CA2766465C - Calandria tube rolled joint leak test tool and service cart - Google Patents

Abstract

Methods and systems for testing a joint assembly coupling a calandria tube to a tube sheet in a reactor. One method includes (a) inserting a test tool into a lattice site containing the joint assembly, the test tool including at least two seals that define an enclosed volume surrounding the joint assembly. The method also includes (b) drawing a vacuum in the enclosed volume, (c) stopping drawing the vacuum in the enclosed volume and allowing the vacuum to decay over a predetermined decay period, (d) measuring a change in pressure in the enclosed volume during the decay period and calculating a leak rate based on the change in pressure, (e) repeating (b) through (d) to generate a plurality of leak rates, and (f) determining an equilibrium leak rate based at least on the plurality of leak rates. The method also includes performing diagnostics during the testing method.

Description

= CA 2766465 2017-03-01 Attorney Docket No. 027813-9061-CA00 CALANDRIA TUBE ROLLED JOINT LEAK TEST TOOL AND SERVICE CART
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional Application No.
61/433,431 of the same title filed January 17, 2011.
FIELD OF THE INVENTION

[0002] The present invention relates to methods and systems for retubing nuclear reactors and, in particular, methods and apparatus for testing a calandria tube rolled joint for a leak.
SUMMARY

[0003] A nuclear reactor has a limited life of operation. For example, second generation CANDUTm-type reactors ("CANada Deuterium Uranium") are designed to operate for approximately 25 to 30 years. After this time, the existing fuel channels can be removed and new fuel channels can be installed. Performing this "retubing" process can extend the life of a reactor. For example, retubing a CANDUTm-type reactor can extend the reactor's life by an additional 25 to 40 years. Without performing the retubing a reactor that reaches the end of its useful life is typically decommissioned and replaced with a new reactor, which poses significant costs and time. Alternatively, replacement energy sources may be used to extend the life of a reactor. However, replacement energy sources are often more expensive than installing a new reactor, and can be difficult to acquire.

[0004] During retubing, calandria tubes are replaced, which requires replacing calandria tube rolled joints that hold the calandria tube in the reactor. Traditionally, rolled joints are leak tested by applying helium tracer gas to the calandria side of the rolled joint. The helium tracer gas is then pulled through the joint by a vacuum pump into a helium leak detector.
Deployment of this traditional leak test method, however, is difficult due to the severe constraints in accessibility and the radioactive environment present during retubing operations. Furthermore, this test often requires a long test time and, once started, cannot be interrupted to perform other diagnostic functions without requiring that the test be restarted.

Attorney Docket No. 027813-9061-CA00

[0005] Therefore, embodiments of the present invention provide methods and systems for confirming the leak tightness of in-reactor calandria tube joints during retube operations. One embodiment of the invention provides a method for testing a joint assembly coupling a calandria tube to a tube sheet in a reactor. The method includes (a) inserting a test tool into a lattice site containing the joint assembly, the test tool including at least two seals that define an enclosed volume surrounding the joint assembly. The method also includes (b) drawing a vacuum in the enclosed volume, (c) stopping drawing the vacuum in the enclosed volume and allowing the vacuum to decay over a predetermined decay period, (d) measuring a change in pressure in the enclosed volume during the decay period and calculating a leak rate based on the change in pressure, (e) repeating (b) through (d) to generate a plurality of leak rates and (f) determining an equilibrium leak rate based at least on the plurality of leak rates.

[0006] Another embodiment of the invention provides a system for testing a joint assembly coupling a calandria tube to a tube sheet in a reactor. The system includes a pump for drawing a vacuum on an enclosed volume surrounding the joint assembly and a test tool coupled to the pump by at least one hose. The test tool includes a test tool head that includes at least two seals for defining the enclosed volume and an inlet for drawing the vacuum on the enclosed volume.
The test tool also includes a pressure gauge for measuring a pressure in the enclosed volume, a vacuum tube for drawing the vacuum on the enclosed volume, and at least one valve for repeatedly drawing the vacuum on the enclosed volume and letting the vacuum decay over a predetermined decay period. The pressure gauge provides a plurality of pressure readings in the enclosed volume during the repeated drawings of the vacuum and vacuum decays, the plurality of pressure readings used to calculate an equilibrium leak rate of the joint assembly.

[0007] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a perspective view of a CANDUTM reactor.

[0009] FIG. 2 is a cut-away view of a CANDUTm-type nuclear reactor fuel channel assembly.

Attorney Docket No. 027813-9061-CA00

[0010] FIG. 3 is a cross-sectional view of a calandria tube rolled joint assembly before being rolled according to some embodiments of the invention.

[0011] FIG. 4 is a cross-sectional view of the calandria tube rolled joint assembly of FIG. 3 after being rolled according to some embodiments of the invention.

[0012] FIG. 5 is a cross-sectional view of the calandria tube rolled joint assembly of FIG. 3 and potential leak paths associated with the rolled joint assembly.

[0013] FIG. 6 is a perspective view of a calandria tube rolled joint leak test tool according to some embodiments of the invention.

[0014] FIG. 7 is a flow chart illustrating a leak test method performed using the leak test tool of FIG. 6 according to some embodiments of the invention.

[0015] FIG. 8 is a cross-sectional view of the test tool of FIG. 6 installed in a lattice site.

[0016] FIG. 9 is a cross-sectional view of an enclosed volume generated when the test tool of FIG. 6 is installed in a lattice site.

[0017] FIG. 10 is a graph of a vacuum decay trend resulting from a vacuum decay leak test performed by the test tool of FIG. 6.

[0018] FIG. 11 is a graph of a vacuum decay trend resulting from a vacuum decay leak test performed by the test tool of FIG. 6 and an ambient helium trend resulting from an ambient helium leak test performed by the test tool of FIG. 6.

[0019] FIG. 12 is a cross-sectional view of areas supplied with helium using the test tool of FIG. 6 to test one or more seals of the test tool.

[0020] FIG. 13 is a graph of helium readings associated with a leaking seal of the test tool of FIG. 6.

[0021] FIG. 14 is a perspective view of a helium leak detector used with the test tool of FIG.
6 according to some embodiments of the invention.

= CA 2766465 2017-03-01 Attorney Docket No. 027813-9061-CA00

[0022] FIG. 15 is a perspective view of a service cart used with the test tool of FIG. 6 according to some embodiments of the invention.
DETAILED DESCRIPTION

[0023] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0024] FIG. 1 is a perspective of a reactor core of a CANDUTm-type reactor 6. The reactor core is typically contained within a vault that is sealed with an air lock for radiation control and shielding. A generally cylindrical vessel, known as a calandria 10, contains a heavy-water 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 FIG. 1, a number of fuel channel assemblies 28 pass through the tube sheets 18 of calandria 10 from the first end 22 to the second end 24.

[0025] FIG. 2 is a cut-away view of the fuel channel assembly 28. As illustrated in FIG. 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 insert 34 within each bore is used to secure the CT 32 to the tube sheet 18 and form a rolled joint assembly.

[0026] 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.

Attorney Docket No. 027813-9061-CA00 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.

[0027] 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.

[0028] As also shown in FIG. 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 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 fitting 50 using a coupling assembly 56 including a number of screws, washers, seals, and/or other types of connectors.

[0029] 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 FIG. 1, feeder tubes 59 are connected to the feeder assemblies 54 that carry coolant to or away from the reactor 6.

[0030] 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. The positioning hardware assemblies 60 are used to set an end of a fuel channel . . . , CA 2766465 2017-03-01 Attorney Docket No. 027813-9061-CA00 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.

[0031] 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.

[0032] It should be understood that although a CANDUTm-type reactor is illustrated in FIGS.
1 and 2, the methods and systems described below for retubing a reactor also apply to other types of reactors containing similar components as illustrated in FIGS. 1 and 2.

[0033] During the retubing process, many of the components of the reactor 6 are removed and replaced. In particular, new fuel channel assemblies 28 are placed in the reactor 6 after the existing fuel channel assemblies 28 have been removed. In some embodiments, the PTs 36 and the CTs 32 are made from zirconium alloys and the end fittings 50 and the calandria 10 are made of stainless steel. Therefore, because welding zirconium to steel is not possible, a mechanical joint is used to attach the PTs 36 and the CTs 32 to the end-fittings 50 and the calandria 10. In particular, as noted above, a rolled joint assembly is used to secure the CT
32 to the tube sheet 18. Although not discussed in detail below, it should be understood that the rolled joint assembly used to secure the CTs 32 to the tube sheets 18 can be similar to a rolled joint assembly used to secure the PTs 36 to the end-fittings 50, and the methods and apparatus discussed below with respect to the rolled joint assembly used with the CTs 32 can also be used to test the leak tightness of a rolled joint assembly used with the PTs 36.

[0034] FIG. 3 illustrates a rolled joint ("RJ") assembly 90 used to secure the CT 32 to the tube sheet 18. As shown in FIG. 3, the RJ assembly 90 includes the CT 32, the tube sheet 18, and the CT insert 34. The CT insert 34 can be constructed from stainless steel and can include an insert flange 100 and a shoulder 102. The flange 100 abuts an outward face 104 of the tube Attorney Docket No. 027813-9061-CA00 sheet 18, and the shoulder 102 abuts an inner surface area 106 of a bore in the tube sheet 18. The inner surface area 106 can include one or more grooves 110 that abut the shoulder 102 of the CT
insert 34. As shown in FIG. 3, a gap 112 between the shoulder 102 and the inner surface area 106 accepts the CT 32.

[0035] After the CT 34 is placed in the bore of the tube sheet 18 and the CT 32 is positioned within the gap 112, a rolling tool is used to deform and extend the CT insert 34, the tube sheet 18, and the CT 32 to sandwich the CT 32 between the CT insert 34 and the tube sheet 18 and form a mechanical joint between these components. As shown in FIG. 4, after rolling the CT
insert 34, the flange 100 is deformed against the outward face 104 of the tube sheet 18 and the shoulder 102 extrudes into the grooves 110. Furthermore, the CT 32 is deformed into the gap 112 between the CT insert 34 and the tube sheet 18.

[0036] FIG. 5 illustrates an installed RJ assembly 90. As shown in FIG. 5, there are potential leak paths 110 through the assembly 90. For example, the leak paths 110 can include a path between the CT 32 and the tube sheet 18 bore, where the moderator would leak from the calandria 10 into the lattice tube site, and a path between the CT 32 and the CT insert 34, where the moderator would leak from the calandria 10 into the CT 32.

[0037] In some embodiments, the newly-fabricated RJ assembly 90 must meet leak tightness criteria to ensure that the mechanical joint is tight enough for reactor operation. Therefore, once the RJ assembly 90 is installed (and before the PT 36 is installed inside the CT 32), a test is performed to verify the leak tightness of the RJ assembly 90. For example, using a leak test as described below, a RJ assembly 90 leak rate can be accurately quantified in a range from approximately 5x10-5 cc/s to approximately 5x10-3 cc/s. Therefore, the leak test can be used to identify RJ assemblies 90 having a leak rate outside of required engineering specifications, which can then be inspected and, in some situations, replaced to ensure proper reactor operation.

[0038] The leak tightness of the installed RJ assembly can be tested using a CT RJ leak test tool. FIG. 6 illustrates a CT RJ leak test tool 200 according to one embodiment of the invention.
In some embodiments, the test tool 200 is approximately 70.0 inches long and includes a tool head 202. The tool head 202 includes at least two seals 204. For example, as shown in FIG. 6, in some embodiments, the tool head 202 includes an inboard seal 204a and an outboard or face Attorney Docket No. 027813-9061-CA00 seal 204b. The seals 204a and 204b can be constructed from rubber and can include o-rings.
The inboard seal 204a seals axially onto an inner diameter of the CT 32 and the outboard seal 204b seals on the outward face 104 of the tube sheet 18. As described below in more detail, the tool head 202 is inserted inside the CT 32 and the seals 204 are used to create an enclosed volume around the RJ assembly 90.

[0039] As shown in FIG. 6, the tool head 202 is attached to a vacuum tube 206. The vacuum tube 206 is used to create the vacuum in an enclosed area around the RJ
assembly 90. In particular, as shown in FIG. 6, the tool head 202 includes an inlet 208 that connects with the vacuum tube 206 and is used to draw the vacuum around the RJ assembly 90. One or more shield plugs 210 (e.g., split shield plugs) can be used to support the vacuum tube 206 and the tool head 202. The shield plugs 210 can also be used to balance the weight of the tool 200 and keep the tool 200 straight as the tool 200 is inserted into a lattice site. The shield plugs 210 can also be used to provide shielding from radiation escaping through the lattice site.

[0040] The tool 200 also includes one or more valves 212 used to draw and stop drawing the vacuum around the RJ assembly 90. In addition, as shown in FIG. 6, the tool 200 includes one or more pressure gauges 213 (e.g., Pirani Gauges). The pressure gauges 213 provide a pressure reading within the vacuum tube 206 and, subsequently, a pressure reading within the enclosed area around the RJ assembly 90. The pressure gauges 213 can also be used to verify that one or both valves 212 have closed or opened properly. For example, each valve 212 can be associated with a pressure gauge and, when one valve 212 should be opened or closed, the pressure valve associated with the other valve 212 can be used to verify that valve 212 opened or closed properly. Providing this diagnostic functionality allows issues with the test tool 200 to be identified as soon as possible and allows issues to be corrected before test readings are generated.
In some embodiments, the valves 212 are operated automatically by various automated controllers. In other embodiments, the valves 212 are operated manually by one or more human operators. Similarly, readings from the pressure gauge(s) 213 can be collected manually or can be automatically logged or transmitted to a control system.

[0041] The vacuum tube 206 is also connected to a helium leak detector 214 (e.g., an Alcatel Helium Leak Detector) that includes a pump, such as a turbo pump or a roughing pump. The Attorney Docket No. 027813-9061-CA00 pump is used to create the vacuum around the RJ assembly 90. The helium leak detector 214 also detects a level of helium in the gas drawn from around the RJ assembly 90 to create the vacuum. The vacuum tube 206 can be connected to the helium leak detector 214 by a flexible hose 216, such as a bellows hose.

[0042] As shown in FIGS. 6 and 8, the test tool 200 can also include a threaded rod or lead screw 218 contained within a hollow tube 220. The hollow tube 220 can be used to support and shield the components of the tool 200, such as the threaded rod or lead screw 218. The shield plugs 210 can also support the hollow tube 220.

[0043] The threaded rod or lead screw 218 is used to expand and retract the inboard seal 204a. In particular, to allow the tool head 202 to be inserted into the lattice site, the inboard seal 204a can be positioned in a retracted position. After the tool head 202 is inserted in the CT 32, the threaded rod or lead screw 218 can be actuated (e.g., rotated) to radially expand the inboard seal 204a to create a tight seal between the seal 204a and the CT 32. A handle or wrench 224 located at a tool face 222 can allow an operator (or automated controllers) to actuate the threaded rod or lead screw 218.

[0044] The test tool 200 can also include a pair of stainless steel tubes 230. As described below in more detail, the stainless steel tubes 230 supply a helium gas mixture to one or more areas of the tool head 202. In particular, a first stainless steel tube 230a can supply helium gas to the inside of the CT 32 inboard of the inboard seal 204a (toward the center of the calandria 10).
The second stainless steel tube 230b can supply a helium gas mixture to the lattice site outboard of the outboard seal 204b (toward the face of the reactor 6). As described in more detail below, the helium supplied by the stainless steel tubes 230a and 230b are used to test the seals 204a and 204b of the test tool 200. The stainless steel tubes 230a and 230b can be connected to one or more supply bottles of a helium gas mixture (e.g., 1% helium nitrogen) (see FIG. 15).

[0045] FIG. 7 illustrates a method of using the test tool 200 to test the leak tightness of a RJ
assembly 90. As shown in FIG. 7, to start the method, the test tool 200 is inserted into the CT 32 after the RJ assembly 90 has been installed but before the PT 36 is installed (at 300). FIG. 8 illustrates the test tool 200 inserted into the CT 32. As shown in FIG. 8, the test tool head 202 is inserted into the CT 32 until the outboard seal 204b engages the outward face 104 of the tube = Attorney Docket No. 027813-9061-CA00 sheet 18. Therefore, the outboard seal 204b engages with the outward face 104 of the tube sheet 18 to create one side of the volume to be vacuumed. The inboard seal 204a engages with an inner diameter of the CT 32 and, as noted above, can be engaged with the CT 32 using the threaded rod or lead screw 218. It should be understood that using the threaded rod or lead screw 218 to expand the seal 204a is optional, and, in some embodiments, the inboard seal 204a is not selectively expandable and is inserted into the CT 32 in an expanded position. In addition, in some embodiments, the outboard seal 204b can also be selectively expanded and retracted using the threaded rod or lead screw 218 or a similar actuating mechanism.

[0046] As shown in FIG. 8, with the test tool 200 inserted in the CT 32, the seals 204a and 204b define an enclosed volume 310 around a perimeter of the inside diameter of the CT 32 that surrounds the RJ assembly 90. Returning to FIG. 8, once the test tool 200 is inserted into the CT
32, a vacuum decay test is performed. As shown in FIG. 8, the vacuum decay test includes using the vacuum tube 206 and the pump included in the helium leak detector 214 to draw a vacuum on the enclosed volume 310 (at 310). In some embodiments, the vacuum is drawn for approximately two to five minutes. FIG. 9 illustrates the test tool 200 with a vacuum drawn on the enclosed area 310.

[0047] After the vacuum is drawn, the vacuum is no longer drawn for a period of time (a "decay period") (e.g., approximately two minutes) while the enclosed volume 310 remains sealed (i.e., the pump included in the helium leak detector 214 is turned off or disconnected from the tool 200, such as through the use of the valves 212) (at 312). For example, one or both of the valves 212 are closed during the decay period, which stops the pump from drawing a vacuum in the enclosed volume 310. During the decay period, the vacuum decays (i.e., the enclosed volume 310 begins to re-pressurize) due to ambient air leaking through the RJ
assembly 90 (along one or more of the leak paths 110) at a rate that depends on the size of the leak. In particular, the higher pressure of the ambient air is drawn through the leak paths 110 due to the lower pressure inside the enclosed volume 310. As ambient air leaks through the leak paths 110, the pressure inside the enclosed area 310 increases. Therefore, during the decay period and/or at the end of the decay period, the pressure inside the enclosed volume 310 is measured (e.g., using the pressure gauges 213) (at 314). The change in pressure within the enclosed volume 310 during the decay period, the length of time of the decay period, and the volume of the enclosed Attorney Docket No. 027813-9061-CA00 volume 310 is used to calculate a vacuum decay leak rate. In particular, a vacuum decay leak rate can be calculated using the following equation:

[0048] q = V dP
di' Where q is the decay leak rate and V is the volume of the enclosed volume 310.

[0049] As shown in FIG. 7, the vacuum decay test described above can be repeated one or more times to obtain a vacuum decay trend. In particular, after the decay period, the vacuum can be redrawn (e.g., by reopening one or both of the valves 212) for approximately two to five minutes (at 310) and then can be allowed to decay again for the decay period (at 312) while the pressure of the enclosed volume 310 is measured (at 314). With each repeated vacuum decay leak test, the calculated vacuum decay lake rate gravitates toward an actual or equilibrium leak rate.

[0050] For example, FIG. 10 illustrates a vacuum decay trend 400 that illustrates the measured pressure (in Torres) within the enclosed volume 310 as the vacuum is drawn and then allowed to decay numerous times. As shown in FIG. 10, the pressure (in Torres) can be measured substantially continuously or can be measured at predetermined time intervals. As also shown in FIG. 10, the pressure rises during each decay period (e.g., at 300 seconds, at 600 seconds, at 900 seconds, etc.). Similarly, after the decay period has ended and one or both of the valves 212 are reopened (e.g., at 400 seconds, at 700 seconds, at 1000 seconds, etc.), the pressure decreases as the vacuum is redrawn on the enclosed volume 310. As shown in FIG. 10, the slopes of the pressures changes during each vacuum decay leak test decrease over time due to the evacuation of cavities included in the enclosed volume 310 and due to reduced off-gassing. Off-gassing occurs when a vacuum is drawn in the enclosed volume 310 and draws molecules off the surface of components of the test tool 200, the CT 32, and/or other components included in the reactor 6. The drawn molecules take on a gaseous form that add to the volume of gas within the enclosed volume 310, which results in an increased pressure within the enclosed area 310.
Therefore, pressure rises due to off-gassing can provide a false indication of a high leak rate for a RJ assembly 90. However, as shown in FIG. 9, the effect of off-gassing decreases over time with each vacuum decay test. Therefore, running multiple vacuum decay tests reduces the effect Attorney Docket No. 027813-9061-CA00 of off-gassing in the results of the test. Furthermore, observing a decreasing linear trend in the off-gassing effect ensures an operator that the RJ assembly 90 is operating properly and provides a faster result than other vacuum decays tests that are run only once for an extended period of time. In addition, observing the trend of the off-gassing effect can provide diagnostic information to an operator. For example, the trend or shape of the off-gassing effect can signify whether other (e.g., non-metal) debris is located inside the CT 32 and/or other locations of the reactor that may cause operational concerns.

[0051] Returning to FIG. 7, in some embodiments, the test tool 200 can also be used to perform an ambient helium leak test. Also, as illustrated in FIG. 7, in some embodiments, the ambient helium leak test can be performed simultaneously with the vacuum decay test. For example, while the vacuum decay test is being performed, the helium leak detector 214 can measure the amount of helium inside the enclosed volume 310 (at 320). The measured amount of helium can be compared to the amount of ambient helium in the air surrounding the reactor 6 (e.g., approximately 5.2 ppm). Therefore, the amount of helium measured in the enclosed volume 310 will depend on the leak size. In particular, the larger the size of the leak, the closer the amount of helium measured in the enclosed volume 310 will be to the ambient helium amount. For example, an ambient helium leak rate can be calculated using the following equation:

[0052] = ____________ Helium Reading q AmbientHelium

[0053] As shown in FIG. 7, the ambient helium leak test can be repeated (e.g., repeated each time the vacuum decay test is performed) to obtain multiple leak rate calculations. For example, FIG. 11 illustrates a helium leak rate trend 500 graphed over vacuum decay rates. As illustrated in FIG. 11, over time, the ambient helium leak rate approaches the vacuum decay leak rate.
Therefore, both rates reach a leak rate that represents a true or equilibrium leak rate for the RJ
assembly 90. The time before the rates reach the equilibrium leak rate depends on the size of the leak. For example, the larger the leak, the faster the rates will reach the equilibrium leak rate.
The equilibrium leak rate can be compared to engineering specifications to ensure that the RJ
assembly 90 is properly installed and ready for operational use.

Attorney Docket No. 027813-9061-CA00

[0054] Executing the ambient helium leak test and the vacuum decay leak test simultaneously as described above allows a user to ensure accuracy of the result, and the ambient helium leak test provides secondary confirmation of the test results of the vacuum decay leak test. Furthermore, running the two tests simultaneously creates a leak rate measurement approximately every five minutes. Therefore, if an acceptable leak rate is reached early in the test, the test duration is shortened. Furthermore, the transient trend from the vacuum decay leak test allows the test to be optimized with respect to the duration of the test.
The transient trend from the vacuum decay leak test also provides additional information about the conditions under testing, such as off-gassing as described above.

[0055] Returning to FIG. 7, in some embodiments, the test tool 200 can be tested to ensure that it is properly installed in the lattice site. For example, if the seals 204 of the test tool 200 are not tight, the vacuum decay leak test and the ambient helium leak test cannot be performed successfully. In particular, if one or both of the seals 204 are not secure, a large pressure rise will be measured during the vacuum decay test and an ambient helium amount will be measured during the ambient helium leak test, both of which will result in a false leak rate for the RJ
assembly 90.

[0056] To prevent these false leak rates, after the test tool 200 is installed, the seals 204a and 204b can be tested (at 330). In particular, the stainless steel tubes 230 can be used to supply helium to areas outside of the enclosed volume 310 (e.g., each end of the enclosed volume 310 as defined by the seals 204a and 204b). For example, FIG. 12 illustrates the test tool 200 and the stainless steel tubes 230. With the test tool 200 installed in the lattice site, the first stainless steel tube 230a extends past the inboard seal 204a and supplies helium to an area 600 between the inboard seal 204a and the end of the test tool 200 inserted into the CT 32. If the inboard seal 204a is not properly sealed to the CT 32, the supplied helium will leak into the enclosed volume 310 and will be detected by the helium leak detector 214. Similarly, as shown in FIG. 12, the second stainless steel tube 230b supplies helium to an area 610 between the outboard seal 204b and the tool face 222. If the outboard seal 204b is not properly sealed to the tube sheet 18, the supplied helium will leak into the enclosed volume 310 and will be detected by the helium leak detector 214.

Attorney Docket No. 027813-9061-CA00 100571 As described above, because the ambient helium leak test uses only ambient helium (as compared to supplied helium as used in existing helium leak tests), a large amount of helium detected by the helium leak detector 214 (i.e., an amount greater than the ambient helium amount) indicates that one or both of the seals 204a and 204b is leaking and the test should be stopped and restarted (e.g., the test tool 200 should be repositioned) to ensure a proper leak test is performed. For example, FIG. 13 illustrates a graph 700 of sample helium readings from the helium leak detector 214 when the inboard seal 204a is leaking. As illustrated in FIG. 13, when the inboard seal 204a leaks, the helium leak detector 214 detects a high level of helium when the vacuum is drawn on the enclosed volume 310 (e.g., at approximately 400 seconds) because the supplied helium at the area 600 has leaked into the enclosed volume 310.
[0058] As illustrated in FIG. 7, the seal test (at 330) can be performed simultaneously with the vacuum decay leak test and the ambient helium leak test. In fact, because the ambient helium leak test detects the amount of helium in the enclosed area 310 (at 320), the helium measurements taken for the ambient helium leak test are the same measurements needed to perform the seal test (at 330). In some embodiments, the seals 204a and 204b are tested before beginning the decay period. However, the seals 204 can be tested at any stage when the pump valve drawing the vacuum is open (i.e., anytime the vacuum is being drawn).
Also, in some embodiments, the helium supplied through the stainless steel tubes 230 can be controlled (e.g., automatically or manually) to turn the helium supply on and off For example, in some embodiments, the helium supplied through the stainless steel tubes 230 is turned on when the vacuum is drawn on the enclosed volume 310 and is turned off when the vacuum is no longer drawn (i.e., during the vacuum decay period). Also, in some embodiments, the helium supplied by each stainless steel tube 230 can be controlled independently and turned on and off to test each seal 204 separately. Testing each seal 204 separately can identify which of the two seals 204 (if either) is leaking. It should be understood that the stainless steel tubes 230 are optional and, in some embodiments, only one stainless steel tube 230 is used to supply helium to one or multiple areas to test the tightness of one or both seals 204 of the test tool 200. For example, in some embodiments, only one stainless steel tube 230 is used to test the tightness of the outboard seal 204b.

Attorney Docket No. 027813-9061-CA00 [0059] In some embodiments, the helium leak detector 214 can be installed on a cart 800 as illustrated in FIG. 14. The cart 800 can include a handle and wheels that allow the cart 800 to be positioned as needed during the leak testing of a RJ assembly 90. In some embodiments, the cart 800 is installed on a larger cart 900 as illustrated in FIG. 15. The larger cart 900 can hold the cart 800 and one or more supply bottles 902 that supply a helium gas mixture to the stainless steel tubes 230. The cart 900 can be approximately 55.0 inches long, approximately 24.0 inches wide, and approximately 54.0 inches high.
[0060] The carts 800 and 900 can include connections for connecting the test tool 200 to the carts 800 and 900 and/or the components carried on the carts 800 and 900. In some embodiments, the cart 800 and/or the cart 900 can also include the valves 212 and the pressure gauges 213 (or valves and gauges in addition to the valves 212 and gauges 213 on the test tool 200). The cart 800 and/or the cart 900 can also include a local control panel ("LCP") unit that allows an operator to program the helium leak detector 214 and/or other components carried on the cart 800 and/or the cart 900. In some embodiments, the LCP unit can also provide a data log and summary report file of the vacuum decay leak test, the ambient helium leak test, and/or the seal test.
[0061] It should be understood that in practice, multiple test tools 200 (and associated carts 800 and 900) can be used to test the leak tightness of a RJ assembly 90. For example, in some embodiments, thirty-eight test tools 200 can be used, including twenty-four for production use, twelve for use a spares, and two for training purposes. Similarly, six carts 900 can be used, including two for production use, two for use as spares, and two for training purposes. Using the multiple test tools 200 and carts 900 separates the testing process into semi-independent batch-type operations, which increases efficiency. For example, using multiple test tools 200 and associated carts allows RJ assemblies 90 at multiple lattice sites on the same or opposite end of the reactor 6 to be tested in parallel.
[0062] Also, maintenance can be performed on the test tool 200 to ensure that the test tool 200 functions properly over time. For example, in some embodiments, the seals 204a and 204b of the test tool 200 can become worn with use and can be replaced regularly to maintain the quality and consistency of the test. In some embodiments, the seals 204 can be replaced after Attorney Docket No. 027813-9061-CA00 every five test operations. The pressure gauges 213 of the tool 200 can also be calibrated annually. In addition, the helium leak detector 214 can include a calibrated leak sensor, which can be replaced or re-calibrated as recommended by the manufacturer.
[0063] It should be understood that although the above testing methods and systems are described as being used during a retubing process, the same methods and systems can be used to perform maintenance and tests of operating reactors. For example, if a particular fuel channel assembly 28 is malfunctioning in a reactor, the tightness of the RJ assembly 90 can be tested to identify whether the RJ assembly 90 is malfunctioning. In this situation, the PT 36 can be removed to allow the test tool 200 to access to the RJ assembly 90.
[0064] Thus, embodiments of the present invention provide, among other things, methods and tools for testing the leak tightness of a RJ assembly. It should be understood, however, that the methods and systems described herein can be performed in various orders and configurations, and some steps can be performed in parallel to other steps. Some steps can also be combined or distributed among more steps. Also, the details of the methods and systems can be modified according to the specific configuration of the CTs, the inserts, and/or the reactor being retubed.
[0065] Various features and advantages of the invention are set forth in the following claims.

Claims (20)

What is claimed is:

1. A method of testing a joint assembly coupling a calandria tube to a tube sheet in a reactor, the method comprising:
(a) inserting a test tool into a lattice site containing the joint assembly, the test tool including at least two seals that define an enclosed volume surrounding the joint assembly;
(b) drawing a vacuum in the enclosed volume;
(c) stopping drawing the vacuum in the enclosed volume and allowing the vacuum to decay over a predetermined decay period;
(d) measuring a change in pressure in the enclosed volume during the decay period and calculating a leak rate based on the change in pressure;
(e) repeating (b) through (d) to generate a plurality of leak rates; and (f) determining an equilibrium leak rate based at least on the plurality of leak rates.

2. The method of Claim 1, further comprising comparing the equilibrium leak rate to a quality leak rate range to identify when the joint assembly is properly installed.

3. The method of Claim 1, further comprising radially expanding at least one of the at least two seals of the test tool after the test tool is inserted into the lattice site.

4. The method of Claim 1, further comprising:
(g) supplying helium to at least one area outside of the enclosed volume;
(h) measuring an amount of helium in the enclosed volume;
(i) calculating a second leak rate based on the measured amount of helium in the enclosed volume and an ambient helium amount; and (j) repeating (h) through (i) to generate a plurality of second leak rates.

5. The method of Claim 4, wherein determining the equilibrium leak rate includes determining the equilibrium leak rate based on the plurality of leak rates and the plurality of second leak rates.

6. The method of Claim 1, further comprising:
(g) supplying helium to at least one area outside of the enclosed volume;
(h) measuring an amount of helium inside the enclosed volume; and (i) determining when one of the two seals of the test tool is leaking based on the measured amount of helium inside the enclosed volume.

7. The method of Claim 6, further comprising repeating (g) through (h).

8. The method of Claim 6, wherein supplying helium includes supplying helium when the vacuum is drawn on the enclosed volume.

9. The method of Claim 6, further comprising stopping supplying helium to the at least one area outside of the enclosed volume during the decay period.

10. A system for testing a joint assembly coupling a calandria tube to a tube sheet in a reactor, the system comprising:
a pump for drawing a vacuum on an enclosed volume surrounding the joint assembly;
a test tool coupled to the pump by at least one hose and including a test head including at least two seals for defining the enclosed volume and an inlet for drawing the vacuum on the enclosed volume, a pressure gauge for measuring a pressure in the enclosed volume, a vacuum tube for drawing the vacuum on the enclosed volume, and at least one valve for repeatedly drawing the vacuum on the enclosed volume and letting the vacuum decay over a predetermined decay period, wherein the pressure gauge provides a plurality of pressure readings in the enclosed volume during the repeated drawings of the vacuum and vacuum decays, the plurality of pressure readings used to calculate an equilibrium leak rate of the joint assembly.

11. The system of Claim 10, further comprising a helium leak detector for detecting an amount of helium in the enclosed volume.

12. The system of Claim 11, wherein the helium leak detector contains the pump and is connected to the test tool by the at least one hose.

13. The system of Claim 12, wherein the detected amount of helium in the enclosed volume is compared to an ambient helium amount to determine the equilibrium leak rate of the joint assembly.

14. The system of Claim 10, wherein the at least two seals includes an inboard seal that engages an inside diameter of the calandria tube and an outboard seal that engages a face of the tube sheet.

15. The system of Claim 10, wherein the test tool further includes at least one of a threaded rod and a lead screw rotatable to expand at least one of the at least two seals.

16. The system of Claim 10, wherein the test tool further includes at least one tube for supplying helium to at least one area outside of the enclosed volume to test the tightness of at least one of the at least two seals.

17. The system of Claim 10, further comprising at least one automated controller for controlling the valve.

18. The system of Claim 10, further comprising a cart for carrying the pump.

19. The system of Claim 10, further comprising a control unit for logging the plurality of pressure readings.

20. The system of Claim 10, further comprising at least one shield plug for supporting the vacuum tube and for shielding radiation.