Defective fuel bundle positioning system

Abstract

A defective fuel bundle positioning system for a heavy water moderated nuclear fission reactor having a refueling machine, the system including a test tool defining an interior volume, the test tool configured to be received in a corresponding fuel channel of the refueling machine and the reactor; and a test container defining an interior volume, wherein the test container is configured to be received in the interior volume of the test tool and, when the test tool is disposed in the corresponding fuel channel of the reactor, the interior volume of the test container is configured to receive primary fluid from the reactor.

Description

[0001] Priority requirements

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 914,158, filed October 11, 2019, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The currently disclosed invention generally relates to systems and methods of using for detecting fuel leaks in nuclear reactors, and more specifically, to a system and method of using for detecting fuel leaks in heavy water-moderated fission nuclear reactors. Background Technology

[0004] Used to detect heavy water-moderated nuclear fission reactors (e.g.) Figures 1A to 1C Known systems and methods for fluid leakage from a faulty fuel rod bundle in a CANDU (CANDU) reactor are often inefficient, time-consuming, and costly (e.g., some reactors have delayed neutron systems where each outlet end fitting has a small sample tube, all of which are aggregated in a sampling chamber where a neutron detector measures the presence of fission products from each sample tube). Figures 1A to 1C As shown, in an exemplary reactor 100, an existing reactor feeder 106 is used to insert each fuel rod bundle into the pressure tube of the corresponding fuel passage 102 on the primary fluid side of the reactor 100. Figure 1C As shown, the feeder 106 includes a loader 108 and a receiver 109, each configured to interact with a corresponding set of fuel passage end fittings 103a and 103b located at opposite ends of a plurality of fuel passage pressure pipes. Figure 1C As shown, the charging unit 108 is located upstream of the reactor core 101 (meaning that the primary coolant flows from left to right (arrow 107) through the reactor core) and enters each fuel passage pressure pipe 102 through the corresponding fuel passage end fitting 103a, while the receiving unit 109 is located downstream of the reactor core 101 and enters the desired fuel passage pressure pipe 102 through the corresponding fuel passage end fitting 103b. However, it should be noted that in other embodiments of the reactor, the charging unit 108 may be located downstream of the reactor core 101, while the receiving unit 109 may be located upstream of the reactor core 101 (in short, the reactor may be configured with "fuel and liquid flow in the same direction" or "fuel and liquid flow in opposite directions").

[0005] The presence of gaseous fission products in the primary fluid indicates the presence of one or more failed fuel rod bundles. One known method for determining the location of a failed fuel rod bundle involves sampling a primary sample from a main header. However, there are only two headers, each receiving fluid flow from one of the designated half of the fuel channels 102. Therefore, detecting gaseous fission products in one of the headers can only limit the location of the failed fuel rod bundle to any one of the 122 fuel channels. It should be noted that different CANDU reactors have different numbers of fuel channels. Therefore, the number of fuel channels associated with each header may vary. In another approach, the presence of neutrons in the primary fluid flow is monitored when particles leak from the fuel rod bundle. In a neutron monitoring system, a vent line can be connected to each individual fuel channel 102 and used to sample the primary fluid flowing out of that fuel channel 102. Water from each fuel channel 102 can be sampled via a corresponding vent line terminating in the detector matrix. This system is complex and very expensive due to the large absolute number of fuel channels, each with a designated vent line (leading some reactor designs to omit this system). Similarly, the ability to retrofit existing reactors with neutron monitoring venting systems is limited by the excessive downtime required for installation. Finally, feed scanning involves directing the detector through the existing feed network that collects water leaving the fuel passageway and into the header. By correlating the scanner's location with the feed line, the location of the fault source can often be inferred. This process can also be very time-consuming and can only be used during reactor shutdowns, such as during planned outages.

[0006] During normal operation, a typical fuel bundle lasts approximately one year. Most fuel bundle failures occur during the lifespan of a fuel bundle when it is moved from a high-radiation zone to a low-radiation zone within the reactor, or vice versa. Flux along reactor channels is lower at both ends, so a transfer may involve moving into or out of a more intense central zone, and the transfer of fuel in one channel can disturb adjacent channels, potentially exacerbating a developing failure in the latter. Changes in operating temperature associated with moving fuel bundles can cause them to bend and bulge, leading to potential failures. Similarly, if temperature changes are not the primary cause of failure, they can be pressure sources that allow already developed cracks to form. If undetected leak rates become too high, or have persisted for too long to accumulate into unacceptable levels of emissions, and cannot be located, it may be necessary to “derating” the reactor until one or more failed fuel bundles can be located. As expected, reducing the reactor’s operating power limits will increase operating costs and may not meet required reactor power output. Another reason for needing to locate fuel rod bundles more quickly is that long-term deterioration of fuel rod bundles often masks the root cause of the initial defects and hinders preventative measures to be taken in fuel production or reactor operation.

[0007] Therefore, at least one system and method are still needed to detect fuel leaks in fission-type nuclear reactors in a timely manner. Summary of the Invention

[0008] One embodiment of the present invention provides a defective fuel rod bundle positioning system for a heavy water moderated nuclear fission reactor with a feeder. The system includes a test tool defining an internal volume, the test tool being configured to be received in a corresponding fuel passage of the feeder and the reactor; and a test container defining an internal volume, wherein the test container is configured to be received in the internal volume of the test tool, and, when the test tool is positioned in a corresponding fuel passage of the reactor, the internal volume of the test container is configured to receive primary fluid from the reactor.

[0009] Another embodiment of the present invention includes a method for detecting fuel leakage in a heavy water moderated nuclear fission reactor having multiple fuel channels and a feeder, the method comprising the steps of: providing a test container with a defined internal volume; placing the test container inside the feeder; engaging the feeder with a corresponding fuel channel; inserting the test container into the corresponding fuel channel; drawing primary fluid from the corresponding fuel channel into the internal volume of the test container; and removing the test container from the fuel channel.

[0010] One or more embodiments of the invention are illustrated in conjunction with the accompanying drawings, which are included and form part of this specification, and together with the textual description, serve to explain the principles of the invention. Attached Figure Description

[0011] The invention will now be described more fully below with reference to the accompanying drawings, which illustrate some, but not all, embodiments of the invention. In fact, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to enable this disclosure to meet applicable legal requirements.

[0012] Figures 1A to 1C These are different views of a heavy water moderated fission reactor and its corresponding container penetrations;

[0013] Figure 2 yes Figure 1A-1C The diagram shows a reactor feeder according to an embodiment of the present disclosure, in which the feeder receives test tools via an access port (e.g., an auxiliary or maintenance port in a maintenance or fuel rod bundle loading / unloading area);

[0014] Figures 3A to 3E yes Figure 2 The diagram shows a test tool that is inserted into the downstream end of a corresponding fuel passage in the reactor to sample the primary coolant flowing through it.

[0015] Figure 4 This is a schematic diagram of a charging machine (or a receiving machine from a downstream end fitting) that unloads activated test equipment at an auxiliary port of the reactor for transfer to the test area; and

[0016] Figure 5 This is a schematic diagram illustrating the monitoring of activated testing tools to detect potentially contaminated primary fluids.

[0017] Reference numerals used repeatedly in this specification and drawings are used to indicate the same or similar features or elements of this disclosure. Detailed Implementation

[0018] The present invention will now be described with reference to preferred embodiments and one or more examples shown in the accompanying drawings. Each example provided is for illustrative purposes only and does not constitute any limitation thereof. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope and spirit. For example, features shown or described as part of one embodiment may also be used in another embodiment, resulting in another different embodiment. Therefore, the present invention is intended to cover such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0019] This disclosure relates to a system and procedure for facilitating the location of fuel channels within a CANDU reactor containing defective fuel rod bundles while the reactor is still operational, i.e., generating electricity under normal operating conditions and with the fuel string undisturbed. Similarly, the currently disclosed system and procedure can also be used when the reactor has been shut down or during a shutdown.

[0020] Please refer to the following: Figure 2To initiate a fluid sampling, the receiver 109 of the reactor feeder 106 is positioned and locked at the reactor auxiliary port 110. As previously mentioned, whether the reactor is a "fuel-liquid flow in the same direction" or "fuel-liquid flow in opposite directions" type determines whether the receiver or the feeder is located downstream of reactor 101. The auxiliary port fuel carrier 112 and the shielded plug slot 114 are installed. After ensuring there is an empty cartridge position in the feeder 108, the auxiliary port shielded plug is removed. Next, the test tool 120 is placed on the slot 114, ensuring the test tool 120 is correctly oriented. The test tool 120 is preferably similar in size to a conventional fuel rod bundle, and includes a test container 122 disposed therein. As discussed in more detail below, it is preferable to activate the test container 122 using the plunger of the feeder 108 when the test container 122 is within the desired fuel passage. This means that the desired end of the test tool 120 must be positioned adjacent to the plunger 111 so that it can contact the plunger 111 for activation when needed. Next, the feed tube / plunger 111 of the feeder 108 is engaged with and locked onto the test tool 120. The feed tube / plunger 111 of the feeder 108 is retracted, leaving the test tool 120 stored in an empty position in the feeder's hopper. The feed tube / plunger 111 releases the test tool from the hopper, retracts further, and allows the hopper to rotate to the next empty position. In this example, up to eight test tools 120 can be loaded into the hopper of the feeder 108, depending on the number of fuel passage samples to be collected. However, it should be noted that in other embodiments, the hopper may contain fewer or more than eight test tools. After replacing the auxiliary port shield and disengaging the loader 108, move the loader 108 to the desired fuel passage 102 to be tested.

[0021] Please refer to the following: Figures 3A to 3E The loader 108 is positioned near the target fuel channel 102 and locked onto the corresponding fuel channel end fitting 103. Figure 3A After removing the fuel passage cap 130 and shielding plug 132 and storing them in the hopper position, the hopper is rotated to the test tool position, the loading tube / plunger 111 engages with the test tool 120, and the test tool 120 is installed into the fuel passage 102 in the same manner as the fuel rod bundle carrier. Figure 3B Next, the test container 122 is activated using the loading tube / plunger 111 of the loading machine 108 to obtain a sample of primary fluid from the target fluid channel 102. Figure 3CThe intake of primary fluid only begins after activation by relative movement of the plunger and / or the loading tube. Primary liquid then enters until the pressure of the internal volume is balanced with the pressure of the fuel passage. The lower pressure can be pre-pressurized gas, atmosphere, or vacuum. Upon balancing with the fuel passage, release or relative movement of the loading tube / plunger 111 returns the test container 122 to a sealed state. The sample volume of the test container 122 can be provided by increasing the internal volume, for example, by releasing or expanding a contracted or compressed bellows / bellows box through relative movement of the loading tube / plunger 111 or by the action of releasing a trigger when in passage conditions. The sample volume of test container 122 can be increased by: the action of a trigger of the release spring piston of the loading tube / plunger 111, which causes the piston to retract and water to be taken in; provided by positive displacement, wherein the movement of the loading tube / plunger 111 clamps the piston extension and draws water into the syringe-type canister; and provided by porous media, where liquid is wicked / absorbed when the valve is opened or the diaphragm is perforated. Test container 122 preferably also self-seales after a single fluid sample is obtained. After sample acquisition, the loading tube / plunger 111 of the feeder 108 retracts, so that the test tool 120 and the corresponding test container 122 are stored in the desired position within the feeder 108's hopper. Figure 3D After installing the shielding plug 132 and the channel cap 130, disengage the feeder 108 from the fuel channel outlet end fitting 103. Repeat the above steps at each target fuel channel 102 until the desired number of primary fluid samples are obtained. The feeder 108's hopper is capable of holding up to eight test tools 120 and their corresponding test containers 122. Figure 3E ).

[0022] Please refer to the following: Figure 4 After collecting the desired number of primary fluid samples, the loading machine 108 is returned to and locked onto the auxiliary port 110. As previously described, the auxiliary port fuel carrier 112 is attached to the shielding plug slot 114 before the auxiliary port shielding plug is removed. The tool carrier 120 advances onto the slot 114 in the same manner as retrieving the auxiliary tool. Next, each test container 122 is removed from the corresponding test tool 120 until each previously activated test container 122 has been unloaded. If additional samples are to be collected, an unactivated empty test container 122a can be loaded into the test tool 120 and then into the loading machine 108, as previously described. Upon completion of the unloading operation, the auxiliary port shielding plug is installed, and the auxiliary port slot 114 is removed. Finally, the loading machine 108 is detached from the auxiliary port 110, and further testing of the fuel addition procedure can proceed as needed. After removing the activated test container 122 from the corresponding test tool 120, the test container 122 is placed in the transport box 140 for transfer to the analysis facility. Figure 5 As shown, the primary fluid sample within the activated test container 122 is moved to the laboratory for analysis by the detection device 150. It should be noted that the primary sample can be analyzed in the field or at an off-site facility. For example, if the measuring equipment allows, the sample can be analyzed near a port. After analysis, the test container 122 can be emptied and prepared for future use.

[0023] The aforementioned fuel leak detection system and method offer several advantages over known testing systems and methods. For example, initial results of fluid testing can be obtained within 4 to 6 hours of operation commencement, and up to 16 fuel channels can be tested in a single feeder stroke. The method is non-destructive because it can be used while the reactor is operating online at full power without modifying piping or existing CANDU feeders. The ability to pinpoint leak locations faster than previous methods allows for maximum reactor operation and reduces the risk of reactor derating or shutdown. Early detection of defective fuel bundles also makes it easier to identify potential causes of fuel leaks due to less corrosion occurring throughout the leak process. This system does not cause physical disturbance to the fuel because it does not manipulate the fuel bundles within the fuel channels during testing and does not prematurely add (new / incompletely depleted) fuel as a means of inferentially changing the feed manifold monitoring type during detection. Current methods use inferential logic that examines changes in leak rate indicators after selective fuel transfer to alter the temperature of nearby fuel bundles by moving a fuel bundle in one channel to a different flux / temperature location. Leaking rod bundles near the transfer point may increase or decrease the emission of their leaking fission products. Multiple feeds are typically required to determine which channel is leaking. A channel or channel region cannot be "fuel overloaded" in a short period, as the accumulation of new fuel in one area will generate excessive power in surrounding channels or reactor regions. This approach usually requires batching with sufficient intervals for the new rod bundles to decay; the main problem with this approach is the prolonged residence time of the rod bundles, increased emissions, increased risk of defect degradation, and increased risk of reactor derating. It should be noted that because the system described above includes test tools and test containers integrated with existing CANDU feeders and systems, the system can be transferred to any CANDU reactor site without modification.

[0024] While one or more preferred embodiments of the invention have been described above, those skilled in the art will understand that various modifications and variations can be made without departing from the scope and spirit of the invention. For example, in some reactors, an auxiliary port is a preferred embodiment, but a tool path that enters through a new fuel feeder / port and exits through a spent fuel port can also be used. The spent fuel port in the spent fuel bin can serve as a means of recovering the waste canister and keeping it shielded before bottling and transport. In some reactors, a feeder tool or maintenance port can be used as an auxiliary port. Alternatively, a new fuel port and a spent fuel tunnel path can be used to recover the waste canister and retrieve the tool from the spent fuel bin. After recovering the waste canister, a preferred embodiment is to bottle the waste canister and move it to an existing neutron detector. Alternatively, a local detector can be provided at / above the auxiliary port or near the spent fuel bin to avoid transport. The tool can be reset using an empty canister by replacing the waste canister in the tool returned to the manufacturing plant. This can be achieved by ensuring an inventory of available refurbished tools and waste canisters. Refurbished and returned tools can be stored locally or off-site. The contents of the tank after measurement should be returned to a heavy water recovery / cleaning facility located on-site or off-site. This invention is intended to cover such modifications and variations that fall within the scope and spirit of the appended claims and their equivalents.

Claims

1. A defective fuel bundle positioning system for a heavy water moderated nuclear fission reactor having a load machine, comprising: a test tool defining an interior volume, the test tool configured to be received in a corresponding fuel channel of the load machine and the reactor; and a test container defining an interior volume, wherein the test container is configured to be received in the interior volume of the test tool and, when the test tool is disposed in the corresponding fuel channel of the reactor, the interior volume of the test container is configured to receive primary fluid from the reactor, wherein the load machine further comprises a plunger configured to activate the test container such that the primary fluid is received in the interior volume of the test container.

2. The system of claim 1, wherein the test container is configured to draw the primary fluid into the interior volume of the test container by initially placing the interior volume of the test container at a lower pressure than the pressure of the primary fluid.

3. The system of claim 1, wherein the plunger of the load machine is configured to insert and withdraw the test tool into and from the corresponding fuel channel of the reactor.

4. The system of claim 3, wherein the test container further comprises one of a bellows and a piston, the bellows or piston configured to draw the primary coolant into the interior volume of the test container.

5. The system of claim 1, wherein the load machine comprises a receiver and a charger.

6. A method of detecting a fuel leak in a heavy water moderated nuclear fission reactor comprising a plurality of fuel channels and a load machine, comprising the steps of: providing a test tool defining an interior volume; providing a test container defining an interior volume; placing the test container in the interior volume of the test tool; placing the test container in the load machine after placing the test container in the interior volume of the test tool; engaging the load machine with a corresponding one of the fuel channels; inserting the test container into the corresponding fuel channel; drawing primary fluid from the corresponding fuel channel into the interior volume of the test container; and removing the test container from the fuel channel.

7. The method of claim 6, wherein the step of providing a test container further comprises: providing the test container having an interior volume at a lower pressure than a pressure of a primary coolant within the nuclear fission reactor.

8. The method of claim 6, further comprising the step of operating the nuclear fission reactor under normal operating conditions for the generation of electricity when inserting the test container into the corresponding fuel channel.

9. The method of claim 6, wherein the step of drawing the primary fluid into the interior volume of the test container further comprises retracting one of a bellows and a piston disposed within the test container.

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