Hierarchical pressure monitoring and depressurization of high burnup spent fuel cask operations

Abstract

This invention discloses a method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization, belonging to the field of nuclear fuel cycle technology, and includes three stages: loading, transfer, and unloading. In the loading stage, the container is connected to the loading well through-hole and filled with water to balance the water level before loading fuel. After completion, leakage testing and radiation monitoring are performed. In the transfer stage, a qualified container is transported as a whole to the target facility using a tractor. In the unloading stage, before opening the lid, the pressure in the lid chamber and inner chamber is detected via a quick-connect coupling. If overpressure occurs, the pressure is controlled by connecting to the facility's exhaust gas system. After fuel assembly damage monitoring, the container's inner cavity is cooled and cleaned. Subsequent steps include precise positioning, inner lid disassembly and cleaning for protection, and closed-loop recording. This method solves the problems of low positioning efficiency, high high-altitude risks, high personnel radiation dose, and equipment vulnerability in existing operations. It achieves graded pressure control and systematic pollution prevention and control, improving the safety, accuracy, and efficiency of operations, and has strong compatibility with existing facilities.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel cycle technology, specifically relating to a method for operating a high burnup spent fuel transfer container with staged pressure monitoring and depressurization. Background Technology

[0002] Spent fuel assemblies are nuclear fuel assemblies that have been removed from nuclear reactors, reached their predetermined burnup level, and are no longer intended for use. They are highly radioactive and pose decay heat and criticality risks, thus requiring strict safety constraints throughout the reprocessing process. Spent fuel transfer containers, as key equipment ensuring the safety of spent fuel transfer within nuclear power plants, are heavy or extra-heavy equipment, with an empty weight reaching hundreds of tons. The total weight increases further after loading spent fuel.

[0003] During the operation of a nuclear power plant, the need for spent fuel assembly transfer is relatively frequent. The core process of this operation mainly includes three key stages: loading, in-plant transfer, and unloading, and the standard operating procedures are extremely complex. Inside the fuel building, a series of precise operations must be completed in sequence, including filling the transfer container with water, opening the lid, docking with the loading well, loading spent fuel assemblies, as well as sealing, draining, drying, leak detection, and radiation monitoring. After completing the above operations, the transfer container is transported to the target building by a heavy-duty tractor. Finally, within the target building, strict operations such as radioactivity and contaminant detection, pressure monitoring, opening the lid, decontamination, cooling, and unloading of fuel must be performed.

[0004] The current operation of spent fuel transfer containers still faces many technical challenges. Firstly, there are issues with positioning accuracy and efficiency. Millimeter-level precise positioning of the containers relies entirely on human experience, which is prone to errors due to human judgment, communication delays, and differences in operational skills, leading to low positioning efficiency. Secondly, the safety risks of high-altitude operations are high. Heavy-duty containers weighing hundreds of tons need to be suspended for extended periods below narrow wellheads, placing stringent demands on the crane's braking and control systems. Misjudgments by personnel, communication misunderstandings, or momentary equipment failures can all cause the container to fall uncontrollably, shake violently, or even collide with the wellhead's penetration structure. Damage to the container's shielding or the wellhead's sealing structure could also trigger radioactive leaks. Thirdly, the radiation safety risks to operators are significant. Command personnel must continuously observe operations in high-radiation areas near the wellhead. The lack of convenient operating structures results in prolonged exposure time for personnel, posing a significant risk of cumulative radiation dose. Fourthly, the risk of equipment damage is high. Frequent micro-movements during operation can easily cause abnormal wear on critical components such as crane motors, wire ropes, and brakes, significantly shortening the equipment's lifespan.

[0005] To address the technical bottlenecks in spent fuel transfer operations, the nuclear industry urgently needs to develop a comprehensive operational solution for high burnup spent fuel transfer containers to resolve efficiency and safety issues in existing transfer processes. Existing technologies have significant shortcomings in operational efficiency, safety, positioning accuracy, and radiation protection, and lack systematic pressure control, contamination control, and efficient operational interface design. The industry urgently needs a spent fuel transfer container placement method and supporting technical solutions that can overcome these drawbacks and achieve safe, precise, and efficient operation. Furthermore, this solution must be seamlessly integrated with the existing loading shaft structure of nuclear power plants. This invention is proposed to solve these technical problems. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide an operation method for high burnup spent fuel transfer containers with graded pressure monitoring and depressurization, which solves the technical problems of low positioning accuracy and poor efficiency, high safety risks of high-altitude operation, high radiation dose to operators, easy equipment damage, and lack of systematic pressure control, pollution control and efficient operation interface design in existing spent fuel transfer container operations. It enables safe, accurate and efficient high burnup spent fuel transfer operations, while improving the compatibility and integration of this operation method with existing nuclear power plant facilities and processes, without the need for large-scale modification of existing plant buildings, equipment and other facilities.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization includes a loading stage, a transfer stage, and an unloading stage. In the loading stage, after connecting the transfer container to the loading well penetration, water is filled into the loading well penetration until its water level is level with the bottom water level of the loading well. Then, the high-burnup spent fuel assemblies are loaded. After loading, the transfer container undergoes a leak test. If the test is successful, sealing and radiation monitoring are performed. In the transfer stage, the transferred container, having passed both the leak test and radiation monitoring, is transported to the target transfer facility. In the unloading stage, before opening the transfer container, a detection instrument is installed via a pre-set quick connector to sequentially detect the pressure in the cover chamber between the outer and inner covers and the inner chamber of the transfer container. If the pressure in any chamber exceeds a preset threshold, the chamber is connected to the plant's exhaust gas system via an exhaust pipe for controlled depressurization. After depressurization, damage monitoring of the high-burnup spent fuel assemblies is performed, followed by cooling and cleaning of the inner cavity of the transfer container.

[0009] The graded pressure monitoring and depressurization described in this invention is a specialized pressure control mechanism designed for the dual independent chamber structure of high-burnage spent fuel transport containers. Its "graded" nature is reflected in three dimensions: spatial graded, threshold graded, and process graded. First, spatial graded pressure monitoring is performed on the two independent physical chambers—the chamber between the outer and inner covers of the transport container and the inner chamber of the container—to avoid pressure interference between chambers. Second, threshold graded pressure monitoring sets independent pressure safety thresholds for each chamber, and overpressure judgment criteria are set as needed to achieve targeted depressurization. Third, process graded pressure monitoring and depressurization operations strictly follow the sequence of "chamber between covers → inner chamber of the container" to ensure the orderly and accurate control process.

[0010] This invention divides the entire spent fuel transportation process into three standardized stages: loading, transportation, and unloading. This makes the operation process more systematic and standardized, improving the feasibility of on-site operations. In the loading stage, static pressure difference is eliminated by leveling the water level, controlling the spread of radioactive contamination from the source. Combined with leak detection and radiation monitoring, this strengthens the safety barrier during loading. In the unloading stage, a graded pressure monitoring and controlled pressure relief mechanism is designed for the cover chamber and the inner chamber. Pre-set quick connectors are used to complete accurate pressure measurement and safe pressure relief, avoiding radioactive leakage accidents caused by abnormal pressure when the cover is opened, thus improving the inherent safety level of the operation. After pressure relief, fuel damage monitoring is carried out before cooling and cleaning, forming an integrated unloading preparation process. Fuel integrity verification is a prerequisite for subsequent operations, ensuring the safety of unloading operations and improving the efficiency of operation coordination.

[0011] Furthermore, during the loading phase, after the high-burnup spent fuel assembly is loaded, the manhole cover at the bottom of the loading well is closed first, then the water level inside the transfer container is lowered to separate the container from the loading well penetration, and the loading well penetration is dried and cleaned. After that, a leak inspection operation is performed on the transfer container.

[0012] After loading is completed, the well cover should be closed before separating the container to avoid radiation safety risks caused by exposure of spent fuel assemblies; the penetrating parts should be dried and cleaned to remove residual contaminants and accumulated water to avoid affecting subsequent equipment and operations, while improving the accuracy of leak detection results; each step should be connected in an orderly manner to reduce the randomness and probability of errors in manual operation and improve the overall efficiency of loading operations.

[0013] Furthermore, the leakage inspection of the transshipment container includes sequential internal leakage inspection and external cover leakage inspection. Before the internal leakage inspection, the transshipment container must also be drained, vacuum dried and filled with helium.

[0014] The graded leak testing method, which combines internal and external sealing, enables comprehensive testing of the container's sealing performance, improves the reliability of sealing tests, and effectively avoids radioactive leaks caused by container seal failure. Pre-test drainage, vacuum drying, and helium filling eliminate interference from water and air, and utilize the leak detection properties of helium to enhance the sensitivity of internal leak testing, enabling timely detection of even minor sealing defects. Standardized leak pretreatment and graded testing procedures meet the stringent safety testing requirements of the nuclear industry, ensuring the sealing safety of the container during transport.

[0015] Furthermore, during the transshipment phase, the transshipment containers that have been loaded and have passed leak testing and radiation monitoring are transported together with a dedicated transfer trailer to the target transshipment facility plant by a tractor.

[0016] The transshipment phase adheres to standardized transfer requirements, allowing only inspected and qualified containers to be transferred, thus mitigating the safety risks associated with the transfer of unqualified containers. A combined transfer mode using a tractor and dedicated transport trailer is employed, adapting to the transfer needs of heavy containers weighing hundreds of tons, improving the stability of the container transfer process, and preventing damage to the container structure or seal failure caused by bumps or shaking during transport. The overall transfer eliminates the need for disassembling containers mid-transfer, reducing transfer steps, improving efficiency, and simultaneously reducing the frequency of contact between operators and containers, thereby lowering radiation exposure doses.

[0017] Furthermore, during the unloading phase, before installing the testing instruments through the preset quick connectors to test the pressure, the process also includes on-site inspection of the transshipment container, hoisting and positioning, and surface cleaning. The on-site inspection involves testing the surface of the transshipment container for radioactivity and contaminants, and the test results are recorded in the unloading report.

[0018] Before pressure monitoring, a pre-process is established, including entry inspection, hoisting and positioning, and surface cleaning, to ensure multi-layered control during unloading operations. Entry inspection detects and records the radioactivity and contaminants on the container surface, allowing for timely monitoring of the container's external safety status and meeting the traceability management requirements of the nuclear industry. Surface cleaning removes contaminants specifically based on the test results, effectively controlling the spread of radioactive contamination and ensuring the environmental safety of the unloading plant and the safety of operators. Specialized lifting equipment enables precise docking between the container and the unloading facilities, reducing manual fine-tuning operations, improving positioning accuracy and efficiency, and simultaneously reducing equipment wear caused by frequent crane micro-movements, thus extending equipment lifespan.

[0019] Furthermore, the pre-designed quick connectors include a cover hole quick connector, an inner cover drain hole quick connector, and an air inlet quick connector. The pressure in the cover chamber is detected by installing a testing instrument through the cover hole quick connector, and the pressure in the inner chamber of the transport container is detected by installing a testing instrument through the inner cover drain hole quick connector. When the pressure in the inner chamber of the transport container exceeds the limit, the exhaust pipe is connected to the plant's waste gas system through the air inlet quick connector to implement controlled pressure relief.

[0020] The pre-designed quick-connect couplings are functionally subdivided, with dedicated interfaces for pressure measurement and depressurization in different chambers. This avoids operational and detection errors caused by mixing interfaces, improving the accuracy of pressure monitoring and depressurization operations. The modular design of the quick-connect couplings allows for rapid assembly and disassembly of testing instruments and exhaust pipes, significantly shortening pipe connection operation time, improving work efficiency during the unloading phase, and reducing the exposure time of operators in radioactive areas, thus lowering radiation dose. The depressurization pipeline is directly connected to the plant's exhaust gas system, enabling standardized and harmless treatment of overpressured gases and avoiding environmental and personnel safety risks associated with direct emission of radioactive gases.

[0021] Furthermore, damage monitoring of the high burnout spent fuel assembly involves sampling the internal gas through the water hole in the inner cover of the transfer container and conducting radioactivity testing on the sampled gas to verify that the high burnout spent fuel assembly is undamaged.

[0022] Non-contact verification of fuel assembly damage is achieved through gas sampling and radioactivity detection. The test can be completed without opening the cap, avoiding the radiation and leakage risks caused by fuel assembly exposure during the test. The sampling method from the water hole in the inner cap is compatible with the container structure design, making the operation convenient and the sample representative, which can accurately reflect the integrity status of the fuel assembly. The early verification that the fuel assembly is not damaged provides a safe premise for subsequent cooling, cleaning, and unloading. If damage is found, emergency measures can be taken in time to prevent the accident from escalating and improve the safety protection level of the unloading operation.

[0023] Furthermore, during the cooling and cleaning operation of the inner cavity of the transport container, the deionized water system is connected to the inlet and outlet holes of the inner cover of the transport container through the quick connectors of the drain hole and air inlet hole. Deionized water is injected into the inner cavity of the transport container at a constant flow rate for cooling and cleaning until the outlet water temperature drops to the preset safe range, and then the cooling and cleaning pipeline is removed.

[0024] By utilizing existing quick-connect couplings, the deionized water system can be quickly connected to the container without the need for additional connection structures, improving the convenience and efficiency of cooling and cleaning operations. Simultaneously, interface reuse simplifies the container's structural design. Using a constant flow rate of deionized water for cooling and cleaning effectively cools the container's internal cavity, reducing safety risks from decay heat, while also thoroughly cleaning radioactive contaminants within the cavity. This integrated cooling and decontamination operation reduces the time required for separate processes. Using the outlet water temperature as the operation termination indicator enables standardized control of the cooling and cleaning operation, avoiding under- or over-operation due to human judgment, and improving operational standardization and reliability.

[0025] Furthermore, during the unloading phase, after cooling and cleaning the inner cavity of the transport container, the clamping flange of the transport container is first removed, and then a special unloading lifting tool is connected to lift the transport container directly above the unloading well and precisely position it at the designated interface position of the unloading well. Subsequently, the inner cover of the transport container is removed, and the removed inner cover is cleaned, inspected, and protected. When removing the inner cover of the transport container, the inner cover is immediately rinsed with deionized water to remove dirt after it is exposed above the water surface, and the sealing groove of the inner cover is protected during the operation. If the removed inner cover is found to be damaged or excessively worn after inspection, it is immediately replaced.

[0026] The core unloading operations after cooling and cleaning are refined and standardized, with each step seamlessly connected to ensure smooth unloading and improve operational efficiency. Specialized unloading lifting equipment is used to achieve precise positioning of the container and unloading well, eliminating errors from manual positioning, improving positioning accuracy, and reducing the need for crane micro-movements, thus reducing equipment wear. Once the inner cover is exposed above the water surface, it is immediately rinsed to remove surface radioactive contaminants and effectively control the spread of pollution. During operation, the inner cover sealing groove is protected, and the disassembled inner cover is cleaned, inspected, and replaced to ensure the sealing components are in good working order. This strengthens the sealing safety barrier for container reuse and extends the container's service life.

[0027] Furthermore, at the end of the unloading phase, the unloading sequence number of the high-burning-consumption spent fuel assembly, the operation process, and the final storage location in the transfer tank grid are recorded in detail in the unloading report, completing the closed-loop management of the operation process.

[0028] The unloading phase incorporates a closed-loop record management system, meticulously documenting the unloading sequence number, operational process, and final storage location of spent fuel assemblies. This meets the stringent quality assurance and operational traceability requirements of the nuclear industry, facilitating subsequent verification, traceability, and management. The closed-loop management throughout the entire process ensures comprehensive coverage of loading, transfer, and unloading operation information, creating a complete operational archive. These records allow for the timely identification and optimization of operational issues, continuously improving the standardization and normalization of operations and guaranteeing the safe and orderly conduct of the entire spent fuel transfer process.

[0029] The beneficial effects of this invention are as follows: By eliminating static pressure differences through leveling the water level during the loading stage, the spread of radioactive contamination is effectively controlled from the source. Combined with leak detection and radiation monitoring measures, the safety protection capabilities of the loading process are strengthened, overcoming the shortcomings of existing technologies that lack systematic pollution control. An innovative design incorporates graded pressure monitoring and controlled pressure relief mechanisms for the cover chamber and inner chamber. Through pre-set quick-connect fittings and the plant's exhaust gas system, safe pressure relief is achieved, completely avoiding radioactive leakage accidents caused by abnormal pressure during the cover process. This fills the gap in existing technologies for systematic pressure control and significantly improves the inherent safety level of spent fuel transfer operations. Fuel damage monitoring is used as a pre-operation for cooling and cleaning, forming an integrated unloading preparation process. Fuel integrity verification is a necessary prerequisite for subsequent operations, further strengthening the safety defenses of unloading operations. At the same time, the operational process is optimized, improving the overall efficiency of high-burnage spent fuel transfer operations.

[0030] The following describes in detail the operation method of the high-burnup spent fuel transfer container for graded pressure monitoring and depressurization, in conjunction with the embodiments and reference numerals in the accompanying drawings. Attached Figure Description

[0031] Figure 1 An external view of the transport container to which the operation method of the present invention applies;

[0032] Figure 2 for Figure 1 AA cross-section view;

[0033] Figure 3 for Figure 1 The C-direction view;

[0034] Figure 4 for Figure 3 BB cross-section;

[0035] Figure 5 for Figure 4 Enlarged view of a portion at point A;

[0036] Figure 6 for Figure 1 View from direction C (with the outer cover removed);

[0037] Figure 7 for Figure 1 View from direction C (with the outer cover and inner cover removed, and the flange tightened).

[0038] Figure Labels

[0039] 1. Transfer container; 2. Inner cylinder; 3. Inner cylinder water hole; 4. Water hole cover; 5. Outer cover; 6. Inner cover clamping flange; 7. Inner cover; 8. Cover chamber; 9. Container inner chamber; 10. Cover hole cover; 11. Cover hole cover screw; 12. Inner cover water hole; 13. Inner cover air inlet; 14. Inspection hole; 15. Sealing ring; 16. Lifting trunnion. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the following description will be provided in conjunction with the embodiments of the present invention and the accompanying drawings. Figure 1-7 The technical solution of the present invention will be clearly and completely described herein. Obviously, the described embodiment is one embodiment of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] like Figure 1-7 As shown, this invention discloses an operation method for a high burnup spent fuel transfer container with graded pressure monitoring and depressurization. The object of operation is a transfer container 1 adapted to high burnup spent fuel assemblies. This container is a heavy-duty special container with a capacity of hundreds of tons, which can be seamlessly integrated with existing infrastructure such as loading wells in nuclear power plants. It includes core structures such as an inner cylinder 2, an inner cylinder water hole 3, a water hole cover 4, an outer cover 5, an inner cover clamping flange 6, and an inner cover 7, forming two independent chambers: a cover chamber 8 and an inner container chamber 9. It is equipped with a cover hole cover 10, a cover hole cover screw 11, an inner cover water hole 12, an inner cover air inlet 13, a detection hole 14, and a sealing ring 1. 5. Lifting trunnions 16 and various pre-set quick connectors such as quick connectors for the cover hole, quick connectors for the inner cover drainage hole, and quick connectors for the air inlet hole; The core of this method is to divide the entire spent fuel transfer process into sequential loading, transfer, and unloading stages. It integrates multiple pressure monitoring and safety depressurization, graded sealing treatment, full-process radiation and leakage monitoring, systematic pollution control, and modular quick connector operation interfaces to achieve safe, accurate, and efficient spent fuel transfer operations. At the same time, it can significantly reduce the radiation dose to operators, reduce equipment wear, and improve the standardization and traceability of the operation process.

[0042] This invention divides the entire spent fuel transportation process into three standardized stages: loading, transportation, and unloading. This makes the operation process more systematic and standardized, improving the feasibility of on-site operations. During the loading stage, static pressure differences are eliminated by leveling the water level, controlling the spread of radioactive contamination at its source. Combined with leak detection via the detection port 14 and continuous radiation monitoring, a robust safety barrier is established during loading. The double-seal protection of the sealing ring 15 also provides a fundamental guarantee for the container's sealing performance. During the unloading stage, a graded pressure monitoring and controlled pressure relief mechanism is designed for the cover chamber 8 and the container's inner chamber 9. Pre-set quick-connect fittings enable accurate pressure measurement and safe pressure relief, preventing open circuits. The radioactive leakage accident caused by abnormal pressure during the sealing process improves the inherent safety level of the operation. After depressurization, fuel damage monitoring is carried out before cooling and cleaning, forming an integrated unloading preparation process. Fuel integrity verification is a prerequisite for subsequent operations, which not only ensures the safety of unloading operations but also improves the efficiency of operation connection. The entire operation relies on the lifting trunnion 16 to achieve the smooth lifting and transfer of the transport container 1, ensuring the stability of each operation. At the same time, through remote control and process optimization, the technical bottlenecks of existing technologies, such as reliance on manual positioning, high risk of high-altitude operation, high radiation dose to personnel, and easy wear and tear of equipment, are fundamentally solved.

[0043] In this embodiment of the invention, a pre-loading assessment of the high-burnup spent fuel assembly to be loaded is required before loading to verify that it meets the physical, thermal, and radiation safety requirements for loading. Simultaneously, the transfer container 1 is cleaned or decontaminated, completing dual preparations before loading. After the high-burnup spent fuel assembly is loaded, the manhole cover at the bottom of the loading well is closed first, then the water level inside the transfer container 1 is lowered to separate the container from the loading well penetration, and the loading well penetration is dried and cleaned. Then, a leak test is performed on the transfer container 1. Closing the manhole cover before separating the container after loading avoids the radiation safety risks associated with exposure of the spent fuel assembly; drying and cleaning the penetration removes residual contaminants and accumulated water to avoid affecting subsequent equipment and operations, while also improving the accuracy of the leak test results; the orderly connection of each step reduces the randomness and probability of errors in manual operation, improving the overall efficiency of the loading operation. In this stage, the inner cylinder water hole 3 and water hole cover 4 cooperate to achieve water filling and sealing of the transfer container 1, ensuring the convenience of water filling and the container's sealing performance.

[0044] In this embodiment of the invention, the leakage inspection of the transport container 1 includes sequential internal leakage inspection and external cover leakage inspection. Before the internal leakage inspection, the transport container 1 needs to undergo drainage, vacuum drying, and helium filling. Both inspections are completed through the detection port 14 for data acquisition and detection. The graded leakage inspection method with an internal cover and an external cover achieves comprehensive testing of the container's sealing performance. The sealing effect of the sealing ring 15 is simultaneously included in the testing range, improving the reliability of the sealing test and effectively avoiding radioactive leakage caused by container sealing failure. The drainage, vacuum drying, and helium filling operations before inspection eliminate the interference of water and air on the leak detection work. The leak detection characteristics of helium are used to improve the sensitivity of the internal leakage inspection and detect minor sealing defects in a timely manner. The standardized leak detection pretreatment and graded inspection process meet the stringent safety testing requirements of the nuclear industry and ensure the sealing safety of the container during transport.

[0045] In this embodiment of the invention, during the transshipment stage, the transshipment container 1, which has passed both leak testing and radiation monitoring, is transported as a whole to the target transshipment facility by a tractor and a dedicated transfer trailer. The lifting and securing of the transshipment container 1 is achieved entirely using the lifting trunnions 16. During the transshipment process, the container 1 is kept vertical to prevent shaking caused by sudden acceleration or braking, ensuring compatibility between the transport channel and the container. Standardized transshipment requirements are implemented during the transshipment stage, allowing only inspected and qualified containers to be transported, thus mitigating the safety risks associated with transporting unqualified containers. The overall transshipment mode using a tractor and a dedicated transfer trailer is suitable for transporting heavy containers of hundreds of tons, improving the stability of the container transport process and preventing damage to the inner cylinder 2, outer cover 5, or sealing ring 15 caused by bumps or shaking during transport. The overall transshipment eliminates the need for disassembling the container midway, reducing transshipment steps, improving efficiency, and minimizing contact between operators and the container, thus reducing radiation exposure.

[0046] In this embodiment of the invention, during the unloading stage, before installing the testing instrument to test the pressure through the preset quick connector, the unloading process also includes the operation of entering the transport container 1 for inspection, hoisting and positioning, and surface cleaning. The entry inspection involves testing the surface of the transport container 1 for radioactivity and contaminants, and recording the test results in the unloading report. The hoisting and positioning process is achieved by using the hoisting trunnion 16 in conjunction with a special lifting tool. The container is first hoisted into the preparation well to complete the preparatory operations such as inspection, depressurization, and cleaning, and then transferred to the unloading well to carry out subsequent operations. Before pressure monitoring, a pre-processing procedure is set up, including entry inspection, hoisting and positioning, and surface cleaning, to achieve multi-layered control over the unloading operation. Entry inspection detects and records the radioactivity and contaminants on the container surface, allowing for timely monitoring of the container's external safety status and meeting the traceability management requirements of the nuclear industry. Surface cleaning removes contaminants in a targeted manner based on the test results, effectively controlling the spread of radioactive contamination and ensuring the environmental safety of the unloading plant and the safety of operators. Through the precise cooperation of specialized lifting tools and hoisting trunnions 16, precise docking of the container and unloading facilities is achieved, reducing manual fine-tuning operations, improving positioning accuracy and efficiency, and reducing equipment wear caused by frequent micro-movements of the crane, thus extending the equipment's service life.

[0047] In this embodiment of the invention, the preset quick connector includes a quick connector for the cover hole, a quick connector for the inner cover drain hole, and a quick connector for the air inlet. The quick connector for the cover hole is used to install a testing instrument to detect the pressure of the cover chamber 8. This connector, together with the cover hole cover 10 and the cover hole cover screw 11, achieves sealing in the non-testing state. The quick connector for the inner cover drain hole is used to install a testing instrument to detect the pressure of the container chamber 9 of the transfer container 1. When the pressure in the container chamber 9 of the transfer container 1 exceeds the limit, the air inlet quick connector is used to connect an exhaust pipe to the plant exhaust gas system to implement controlled pressure relief. This connector is compatible with the air inlet 13 of the inner cover. The pre-designed quick-connect couplings are functionally subdivided, with dedicated interfaces for pressure measurement and depressurization in different chambers. This avoids operational and detection errors caused by mixing interfaces, improving the accuracy of pressure monitoring and depressurization operations. The modular design of the quick-connect couplings allows for rapid assembly and disassembly of testing instruments and exhaust pipes, significantly shortening pipe connection operation time, improving work efficiency during the unloading phase, and reducing the exposure time of operators in radioactive areas, thus lowering radiation dose. The depressurization pipeline is directly connected to the plant's exhaust gas system, enabling standardized and harmless treatment of overpressured gases and avoiding environmental and personnel safety risks associated with direct emission of radioactive gases.

[0048] In this embodiment of the invention, damage monitoring of high burnup spent fuel assemblies involves sampling internal gas through the water hole 12 in the inner cover of the transfer container 1 and performing radioactivity testing on the sampled gas to verify that the high burnup spent fuel assemblies are undamaged. This non-contact verification of fuel assembly damage via gas sampling and radioactivity testing eliminates the need to open the container, avoiding the radiation and leakage risks associated with fuel assembly exposure during testing. Sampling through the water hole 12 in the inner cover is compatible with the container's structural design, is convenient, and ensures representative sampling that accurately reflects the integrity of the fuel assembly. Early verification of the fuel assembly's lack of damage provides a safe prerequisite for subsequent cooling, cleaning, and unloading. If damage is detected, emergency measures can be taken promptly to prevent the accident from escalating and improve the safety level of the unloading operation.

[0049] In this embodiment of the invention, during the cooling and cleaning operation of the inner cavity of the transport container 1, the deionized water system is connected to the inner cover inlet and outlet holes and the inner cover air inlet 13 of the transport container 1 through the quick connector of the inner cover drain hole and the quick connector of the air inlet hole. Deionized water is continuously injected into the inner cavity 9 of the transport container 1 at a constant flow rate. First, the deionized water is used to absorb the decay heat to achieve cooling of the inner cavity. Then, the radioactive contaminants in the inner cavity are flushed by the water flow, realizing the integrated operation of cooling and decontamination. The cooling and cleaning pipeline is removed after the outlet water temperature drops to the preset safe range. By utilizing existing quick-connect couplings, the deionized water system can be quickly connected to the container without the need for additional connection structures, improving the convenience and efficiency of cooling and cleaning operations. This also allows for interface reuse, simplifying the container's structural design. Using a constant flow rate of deionized water for cooling and cleaning effectively cools the container's interior, reducing safety risks from decay heat, and thoroughly cleans radioactive contaminants within the interior, reducing the time required for individual operations. Using the outlet water temperature as the operation termination indicator enables standardized control of the cooling and cleaning operation, avoiding under- or over-operation due to human judgment, and improving the standardization and reliability of the operation.

[0050] In this embodiment of the invention, during the unloading stage, after cooling and cleaning the inner cavity of the transshipment container 1, the inner cover clamping flange 6 of the transshipment container 1 is first removed. Then, a special unloading lifting tool is connected through the lifting trunnion 16 to lift the transshipment container 1 from the preparation well to directly above the unloading well. Its outer surface is rinsed with deionized water to reduce contaminants. The container is slowly lowered so that it is precisely positioned at the designated interface position of the unloading well. Subsequently, the inner cover 7 of the transshipment container 1 is removed and the removed inner cover 7 is cleaned, inspected, and protected. When removing the inner cover 7 of the transshipment container 1, the inner cover 7 is immediately rinsed with deionized water to remove contaminants after it is exposed to the water surface. During the operation, the sealing groove of the inner cover 7 is protected. The sealing groove cooperates with the sealing ring 15 to achieve container sealing. The core unloading operation steps after cooling and cleaning are refined and standardized, with each step seamlessly connected to ensure smooth unloading and improve operational efficiency. The use of a dedicated unloading hoist and lifting trunnion 16 ensures precise positioning of the container and unloading well, eliminating errors from manual positioning, improving positioning accuracy, and reducing the need for fine-tuning of the crane, thus reducing equipment wear. Once the inner cover 7 is exposed above the water surface, it is immediately rinsed to remove surface radioactive contaminants and effectively control the spread of pollution. During operation, the sealing groove of the inner cover 7 is protected; the removed inner cover 7 is cleaned, inspected, and replaced to ensure the sealing components are in good working order, thus building a strong safety barrier for container reuse and extending the container's service life.

[0051] In this embodiment of the invention, at the end of the unloading phase, the unloading sequence number, operation process, and final storage location in the transfer pool rack of the high burnout spent fuel assembly are recorded in detail in the unloading report, completing the closed-loop management of the operation process. The unloading phase includes a closed-loop record management system, meticulously recording the unloading sequence number, operation process, and final storage location of the spent fuel assembly. This meets the stringent quality assurance and operational traceability requirements of the nuclear industry, facilitating subsequent verification, traceability, and management. The closed-loop management of the entire process achieves full coverage of loading, transfer, and unloading operation information, forming a complete operation archive. Through these records, problems in the operation can be identified and optimized in a timely manner, continuously improving the standardization and normalization of operations and ensuring the safe and orderly conduct of the entire spent fuel transfer process.

[0052] The transport container 1 used in this invention is a dedicated heavy-duty container adapted to high-burnup spent fuel assemblies. Its overall structure balances strength and functional adaptability, precisely matching the transport characteristics of high-burnup spent fuel assemblies. The container's maximum external dimensions are Φ2500mm × 5934mm (diameter × height), with an unloaded weight (including the basket) of approximately 103,898 kg and a fully loaded weight of approximately 113,747.6 kg. This invention employs a standardized quick-connect design throughout. The quick-connect connectors for the cover hole, inner cover drain hole, and air inlet are dedicated functional interfaces for pressure measurement, pressure relief, and cooling cleaning of different chambers, avoiding operational errors and detection errors caused by mixing interfaces. This enables rapid connection and switching of pressure testing pipelines, exhaust and pressure relief pipelines, and cooling water pipelines, significantly shortening pipeline connection operation time, improving operational efficiency at each stage, and minimizing energy consumption. This method minimizes the exposure time of operators in radioactive areas, reduces radiation exposure, and effectively implements the principle of optimal radiation protection. Detection holes 14 are respectively set between the double sealing rings 15 of the outer cover 5, inner cover 7, inner cover clamping flange 6, and water hole cover 4, enabling precise monitoring of leakage at each sealing surface and providing accurate technical support for graded sealing treatment. The inner cylinder 2, as the main structure of the transfer container 1, provides a stable installation foundation for the container's inner chamber 9, lifting basket assembly, etc. Its upper circumferential lifting trunnions 16 ensure the safety and stability of container lifting operations, while the lower inner cylinder water hole 3 adapts to the filling and draining operation requirements at each stage. All structures and interfaces work together to ensure the smooth implementation of the operating method of this invention. Furthermore, this method can be seamlessly integrated with the existing plant structure, crane equipment, and standard operating procedures of nuclear power plants without large-scale modification of existing facilities, demonstrating strong practicality and scalability.

[0053] To make the technical solution of the present invention more practical and reproducible, the following embodiments are given in conjunction with specific application scenarios, and the specific operation process applicable to 14-foot high burnup spent fuel assemblies is described in detail:

[0054] Example 1: Operating Procedures for 14-Foot High Burnout Spent Fuel Assemblies

[0055] (a) Loading stage

[0056] 1. Before loading, assess the 14-foot high burnout spent fuel assembly to be loaded and verify that it meets the physical, thermal and radiation safety requirements for loading.

[0057] 2. Clean or decontaminate the transshipment container 1, and place the transshipment container 1 on the transfer trailer by engaging the vertical lifting device with the lifting trunnion 16. The transfer trailer then transports the container to the fuel plant.

[0058] 3. Remove the water hole cover 4, fill the transfer container 1 with water through the automatic control system in the fuel plant, and after filling with water, remove the outer cover 5, the inner cover clamping flange 6 and the inner cover 7 of the container;

[0059] 4. Connect the transfer container 1 to the penetrating part at the bottom of the loading well, fill the penetrating part with water until there is no height difference between its water level and the water level at the bottom of the loading well. After confirming that everything is correct, open the manhole cover at the bottom of the loading well and load the 14-foot high spent fuel assembly.

[0060] 5. After loading is completed, first close the manhole cover at the bottom of the loading well, then lower the water level inside the transfer container 1, separate the transfer container 1 from the penetrating part at the bottom of the loading well, and dry and clean the penetrating part;

[0061] 6. Install the inner cover 7 and the inner cover clamping flange 6, drain, vacuum dry and fill the transport container 1 with helium, and complete the leak test inside the container.

[0062] 7. Install container cover 5 and perform a leak test at the outer cover of transport container 1;

[0063] 8. Conduct comprehensive radiation monitoring on transshipment container 1 to confirm that its surface contamination and radiation levels meet transportation requirements.

[0064] (II) Relocation Phase

[0065] After confirming that the transshipment container 1 has been loaded, sealed, and that the leakage test and radiation monitoring have all passed, the transshipment container 1 and the transfer trailer are transferred together to the transshipment facility plant by a towing vehicle.

[0066] (III) Unloading Phase

[0067] 1. In accordance with relevant nuclear industry requirements, conduct radioactivity and contaminant testing on the surface of transshipment container 1, and record the test results in detail in the container unloading report;

[0068] 2. Use a special lifting tool to lift the transfer container 1 out of the spent fuel container transfer trailer and place it smoothly into the prepared well;

[0069] 3. Based on the results of radioactivity and contaminant detection, the outer surface of transshipment container 1 was cleaned in a targeted manner;

[0070] 4. Remove the container cover 10 and cover screw 11, install a pressure gauge at the quick connector of the cover hole, and check whether there is excess pressure between the inner and outer covers during transportation. If there is excess pressure, connect an exhaust pipe to the plant exhaust gas system at the quick connector of the cover hole for controlled pressure relief.

[0071] 5. Remove the outer cover 5 and connecting bolts from the container, clean the outer cover 5 and store it in a temporary storage area with a protective mat.

[0072] 6. Install a pressure gauge at the quick connector of the drain hole in the inner cover to check whether there is excess pressure in the inner cavity of the container during transportation. If there is excess pressure, connect an exhaust pipe to the factory exhaust gas system at the quick connector of the air inlet to release the pressure.

[0073] 7. Take internal gas samples from the 12 water holes in the container cap and conduct radioactivity testing to verify that the 14-foot-high spent fuel assembly was not damaged;

[0074] 8. Connect the quick connector for deionized water in the plant to the quick connector for drain hole in the container cover, and connect the other quick connector for drain pipe to the quick connector for air inlet 13 in the container cover. Open the deionized water valve in the plant and inject deionized water into the container cavity at a flow rate of 2 m³ / h for cooling. After the container is full, the water will flow out from the drain pipe at air inlet 13 until the water temperature drops below 60°C. Then disconnect the water inlet pipe and the drain pipe from the container cover.

[0075] 9. Remove the inner cover clamping flange 6 and connecting bolts from the container, clean it, and store it properly;

[0076] 10. Securely connect the container crane hook to the special lifting tool, and confirm that the special lifting tool and the container lifting trunnion are reliably engaged. At the same time, use slings to connect the rotating lifting ring on the inner cover 7 to the special lifting tool.

[0077] 11. Disconnect all exhaust pipes connected to the quick-connect fittings at the exhaust ports and clean any remaining sealant from the connections;

[0078] 12. Hoist the transport container 1 to the top of the unloading well, wash the outer surface of the container with deionized water to minimize contaminants, and slowly lower the container until it is precisely located at the designated interface position of the unloading well.

[0079] 13. Remove the container-specific lifting tool from the container trunnion and lift the inner cover 7. When the container-specific lifting tool and the inner cover 7 are exposed above the water surface, clean them with deionized water to remove dirt. During the operation, pay special attention to protecting the sealing groove of the inner cover 7.

[0080] 14. Thoroughly clean the removed container inner lid 7 and check for any damage or excessive wear. If any is found, replace it immediately. At the same time, properly protect all disassembled parts.

[0081] 15. Record in detail the unloading sequence number, operation process, and final storage location of the 14-foot high spent fuel assembly in the unloading report, and complete the closed-loop record of the entire process.

[0082] The operating method for the 14-foot high spent fuel transport container of this invention has significant technical advantages over existing technologies. Firstly, it features a systematized process, breaking down the complex nuclear fuel transport operation into three logically rigorous and clearly defined standardized stages: loading, transport, and unloading. This significantly improves the operability and standardization of the operation, adapting to the large-scale transport operation requirements of nuclear power plants. Secondly, it offers multiple layers of safety, innovatively integrating graded pressure monitoring and controlled pressure relief mechanisms for the cover chamber and the container's inner chamber. This allows for the immediate detection and handling of pressure anomalies after transport, fundamentally avoiding potential risks such as radioactive leakage caused by pressure imbalance during the capping process. It also eliminates the risks of falls and collisions during the delicate handling of heavy-load containers at height. Thirdly, it ensures controllable contamination, eliminating static pressure differences through water level equalization during the loading stage and ensuring control during hoisting and cap opening. The system comprises a series of steps, including immediate cleaning and decontamination, and pre-unloading gas sampling to verify fuel integrity, forming a comprehensive pollution control system that effectively controls the risk of radioactive contamination spread and ensures the safety of personnel and the environment. Fourthly, it ensures high operational efficiency by employing standardized quick-connect couplings throughout the process for rapid connection and switching of pressure testing pipelines, venting and depressurization pipelines, and cooling water pipelines. It also clearly defines key operating parameters such as a 2 m³ / h cooling water flow rate and a 60°C outlet water temperature, reducing manual operation time and the frequency of fine-tuning, minimizing the uncertainty of human operation, and avoiding abnormal wear caused by frequent equipment micro-movements. Fifthly, it ensures traceability by recording data and generating dedicated unloading reports at key operational stages such as entry inspection, pressure monitoring, and unloading completion, achieving full traceability of information throughout the operation and meeting the stringent quality assurance requirements of nuclear safety regulations. Furthermore, this method, through its remote control design, significantly shortens the exposure time of operators in radioactive areas, significantly reduces radiation dose, and can be seamlessly integrated with existing nuclear power plant loading shafts, cranes, and other facilities without requiring large-scale modifications to existing plants and equipment, demonstrating strong practicality and engineering promotion value.

[0083] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0084] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment includes only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization, characterized in that, This includes the sequential loading, transport, and unloading phases; During the loading stage, after the transfer container is connected to the loading well penetration, water is filled into the loading well penetration until its water level is level with the water level at the bottom of the loading well. Then, the loading operation of the high-burnup spent fuel assembly is carried out. After the loading operation is completed, the transfer container is tested for leakage. After the test is passed, the sealing and radiation monitoring are completed. During the transshipment phase, transshipment containers that have been loaded and have passed leak testing and radiation monitoring will be transferred to the target transshipment facility plant. During the unloading phase, before opening the container, a detection instrument is installed via a pre-set quick connector to sequentially detect the pressure in the inter-lid chamber between the outer and inner lids and the inner chamber of the container. If the pressure in any chamber exceeds a preset threshold, the chamber is connected to the plant's exhaust gas system via an exhaust pipe for controlled depressurization. After depressurization, damage monitoring of the high-burning-consumption spent fuel assembly is performed first, followed by cooling and cleaning of the inner chamber of the container.

2. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 1, characterized in that, During the loading phase, after the high-burning-consumption spent fuel assembly is loaded, the manhole cover at the bottom of the loading well is closed first, then the water level inside the transfer container is lowered to separate the container from the loading well penetration, and the loading well penetration is dried and cleaned. After that, a leak inspection operation is performed on the transfer container.

3. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 2, characterized in that, The leakage inspection of the transshipment container includes an internal leakage inspection and an external cover leakage inspection performed sequentially. Before the internal leakage inspection, the transshipment container must also be drained, vacuum dried, and filled with helium.

4. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 1, characterized in that, During the transshipment phase, the transshipment containers that have been loaded and have passed leakage inspection and radiation monitoring are transported together with a special transfer trailer to the target transshipment facility plant by a tractor.

5. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 1, characterized in that, During the unloading phase, before installing the testing instrument to detect the pressure through the preset quick connector, the process also includes entering the transport container for inspection, hoisting and positioning, and surface cleaning. The entering inspection involves detecting radioactivity and contaminants on the surface of the transport container, and the test results are recorded in the unloading report.

6. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 5, characterized in that, The preset quick connectors include a cover hole quick connector, an inner cover drain hole quick connector, and an air inlet quick connector. The cover hole quick connector is used to install a detection instrument to detect the pressure in the cover chamber, and the inner cover drain hole quick connector is used to install a detection instrument to detect the pressure in the inner chamber of the transport container. When the pressure in the inner chamber of the transport container exceeds the limit, the air inlet quick connector is used to connect an exhaust pipe to the plant's waste gas system to implement controlled pressure relief.

7. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 6, characterized in that, The damage monitoring of the high burnout spent fuel assembly involves sampling the internal gas through the water hole in the inner cover of the transfer container and conducting radioactivity testing on the sampled gas to verify that the high burnout spent fuel assembly is undamaged.

8. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 7, characterized in that, During the cooling and cleaning operation of the inner cavity of the transshipment container, the deionized water system is connected to the inlet and outlet holes of the inner cover of the transshipment container through the quick connector of the drain hole and the quick connector of the air inlet hole. Deionized water is injected into the inner cavity of the transshipment container at a constant flow rate for cooling and cleaning until the outlet water temperature drops to the preset safe range, and then the cooling and cleaning pipeline is removed.

9. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 8, characterized in that, During the unloading phase, after cooling and cleaning the inner cavity of the transport container, the clamping flange of the transport container is first removed, and then a special unloading hoist is connected to lift the transport container to the top of the unloading well and precisely position it at the designated interface position of the unloading well. Then, the inner cover of the transport container is removed and the removed inner cover is cleaned, inspected, and protected. When removing the inner cover of the transport container, the inner cover is immediately rinsed with deionized water to remove dirt after it is exposed to the water surface, and the sealing groove of the inner cover is protected during the operation. If the removed inner cover is found to be damaged or excessively worn after inspection, it is replaced immediately.

10. The method for operating a high-burnup spent fuel transfer container with graded pressure monitoring and depressurization according to claim 9, characterized in that, At the end of the unloading phase, the unloading sequence number of the high-burning spent fuel assembly, the operation process, and the final storage location in the transfer tank grid are recorded in detail in the unloading report, thus completing the closed-loop management of the operation process.

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