An integrated modular molten salt reactor core assembly and core replacement method

Abstract

The application relates to a kind of integrated modular molten salt reactor core assembly and core replacement method, which includes in-plant modular pre-assembly step, on-site integral assembly step, core integral replacement step;The in-plant modular pre-assembly step independently completes the assembly and detection of container module, graphite core module and integrated top module, and then is integrally transported;The on-site integral assembly step assembles the three groups of prefabricated modules in position, and connects the molten salt flow path;The core integral replacement step hoists out and replaces the graphite core module integrally, without disassembling the in-core components throughout.The application divides the reactor assembly process into three major procedures: in-plant modular pre-assembly, on-site integral assembly and core integral replacement, which can complete the complete assembly and detection of container module, graphite core module and integrated top module in the factory building, and then transport them to the construction site for unified assembly, greatly reducing the on-site operation procedures in the radiation field, improving the overall assembly accuracy and shortening the construction period.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor construction and operation technology, specifically relating to an integrated modular molten salt reactor core assembly and core replacement method. Background Technology

[0002] Molten salt reactors use molten salt as the nuclear fuel carrier and primary loop heat exchange medium, possessing inherent advantages such as high safety, flexible fuel cycle paths, and a wide operating temperature range, making them a key development direction for next-generation advanced nuclear reactors. Existing conventional molten salt reactor cores are monolithic, fixed, welded, and integral structures, lacking independently separable, prefabricated, and transportable modular units. Traditional assembly and refueling processes have numerous inherent drawbacks, specifically as follows:

[0003] First, all components of the reactor are assembled piecemeal on site, resulting in a long construction period and difficulty in controlling assembly precision. In traditional molten salt reactors, all components, including the main container, shielding graphite, heat exchangers, distribution pipelines, and top control mechanisms, must be hoisted, aligned, welded, and calibrated on-site for radiation protection construction. There is no modular pre-assembly process in the factory, and high-precision dimensional verification, pipeline sealing testing, and component coaxiality adjustment all rely on on-site completion. On-site conditions are complex and there are many interference factors. Multi-layer graphite blocks are simply attached and stacked without a layer-by-layer pin locking process, making it easy for graphite blocks to slip and misalign between layers. Metal supports and graphite shielding components do not have pre-reserved deformation gaps to accommodate thermal expansion differences, making it easy for compression interference to occur during on-site assembly. The molten salt feed channel at the bottom of the reactor lacks a pre-integrated molding process, and the openings are prone to leaving dead corners and uneven flow distribution in multiple heat exchange branches. The upper and lower pipelines of the heat exchangers are all rigidly welded together, and dimensional deviations caused by manufacturing and hoisting cannot be compensated for in advance, making on-site alignment difficult, and assembly stress cannot be eliminated, which can easily lead to pipeline leakage risks.

[0004] Secondly, the lack of a prefabricated, integrated refueling process for core replacement results in high radiation exposure risks and lengthy downtime maintenance cycles. Existing molten salt reactor cores have integrated welded and fixed graphite, heat exchange, and shielding structures, lacking prefabricated integrated core units and detachable dedicated lifting and support structures. Replacing aging graphite cores requires a complete disassembly process: first, removing all piping, control sleeves, and heat exchange equipment at the top of the reactor; then, disassembling multiple layers of graphite blocks and shielding components layer by layer; and finally, reassembling them piece by piece in reverse and recalibrating the seals and sleeve coaxiality. Throughout the disassembly and restoration process, operators are exposed to a high radiation dose for extended periods. The entire process can take months, leading to prolonged reactor downtime and significantly reducing the economic efficiency of the power plant. A small number of modular graphite cores can only be assembled layer by layer on-site, lacking the integrated process of a one-time, three-dimensional composite core in the factory, making it impossible to lift and replace the entire core as a whole, still relying on on-site disassembly operations.

[0005] Third, the top-mounted equipment lacks an integrated pre-assembly and commissioning process at the factory, resulting in a huge workload for on-site assembly and commissioning. Traditionally, the molten salt pump chamber, diversion pipelines, and control and start-up sleeve support structures at the top of the reactor are processed separately and transported to the site for assembly. There is no pre-commissioning process at the factory for the universal joint compensation performance, sleeve coaxiality, and flange pressure sealing performance. The control rods and start-up sleeves are only simply fixed at both ends, lacking a multi-point support and synchronous correction process. Under fluid vibration and temperature deformation, the sleeves are prone to displacement and swaying, causing subsequent control actions to be stuck. The top-mounted pipelines and the heat exchanger below can only be rigidly connected on-site, without a double-end universal flexible plug-in assembly process. It is impossible to synchronously compensate for the double assembly deviations of the upper and lower modules, resulting in numerous repeated on-site correction processes.

[0006] Fourth, the reactor shielding and heat exchange structures are constructed in stages on-site, resulting in high material costs and low neutron utilization efficiency. Traditional processes do not pre-install the bottom support assembly in the plant, and the bottom sealed cavity cannot be simultaneously formed and filled with shielding graphite. The internal cavity volume is large, requiring the addition of a large amount of expensive molten salt fuel on-site, leading to high operating material costs. The neutron reflector layer on the outside of the reactor core is only partially laid on-site, without an integrated pre-installation process for the casing and side reflector layer, resulting in large lateral neutron leakage and low nuclear fuel fission utilization. Summary of the Invention

[0007] To address the problems of existing molten salt reactors, such as the need for piecemeal assembly of all components on-site, poor construction precision, long construction periods, the need to disassemble all internal components for core replacement, high risk of radiation exposure for operators, long downtime maintenance cycles, lack of deviation compensation methods for pipeline assembly, and lack of modular pre-assembly and overall non-destructive replacement processes, this invention aims to provide an integrated modular molten salt reactor core assembly and core replacement method.

[0008] The integrated modular molten salt reactor core assembly and replacement method according to the present invention includes an in-plant modular pre-assembly step, an on-site overall assembly step, and an overall core replacement step. The in-plant modular pre-assembly step independently completes the assembly and testing of the container module, graphite core module, and integrated reactor top module before overall transport. The on-site overall assembly step aligns and assembles the three prefabricated modules, connecting them to the molten salt flow path. The overall core replacement step involves hoisting out and replacing the graphite core module as a whole, without disassembling any internal reactor components. This invention, through a complete process of modular in-plant prefabrication, on-site overall assembly, and non-destructive replacement of modules, abandons the traditional on-site assembly and disassembly-for-refueling method. It can transfer high-precision assembly processes to a controlled environment in the plant, reducing on-site irradiation time and shortening construction and downtime refueling cycles.

[0009] In a preferred embodiment, the pre-assembly of the container module in the factory includes pre-assembly of an integrated bottom support assembly, pre-positioning of the square channels, and insertion and assembly of the universal joint-type lower socket pipe fitting at the bottom of the heat exchanger. This invention, through the overall pre-assembly of the bottom support and the pre-forming process of the universal joint insertion of the heat exchange pipeline, enables synchronous and precise alignment of the multi-channel square channel flow distribution structure, avoiding the defects of pipeline misalignment and uneven flow caused by scattered assembly on site, and ensuring consistent operating conditions for the four sets of heat exchange branches.

[0010] In a preferred embodiment, during pre-assembly of the container module, the outer graphite is stacked in layers, and positioning pins are simultaneously installed between each layer of graphite blocks and between the graphite blocks and the outer support plate of the casing to limit the movement layer by layer. This invention adopts a pre-assembly process of locking graphite layers with pins, which can restrain the smooth movement of graphite caused by the buoyancy of the medium and thermal deformation, avoid the generation of graphite debris, the squeezing and blockage of the heat exchange channel gaps, and improve the structural stability of the reactor during long-term operation.

[0011] In a preferred embodiment, the graphite core module is pre-assembled in the factory using a through-type graphite cylindrical pin that penetrates multiple layers of graphite in the core. The bottom layer is equipped with a clamping band for circumferential pre-tensioning, and the top layer is pressed with a clamping steel plate to form a three-dimensional limiting integrated structure. This invention produces a three-dimensional composite limiting core in the factory in one piece, which has anti-buoyancy, anti-interlayer misalignment, and anti-radial opening capabilities upon leaving the factory. No secondary reinforcement and calibration are required after on-site hoisting and placement into the tank.

[0012] In a preferred embodiment, during the pre-assembly stage of the graphite core module, a lifting rod is inserted and threadedly locked to the core base plate. After passing inspection, the module is transported as a whole. This invention pre-installs the lifting and bearing structure inside the core module simultaneously, providing a unified force-bearing carrier for module transportation, tank loading, and subsequent replacement. After assembly, the lifting rod can be removed separately, leaving no residual components that interfere with the flow channels within the reactor core.

[0013] In a preferred embodiment, the integrated reactor top module is pre-installed in the factory, with pre-compensation of the universal joint compensation performance of the pump chamber loop connector completed, and the coaxiality of the start-up sleeve and control rod sleeve simultaneously corrected. This invention completes the universal joint connector adaptation and sleeve coaxiality correction in advance in the factory, eliminating potential risks of on-site pipeline connection deviations and sleeve vibration offsets, enabling flow path connection to be completed with a single hoisting of the reactor top module.

[0014] In a preferred embodiment, during the overall on-site assembly stage, the lower end of the heat exchanger forms a double-ended flexible plug-in flow channel via a lower socket fitting and the upper end via a pump chamber circuit connector, adaptively compensating for cumulative deviations in module manufacturing and hoisting. This invention employs a double-ended flexible plug-in assembly process for the heat exchanger, eliminating assembly stress caused by rigid connections, preventing pipeline fatigue cracking and media leakage, and reducing on-site assembly accuracy requirements.

[0015] In a preferred embodiment, the core replacement process includes three consecutive lifting steps: lifting the integrated top module as a whole, lifting the old graphite core module out as a whole using lifting rods, and inserting the new prefabricated graphite core module as a whole. This invention, through a phased, integrated lifting replacement process, eliminates the need to dismantle existing equipment such as the top module, heat exchangers, and shielding supports, significantly simplifying the refueling operation and reducing the time personnel spend in close contact with radioactive media.

[0016] In a preferred embodiment, the entire core replacement process preserves the original assembly structure of the internal heat exchanger, external graphite, shroud, and side reflector of the reactor module without disassembly. This invention only replaces the graphite core module, while the remaining internal structures remain in their complete assembly state, eliminating numerous disassembly, reassembly, and re-inspection procedures and significantly shortening reactor downtime for maintenance.

[0017] In a preferred embodiment, after the pipeline is assembled and connected on-site, the overall flow path connectivity test is carried out directly. Utilizing the stress-free assembly advantage of the double universal joint structure, the uniformity of flow in all four heat exchange branches is verified in one go. This invention relies on a double-ended universal flexible pipeline structure to achieve overall synchronous flow path testing, which can quickly determine whether the molten salt distribution in the four paths is balanced, eliminating the need for individual calibration and adjustment of each path, thus improving the efficiency of on-site assembly and testing.

[0018] This invention divides the reactor assembly process into three major steps: modular pre-assembly in the factory, overall assembly on site, and overall core replacement. It allows for the complete assembly and testing of the container module, graphite core module, and integrated reactor top module within the factory before transporting them to the construction site for unified assembly. This significantly reduces on-site operations within the radiation field, improves overall assembly accuracy, and shortens the construction cycle. During core replacement, only the reactor top is lifted off, the old core is lifted out, and the new prefabricated core is installed in stages. The internal heat exchange and shielding support structures of the container are preserved throughout the process, significantly reducing the radiation exposure time for workers. The process reduces the refueling cycle of the compressed reactor; on-site assembly relies on the universal flexible plug-in structure at both ends of the heat exchanger to adaptively offset the cumulative dimensional deviations caused by manufacturing and hoisting, eliminating the need for repeated manual alignment and correction, and eliminating the assembly stress caused by rigid pipe connections. After assembly, the uniformity of flow in four heat exchange branches can be verified at one time; the graphite core can be formed into an integrated unit with complete three-dimensional constraints during the pre-assembly stage in the factory, and there is no need for on-site layered assembly before delivery. The entire process, from construction, assembly, operation and maintenance to refueling, overcomes the various defects of traditional on-site scattered assembly and full disassembly refueling processes. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the modular main structure of the integrated molten salt reactor core of the present invention;

[0020] Figure 2 This is a schematic diagram of the modular main structure of the container of the present invention;

[0021] Figure 3 This is a schematic diagram of the heat exchanger structure and arrangement of the present invention;

[0022] Figure 4 This is an enlarged schematic diagram of the square channel of the present invention;

[0023] Figure 5 This is a schematic diagram of the molten salt nozzle arrangement of the main container of the present invention;

[0024] Figure 6 This is a schematic diagram of the graphite core module structure of the present invention;

[0025] Figure 7 This is a schematic diagram of the lifting rod structure and arrangement of the present invention;

[0026] Figure 8 This is a schematic diagram of the integrated stack top module structure of the present invention;

[0027] Figure 9 This is a schematic diagram of the loop pipe section arrangement of the present invention;

[0028] Figure 10 This is a schematic diagram of the internal circulation process of the molten salt reactor according to the present invention. Detailed Implementation

[0029] like Figure 1 As shown, the integrated molten salt reactor core modular structure of the present invention includes an integrated reactor top module 1, a container module 2, and a graphite reactor core module 3.

[0030] The graphite core module 3 is located in the lower region inside the container module 2, serving as the carrier unit for the core fission reaction. Here, fissile nuclides in the primary circuit fuel molten salt undergo chain fission, releasing heat. The container module 2, as the overall supporting structure, integrates an internal heat exchange structure (i.e., Figure 3 The heat exchanger 210 cools the graphite core module 3 on one hand and transfers and distributes the fission heat generated by the graphite core module 3 within the primary loop on the other. The integrated top module 1 is located on the top of the equipment and is supported and installed on the main vessel flange of the container module 2. Its lower structure extends into the interior of the container module 2 and is located above the graphite core module 3. It is used to drive the fuel molten salt circulation that runs through the container module 2 and the graphite core module 3, regulate the nuclear reaction rate inside the graphite core module 3, and seal the top cavity of the container module 2.

[0031] This invention breaks down the entire reactor body into three independent prefabricated modules. Compared with the traditional integrated molten salt reactor, it can realize batch prefabrication in the factory, independent transportation, and rapid on-site assembly. At the same time, the old graphite core module 3 can be lifted out separately for replacement, solving the technical defects of traditional reactor cores that cannot be replaced as a whole, long on-site construction cycle, and high risk of irradiation refueling.

[0032] like Figure 2 and Figure 3 As shown, container module 2 is the basic structure for modular installation of the reactor core, including main container 21, outer graphite 22, shroud 23, side reflector layer 24, shroud outer support plate 25, shroud assembly bottom plate 26, support ring 27, bottom plate support 28, lower chamber graphite 29 and heat exchanger 210.

[0033] The main container 21 serves as the mounting base for the entire module, supporting various other structures and equipment. The main body of the main container 21 is a vertical cylindrical wall with a molten salt inlet pipe 211 mounted on it. The upper end of the main body is open, forming a main container flange for sealing and securing the integrated top module 1 above. The lower end of the main body is a downward-arching, arc-shaped lower head.

[0034] The base plate support 28 is a segmented ring component, consisting of an upper ring structure, a middle circular plate, and a lower ring structure. It is fixedly supported on the inner wall of the lower end cap of the main container 21 and forms the basis of the entire support structure at the bottom of the container module.

[0035] The support ring 27 is coaxially arranged with the bottom plate support 28 and is located on the radial outer side of the bottom plate support 28. It is also fixed on the inner wall of the lower end cap of the main container 21.

[0036] The outer support plate 25 of the outer casing is arranged concentrically with the main container 21 and is fixedly installed on the upper end face of the support ring 27.

[0037] On the radial inner side of the outer support plate 25 of the outer cylinder, the bottom plate 26 of the outer cylinder assembly is fixedly installed on the upper end face of the bottom plate support 28. On the one hand, it serves as the bottom bearing base of the outer cylinder 23 and its inner side reflective layer 24, supporting the outer cylinder 23 and the side reflective layer 24; on the other hand, after the graphite core module 3 is hoisted into place, it is placed as a whole in the internal cavity of the outer cylinder 23, and its bottom is supported by the bottom plate 26 of the outer cylinder assembly. Therefore, the bottom plate 26 of the outer cylinder assembly also bears the overall load of the graphite core module 3.

[0038] The main container 21 is enclosed by the lower end cap, the bottom plate 26 of the surrounding cylinder assembly, the outer support plate 25 of the surrounding cylinder, the support ring 27 and the bottom plate support 28 to form a closed chamber. The interior of this chamber is completely filled with the lower chamber graphite 29, which is used to reduce the amount of fuel molten salt used and reduce the cost of molten salt material input.

[0039] The outer graphite columns 22 are arranged circumferentially along the inner wall of the vertical cylinder of the main container 21, forming four groups of graphite columns. These four groups of graphite columns and four heat exchangers 210 are distributed alternately along the circumference, forming a graphite column-heat exchanger-graphite column-heat exchanger arrangement. It should be understood that the function of the outer graphite columns 22 is to fill the cavity to reduce the amount of molten salt used. The outer support plate 25 is located at the bottom of the outer graphite columns 22, providing vertical support and, in conjunction with positioning pins, achieving lateral positioning. Each group of outer graphite columns 22 consists of multiple stacked graphite blocks. Positioning pins are installed between adjacent graphite blocks and between the graphite blocks and the outer support plate 25 to effectively prevent horizontal displacement and misalignment of the graphite columns. Compared to the traditional graphite arrangement in the stack without graphite limiting structure, the multi-layer positioning pin limiting structure can prevent graphite from slipping and misaligning under the buoyancy and thermal expansion of high-temperature molten salt. If the graphite column slips, it will squeeze the molten salt flow gap around the heat exchanger and wear to produce graphite debris, which will then cause blockage of the molten salt distribution channel and the heat exchange channel of the heat exchanger in the stack.

[0040] The surrounding cylinder 23 is a rigid metal support cylinder set within the hollow area formed by the outer graphite 22. A gap is reserved between the surrounding cylinder 23 and the outer graphite 22. This gap is only used to compensate for the difference in thermal expansion between the graphite component and the metal component under high-temperature conditions, and to avoid deformation caused by mutual compression after thermal deformation.

[0041] The side reflector layer 24 is an independent graphite lining component integrally bonded to the inner wall of the casing 23. The side reflector layer 24 is the core component for realizing neutron reflection, and together with the casing 23, it forms a complete neutron reflection and lateral shielding structure on the outside of the graphite core module 3.

[0042] Each heat exchanger 210 has an upper connecting pipe 2101 arranged upwards along its own central axis, serving as an interface for connecting to the molten salt pump pipeline within the integrated top module 1. Each heat exchanger 210 also has a lower pipe port 2102 arranged downwards along its central axis, used for connecting to the heat exchanger connecting pipe 2103. The lower socket fitting 2104 is a socket-type connection component; its upper section inserts into the lower pipe port 2102 of the heat exchanger 210, and its lower section inserts into the heat exchanger connecting pipe 2103. The connection section uses a universal joint structure to compensate for installation alignment, reducing assembly precision requirements, while also minimizing pipe gaps and reducing molten salt bypass. Compared to rigid direct-insertion pipes, this invention eliminates the need for high-precision on-site alignment, significantly improving assembly error tolerance.

[0043] like Figure 3 and Figure 4As shown, four square openings are evenly distributed circumferentially on the annular sidewall of the base plate support 28 for assembling square channels 281. The square channels 281 are arranged horizontally radially along the base plate support 28, and their main body is a square channel that connects upward to the cylindrical heat exchanger nozzle 2103.

[0044] One end of the square channel 281 near the side wall of the main container 21 is flush with the square opening on the side wall of the bottom plate support 28 without any uneven steps. This flush end face directly corresponds to the molten salt inlet pipe 211, which not only eliminates fluid stagnation dead zones, but also avoids turbulent flow of fuel molten salt flowing out of the molten salt inlet pipe 211, so that the four square channels 281 can obtain a uniform fuel molten salt feed flow rate, ensuring a balanced heat exchange load for the four heat exchangers 210.

[0045] In addition to the molten salt inlet pipe 211 mentioned above, the main container 21 also has a molten salt outlet pipe 212 on its vertical cylindrical wall. For example... Figure 5 As shown, the sidewall of the main vessel 21 has four molten salt inlet holes and four molten salt outlet holes evenly opened along the circumference. The hole positions correspond to the welding of four molten salt inlet pipes 211 and four molten salt outlet pipes 212, respectively. The two types of pipes only serve as communication channels between the heat exchange flow channel inside the heat exchanger 210 and the primary loop pipeline outside the stack.

[0046] Molten salt inlet pipe 213 horizontally penetrates the side wall of the main vessel 21 and is coaxially arranged with molten salt inlet pipe 211. One end of it connects to the external primary loop pipeline, and the other end connects to the internal flow channel of heat exchanger 210 through a square channel 281 at the bottom plate support, introducing the low-temperature primary loop fuel molten salt into the heat exchanger 210 for heat absorption and heating. Molten salt outlet pipe 214 also horizontally penetrates the side wall of the main vessel 21 and is coaxially arranged with molten salt outlet pipe 212. One end of it connects to the internal flow channel of heat exchanger 210 through the top pipeline, and the other end connects to the external primary loop pipeline, exporting the primary loop fuel molten salt that has completed heat absorption and heating in the heat exchanger 210.

[0047] Container Module 2 adopts a factory pre-assembly followed by overall transportation. The complete in-factory pre-assembly sequence of Container Module 2 is briefly described below:

[0048] 1) The main container 21 cylinder is positioned and fixed, and the inner wall cleaning inspection is completed;

[0049] 2) Pre-assembled assembly hoisting: The lower chamber graphite 29, bottom plate support 28, and support ring 27 are pre-assembled into an integral structure and hoisted and fixed to the lower head of the main vessel 21; the bottom plate support 28 is pre-assembled with four square channels 281 around its circumference, and the heat exchanger pipe 2103 is integrally formed above the square channels 281.

[0050] 3) Central frame in place: The entire assembly of the cofferdam 23 and the cofferdam assembly base plate 26 is hoisted to the central area of ​​the base plate support 28 to establish the separation benchmark between the core and the outer heat exchange zone;

[0051] 4) External support assembly: The outer support plate 25 of the outer tube is laid circumferentially on the top surface of the support ring 27, and the inner side abuts against the outer wall of the outer tube 23 for limiting;

[0052] 5) Heat exchanger piping alignment and assembly: hoist four heat exchangers 210, and connect the lower pipe port 2102 of the heat exchanger to the heat exchanger connecting pipe 2103 through the lower socket fitting 2104 to complete the piping connection between the heat exchanger and the square channel 281.

[0053] 6) Outer graphite stacking: The outer graphite 22 is stacked in layers on top of the outer support plate 25 of the outer cylinder, and the positioning pins between the layers and between the graphite and the support plate are assembled simultaneously to achieve lateral positioning of the graphite;

[0054] 7) Side reflective layer installation: The side reflective layer 24 is installed as a whole onto the inner wall of the casing 23.

[0055] All internal components are pre-assembled in the factory building in one go. After the pipeline sealing and dimensional accuracy are inspected and qualified, the whole assembly is transported to the nuclear power construction site. Compared with the traditional solution of assembling in stages and piecemeal on the construction site, the construction period of equipment assembly on the nuclear power site is greatly shortened. At the same time, the constant temperature and controllable environment in the factory can improve the alignment and assembly accuracy of square channels, heat exchanger pipelines and graphite structures, and reduce the risk of on-site assembly interference and media leakage.

[0056] like Figure 6 As shown, the graphite core module 3 includes a clamping steel plate 31, a core graphite 32, a clamping band 33, a core base plate 34, a graphite cylindrical pin 35, and a lifting rod 4.

[0057] The graphite 32 in the reactor core is the core component for nuclear fission reaction and heat transfer. It has molten salt channels 321 inside for the flow of molten salt from the primary loop fuel. In this embodiment, the graphite blocks 32 are stacked vertically in five layers. Adjacent layers of graphite blocks are positioned and locked together by interlocking graphite cylindrical pins 35. A pressure plate 31 applies axial constraint to the top layer of graphite blocks. The bottom graphite blocks rest on the support structure 33 and the base 34. The channels 341 of the base and the molten salt channels 321 within the graphite blocks are connected end-to-end, forming a complete molten salt flow path. The graphite cylindrical pins 35 can restrict the lateral displacement of the graphite blocks 32 during core assembly and hoisting, preventing the entire structure from disintegrating. They can also counteract the upward force caused by the buoyancy of the molten salt under high-temperature molten salt conditions, preventing the graphite blocks between layers from separating and becoming misaligned, ensuring the molten salt channels 321 are structurally sound and unobstructed. Compared to the traditional single pressure plate limiting solution, it can simultaneously adapt to three types of working conditions: hoisting and transportation, high temperature buoyancy load, and material thermal expansion deformation, resulting in higher reliability of reactor core operation.

[0058] The core base plate 34 is a hollow circular ring structure. The annular top surface of the ring completely supports the core graphite 32 from below, serving as the bottom support and positioning base for the graphite core module 3. Flow channel openings 341 are evenly distributed circumferentially at the bottom of the ring. The low-temperature primary circuit fuel molten salt enters the cavity above the ring through the flow channel openings 341, and then flows longitudinally upwards into the molten salt flow channel 321 inside the core graphite 32. The bottom of the core graphite 32 and the core base plate 34 are connected, positioned, and constrained by graphite cylindrical pins 35. A clamping band 33 is provided on the outer side of the bottom graphite and the core base plate 34. The clamping band 33 forms a circumferential pre-tightening and reinforcement of the bottom graphite, which counteracts the circumferential expansion trend caused by the thermal expansion of graphite under high temperature conditions, eliminates the gaps caused by the opening of the block, and works with the graphite cylindrical pin 35 to constrain the circumferential, radial and interlayer displacement of the core graphite 32, ensuring the integrity and stability of the overall core structure under high temperature molten salt conditions and avoiding deformation and blockage of the molten salt flow channel.

[0059] The clamping steel plate 31 is pressed onto the top of all the graphite 32 in the reactor core, playing a key role in preventing axial buoyancy. It can continuously counteract the upward buoyancy force generated by the high-temperature molten salt in the reactor core on the entire reactor core, preventing the reactor core from lifting axially and locking the reactor core in the installation reference position within the container module 2. The clamping steel plate alone can only limit the overall buoyancy and cannot restrain the lateral slippage between graphite layers; the graphite cylindrical pin alone can only control the interlayer misalignment, and the bottom graphite still has the risk of radial dispersion. This invention adopts a composite limiting structure of graphite cylindrical pin (full height limit), bottom clamping band 33 (bottom radial reinforcement) and top clamping steel plate 31 (overall axial buoyancy prevention), which coordinates the restraint of the reactor core graphite from three dimensions: interlayer lateral, bottom circumferential, and overall axial, adapting to all working conditions such as hoisting, high-temperature buoyancy, and thermal expansion deformation.

[0060] The graphite core module 3 has multiple vertical hoisting channels pre-reserved along its circumference inside for the installation of hoisting rods 4, such as... Figure 7 As shown in the illustration, this embodiment schematically arranges three lifting rods 4. The number of lifting rods 4 can be flexibly selected according to the module size and lifting load. The lifting rod 4 is a continuous rod, passing sequentially from top to bottom through the clamping steel plate 31, the multi-layer core graphite 32, and the core base plate 34. Threaded holes are machined at corresponding positions on the core base plate 34, and the lower end of the lifting rod 4 is screwed into and locked with the threaded holes. It should be understood that the middle section of the lifting rod 4... Figure 7 The middle section is covered by the graphite core 32, with only the top section protruding above the clamping steel plate 31 and exposed for docking with external hoisting and transfer tools.

[0061] The graphite core module 3 adopts a factory pre-assembly and then overall transportation mode. The complete factory pre-assembly sequence of the graphite core module 3 is briefly described below:

[0062] 1) The core bottom plate 34 is horizontally positioned and fixed, and the bottom flow channel opening 341 is cleaned and inspected.

[0063] 2) The bottom core graphite blocks 32 are stacked in layers on the annular support platform of the core base plate 34, aligned with the positioning holes of the base plate, and the graphite cylindrical pins 35 are inserted so that the bottom end of the pin is inserted and fixed in the core base plate 34.

[0064] 3) Install a clamping band 33 at the outer ring step of the bottom graphite block 32 to pre-tighten the bottom graphite in the circumference and eliminate the gap caused by thermal expansion.

[0065] 4) Stack the middle and upper layers of graphite blocks 32 upwards one by one. Each layer of graphite blocks is connected by a through graphite cylindrical pin 35 to achieve interlayer alignment and locking, ensuring that the molten salt flow channels 321 inside each layer of graphite are precisely aligned vertically.

[0066] 5) After all graphite blocks 32 are stacked to the designed total number of layers, the clamping steel plate 31 is pressed and covered onto the upper surface of the top layer of graphite blocks; the top of the graphite cylindrical pin 35 abuts against the lower surface of the clamping steel plate 31, relying on the clamping steel plate 31 to provide axial preload. There are two types of failure risks under reactor operating conditions: first, the density of graphite material is lower than that of molten salt, causing the core to tend to float upwards due to the buoyancy of the medium; second, graphite undergoes axial contraction after long-term neutron irradiation, resulting in a reduced core height, making it easy for the graphite cylindrical pins and the pin holes of the clamping steel plate to detach, and the interlayer graphite loses its axial constraint. This structure, through the preload design of the graphite cylindrical pins 35 and the clamping steel plate 31 abutting against each other, can simultaneously counteract the core floating tendency caused by the buoyancy of high-temperature molten salt, compensate for the gaps formed by graphite irradiation contraction, and prevent pin hole detachment and graphite interlayer misalignment failures.

[0067] 6) Pass the lifting rod 4 through the pre-reserved lifting channels inside the clamping steel plate 31 and each layer of core graphite 32 from top to bottom, and screw the bottom end of the lifting rod 4 into the threaded hole of the core bottom plate 34 to lock and fix it.

[0068] 7) Perform dimensional remeasurement, flow channel continuity inspection, pin limit reliability test, clamping band preload test, and lifting rod locking reliability test on the overall module;

[0069] 8) After the inspection is qualified, the top of the lifting rod 4 is connected and fixed to the lifting and transfer tooling, the whole set of graphite core module 3 is protected and encapsulated, and the whole is transferred to the assembly station of container module 2. After the module is lowered into place and the accuracy is verified, all lifting rods 4 are rotated out in the opposite direction and removed to complete the core pre-loading into the container.

[0070] like Figure 8 As shown, the integrated top module 1 includes a top structure 11, a start-up system 12, a control rod system 13, a casing support channel 14, a top cover cylinder 15, a molten salt pump chamber 16, a loop pipe section 17, an upper chamber end cap 18, and a pump chamber loop pipe 19.

[0071] The top cover cylinder 15 serves as the main support and mounting base for the integrated stack top module 1. Its upper end is equipped with a flange structure for connecting and fixing the stack top structure 11; its lower end is welded integrally with the upper chamber head 18, together forming the lower cavity of the module. The integrated stack top module 1 is fixed to the main container flange of the container module 2 via the flange on the outside of the top cover cylinder 15, and is erected entirely above the container module 2. The lower structure extends into the interior of the container module 2. (See attached image.) Figure 1 .

[0072] The molten salt pump chamber 16, located in the lower cavity of the module, extends vertically through the top center of the upper chamber head 18. A flange interface 161 is provided at the upper end of the molten salt pump chamber 16 for assembling the primary loop molten salt pump, which is not shown in the attached drawings. The molten salt pump chamber 16 provides installation and operating space for the molten salt pump. When the molten salt pump is operating, it draws the primary loop fuel molten salt, after heat absorption and heating inside the heat exchanger 210, upwards and transports it to the loop pipe section 17, providing a forced driving force for the circulation of the entire primary loop fuel molten salt closed pipeline.

[0073] Within the lower cavity of the module, along the central symmetrical direction of the molten salt pump chamber 16, two loop pipe sections 17 are symmetrically arranged on the outer side of the chamber wall, namely loop pipe section 1 and loop pipe section 2. The specific pipe layout structure is as follows: Figure 9 As shown. Each branch pipe segment 17 further branches into two branch pipe segments, forming a total of four branch pipe segments, each corresponding to one of the four heat exchangers 210 in the lower container module 2, for connecting to the upper pipe 2101 of the heat exchanger 210 (see...). Figure 3 The pump chamber circuit connector 19 is a socket-type connection component. Its upper section is inserted into the lower pipe opening of each branch pipe section, and its lower section is inserted into the upper connector 2101. The connection section uses a universal joint structure to compensate for installation alignment and reduce assembly accuracy requirements. During the overall hoisting and docking of the integrated stack top module 1, the universal joint structure can autonomously adjust its position and angle according to changes in the on-site assembly gaps, ensuring that the pump chamber circuit connector 19 is accurately inserted into the upper connector 2101 of the heat exchanger 210, achieving flow path connectivity. Compared to rigid direct-insertion pipes, the universal adaptive connector of this invention significantly reduces the assembly accuracy requirements for the overall hoisting of the stack top.

[0074] The upper chamber head 18 is provided with a sleeve support channel 14, which is used to neatly arrange and reliably support the control rod system 13, the reactor start-up system 12 and the sleeve structure of the two, so as to ensure that the various equipment are fixed in position and operate reliably under high temperature and vibration conditions.

[0075] The control rod system 13 is the core equipment for reactor reactivity control. By inserting and withdrawing the control rods, it regulates the neutron reaction rate inside the reactor core, thereby enabling functions such as reactor startup, power regulation, normal shutdown, and emergency safety shutdown. The matching control rod sleeve 131 penetrates vertically through the integrated reactor top module 1 and extends into the graphite core module 3 at its lower end. It not only guides the up-and-down reciprocating movement of the control rods but also isolates them from the high-temperature molten salt, protecting the control rod equipment from molten salt corrosion and erosion.

[0076] The reactor start-up system 12 is used during the reactor start-up phase. By introducing a neutron source into the core and supplementing the neutron flux, it enables the reactor to smoothly transition from a subcritical state to a critical state, achieving a safe start-up. The matching start-up system sleeve 121 penetrates vertically through the integrated reactor top module 1 and extends into the graphite core module 3 at its lower end, providing an installation and operation channel for the start-up equipment while isolating the high-temperature molten salt to ensure the stable conduct of the start-up operation.

[0077] The reactor top structure 11 is fixedly installed on the upper flange face of the top cover cylinder 15, and has two core functions: sealing and support. The sealing function relies on the flange connection and matching seals to ensure the overall sealing of the reactor top, prevent leakage of high-temperature molten salt and radioactive media, and maintain stable internal pressure. The support function provides stable installation support for reactor top equipment such as molten salt pumps, control rod system 13, and reactor start-up system 12, while bearing the weight of the module itself and vibration loads during operation, ensuring the safe operation of the equipment.

[0078] The integrated stacker top module 1 adopts a factory pre-assembly and then overall transportation mode. The complete factory pre-assembly sequence of the integrated stacker top module 1 is briefly described below:

[0079] 1) Position the top cover cylinder 15 horizontally using the fixing fixture, and complete the cleaning of the inner wall of the cylinder and the flatness inspection of the upper and lower flanges;

[0080] 2) Hoist the upper chamber head 18 and fully weld it to the lower end of the top cover cylinder 15 with the annular bevel. After the welding is completed, perform non-destructive testing and a water pressure test to form the main body of the lower cavity of the stack top.

[0081] 3) The molten salt pump chamber 16 is assembled in the center position. The molten salt pump chamber 16 vertically penetrates the center opening of the upper chamber head 18 and is welded and sealed. The upper flange interface 161 is finished and the sealing surface is inspected.

[0082] 4) Two branch pipe sections 17 are symmetrically assembled on both sides of the molten salt pump chamber 16. Each branch pipe section 17 branches downwards into two branch pipe sections. After the branch pipe sections are positioned and fixed, the pump chamber circuit connector 19 is pre-installed: the upper section of the pump chamber circuit connector 19 is inserted into the lower pipe port of each branch pipe section. The connector is self-adjusted and aligned by its own universal joint structure to achieve flexible plug-in assembly without rigid welding.

[0083] 5) Install and fix the sleeve support channel 14 at the reserved opening of the upper chamber head 18 to position the sleeve installation benchmark of the control rod and the start-up equipment.

[0084] 6) Install and fix the start-up system sleeve 121 and control rod sleeve 131 in sequence. The two types of sleeves vertically penetrate the top cover cylinder 15 and the upper chamber head 18. They are supported and limited in sections by the sleeve support channel 14 to correct the coaxiality of the sleeves.

[0085] 7) Hoist the top structure 11 and fix it to the upper flange face of the top cover cylinder 15 by flange bolts. Install high temperature sealing gaskets between the flanges to complete the overall sealing assembly of the top.

[0086] 8) Assemble the reactor start-up system 12 and the control rod system 13 onto the upper ends of the reactor start-up sleeve 121 and the control rod sleeve 131 respectively to complete the positioning and fixing of the drive mechanism;

[0087] 9) Module pre-installation performance debugging: Conduct universal compensation stroke test on all pump chamber circuit pipes 19 to verify the adaptive adjustment capability of pipe angle; then carry out overall full-item inspection: pipeline sealing test, sleeve straightness test, flange sealing pressure test, and re-measurement of installation dimensions of each equipment;

[0088] 10) After all the tests and commissioning items are qualified, the module is sealed with dustproof and anti-collision protection and transported to the nuclear power site as a whole. During the on-site hoisting and docking, the lower section of the pump cavity circuit pipe 19 can be adaptively inserted into the upper pipe 2101 of the heat exchanger 210 to complete the complete flow path connection of the fuel molten salt.

[0089] like Figure 10 As shown, the overall workflow of this molten salt reactor is as follows:

[0090] The low-temperature primary fuel molten salt enters the internal flow channel of heat exchanger 210 through the molten salt inlet pipe 211 (blue "molten salt into the reactor" in the figure) on the side wall of the main vessel, and flows sequentially through the lower port 2102 of the heat exchanger, the lower socket pipe fitting 2104, the heat exchanger pipe 2103 and the square channel 281 to the bottom annular flow collection cavity below the core bottom plate 34.

[0091] The cryogenic fuel molten salt collected in the bottom annular collection cavity flows upward from the flow channel opening 341 of the core bottom plate 34 into the molten salt flow channel 321 of the graphite core module 3; the cryogenic fuel molten salt absorbs the heat released by nuclear fission inside the graphite 32 core, heats up to form high temperature fuel molten salt, and flows upward continuously along the vertical red arrow, flowing out from the top of the graphite core module 3.

[0092] The high-temperature fuel molten salt produced from the graphite core module 3 rises vertically along the pinkish-purple pipeline and flows into the integrated top module 1 above through the container module 2. The high-temperature molten salt is collected in the molten salt pump chamber 16 at the center of the top of the reactor. It relies on the built-in molten salt pump to provide the driving force for the circulation of the entire system, and then symmetrically diverts to the loop pipe sections 17 on both sides. The diverted high-temperature fuel molten salt is connected downward to the upper pipe 2101 of the heat exchanger through the pump chamber loop pipe 19, and enters the interlayer of the heat exchanger 210 from top to bottom. Finally, it is discharged from the reactor body through the side wall molten salt outlet pipe 212 (pinkish-purple "molten salt out of the reactor").

[0093] The low-temperature molten salt in the internal flow channel and the high-temperature molten salt in the jacket are both primary loop fuel molten salts. The media are from the same source and are physically isolated and exchange heat only through the metal tube wall of the heat exchanger.

[0094] The four heat exchangers in container module 2 correspond to four fuel molten salt branches that operate synchronously in parallel; the bottom annular collection chamber and the flush square channel structure ensure uniform distribution of the four flow paths, enabling the system to operate continuously and stably.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any simple equivalent substitutions, modifications, and alterations made within the inventive concept of the present invention, based on the technical solutions of the present invention, should fall within the scope of protection defined by the claims of the present invention. Structures and assembly processes not described in detail in this specification are conventional and well-known technologies in the art and will not be elaborated further.

Claims

1. A method for assembling and replacing the core of an integrated modular molten salt reactor, characterized in that, This includes modular pre-assembly in the plant, overall assembly on site, and overall core replacement. The modular pre-assembly steps in the plant independently complete the assembly and testing of the container module (2), graphite core module (3), and integrated stack top module (1) before overall transportation. The on-site overall assembly step involves aligning and assembling the three prefabricated modules and connecting the molten salt flow path. The core replacement process involves lifting out and replacing the graphite core module (3) as a whole without disassembling any internal components.

2. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 1, characterized in that, The container module (2) is pre-assembled in the factory, including the pre-assembly of an integrated bottom support assembly, the pre-positioning of a square channel (281), and the insertion and assembly of a universal head type insert pipe fitting (2104) at the lower end of the heat exchanger (210).

3. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 2, characterized in that, When the container module (2) is pre-installed, the outer graphite (22) is stacked in layers, and positioning pins are installed between each layer of graphite blocks and between the graphite blocks and the outer support plate (25) of the casing to limit the positioning layer by layer.

4. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 1, characterized in that, The graphite core module (3) is pre-installed in the factory using a through-type graphite cylindrical pin (35) that penetrates multiple layers of graphite core (32). The bottom layer is equipped with a clamping band (33) for circumferential pre-tightening, and the top layer is pressed with a clamping steel plate (31) to form a three-dimensional limiting integrated structure.

5. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 4, characterized in that, During the pre-assembly stage of the graphite core module (3), the hoisting rod (4) is installed and threadedly locked to the core base plate (34). After passing the inspection, it is transported as a whole with the module.

6. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 1, characterized in that, The integrated reactor top module (1) is pre-installed in the factory and the pump chamber circuit pipe (19) is pre-tested for universal compensation performance. The coaxiality of the reactor start-up sleeve (121) and control rod sleeve (131) is simultaneously corrected.

7. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 1, characterized in that, During the overall assembly stage on site, the heat exchanger (210) forms a double-ended flexible plug-in flow channel through the lower end of the insert pipe fitting (2104) and the upper end through the pump cavity circuit pipe fitting (19), which adaptively compensates for the cumulative deviation of module manufacturing and hoisting.

8. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 1, characterized in that, The core replacement process includes three continuous lifting procedures: lifting the integrated top module (1) as a whole, lifting the old graphite core module (3) through the hoisting rod (4) as a whole, and placing the new prefabricated graphite core module (3) as a whole.

9. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 8, characterized in that, The original assembly structure of the container module (2), internal heat exchanger (210), external graphite (22), shroud (23), and side reflector (24) is not disassembled during the entire core replacement process.

10. The method for assembling and replacing the core of an integrated modular molten salt reactor according to claim 7, characterized in that, After the pipelines are assembled and connected on site, the overall flow path connectivity test is carried out directly. Taking advantage of the stress-free assembly of the double universal joint structure, the uniformity of the flow of the four heat exchange branches is verified at one time.

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