An Am-Be neutron source assembly and core suitable for use in a large nuclear power reactor

Abstract

The application discloses an Am-Be neutron source assembly and a reactor core suitable for a large nuclear power reactor, the neutron source assembly comprising a star-shaped frame and a plurality of neutron source rods hung on the star-shaped frame; the neutron source rods are loaded with Am-Be materials to provide a neutron source for physical start of the reactor core; the number of the neutron source rods depends on the attenuation caused by the water gap thickness of the lower section of the pressure vessel. The neutron source rod comprises a neutron source rod cladding, a pressing tube and Am-Be material blocks, and the Am-Be material blocks are arranged in the neutron source rod cladding. The neutron source rod further comprises Sb-Be material blocks, and the Am-Be material blocks and the Sb-Be material blocks are alternately arranged along the axial direction of the neutron source rod cladding. The application saves the high procurement cost of Cf-252 sources, avoids the problem that there is no neutron source available due to long-term shutdown of the power plant caused by various accidents, and no longer uses a separate secondary neutron source of the reactor core.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor design technology, specifically to an Am-Be neutron source assembly and core suitable for large nuclear power reactors. Background Technology

[0002] During fuel loading and startup, it is necessary to monitor the core fission reaction rate and its changes to prevent the reactor from reaching an uncontrollable instantaneous criticality state. Current monitoring methods involve deploying external nuclear monitoring instruments at specific locations outside the core. By monitoring the neutrons traveling from the core to these instruments, the core fission reaction rate and its changes are tracked.

[0003] The pressure vessel of a large nuclear power reactor is generally under high temperature and high pressure. Its complex structure and the presence of boron in the coolant can interfere with neutron detection. Therefore, the detectors for the external nuclear measurement system must be located outside the pressure vessel. To mitigate the performance degradation of the pressure vessel materials after irradiation in the high-temperature and high-pressure environment, a thick shielding layer exists between the pressure vessel and the reactor core, and the pressure vessel itself is also relatively thick. Consequently, compared to low-temperature and low-pressure test reactors, the attenuation between the reactor core and the location of the external nuclear measurement system instruments outside the pressure vessel is significantly greater.

[0004] During fuel loading and startup, it is necessary to monitor the core fission reaction rate and its changes. Due to the low subcriticality of the core, an external neutron source needs to be added to the core to provide additional neutrons in order to increase the core fission reaction rate and increase the number of neutrons received by the external source range detector to reach its basic range.

[0005] Currently, in operational nuclear power plants, monitoring during the first cycle uses an external source range detector, located far from the reactor core. Two primary neutron source assemblies are placed within the core. Each assembly consists of two bundles of neutron source rods. One bundle is the primary neutron source, typically made of californium (Cf-252), though polonium-beryllium (Po-Be) sources are also used. This releases neutrons during the initial startup, providing additional neutrons for scenarios such as the initial physical startup. The other bundle is made of antimony-beryllium neutron source rods, which release neutrons after activation over a period of time after being installed in the reactor. Normally, the first cycle is only started a few times during the commissioning phase, requiring only neutrons from the primary neutron source. However, there are scenarios where the first cycle commissioning time is long, or where the reactor is shut down for an extended period after operation. In such cases, the irradiated Cf-252 source may no longer provide enough additional neutrons. The antimony-beryllium neutron source rods on the other side of the primary neutron source assembly can supplement this by providing a certain amount of additional neutrons. Starting from the second cycle, two additional sets of secondary neutron source assemblies (antimony-beryllium (Sb-Be) sources) are used to improve the neutron flux and count rate at the detector.

[0006] However, the use of neutron sources in currently operating nuclear power plants in China has the following drawbacks:

[0007] 1) Cf-252 sources are difficult and costly to produce. Due to their short half-life, secondary neutron sources need to be placed in the reactor core. 2) Po-Be sources are highly toxic, and the short half-life of Po-210 makes it difficult to schedule reactor startup. Secondary neutron sources also need to be placed in the reactor core. 3) Sb-Be sources pose a risk of increasing the specific activity of Sb-124 in the primary coolant. 4) Both Po-Be and Sb-Be sources have short half-lives. Cf-252 has a half-life of about 2.6 years, but it is expensive. Therefore, conservative considerations are not taken into account when purchasing it. When the power plant experiences a long-term shutdown due to various accidents, the neutron source intensity is too low, making it difficult to effectively monitor the reactor during startup. Summary of the Invention

[0008] The purpose of this invention is to provide an Am-Be neutron source assembly and core suitable for large nuclear power reactors. The Am-Be neutron source provided by this assembly can replace traditional primary neutron sources (Cf-252 neutron sources, Po-Be neutron sources) in the reactor, saving the high procurement costs of Cf-252 sources. Using the Am-Be neutron source eliminates the need for a separate secondary neutron source (Sb-Be material) in the core, while still meeting the requirements for core loading and criticality monitoring. It also avoids the problem of prolonged reactor shutdowns due to unforeseen circumstances, resulting in a lack of available neutron sources, which can occur with short-half-life neutron sources. This invention allows for a rational arrangement within the core, ensuring that the count rate and fission neutron fraction at the reactor detectors in the first and subsequent cycles meet design requirements.

[0009] This invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides an Am-Be neutron source assembly suitable for large nuclear power reactors, the neutron source assembly comprising a star-shaped frame and a plurality of neutron source rods suspended on the star-shaped frame;

[0011] The neutron source rods are loaded with Am-Be material to provide a neutron source for the physical startup of the reactor core; the number of neutron source rods depends on the attenuation caused by the thickness of the water gap in the descending section of the pressure vessel.

[0012] Furthermore, the neutron source rod includes a neutron source rod cladding, a clamping tube, and an Am-Be material core. The Am-Be material core is disposed inside the neutron source rod cladding. The top end of the Am-Be material core is connected to one end of the neutron source rod cladding through the clamping tube, and the bottom end of the Am-Be material core is connected to the other end of the neutron source rod cladding through the clamping tube. The clamping tube is used to restrict the axial displacement of the Am-Be material core along the neutron source rod cladding.

[0013] Furthermore, the neutron source rod further includes a gasket, which is arranged between the Am-Be material pellet and the pressing tube and is used to protect the Am-Be material pellet.

[0014] Furthermore, the material of the Am-Be material pellet is a ceramic material or an alloy material, which can withstand the strong irradiation conditions in the core region for a long time.

[0015] Furthermore, a neutron source with the outer diameter of the Am-Be material pellet close to the inner diameter of the neutron source rod cladding is provided to increase the cross-sectional area of the pellet and the source strength per unit length of the neutron source.

[0016] Furthermore, the number of Am-Be material pellets is multiple, and the total length of the multiple Am-Be material pellets is slightly longer than the length of the sensitive area of the out-of-core detector.

[0017] Furthermore, the relationship between the total length of the multiple Am-Be material pellets and the length of the sensitive area of the out-of-core detector is: 0 cm < h2 - h1 ≤ 70 cm, where h2 is the total length of the combined multiple Am-Be material pellets and h1 is the length of the sensitive area of the out-of-core detector.

[0018] Furthermore, the neutron source rod further includes Sb-Be material pellets, and the Am-Be material pellets and the Sb-Be material pellets are arranged alternately along the axial direction of the neutron source rod cladding.

[0019] The total length of the Am-Be material pellets and the Sb-Be material pellets is slightly longer than the length of the sensitive area of the out-of-core detector.

[0020] In a second aspect, the present invention further provides a core for a large power reactor, which includes the above-mentioned Am-Be neutron source assembly applicable to a large nuclear power reactor; the above-mentioned Am-Be neutron source assembly applicable to a large nuclear power reactor is arranged in the fuel assembly in the second column of the peripheral components of the large nuclear power reactor core; an out-of-core detector is arranged outside the core;

[0021] The above-mentioned Am-Be neutron source assembly applicable to a large nuclear power reactor is used to provide neutrons with a weak source strength during the first cycle startup of the reactor, and at the same time can ensure the neutron fluence rate and count rate of the out-of-core nuclear instrumentation; and is used to provide neutrons for the physical startup of the reactor in subsequent cycles after the Am-Be material is irradiated by neutrons.

[0022] Furthermore, this core is applied to existing reactors with different neutron attenuation characteristics or existing reactors with weak neutron attenuation characteristics, where the attenuation characteristic refers to the attenuation degree from the core to the outer wall of the pressure vessel.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] This invention discloses an Am-Be neutron source assembly and core suitable for large nuclear power reactors. The neutron source assembly includes neutron source rods containing Am-Be neutron source chips, the number of which is adjustable according to design requirements. The Am-Be material can be ceramic or metallic. Maximum effective neutron output can be achieved by adjusting the chip assembly length to be slightly longer than the detector's sensitive area, and by adjusting the chip diameter to match the inner diameter of the neutron source rod cladding. The center position of the chip is kept as consistent as possible with the center of the detector's sensitive area. The Am-Be neutron source can be arranged in the fuel assembly of the second row of the outer perimeter assembly of the large nuclear power reactor core. This invention: 1) saves on the high procurement cost of Cf-252 sources; 2) avoids the problem of power plants being without neutron sources due to prolonged shutdowns caused by various unforeseen circumstances, which may result from short half-life neutron sources; 3) eliminates the need for a separate core secondary neutron source (Sb-Be material). Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 This is a schematic diagram of an Am-Be neutron source assembly structure suitable for large nuclear power reactors according to the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of an Am-Be neutron source component loaded with Am-Be material according to Embodiment 1 of the present invention.

[0028] Figure 3 This is a schematic diagram of the structure of the Am-Be neutron source component loaded with Am-Be and Sb-Be materials in Embodiment 2 of the present invention.

[0029] Figure 4 This is a schematic diagram of a core structure for a large power reactor according to Embodiment 3 of the present invention.

[0030] Figure 5 This is an example diagram illustrating the arrangement of 7 sets of neutron source rods within a 17×17 rod-shaped fuel assembly according to Embodiment 3 of the present invention.

[0031] Figure reference numerals and corresponding component names:

[0032] 1-Star-shaped frame, 2-Neutron source rod, 3-Neutron source rod cladding, 4-Compression tube, 5-Gasket, 6-Am-Be material core, 7-External detector, 8-Sb-Be material core. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0035] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] In the description of this invention, the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0037] This invention addresses a large nuclear reactor and proposes the use of an Am-Be neutron source assembly for reactor startup. The Am-Be neutron source is inexpensive and has a long half-life of 432 years, eliminating concerns about source intensity decay throughout the reactor's lifespan. After neutron irradiation, the Am in the Am-Be material transforms into nuclides such as Cm-244 and Cf-252, which can release neutrons through decay. The Be in the Am-Be material can also react with decay photons to produce photo-induced neutrons. These neutrons can provide neutrons for the physical startup of the reactor after an unexpected shutdown in the later stages of the first cycle and in subsequent cycles. The drawback of the Am-Be neutron source is its relatively low source intensity per unit volume, which is not conducive to maintaining a high neutron flux level in a subcritical core. Based on this, the present invention proposes an Am-Be neutron source assembly suitable for large nuclear power reactors. By increasing the length of the Am-Be neutron source (the length should match the length of the sensitive area of ​​the source range detector), the source intensity in a single neutron source rod is increased, the number of Am-Be neutron source rods is increased, and the arrangement of neutron sources in the reactor core is optimized. Under the premise of ensuring that the fission neutron fraction is met during startup, the proposed Am-Be neutron source can be applied to large nuclear power reactors. By using Am-Be material and alternating arrangement of Sb-Be sources inside the neutron source rods, the neutron source assembly no longer needs to arrange Sb-Be source rods, reducing the number of neutron source rods required.

[0038] Example 1

[0039] like Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of an Am-Be neutron source assembly structure suitable for large nuclear power reactors according to the present invention. Figure 1 a) is a plan view. Figure 1 b) is a top view. This invention provides an Am-Be neutron source assembly suitable for large nuclear power reactors. This embodiment targets reactors with different neutron decay characteristics (referring to the degree of decay from the reactor core to the outer wall of the pressure vessel). The specific implementation scheme is as follows:

[0040] The neutron source assembly includes a star-shaped frame 1 and several neutron source rods 2 suspended on the star-shaped frame 1;

[0041] Neutron source rod 2 is loaded with Am-Be material; it provides a neutron source for core physics startup.

[0042] The number of neutron source rods 2 depends on the attenuation caused by the thickness of the water gap in the descending section of the pressure vessel.

[0043] Among them, large nuclear-powered pressurized water reactors refer to pressurized water reactors with a coolant temperature of not less than 250°C, a pressure of not less than 12MPa, and a core thermal power of not less than 50MW under normal operating conditions.

[0044] As a further implementation, the neutron source rod 2 includes a neutron source rod cladding 3, a compression tube 4, and an Am-Be material pellet 6. The Am-Be material pellet 6 is disposed inside the neutron source rod cladding 3; the top end of the Am-Be material pellet 4 is connected to one end of the neutron source rod cladding 3 through the compression tube 4, and the bottom end of the Am-Be material pellet 6 is connected to the other end of the neutron source rod cladding 3 through the compression tube 4; the compression tube 4 is used to limit the axial displacement of the Am-Be material pellet 4 along the neutron source rod cladding 3.

[0045] As a further implementation, the neutron source rod 2 further includes a gasket 5. The gasket 5 is disposed between the Am-Be material pellet 6 and the compression tube 4 and is used to protect the Am-Be material pellet 6.

[0046] As a further implementation, the material of the Am-Be material pellet 6 is a ceramic material or an alloy material, which can withstand the strong irradiation conditions in the core region for a long time.

[0047] As a further implementation, for the neutron source with the outer diameter of the Am-Be material pellet 6 being close to the inner diameter of the neutron source rod cladding 3, the cross-sectional area of the pellet is increased, and the neutron source strength per unit length is increased.

[0048] As a further implementation, the number of the Am-Be material pellets 4 is multiple. Appropriately combining several Am-Be material pellets axially can increase the total length of the Am-Be material; the total length of the multiple Am-Be material pellets 4 is slightly longer than the sensitive region length of the out-of-core detector 7.

[0049] As a further implementation, the relationship between the total length of the multiple Am-Be material pellets 4 and the sensitive region length of the out-of-core detector 7 is: 0 cm < h2 - h1 ≤ 70 cm, where h2 is the total length of the combined multiple Am-Be material pellets 4, and h1 is the sensitive region length of the out-of-core detector 7.

[0050] The neutron source assembly of this embodiment can be arranged in the fuel assembly in the second row of the peripheral components of the core of a large nuclear power reactor, reducing the demand for neutron source strength and the number of neutron source rods.

[0051] After the implementation of the embodiment of the present invention, the main effects that can be achieved are as follows:

[0052] (1) In a reactor with the current typical neutron attenuation characteristics (referring to the attenuation degree from the core to the outer wall of the pressure vessel), a neutron source assembly can be provided that has a neutron source strength relatively weaker than the traditional Cf source during the first cycle startup of the reactor, but can still ensure the neutron fluence rate and counting rate of the out-of-core nuclear instrumentation using the traditional nuclear power neutron source design with the Cf source.

[0053] (2) After receiving neutron irradiation, the Am in the Am-Be material will be converted into nuclides such as Cm-244 and Cf-252 that can release neutrons through decay. The Be in the Am-Be material can also react with decay photons to produce photo-excited neutrons. The Am-Be neutron source can be used in subsequent cycles. The neutrons generated by the above effects can provide neutrons for the physical startup of the reactor in subsequent cycles.

[0054] (3) The Am-Be neutron source is used in the first and subsequent cycles to replace the currently used primary neutron source (Cf-252 neutron source, Po-Be neutron source) and secondary neutron source (Sb-Be neutron source). The use of the primary neutron source Cf-252 and Po-Be is eliminated, saving related costs and ensuring that the neutron source intensity can still be maintained under special conditions such as delays in the completion of the first reactor. The use of the secondary neutron source (Sb-Be neutron source) is eliminated to ensure that the neutron source can still provide sufficient neutrons during occasional long shutdown overhaul intervals, avoiding the defects caused by the use of the Sb-Be neutron source.

[0055] Example 2

[0056] like Figure 3 As shown, the difference between this embodiment and Embodiment 1 is that this embodiment is for reactors with relatively weak neutron decay characteristics (referring to the degree of decay from the reactor core to the outer wall of the pressure vessel).

[0057] Based on Example 1, the neutron source rod 2 also includes an Sb-Be material core 8, and the Am-Be material core 6 and the Sb-Be material core 8 are arranged alternately along the axial direction of the neutron source rod cladding 3.

[0058] The total length of Am-Be material chip 6 and Sb-Be material chip 8 is slightly longer than the length of the sensitive area of ​​the off-pile detector 7.

[0059] This invention, under the condition of relatively low requirements for the additional neutron source strength, uses Am-Be material chips and Sb-Be material chips arranged alternately along the axial direction to increase the source strength when the overhaul time is short, reduce the average energy of the additional neutrons, increase the fraction of additional neutron fission neutrons, and improve the reliability of monitoring.

[0060] The main effects that can be achieved after implementing the embodiments of the present invention are as follows:

[0061] (1) In reactors with low neutron decay characteristics, a neutron source assembly that provides a neutron source strength relatively weaker than the conventional Cf source can be provided during reactor first cycle startup, but can still ensure that the neutron flux rate and count rate of off-site nuclear instruments are using the conventional nuclear power neutron source design of Cf source. Similar to Implementation Scheme 1, it can obtain the benefits of replacing the currently used primary neutron source (Cf-252 neutron source, Po-Be neutron source) and secondary neutron source (Sb-Be neutron source).

[0062] (2) In reactors with low neutron decay characteristics, the initial energy level of the additional neutron source provided by neutrons can be further reduced in subsequent cycles. This can be used for low-leakage core layout schemes. Under the conditions of high burnup of peripheral components and lack of fissile nuclides, a high fissile neutron share of source range monitoring equipment can still be achieved, thereby improving the reliability of critical monitoring.

[0063] Example 3

[0064] like Figure 4 and Figure 5 As shown, the difference between this embodiment and Embodiment 1 is that this embodiment provides a reactor core for a large nuclear power reactor, which includes an Am-Be neutron source assembly suitable for a large nuclear power reactor as described in Embodiment 1; the Am-Be neutron source assembly suitable for a large nuclear power reactor is arranged in the fuel assembly of the second column of the outer periphery assembly of the large nuclear power reactor core, reducing the requirement for neutron source strength and reducing the number of neutron source rods;

[0065] An external detector 7 is installed outside the reactor core;

[0066] The aforementioned Am-Be neutron source assembly, suitable for large nuclear power reactors, is used to provide weak neutrons during the reactor's first cycle startup, while ensuring the neutron flux and count rate of off-site nuclear instruments; and to provide neutrons for the physical startup of the reactor in subsequent cycles after the Am-Be material has received neutron irradiation.

[0067] Among them, large nuclear-powered pressurized water reactors refer to pressurized water reactors with a coolant temperature of not less than 250°C, a pressure of not less than 12MPa, and a core thermal power of not less than 50MW under normal operating conditions.

[0068] Figure 4 The image shows the fuel assemblies that may be arranged in the Am-Be neutron source assembly of reactor core 177. Figure 4 S in the middle is a fuel assembly that can be used to arrange neutron source components.

[0069] As a further implementation, the core is applied to existing reactors with different neutron decay characteristics or existing reactors with weaker neutron decay characteristics.

[0070] The present invention discloses a reactor core for a large nuclear power reactor, which utilizes neutrons released from an Am-Be neutron source or a neutron source combining Am-Be and Sb-Be materials to meet the critical safety monitoring requirements during all fuel cycles and physical startup of a large nuclear power reactor.

[0071] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An Am-Be neutron source assembly suitable for large nuclear power reactors, characterized in that, The Am-Be neutron source assembly includes a star-shaped frame (1) and a number of neutron source rods (2) suspended on the star-shaped frame (1); The neutron source rod (2) is loaded with Am-Be material to provide a neutron source for the startup of core physics; the number of the neutron source rods (2) depends on the attenuation caused by the water gap thickness in the downcomer of the pressure vessel; The neutron source rod (2) includes a neutron source rod cladding (3), a compression tube (4), and Am-Be material pellets (6). The Am-Be material pellets (6) are arranged inside the neutron source rod cladding (3); the top end of the Am-Be material pellets (6) is connected to one end of the neutron source rod cladding (3) through the compression tube (4), and the bottom end of the Am-Be material pellets (6) is connected to the other end of the neutron source rod cladding (3) through the compression tube (4); the compression tube (4) is used to limit the axial displacement of the Am-Be material pellets (6) along the neutron source rod cladding (3); The number of the Am-Be material pellets (6) is multiple, and the total length of the multiple Am-Be material pellets (6) is longer than the sensitive area length of the out-of-core detector (7); The neutron source rod (2) further includes Sb-Be material pellets (8), and the Am-Be material pellets (6) and the Sb-Be material pellets (8) are arranged alternately along the axial direction of the neutron source rod cladding (3); The total length of the Am-Be material pellets (6) and the Sb-Be material pellets (8) is longer than the sensitive area length of the out-of-core detector (7).

2. The Am-Be neutron source assembly suitable for large nuclear power reactors according to claim 1, characterized in that, The neutron source rod (2) further includes a gasket (5), and the gasket (5) is arranged between the Am-Be material pellets (6) and the compression tube (4) for protecting the Am-Be material pellets (6).

3. The Am-Be neutron source assembly suitable for large nuclear power reactors according to claim 1, characterized in that, The material of the Am-Be material pellets (6) is ceramic material or alloy material.

4. The Am-Be neutron source assembly suitable for large nuclear power reactors according to claim 1, characterized in that, The outer diameter of the Am-Be material pellets (6) is close to the inner diameter of the neutron source rod cladding (3).

5. An Am-Be neutron source assembly suitable for large nuclear power reactors according to claim 1, characterized in that, The relationship between the total length of the multiple Am-Be material pellets (6) and the sensitive area length of the out-of-core detector (7) is: 0 cm < h2 - h1 ≤ 70 cm, where h2 is the total length of the combined multiple Am-Be material pellets (6), and h1 is the sensitive area length of the out-of-core detector (7).

6. A reactor core for a large nuclear power reactor, characterized in that, The core of the large nuclear power reactor includes an Am-Be neutron source assembly suitable for a large nuclear power reactor as described in any one of claims 1 to 5; the described Am-Be neutron source assembly suitable for a large nuclear power reactor is arranged in the fuel assembly in the second row of the core peripheral components of the large nuclear power reactor; an out-of-core detector (7) is arranged outside the core of the large nuclear power reactor; The described Am-Be neutron source assembly suitable for a large nuclear power reactor is used to provide neutrons with different intensities for the startup of the first cycle of the reactor, and can ensure the neutron fluence rate and counting rate of the out-of-core nuclear instrumentation; and is used to provide neutrons for the startup of reactor physics in subsequent cycles after the Am-Be material is irradiated by neutrons.

7. A reactor core for a large nuclear power reactor according to claim 6, characterized in that, The core of the large nuclear power reactor is applied to existing reactors with different neutron attenuation characteristics or existing reactors with weak neutron attenuation characteristics; The attenuation characteristics refer to the degree of attenuation from the core of a large nuclear power reactor to the outer wall of the pressure vessel.

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