CA3066139A1 - Pressure tube-to-end fitting coupling and method of assembling nuclear reactor fuel channel assembly - Google Patents

Abstract

A nuclear reactor core comprises a calandria having a shell and a tube sheet defining an aperture, a calandria tube coupled to the tube sheet and extending into the shell, a lattice tube coupled to the tube sheet and extending away from the shell, an end fitting body positioned at least partially in the lattice tube, a pressure tube positioned at least partially in the calandria tube and have an end secured to the end fitting body; and an end fitting liner positioned at least partially in the end fitting body coaxial with the pressure tube. An end of the end fitting liner adjacent the pressure tube includes a first inner surface having a roller clearance counter bore. The counter bore provides clearance to avoid contact between a rolling tool and the end fitting assembly.

Description

2 PCT/CA2018/050765 PRESSURE TUBE-TO-END FITTING COUPLING AND
METHOD OF ASSEMBLING NUCLEAR REACTOR FUEL CHANNEL ASSEMBLY
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from US Provisional Patent Application No.
62/524,267 filed on June 23, 2017, the contents of which are hereby incorporated by reference.
FIELD
[0002] This relates to methods and systems for coupling a pressure tube to an end fitting in a nuclear reactor fuel channel assembly.
BACKGROUND

[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 significantly, as an alternative to decommissioning the reactor. 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. 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, and severing and removing pressure tubes and calandria tubes.

[0004] After the removal process is complete, an inspection and installation process is typically performed. For example, tube sheets positioned at each end of the reactor may include a plurality of bores. Each of the plurality of bores supports a fuel channel assembly that spans between the tube sheets. When a fuel channel assembly is removed, each tube sheet bore is inspected to ensure that the removal of the fuel channel assembly has not damaged the tube sheet bore and that the tube sheet bore is ready for insertion of a new fuel channel assembly.

[0005] After the tube sheets are confirmed to be in suitable condition, the calandria tubes, pressure tubes, end fittings, and other components can be re-installed into the bores. For each fuel channel assembly, part of this process involves inserting a sub-assembly consisting of an end fitting and pressure tube that has been rolled on one side of the reactor (for example, in an assembly area), inserting an end fitting body into the opposite side lattice tube, rolling the end of the pressure tube into the end fitting body, and inserting an end fitting liner into the end fitting.

[0006] Accordingly, there is a need for improved systems and methods for coupling a pressure tube to the end fitting of a fuel channel assembly without damaging the end fitting or end fitting liner.
SUMMARY

[0007] The present provides a nuclear reactor core comprising a calandria vessel having a shell and a tube sheet on an end of the shell and defining an aperture, a calandria tube coupled to the tube sheet (e.g., using a calandria insert) and extending into the annular shell, a lattice tube coupled to the tube sheet (e.g., integrally) and extending toward an exterior of the reactor core, an end fitting body positioned at least partially in the lattice tube, a pressure tube positioned at least partially in the calandria tube and have an end secured to the end fitting body, and an end fitting liner positioned at least partially in the end fitting body coaxial with the pressure tube. An end of the end fitting liner adjacent the pressure tube includes a first inner surface having a roller clearance counter bore.

[0008] The present also provides a method of securing a pressure tube to an end fitting body in a nuclear reactor core including a calandria vessel having a shell and a tube sheet on an end of the shell, a calandria tube coupled to the tube sheet and extending into the annular shell, a lattice tube coupled to the tube sheet and extending outwardly away from the reactor core, and an end fitting body positioned at least partially in the lattice tube. The method comprises inserting an inner end of an end fitting liner into an end fitting body, positioning the pressure tube inside the calandria tube with an end of the pressure tube axially overlapped with a portion of the end fitting body, introducing a rolling tool into the end fitting liner until a roller of the rolling tool is axially overlapped with the pressure tube, deforming the end of the pressure tube into the end fitting body by rotating the rolling tool and moving the roller radially outward into contact with the pressure tube, and axially overlapping (i.e., positioning to establish common axial position(s)) the roller with the inner end of the end fitting liner during the deforming step. In one embodiment, the inner surface of the inner end of the end fitting liner includes a counter bore, and the step of axially overlapping includes positioning at least a portion of the roller in the counter bore. In some embodiments, the end fitting liner includes a latch, and the step of introducing a rolling tool includes moving the latch to an unlatched position, such as by axial movement of the rolling tool.

[0009] According to an aspect, there is provided a nuclear reactor core comprising: a calandria vessel having a shell and a tube sheet on an end of the shell and the tube sheet defining an aperture; a calandria tube coupled to the tube sheet and extending into the annular shell; a lattice tube coupled to the tube sheet and extending outwardly away from the reactor core; an end fitting body positioned at least partially in the lattice tube; a pressure tube positioned at least partially in the calandria tube and having an end secured to the end fitting body; and an end fitting liner positioned at least partially in the end fitting body coaxial with the pressure tube, wherein an end of the end fitting liner adjacent the pressure tube includes a first inner surface having a counter bore.

[0010] According to another aspect, there is provided a method of securing a pressure tube to an end fitting body in a nuclear reactor core including a calandria vessel having a shell and a tube sheet on an end of the shell, a calandria tube coupled to the tube sheet and extending into the annular shell, a lattice tube coupled to the tube sheet and extending outwardly away from the reactor core, and an end fitting body positioned at least partially in the lattice tube, the method comprising:
inserting an inner end of an end fitting liner into the end fitting body; positioning the pressure tube inside the calandria tube with an end of the pressure tube axially overlapped with a portion of the end fitting body; introducing a rolling tool into the end fitting liner until a roller of the rolling tool is axially aligned with the pressure tube; deforming the end of the pressure tube into the end fitting body by rotating the rolling tool to move the roller radially outward into contact with the pressure tube; and axially aligning the roller with the inner end of the end fitting liner during the deforming.

[0011] Other features will become apparent from the drawings in conjunction with the following description.
BRIEF DESCRIPTION OF DRAWINGS

[0012] In the figures which illustrate example embodiments:

[0013] FIG. 1 is a perspective view of a CANDUTm-type reactor.

[0014] FIG. 2 is a cutaway perspective view of a CANDUTm-type nuclear reactor fuel channel assembly, according to an embodiment.

[0015] FIG. 3 is a cross-sectional view along lines I-I of a portion of the fuel channel assembly shown in FIG. 2 immediately outboard of the tube sheet at the bottom of FIG. 2, according to an embodiment.

[0016] FIG. 4A is a cross-sectional view of the portion of the fuel channel assembly of FIG. 3, shown without a fuel bundle and with a joint rolling tool axially inserted into the fuel channel assembly to a first axial working position with rollers of the joint rolling tool in a retracted position, according to an embodiment.

[0017] FIG. 4B is a cross-sectional view of the portion of the fuel channel assembly of FIG. 3, shown without a fuel bundle and with a joint rolling tool axially inserted into the fuel channel assembly to a second axial working position with rollers of the joint rolling tool in an extended position, according to an embodiment.

DETAILED DESCRIPTION

[0018] FIG. 1 is a perspective view of a reactor core of a CANDUTm-type Pressurized Heavy Water Reactor (PHWR) 6. In some embodiments, the PHWR may be a 100-300 MW CANDUTM reactor, a 600MW CANDUTM reactor, a 900MW CANDU TM
reactor, or a 1000 MW CANDUTM reactor. The reactor core is typically contained within a vault that is sealed with an air lock for radiation control and shielding.
Although aspects of the disclosure are described with particular reference to the CANDUTm-type reactor 6 for convenience, the disclosure is not limited to CANDUTm-type reactors, and may be useful outside this particular field as well. In use, the reactor core is typically contained within a vault that is sealed with an air lock for radiation control and shielding.

[0019] A generally cylindrical vessel, known as calandria vessel 10 of the CANDUTm-type reactor 6, contains a heavy-water moderator. In some embodiments, calandria vessel 10 has an annular shell 14 and a tube sheet 18 at a first end 22 and a second end 24. Tube sheets 18 include a plurality of apertures 19 (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 tube sheets 18 of calandria vessel 10 from first end 22 to second end 24.

[0020] As shown in FIG. 2, 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 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 tube sheet 18 at each end 22, 24 of the reactor core. A lattice tube 65 spans the distance between tube sheet 18 and end shield 64 at each pair of bores 19 (i.e., in the tube sheet 18 and the end shield 64, respectively). In the embodiment illustrated in FIG. 2, the lattice tube 65 is formed integrally with the tube sheet 18, but in some embodiments could be formed as a separate part.

[0021] FIG. 2 illustrates a cutaway view of one fuel channel assembly 28 of the reactor core illustrated in FIG. 1. As illustrated in FIG. 2, each fuel channel assembly 28 includes a calandria tube ("CT") 32 surrounding other components of the fuel channel

22 PCT/CA2018/050765 assembly 28. Calandria tubes 32 each span the distance between tube sheets 18 from first end 22 to second end 24. Also, the opposite ends of each calandria tube 32 are received within and sealed to respective bores in the tube sheets 18. In some embodiments, a rolled joint insert such as a calandria insert 70 is used to secure each calandria tube 32 to tube sheet 18 within a bore 19. A pressure tube ("PT") 36 forms an inner wall of fuel channel assembly 28. Pressure tube 36 provides a conduit for reactor coolant and fuel bundles or assemblies 40. Pressure tube 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 pressure tube 36 and its corresponding calandria tube 32.
[0022] 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 calandria tube 32 and pressure tube 36.
Annulus spacers 48 maintain the gap between pressure tube 36 and corresponding calandria tube 32, while allowing passage of annulus gas through and around annulus spacers 48.

[0023] As also shown in FIG. 2, each end of each fuel channel assembly 28 is provided with an end fitting assembly 50 located outside of corresponding tube sheet 18. Each end fitting assembly 50 includes an end fitting body 57 and an end fitting liner 59. 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.

[0024] Feeder assemblies 54 feed reactor coolant into or remove reactor coolant from the PTs 36 via feeder tubes. In particular, for a single fuel channel assembly 28, a feeder assembly 54 on one end of the fuel channel assembly 28 acts as an inlet feeder, and a feeder assembly 54 on the opposite end of the fuel channel assembly 28 acts as an outlet feeder.

[0025] As shown in FIG. 2, 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. Lattice tube 65 (described above) encases the connection between the end fitting assembly 50 and the pressure tube 36 containing the fuel assemblies 40. Shielding ball bearings 66 and cooling water surround the exterior of the lattice tubes 65, which may provide additional radiation shielding.

[0026] A positioning hardware assembly 60 and bellows 62 are also coupled to each end fitting assembly 50. 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.
Positioning hardware assemblies 60 may 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.
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 end shield 64 are threaded. Again, it should be understood that although a CANDUTm-type reactor is illustrated in FIGS. 1-2, in other embodiments, the features described may also apply to other types of reactors, including reactors having components that are similar to those illustrated in FIGS. 1-2.

[0027] Referring to FIGS. 3 and 4A, 4B, calandria tube 32 includes ends positioned in corresponding openings in tube sheet 18. Each end includes a calandria insert 70 that is rolled radially outwardly to secure the calandria tube 32 to the tube sheet 18. The pressure tube 36 is then inserted into the calandria tube 32 and held concentrically within and with respect to calandria tube 32 by annular spacers 48 (see FIG. 2).

[0028] End fitting assembly 50 (see FIG. 2), including end fitting body 57 and end fitting liner 59, is then inserted into lattice tube 65 such that an inner end of the end fitting assembly 50 receives the end of pressure tube 36, as shown in FIG. 3.
End fitting body 57 can include a series of annular grooves 72 adapted to facilitate securing the pressure tube 36 to the end fitting assembly 50 and creating a fluid-tight seal therebetween, as described below in more detail. After the end fitting assembly 50 is inserted into lattice tube 65, annular grooves 72 will be axially overlapped with the end of pressure tube 36.

[0029] End fitting liner 59 includes an inner support surface 73 that can support an end of a fuel bundle 40 during insertion into fuel channel assembly 28, and in some embodiments during operation of the nuclear reactor. It can be seen that the inner end of end fitting liner 59 also includes a counter bore 74 defining an inner counter bore surface with an inner diameter that is larger than support surface 73. In some embodiments, a counter bore region of end fitting body 57 may also have an inner diameter that is greater than a surface of the remaining end fitting body 57.

[0030] The end fitting liner 59 illustrated in FIG. 3 also includes a pivotable latch 76 that is biased toward the latched position.

[0031] In some embodiments, latch 76 has a hinge (not shown) at a first end of arm 92. Latch 76 rotates about axis A by way of hinge . At a second end, opposing the first end of arm 92, latch 76 may have a ramp 94 leading to a ledge 96. Ledge 96 may form a right angle. Latch 76 may be formed of metal, for example, spring steel, and operatively connected to the wall of end fitting liner 59. Latch 76 may be spring-loaded to bias into a latched position, for example as shown in FIG. 3.

[0032] Latch 76 is designed to retain the fuel bundle 40 in the pressure tube 36.
Latch 76 may inhibit axial movement of fuel bundle 40 once fuel bundle 40 engages with ledge 96 of latch 76. In other embodiments, no such latch 76 is provided.

[0033] In order to secure pressure tube 36 to end fitting assembly 50, the end of pressure tube 36 is roll-formed radially outwardly such that the end of the pressure tube 36 is deformed into annular grooves 72 on the inside surface of end fitting body 57, as shown in FIG. 3. This rolling operation may be accomplished using a rolling tool 78, such as PT Rolled Joint Expander Part No. RT38-17000-010 manufactured by Commonwealth Manufacturing, Mississauga, Ontario, Canada.

[0034] As shown in FIGS. 4A and 4B, in some embodiments rolling tool 78 has a leading end 82. Axis D extends through the center of rolling tool 78. In some embodiments, rolling tool 78 includes a cage 84. Cage 84 may be generally cylindrical, with a hollow center extending axially from leading end 82 to an opposing end.
Cage 84 also includes apertures extending radially around the curved surface of cage 84, in which rollers 80 are retained.

[0035] In some embodiments, cage 84 may be integrally formed or attached to a collar 88 and a body 89. Collar 88 and body 89 may be generally cylindrical, with a hollow center extending radially along axis D.

[0036] A mandrel 86 extends through the hollow center of cage 84, collar 88 and body 89. Mandrel 86 may be tapered, with the smaller diameter end of mandrel adjacent leading end 82 of rolling tool 78, and mandrel 86 may be operable to move axially within the hollow center of cage 84 to make contact and apply radial force on rollers 80 to move rollers 80 radially with reference to axis D.

[0037] A rolling operation to secure pressure tube 36 to end fitting assembly 50 will now be described in more detail.

[0038] A rolling operation may be initiated by inserting rolling tool 78 through end fitting liner 59 in direction B.

[0039] Prior to inserting rolling tool 78 through end fitting liner 59, a protective sleeve 79 may be inserted in end fitting liner 59. In some embodiments, protective sleeve 79 may be cylindrical in shape with an outer diameter sized to fit within end fitting liner 59 and an inner diameter sized to provide clearance for rolling tool 78.
Protective sleeve 79 may be formed of metal, or other suitable material as would be known by a person skilled in the art. Protective sleeve 79 may prevent rolling tool 78 from directly contacting end fitting liner 59, and thus may prevent rolling tool 78 from damaging end fitting liner 59, as the mass and lubricant of rolling tool 78 may scratch end fitting liner 59 if it comes into contact with it. In some embodiments, protective sleeve 79 remains in fuel assembly 40 for the duration of use of rolling tool 78, and is removed from fuel channel assembly 40 during operation of reactor 6.

[0040] During insertion of rolling tool 78 through end fitting liner 59, leading end 82 of rolling tool 78 may engage the latch 76 (if present), and pivot the latch 76 to an unlatched position (see FIGS. 4A and 4B) to provide the needed clearance for further insertion of rolling tool 78. Upon sufficient axial insertion of rolling tool 78 towards pressure tube 36 (i.e., in direction B as shown in FIGS. 4A and 4B), leading end 82 of rolling tool 78 engages ramp 94 of latch 76. As leading end 82 of rolling tool 78 is moved toward pressure tube 36, rolling tool 78 (e.g., leading end 82 of rolling tool 78) cams against ramp 94 of latch 76 to pivot latch 76, rotating latch 76 in a counter-clockwise direction C about axis A, toward an unlatched position. With continued movement of rolling tool 78 in direction B, latch 76 is pivoted sufficiently in direction C
about axis A to enable rolling tool 78 to continue to pass latch 76.

[0041] In some embodiments, protective sleeve 79 may be inserted in end fitting liner 59 prior to inserting rolling tool 78 through end fitting liner 59, such that with axial insertion of protective sleeve 79 in direction B as shown in FIGS. 4A and 4B, protective sleeve 79 engages ramp 94 of latch 76, in a similar manner to that described above.
Latch 76 may then move to an unlatched position, to enable protective sleeve 79 to continue to pass latch 76 to the position illustrated in FIGS. 4A and 4B.
Rolling tool 78 may then be inserted into protective sleeve 79.

[0042] Rolling tool 78 is inserted until its rollers 80 are axially overlapped with the end of pressure tube 36 adjacent annular grooves 72 of end fitting body 57 into a working position, as shown in FIGS. 4A and 4B.

[0043] FIG. 4A is a cross-sectional view of the portion of the fuel channel assembly of FIG. 3, shown without a fuel bundle and with rolling tool 78 axially inserted into fuel channel assembly 28 to a first axial working position with rollers 80 of rolling tool 78 in a retracted and starting position, according to an embodiment. FIG.
4B is a cross-sectional view of the portion of the fuel channel assembly of FIG. 3, shown without a fuel bundle and with rolling tool 78 axially inserted into the fuel channel assembly 28 to a second axial working position with rollers 80 of rolling tool 78 in an extended position, according to an embodiment.

[0044] In the first axial working position shown in FIG. 4A, rollers 80 of rolling tool 78 are axially aligned and overlapped with counter bore 74 of end fitting liner 59. Rolling tool 78 can then be rolled about the axis of rolling tool 78, and rollers 80 can be moved radially and outwardly away from axis D and at least part of rolling tool 78 may move axially in direction B, to the second axial working position shown in FIG. 4B.
In the first axial working position, rollers 80 of rolling tool 78 may be in a starting position that is approximately one inch outboard of the second axial working position shown in FIG. 4B, in which rollers 80 are in a final roller position.

[0045] Rollers 80 may be actuated radially, for example, by rotating a ball screw (not shown) that is operatively connected to mandrel 86. As mandrel 86 actuates axially in direction B, the diameter of the tapered mandrel 86 that contacts rollers 80 increases, thus pushing rollers 80 radially outwardly.

[0046] Radial outward movement of rollers 80 may deform the end of pressure tube 36 into annular grooves 72 of end fitting body 57, thereby creating a fluid-tight joint between pressure tube 36 and end fitting body 57 as shown in FIG. 4B.

[0047] During this operation, counter bore 74 has a large enough inner diameter such that contact between rolling tool 78 and end fitting liner 59 may be avoided, for example, in the first axial working position shown in FIG. 4A, and even as rollers 80 of rolling tool 78 expand until the rolled joint has been completed. In this manner, deformation (and in some embodiments, even contact) between rolling tool 78 and end fitting liner 59 may be avoided altogether. Such deformation or contact may be undesirable, as damage to end fitting liner 59 may result. Similarly, in some embodiments, a counter bore region of end fitting body 57 may also have an inner diameter that is large enough such that contact between rolling tool 78 and end fitting body 57 may be avoided when rolling tool 78 and rollers 80 are in a retracted and starting position, for example, in the first axial working position shown in FIG. 4A, or in the second axial working position shown in FIG. 4B.

[0048] In some embodiments, roller(s) 80 of the rolling tool 78 are positioned in counter bore 74 during the rolling operation. The final inner diameter of the rolled portion of pressure tube 36 may be smaller than the diameter of counter bore 74 in the end of end fitting liner 59.

[0049] As described above, rolling tool 78 begins its rolling operation in an axial position in which at least one roller 80 of rolling tool 78 overlaps (i.e., shares one or more common axial locations with) end fitting liner 59. In those embodiments (such as the illustrated embodiment) in which pressure tube 36 and end fitting liner 59 are spaced from one another by a gap, at least one roller 80 therefore also spans the gap when the rolling operation begins.

[0050] In some embodiments, the entire pressure tube-to-end fitting rolling operation takes place without significant axial movement of rolling tool 78.
In other words, rollers 80 of rolling tool 78 expand outwardly to create the rolled joint as described above without any needed axial movement of rolling tool 78.

[0051] However, in other embodiments, the rolling operation begins with at least one roller 80 in the position described above (i.e., overlapping a portion of end fitting liner 59 and pressure tube 36 and expanded to the rolling position), but rolling tool 78 is moved axially toward tube sheet 18 as the rolling operation continues in a "propulsive rolling" process.

[0052] In some embodiments (i.e., those including axial movement of the rolling operation), the "propulsive rolling" process may continue until a predetermined axial position of rolling tool 78 is reached, such as a set axial stop position of rolling tool 78.
Once this end rolling position is reached, roller(s) 80 of rolling tool 78 can be retracted to complete the rolling operation, and rolling tool 78 can be axially withdrawn from fuel channel assembly 28.

[0053] In propulsive rolling operations, the axial range of positions of the roller(s) when performing their rolling operations are greater than in those rolling operations in which rolling tool 78 is stationary during the rolling operation. Therefore, counter bore 74 of end fitting liner 59 may provide additional axial room for the propulsive rolling operation and may avoid damage to end fitting liner 59 as described above.

Furthermore, the greater inner diameter of counter bore 74 may only extend the axial distance needed for operation of rolling tool 78, thus the remainder of end fitting liner 59 may be kept at a desired thickness to maintain structural integrity of end fitting liner 59.
Thus, a rolling operation of pressure tube 36 to end fitting body 57 may be allowed with end fitting liner 59 in place within fuel assembly 28.

[0054] In some embodiments, a rolling operation can begin without the roller(s) 80 sharing ("overlapping" or in axial alignment with) the same axial position of some or any of annular grooves 72 described above (i.e., instead being positioned so that roller(s) 80 are positioned axially outboard, or to the right as illustrated in FIGS. 4A and 4B, of some or all of annular grooves 72, depending at least in part upon the dimensions of the rolling tool, pressure tube 36, and end fitting body 57).

[0055] The initial phase of the rolling operation, where the rollers travel axially inboard, for example, from the first axial working position shown in FIG. 4A, is referred to as rolling to "nip up", "nip up" being the state where all of the initial clearances between pressure tube 36 and end fitting body 57 have been taken up. By beginning rolling operation with rolling tool 78 axially overlapping with end fitting liner 59 and in particular, with rolling tool 78 axially overlapping with counter bore 74 of end fitting liner 59, (for example, as shown in the first axial working position of FIG. 4A) during rolling to nip up, rollers 80 may be rolling less surface area of pressure tube 36 and therefore less force may be applied to pressure tube 36 and the tooling that is holding pressure tube 36 and end fitting body 57 in place. This may avoid pressure tube 36 and end fitting body 57 shifting out of position, and rolling with less force may reduce the risk of the components (such as pressure tube 36 and end fitting body 57) moving. After nip up, pressure tube 36 and end fitting body 57 may be solidly connected and the high force portion of the rolling operation may occur, with rollers 80 extending radially outwardly to complete the formation of a rolled joint of pressure tube 36 and end fitting body 57.

[0056] Of course, the above described embodiments are intended to be illustrative only and in no way limiting. The described embodiments are susceptible to many modifications of form, arrangement of parts, details and order of operation. This is intended to encompass all such modification within its scope, as defined by the claims.

Claims (13)

WHAT IS CLAIMED IS:

1. A nuclear reactor core comprising:
a calandria vessel having a shell and a tube sheet on an end of the shell and the tube sheet defining an aperture;
a calandria tube coupled to the tube sheet and extending into the annular shell;
a lattice tube coupled to the tube sheet and extending outwardly away from the reactor core;
an end fitting body positioned at least partially in the lattice tube;
a pressure tube positioned at least partially in the calandria tube and having an end secured to the end fitting body; and an end fitting liner positioned at least partially in the end fitting body coaxial with the pressure tube, wherein an end of the end fitting liner adjacent the pressure tube includes a first inner surface having a counter bore.

2. The nuclear reactor of claim 1, wherein the counter bore defines a first axial segment of the end fitting liner having an inner diameter that is greater than an inner diameter of a second axial segment of the end fitting liner.

3. The nuclear reactor of claim 2, wherein the inner diameter of the first axial segment is sized to allow clearance for a rolling tool in an extended position in which rollers of the rolling tool are in radial contact with the pressure tube.

4. The nuclear reactor of claim 2, wherein the inner diameter of the first axial segment is greater than an inner diameter of the pressure tube.

5. The nuclear reactor of claim 1, further comprising a calandria insert securing the calandria tube to the tube sheet.

6. The nuclear reactor of claim 1, wherein the lattice tube is integrally formed with the tube sheet.

7. The nuclear reactor of claim 1, wherein the end fitting body includes a second inner surface secured to an outer surface of the end of the pressure tube.

8. The nuclear reactor of claim 7, wherein the end of the pressure tube has a third inner surface with a diameter that is smaller than a diameter of the first inner surface of the end fitting liner.

9. A method of securing a pressure tube to an end fitting body in a nuclear reactor core including a calandria vessel having a shell and a tube sheet on an end of the shell, a calandria tube coupled to the tube sheet and extending into the annular shell, a lattice tube coupled to the tube sheet and extending outwardly away from the reactor core, and an end fitting body positioned at least partially in the lattice tube, the method comprising:
inserting an inner end of an end fitting liner into the end fitting body;
positioning the pressure tube inside the calandria tube with an end of the pressure tube axially overlapped with a portion of the end fitting body;
introducing a rolling tool into the end fitting liner until a roller of the rolling tool is axially aligned with the pressure tube;
deforming the end of the pressure tube into the end fitting body by rotating the rolling tool to move the roller radially outward into contact with the pressure tube; and axially aligning the roller with the inner end of the end fitting liner during the deforming.

10. The method of claim 9, wherein the inner end of the end fitting liner includes a counter bore, and wherein the axially overlapping includes positioning at least a portion of the roller in the counter bore.

11. The method of claim 9, wherein the counter bore defines a first axial segment of the end fitting liner having an inner diameter that is greater than an inner diameter of a second axial segment of the end fitting liner.

12. The method of claim 9, wherein the end fitting liner includes a latch, and wherein introducing a rolling tool includes moving the latch to an unlatched position.

13. The method of claim 9, further comprising axially moving the roller during the deforming.