A method for starting up a nuclear reactor head cycle

Abstract

This invention relates to a method for the first cycle startup of a nuclear reactor, comprising the following steps: determining the reactor insertion time of a universal secondary neutron source assembly based on the operating cycle of an existing nuclear power plant and the initial fuel loading plan of a newly built nuclear power plant; utilizing the irradiation conditions provided by the existing nuclear power plant, irradiating the universal secondary neutron source assembly with the existing nuclear power plant before loading it into the newly built nuclear power plant for its first operation, thus replacing the primary neutron source required for the initial startup of the nuclear power plant. By using a more readily available universal secondary neutron source assembly and utilizing the irradiation conditions provided by an existing nuclear power plant, irradiating the universal secondary neutron source assembly with the existing nuclear power plant before loading it into the newly built nuclear power plant for its first operation, the invention replaces the primary neutron source required for the initial operation of the nuclear power plant, thereby solving the problem of primary neutron source supply.

Description

Technical Field

[0001] This invention relates to the field of nuclear power reactor technology, specifically to a method for the first cycle startup of a nuclear reactor. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Nuclear reactors require a neutron source for startup. The role of the neutron source is to provide a basic neutron count level during the reactor loading process to criticality, so as to ensure that the external source range detector can operate normally and respond to the core breeding neutrons, overcome the blind zone of the source range detector, and ensure that the reactor has a sufficient neutron count rate for criticality safety monitoring and to ensure the safe startup of the reactor in the subcritical state.

[0004] A primary neutron source (also known as a "first-cycle neutron source") is used for the initial startup of a nuclear reactor and is removed from the core after the first cycle. Early nuclear power plants used Po-Be (polonium-beryllium) sources, utilizing alpha ions emitted from the decay of Po-210 to bombard Be nuclei and emit neutrons. Current nuclear power plants mostly use californium sources, utilizing... 252 Cf decay emits neutrons.

[0005] Secondary neutron sources (also known as "secondary neutron sources") are used for restarting and safety monitoring of reactors in cycles other than the initial cycle. They do not emit neutrons when not irradiated and are typically added to the reactor during the initial fuel loading. After activation by irradiation within the reactor, they are used for refueling cycles. Secondary neutron sources generally use antimony-beryllium (Sb-Be) sources.

[0006] Most pressurized water reactor nuclear power plants are designed for startup with an external neutron source (referred to as "active startup"). The supply of a primary neutron source is limited by technological level, economic cost and other factors, resulting in high construction costs for current nuclear power plants.

[0007] Existing technologies have proposed some methods to replace primary neutron sources, such as extending passive start-up technology to pressurized water reactor nuclear power plants with different technical routes. However, such methods require strict safety supervision and are difficult to implement. In addition, some alternative methods still have the problems of high procurement costs, significant impact on core design, and applicability only to the same or similar reactor types. Summary of the Invention

[0008] To address at least one of the technical problems mentioned above, this invention provides a method for the first cycle startup of a nuclear reactor. This method utilizes the irradiation conditions provided by an in-service nuclear power plant, and installs a universal secondary neutron source assembly into the nuclear power plant during its first operation after irradiation by the in-service nuclear power plant, replacing the primary neutron source required for the first operation of the nuclear power plant.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A first aspect of the present invention provides a method for starting the first cycle of a nuclear reactor, including the following steps:

[0011] Determine the in-core time of the general-purpose secondary neutron source assembly according to the operating cycle of the in-service nuclear power plant and the first fuel loading plan of the newly built nuclear power plant;

[0012] Utilize the irradiation conditions provided by the in-service nuclear power plant. After irradiating the general-purpose secondary neutron source assembly in the in-service nuclear power plant, load it into the newly built nuclear power plant for the first operation to replace the primary neutron source required when the nuclear power plant is first started.

[0013] Determine the irradiation time of the general-purpose secondary neutron source assembly according to the operating cycle of the in-service nuclear power plant and the first fuel loading plan of the newly built nuclear power plant. Specifically: According to the production plan of unit A of the in-service pressurized water reactor nuclear power plant and the first fuel loading plan of unit B of the newly built pressurized water reactor nuclear power plant, determine the refueling outage time t1 of unit A and the first fuel loading time t2 of unit B; within the time period from T1 to T2, select one or more in-service units A to provide irradiation conditions; where T = t2 - t1, T1 < T < T2, T1 is the first set time, and T2 is the second set time.

[0014] Load at least two groups of general-purpose secondary neutron source assemblies before unit A operates. As unit A operates and is irradiated, when unit A undergoes refueling outage, take out the irradiated general-purpose secondary neutron source assemblies and transfer them to unit B.

[0015] When unit B is first fuel loaded, load the general-purpose secondary neutron source assemblies irradiated in unit A to provide the required neutron count rate during the first fuel loading and startup of unit B.

[0016] Calculate the source strength of the secondary neutron source assembly after irradiation, calculate the decay of the source strength over time after shutdown, and calculate the neutron count rate of the out-of-core range detector. Obtain the change in the neutron count rate of the out-of-core range detector of unit B during the fuel loading process after the general-purpose secondary neutron source is irradiated in unit A, transported, and loaded into unit B, and ensure that the neutron count rate during the fuel loading and startup of unit B meets the requirements.

[0017] The first set time T1 is determined according to the time period for taking out, transferring, and installing the general-purpose secondary neutron source assembly.

[0018] The second set time T2 is determined according to the source strength reached by the general-purpose secondary neutron source assembly after irradiation and the neutron count rate that can still meet the requirements during the fuel loading and startup of unit B after decay within the set time.

[0019] The general-purpose secondary neutron source assembly is a general-purpose antimony-beryllium neutron source assembly.

[0020] The universal secondary neutron source assembly is compatible with the fuel assemblies of in-service nuclear power plants.

[0021] The general-purpose secondary neutron source assembly includes a resistance plug rod and a secondary neutron source rod arranged side by side on a base plate; the secondary neutron source rod has an antimony-beryllium core block in a designated area inside, and the base plate is connected to a pressure plate by a pressure spring.

[0022] Compared with existing technologies, one or more of the above technical solutions have the following beneficial effects:

[0023] 1. By using more readily available universal secondary neutron source assemblies and utilizing the irradiation conditions provided by existing nuclear power plants, the universal secondary neutron source assemblies can be irradiated by existing nuclear power plants and then installed in nuclear power plants that are operating for the first time, thereby replacing the primary neutron source required for the initial operation of the nuclear power plant and thus solving the problem of primary neutron source supply.

[0024] 2. Because it uses a universal secondary neutron source component, the supporting transport container and operating tools are universal and can be reused multiple times, thereby significantly reducing the cost of use.

[0025] 3. Due to the use of universal secondary neutron source components, the current mainstream pressurized water reactor nuclear power plants can still retain the characteristics of external neutron source start-up mode without modifying the core design. Compared with fuel loading and start-up without external neutron source, the fuel loading and start-up process is shorter and more economical because it avoids the occurrence of neutron monitoring blind spots. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a schematic diagram of the nuclear reactor head cycle ignition process provided by the present invention;

[0028] Figure 2 A schematic diagram of the general-purpose secondary neutron source component structure provided by the present invention;

[0029] In the diagram: 1. Seat plate, 2. Resistance plug rod, 3. Secondary neutron source rod, 4. Antimony-beryllium core block, 5. Compression spring. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0032] Primary neutron sources (also known as "first-stage neutron sources") are used for the initial startup of nuclear power plants and are removed from the reactor core after the first cycle. Primary neutron sources used in commercial nuclear power units are nuclides that spontaneously emit neutrons through nuclear reactions such as spontaneous fission. Early nuclear submarine reactors and nuclear power plants used Po-Be (polonium-beryllium) sources, utilizing... 210 Alpha ions emitted from the decay of Po bombard Be nuclei, emitting neutrons. Currently, most commercial nuclear power plants use californium sources. 252 Cf decay emits neutrons.

[0033] Secondary neutron sources (also known as "secondary neutron sources") generally use antimony-beryllium (Sb-Be) sources. They do not emit neutrons when not irradiated. They are loaded into the reactor during the first cycle of refueling and activated by irradiation in the reactor before being used for refueling cycles.

[0034] As described in the background section, primary neutron sources and secondary neutron sources are not interchangeable. The supply of primary neutron sources is hampered by manufacturing difficulties and economic constraints, among other factors. 252 The supply of CF is facing a bottleneck, and existing technologies offer alternatives to primary neutron sources, but these methods still have problems.

[0035] 1. The promotion of passive start technology is difficult.

[0036] The paper "CN111312419B: A Core Loading Method for Pressurized Water Reactors Without an External Primary Neutron Source in the First Core" proposes a method to eliminate the primary neutron source in the first core of a pressurized water reactor (PWR) nuclear power plant. Essentially, it extends the passive startup method of Russian-designed VVER nuclear power plants to other PWR technologies. Among most domestically operated and under-construction nuclear power plants, only those using the Russian VVER technology adopt the original Russian-designed passive startup method. Other American, French, and domestically developed nuclear power models all employ designs with external neutron sources. In the first cycle, a neutron source is used to increase the reactor core's base count rate, ensuring that the core reactivity is effectively monitored throughout the entire fuel loading and startup process using an external source range detector, eliminating blind spots in monitoring. Applying passive startup technology to nuclear power plants that previously used external neutron sources requires rigorous nuclear safety review and regulatory approval before implementation. Currently, the technology is quite challenging, and there are no successful practical applications.

[0037] 2. Some methods still require the purchase of a neutron source.

[0038] The invention described in CN115547526A, "An Am-Be Neutron Source Assembly and Core Applicable to Large Nuclear Power Reactors," employs a hybrid loading method of Am-Be (Americium-Beryllium) and Sb-Be (Antimony-Beryllium) neutron source pellets to achieve integrated application of primary and secondary neutron sources. The Am-Be neutron source is the primary neutron source, capable of spontaneously emitting neutrons in the initial reactor core loading. The Sb-Be neutron source is the secondary neutron source, not emitting neutrons during the initial core loading and startup, but emitting neutrons after activation by irradiation during the initial core operation. However, this method still requires the procurement of Am-Be neutron sources as primary neutron source materials. Due to the lower activity of Am-Be sources, the neutron emissivity per unit mass of source material is far lower than that of Cf-252, thus requiring a larger quantity of source material and resulting in higher procurement costs. Furthermore, Am-Be sources are still subject to technological limitations and require importation.

[0039] 3. Some methods have a significant impact on core design.

[0040] The three methods, "CN115472321A A method for criticality monitoring of core loading with low burnup fuel assemblies in the first cycle," "CN115171922A A method for loading low burnup fuel assemblies into the initial core of a pressurized water reactor," and "CN110322975A A passive start-up method for the initial core of a nuclear reactor," all utilize neutrons emitted during the decay of irradiated spent fuel assemblies to replace the primary neutron source, achieving start-up of the first reactor core without an external neutron source. Because they use irradiated fuel assemblies, this significantly impacts the core design of nuclear power plants, including:

[0041] The burnup levels and burnup distribution of these fuel assemblies are closely related to the burnup history of the fuel assembly. For each nuclear power unit, the reactor core designed using these irradiated fuel assemblies is unique. Therefore, it is necessary to conduct independent safety analysis and demonstration for specific core designs. The demonstration and analysis costs are high and there is no advantage of standardized design.

[0042] • To maintain the symmetry of the reactor core design, multiple irradiated fuel assemblies are required. Since the backup reactivity of irradiated fuel assemblies is low, this design will significantly reduce the backup reactivity of the reactor core, thereby shortening the operating cycle length of the nuclear power plant and reducing operating economics.

[0043] In addition, these spent fuel assemblies need to be transported from other in-service units, and the spent fuel assemblies still contain high levels of radiation, which involves high transportation costs.

[0044] 4. Some methods are only applicable to the same or similar heap types.

[0045] Both "CN113689962A A Method for Supplying Secondary Neutron Sources for First Cycle Start-up of Nuclear Power Plants" and "CN103345947B A Method for Ignition of Nuclear Reactors Using Secondary Neutron Sources" utilize secondary neutron sources activated by irradiation in existing power plants for the first core loading and start-up of new nuclear power plants. However, these methods are only applicable to reactor designs of the same or similar types using the same secondary neutron source. For reactor types with a small number of existing units, the neutron source intensity from irradiation decreases rapidly over time, making it difficult to match the irradiation and utilization time windows.

[0046] Therefore, the following embodiments provide a method for the first cycle startup of a nuclear reactor. Based on a universal secondary neutron source design, it makes full use of mainstream in-service pressurized water reactors to provide irradiation conditions for the secondary source. Taking future mainstream new pressurized water reactor nuclear power plants such as CAP1000, CAP1400 and Hualong One as application objects, it solves the problem of matching the time window for secondary neutron source irradiation, transportation and utilization caused by the decrease in source intensity over time. It can serve as a universal solution to the common problems of primary neutron source supply.

[0047] Example 1:

[0048] like Figure 1 As shown, a method for starting up a nuclear reactor head cycle includes the following steps:

[0049] 1) It adopts a universal Sb-Be source assembly suitable for CPR1000, CAP1000, CAP1400 and Hualong One nuclear power plants. This assembly is compatible with the 12-foot and 14-foot 17x17 fuel assemblies used in the aforementioned nuclear power plants;

[0050] 2) For the newly built pressurized water reactor nuclear power unit A (which may be CAP1000, CAP1400 or Hualong One nuclear power plant), based on its expected first fuel loading schedule, select an in-service pressurized water reactor nuclear power unit B whose expected shutdown overhaul time matches that of the unit, and irradiate it with a universal secondary neutron source during the first fuel cycle before the overhaul.

[0051] 3) When Unit B is shut down for major overhaul, the irradiated and activated general-purpose secondary neutron source components are unloaded, transferred and transported to Unit A.

[0052] 4) When Unit A is initially loaded with fuel, a universal secondary neutron source assembly that has been irradiated and activated is loaded to replace the primary neutron source, providing a basic neutron count rate for the loading and startup of Unit A.

[0053] 5) Using a program that calculates the source intensity after irradiation of the secondary neutron source assembly, the source intensity decay over time after shutdown, and the neutron count rate of the external source range detector, calculates the change in the neutron count rate of the external source range detector of Unit A over time after the general-purpose secondary neutron source is irradiated by Unit B, transported and installed in Unit A, to ensure that the neutron count rate meets nuclear safety requirements during the fuel loading and startup of Unit A.

[0054] Specifically:

[0055] 1. Requirements of pressurized water reactor nuclear power plants for neutron sources during fuel loading and startup

[0056] For pressurized water reactor nuclear power plants, the role of the neutron source is to provide a basic neutron count level during the reactor loading process to criticality. This ensures that the source range detector can operate normally and respond to core breeding neutrons, overcomes the blind zone of the source range detector, and ensures that the reactor has a sufficient neutron count rate for criticality safety monitoring and safe reactor startup during the subcritical state. Counting is also required during reactor shutdown. Typically, a count rate of at least 2 counts per second is required during a complete shutdown. When the effective multiplication factor (keff) is approximately 0.99, the count rate should be greater than 10 counts per second. When the count rate is less than 2 counts per second, it is recommended to use the "near-criticality" experimental technique. Nuclear safety monitoring during fuel loading (i.e., subcritical monitoring) uses the source range channel of the permanent nuclear instrumentation system and / or the temporary in-core neutron counting device to continuously monitor the neutron count rate changes in the core region. From the time the first set of fuel assemblies is loaded, the reactor core is under criticality safety monitoring. The external source range channel after fuel loading should have a stable and effective neutron count rate signal. For nuclear power plants using external neutron source fuel loading, it is recommended to have a value of not less than 0.5 cps (signal-to-noise ratio greater than 2).

[0057] The primary neutron source is used for the initial startup of a nuclear power plant and is removed from the reactor core after the first cycle. In pressurized water reactor nuclear power units, the primary neutron source is a nuclide that can spontaneously emit neutrons through nuclear reactions such as fission and decay. Early nuclear submarine reactors and the Qinshan Nuclear Power Plant used Po-Be sources, utilizing… 210 Alpha ions emitted from the decay of Po bombard Be nuclei, emitting neutrons. Currently, most commercial nuclear power plants use californium sources. 252 Cf decays and emits neutrons. Secondary neutron sources commonly use antimony-beryllium (Sb-Be) sources. Newer Sb-Be secondary neutron sources are constructed by mixing and pressing natural Sb-Be powder into core blocks and stacking them. They do not emit neutrons themselves; instead, they are loaded into the reactor core during the initial and subsequent refueling cycles. After being irradiated with neutrons within the core, they release neutrons. The principle is as follows:123 Sb nuclides are produced after capturing neutrons during irradiation. 124 Sb nuclide:

[0058] 123 Sb+n→ 124 Sb+γ (1)

[0059] The gamma rays produced by the decay of Sb-124 react with Be-9 to release neutrons.

[0060]

[0061] In this way, the irradiated and activated secondary neutron source can release neutrons during subsequent refueling cycles and startup, increasing the neutron flux level in the core region and providing a considerable baseline neutron count rate for the external source range detector, thereby avoiding a "blind zone" in core neutron monitoring. During irradiation, within the Sb-Be source... 124 The Sb content increases with increasing irradiation time and gradually reaches equilibrium; after shutdown, as... 124 Sb decays (half-life 60.2 days), decreasing by an order of magnitude every 6.6 months. Therefore, after secondary neutron source irradiation, it can only provide a sufficiently high neutron emission rate for a certain period of time. After a long period of decay, its source strength will be insufficient to provide a neutron count rate that meets regulatory requirements for off-pile source range detectors. After reactivation by irradiation, the secondary neutron source can regain its ability to release a sufficiently high neutron emission rate.

[0062] 2. General-purpose secondary neutron source components

[0063] In pressurized water reactor nuclear power plants, secondary neutron sources are fixed in the fuel assemblies as secondary neutron source assemblies, which are then loaded into the reactor core. The secondary neutron source rods are fixed to the clamping assembly and inserted into the control rod guide tubes of the fuel assembly. Therefore, the structural design of the secondary neutron source assembly needs to match the design of the fuel assemblies used in the nuclear power plant, including the radial grid spacing, guide tube / source rod positions, axial dimensions, and the structural design of the clamping components. Figure 2 A schematic diagram of a typical secondary neutron source assembly in a pressurized water reactor nuclear power plant is presented.

[0064] like Figure 2 As shown, the secondary neutron source assembly includes a resistance plug rod 2 and a secondary neutron source rod 3 (also known as a second-stage neutron source rod) connected to the base plate 1 and arranged in parallel. The secondary neutron source rod has an antimony-beryllium core block 4 in a designated area inside. The base plate 1 is connected to a pressure plate by a pressure spring 5.

[0065] Currently, the common pressurized water reactor nuclear power plant types and their fuel assembly sizes for active start-up technologies are shown in Table 1.

[0066] Table 1: Types of Pressurized Water Reactor Nuclear Power Plants and Fuel Assembly Sizes for Common Active Start-up Technologies

[0067]

[0068] Table 1 shows that there are two types of fuel assemblies used in commercial pressurized water reactor nuclear power plants. The main differences and similarities in appearance between these two types of fuels are as follows:

[0069] In the radial direction, all are arranged in a 17×17 dummy element configuration;

[0070] In the radial direction, the fuel rod and control rod guide tubes are in the same position;

[0071] In the radial direction, the outer diameter of the fuel rod and the inner and outer diameters of the control rod guide tube are the same;

[0072] Axially, the heights of the fuel active zones are 12 feet and 14 feet, respectively, and the overall heights of the fuel assemblies also differ.

[0073] The secondary neutron sources that are inserted with the fuel assembly have different initial heights in the clamping components and different shapes in the connecting plates, but their maximum dimensions are the same.

[0074] Based on the above similarities and differences, a universal secondary neutron source suitable for the reactor cores and fuel assemblies of CAP1000, CAP1400, and Hualong One nuclear power plants can be designed, which has the following characteristics:

[0075] In the radial direction, up to 24 secondary neutron source rods can be installed to adjust the loading of secondary neutron source material, thereby meeting different requirements for neutron emissivity after irradiation;

[0076] Axially, the external dimensions can be fitted into 12-foot fuel assemblies to meet fuel handling and operational requirements;

[0077] Axially, the stacking height of the secondary neutron source material in each fuel rod can be adjusted within a range of 330 cm to adjust the loading amount of secondary neutron source material, thereby meeting different requirements for neutron emissivity after irradiation.

[0078] 3. Method of using a universal irradiation secondary neutron source assembly to replace a primary neutron source

[0079] Based on universal secondary neutron source assemblies, irradiation conditions can be provided by most existing pressurized water reactor nuclear power plants. The irradiated universal secondary neutron source assemblies can be installed in the core of a newly built pressurized water reactor nuclear power plant, replacing the primary neutron source within a certain time window and meeting the neutron count rate monitoring requirements for core loading and startup. By selecting units whose shutdown schedule matches the fuel loading and startup schedule of the newly built pressurized water reactor nuclear power plant, or by selecting multiple units to provide irradiation conditions, the neutron count rate monitoring requirements for core loading and startup can be met within a longer time window, thus adapting to the commissioning schedule of the newly built pressurized water reactor nuclear power plant.

[0080] Therefore, the method for using a universal secondary neutron source assembly to replace the primary neutron source in the first reactor core of a newly built pressurized water reactor nuclear power plant is as follows:

[0081] 1) Based on the production plan of the in-service pressurized water reactor nuclear power plant unit A and the initial fuel loading plan of the newly built pressurized water reactor nuclear power plant unit B, and following the principle that the shutdown and refueling time of unit A is one to two months before the initial fuel loading time of unit B, one or more units A shall be selected to provide irradiation conditions.

[0082] 2) Before unit A is put into operation, at least two sets of general-purpose Sb-Be source components are installed and irradiated while unit A is in operation.

[0083] 3) When Unit A is shut down for refueling, the irradiated general-purpose Sb-Be neutron source components are removed and transferred to Unit B through in-plant transfer, off-plant transportation and other measures.

[0084] 4) When Unit B is first loaded, a pre-irradiated general-purpose Sb-Be neutron source assembly is loaded to provide a sufficient neutron count rate during the initial loading and startup of Unit B.

[0085] 5) For the above-mentioned unit A, the AP1000, CAP1000, CAP1400, Hualong One, M310 and their improved versions can be selected from those currently in service;

[0086] 6) Unit B mentioned above can be a newly built CAP1000, CAP1400 and Hualong One unit;

[0087] 7) The determination of the above time T1 should take into account the time cycle of removing, transferring and installing the general-purpose Sb-Be neutron source components;

[0088] 8) The determination of the above time T2 should take into account the source intensity reached after irradiation of the general-purpose Sb-Be neutron source component, and its ability to provide a sufficiently high neutron count rate after decay at the set time.

[0089] The advantages of the above method are as follows:

[0090] 1) Due to the adoption of universal secondary neutron source components, existing in-service units can be used to provide irradiation conditions for the initial fuel loading and start-up of current mainstream pressurized water reactor nuclear power plants, providing a universal solution to the primary neutron source supply problem in the nuclear energy industry.

[0091] 2) Due to the use of a universal secondary neutron source assembly, the matching irradiated Sb-Be source transport container and operating tools are universal, and the universal secondary neutron source assembly can be reused multiple times, thereby significantly reducing the cost of use.

[0092] 3) By adopting universal secondary neutron source components, the current mainstream pressurized water reactor nuclear power plants can still retain the characteristics of external neutron source start-up mode without modifying the core design. Compared with fuel loading and start-up without external neutron source, the time cycle is shorter and the economy is better.

[0093] Based on the investigation, with more than 40 units providing irradiation conditions, units that can be shut down can be provided at intervals of about one month, thus providing a universal secondary source and solving the time window problem.

[0094] Various modifications and variations can be made to this invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for starting up a nuclear reactor in its initial cycle, characterized in that, The steps include: According to the operating cycle of the in-service nuclear power plant and the first fuel loading plan of the newly built nuclear power plant, determine the irradiation time of the general-purpose secondary neutron source assembly, specifically: according to the production plan of unit A of the in-service pressurized water reactor nuclear power plant and the first fuel loading plan of unit B of the newly built pressurized water reactor nuclear power plant, determine the refueling outage time t1 of unit A and the first fuel loading time t2 of unit B; within the time period from T1 to T2, select one or more in-service units A to provide irradiation conditions; where T = t2 - t1, T1 < T < T2, T1 is the first set time, and T2 is the second set time; the first set time T1 is determined according to the time cycle for removing, transferring, and installing the general-purpose secondary neutron source assembly; the second set time T2 is determined according to the source strength reached after irradiation of the general-purpose secondary neutron source assembly and the neutron count rate that can still meet the requirements during the fuel loading and startup of unit B after decay within the set time; calculate the source strength after irradiation of the secondary neutron source assembly, the decay of the source strength over time after shutdown, and the neutron count rate of the ex-core range detector, and obtain the change in the neutron count rate of the ex-core range detector of unit B during the fuel loading process after the general-purpose secondary neutron source is irradiated by unit A, transported, and loaded into unit B. Utilize the in-service nuclear power plant to provide irradiation conditions. After irradiating the general-purpose secondary neutron source assembly in the in-service nuclear power plant, load it into the newly built nuclear power plant during its first operation to replace the primary neutron source required during the first startup of the nuclear power plant; the general-purpose secondary neutron source assembly is adapted to the fuel assembly of the in-service nuclear power plant; the general-purpose secondary neutron source assembly includes a resistance plug rod and a secondary neutron source rod that are connected to the seat plate and arranged in parallel; there are antimony-beryllium pellets in the set area inside the secondary neutron source rod, and the seat plate is connected to the pressing plate through a compression spring.

2. The method for starting up a nuclear reactor in a head cycle as described in claim 1, characterized in that, According to the operating cycle of the in-service nuclear power plant and the first fuel loading plan of the newly built nuclear power plant, determining the irradiation time of the general-purpose secondary neutron source assembly further includes: Load at least two groups of general-purpose secondary neutron source assemblies before unit A starts operating. Along with the operation of unit A and irradiation, when unit A undergoes refueling outage, remove the irradiated general-purpose secondary neutron source assemblies and transfer them to unit B.

3. The method for starting up a nuclear reactor in a head cycle as described in claim 2, characterized in that, When unit B conducts its first fuel loading, load the general-purpose secondary neutron source assemblies irradiated by unit A to provide the required neutron count rate during the first fuel loading and startup of unit B.

4. The method for starting up a nuclear reactor in a head cycle as described in claim 1, characterized in that, The general-purpose secondary neutron source assembly is a general-purpose antimony-beryllium neutron source assembly.

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