the vault wall, or reactivity mechanisms deck, through which a thimble extend is also referred to herein as a “Penetration”.

[0059] When cutting vertical thimbles 77 or horizontal thimbles 88 thimbles several options are available. In an embodiment, thimbles 77, 88 may be cut from calandria shell 14 and carefully removed from inside calandria shell 14. In another embodiment, thimbles 77, 99 may be cut from calandria shell 14 while leaving the remaining portion inside calandria shell 14. In another embodiment, thimbles 77, 88 may be cut from calandria shell 14, from deck 30, while leaving portions of thimbles 77, 88 inside the vessel and inside Calandria Vault.

[0060] To remove vertical thimbles 77 or horizontal thimbles 88 from its channel in vault 11 , the cutting tool may not pass through its respective vault 11 penetration. Some thimbles may be have large internal diameters (ID) enough to insert an off the shelve ID pipe cutter; however, some thimbles have smaller diameter and require special cutter tooling. Example small ID thimbles include horizontal flux detector thimbles and vertical flux detector unit thimbles.

[0061] Horizontal thimbles 88 may comprise an ion chamber thimble 300 shown in FIG. 3. Example methods for removing ion chamber thimble 300 from a calandria vessel 10 is described below.

[0062] In an embodiment, access tube 301 of ion chamber thimble 300 may be cut, e.g. by inserting a pipe cutter through the ion chamber penetration 302. The cut may be performed on access tube 301 close to, e.g. adjacent to, nozzle 14a for shell 14 shown as line A-A. Alternatively, cut along line A-A may be performed from inside vault 11 when vault 11 is open.

[0063] Ion Chamber 300 may be removed via penetration 302 as described below. In an example, to remove ion chamber 300 from penetration 302, protective sleeve 303 may be removed to allow access to bellows 31 b. Bellows 31b may be cut along line B-B close to, e.g. adjacent to, an exterior wall 11a of vault 11. Subsequently, access tube 301 can be removed by sliding it out of ion chamber penetration tube 302.

[0064] Horizontal thimbles 88 may comprise a liquid injection shutdown unit thimble 400 shown in FIG. 4 which may be cut using one of several methods. In anembodiment, liquid injection shutdown unit 400 may be cut at the straight section of the tube close to, e.g. adjacent to, calandria shell 14 along line C-C using an internal pipe cutter inserted through the inner diameter of the tube. As shown, cut along line C-C may be proximate or adjacent to a nozzle 14b of calandria shell 14. The liquid injection shutdown unit thimble 400 may be removed via penetration 402 as described below. In another embodiment, injection tube 401 of liquid injection shutdown unit thimble 400 may be cut along line C-C from the outside by extending a cutting tool through penetration 402 along an outside of injection tube 401. In another embodiment, injection tube 401 of liquid injection shutdown unit thimble 400 may be cut from the inside of calandria shell 14 using an extendable robot arm inserted into the calandria shell, e.g. through another penetration in vault 11. During cutting, the inner volume of vault 11 may be maintained at vacuum pressure (a pressure lower than pressure surrounding vault 11) to mitigate against dust and debris from cutting to migrate outside calandria shell 14. In an example, vault 11 may be coupled to an active ventilation system to reduce the pressure inside vault 11. An example active ventilation system is described in U.S. Provisional Patent Application No. 63 / 627,397, the entire contents of which are hereby incorporated by reference.

[0065] Liquid injection shutdown unit thimble 400 may be removed via penetration402 as described below. In an example, to remove liquid injection shutdown unit 400 from penetration 402, protective sleeve 403 may be removed to allow access bellows 41b and flange 41 f. As shown in FIG. 4, bellows 41b and injection tube may be coupled to end wall 64 by flange 41 f. Flange 41 f may be cut along line D-D close to an exterior wall 64. Subsequently, injection tube 401 can be removed by sliding it out of penetration 402.

[0066] Horizontal thimbles 88 may comprise a horizontal flux detector thimble 500 shown in FIG. 5 which may be cut using one of several methods. In an embodiment, horizontal flux detector thimble 500 may be separated from calandria 14 by cutting along line E-E of calandria 14 adjacent to where horizontal flux detector thimble 500 couples to calandria. In an example, the cut along line E-E may be a circumferential cut performed around a shroud pipe 551 of horizontal flux detector thimble 500. The cut along line E-E may be performed by inserting a cutting tool through an adjacent thimble penetration, e.g. penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After horizontal flux detector thimble 500 is separated from calandra 14, thimble 500 may then be removed via calandria vault penetration 502as described below. In another embodiment, as shown in FIG. 6, horizontal flux detector thimble 500 may be cut along line F-F proximate or adjacent to nozzle 14c of calandria shell 14.

[0067] Horizontal flux detector thimble 500 may be removed via penetration 502 as described below. In an example, to remove horizontal flux detector thimble 500 from penetration 502, protective sleeve 503 may be removed to allow access to bellows 41b and flange 51 f. As shown in FIG. 6, bellows 51b and guide tube 501 may be coupled to end wall 64 by flange 51 f. Flange 41 f may be cut along line Z-Z close to an exterior wall 64. Subsequently, guide tube 501 can be removed by sliding it out of penetration 502. After the cut along line Z-Z, thimble 500 may be pulled through penetration 502 to remove thimble 500 from calandria vessel 10. Alternatively, thimble 500 may be pushed back into the Calandria shell 14 to removal at a later time.

[0068] Vertical thimbles 77 may comprise a viewing port assembly thimble 700 shown in FIG. 7 which may be cut using one of several methods. In an embodiment, viewing port assembly thimble 700 may be cut at straight section of viewing tube 701 close to calandria shell 14 along line F-F using an internal pipe cutter. To access internal diameter of tube 701 , protective cover 703 and shield plug 704 may be removed from viewing port assembly thimble 700 to allow access to tube 701 . In another embodiment, cut along line F-F may be performed by inserting a cutting tool through an adjacent thimble penetration, e.g. penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After viewing port assembly thimble 700 is separated from calandra shell 14, thimble 700 may then be removed via calandria vault penetration 702 as described below.

[0069] Viewing port assembly thimble 700 may be removed via penetration 702 as described below. In an example, to remove viewing port assembly thimble 700 from penetration 702, protective cover 703 may be removed to allow access bellows 71 b and insert sleeve 71s. As shown in FIG. 7, bellows 71b and viewing tube 701 may be coupled to reactivity mechanism deck 30 by insert sleeve 71s. Sleeve 71s may be cut along line G-G close to reactivity mechanism deck 30. In an example, cut G-G may be a circumferential cut. Subsequently, tube 701 can be removed by sliding it out of penetration 702, e.g. by pulling it through penetration 702 to remove viewing port assembly thimble 700 from calandria vessel 10.

[0070] Vertical thimbles 77 may comprise a shut-off unit thimble 800 shown in FIG. 8 which may be cut using one of several methods. In an embodiment, shut-off unit thimble 800 may be cut at straight section of shut-off tube 801 close to calandria shell 14 along line H-H using an internal pipe cutter. To access internal diameter of tube 801 , drive mechanism assembly 803 may be removed from shut-off unit thimble 800 to allow access to tube 801. In another embodiment, cut along line H-H may be performed by inserting a cutting tool through an adjacent thimble penetration, e.g. penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After shut-off unit thimble 800 is separated from calandra shell 14, thimble 800 may then be removed via calandria vault penetration 802 as described below.

[0071] Shut-Off unit thimble 800 may be removed via penetration 802 as described below. In an example, to remove shut-off unit thimble 800 from penetration 802, drive mechanism assembly 803 may be removed to allow access to insert sleeve 81 s. Reactivity mechanisms deck shielding collar may also be cut and removed to access insert sleeve 81s. As shown in FIG. 8, tube 801 may be coupled to reactivity mechanism deck 30 by insert sleeve 81s. Sleeve 81s may be cut along line l-l close to, e.g. adjacent to, reactivity mechanism deck 30. In an example, cut l-l may be a circumferential cut. Subsequently, tube 801 can be removed by sliding it out of penetration 802, e.g. by pulling it through penetration 802 to remove shut-off unit thimble 800 from calandria vessel 10. In an embodiment, shut-off unit thimble 800, including tube 801 , bellows 81 b, and sleeve 81s may be lifted from penetration 802.

[0072] Vertical thimbles 77 may comprise a vertical flux detector thimble 900 shown in FIG. 9 which may be cut using one of several methods. In an embodiment, vertical flux detector thimble 900 may be cut at straight section of show-off guide tube 901 close to calandria shell 14 along line J-J using a pipe cutter. Pipe cutter may be inserted through an adjacent thimble penetration, e.g. penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After vertical flux detector thimble 900 is separated from calandra shell 14, thimble 900 may then be removed via calandria vault penetration 902 as described below.

[0073] Vertical flux detector thimble 900 may be removed via penetration 902 as described below. In an example, to remove vertical flux detector thimble 900 from penetration 902, to insert sleeve 91s may be cut. As shown in FIG. 9, tube 901 may becoupled to reactivity mechanism deck 30 by insert sleeve 91s. Sleeve 91s may be cut along line K-K close to reactivity mechanism deck 30. In an example, cut K-K may be a circumferential cut. Subsequently, tube 901 can be removed by sliding it out of penetration 802, e.g. by pulling it through penetration 902 to remove shut-off unit thimble900 from calandria vessel 10. In an embodiment, shut-off unit thimble 900, including tube 901 , bellows 91 b, and sleeve 91s may be lifted from penetration 902.

[0074] Vertical thimbles 77 may comprise a liquid zone control unit thimble 1000 shown in FIG. 10 which may be cut using one of several methods. In an embodiment, liquid zone control units thimble 1000 may be cut at straight section of liquid zone tube1001 close to calandria shell 14 along line L-L using an internal pipe cutter. To access internal diameter of tube 1001 , shielding collar 1003 may be removed from liquid zone control units thimble 1000 to allow access to tube 1001. In an embodiment, pipe cutter may be inserted through an adjacent thimble penetration, e.g. penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After liquid zone control units thimble 1000 is separated from calandra shell 14, thimble 1000 may then be removed via calandria vault penetration 902 as described below.

[0075] Liquid zone control unit thimble 1000 may be removed via penetration1002 as described below. In an example, to remove liquid zone control units thimble 1000 from penetration 1002, to insert sleeve 101s may be cut. As shown in FIG. 10, tube901 may be coupled to reactivity mechanism deck 30 by insert sleeve 101s. Sleeve 101s may be cut along line M-M close to reactivity mechanism deck 30. In an example, cut M- M may be a circumferential cut. Subsequently, tube 1001 can be removed by sliding it out of penetration 1002, e.g. by pulling it through penetration 1002 to remove liquid zone control unit 1000 from calandria vessel 10. In an embodiment, liquid zone control unit thimble 1000, including tube 1001 , bellows 101b, and sleeve 101s may be lifted from penetration 1002.

[0076] Vertical thimbles 77 may comprise a control absorber units thimble 1100 shown in FIG. 11 which may be cut using one of several methods. In an embodiment, control absorber units thimble 1100 may be cut at straight section of control absorber tube 1101 close to calandria shell 14 along line 0-0 using an internal pipe cutter. In an embodiment, pipe cutter may be inserted through an adjacent thimble penetration, e.g.penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After control absorber units thimble 1100 is separated from calandra shell 14, thimble 1100 may then be removed via calandria vault penetration 1102 as described below.

[0077] Control absorber units thimble 1100 may be removed via penetration 1102 as described below. In an example, to remove control absorber units thimble 1100 from penetration 1102, insert sleeve 111s and / or shielding collar 1103 may be cut. As shown in FIG. 11 , tube 1101 may be coupled to reactivity mechanism deck 30 by insert sleeve 111s. Sleeve 111s and / or shielding collar 1103 may be cut along line 0-0 close to reactivity mechanism deck 30. In an example, cut 0-0 may be a circumferential cut. Subsequently, tube 1101 can be removed by sliding it out of penetration 1102, e.g. by pulling it through penetration 1102 to remove control absorber units thimble 1100 from calandria vessel 10. In an embodiment, control absorber units thimble 1100, including tube 1101 , bellows 111 b, and sleeve 111s may be lifted from penetration 1102.

[0078] Vertical thimbles 77 may comprise an adjuster unit thimble 1200 shown in FIG. 12 which may be cut using one of several methods. In an embodiment, adjuster unit thimble 1200 may be cut at straight section of control absorber tube 1201 close to calandria shell 14 along line P-P using an internal pipe cutter, e.g. above a belled end at the straight section shown in FIG. 12. In an embodiment, pipe cutter may be inserted through an adjacent thimble penetration, e.g. penetration 402 after liquid injection shutdown unit 400 is removed, or through a lattice tube 65 into calandria vessel 10. After control adjuster unit thimble 1200 is separated from calandra shell 14, thimble 1200 may then be removed via calandria vault penetration 1202 as described below.

[0079] Adjuster unit thimble may be removed via penetration 1202 as described below. In an example, to remove adjuster unit thimble 1200 from penetration 1202, insert sleeve 121s and / or shielding collar 1203 may be cut. As shown in FIG. 12, tube 1201 may be coupled to reactivity mechanism deck 30 by insert sleeve 121s. Sleeve 121s and / or shielding collar 1203 may be cut along line Q-Q close to reactivity mechanism deck 30. In an example, cut Q-Q may be a circumferential cut. Subsequently, tube 1201 can be removed by sliding it out of penetration 1202, e.g. by pulling it through penetration 1202 to remove control absorber units thimble 1200 from calandria vessel 10. In anembodiment, control absorber units thimble 1200, including tube 1201 , bellows 121 b, and sleeve 121s may be lifted from penetration 1202.

[0080] FIGs. 13A-13B illustrates an example cutting tool 1300 for cutting a thimble of a nuclear reactor, e.g. thimbles described above according to this disclosure. Cutting tool 1300 may comprise a support member 1301 and a cutting member 1302 coupled to support member 1301. In an embodiment, cutting member 1302 be a saw, such as an internal diameter saw, an outer diameter tubing cutter, cutting blade, or other cutting member suitable for cutting a thimble. As shown in FIG. 13A, cutting member 1302 is an internal diameter saw inserted into the internal diameter of thimble 1304. As shown in FIG. 13B, cutting member 1302 is an outer diameter tubing cutting inserted in the penetration between thimble 1304 and vault 11 or alternatively the reactivity mechanisms deck of the nuclear reactor. Cutting member 1302 or support member 1301 may be coupled to a motor for rotating cutting member 1302 about a longitudinal axis of support member 1301 to cut example thimble 1304. Thimble 1304 may any thimble of a nuclear reactor such as vertical thimbles 77 and horizontal thimble 88 described above according to this disclosure. At least one radiation shield 1303 may be coupled to support member 1301. Radiation shield 1303 may comprise at least one of proximal shield 1303A and distal shield(s) 1303B. Distal radiation shield(s) 1303B may be configured for insertion into the inner diameter of the thimble 1304. The at least one distal radiation shield 1303B may be about equal to the inner diameter of the thimble. In an embodiment, the at least one radiation shield 1303 may comprise a proximal radiation shield 1303A and at least one distal radiation shield 1303B, where the proximal radiation shield 1303A may be configured to overlap with aperture 1306 defined by the thimble 1304, and the at least one distal radiation shield 1303B may be configured for insertion through aperture 1306. A plurality of distal radiation shields may be provided which may be spaced a distance apart to define a chamber between the radiation shield for mitigating against radioactive dust migration out of the nuclear reactor. In the non-limiting example illustrated in FIG. 13A and 13B, seven radiation shields are provided; however, other embodiments may comprise more or less radiation shield(s). The at least one radiation shield 1303, e.g. proximal shield 1303A, may be configured to overlap with an aperture of thimble when view along a longitudinal axis of the thimble as illustrated as line R-R, the radiation shield defining a plane S-S overlapping with the cross-sectional area of thethimble. At least one radiation shield 1303 has an area greater than or equal to the cross- sectional area of aperture 1306 defined by thimble. When cutting tool 1300 is inserted into thimble 1304, radiation shield 1303 overlaps with the aperture defined by thimble 1304 and / or the protrusion defined by the vault to block radiation projecting through the aperture and protect workers in the vicinity of the thimble.

[0081] In an embodiment, at least one camera 1305 may be coupled to the support member for recording visual image data of the cutting member and / or the thimble. Camera 1305 may be positioned on either side of cutting member 1302.

[0082] In an embodiment, at least one radiation shield 1303 is configured to sealable couple to the thimble and / or a portion of the containment wall coupled to the thimble to prevent fluid communication between the inside and outside of the containment wall. As shown in FIG. 13A radiation shield 1303 may couple to the end of thimble 1304 and / or a portion of the containment wall coupled to the thimble, and / or an internal surface of thimble 1304, to stop fluid communication between the exterior of vault 11 and the open end of thimble 1304 when cut. This may stop debris from decommissioning or refurbishing operations of the nuclear reactor from leaving the shielded reactor vault.

[0083] FIG. 14 is schematic diagram illustrating an example method 1400 of cutting and removing a thimble from a nuclear reactor, e.g. a heavy water nuclear reactor. In an example, the thimble may be coupled to a calandria shell and a containment wall of the nuclear reactor. In an embodiment, the containment wall is an reactivity mechanism deck or an outer wall of the nuclear reactor. Example thimbles include an ion chamber thimble, an liquid injection shutdown unit thimble, an horizontal flux detector thimble, viewing port assembly thimble, shut-off unit thimble, vertical flux detector thimble, liquid zone control unit thimble, control absorber units thimble, and an adjuster unit thimble.

[0084] At 1402, the method comprises providing a cutting tool, e.g. cutting tool 1300 describe above, having a cutting member and at least one radiation shield configured to overlap with an aperture defined by the thimble. The radiation shield defines a plane and has an area greater than or equal to a cross-sectional area of the aperture.

[0085] At 1404, the cutting tool is inserted through the containment wall, e.g. a vault or reactivity mechanisms deck of the nuclear reactor. In an embodiment, the cutting tool is inserted through the inner diameter of the thimble, see. e.g. FIG. 13A. In anotherembodiment, the cutting tool is inserted through a gap defined between an external diameter of the thimble and the containment wall, see e.g. FIG. 13B. In another embodiment, the cutting tool may be inserted through a lattice tube of the nuclear reactor where the cutting tool is extended to a position to cut the thimble.

[0086] At 1406, the at least one radiation shield is overlapped with the aperture of the thimble. The at least one radiation shield overlaps the entire cross-sectional area of the aperture when viewed along a longitudinal axis of the thimble. In an embodiment, the at least one radiation shield sealable couples to the thimble and / or containment wall, e.g. the radiation shield may sealably couple with the inner surface of the thimble and / or containment wall to prevent fluid communication through the aperture preventing debris and / or toxic material from leaving the nuclear reactor.

[0087] At 1408, the thimble is cut at a first location adjacent to the calandria shell to decouple the thimble from the calandria shell.

[0088] At 1410, the thimble is cut at a second location to decouple the thimble from the containment wall.

[0089] At 1420, the thimble is removed through a penetration in the containment wall.

[0090] In an embodiment, the containment wall defines an inner volume of the nuclear reactor and method 1400 comprises maintaining the inner volume of the nuclear reactor, e.g. vault 11 , at vacuum pressure to prevent dust and debris generated from cutting the thimbles from migrating outside calandria shell.

[0091] In an embodiment, the at least one radiation shield comprises a proximal radiation shield and at least one distal radiation shield. The proximal radiation shield may be configured to overlap with the aperture defined by the thimble, and the at least one distal radiation shield may be configured for insertion through the aperture. In another embodiment, the at least one distal radiation shield has a diameter about equal to the inner diameter of the thimble.

[0092] In an embodiment, the at least one distal radiation shield is configured to insertion into the inner diameter of the thimble.

[0093] In an embodiment, the thimble is an ion chamber thimble, an liquid injection shutdown unit thimble, an horizontal flux detector thimble, viewing port assembly thimble, shut-off unit thimble, vertical flux detector thimble, liquid zone control unit thimble, control absorber units thimble, or an adjuster unit thimble.

[0094] In an embodiment, the at least one radiation shield sealable couples to the containment wall or the thimble.

[0095] Cutting tool 1300 and method 1400 may allow cutting thimble(s) of a nuclear reactor while the existing radiation shielding is intact. Vault 11 may be the primary shielding which is kept in place and intact to protect workers during decommissioning or refurbishment of a nuclear reactor. Radiation shielding of cutting tool 1300 may then prevent radiation from escaping the reactor that passes through openings caused by cutting thimbles of a nuclear reactor. The Radiation shielding of the cutting tool may thus enhance safety for operators work around the nuclear reactor.

[0096] Alternate embodiments

[0097] The above description is meant to be exemplary only, and one skilled in the relevant arts will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. The present disclosure may be embodied in other specific forms without departing from the subject matter of the claims. The present disclosure is intended to cover and embrace all suitable changes in technology. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. Also, the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

[0098] As can be understood, the detailed embodiments described above and illustrated are intended to be examples only. The invention is defined by the appended claims.

[0099] The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

Claims

WHAT IS CLAIMED IS:

1. A method of cutting and removing a thimble from a nuclear reactor, the thimble coupled to a calandria shell and a containment wall of the nuclear reactor, the method comprising: providing a cutting tool having a cutting member and at least one radiation shield configured to overlap with an aperture defined by the thimble, the radiation shield defining a plane, the radiation shield having an area greater than or equal to a cross-sectional area of the aperture; inserting a cutting tool through the containment wall; overlapping the at least one radiation shield with the aperture of the thimble, the at least one radiation shield overlapping the entire cross-sectional area of the aperture when viewed along a longitudinal axis of the thimble; cutting the thimble at a first location adjacent to the calandria shell to decouple the thimble from the calandria shell; cutting the thimble at a second location to decouple the thimble from the containment wall; removing the thimble through a penetration in the containment wall.

2. The method of claim 1 , wherein the containment wall is an reactivity mechanism deck or an outer wall of the nuclear reactor.

3. The method of any one of claims 1-2, wherein the cutting tool is inserted through the inner diameter of the thimble.

4. The method of any one of claims 1-2, wherein the cutting tool is inserted through a gap defined between an external diameter of the thimble and the containment wall.

5. The method of any one of claims 1-2, wherein the cutting tool is inserted through lattice tube of the nuclear reactor.

6. The method of any one of claims 1-5, wherein the at least one radiation shield comprises a proximal radiation shield and at least one distal radiation shield, the proximalradiation shield configured to overlap with the aperture defined by the thimble, and the at least one distal radiation shield configured for insertion through the aperture.

7. The method of claim 6, wherein the at least one distal radiation shield has a diameter about equal to the inner diameter of the thimble.

8. The method of claim 6 or 7, wherein the at least one distal radiation shield is configured to insertion into the inner diameter of the thimble.

9. The method of any one of claims 1-8, wherein the thimble is an ion chamber thimble, an liquid injection shutdown unit thimble, an horizontal flux detector thimble, viewing port assembly thimble, shut-off unit thimble, vertical flux detector thimble, liquid zone control unit thimble, control absorber units thimble, or an adjuster unit thimble.

10. The method of any one of claims 1-9, wherein the containment wall defines an inner volume of the nuclear reactor, and the method comprises maintaining the inner volume at vacuum pressure to mitigate against dust and debris from cutting to migrate outside calandria shell.

11. The method of any one of claims 1-Erreur ! Source du renvoi introuvable., wherein the at least one radiation shield sealable couples to the containment wall or the thimble.

12. A cutting tool for cutting a thimble of a nuclear reactor, the cutting tool comprising: a support member; a cutting member coupled to the support member; and at least one radiation shield coupled to the support member, the at least one radiation shield configured to overlap with an aperture defined by a thimble, the radiation shield defining a plane having an area greater than or equal to a cross- sectional area of the aperture defined by the thimble.

13. The cutting tool of claim 12 comprising at least one camera coupled to the support member for recording visual image data of the cutting member and / or the thimble.

14. The cutting tool of any one of claims 12-13, wherein the at least one radiation shield is configured to sealable couple to the thimble.

15. The cutting tool of any one of claims 12-14, wherein the support member and the cutting member are configured to be inserted into the inner diameter of the thimble.

16. The cutting tool of any one of claims 12-14, wherein the support member and the cutting member are configured to be inserted in a penetration between the thimble and a vault or reactivity mechanisms deck of the nuclear reactor.

17. The cutting tool of any one of claims 12-16, wherein the cutting member is an internal diameter saw, an outer diameter tubing cutter, or a cutting blade.

18. The cutting tool of any one of claims 12-17, wherein the at least one radiation shield comprises a proximal radiation shield and at least one distal radiation shield, the proximal radiation shield configured to overlap with the aperture defined by the thimble, and the at least one distal radiation shield configured for insertion through the aperture.

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