CA2766476A1 - Methods for calandria tube sheet bore preparation, cleaning, and inspection for use in retubing of a nuclear reactor - Google Patents

Abstract

A method of preparing a calandria tube sheet bore for receiving a calandria tube. The method includes the steps of polishing the bore of the calandria tube sheet; and inspecting the bore, wherein the steps of polishing the bore and inspecting the bore are repeated if there are geometric deviations from a uniform engineered surface in the bore that provide a potential leak pathway in the final fabricated joint.

Description

Attorney Docket No. 027813-9040-CAOO

METHODS FOR CALANDRIA TUBE SHEET BORE PREPARATION, CLEANING, AND INSPECTION FOR USE IN RETUBING OF A NUCLEAR REACTOR
CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U. S. Provisional Patent Application No.
61/433,213, filed January 15, 2011, the contents of which are herein incorporated by reference.
BACKGROUND

[0002] The present invention relates to methods and apparatus for retubing of a nuclear reactor.

[0003] More specifically, the invention relates to methods for calandria tube sheet bore preparation, cleaning, and inspection during retubing of a CANDU-type nuclear reactor. The CANDU ("CANada Deuterium Uranium") reactor is a pressurized heavy-water moderated, fission reactor capable of using fuels composed of natural uranium, other low-enrichment uranium, recycled uranium, mixed oxides, fissile and fertile actinides, and combinations thereof.
SUMMARY

[0004] In one embodiment, the invention provides a method of preparing a calandria tube sheet bore for receiving a calandria tube. The method includes the steps of polishing the bore of the calandria tube sheet; and inspecting the bore, wherein the steps of polishing the bore and inspecting the bore are repeated if there are geometric deviations from a uniform engineered surface in the bore that provide a potential leak pathway in the final fabricated joint.

[0005] In another embodiment the invention provides a method of preparing a calandria tube sheet bore for receiving a calandria tube. The method includes the steps of polishing the bore of the calandria tube sheet; and inspecting the bore, wherein the steps of polishing the bore and inspecting the bore are repeated if a surface roughness of the bore is greater than a preinstalled surface roughness of the bore.

[0006] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

Attorney Docket No. 027813 -9040-CA00 BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

[0008) Figure 1 is a perspective view of a reactor core of a CANDU-type reactor 6.

[0009] Figure 2 is a cut-away view of the fuel channel assembly.

[0010] Figure 3 shows an embodiment of Single Site Logic for Tube Sheet Bore Inspection and Cleaning.

[0011] Figure 4 shows an embodiment of a CTSB Inspection Tool with mounting saddle and a cross-section of a lattice tube.

[0012) Figure 5 shows an embodiment of Single Site Logic for Bellows and Lattice Tube Inspection Series.

[0013) Figures 6A-6E show flow charts corresponding to embodiments of the process of calandria tube sheet bore preparation, cleaning, and inspection.

[0014] Figure 7 shows a cross-section of a calandria tube sheet bore.

[0015] Figure 8 shows a cross-section of a calandria tube sheet bore including a calandria tube and a calandria tube insert.

DETAILED DESCRIPTION

[0016) Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0017] Figure 1 is a perspective view of a reactor core of a CANDU-type reactor 6. The reactor core is typically contained within a vault that is sealed with an air lock for radiation Attorney Docket No. 027813-9040-CAOO

control and shielding. A generally cylindrical vessel, known as a calandria 10, 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 bores that accept a fuel channel assembly 28. As shown in Figure 1, a number of fuel channel assemblies 28 pass through the tube sheets 18 of calandria 10 from the first end 22 to the second end 24.

[00181 Figure 2 is a cut-away view of the fuel channel assembly 28. As illustrated in Figure 2, each fuel channel assembly 28 is surrounded by a calandria tube ("CT") 32.
The CT 32 forms a first boundary between the heavy water moderator of the calandria 10 and the fuel bundles or assemblies 40. The CTs 32 are positioned in the bores on the tube sheet 18. A
CT rolled joint insert 34 within each bore is used to secure the CT 32 to the tube sheet 18.

[00191 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 the 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 the PT 36 and the CT 32. The annulus space 44 is normally filled with a circulating gas, such as dry carbon dioxide, helium, nitrogen, air, or mixtures thereof.
The annulus space 44 and gas are part of an annulus gas system. The annulus gas system has two primary functions.
First, a gas boundary between the CT 32 and PT 36 provides thermal insulation between hot reactor coolant and fuel within the PTs 36 and the relatively cool CTs 32.
Second, the annulus gas system provides an indication of a leaking CT 32 or PT 36 via the presence of moisture, deuterium, or both in the annulus gas.

[00201 An annulus spacer or garter spring 48 is disposed between the CT 32 and PT 36. The annulus spacer 48 maintains the gap between the PT 36 and the corresponding CT
32, while allowing the passage of the annulus gas through and around the annulus spacer 48. Maintaining the gap helps ensure safe and efficient long-term operation of the reactor 6.

[00211 As also shown in Figure 2, an end fitting 50 is attached around the fuel channel assembly 28 outside of the tube sheet 18 at each end 22, 24. At the front of each end fitting 50 is a closure plug 52. Each end fitting 50 also includes a feeder assembly 54. The feeder assemblies 54 feed reactor coolant into or remove reactor coolant from the PTs 36. In particular, for a single Attorney Docket No. 027813-9040-CAOO

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 Figure 2, the feeder assemblies 54 can be attached to the end fitting 50 using a coupling assembly 56 including a number of screws, washers, seals, and/or other types of connectors.

[0022] Coolant from the inlet feeder assembly flows along a perimeter channel of the end fitting 50 until it reaches a shield plug 58. The shield plug 58 is contained inside the end fitting 50 and provides radiation shielding. The shield plug 58 also includes a number of openings that allow the coolant provided by the inlet feeder assembly to enter an end of a PT 36. A shield plug 58 located within the end fitting 50 at the other end of the fuel channel assembly 28 includes similar openings that allow coolant passing through the PT 36 to exit the PT
36 and flow to the outlet feeder assembly 54 through a perimeter channel of another end fitting 50 at the opposite face of the reactor 6. As shown in Figure 1, feeder tubes 59 are connected to the feeder assemblies 54 that carry coolant to or away from the reactor 6.

[0023] Returning to Figure 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. The positioning hardware assemblies 60 are used to set an end of a fuel channel assembly 28 in either a locked or unlocked position. In a locked position, the end of the fuel channel assembly 28 is held stationary. In an unlocked position, the end of the fuel channel assembly 28 is allowed to move. A tool can be used with the positioning hardware assemblies 60 to switch the position of a particular fuel channel assembly 28.

[0024] The positioning hardware assemblies 60 are also coupled to an end shield 64. The end shields 64 provide additional radiation shielding. Positioned between the tube sheet 18 and the end shield 64 is a lattice sleeve or tube 65. The lattice tube 65 encases the connection between the end fitting 50 and the PT 36 containing the fuel assemblies 40.
Shielding ball bearings 66 and cooling water surround the exterior the lattice tubes 65, which provides additional radiation shielding.

[0025] The following is a description of various embodiments of methods for calandria tube sheet bore preparation, cleaning, and inspection for use in retubing (replacing some or all of the Attorney Docket No. 027813-9040-CAOO

calandria tubes) of a nuclear reactor, in particular a CANDU-type reactor, which can ensure that the calandria tube sheet bore (CTSB) is clean, smooth, and is dimensionally fit for a new calandria tube joint to be made. This process is important for, among other things, ensuring a leak-tight joint.

100261 Calandria Tube Sheet Bore Preparation, Cleaning, and Inspection Series [00271 The purpose of the CTSB Cleaning and Inspection series is to prepare the CTSB for the new calandria tube (CT) rolled joint. The tools included for production in the CTSB
Cleaning and Inspection series may include:

[00281 = Lattice Tube Inspection Tool [00291 = CTSB Cleaning Tool and Head [00301 = Polishing Tool Head [00311 = Swab Tool Head [00321 = Laser Tracker System [00331 = CTSB Inspection Tool [00341 = CTS Bore Gauge Tool 100351 = CTSB Refurbishment Tool [00361 = CTSB Narrow Grooves Refurbishment Tool 100371 The tool set and sequence of operations will be defined based on the technical specification for the respective processes, where the technical specifications themselves may be based on results of the Rolled Joint Qualification Program.

[00381 Tool Set - Production Tools - Lattice Tube Inspection Tool:

Attorney Docket No. 027813-9040-CA00 [0039] The Lattice Tube Inspection Tool will vacuum loose debris and perform a visual inspection of the bore. The radiation tolerant camera used within the tool is a Pan-Tilt-Zoom (PTZ) color camera that is capable of delivering high-definition resolution.

[0040] The Lattice Tube Inspection Tool is installed and operated from within either the Lattice Sleeve Handling Tool carriage or Slide Table. The Tool is semi-automated, as an Operator may be required to deploy the vacuum. In one embodiment, the tool dimensions are: 8"
(W) x 48" (L); the tool weight is: 300 lbs.; and the quantities required are four: two for production, one as a spare, and one for training.

[0041] Radiation damage requires that the image quality of the camera be checked every 60 lattice sites. The image quality is verified by visually confirming the electrical discharge machining (EDM) notches on a qualification piece.

[0042] CTSB Cleaning Tool and Head:

[0043] The CTSB Cleaning Tool and Head is used to clean the surface of the bore and remove any slivers of material that may be left in the grooves after CT
removal. It is a manually-delivered and manually-operated tool. In one embodiment, the tool dimensions are: 12" (W) x 135" (L); the tool weight is: 250 lbs.; and the quantities required are four:
two for production, one as a spare, and one for training.

[0044] The brushes should be changed every 1-20 lattice sites or as frequently as needed to maintain the consistency and quality of the process. This maintenance occurs as a parallel process with other reactor face work.

[0045] Polishing Tool Head:

[0046] The Polishing Tool Head is used to clean the bore surface and the grooves after CT
removal. In some embodiments, it is a manually-delivered and manually-operated tool; in other embodiments, it is a manually-delivered and automatically-operated tool; in still other embodiments, it is an automatically-delivered and manually-operated tool; and in yet other embodiments, it is an automatically-delivered and automatically-operated tool.
In one Attorney Docket No. 027813-9040-CAOO

embodiment, the tool head dimensions are: 10" (W) x 12"(L); the tool head weight is: 30 lbs.;
and the quantities required are four: two for production, one as a spare, and one for training.
[00471 The polishing tool uses pads, a disc, a wheel, brushes, or other abrading material to gradually wear down and or plastically deform the surface of the bore in order to smooth the surface sufficiently for providing a leak tight joint with a calandria tube.
The polishing pads (or disc, wheel, brush, or other material, as the case may be) and other consumables related to polishing should be changed regularly in order to maintain the consistency and quality of the end product (e.g. every 1-20 lattice sites during the series). This maintenance occurs as a parallel process with other reactor face work. Polishing of the CTSB can ensure a leak tight calandria tube joint. For purposes of the present application, a leak tight calandria tube joint includes a joint having an acceptable amount of leakage as defined by engineering and/or operational requirements for the project.

[0048) Swab Tool Head:

[00491 The Swab Tool Head is used to perform a final cleaning with isopropyl alcohol on the bore. It is a manually-delivered and manually-operated tool. In one embodiment the tool head dimensions are: 12" (W) x 12" (L); the tool head weight: 30 lbs.; and the quantities required are four: two for production, one as a spare, and one for training.

[00501 In various embodiments, changing of the swab head cloths occurs at every lattice site during the series or as required to maintain the consistency and quality of the desired result. It occurs as a parallel process with other reactor face work.

[00511 CTSB Inspection Tool:

[00521 In various embodiments, the CTSB Inspection Tool (Figure 4) is a multi-function tool. In some embodiments, the CTSB Inspection Tool utilizes a laser sensor that gathers 360 data across the axis of the bore. This information is then analyzed off-line for average bore I.D.
and for any possible damage or indications that would impede acceptable rolling of a new calandria tube. This Tool is also used as part of the Laser Tracker System to measure the calandria Tubesheet-to-Tubesheet (TS-to-TS) datum distance at each lattice site. This is Attorney Docket No. 027813-9040-CAOO

manually-delivered and has an automated operation. In one embodiment, the tool dimensions are: 10" (W) x 135" (L); the tool weight is: 650 lbs.; and the quantities required are four: two for production, one as a spare, and one for training.

[0053] In various embodiments, it is recommended that an internal tool calibration check occur at every 20 lattice sites during the series. In some embodiments, the time required to complete this check is approximately 10 - 15 minutes.

[0054] CTS Bore Gauge Tool:

[0055] In one embodiment, the CTS Bore Gauge Tool is used to gather spot CTSB
inner diameter (I.D.) information. It is a manually-delivered and manually-operated tool. In one embodiment, the tool dimensions are: 8" (W) x 135" (L); the tool weight is: 30 lbs.; and the quantities required are four: two for production, one as a spare, and one for training. No scheduled maintenance of this tool is required during the series.

[0056] CTSB Refurbishment Tool:

[0057] In various embodiments, the CTSB Refurbishment Tool is a completely automated tool used to complete the following operations:

[0058] = inspect the condition of the calandria side tube sheet bore by means of a video camera and a laser beam [0059] = brushing of the calandria side tube sheet bore utilizing stainless steel brushes [0060] = resurfacing of the tube sheet bore grooves and re-establishing new sharp sealing edges for leak tightness.

[0061] In one embodiment, the tool dimensions are: 24" (W) x 195" (L); the tool weight is:
1600 lbs.; and the quantities required are four: two for production, one as a spare, and one for training.

[0062] No scheduled maintenance of this tool is required during the series.
[0063] Contingency Tools Attorney Docket No. 027813-9040-CAOO

[00641 CTSB Refurbishment Tool:

[00651 The CTSB Refurbishment Tool, which is described above, can also be used to perform resurfacing/milling of the tube sheet bore grooves in order to create sharp edges for leak tightness. This tool could serve as a baseline tool for tube sheet bore inspection and tube sheet bore brushing, and a contingency tool for tube sheet bore milling operation.

[00661 CTSB Narrow Grooves Refurbishment Tool:

[00671 The CTSB Narrow Groove Refurbishment Tool is a single point cutter manual tool that could be used prior to FC installation to refurbish CTSB narrow grooves with or without the presence of the CT. In one embodiment, the tool dimensions are: 7" (W) x 117"
(L); the tool weight is: 250 lbs.; and the quantities required are four: two for production, one as a spare, and one for training. No scheduled maintenance of this tool is required during the series.

[0068] Tube Sheet Bore Cleaning & Inspection [00691 The main purpose of the Tube Sheet Bore Cleaning and Inspection series is to inspect and prepare the tube sheet bore to install the new calandria tube. The series was performed using a combination of tools. In various embodiments, a brush tool may be used to clean the bore surface and remove any slivers of material that may be left in the grooves after calandria tube removal. The side facing inspection tool is used to vacuum loose debris and perform a visual inspection of the bore prior to laser scanning with the inspection tool. The calandria Tube Sheet Bore (CTSB) inspection tool performs a laser scan of the bore and a portion of the split bearing sleeve to measure and document condition. Using the inspection tool with the global coordinate system laser tracker the distance between the tube sheets from one reactor face to the other face is measured to calculate the new calandria tube installation length.

[00701 In those embodiments in which the Tube Sheet Bore Cleaning and Inspection series is performed at a high production rate, the optimization of the processes and tools as outlined contribute to minimizing the amount of time required to complete the work, resulting in lower costs and lower radiation exposure to workers.

Attorney Docket No. 027813-9040-CAOO

[00711 The following are among the major tools used in this series: the lattice sleeve handling tool; the CTSB inspection tool; the CTSB brush tool; and the laser tracker system.
[00721 The most intricate tool used in this series is the CTSB inspection tool, which in some embodiments can be used in the CTSB replication step. The CTSB inspection tool is used to measure the diameter of the CTSB at various locations for calandria tube installation and to profile the dimensions of scratches or other geometric deviations on the CTSB
surface that could potentially result in a substantial leak when the calandria tube is rolled into the CTSB. The acceptability of the CTSB surfaces and rolled joint grooves can be determined using data collected by this tool. Split-Bearing Sleeve to CTSB distance is measured by linear scan from the outboard edge of the tube sheet to the inboard edge of the split bearing sleeve to determine the position of the split bearing relative to the CTSB outboard edge. In addition, a retro-reflector is used with the global coordinate system laser tracker to determine the distance between the East and West Calandria tube sheets. A target can also be mounted on the alignment cap to assist the worktable aligning the tool with a lattice site. The CTSB inspection tool incorporates a laser displacement sensor for accurate distance measurements.

[00731 The global coordinate system laser tracker is a multi-function tool that is used to accurately survey and measure various elements during retubing in a reactor, including establishing the global coordinate system and TS-to-TS measurements. In those embodiments in which a laser tracker on the heat exchange platform is unable to gain line-of-sight to a target due to obstructions from objects such as scaffolding, this can be addressed by installing an additional laser tracker, for a total of two per face, such that when one tracker cannot see the target the other laser tracker can be used instead. As a result all measurements needed for all sites can be acquired successfully without critical time being lost.

[00741 Lattice Tube & Bellows Inspections [00751 Fuel channel bellows are not normally required to be replaced during retubing as they are able to be reset and used for the extended life of the reactor. They must be inspected and refurbished to some degree before installation of the new replacement fuel channel (FC) assemblies.

Attorney Docket No. 027813-9040-CAOO

[00761 The major tools used in this series can include a bellows inspection and cleaning tool;
an AGS pigtail flow verification and blockage removal tool; a side facing inspection tool; and a split bearing rotation tool.

[00771 In various embodiments, there are several steps in the process of calandria tube sheet bore preparation, cleaning, and inspection. These processes might be carried out as part of a complete retubing project or during replacement of one or a limited number of tubes on a CANDU reactor. As discussed below, these steps may be carried out a number of different orders; several orders of steps are presented below (see also Figures 3, 6A-6E), although other orderings of the steps are also possible.

[00781 A. Visual Inspection [00791 In various embodiments, reactor tube sheet bores will be visually examined to ensure that the conditioning (polishing) process removed the adherent deposits and to ensure that the bore surface condition meets the acceptance criteria in preparation for calandria tube installation.
The tubesheet bore conditioning and subsequent bore visual examination will generally occur after the disassembly of the original calandria tube rolled joint. The tubesheet bore visual examination is to confirm that the tubesheet bore surface condition is clean so that when rolled into, the calandria tube rolled joint will be strong and leak tight. In various embodiments, visual inspection may be performed using the Lattice Tube Inspection Tool.

[00801 B. Conditioning/Polishing [00811 In this step, the CTSB is conditioned after the original rolled joint is disassembled in order to remove adherent deposits and debris accumulated over time, in preparation for making replacement rolled joints. This process is intended to remove adherent bore deposits and debris and restore the tube sheet bore to a known condition without damaging the bore. In various embodiments, conditioning/polishing may be performed using the Polishing Tool Head.

[00821 In various embodiments, the target surface roughness for the inner surface of the bore of the calandria tube sheet is less than 400 g in.. In some embodiments, the surface roughness is measured in the axial direction (i.e. parallel to the long axis of the calandria tube). In other Attorney Docket No. 027813 -9040-CAOO

embodiments, the surface roughness is measured over less than the full thickness of the bore. In some embodiments, the polishing step is intended to produce a target surface roughness that is comparable to a preinstalled surface roughness for a calandria tube sheet bore. In general, "preinstalled surface roughness" refers to the roughness of an engineered surface that meets criteria to produce a leak tight joint, such as a surface produced by controlled manufacturing operations. Thus, in various embodiments, the average surface roughness of the bore may be less than 400 g in., less than 350 g in., less than 300 g in., less than 250 g in., less than 200 in., less than 150 g in., or less than 100 in.

[0083] In some cases, the surface of the calandria tube sheet bore may contain large continuous or semi-continuous geometric deviations from a desired uniform engineered surface.
The deviations may be made of one or more of scratches, pits, burrs, and/or adhered material (e.g. slivers). In some cases, the deviations, either singly or in groups, may provide a potential leak path at the interface between the calandria tube and the calandria tube sheet bore, particularly when the deviation is axially-oriented. Figure 7 shows a cross-section of a calandria tube sheet 18 with a bore 19 therethrough, the bore 19 having a central axis that is defined by the long axis 33 of the calandria tube that goes through the bore 19. The bore 19 is shown with several geometric deviations on its inner surface, including a first deviation 19A that is parallel to the long axis 33 of the calandria tube, a second deviation 19B that is eccentric or spiral and which is not parallel to the long axis 33 of the calandria tube, and a third deviation 19C that is circumferential and is also not parallel to the long axis 33 of the calandria tube and in fact is approximately perpendicular to the long axis 33 of the calandria tube. Figure 8 shows a cross-section of a final rolled joint assembly in a bore in a calandria tube sheet

18. The rolled joint assembly includes a calandria tube 32 and a calandria tube insert 34. The surface of the bore in the calandria tube sheet 18 has engineered features including several grooves 104. As seen in Figure 8, a tight fit of the calandria tube 32 and the calandria tube insert 34 against the surface of the bore facilitates the formation of a leak tight joint.

[0084] If inspection reveals that at least some of the deviation 19A are axial, e.g. parallel to a long axis 33 of the calandria tube 32, then the bore 19 generally will be polished again (or in some cases refurbished/milled; see below) to prevent possible leakage that could occur through the axial deviation 19A. In various embodiments a deviation is considered substantially parallel Attorney Docket No. 027813-9040-CAOO

to the axis of the bore if it is within approximately 1 , approximately 2 , approximately 3 , approximately 4 , approximately 5 , approximately 10 , approximately 15 , approximately 20 , or approximately 25 of the long axis of the calandria tube 32.

[0085] Polishing and inspection are repeated until there are few or no axially-oriented geometric deviations. In some embodiments, polishing and inspection are repeated until any remaining deviations, to the extent there are any, are substantially non-axial in orientation. For example, geometric deviations that are eccentric, spiral, and/or or circumferential pose less of a risk for leakage and in some cases their presence on the surface of the bore can be tolerated.
According to embodiments of the invention, repeating of polishing is indicated when approximately 1%, approximately 2%, approximately 3%, approximately 4%, approximately 5%, approximately 10%, approximately 15%, approximately 20%, approximately 25%, approximately 50%, approximately 75%, approximately 90%, approximately 95%, approximately 99%, or approximately 100% of the deviations in the surface of the bore are axial.
[0086] C. Swabbing [0087] In certain embodiments, swabbing is performed in order to collect dust from the CTSB. Residual dust could compromise the tightness of the Roll Joint between CT and CTSB.
In various embodiments, swabbing is completed in two steps: 1) Alcohol swab 2) Dry swab. In various embodiments, the swabs may include an absorbent material which does not release fibers or other solid elements which could contaminate the bore or other parts of the reactor. In various embodiments, swabbing may be performed using the Swab Tool Head.

[0088] D. Bore Gauging [0089] This process takes measurements of the CTSB diameter in the wide groove area.
This information is required for proper set up of the Roll Joint Expanders. In various embodiments, bore gauging may be performed using the CTS Bore Gauge Tool.

[0090] E. CTSB Refurbishment [0091] In various embodiments, the CTSB Refurbishment tool is used to perform resurfacing/milling of the tube sheet bore grooves in order to create sharp edges for leak Attorney Docket No. 027813-9040-CA00 tightness. Thus, in some embodiments the bore may be milled (refurbished) at various stages. In one embodiment, the bore is milled prior to any polishing or inspecting steps are performed. In general, the bore may be `machined', i.e. material may be removed from the surface of the bore through the use of one or more of a single-point or multi-point cutting tool, a boring bar, a milling cutter, and/or a grinder.

[00921 F. Replication [0093] In some embodiments, the tube sheet bore is replicated by having a mold taken of the bore. The mold is taken and used for further examination of the bore and for obtaining the data necessary for CTSB refurbishment. Other methods of obtaining information about the surface of the bore include laser scanning and optical light scanning or other methods which acquire data to characterize the surface in question for further examination, where the acquired data provides quantitative information about the surface which can be analyze using one or more techniques such as visual displays of the data or analysis using spreadsheets. In various embodiments, laser-based replication may be performed using the CTSB Inspection Tool.

[0094] G. TS-to-TS measurement [0095] In various embodiments, tube sheet-to-tube sheet (TS-to-TS) measurements are used to determine the length of a calandria tube. That is, the distance between tube sheets is indicative of the length of the calandria tube. In various embodiments, tube sheet-to-tube sheet measurements are obtained following each polishing step, while in other embodiments tube sheet-to-tube sheet measurements are obtained following only some of the polishing steps, and in still other embodiments tube sheet-to-tube sheet measurements are not obtained. In various embodiments, tubesheet-to-tubesheet measurements are obtained using the CTSB
Inspection Tool.

[0096] In any step that involves removal of material (e.g. polishing or machining), accurate tool placement (e.g. in one or all of the x, y, and z axes as well as with respect to roll, pitch, and yaw) relative to the existing calandria tube sheet bore is important so that the central axis of the bore is not significantly altered by the material removal process. Tool placement is more critical for machining than for polishing, although it is important for both types of procedures.

Attorney Docket No. 027813-9040-CAOO

[00971 In various embodiments, the steps listed above can be implemented in a number of different sequences, as shown in Figures 6A-6E. Figures 6A-6E provide flow charts depicting several of the possible sequences in which the steps can be implemented. In addition to the linear sequences of steps that are listed, additional steps may be performed in conjunction with some of those that are listed. For example, following the polishing/conditioning step in the sequences of steps shown in the flow charts of Figures 6A-6D, tube sheet-to-tube sheet measurements can be obtained. Similarly, prior to completion of the final steps in the sequences shown in the flow charts of Figures 6B-6D, a final FME (foreign material exclusion) visual check can be performed.

[00981 Figure 3 provides another embodiment of a procedure for bore preparation, cleaning, and inspection which can be used as part of a complete retubing project or during replacement of one or a limited number of tubes on a CANDU reactor. In addition to the list of steps, Figure 3 also includes an estimate of the amount of time each step may take.

[00991 Thus, the invention provides, among other things, methods for calandria tube sheet bore preparation, cleaning, and inspection during retubing of a CANDU-type nuclear reactor.

Claims (26)

What is claimed is:

1. A method of preparing a calandria tube sheet bore in a previously-operated reactor for receiving a calandria tube, the method comprising:
polishing the bore of the calandria tube sheet; and inspecting the bore, wherein the steps of polishing the bore and inspecting the bore are repeated if there are geometric deviations from a uniform engineered surface in the bore that provide a potential leak pathway in the final fabricated joint.

2. The method of claim 1, further comprising swabbing the bore after polishing the bore and before inspecting the bore.

3. The method of claim 1, further comprising swabbing the bore after inspecting the bore.

4. The method of claim 1, further comprising gauging the bore after polishing the bore and before inspecting the bore.

5. The method of claim 1, further comprising gauging the bore after inspecting the bore.

6. The method of claim 1, further comprising replicating the bore prior to polishing the bore.

7. The method of claim 1, further comprising replicating the tube sheet bore prior to polishing the bore.

8. The method of claim 7, wherein replicating the bore includes at least one of having a mold taken of the bore, laser scanning the bore, and optical light scanning the bore.

9. The method of claim 1, further comprising machining the bore prior to polishing the bore.

10. The method of claim 9, wherein machining includes at least one of using a single-point cutting tool, using a multi-point cutting tool, using a boring bar, using a milling cutter, and using a grinder.

11. The method of claim 1, further comprising measuring a distance between tube sheets in the calandria.

12. The method of claim 1, wherein the steps of polishing the bore and inspecting the bore are not repeated if substantially all of the geometric deviations have been reduced to a level that is acceptable for making a joint.

13. The method of claim 1, wherein the bore has an axis that extends through the bore and is normal to a face of the bore, and wherein the steps of polishing the bore and inspecting the bore are not repeated if substantially all of the geometric deviations are circumferential relative to the axis of the bore.

14. The method of claim 1, further comprising removing an existing calandria tube prior to polishing the bore.

15. A method of preparing a calandria tube sheet bore for receiving a calandria tube, the method comprising:
polishing the bore of the calandria tube sheet; and inspecting the bore, wherein the steps of polishing the bore and inspecting the bore are repeated if a surface roughness of the bore is greater than a preinstalled surface roughness of the bore.

16. The method of claim 15, wherein the steps of polishing the bore and inspecting the bore are repeated if a surface roughness of the bore is less than 200 µ in.

17. The method of claim 15, wherein the steps of polishing the bore and inspecting the bore are repeated if a surface roughness of the bore is less than 100 µ in.

18. The method of claim 15, further comprising swabbing the bore after polishing the bore and before inspecting the bore.

19. The method of claim 15, further comprising swabbing the bore after inspecting the bore.

20. The method of claim 15, further comprising gauging the bore after polishing the bore and before inspecting the bore.

21. The method of claim 15, further comprising gauging the bore after inspecting the bore.

22. The method of claim 15, further comprising replicating the bore prior to polishing the bore.

23. The method of claim 15, further comprising replicating the tube sheet bore prior to polishing the bore.

24. The method of claim 15, further comprising milling the bore prior to polishing the bore.

25. The method of claim 15, further comprising measuring a distance between tube sheets in the calandria.

26. The method of claim 15, further comprising removing an existing calandria tube prior to polishing the bore.