Loading step design method for overhaul reactor core of Hualong No.1 nuclear power plant
By optimizing the snake-shaped loading mode and direct insertion method, the loading difficulties caused by deformation during the loading process of nuclear fuel components is solved, and the safety and efficiency of core loading of Hualong No. 1 nuclear power plant has been improved.
Patent Information
- Application Number
- CN202510490181.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-18
- Publication Date
- 2025-08-08
AI Technical Summary
In the prior art, nuclear fuel components cannot successfully enter the pins of the lower grid plate of the core due to deformation during the loading process. Especially when the core space is limited, the operation difficulty and risk increase, and the loading time is extended.
The serpentine loading mode is adopted, and the loading starts from 180° to 270° quadrant, and gradually fills the fuel assembly to the 0° to 90° quadrant, ensuring that each component has at least two side support, and the spent fuel assembly is loaded by direct insertion when the core space is limited. The tic toe space formed by adjacent fuel assembly and core enclosure is used to replace the small boot guide, reducing the movement and risk of the small boot up.
It effectively reduces the risk of loading failure caused by deformation of fuel components, avoids interference and bumps of wire ropes on the boots, improves the safety and efficiency of loading, and reduces operating time.
Smart Images
Figure CN120452861A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of operation for loading and unloading nuclear fuel assemblies in a Hualong One nuclear power plant reactor, and specifically relates to a method for designing a core loading sequence for a Hualong One nuclear power plant overhaul. The method can avoid situations in which loading cannot be performed due to the deformation characteristics of nuclear fuel assemblies, significantly improve the safety and efficiency of nuclear power plant loading, and can be promoted for use. Background Art
[0002] Reactor loading in nuclear power plants is a critical path in the refueling overhaul schedule and a top priority. The safe and efficient operation of fuel assemblies is crucial for improving the economic benefits of nuclear power plants. Due to the inherent characteristics of fuel assemblies, they deform after irradiation within the core. This prevents the pin holes in the lower tube sockets of the fuel assemblies from smoothly entering the pins in the lower grid plate during loading. Therefore, auxiliary loading methods are used to address this issue. However, in the later stages of loading, as more fuel assemblies are loaded, the space in the core gradually decreases. This increases the difficulty and risk of operating these auxiliary loading methods, and also increases the time required. Summary of the Invention
[0003] The purpose of the present invention is to provide a core loading sequence design method for the overhaul of the Hualong One nuclear power plant, which is based on the optimization of the existing serpentine loading method, considers the influence of the small boot upper on the loading operation, and provides a new loading design method.
[0004] In order to achieve the above object, the technical solution adopted by the present invention is:
[0005] A method for designing a core loading sequence for overhaul of a Hualong One nuclear power plant adopts a serpentine loading mode, starting with loading from the coamings in the 180° to 270° quadrants and gradually filling fuel assemblies in the 0° to 90° quadrants to ensure that all fuel assemblies always have at least two side supports. After the fourth-to-last row of fuel assemblies is loaded using the serpentine loading mode, loading begins from 270° to 90° in step 159. After completing the 09 coordinate column, loading is sequentially performed linearly toward 0° until the remaining fuel assemblies in the 10 / 11 / 12 coordinate columns are loaded. After the remaining three groups of fuel assemblies in the K coordinate row are loaded sequentially, a small boot top water extraction operation is performed. In the last five steps, three groups of new fuel assemblies are first loaded. Steps 176 and 177 are for the spent fuel assemblies, which are directly inserted.
[0006] Reduce the probability of fuel assemblies moving over other fuel assemblies already loaded into the core.
[0007] The last two groups of spent fuel assemblies were successfully loaded by replacing the restraining and guiding role of the small boot by using the tic-tac-toe space formed by adjacent fuel assemblies and the core enclosure.
[0008] The beneficial effects achieved by the present invention are:
[0009] After optimizing these steps, all spent fuel assemblies inserted directly into the reactor were guided by two sides of the new fuel assembly, reducing the risk of assembly deformation encroaching on the designated position during late loading. Furthermore, while fully utilizing the small shoe, it was immediately lifted out of the core pool, eliminating the risk of interference with the small shoe's wire ropes during loading and the risk of the small shoe bumping the fuel assembly during movement. Furthermore, the situation in which deformation and failure to load the fuel assembly were largely avoided was avoided. The final two groups of spent fuel assemblies were successfully loaded, using the "well" space formed by adjacent fuel assemblies and the core enclosure to replace the restraining and guiding function of the small shoe. BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Figure 1 The core fuel assembly layout diagram is for the start of the second cycle;
[0011] Figure 2 Schematic diagram of the bending of fuel assemblies after irradiation in the core;
[0012] Figure 3 The lower tube seat of the fuel assembly cannot enter the positioning pin of the lower core plate;
[0013] Figure 4 For the use of small boot uppers;
[0014] Figure 5 This is the bridge loading step table;
[0015] Figure 6 This is the diagonal loading step table;
[0016] Figure 7 It is a serpentine charging step table;
[0017] Figure 8 For the movement of the little boot gang;
[0018] Figure 9 charging plan for overhaul;
[0019] Figure 10 Loading fuel assemblies for steps 159-169;
[0020] Figure 11 Load fuel assemblies for steps 170-177. DETAILED DESCRIPTION
[0021] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
[0022] Hualong One reactor core fuel assembly layout:
[0023] The Hualong One unit reactor core has a total of 177 AFA3G fuel assemblies, which are arranged upright in the space surrounded by the upper grid plate, lower grid plate and enclosure of the core. The pins on the lower grid plate provide positioning and guidance for the normal placement of the fuel assemblies.
[0024] The first cycle core fuel assemblies were loaded in three zones, corresponding to three enrichments of 1.8%, 2.4%, and 3.2%. Starting from the second cycle, the core was loaded using a low leakage (IN-OUT) method, with 68 new fuel assemblies loaded each time. The core fuel assembly layout is as follows: Figure 1 As shown, the green cells in the figure represent new fuel assemblies and the yellow cells represent spent fuel assemblies.
[0025] Effect of fuel assembly deformation on assembly loading:
[0026] Since the fuel assembly is constrained by the upper grid plate, lower grid plate and surrounding plate in the core, it grows due to irradiation during the irradiation process, and the length increases to form a "C" shape bend. As the length of the assembly continues to increase or the pressing force continues to increase, the curvature of the assembly increases. Because the increase in the curvature of the assembly is constrained by the adjacent assemblies, when the curvature can no longer increase, it can only be transformed into an "S" shape that can accommodate a larger additional length. Similarly, if the length of the assembly is further increased or the pressing force is further increased, the curvature is transformed into a "W" shape that can accommodate a larger additional length (see Figure 2 ).
[0027] According to the operating experience of Fuqing Nuclear Power Plant, the bending amount after one cycle is usually within 7mm, and the bending amount after two cycles is usually within 12mm. The bending deformation of the fuel assembly will cause the relative position of the upper tube seat and the lower tube seat of the fuel assembly to change. When the upper tube seat is positioned at the target position, the guide pin hole of the lower tube seat cannot enter the positioning pin of the grid plate under the core, causing the fuel assembly to fail to load. The deformed fuel assembly will affect the loading of the fuel assembly close to it. The deformed part will produce a pushing effect during the loading process of the adjacent fuel assembly, causing the position of the lower tube seat of the adjacent fuel assembly to change, resulting in loading difficulties (see Figure 3 ).
[0028] like Figure 4 In order to avoid the situation where the fuel assembly cannot be positioned in the core due to excessive deformation, a small boot is usually used to guide the spent fuel assembly. When using the small boot, the refueling supervisor first moves the small boot to the lower core grid plate of the positioned fuel assembly, and its two positioning pins are inserted into the water flow holes of the lower core grid plate. The two guiding slopes face the target position of the fuel assembly, providing a smooth guiding surface for the lower tube seat of the fuel assembly, which serves as a preliminary guide before the fuel assembly is positioned, so that the lower tube seat of the fuel assembly slides into the positioning pins along the guide surface.
[0029] Loading sequence study:
[0030] The core of the Hualong One unit at the Fuqing Nuclear Power Plant utilizes a full-load, full-load refueling method. During each refueling cycle, all 177 fuel assemblies are removed from the core and transported to the spent fuel storage racks in the fuel building for storage. The relevant assemblies are then swapped within the racks, and finally, the 177 fuel assemblies for the next fuel cycle are loaded into the core. Based on current refueling examples from other domestic nuclear power plants, there are three main refueling sequence schemes: bridge loading, diagonal loading, and serpentine loading. The first reactors of domestic nuclear power plants generally use the bridge loading method, while serpentine loading is primarily used for refueling.
[0031] Study on bridge loading sequence:
[0032] The overall idea of the bridge loading sequence is: loading starts from the middle of the core, first completing the loading of the middle three rows (07, 08, 09), and then completing the loading of the middle three columns (J, H, G). The main design scheme is as follows Figure 5 shown.
[0033] Fuel assemblies are loaded around the core, starting with the upper right corner, followed by the upper left, then the lower right, and finally the lower left. Currently, a small number of nuclear power units use a bridge-type loading scheme for initial fuel loading.
[0034] Disadvantages: During bridge loading, most fuel assemblies lack two adjacent surfaces to effectively support them when they are loaded into the core (e.g., steps 5, 6, and 7). This fails to meet regulatory requirements for spent fuel assemblies to have two adjacent surfaces for support. For safety reasons, the loading plan should ensure that as many fuel assemblies as possible have two support surfaces when loaded into the core.
[0035] Study on diagonal charging sequence:
[0036] The idea of diagonal loading sequence is as follows: start loading from 180°-270° of the core, and follow this sequence in the subsequent loading process. Finally, close the core enclosure with a "grid" pattern. The main design schemes are as follows: Figure 6 shown.
[0037] Disadvantages: After each row of components is loaded, the small boot needs to be moved to the starting point of the next row, which greatly increases the risk of moving the small boot in the core area.
[0038] Study on serpentine charging sequence:
[0039] The oblique charging sequence is currently widely used in overhaul charging. The charging sequence is as follows: Figure 4 As shown. Figure 4 It can be seen that the idea of the serpentine loading sequence is as follows. This scheme starts with loading from the coamings in the 180° to 270° quadrants, and gradually fills the fuel assemblies in the 0° to 90° quadrants in a "serpentine" loading manner. The main design schemes are as follows: Figure 7 shown.
[0040] Advantages: Because irradiated fuel assemblies deform, it is necessary to ensure that each fuel assembly is supported on adjacent surfaces during loading. At the same time, the number of four-sided supports should be minimized. Furthermore, because "small boots" are used to assist in positioning the fuel assemblies during loading, their movement is minimized, with end-to-end connections being used.
[0041] Core loading sequence:
[0042] The overall fuel loading operation plan for the Fuqing Nuclear Power Plant overhaul adopts a "snake" loading mode, such as Figure 4 As shown, priority is given to loading the coaming starting from the 180° to 270° quadrants, and gradually filling the fuel assemblies in the 0° to 90° quadrants in a "snake" loading manner to ensure that all fuel assemblies always have at least two side supports and reduce the probability of fuel assemblies moving above other fuel assemblies already loaded into the core.
[0043] Limitations of the "snake" charging mode:
[0044] like Figure 8 When using the "snake" loading mode to operate the third-to-last row of small boots, the small boots need to be rotated at an appropriate angle and moved in the direction indicated by the arrow. The boots cannot be lowered during the movement. They can only be lowered after being moved to a more open position. The entire moving operation is difficult and has a high risk of collision with the fuel assembly and the core enclosure. The fuel assembly rod bundle may be damaged if you are not careful.
[0045] During an overhaul and refueling at a similar power plant, a refueling supervisor, while attempting to move a small boot, became stuck between the core coaming and the fuel assembly. The supervisor resorted to pulling the wire rope at multiple angles to remove the boot. As the remaining space in the core became increasingly limited, the boot's wire rope could easily fall into the assembly to be loaded if it slackened slightly. Consequently, the angle between the boot's wire rope and the vertical direction became very small, making it difficult to observe. To avoid interference between the assembly and the boot's wire rope during loading, the offset loading method could not be used. At this point, both moving the boot and pulling the wire rope would become difficult and posed a significant risk.
[0046] by Figure 9 Taking the overhaul loading plan as an example, the loading operation sequence generally uses a "snake-shaped" loading mode in the early and middle stages of loading, and makes full use of the small boot guide method to successfully complete the loading of most fuel assemblies.
[0047] However, by the time the fuel assemblies reach step 159, the remaining space in the core is extremely limited. If the remaining four rows of fuel assemblies continue to be loaded according to the "snake" loading plan shown in the figure, since nine of the fourth-to-last row contain spent fuel assemblies, these nine assemblies will need to be guided by the small shoe. Given the extremely limited remaining space in the core, moving the small shoe on the lower grid plate using conventional loading methods would likely cause the shoe's wire rope to enter the lower fuel assembly sockets and fuel rods.
[0048] At this time, you can consider not using the small shoe for loading. When loading the fourth-to-last row of fuel assemblies, if the first loading attempt fails, you can use the 180° rotation positioning method to turn the deformation direction of the lower tube seat of this group of fuel assemblies toward the lateral support surface, and use the lateral support surface to guide and correct the lower tube seat to complete the loading of the fuel assembly. However, this process requires rotating the loading and unloading machine tower and re-lifting and placing the fuel assembly. It takes about 2.5 hours to load each group of fuel assemblies, which is extremely time-consuming and greatly increases the operational risk. During the overhaul and unloading of the Fuqing Nuclear Power Plant, there were multiple cases of deformation of the fuel assembly due to movement within the 25a reactor. At the same time, the small shoe was not used for guidance. The fuel assembly was rotated 180 degrees and loaded into the core, which greatly extended the unloading period.
[0049] According to the above analysis, the "snake-shaped" loading mode is not applicable to the loading of the last three rows of fuel assemblies in the annual refueling core of the Hualong One nuclear power unit (not the first reactor).
[0050] Optimization of loading operation sequence:
[0051] The focus of optimizing the loading operation sequence is to solve the problem of difficulty and time-consuming loading of the last four rows of fuel assemblies in the annual core replacement of the Hualong unit (not the first reactor). Under the condition of limited core space, how to give full play to the guiding role of the small boot while reducing the risk of using the small boot; how to convert the unknown deformation of the fuel assembly into a known quantity and avoid the extension of loading time caused by the use of the 180° rotation positioning method are the key points that need to be comprehensively considered and balanced when designing the loading operation plan.
[0052] Through the study of the core loading diagram of each refueling cycle of the Hualong unit, and taking into account the risks of small boot operation and 180° rotation of the loader and unloader, the "snake" loading mode is adopted to load the fourth to last row of fuel assemblies. Figure 10 As shown, it is possible to consider loading from 270°-90° starting from step 159. After completing the 09 coordinate column, loading is sequentially performed linearly toward the 0° direction until the remaining fuel assemblies of the 10 / 11 / 12 coordinate columns are loaded.
[0053] like Figure 11As shown, after the remaining three fuel assemblies of the K coordinate row are loaded in sequence, the small boot water removal operation is carried out, and the loading of the three new fuel assemblies is completed first in the last five steps; steps 176 and 177 are for the spent fuel assembly, and are close to the core enclosure, so direct insertion is performed in consideration of the last two steps.
[0054] After optimizing these steps, all spent fuel assemblies inserted directly into the reactor were guided by two sides of the new fuel assembly, reducing the risk of assembly deformation encroaching on the designated position during late loading. Furthermore, while fully utilizing the small shoe, it was immediately lifted out of the core pool, eliminating the risk of interference with the small shoe's wire ropes during loading and the risk of the small shoe bumping the fuel assembly during movement. Furthermore, the situation in which deformation and failure to load the fuel assembly were largely avoided was avoided. The final two groups of spent fuel assemblies were successfully loaded, using the "well" space formed by adjacent fuel assemblies and the core enclosure to replace the restraining and guiding function of the small shoe.
[0055] Through the physical properties and layout characteristics of new fuel assemblies and spent fuel assemblies, through in-depth research on the Hualong One loading sequence, combined with the use characteristics of the small boot upper of the loading auxiliary tool, the optimized loading sequence successfully avoided the failure to meet requirements due to deformation of the fuel assemblies.
[0056] This loading sequence has been fully verified in the overhaul loading operation method, and all fuel assemblies were successfully loaded at one time. This loading operation method has strong application value for the annual core replacement loading operation of the "Hualong One" core.
Claims
1. A method for designing a core loading sequence for a Hualong One nuclear power plant overhaul, characterized by: A serpentine loading mode is used, starting with loading from the enclosures in the 180° to 270° quadrants, and gradually filling the fuel assemblies in the 0° to 90° quadrants to ensure that all fuel assemblies always have at least two side supports. After the fourth-to-last row of fuel assemblies is loaded using the serpentine loading mode, step 159 begins loading from 270°-90°. After completing the 09 coordinate column, loading is performed linearly toward 0° until the remaining fuel assemblies in the 10 / 11 / 12 coordinate columns are loaded. After completing the loading of the remaining three groups of fuel assemblies in the K coordinate row, the small boot water extraction operation is performed. In the last five steps, the loading of three new fuel assemblies is completed first; steps 176 and 177 are for spent fuel assemblies, which are directly inserted.
2. The method for designing a core loading sequence for a Hualong One nuclear power plant overhaul according to claim 1, characterized in that: Reduce the probability of fuel assemblies moving over other fuel assemblies already loaded into the core.
3. The method for designing a core loading sequence for a Hualong One nuclear power plant overhaul according to claim 1, characterized in that: The last two groups of spent fuel assemblies were successfully loaded by replacing the restraining and guiding role of the small boot by using the tic-tac-toe space formed by adjacent fuel assemblies and the core enclosure.