WO2018232530A1

WO2018232530A1 - System and method for aligning nuclear reactor tubes and end fittings using tube rotation

Info

Publication number: WO2018232530A1
Application number: PCT/CA2018/050775
Authority: WO
Inventors: Jean-Claude Stranart; Reza Ziaei
Original assignee: Candu Energy Inc.
Priority date: 2017-06-23
Filing date: 2018-06-22
Publication date: 2018-12-27
Also published as: CN111194470A; CN111194470B; KR20200019884A; KR102592470B1; CA3066103A1; RO134275A2

Abstract

A method for orienting a pressure tube of a nuclear reactor relative to a calandria tube of the nuclear reactor. The method includes the steps of rotating the pressure tube with respect to the calandria tube to orient a bow of the pressure tube with respect to a bow of the calandria tube; inserting the pressure tube into the calandria tube; rotating the pressure tube with respect to the calandria tube to orient the bow of the pressure tube with respect to the bow of the calandria tube; and securing the pressure tube in the operational position.

Description

SYSTEM AND METHOD FOR ALIGNING NUCLEAR REACTOR TUBES AND END

FITTINGS USING TUBE ROTATION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims all benefit including priority to United States Provisional Patent Application 62/524,422, filed June 23, 2017, and entitled: "SYSTEM AND METHOD FOR ALIGNING NUCLEAR REACTOR TUBES AND END FITTINGS USING TUBE ROTATION", which is hereby incorporated by reference in its entirety.

FIELD

[0002] The present disclosure relates to the field of nuclear reactor fuel channel assemblies, and some embodiments relate to systems and methods for positioning a pressure tube with respect to a calandria tube in a nuclear reactor fuel channel assembly.

BACKGROUND

[0003] Nuclear reactors are designed to have an operational lifespan. For example, second generation CANDU™-type reactors ("CANada Deuterium Uranium") can be designed to operate for approximately 25 to 30 years. After this time, the existing fuel channels can be removed and fuel channels can be installed.

[0004] Properly aligning fuel channel components which can include positioning elongated tubes into existing apertures or bores can be a challenge.

SUMMARY

[0005] In one embodiment, the disclosure provides a method of assembling a fuel channel assembly of a nuclear reactor. The method includes: orienting a subassembly, comprising a pressure tube engaged with a first end fitting, in the fuel channel assembly in an intermediate position, the intermediate position based on an orientation of a bow of the pressure tube;

engaging the subassembly with a second end fitting positioned at a reactor tube sheet; rotating the subassembly and the second end fitting to orient the pressure tube in an operational position; and securing the pressure tube in the operational position. [0006] In another embodiment, the disclosure provides a method of assembling a fuel channel assembly of a nuclear reactor. The method includes determining an orientation of a bow of a pressure tube of the fuel channel assembly; determining an orientation of a bow of a calandria tube of the fuel channel assembly; installing the calandria tube in an operational position; orienting the pressure tube with respect to a first end fitting in a predetermined orientation; engaging the pressure tube with the first end fitting to form a subassembly; orienting the subassembly in an insertion position; inserting the subassembly into the calandria tube;

engaging the subassembly with a second end fitting positioned in a reactor tubesheet in the predetermined orientation in a predetermined orientation; rotating the subassembly and the second end fitting with respect to the calandria tube to orient the pressure tube in an operational position.

[0007] In another embodiment, the disclosure provides a method for orienting a pressure tube of a nuclear reactor relative to a calandria tube of the nuclear reactor. The method includes securing the calandria tube within the nuclear reactor in an any orientation; engaging the pressure tube with a first end fitting to form a subassembly; rotating the pressure tube with respect to the calandria tube to orient a bow of the pressure tube in a predetermined orientation; inserting the pressure tube into the calandria tube; and rotating the pressure tube with respect to the calandria tube to orient the pressure tube in the operational position.

[0008] In another embodiment, the disclosure provides a method for orienting a pressure tube of a nuclear reactor relative to a calandria tube of the nuclear reactor. The method includes securing the calandria tube within the nuclear reactor in a preferred orientation; engaging the pressure tube with a first end fitting to form a subassembly, the pressure tube being in any orientation with respect to the first end fitting; inserting the pressure tube into the calandria tube; engaging the subassembly with a second end fitting; rotating the subassembly and the second endfitting relative to a reference point on the reactor to an predetermined orientation; engaging the pressure tube to the second end fitting; securing the pressure tube to the second end fitting at reactor face in the predetermined orientation; and rotating the subassembly and the second end fitting with respect to the calandria tube to orient the pressure tube in an operational position. [0009] Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a perspective view of a CANDU™-type reactor.

[0011] FIG. 2 is a cutaway view of a CANDU™-type reactor fuel channel assembly.

[0012] FIG. 3 is a schematic representation of a cross-section of a reactor fuel channel in an operational position according to an embodiment of the disclosure.

[0013] FIG. 4 is a schematic representation of a reactor fuel channel in an insertion position according to an embodiment of the disclosure.

[0014] FIG. 5 is a flow chart illustrating an installation process for installing a pressure tube in the reactor according to an embodiment of the disclosure.

[0015] FIG. 6 is a flow chart illustrating show aspects of an example installation process for installing a pressure tube in the reactor according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0016] Before any embodiments of the disclosure 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. In any disclosed embodiment, the terms

"approximately" or "generally" may be substituted with "within a percentage of what is specified, where the percentage includes 0.1, 1, 5, and 10 percent.

[0017] FIG. 1 is a perspective of a reactor core of an exemplary CANDU™-type Pressurized Heavy Water Reactor (PHWR) reactor 6. In some embodiments, the PHWR may be a 100-300 MW CANDU™ reactor, a 600MW CANDU™ reactor, a 900MW CANDU™ reactor, or a 1000 MW CANDU™ 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 CA DU™-type reactor 6 for convenience, the disclosure is not limited to CA DU™-type reactors, and may be useful outside this particular field as well.

Returning to FIG. 1, a generally cylindrical vessel, known as the calandria 10 of the CANDU™- type reactor 6, contains a heavy -water 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 (referred to herein as "bores") 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 the calandria 10 from the first end 22 to the second end 24.

[0018] 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 bores (i.e., in the tube sheet 18 and the end shield 64, respectively).

[0019] FIG. 2 is 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 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 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. 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. [0020] 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 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. 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. 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 of the lattice tubes 65, which provides additional radiation shielding. In the illustrated construction, the end fittings 50 are engaged with the ends of the PTs 36. For the purpose of convenience, when referring to specific end fittings 50, the end fitting 50 closest to the reactor face will be indicated with the symbol " ' " and the end fitting 50 closest to a subassembly side (e.g. the side of the fuel channel assembly 28 farthest from the reactor face) will be indicated with the symbol " " ".

[0021] Returning to FIG. 2, 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 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 CA DU™-type reactor is illustrated in FIGS. 1-2, the disclosure may also apply to other types of reactors, including reactors having components that are similar to those illustrated in FIGS. 1-2. [0022] As the reactor 6 ages, it may be necessary to remove the CTs 32 and the PTs 36 and replace the CTs 32 and PTs 36 with new CTs 32 and PTs 36 in a process known as "retubing". In some embodiments, the PTs 36 are installed within newly installed CTs 32. In other embodiments, the PTs 36 may be installed in existing CTs 32.

[0023] Positioning the CTs 32 and the PTs 36 is complex due to the shape of the CTs and the PTs. The CTs 32 and the PTs 36 have a bowed shape with respect to a reference point, such as an axial centerline, due to their elongated shape and manufacturing process. In some instances, a bowed portion of the CT 32 or the PT 36 may be located proximate a center of the CT 32 or the PT 36. In other instances, the bowed portion of the CT 32 or the PT 36 may be off-center, for example closer to one of the ends of the CT 32 or the PT 36, or proximate one of the ends of the CT 32 or the PT 36. A bow of the CTs 32 or a bow of the PTs 36 is generally measured before the CTs 32 or the PTs 36 are installed in the reactor 6 to determine a position of the bow in a rotational orientation and an axial location. The term "rotational orientation" is generally used to refer to an angular orientation with respect to a known reference point, such as a "12 o'clock position". The term "axial location" is generally used to refer to a positon along a longitudinal extent of the CT 32 or the PT 36. In some embodiments, the PTs 36 include markings to indicate the rotational orientation and/or axial position of the bow. Since the PTs 36 are positioned inside of the CTs 32, the bow of each PT 36 is oriented rotationally and axially with respect to each respective CT 32 ensure that the annulus space 44 between the PT 36 and the CT 32 is adequately sized to allow for circulation of gas in the annulus space 44.

[0024] In some embodiments, the bow of the CTs 32 or the bow of the PTs 36 may be measured by the manufacturer at the point of manufacture. In other embodiments, the bow of the CTs 32 or the PTs 36 may be measured on-site (e.g. at the point of installation or at a nearby staging location) to account for any changes in the bow of the CTs 32 or the PTs 36 that occurred during transportation. In some embodiments, the bow of the CTs 32 or the bow of the PTs 36 may be measured using a laser.

[0025] FIG. 3 illustrates a schematic representation of a cross-section of a fuel channel assembly 28 in an operational position according to some embodiments. As shown in FIG. 3, the CT 32 and the PT 36 are largely unsupported along their longitudinal extents when the CT 32 and the PT 36 are installed in the reactor 6. In the operational position, the CT 32 and the PT 36 are generally positioned so that the bows face upward (e.g. the position of maximum bow is downward with respect to the ends of the CT 32 or the PT 36). A plurality of garter springs 48 is positioned along the longitudinal extent of the PT 36 to prevent contact between the PT 36 and the CT 32. In embodiment of FIG. 3, the fuel channel assembly 28 includes four garter springs 48. The position of the bow of the CT 32 is generally proximate a third garter spring 48" ' . The position of the bow may be different in other embodiments or in embodiments using more or fewer garter springs 48.

[0026] FIG. 4 illustrates a schematic representation of a cross-section of a fuel channel assembly 28 in an insertion position according to some embodiments. The PT 36 shown FIG. 4 has been rotated generally 180 degrees relative to the operational position (FIG. 3) so that the bow of the PT 36 faces downward (e.g. the position of maximum bow is upward with respect to the ends of the CT 32 or the PT 36).

[0027] FIG. 5 is a flow chart illustrating an installation process for the PT 36 of the reactor 6 according to an embodiment of the disclosure. During the installation process, the PT 36 is positioned with the CT 32 that has been secured within the bores of the tube sheets 18 using CT rolled joint inserts 34. As an initial step, an end of the PT 36 is positioned with respect to the end fitting 50" and secured to the end fitting to form a subassembly 38 (block 72). In some embodiments, the PT 36 is positioned in a predetermined or optimized orientation with respect to end fitting 50". In some embodiments, the PT 36 is engaged with the end fitting 50" off-site, for example in a clean room. In other embodiments, the PT 36 is engaged with the end fitting 50" at the worksite. The end fitting 50' is engaged with the tube sheet 18 proximate the reactor face (block 74). In some embodiments, block 72 may occur before block 74, block 72 may occur after block 74, or block 72 may occur at the same time as block 74. After the PT 36 has been secured to the end fitting 50", the natural bow of the PT 36 is verified (e.g. rotational orientation and/or axial position is visualized or measured) (block 80). The subassembly 38 is then rotated by an angle of rotation with respect to the end fitting 50' to orient the subassembly 38 in an insertion position in which the bow is oriented to optimize alignment between the end of the PT 36 and the end fitting 50' (FIG. 4) (block 82). The angle of rotation may be between 0 to 360 degrees. In some embodiments, the angle of rotation is approximately 180 degrees with respect to a bow-upward orientation (e.g. the bow faces downward) to cause the force of gravity acting on the PT 36 to reduce the bow. . In other embodiments, the angle of rotation is approximately 90 degrees from a bow-upward orientation, to reduce sagging of the bowed area due to gravity. In embodiments in which the rotational position of the bow of the PT 36 is marked, the marking on the PT 36 may be aligned with a specific position along a circumference of the CT 32 or the tube sheet bore 18 (e.g. the "twelve o'clock position").

[0028] With continued reference to FIG. 5, an end of the PT 36 that is not engaged with the end fitting 50" is inserted into the CT 32 and the PT 36 is then translated (e.g. rolled) in an axial direction 86 (FIG. 3) with respect to the CT 32 so that the PT 36 slides within the CT 32 until the end of the PT 36 mates with a bore of the end fitting 50' closest to the reactor face in a predetermined orientation(block 90). The rotation of the subassembly 38 described in block 82 orients the bow of the PT 36 to reduce the effect of gravity-induced misalignment of the bow of the PT 36 and the bore of the end fitting 50' to improve alignment between the PT 36 and the end fitting 50' . In embodiments in which the axial position of the axial bow of the PT 36 is marked, the axial rolling stops when the marking on the PT 36 reaches a predetermined axial position with respect to the end fitting 50' . Next, the PT 36 is fully inserted into the bore of the end fitting 50' in the predetermined orientation and a rolled joint is formed between the PT 36 and the end fitting 50' (block 92). Next, the subassembly 38 and the end fitting 50' are rotated with respect to the CT 32, the GSC, or another reference point on the reactor 6 to orient the PT 36 into the operational position (FIG. 3)(block 94). In some embodiments, the subassembly 38 is rotated in the opposite direction and by approximately the same angle as the rotation in block 82. The subassembly 38 and the end fitting 50' are then secured in the operational position (block 102). In some embodiments, the PT 36 is secured relative to the CT 32 when the PT 36 is in the operational position. In some embodiments, the PT 36 is positioned relative to the centerline of the CT 32, relative to a bore in the tube sheet 10, the GCS, or another reference point on the reactor 6. In other embodiments, the PT 36 may be positioned so the bow of the PT 36 is aligned with the bow of the CT 32. In other embodiments, the PT 36 may be oriented in any axial or rotational position with respect to the CT 32.

[0029] In some embodiments, the bow of the CT 32 may be measured after the CT 32 has been secured within the bores of the of the tube sheet 18. A rotational or axial orientation of the bow of the PT 36 may be measured before the PT 36 is rolled into the CT 32, after the PT 32 has been rolled into the CT 32, but before the PT 36 has been rotated into the operational position, or at any point during the rolling of the PT 36 into the CT 32. A rotational or axial orientation of the bow of the PT 36 may be measured after the PT 36 has been rotated into the operational position, but before the PT 36 has been secured relative to the CT 32. A rotational or axial orientation of the bow of the PT 36 may be measured after the PT 36 has been secured in the operational position. In some embodiments, none of these measurements are taken. In other embodiments, some of these measurements may be taken, or all of these measurements may be taken.

[0030] In some embodiments, a retube tooling platform ("RTP"), and other tool and equipment supports may be installed proximate the reactor 6 during retooling operations. The RTP is an adjustable platform upon which much of the fuel channel component removal and installation operations are performed. In some embodiments, the RTP is a stand-alone machine that does not rely on existing plant structures for positioning or movement. The RTP can be precision-located within the vault, relative to the center point of the calandria 10, using laser tracker technology. By positioning the columns in this way, the RTP is positioned to the as-built location of the calandria 10 (including pitch and yaw), which provides a precision tooling base that permits the use of high accuracy indexing to each lattice site. Installed and mounted on the RTP, and serving as the basis for tool delivery during the removal phase, are one or more installation work tables ("IWTSs"). The IWTs provide a platform that supports retubing equipment. A global coordinate system ("GCS") can be set up in the vault. The GCS allows accurate and repeatable measurements to be made throughout the reactor building. The GCS is a virtual coordinate system, where the origin is positioned as close to the center of the calandria 10 as possible.

[0031] In some embodiments, the rotational device may include a grasping member, a rotational actuator, and a position sensor. The grasping member may be adapted to grasp at least an inner wall or an outer wall of the PT 36. In some embodiments, the grasping member may include clamp arms actuable to grasp the PT 36. In other embodiments, the grasping member may include an adjustable collar for engaging the PT 36 to evenly distribute a grasping force about the circumference of the PT 36, reducing the potential for deformation of the PT 36 by the grasping member. In embodiments in which the adjustable collar is adapted to engage the outer wall of the PT 36, the adjustable collar may be tightenable around the PT 36. In embodiments in which the adjustable collar is adapted to engage the inner wall of the PT 36, the adjustable collar may be expandable to grasp the inner wall of the PT 36 after the adjustable collar has been positioned within the PT 36. In some embodiments, the grasping mechanism may include a first adjustable collar to grasp the outer wall of the PT 36 and a second adjustable collar to grasp the inner wall of the PT 36. In a preferred embodiment, the grasping member may grasp both the inner wall and the outer wall of the PT 36 to prevent deformation of the PT 36.

[0032] In some embodiments, the rotational actuator may be a motor adapted to rotate an output shaft engaged with at least a portion of the grasping member. The motor may be controlled to a high degree of precision and be actuable to rotate the grasping member to a high degree of precision. In some embodiments, the position sensor may be a rotary encoder engaged with an output shaft of the motor to sense an angle rotation of the output shaft. In other constructions, the position sensor may be mounted proximate the PT 36 to sense an angle of rotation of the PT 36. Exemplary position sensors include laser, optical, or magnetic rotary encoders.

[0033] In some embodiments, the ram may include a grasping member, a translational actuator, and a position sensor. The grasping member may be adapted to grasp at least an inner wall or an outer wall of the PT 36. The grasping member may be substantially similar to the grasping member described above with respect to the rotational member. The translational actuator is adapted to actuate the grasping member in a linear direction that is generally parallel to a longitudinal axis of the PT 36 or the CT 32. Exemplary translational actuators may include servo motors, pneumatic actuators, or hydraulic cylinders. In some embodiments, the position sensor may be engaged with an output shaft of the motor to sense translation of the output shaft. In other embodiments, the position sensor may be mounted proximate the PT 36 to sense translation of the PT 36. In some embodiments, the position sensor may include laser, optical, or magnetic proximity sensors. In other embodiments, the position sensor may include a proximity sensor, such as a laser proximity sensor, adapted to sense a distance to a marked portion of the output of the translational actuator or a marked portion of the PT 36. [0034] In some embodiments, the rotational device and the ram may be separate tools. In other embodiments, the rotational device and the ram may be included in the same tool.

[0035] In embodiments that include the RTP and the IWTs, tools used to install the PTs 36 may be positioned on the RTP or the IWTs. Tools installed on the RTP or the ITWs may be positioned and actuated with high precision with respect to the PTs 36 and the CTs 32 using the GCS. For example, the rotational device may be positioned with respect to the CT 32 using the GCS. The grasping means of the rotational device and/or the translational actuator of the rotational device may be controlled (e.g. rotated or repositioned) using coordinates of the GCS. In another example, the ram may be positioned with respect to the CT 32 using the GCS. The grasping means of the ram and/or the translational actuator of the ram may be controlled (e.g. rotated or repositioned) using coordinates of the GCS.

[0036] In some embodiments, the PT 36 may be manually oriented with respect to the CT 32.

[0037] FIG. 6 shows aspects of another example method of assembling a fuel channel assembly. Any aspects of the examples described above can be similarly applied to this method.

[0038] At 610, a subassembly is oriented in the nuclear reactor in an intermediate position based on an orientation of the bow of a pressure tube. The subassembly includes the pressure tube engaged with a first end fitting.

[0039] In some embodiments, the intermediate position defines a position of the subassembly in the nuclear reaction which is not the final operational position. In some embodiments, in the intermediate position, the subassembly has been inserted into the nuclear reactor bore but has not yet been secured in an operational position (i.e. the position in which the subassembly will be when the nuclear reactor is operating).

[0040] In some embodiments, when in the intermediate position, the bow of the pressure tube is in a downward direction. In some embodiments, the bow of the pressure tube refers to the natural bow of the pressure tube due to manufacturing and/or misalignment when one end is secured to an end fitting. In some embodiments, a bow indicates a direction and/or magnitude of a displacement of a position along the tube relative to the position on the tube if it were perfectly straight. In some embodiments, the bow defines the direction and magnitude of a position having the largest displacement relative to a straight tube. In some embodiments, the direction is defined relative to a reference point (e.g. on the pressure tube).

[0041] In some embodiments, when in the intermediate position, the bow of the pressure tube is in a downward direction. The bow of the pressure tube is in a downward direction when the direction of the bow is below horizontal relative to the ground or the direction of gravity. In some embodiments, when in the intermediate position, the bow of the pressure tube is substantially in the direction of the ground or the direction of gravity. In some situations, when in the a downward direction, the ends of the pressure tube are generally higher than the lowest point of the bow. In some embodiments, when in the intermediate position, the bow of the pressure tube is within 10, 20, 30 or 45 degrees of a vertical downward direction.

[0042] In some embodiments, when in the intermediate position, the bow of the pressure tube is a combination of a natural bowing of the tube, and the bowing caused by gravity. When the natural bow of the pressure tube is oriented in a downward direction, at least an aspects (e.g. a portion of the vector defining the bow) is additive with the bowing caused by gravity's pull on the pressure tube.

[0043] In some situations, by adding the natural bow and the force of gravity, the bowing in the intermediate position can be increased or maximized. In some instances, this may ensure that the resultant combined bowing is in a downward direction.

[0044] At 620, the subassembly in the intermediate position is engage with a second end fitting in the reactor. In some instances, the second end fitting in position at a reactor tube sheet. In some instances, securing the subassembly with the second end fitting when the natural and gravity-induced bowing are additive secures the resulting pressure tube bow in a downward direction.

[0045] At 630, the subassembly is rotated to orient the pressure tube in an operational position. In some embodiments, the pressure tube is rotated into the operational position by rotating the subassembly 90 to 180 degrees. In some embodiments, this rotates the secured bow to be in an upward direction. [0046] The bow of the pressure tube is in an upward direction when the direction of the bow is above horizontal relative to the ground or the direction of gravity. In some embodiments, when in the operational position, the bow of the pressure tube is substantially vertical or the opposite direction of gravity. In some situations, when the bow is in the a upward direction, the ends of the pressure tube are generally lower than the highest point of the bow. In some embodiments, when in the operational position, the bow of the pressure tube is within 10, 20, 30 or 45 degrees of a vertical upward direction.

[0047] In some instances, by ensuring that the bow of the pressure tube is downward when secured in the intermediate position, by rotating the bow to an upward direction, this may help ensure that the theoretical starting bow in the operating position is upward. In some situations, this ensures that at least a portion of the bowing in the operation position is in the opposite direction of the force of gravity. This helps to minimize or otherwise reduce sagging of the pressure tube in operation.

[0048] In some instances, sagging in pressure tube may be undesirable for operation and/or operation lifespan of the fuel channel assembly.

[0049] At 640, the pressure tube is secured in the operational position. In some

embodiments, this includes rolling or otherwise securing the pressure tube relative to the calandria tube, the tube sheet, and/or the nuclear reactor.

[0050] It should also be noted that the embodiments described above and illustrated in the accompanying figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present disclosure. 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 disclosure as set forth in the appended claims.

Claims

CLAIMS What is claimed is:

1. A method of assembling a fuel channel assembly of a nuclear reactor, the method comprising:

orienting a subassembly, comprising a pressure tube engaged with a first end fitting, in the fuel channel assembly in an intermediate position, the intermediate position based on an orientation of a bow of the pressure tube;

engaging the subassembly with a second end fitting positioned at a reactor tube sheet; rotating the subassembly and the second end fitting to orient the pressure tube in an operational position; and

securing the pressure tube in the operational position.

2. The method of claim 1, wherein orienting the subassembly in the intermediate position comprises: engaging the pressure tube with the first end fitting to form the subassembly;

orienting the subassembly in an insertion position; and

inserting the subassembly into a calandria tube installed in the fuel channel assembly;

3. The method of claim 2, wherein when in the insertion position, the bow of the pressure tube is oriented to promote alignment between the subassembly and the second end fitting.

4. The method of claim 2, wherein when in the insertion position, translating the subassembly into the calandria tube orients the pressure tube in the intermediate position.

5. The method of claim 1, wherein in the intermediate position, the bow of the pressure tube is in a downward direction.

6. The method of claim 1, wherein in the operational position, the bow of the pressure tube is in an upward direction.

7. The method of claim 1, wherein in the intermediate position, at least an aspect of a natural bow of the pressure tube and bowing caused by gravity are additive.

8. The method of claim 7, wherein engaging the subassembly with the second end fitting secures the bow caused by a combination of the natural bow and the bowing caused by gravity in the intermediate position.

9. The method of claim 8, wherein in the operational position, the secured bow is in an upward direction.

10. The method of claim 1 comprising determining the orientation of the bow of the pressure tube.

11. The method of claim 10 comprising determining the orientation of the bow of the pressure tube after the pressure tube has been engaged with the first end fitting to form the subassembly.

12. The method of claim 1 comprising:

placing or identifying a marker indicative of a rotational position of the bow on the pressure tube; and

orienting the marker of the pressure tube with respect to a reference position of the calandria tube.

13. The method of claim 1,

placing a marker indicative of an axial position of the bow on the pressure tube; and orienting the marker of the pressure tube with respect to a reference position of the calandria tube.

14. The method of claim 1, comprising fixedly securing the calandria tube within the nuclear reactor.

15. The method of claim 1, comprising orienting the pressure tube with respect to the calandria tube.

16. The method of claim 15, comprising orienting the pressure tube with respect to the calandria tube so that the bow of the pressure tube is rotationally spaced from a bow of the calandria tube.

17. The method of claim 16, wherein orienting the pressure tube with respect to the calandria tube includes rotating the pressure tube by a first angle, and wherein orienting the pressure tube with respect to the calandria tube to align the bow of the pressure tube with respect to the bow of the calandria tube includes rotating the pressure tube by a second angle.

18. The method of claim 17, wherein the first angle is generally the same as the second angle.

19. The method of claim 17, wherein the first angle is one of 90 degrees and 180 degrees.

20. The method of claim 17, wherein the first angle is different than the second angle.

21. The method of claim 17, wherein at least one of the first angle and the second angle is one of 90 degrees or 180 degrees.

22. The method of claim 17, further comprising securing the pressure tube with respect to the calandna tube when the bow of the pressure tube is aligned with respect to the bow of the calandna tube.

23. The method of claim 1, wherein an angle between the pressure tube and an end fitting engaged with the calandria tube is less than 2 microradians.