Nuclear power plant passive high-position oversized pressure-bearing water tank based on rigid-flexible coordination concept and design method of supporting system

Abstract

The invention belongs to the field of nuclear power, and particularly discloses a design method for a passive high-position super-large pressure-bearing water tank and a supporting system of a nuclear power plant based on a rigid-flexible coordination concept. According to the principle that internal and external loads bear pressure independently, an initial water tank scheme is selected, seismic response spectrum and water tank structure modal calculation is carried out, a rigid-flexible coordinated water tank structure scheme is determined, three-dimensional decoupling design evaluation of water tank stress, thermal expansion working conditions and plant structure bearing capacity is carried out, and then coupling anti-seismic calculation of water tank equipment and a structure supporting system is carried out. Local coupling and overall coupling models are designed, rationality evaluation and model optimization are conducted respectively, and finally the design scheme of the water tank and the supporting system is determined. According to the method, the rigid-flexible coordination concept is introduced for the safety system design under the passive and active design concept, the engineering problems of ultra-large capacity, rigidity, seismic resistance, thermal expansion coping and the like are effectively solved, the problem that ultra-large equipment and structural design calculation are conservative is solved, and the engineering economy is improved to the maximum extent.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a design method for a pressure water tank of a nuclear power plant and a supporting structure thereof. Background Art

[0002] The third-generation pressurized water reactor nuclear power plants mostly adopt the safety design concept of combining active and passive. Active means that the safety system needs to rely on external triggers and power sources such as electricity or compressed air to implement the safety function. In contrast, passive means that the safety system does not rely on external triggers and power sources to perform safety functions, but relies on natural convection, deadweight, pressure storage potential and other natural properties to perform. Active and passive systems can achieve complementary advantages, and the diversity design can avoid common cause failures, thereby improving the overall safety of the power plant at a relatively low cost. Passive safety design is the most important design feature of the third-generation nuclear power. The mainstream third-generation nuclear power models in the world, such as AP1000, VVER, APR1400, etc., all adopt passive safety technology; the existing third-generation nuclear power safety design in China adopts an active + passive solution, that is, effective passive safety measures are taken on the basis of the active safety system. The passive safety system is used as a supplement to the active safety system. The passive safety system is activated after the active safety system fails, and the passive system does not need to respond to design basis accidents. According to this concept, active and passive safety systems are safety-level, and active safety systems also need to consider redundancy and configure a large number of safety-level support systems, which leads to complex configuration of the entire safety system and high engineering costs. On the other hand, the cooling water source of the active safety system is arranged inside the containment, which increases the volume of the containment shell and also increases the difficulty of the overall layout of the nuclear island.

[0003] In order to further improve the operating safety of the unit and reduce the engineering cost of mass construction, a passive + active solution is adopted on the basis of the existing active + passive safety technology. The passive system is used as a dedicated safety facility to deal with design basis accidents, and the active system is used as a backup for the failure of the passive system to deal with the design expansion conditions. Replacing the active system with the passive system as a dedicated safety facility can bring huge economic advantages. There is no need to set up a large number of safety-level support systems. The active system as a facility to deal with the design expansion conditions can also be non-safety-level and non-redundant. The simplification of the system has a significant contribution to reducing the cost of power plants. Using the passive system as a dedicated safety facility requires dealing with design basis accidents. Therefore, a large-capacity, high-level design cooling water storage equipment must be used. At the same time, the engineering economy of the water storage equipment must be fully considered to meet the overall requirements of the mass construction of the third-generation nuclear pressure water reactor.

[0004] Based on the above passive + active design concept of the safety system, further design requirements are proposed for the water storage equipment, mainly including:

[0005] First, it is necessary to provide a super-large cooling water source that can meet the needs of the passive core cooling system to ensure reliable cooling of the reactor core under accident conditions. Under accident conditions, the amount of water required for reactor core cooling is thousands of cubic meters. The Westinghouse AP1000 in the United States uses a passive core cooling water source built into the containment with a capacity of 2132m3. In the current design, in order to further improve the economy of nuclear power plants, the passive core cooling water source needs to be placed outside the containment to reduce the volume of the containment. At the same time, in order to meet the requirements of passive core cooling, the capacity needs to be increased to more than twice that of AP1000. Therefore, the water storage tank and its own supporting structure, plant structure support, etc. have increased the difficulty of design and construction.

[0006] Second, the water storage tank in the passive core cooling system must withstand the high temperature and high pressure of the containment under accident conditions. The current design places the water storage tank outside the containment, and the water tank and the inside of the containment need to be connected during the passive water injection process. Under accident conditions, the water tank will be subjected to high temperature (above 150°C) and internal high pressure (about 0.55MPa(a)) at the same time as the containment. The internal pressure will limit the structure and shape of the oversized water tank, and the traditional concrete structure with stainless steel cladding on the inner wall cannot be used. The current design is to use a water storage tank made of pure stainless steel, which needs to consider the high temperature thermal expansion caused by the equipment pressure and the steel structure to form a new pressure water tank.

[0007] Third, the water tank used as a water storage source is a key dedicated safety facility with high earthquake resistance requirements. The water tank that provides water in the safety system is a key dedicated safety facility, a safety function level 1 item, a barrier level 2 item, and a seismic resistance level II, that is, the equipment must be able to withstand the load caused by the ultimate safety ground vibration, and the equipment integrity or sealing must be maintained in the event of an earthquake.

[0008] In the existing technology, for example, the water tanks of the core cooling system built into the AP1000 all adopt a concrete structure with a stainless steel-covered inner wall. When making seismic calculations, conventional seismic calculations can be performed on the plant structure under the premise of considering the fluid-solid coupling effect of the water in the water tank on the concrete structure. The design calculation method is relatively mature and less difficult.

[0009] The current proposed design requires raising the position of the passive containment heat removal system and the pressure water tank supporting its main equipment to meet the design requirements for high-level injection of the passive + active safety system (the bottom height of the water tank is more than 20 meters).

[0010] Based on the safety design concept of combining passive and active, the passive water tank that provides cooling water in the safety injection system is required to be super large in size, heavy in weight when full of water (more than 3,000 tons), and arranged at a high position in the plant. At the same time, it is also necessary to cope with thermal expansion conditions. According to the seismic design standards for third-generation nuclear power plants, large equipment must be designed together with the plant structure, so the pressure water tank must also be coupled and adapted with the plant structure design. In addition, the pressure water tank must also be designed with its own support structure, that is, the water tank support system includes not only its own support structure, but also the plant structure. In the overall design process, the equipment water tank, equipment support structure, and plant structure cannot be simply considered separately. Instead, it is necessary to face the actual engineering situation and comprehensively solve the contradictions in technical design. At present, there is no mature technology and design method for reference. The engineering implementation of the high-position super-large water tank and its structural support system in the safety injection system is extremely difficult. Summary of the invention

[0011] The purpose of the present invention is to provide a design method for a passive high-level ultra-large pressure water tank and support system of a nuclear power plant based on the concept of rigid-flexible coordination, which can adapt to the design requirements of the safety system for water storage equipment under the passive + active design concept, and form a water tank and support system design scheme whose water storage capacity, temperature pressure and seismic requirements all meet the design requirements. At the same time, it can cope with thermal expansion conditions and is compatible with the plant structure scheme, which is convenient for engineering implementation.

[0012] The technical solution of the present invention is as follows:

[0013] A design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination includes the following steps:

[0014] Step 1: Determine the design input, select the initial water tank structure scheme based on the principle that the internal pressure load is borne by the water tank shell and the seismic external load is borne by the water tank support structure, then calculate the water tank structure mode, determine the water tank structure scheme that meets the rigid-flexible coordination evaluation requirements, and perform seismic calculations; then perform a three-dimensional decoupling design assessment of the water tank stress, thermal expansion stress, and plant structure bearing capacity to obtain a water tank structure scheme that meets the decoupling design standards;

[0015] Step 2: Carry out coupled seismic calculation for the water tank equipment and the structural support system. By constructing a local coupling model of the water tank equipment structure and the local structure of the plant supporting the water tank equipment, obtain a water tank equipment and structural support system scheme that meets the requirements of the plant structure force and the deviation range of the supporting structure displacement; and under the water tank equipment scheme that meets the requirements, construct a complete coupling model of the water tank equipment and the plant structure. Through the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure under the complete coupling model, select the final passive high-level super-large pressure water tank scheme.

[0016] Before calculating the water tank structure mode, it is necessary to calculate the seismic response spectrum of the plant structure corresponding to the initial water tank solution, and perform seismic calculation on the water tank structure solution that meets the rigid-flexible evaluation requirements.

[0017] The rigid-flexible coordination evaluation requirements are in accordance with the following principles:

[0018] The rigidity evaluation principle is: z and a z At the same time, satisfying f z ≥0.5×f 0 , and a z ≤0.5×(a t -a 0 );

[0019] The flexibility evaluation principle is: E×ΔL / L≤3×Sm;

[0020] Among them, f z is the main frequency of the water tank equipment, a z is the corresponding earthquake acceleration, and the peak acceleration corresponding to the peak frequency of the earthquake response spectrum is a t and the cutoff frequency f 0 The corresponding earthquake acceleration is a 0 , E is the elastic modulus of the support structure material, ΔL is the deformation of the support structure caused by thermal expansion, L is the size of the support structure before deformation, S m It is the basic allowable stress strength of the supporting structure material.

[0021] The deformation ΔL of the supporting structure caused by the thermal expansion is the deformation of the linear tie rod outside the water tank equipment in the length direction of the tie rod during the rotation around the hinge connection point as the water tank shell expands. In order to meet the flexibility evaluation principle, the tie rod arrangement angle θ should minimize the tie rod deformation ΔL;

[0022] θ=arccos(0.5×d / L)

[0023] The corresponding minimum thermal expansion deformation of the tie rod is:

[0024]

[0025] Among them, d is the expansion displacement of the water tank shell at the chain hinge point, and L is the length of the pull rod before deformation.

[0026] The calculation of the seismic response spectrum of the plant structure adopts a decoupling calculation method, which is specifically:

[0027] a) Establish a simplified water tank mass model and distribute the total mass of the water tank in a full water state to the support points of the plant structure;

[0028] b) Establish the finite element model of the plant structure;

[0029] c) Obtain the seismic response spectrum of the plant structure.

[0030] The determined design inputs include but are not limited to operating conditions, installation elevations, economic indicators, design pressures, design temperatures and applicable standards.

[0031] The seismic calculation in step 1 is specifically as follows:

[0032] a) Establish finite element model of water tank equipment;

[0033] b) Set the boundary conditions at the connection between the water tank equipment and the plant structure;

[0034] For the connection structure between the water tank equipment and the plant structure, the boundary conditions of different connection methods are as follows: for bolt connection support, the bolt hole adopts an oblong hole. When the bolt and the bolt hole are connected, the bolt hole does not bear shear force in the length direction, and only vertical constraint force is applied to it; for multi-faceted contact support of trough support, on the two parallel side planes, only one side plane is subject to displacement constraint perpendicular to the side surface, and the bottom plane is subject to vertical downward displacement constraint; for the tie rod type hinged connection support, three translational direction constraints are applied to the end of the tie rod;

[0035] c) Apply deadweight, internal pressure, external pipe load, earthquake and liquid sloshing load inside the water tank to the water tank equipment;

[0036] d) Calculate the seismic response of the water tank equipment structure.

[0037] d) Calculate the seismic response of the water tank equipment structure as follows:

[0038] The CQC method is used to combine the modal responses of each order before the cutoff frequency in the three directions of the water tank equipment space to obtain the seismic response before the cutoff frequency in the three directions. The modal order is the number of eigenvalues ​​in the modal analysis, and the order is the arrangement of the eigenvalues ​​from small to large.

[0039] For the modal responses that do not participate in the CQC combination after the cutoff frequency in three directions, the lost mass method is used for static correction to obtain the seismic load response in three directions;

[0040] The SRSS method is used to combine the three-directional seismic load responses to obtain the seismic response results of the water tank equipment, that is, the stress and displacement of the water tank equipment shell, internal support and external support, as well as the force of the water tank equipment on the plant structure.

[0041] In the three-dimensional decoupling design evaluation, if any evaluation criterion is not met, return to step 1 to reselect the water tank structure scheme for iterative calculation until the scheme meets all the evaluation criteria.

[0042] The water tank stress assessment method is as follows:

[0043] Design stress assessment criterion σ / [σ]≤0.9; where σ and [σ] are the calculated stress and allowable stress of the water tank respectively;

[0044] If it is satisfied, it is considered that the water tank structure scheme has passed the stress assessment after the earthquake response, and the force exerted by the supporting structure on the powerhouse at the connection point between the water tank equipment and the powerhouse structure is further extracted;

[0045] If not, return to reselect the next water tank equipment and support system solution for iterative calculation until the stress assessment standard of seismic response is met.

[0046] The stress assessment method for thermal expansion condition is:

[0047] Stress assessment criteria for water tank equipment caused by thermal expansion r ≤3×S m ;in, σr Calculate stresses in the device due to thermal expansion, S m It is the basic allowable stress strength of the supporting structure material;

[0048] If the above criteria are met, the water tank structural scheme is considered to meet the requirements of thermal expansion conditions;

[0049] If it is not satisfied, return and reselect the next water tank equipment and support system solution for iterative calculation until the thermal expansion condition requirements are met.

[0050] The method for assessing the bearing capacity of the plant structure is as follows:

[0051] The evaluation criteria are set as follows: the wall reinforcement ratio is 0.5%-3%;

[0052] If it is satisfied, it means that the bearing capacity of the plant structure is qualified;

[0053] If not, return and reselect the next water tank equipment and support system solution for iterative calculation until the plant structure load verification standard is met.

[0054] Make a rationality judgment on the local coupling model of the water tank equipment structure and the local structure of the plant supporting the water tank equipment constructed in step 2;

[0055] The rationality judgment principle is: obtain the force of the water tank equipment on the plant structure and the displacement of the supporting structure of the water tank equipment under the local coupling model, and compare them with the force of the water tank equipment on the plant structure and the displacement of the supporting structure determined after the seismic calculation in step 1. If the deviation is within the set range, the model is reasonable. If it exceeds the set range, return to continue to optimize the local coupling model until the rationality judgment principle is met.

[0056] The deviation is specifically within the setting range:

[0057] If the force exerted by the water tank equipment on the plant structure is less than 0.9 times the force in step one, and the deviation between the displacement of the supporting structure and the displacement calculated in step one is less than or equal to 20%, the local coupling model is considered reasonable; if the above judgment principles are met, the local coupling model is reasonable; otherwise, return to optimize the mesh size and adjust the number of coupling nodes in the multi-point constraint equation, and iterate the finite element calculation again until the force exerted by the water tank equipment on the plant structure and the displacement of the supporting structure of the water tank equipment meet the judgment requirements.

[0058] The local coupling model of the water tank equipment and the plant building structure is constructed in the step 2, specifically: the surface-to-surface connection between the water tank equipment structure model and the local structure model of the plant building is converted into a point-to-point connection, and a grid design is formed by changing the local structure of the plant building supporting the water tank equipment from a shell unit model to a solid unit model, so as to realize the mutual transmission of loads between the water tank equipment and the plant building structure, thereby forming a local coupling model of the water tank equipment and the plant building structure.

[0059] The method for converting the surface-to-surface connection into the point-to-point connection is to use a multi-point constraint equation to establish a coupled connection between the surface and the point, and to establish a coupled connection between the point and the point through a constraint equilibrium equation to achieve the conversion of the connection mode, as shown in the following formula:

[0060] Multi-point constraint equations:

[0061]

[0062] Among them U i is the degree of freedom of node i (node ​​on point), U j is the degree of freedom of the main node j (node ​​on the surface), and n is the number of coupling nodes on the surface;

[0063] C j is the weight coefficient of the main node coupling connection;

[0064] C D is a constant and must satisfy the force and displacement equilibrium equations of the master node and the slave node.

[0065] In the second step, the final passive high-position super-large pressure water tank solution is selected by the water tank equipment stress ratio and the plant structure reinforcement ratio under the complete coupling model, specifically: the seismic response calculation under the initial complete coupling model is performed to obtain the stress ratio k of the water tank equipment. 1 , reinforcement ratio k of the plant structure 2 ; if 0.8≤k 1 ≤0.9, and 0.6≤k 2≤1, the decoupled design of the water tank solution output at the end of step 1 is determined as the final water tank solution; if the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure are other cases, the water tank equipment and support system solution determined in step 1 are optimized, and then return to step 2 for recalculation until the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure both meet 0.8≤k 1 ≤0.9, and 0.6≤k 2 ≤1.

[0066] The optimization of the water tank equipment and support system solution determined in step 1 specifically refers to: reducing the cross-sectional size of the equipment's external support structure, increasing the distribution spacing of the internal support structure, or reducing the thickness of the plant's supporting wall.

[0067] The reduction of the cross-sectional size of the external support structure of the equipment refers to the cross-sectional size of the external support structure of the equipment being the original size (k 1 / 0.9)0.5~0.95 times);

[0068] The increasing of the internal support structure distribution spacing refers to adjusting the internal support structure distribution spacing to 1.05 to 0.9 / k of the original spacing. 1 times;

[0069] The reduction in the thickness of the supporting wall of the plant building refers to adjusting the thickness to k of the original thickness. 2 ~0.9 times.

[0070] The initial water tank structure scheme is:

[0071] In the initial passive high-level super-large pressure water tank structure scheme: the water tank equipment includes a spherical water tank shell as a pressure boundary, a main support arranged in the circumferential direction of the outer side of the water tank shell, an upper pull rod connecting the upper part of the outer side of the water tank shell and the main support, and a lower pull rod connecting the lower part of the outer side of the water tank shell and the main support.

[0072] The water tank equipment achieves structural support for the water tank equipment through a support system. The support system includes a basic plant structure, a supporting ring wall and reinforcing ribs. The basic plant structure is the plant structure connected to the water tank equipment. The supporting ring wall is an annular wall connected to the water tank equipment inside the basic plant structure. A square groove and a supporting pier are processed on the inner side facing the water tank shell. The square groove is used to connect to the main support, and the supporting pier has two layers, which are respectively arranged at the upper and lower parts of the inner side of the supporting ring wall, and are respectively hinged to the upper pull rod and the lower pull rod.

[0073] The remarkable effects of the present invention are as follows:

[0074] Through decoupling design, according to the principle that the internal pressure is borne by the water tank shell and the seismic load is borne by the water tank support structure, the preliminary plan of the water tank equipment and support system is determined, and then the seismic response spectrum of the plant structure and the structural mode of the water tank equipment are calculated respectively to determine the rigidity and flexibility coordination of the water tank equipment. After the rigidity and flexibility coordination, the seismic calculation of the water tank is carried out to obtain the passive water tank equipment and support system plan that is internally pressurized, arranged at a high position, has a large capacity and meets the seismic design requirements;

[0075] The concept of rigid-flexible coordination is introduced to maximize the overall rigidity of the water tank equipment while ensuring the flexibility of thermal expansion release requirements. This effectively solves the contradiction between seismic design and thermal expansion response design, ensuring both the rigidity required by the seismic design of the equipment and the free constraint of the thermal expansion direction of the equipment to release the thermal expansion load.

[0076] The design method combining decoupling and coupling design calculation is conducive to comprehensively analyzing the response mechanism of equipment and structural systems under various working conditions, ensuring the rigor of the design process and design logic, and the design results are as close to the actual project as possible, solving the problem of conservative design calculation of super-large equipment and structures, and maximizing the economic efficiency of the project;

[0077] When determining the input water tank and supporting structure scheme, the design principle is that the internal pressure load is borne by the water tank shell and the seismic external load is borne by the water tank supporting structure. The water tank equipment support function and reasonable equipment support structure design are divided to ensure that the internal pressure and seismic load are borne by different components, and the pressure-bearing boundary only bears the internal pressure, which minimizes the amount of pressure-bearing boundary materials and further improves the economic efficiency of the design scheme engineering construction; BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 An overall schematic diagram of a high-position super-large water tank device and a structural support system provided by an embodiment of the present invention;

[0079] Figure 2a This is a schematic diagram of the water tank equipment;

[0080] Figure 2b It is a schematic diagram of the support system;

[0081] Figure 3 It is the load transfer principle of water tank equipment under thermal expansion conditions;

[0082] Figure 4a It is a schematic diagram of vertical load transfer of high-position super-large water tank equipment under earthquake conditions;

[0083] Figure 4b It is a schematic diagram of horizontal load transfer of high-position super-large water tank equipment under earthquake conditions;

[0084] In the figure: 1. Water tank equipment; 2. Support system; 11. Water tank shell; 12. Main support; 13. Upper tie rod; 14. Lower tie rod; 21. Support ring wall; 22. Basic structure of factory building; 23. Reinforcement ribs; 211. Square groove; 212. Support pier. DETAILED DESCRIPTION

[0085] The present invention will be further described below through the accompanying drawings and specific implementation methods.

[0086] like Figure 1 As shown, the design goal of this method is to realize the design scheme of the water tank equipment 1 and the support system 2 to ensure that the internal pressure and seismic load are borne by different components, reduce the material consumption of the pressure water tank, and improve economy.

[0087] Step 1: Perform decoupling design calculations to determine the structural scheme of the passive high-level super-large pressure water tank S1.1 Clearly define the design input items, i.e. the design requirements

[0088] Including the operating conditions, functional requirements, equipment classification, design principles, design basis, installation elevation, economic indicators, design pressure, and design temperature of high-level super-large water tanks;

[0089] Among them, functional requirements, equipment classification, design principles, and design benchmarks determine the standard specifications that need to be implemented in the design. The rest are specific calculation inputs required for the design.

[0090] S1.2 Select the initial plan for the passive high-level super-large pressure water tank, water tank support structure, and plant structure

[0091] like Figure 2a As shown, the water tank device 1 includes a spherical water tank shell 11 as a pressure-bearing boundary, a main support 12 arranged in the circumferential direction of the outer side of the water tank shell 11, an upper pull rod 13 connecting the upper outer side of the water tank shell 11 and the main support 12, and a lower pull rod 14 connecting the lower outer side of the water tank shell 11 and the main support 12.

[0092] The water tank shell 11 as the pressure-bearing boundary bears the internal load caused by the internal pressure. The main support 12, the upper tie rod 13, the lower tie rod 14 and the internal support 14 constitute the overall support structure of the water tank equipment 1, which is used to bear external loads such as earthquakes. Among them, the main support 12 is the main connection and load transfer mechanism between the water tank equipment 1 and the support system 2, and is arranged in the middle of the pressure-bearing boundary 11; the upper and lower tie rods 13 and 14 are used to enhance the overall rigidity of the water tank equipment 1 and improve the seismic resistance of the water tank equipment 1. The upper tie rod 13 is hinged to the water tank shell 11 at its upper end and hinged to the support system 2 at its lower end. Similarly, the lower tie rod 14 is hinged to the water tank shell 11 at its lower end and hinged to the support system 2 at its upper end.

[0093] like Figure 2bAs shown, the support system 2 includes a basic plant structure 22, a supporting ring wall 21 and reinforcing ribs 23. The basic plant structure 22 is the floor, side wall and other structures of the plant connected to the water tank equipment 1. The supporting ring wall 21 is an annular wall connected to the water tank equipment inside the basic plant structure 22. A square groove 211 and a supporting pier 212 are processed on the inner side facing the water tank shell 11. The square groove 211 is used to connect with the main support 21, and the supporting pier 212 has two layers, which are respectively arranged at the upper and lower parts of the inner side of the supporting ring wall 21, and are respectively hingedly connected to the upper pull rod 13 and the lower pull rod 14.

[0094] The above-mentioned support system 2 realizes the structural support for the water tank equipment and affects the corresponding plant structure design. Therefore, determining the design scheme of the water tank support structure is actually determining the design scheme of the support system.

[0095] Based on the design principle that the internal pressure load is borne by the water tank shell 11 and the earthquake external load is borne by the overall support structure of the water tank, a passive high-position super-large pressure water tank structure scheme, a corresponding water tank support structure scheme, and a corresponding plant structure scheme are selected;

[0096] Through the design of the structure that can bear the internal and external loads in a directional manner, the amount of water tank shell material can be reduced, and the performance requirements of the water tank shell can be strengthened to improve the economy of the overall structure;

[0097] S1.3 Decoupling calculation of seismic response spectrum of powerhouse structure

[0098] a) Establish a simplified water tank mass model

[0099] The total mass of the water tank in the full water state is distributed to the support points of the plant structure to form a simplified water tank mass model. The total mass distribution principle is as follows: the total mass is evenly distributed to the bottom surface of the square groove 211, and 1 / 2 of the total mass is evenly distributed to the support pier 212.

[0100] b) Establish the finite element model of the plant structure

[0101] The finite element model of the plant structure is composed of mass point units of the simplified model of the water tank mass, and the finite element model can be constructed using the software ANSYS;

[0102] c) Obtain the seismic response spectrum of the plant structure

[0103] The finite element model of the plant structure is imported into the professional software SASSI for earthquake SSI analysis, and the soil layer information, seismic motion input and interaction point setting are input to complete the earthquake SSI analysis model; the seismic response analysis of the nuclear island plant is completed in the SASSI software to obtain the seismic response spectrum of the nuclear island plant structure.

[0104] S1.4 Calculation of water tank structural modes

[0105] The BLOCKLANCZOS method is used to calculate the structural mode of the water tank equipment, and the natural frequency, vibration mode and mass ratio of the water tank equipment, as well as the corresponding main frequency of the water tank equipment, are obtained;

[0106] S1.5 Evaluate the rigidity and flexibility characteristics of water tank equipment

[0107] Rigidity evaluation principle: According to the earthquake response spectrum, extract the main frequency f of the water tank equipment z The corresponding earthquake acceleration a z , and measure the peak frequency f of the seismic response spectrum t The corresponding peak acceleration a t and the cutoff frequency f 0 The corresponding earthquake acceleration a 0 ;

[0108] If f z and a z Satisfy the conditions: f z ≥0.5×f 0 , and a z ≤0.5×(a t -a 0 ), the equipment is considered to be rigid enough;

[0109] Otherwise, it is considered that the water tank equipment is not rigid enough;

[0110] Flexible evaluation principles:

[0111] A structure that has no external constraints in the direction of thermal expansion and can expand completely freely is called an absolutely flexible structure. An absolutely flexible structure will not generate additional loads due to thermal expansion, and no load evaluation calculation for thermal expansion is required during design. The internal support of the water tank expands with the water tank shell under thermal expansion conditions and is absolutely flexible. External supports that are freely constrained in the direction of thermal expansion are also absolutely flexible.

[0112] For external supports that are not absolutely flexible, further flexibility evaluation is required.

[0113] If E×ΔL / L≤3×S m , then the flexibility of the non-absolutely flexible external support structure is considered to be sufficient and acceptable; otherwise, it is considered to be insufficiently flexible;

[0114] Where E is the elastic modulus of the support structure material, ΔL is the deformation of the support structure caused by thermal expansion, L is the size of the support structure before deformation, S m It is the basic allowable stress strength of the supporting structure material;

[0115] like Figure 3The load transfer principle of the high-position super-large water tank equipment under thermal expansion conditions is shown in that the spherical pressure-bearing boundary expands radially, driving the upper tie rod 13 and the lower tie rod 14 to rotate around the hinge points at both ends, and the main support 13 slides radially in the square groove 211 of the support system 2. The rotation of the upper tie rod 13 and the lower tie rod 14, as well as the sliding of the main support 12, effectively unload the thermal expansion load and avoid generating a large thermal expansion basic load on the support system 2.

[0116] In this embodiment, a linear tie rod support (upper tie rod 13, lower tie rod 14) is provided outside the water tank device 1 to enhance the overall rigidity of the water tank device 1. During thermal expansion, the water tank shell 11 expands outward, and the tie rod rotates around the hinge connection point as the water tank shell 11 expands. During the rotation, the tie rod generates a deformation ΔL in the length direction. The tie rod arrangement angle can be designed according to the following formula to minimize the tie rod deformation ΔL;

[0117] θ=arccos(0.5×d / L)

[0118] The corresponding minimum thermal expansion deformation of the tie rod is:

[0119]

[0120] Among them, θ is the tie rod arrangement angle, that is, the angle between the normal direction of the water tank shell and the tie rod at the hinge point of the tie rod chain; d is the expansion displacement of the water tank shell at the hinge point of the chain, and L is the length of the tie rod before deformation;

[0121] When the overall rigidity of the water tank equipment and the flexibility of the supporting structure are evaluated to be sufficient, it is considered that the rigidity and flexibility are coordinated, and the next step of design calculation can be carried out;

[0122] If the rigidity and flexibility are not coordinated, return to step S1.2, reselect the scheme of the passive high-level super-large pressure water tank, water tank support structure, and plant structure, and perform iterative calculations until both the rigidity and flexibility evaluation conditions are met, that is, the structural scheme achieves rigidity and flexibility coordination, and then proceed to step 1.6;

[0123] S1.6 Perform seismic calculations on water tank equipment

[0124] a) Establish the finite element model of the water tank equipment

[0125] First, a finite element model of the water tank equipment including model data information such as the support system 2, the containment shell, and the connection between the shell and the support system structure is established. The model establishment method can use the relevant software and methods in step 1.3, which belongs to the existing technology and will not be repeated here.

[0126] b) Set the boundary conditions at the connection between the water tank equipment and the plant structure

[0127] like Figure 4a , Figure 4bAs shown, the design scheme needs to satisfy the separation of vertical seismic loads and horizontal seismic loads in the bearing structure, that is, for vertical seismic loads, when the load is downward, it is borne by the bottom surface of the square groove 211 of the supporting ring wall of the supporting system 2, and when the load is upward, it is borne by the connection structure between the main support 12 and the supporting system 2, and transmitted to the supporting ring wall 21 of the supporting system 2. For horizontal seismic loads, it is borne by the wall between the square grooves 211 of the supporting ring wall 21.

[0128] For the connection structure between the water tank equipment and the plant structure, different connection methods have different ways of applying constraints, so the boundary conditions are set differently. The three boundary conditions are:

[0129] For bolt connection supports, the bolt holes are oblong holes. When the bolts are connected to the bolt holes, the bolt holes do not bear shear force in the length direction, and only vertical restraint force is applied to them.

[0130] For multi-faceted contact supports of trough supports, among the two parallel side planes, only one side plane is subject to displacement constraints perpendicular to the side surface, and the bottom plane is subject to vertical downward displacement constraints;

[0131] For the tie rod type hinged connection support, three translational constraints are applied to the ends of the tie rods (three rotational directions are free);

[0132] c) Apply load to the water tank equipment

[0133] The deadweight, internal pressure, external pipe load, earthquake and liquid sloshing load inside the water tank are applied to the water tank equipment simultaneously. The application of earthquake load means inputting the earthquake response spectrum of the corresponding floor height at the supporting structure of the water tank at different elevations.

[0134] d) Calculate the seismic response of the water tank equipment structure

[0135] The CQC method (Complete Quadratic Combination Method) is used to combine the modal responses of the water tank equipment before the cutoff frequency in three directions to obtain the seismic response before the cutoff frequency in three directions. The modal order is the number of eigenvalues ​​in the modal analysis, and the order is the arrangement of the eigenvalues ​​from small to large.

[0136] For the modal responses that do not participate in the CQC combination after the cutoff frequency in three directions, the lost mass method is used for static correction to obtain the seismic load response in three directions;

[0137] The SRSS method (Square Root of the Sum of the Squares) is used to combine the three-directional seismic load responses to obtain the seismic response results of the water tank equipment, that is, the stress and displacement of the water tank equipment shell, internal support and external support, as well as the force of the water tank equipment on the plant structure;

[0138] S1.7 Evaluation of decoupling design results of water tank scheme

[0139] Carry out the three-dimensional assessment design of water tank stress assessment after earthquake response, thermal expansion stress assessment, and plant structure bearing capacity assessment. If any of the assessment criteria is not met, return to step S1.2 to reselect the next water tank equipment and support system scheme for iterative calculation until the scheme meets all the assessment criteria. The specific assessment includes:

[0140] S1.71 Assessment of water tank stress after earthquake response

[0141] The stress assessment criteria are:

[0142] σ / [σ]≤0.9

[0143] Among them, σ and [σ] are the calculated stress and allowable stress of the water tank respectively;

[0144] If all the above conditions are met, the water tank structure scheme is considered to have passed the stress assessment after the earthquake response;

[0145] If the stress assessment is passed, the force exerted by the supporting structure on the plant building at the connection point between the water tank equipment and the plant building structure is further extracted;

[0146] If it fails, return to step 1.2 and reselect the next water tank equipment and support system solution for iterative calculation until the stress assessment standard of seismic response is met;

[0147] S1.72 Conduct stress assessment for thermal expansion conditions

[0148] Using the finite element model of the water tank equipment established in step S1.6, set the boundary conditions between the water tank equipment and the plant structure and the temperature boundary conditions inside and outside the water tank shell. The temperature boundary conditions refer to the temperature constraints imposed on the water tank shell and internal components at the design temperature, and the temperature constraints imposed on external supporting components at room temperature.

[0149] Finite element calculations were performed to obtain the stress of the water tank equipment caused by thermal expansion;

[0150] The stress of water tank equipment caused by thermal expansion shall be assessed according to the following criteria:

[0151] σ r ≤3×S m

[0152] σ r Calculate stresses in the device due to thermal expansion, S m It is the basic allowable stress strength of the supporting structure material;

[0153] If the above criteria are met, the water tank structural scheme is considered to meet the requirements of thermal expansion conditions;

[0154] If not, return to step S1.2 and reselect the next water tank equipment and support system solution for iterative calculation until the thermal expansion condition requirements are met;

[0155] S1.73 Carry out structural load-bearing capacity assessment of plant buildings

[0156] Using the plant structure finite element model established in step S1.3, apply all other relevant loads of the plant to the model. All relevant loads refer to the reaction forces at various support positions of the water tank equipment under the earthquake condition.

[0157] Combine working conditions according to standard specifications and calculate the wall reinforcement ratio;

[0158] The reasonable reinforcement ratio should be within the range of 0.5%-3%;

[0159] If it is satisfied, it means that the bearing capacity of the plant structure is qualified;

[0160] If not, return to step 1.2 and reselect the next water tank equipment and support system solution for iterative calculation until the plant structure load verification standard is met.

[0161] Step 2: Coupled seismic calculation for water tank equipment and structural support system

[0162] S2.1 Construct a local coupling model of water tank equipment and plant structure

[0163] The surface-to-surface connection between the water tank equipment structure model and the local structure model of the plant is converted into a point-to-point connection. The local structure refers to the local structure of the plant supporting the water tank equipment (generally only the walls and floor slabs of the water tank equipment are connected).

[0164] By changing the local structure of the plant supporting the water tank equipment from a shell unit model to a solid unit model, a grid design is formed to achieve mutual load transfer between the water tank equipment and the plant structure, thereby forming a local coupling model of the water tank equipment and the plant structure;

[0165] The method of converting the surface-to-surface connection into a point-to-point connection is to use a multi-point constraint equation to establish a coupled connection between the surface and the point, and then use a constraint equilibrium equation to establish a coupled connection between the point and the point to achieve the transformation of the connection mode, as shown in the following formula:

[0166] Multi-point constraint equations:

[0167]

[0168] Among them U i is the degree of freedom of node i (node ​​on point), U j is the degree of freedom of the main node j (node ​​on the surface), and n is the number of coupling nodes on the surface;

[0169] C j The weight coefficient of the master node coupling connection is a function related to the distance between the master node and the slave node, and the value range is (-1, 1);

[0170] C D is a constant that must satisfy the force and displacement equilibrium equations of the master node and the slave node, and is generally taken as (-1, 1);

[0171] S2.2 Reasonableness judgment of local coupling model

[0172] The response spectrum method is used to perform finite element calculation on the local coupling model to obtain the force exerted by the water tank equipment on the plant structure and the displacement of the water tank equipment supporting structure;

[0173] Compare the force exerted by the water tank equipment on the plant structure obtained in this step with the force exerted by the water tank equipment on the plant structure corresponding to the water tank equipment and the support system scheme obtained in step 1 through three-dimensional evaluation and design;

[0174] Similarly, the displacement of the water tank equipment support structure obtained in this step is compared with the displacement of the water tank equipment support structure corresponding to the water tank equipment and support system solution determined in step 1;

[0175] If the applied force is less than 0.9 times the applied force in step 1, and the deviation between the displacement of the supporting structure and the displacement calculated in step 1 is less than or equal to 20%, the local coupling model is considered reasonable;

[0176] Otherwise, return to step S2.1 to optimize the grid size and adjust the number of coupling nodes in the multi-point constraint equation. In this embodiment, the number of nodes is adjusted by increasing it to 1.1 times of the original number each time until the iterative calculation meets the requirements.

[0177] S2.3 Determine the complete coupling model of the water tank equipment and plant structure

[0178] Calculate the stress ratio of the water tank equipment: k 1 =σ / [σ];

[0179] Calculate the reinforcement ratio of the plant structure: k 2 =A s / [A s ];

[0180] σ and [σ] are the calculated stress of the water tank equipment and the allowable stress of the material, respectively. s and [A s ] are the reinforcement amounts for coupling design and decoupling design respectively;

[0181] If 0.8≤k 1 ≤0.9, and 0.6≤k 2 ≤1, then the water tank solution decoupling design output by S1.7 is determined as the final water tank solution;

[0182] If k 1 or k 2 For other situations that do not meet the above range, the water tank equipment and support system solution determined in step 1 are locally optimized, and the calculations in steps S2.1-S2.3 are repeated until 0.8≤k 1 ≤0.9, and 0.6≤k 2 ≤1, which means the final solution of passive high-position super-large pressure water tank is formed;

[0183] The principle of local optimization is to reduce the amount of equipment or plant structure materials used to improve the economy of the overall solution;

[0184] In this embodiment, the cross-sectional size of the external support structure of the equipment is reduced (the cross-sectional size of the external support structure of the equipment is the original size (k 1 / 0.9) 0.5 ~0.95 times), increase the internal support structure distribution spacing (the internal support structure distribution spacing is adjusted to 1.05~0.9 / k of the original spacing 1 times), or reduce the thickness of the supporting wall of the plant (the thickness is adjusted to k times the original thickness). 2 ~0.9 times) is used for optimization.

Claims

1. A design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination, characterized in that: The method comprises the following steps: Step 1: Determine the design input, select the initial water tank structure scheme based on the principle that the internal pressure load is borne by the water tank shell and the seismic external load is borne by the water tank support structure, then calculate the water tank structure mode, determine the water tank structure scheme that meets the rigid-flexible coordination evaluation requirements, and perform seismic calculations; then perform a three-dimensional decoupling design assessment of the water tank stress, thermal expansion stress, and plant structure bearing capacity to obtain a water tank structure scheme that meets the decoupling design standards; Step 2: Carry out coupled seismic calculation for the water tank equipment and the structural support system. By constructing a local coupling model of the water tank equipment structure and the local structure of the plant supporting the water tank equipment, obtain a water tank equipment and structural support system scheme that meets the requirements of the plant structure force and the deviation range of the supporting structure displacement; and under the water tank equipment scheme that meets the requirements, construct a complete coupling model of the water tank equipment and the plant structure. Through the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure under the complete coupling model, select the final passive high-level super-large pressure water tank scheme.

2. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 1 is characterized by: Before calculating the water tank structure mode, it is necessary to calculate the seismic response spectrum of the plant structure corresponding to the initial water tank solution, and perform seismic calculation on the water tank structure solution that meets the rigid-flexible evaluation requirements.

3. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 2 is characterized by: The rigid-flexible coordination evaluation requirements are in accordance with the following principles: The rigidity evaluation principle is: z and a z At the same time, satisfying f z ≥0.5×f0, and a z ≤0.5×(a t -a0); The flexibility evaluation principle is: E×ΔL / L≤3×S m ; Among them, f z is the main frequency of the water tank equipment, a z is the corresponding earthquake acceleration, and the peak acceleration corresponding to the peak frequency of the earthquake response spectrum is a t The earthquake acceleration corresponding to the cutoff frequency f0 is a0, E is the elastic modulus of the supporting structure material, ΔL is the deformation of the supporting structure caused by thermal expansion, L is the size of the supporting structure before deformation, S m It is the basic allowable stress strength of the supporting structure material.

4. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 3 is characterized by: The deformation ΔL of the supporting structure caused by the thermal expansion is the deformation of the linear tie rod outside the water tank equipment in the length direction of the tie rod during the rotation around the hinge connection point as the water tank shell expands. In order to meet the flexibility evaluation principle, the tie rod arrangement angle θ should minimize the tie rod deformation ΔL; θ=arccos(0.5×d / L) The corresponding minimum thermal expansion deformation of the tie rod is: Among them, d is the expansion displacement of the water tank shell at the chain hinge point, and L is the length of the pull rod before deformation.

5. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 2 is characterized in that: The calculation of the seismic response spectrum of the plant structure adopts a decoupling calculation method, which is specifically: a) Establish a simplified water tank mass model and distribute the total mass of the water tank in a full water state to the support points of the plant structure; b) Establish the finite element model of the plant structure; c) Obtain the seismic response spectrum of the plant structure.

6. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 1 is characterized by: The determined design inputs include but are not limited to operating conditions, installation elevations, economic indicators, design pressures, design temperatures and applicable standards.

7. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 1 is characterized by: The seismic calculation in step 1 is specifically as follows: a) Establish finite element model of water tank equipment; b) Set the boundary conditions at the connection between the water tank equipment and the plant structure; For the connection structure between the water tank equipment and the plant structure, the boundary conditions of different connection methods are as follows: for bolt connection support, the bolt hole adopts an oblong hole. When the bolt and the bolt hole are connected, the bolt hole does not bear shear force in the length direction, and only vertical constraint force is applied to it; for multi-faceted contact support of trough support, on the two parallel side planes, only one side plane is subject to displacement constraint perpendicular to the side surface, and the bottom plane is subject to vertical downward displacement constraint; for the tie rod type hinged connection support, three translational direction constraints are applied to the end of the tie rod; c) Apply deadweight, internal pressure, external pipe load, earthquake and liquid sloshing load inside the water tank to the water tank equipment; d) Calculate the seismic response of the water tank equipment structure.

8. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 7 is characterized by: d) Calculate the seismic response of the water tank equipment structure as follows: The CQC method is used to combine the modal responses of each order before the cutoff frequency in the three directions of the water tank equipment space to obtain the seismic response before the cutoff frequency in the three directions. The modal order is the number of eigenvalues ​​in the modal analysis, and the order is the arrangement of the eigenvalues ​​from small to large. For the modal responses that do not participate in the CQC combination after the cutoff frequency in three directions, the lost mass method is used for static correction to obtain the seismic load response in three directions; The SRSS method is used to combine the three-directional seismic load responses to obtain the seismic response results of the water tank equipment, that is, the stress and displacement of the water tank equipment shell, internal support and external support, as well as the force of the water tank equipment on the plant structure.

9. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 1 is characterized by: In the three-dimensional decoupling design evaluation, if any evaluation criterion is not met, return to step 1 to reselect the water tank structure scheme for iterative calculation until the scheme meets all the evaluation criteria.

10. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 9, characterized in that: The water tank stress assessment method is as follows: Design stress assessment criterion σ / [σ]≤0.9; where σ and [σ] are the calculated stress and allowable stress of the water tank respectively; If it is satisfied, it is considered that the water tank structure scheme has passed the stress assessment after the earthquake response, and the force exerted by the supporting structure on the powerhouse at the connection point between the water tank equipment and the powerhouse structure is further extracted; If not, return to reselect the next water tank equipment and support system solution for iterative calculation until the stress assessment standard of seismic response is met.

11. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 9, characterized in that: The stress assessment method for thermal expansion condition is: Stress assessment criteria for water tank equipment caused by thermal expansion r ≤3×S m ; Among them, σ r Calculate stresses in the device due to thermal expansion, S m It is the basic allowable stress strength of the supporting structure material; If the above criteria are met, the water tank structural scheme is considered to meet the requirements of thermal expansion conditions; If it is not satisfied, return and reselect the next water tank equipment and support system solution for iterative calculation until the thermal expansion condition requirements are met.

12. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 9, characterized in that: The method for assessing the bearing capacity of the plant structure is as follows: The evaluation criteria are set as follows: the wall reinforcement ratio is 0.5%-3%; If it is satisfied, it means that the bearing capacity of the plant structure is qualified; If not, return and reselect the next water tank equipment and support system solution for iterative calculation until the plant structure load verification standard is met.

13. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 1, characterized in that: Make a rationality judgment on the local coupling model of the water tank equipment structure and the local structure of the plant supporting the water tank equipment constructed in step 2; The rationality judgment principle is: obtain the force of the water tank equipment on the plant structure and the displacement of the supporting structure of the water tank equipment under the local coupling model, and compare them with the force of the water tank equipment on the plant structure and the displacement of the supporting structure determined after the seismic calculation in step 1. If the deviation is within the set range, the model is reasonable. If it exceeds the set range, return to continue to optimize the local coupling model until the rationality judgment principle is met.

14. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 13, characterized in that: The deviation is specifically within the setting range: If the force exerted by the water tank equipment on the plant structure is less than 0.9 times the force in step one, and the deviation between the displacement of the supporting structure and the displacement calculated in step one is less than or equal to 20%, the local coupling model is considered reasonable; if the above judgment principles are met, the local coupling model is reasonable; otherwise, return to optimize the mesh size and adjust the number of coupling nodes in the multi-point constraint equation, and iterate the finite element calculation again until the force exerted by the water tank equipment on the plant structure and the displacement of the supporting structure of the water tank equipment meet the judgment requirements.

15. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 1, characterized in that: The local coupling model of the water tank equipment and the plant building structure is constructed in the step 2, specifically: the surface-to-surface connection between the water tank equipment structure model and the local structure model of the plant building is converted into a point-to-point connection, and a grid design is formed by changing the local structure of the plant building supporting the water tank equipment from a shell unit model to a solid unit model, so as to realize the mutual transmission of loads between the water tank equipment and the plant building structure, thereby forming a local coupling model of the water tank equipment and the plant building structure.

16. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 15, characterized in that: The method for converting the surface-to-surface connection into the point-to-point connection is to use a multi-point constraint equation to establish a coupled connection between the surface and the point, and to establish a coupled connection between the point and the point through a constraint equilibrium equation to achieve the conversion of the connection mode, as shown in the following formula: Multi-point constraint equations: Among them U i is the degree of freedom of node i (node ​​on point), U j is the degree of freedom of the main node j (node ​​on the surface), and n is the number of coupling nodes on the surface; C j is the weight coefficient of the main node coupling connection; C D is a constant and must satisfy the force and displacement equilibrium equations of the master node and the slave node.

17. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 1, characterized in that: In the step 2, the final passive high-level super-large pressure water tank scheme is selected through the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure under the complete coupling model, specifically: the seismic response calculation under the initial complete coupling model is performed to obtain the stress ratio k1 of the water tank equipment and the reinforcement ratio k2 of the plant structure; if 0.8≤k1≤0.9, and 0.6≤k2≤1, then the water tank scheme decoupling design output at the end of step 1 is determined as the final water tank scheme; if the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure are other situations, the water tank equipment and support system scheme determined in step 1 are optimized, and then return to step 2 to recalculate until the stress ratio of the water tank equipment and the reinforcement ratio of the plant structure simultaneously satisfy 0.8≤k1≤0.9 and 0.6≤k2≤1.

18. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 17, characterized in that: The optimization of the water tank equipment and support system solution determined in step 1 specifically refers to: reducing the cross-sectional size of the equipment's external support structure, increasing the distribution spacing of the internal support structure, or reducing the thickness of the plant's supporting wall.

19. The design method for a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 18, characterized in that: The said reduction of the cross-sectional size of the equipment external support structure means that the cross-sectional size of the equipment external support structure is (k1 / 0.9) of the original size. 0.5 ~0.95 times); The increasing of the internal support structure distribution spacing refers to adjusting the internal support structure distribution spacing to 1.05 to 0.9 / k1 times of the original spacing; The reducing the thickness of the supporting wall of the plant building refers to adjusting the thickness to k2 to 0.9 times of the original thickness.

20. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the concept of rigid-flexible coordination as claimed in claim 1, characterized in that: In the step one, the initial water tank structure is as follows: the water tank device (1) includes a spherical water tank shell (11) as a pressure-bearing boundary, a main support (12) arranged in the circumferential direction of the outer side of the water tank shell (11), an upper pull rod (13) connecting the upper outer side of the water tank shell (11) and the main support (12), and a lower pull rod (14) connecting the lower outer side of the water tank shell (11) and the main support (12).

21. The design method of a passive high-level super-large pressure water tank and support system for a nuclear power plant based on the rigid-flexible coordination concept as claimed in claim 20, characterized in that: The water tank equipment (1) is structurally supported by a support system (2). The support system (2) includes a basic plant structure (22), a support ring wall (21) and reinforcing ribs (23). The basic plant structure (22) is a plant structure connected to the water tank equipment (1). The support ring wall (21) is an annular wall connected to the water tank equipment inside the basic plant structure (22). A square groove (211) and a support pier (212) are processed on the inner side facing the water tank shell (11). The square groove (211) is used to connect to the main support (21), and the support pier (212) has two layers, which are arranged at the upper and lower parts of the inner side of the support ring wall (21) and are hingedly connected to the upper pull rod (13) and the lower pull rod (14) respectively.

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