Reactor structure for realizing no starting neutron source in subsequent circulation

Abstract

The utility model provides a reactor structure for realizing a starting-free neutron source in subsequent circulation, which comprises a reactor body and a signal amplification device, and the signal amplification device is of a cavity shell structure and is arranged between a fuel assembly in the reactor and a neutron detector outside the reactor. And the neutron detector is located on a neutron radiation path between the fuel assembly and the neutron detector. According to the utility model, by utilizing the arranged signal amplification device, the thickness of a shielding water layer between the spent fuel assembly and the reactor external source range neutron detector is reduced during the subsequent circulating reactor core loading period, and the number of neutrons reaching the detector is increased, so that the reactor core can be loaded with the spent fuel assembly which does not reach the minimum burnup. The detector can obtain effective counting in the loading process without depending on a neutron source, so that the problem that the neutron fluence rate level in a reactor core is difficult to accurately measure by the out-of-core neutron detector under the condition that the signal-to-noise ratio is large enough is solved.

Description

Technical Field

[0001] This utility model relates to the field of nuclear reactor neutron source technology, and in particular to a reactor structure for realizing a subsequent cycle of start-up neutron source. Background Technology

[0002] During reactor loading and physical startup, the core is in a subcritical state, at which point the neutron flux rate may be so low as to be undetectable. A neutron source is needed to raise the near-zero neutron flux rate to a sufficiently high initial level, ensuring that the source-range neutron detector located outside the reactor can measure the neutron flux rate level inside the core under a sufficiently high signal-to-noise ratio. This ensures that the entire process of neutron flux rate growth during core loading and physical startup is under the supervision of the nuclear detector.

[0003] Neutron sources are generally divided into primary neutron sources and secondary neutron sources. Currently, large nuclear power plants widely use Cf-252 sources as primary neutron sources, mainly for initial reactor fuel loading and startup. These rely on spontaneous fission to generate neutrons without activation, making them particularly expensive. Secondary neutron sources, such as the Sb-Be source, are used for subsequent fuel loading and startup counting after the initial core activation. The use of secondary neutron sources carries the following risks:

[0004] a. If the secondary neutron source rod cladding is damaged, it may lead to Sb-122 and Sb-124 contamination in the reactor primary circuit, increasing the radiation dose to overhaul personnel; if the source rod cladding is damaged, stainless steel fragments may enter the reactor primary circuit, potentially abrading the fuel rod cladding and causing component damage.

[0005] b. The activation of the Sb-Be core in the secondary neutron source rod will produce tritium, which is the main source of tritium in the primary loop. Practical experience shows that eliminating the secondary neutron source can reduce tritium emissions in the primary loop by about 25%.

[0006] The secondary neutron source Sb-Be has a half-life of 60.2 days. After the secondary neutron source is activated and removed from the reactor, there is a time window. If the reactor unit is shut down for too long, there is a risk that the neutron source intensity will decrease due to decay, making it impossible for the external source range neutron detector to obtain an effective count. As the irradiation time of the secondary neutron source in the nuclear reactor increases, the risk of damage to the secondary neutron source rod cladding also increases. At the same time, the amount of tritium generated in the core by the activation of the secondary source material Sb-Be also increases. For new units, if the initial reactor shutdown and overhaul time is too long, there is a risk that the secondary neutron source will decay excessively, and the external source range neutron detector may not be able to obtain an effective count after the neutron source assembly is reinserted into the reactor.

[0007] Therefore, eliminating the secondary neutron source fuel loading and startup in subsequent cycles can achieve benefits such as reducing tritium emissions, avoiding the risk of secondary neutron source failure, reducing solid waste generation (the lifespan of a secondary neutron source in a large nuclear power plant is 15 years), and lowering component procurement costs (the cost of secondary source components and maintenance / replacement is in the range of ~1 million RMB per set). The theoretical basis for eliminating the secondary neutron source fuel loading and startup in subsequent cycles is that spent fuel assemblies contain (α,n) neutron sources and spontaneous fission neutron sources capable of producing a large number of neutrons, and the greater the burnup, the stronger the neutron source. After eliminating the secondary neutron source assemblies, the spent fuel assemblies that have reached a certain burnup level can still allow the external source range neutron detector to obtain effective counts. Therefore, determining the component burnup boundary (minimum burnup) that allows the external source range detector to obtain effective counts is the key to this technology.

[0008] Neutron sources are typically housed in fuel assemblies, which are the second outermost layer of the reactor core. Between the fuel assemblies and the external neutron detectors are structural materials such as enclosures, reflector water layers, baskets, coolant water (water gaps), pressure vessels, insulation layers, and cavities. Water is a good neutron shielding material; therefore, minimizing the thickness of the water layer between the neutron source or spent fuel assembly and the external neutron detectors reduces the minimum source strength or burnup required for an effective neutron count.

[0009] It should be noted that the information disclosed in the above background section is only used to enhance the understanding of the background of this utility model and does not constitute any limitation on this utility model. Utility Model Content

[0010] In view of the shortcomings of the prior art described above, this utility model provides a reactor structure for achieving a subsequent cycle without a startup neutron source. During the subsequent cycle core loading, the thickness of the shielding water layer between the spent fuel assembly and the external neutron detector is reduced, increasing the number of neutrons reaching the detector. This allows the detector to obtain effective counts during the loading process without relying on a neutron source, even after the core has been loaded with spent fuel assemblies that have not reached minimum burnup. This solves the problem that external neutron detectors are unable to accurately measure the neutron flux level in the core under sufficiently high signal-to-noise ratio conditions.

[0011] This invention provides a reactor structure for achieving a subsequent cycle of neutron source-free start-up, including a reactor body and a signal amplification device. The signal amplification device is a hollow shell structure and is installed between the fuel assembly inside the reactor and the neutron detector outside the reactor, and is located on the neutron radiation path between the fuel assembly and the neutron detector.

[0012] In one embodiment of this utility model, the signal amplification device is installed in the coolant water layer of the reactor.

[0013] In one embodiment of this utility model, the contour of the cavity shell of the signal amplification device matches the curvature of the reactor shell.

[0014] In one embodiment of the present invention, the cavity housing of the signal amplification device is located in the circumferential direction of the reactor and covers the path of all neutrons in the fuel assembly near the neutron detector to the sensitive segment of the neutron detector.

[0015] In one embodiment of this utility model, the cavity shell of the signal amplification device covers the neutron arrival path between the two ends of the sensitive section of the neutron detector and the two ends of the active section of the fuel assembly on the cross-section of the reactor.

[0016] In one embodiment of this utility model, the cavity shell of the signal amplification device covers the neutron arrival path between the two ends of the sensitive section of the neutron detector and the two ends of the active section of the fuel assembly on the longitudinal section of the reactor.

[0017] In one embodiment of this utility model, the thickness of the cavity housing of the signal amplification device in the radial direction of the reactor is greater than the minimum required thickness.

[0018] In one embodiment of this utility model, the thickness of the cavity housing of the signal amplification device is less than the thickness of the coolant water layer.

[0019] In one embodiment of the present invention, the outer side of the reactor shell also includes an insulation layer and a concrete layer, and the neutron detector is arranged in the concrete layer.

[0020] In one embodiment of the present invention, the neutron detector is arranged in the concrete layer on the side close to the reactor shell.

[0021] The beneficial effects of this invention include: by utilizing a signal amplification device, the thickness of the shielding water layer between the spent fuel assemblies and the external neutron detector is reduced during subsequent core loading cycles, increasing the number of neutrons reaching the detector. This allows the detector to effectively count neutrons during the loading process even after the core has been loaded with spent fuel assemblies that have not reached minimum burnup, without relying on a neutron source, thus ensuring effective monitoring of the entire loading process. For small nuclear reactors, placing the signal amplification device in the coolant water layer between the fuel assemblies and the detector reduces the water layer thickness and enhances the neutron signal, enabling the elimination of the secondary neutron source in subsequent cycles of small reactors, avoiding the risks of pollution and tritium emissions, and reducing costs. For large nuclear reactors, the signal amplification device increases the number of neutrons reaching the detector, allowing for the earlier elimination of the secondary neutron source. This can proactively avoid risks such as secondary neutron source rod cladding damage and increased tritium levels, resulting in cost reduction benefits.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the present invention. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments conforming to the present invention and, together with the description, serve to explain the principles of the present invention. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0024] Figure 1 This is a top cross-sectional view of the signal amplification device installed in the reactor in this utility model;

[0025] Figure 2 This is a cross-sectional view of the signal amplification device installed in the reactor in this utility model;

[0026] Figure 3 This is a schematic diagram of the fuel assembly loading sequence in this utility model.

[0027] In the diagram: 1. Signal amplification device; 2. Fuel assembly; 3. Neutron detector; 4. Coolant water layer. Detailed Implementation

[0028] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. It should also be understood that the terminology used in the embodiments of this utility model is for describing specific implementation schemes and not for limiting the scope of protection of this utility model.

[0029] Please see Figures 1 to 3 It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding. They are not intended to limit the scope of this invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness or purpose of this invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms used in this specification regarding position, quantity, etc., are merely for clarity and not intended to limit the scope of this invention. Changes or adjustments to these relative relationships, without substantially altering the technical content, should also be considered within the scope of this invention's implementation.

[0030] Please see Figure 1 and Figure 2 This invention provides a reactor structure for achieving a subsequent cycle of neutron source-free startup, comprising a reactor body and a signal amplification device 1. The signal amplification device 1 is a hollow shell structure, installed between the fuel assembly 2 inside the reactor and the neutron detector 3 outside the reactor, and located on the neutron radiation path between the fuel assembly 2 and the neutron detector 3. The signal amplification device 1 is installed within the coolant water layer 4 of the reactor. The contour of the hollow shell of the signal amplification device 1 matches the curvature of the reactor shell.

[0031] Specifically, the reactor structure, from the inside out, includes several parts such as fuel assemblies, reflector water, a basket, coolant water (water gap), a pressure vessel, an insulation layer, and concrete. In this embodiment of the invention, a signal amplification device 1 is installed between the fuel assembly 2 inside the reactor and the neutron detector 3 outside the reactor, positioned on the neutron radiation path between them. In a nuclear reactor, after neutrons are emitted from the fuel assembly 2, they must pass through corresponding structures along the path to reach the neutron detector 3. Placing the signal amplification device 1 on this neutron radiation path ensures that the neutrons are amplified during transmission, thereby optimizing the neutron signal. This allows the neutrons to be fully influenced by the signal amplification device 1 as they travel to the detector, creating conditions for subsequent neutron counting enhancement.

[0032] Furthermore, the signal amplification device 1 is installed within the coolant water layer 4 of the reactor. The coolant water layer 4 is a common structure in reactors; water, as a coolant, not only has excellent heat exchange performance but also serves as a good neutron shielding material. In conventional designs, the presence of the coolant water layer 4 reduces the number of neutrons reaching the neutron detector 3, adversely affecting detector counting. However, by placing the signal amplification device 1 within the coolant water layer 4 and employing a cavity shell structure, the actual thickness of the water layer between the spent fuel assembly 2 and the external source range neutron detector 3 can be reduced, thus decreasing the shielding effect of neutrons during transmission.

[0033] It should be noted that by matching the contour of the cavity shell of the signal amplification device 1 to the curvature of the reactor shell, that is, by forming a uniform shape within the coolant water layer 4, the weakening effect of neutron shielding in different parts of the coolant water layer 4 is balanced. The specific shape of the cavity shell structure of the signal amplification device 1 can be an arc-shaped block matching the curvature of the reactor shell's inner wall, or it can be any other cavity shell shape that can be accommodated within the coolant water layer 4 and meets the signal amplification requirements; these details will not be elaborated upon here. When emitted neutrons pass through the cavity of the device, compared to directly passing through a water layer of the same thickness, they encounter less shielding resistance, allowing more neutrons to pass smoothly and reach the detector. This increases the detector's count, achieving stable amplification of the neutron signal, altering the shielding effect of the coolant water layer 4 on neutrons, thereby adjusting the neutron transmission process and increasing the number of neutrons reaching the neutron detector 3.

[0034] More specifically, during subsequent refueling cycles, a signal amplification device 1 can be placed in the coolant water layer 4 between the fuel assembly 2 and the external source range neutron detector 3. The signal amplification device 1 is a cavity with a shell, and its main function is to reduce the thickness of the water layer between the spent fuel assembly 2 and the external source range neutron detector 3, thereby reducing the neutron shielding capability and increasing the number of neutrons emitted by the spent fuel assembly 2 that reach the external source range neutron detector 3. This ensures that even if the burnup of the spent fuel assembly 2 is lower than the minimum burnup during the refueling process, the external source range neutron detector 3 can still obtain an effective count, thus effectively monitoring the neutron changes throughout the entire refueling process of the reactor core.

[0035] Please see Figure 1 and Figure 2 In one embodiment, the cavity housing of the signal amplification device 1 is located in the circumferential direction of the reactor and covers the path of all neutrons in the fuel assembly 2 near the neutron detector 3 to the sensitive body segment of the neutron detector 3.

[0036] Furthermore, the cavity shell of the signal amplification device 1 covers the neutron arrival path between the two ends of the sensitive section of the neutron detector 3 and the two ends of the active section of the fuel assembly 2 on the cross-section of the reactor. The cavity shell of the signal amplification device 1 also covers the neutron arrival path between the two ends of the sensitive section of the neutron detector 3 and the two ends of the active section of the fuel assembly 2 on the longitudinal section of the reactor.

[0037] Furthermore, the cavity shell of the signal amplification device 1 has a thickness in the reactor radial direction greater than the minimum required thickness. The thickness of the cavity shell of the signal amplification device 1 is less than the thickness of the coolant water layer 4. The outer side of the reactor shell also includes an insulation layer and a concrete layer, with the neutron detector arranged in the concrete layer. The neutron detector is arranged in the concrete layer on the side closest to the reactor shell.

[0038] Specifically, in this embodiment of the invention, the circumferential layout of the reactor relates to the relative positions of the fuel assembly 2 and the neutron detector 3. The cavity shell of the signal amplification device 1, positioned in this direction, acts as a "neutron transmission channel optimizer." After being loaded into the reactor, the fuel assembly 2 emits neutrons in all directions, and these neutrons need to be accurately captured by the neutron detector 3. The cavity shell covers all paths of neutrons reaching the detector circumferentially, ensuring that neutrons emitted from any direction pass through the optimized area of ​​the signal amplification device 1 during their journey to the detector. This reduces losses due to scattering, absorption, and other factors during circumferential radiation transmission, increases the probability of neutrons reaching the detector, and thus enhances the neutron signal received by the neutron detector 3.

[0039] The sensitive section of the neutron detector 3 is the key part of the detector that directly responds to neutron signals; only when neutrons accurately reach this section can effective counting occur. Neutrons emitted from the fuel assembly 2, which is closer to the neutron detector 3, are easily affected by the surrounding structural materials and the coolant water layer 4 when they reach the sensitive section. The cavity shell of the signal amplification device 1 precisely covers this area, minimizing neutron attenuation along this critical path. This provides a relatively smoother transmission environment for neutrons, allowing neutrons emitted from the fuel assembly 2, which is closer to the detector, to reach the sensitive section of the detector more efficiently, thereby improving the detector's ability to capture these neutrons and enhancing the accuracy and effectiveness of the counting.

[0040] Furthermore, multiple neutron transmission paths exist between fuel assembly 2 and neutron detector 3 across the reactor's cross-section, which are fully covered on this plane by the cavity shell of signal amplification device 1. In other words, on the reactor's cross-section, the neutron radiation region between the sensitive section of neutron detector 3 and the corresponding active section of fuel assembly 2 is completely covered by the cavity structure of signal amplification device 1 on a cross-sectional surface. When neutrons emitted from the region between the two ends of the active section of fuel assembly 2 propagate between the two ends of the sensitive section of neutron detector 3, the cavity shell of signal amplification device 1 can optimize the processing of neutrons along these paths. This reduces energy loss and scattering of neutrons as they pass through coolant water layer 4 and other structural materials, ensuring that neutrons reach the sensitive section of the detector with higher intensity and stability, thereby improving the detector's neutron signal reception performance across the cross-section.

[0041] In the longitudinal section of the reactor, complex neutron transport occurs at both axial ends of fuel assembly 2 and neutron detector 3. These paths are covered longitudinally by the cavity shell of signal amplification device 1. In other words, in the longitudinal section of the reactor, the neutron radiation region between the sensitive section of neutron detector 3 and the corresponding active section of fuel assembly 2 is completely covered on one cross-section by the cavity structure of signal amplification device 1. This allows neutrons emitted from both axial ends of fuel assembly 2 to pass through the cavity shell of signal amplification device 1 during their transport to the region between the two ends of the sensitive section of neutron detector 3, reducing the shielding effect. By optimizing the neutron transport path in this region, the cavity shell of signal amplification device 1 effectively increases the number of neutrons reaching the sensitive section of the detector, improving the neutron detector 3's ability to capture neutron signals in the longitudinal section and providing support for accurate monitoring of the neutron situation within the reactor.

[0042] In other words, based on the location of the external source range neutron detector 3, the radial and axial positions of the signal amplification device 1 should be able to cover the path of all neutrons in the fuel assembly 2 near the detector to the sensitive body section of the detector; the cavity thickness should be determined in advance based on the relevant parameters of the reactor core to which the signal amplification device 1 is to be used, and after taking into account a certain margin.

[0043] Furthermore, please refer to Figure 1 and Figure 2 In the direction from the coolant water layer 4 towards the outside of the reactor, there are sequentially a pressure vessel shell, an insulation layer, and a concrete layer (not shown in the attached diagram). The neutron detector 3 can be positioned at a corresponding location within the concrete layer. This arrangement facilitates assembly by placing the neutron detector outside the pressure vessel shell. Furthermore, its location outside the insulation layer and inside the concrete layer avoids impacting the insulation structure and prevents the concrete layer from shielding neutron radiation. The concrete layer also serves as a supporting structure, facilitating the installation of the neutron detector 3 equipment terminal without affecting the overall structural function of the concrete layer.

[0044] More specifically, taking a small-scale stack as an example, see the schematic diagram below. Figure 1During the balanced cycle core loading phase of this small reactor, when the first spent fuel assembly 2 is loaded, the count rate of the external neutron detector 3 is insufficient without the aid of a secondary neutron source. Theoretical calculations show that as other spent fuel assemblies 2 are loaded, the detector count rate will gradually increase and reach an effective count, indicating a monitoring blind zone in the initial loading stage. A water gap of approximately 30 cm thick exists between the core basket and the pressure vessel. The signal amplification device 1 is placed along the path between the detector and the outermost fuel assembly 2 within this water gap. Its axial position is required to cover the sensitive section of the detector and the upper and lower ends of the active region of the fuel assembly 2. This ensures that all neutrons from the spent fuel assemblies 2 loaded into the core during the initial loading stage pass through the signal amplification device 1 on their path to the sensitive section of the detector.

[0045] Please see Figures 1 to 3 In this embodiment of the invention, the operation of the signal amplification device 1 may include the following steps:

[0046] The first step, before the balanced cycle core loading begins, is to place the signal amplification device 1 in the corresponding position of the core.

[0047] The second step is to position the spent fuel assembly 2 near the detector, at which point the external source range neutron detector 3 obtains an effective count (count rate ≥ 2cps).

[0048] In the third and subsequent steps, the spent fuel assemblies 2 in the remaining positions of the reactor core are placed into the corresponding positions in the reactor core in sequence. As more spent fuel assemblies 2 are added to the reactor core, the neutron source intensity of the spent fuel in the reactor core gradually increases. The count rate obtained by the external source range neutron detector 3 gradually increases and meets the count rate requirements. This can overcome the blind spot of supervision and make the entire loading process meet the normal subcritical safety supervision requirements of the reactor core loading.

[0049] Finally, after the core loading is completed or more spent fuel is loaded around the detector, the signal amplification device 1 is removed from the core. At this time, the count rate of the external source range neutron detector 3 will decrease due to the increase in the local water layer thickness, but the neutron source strength provided by the spent fuel assembly 2 that has been loaded into the reactor can still keep the detector at an effective count of 2 cps, ensuring that the core subcritical safety monitoring during subsequent loading or start-up processes is effective.

[0050] More specifically, in another embodiment of this invention, the change in the count rate of the external source range neutron detector 3 before and after the signal amplification device 1 is considered in the theoretical analysis. The calculation results show that after the 16cm thick signal amplification device 1 is placed in the core during the refueling stage, the external source range neutron detector 3 can achieve an effective count rate of 2.5 cps from the moment the first set of spent fuel assemblies 2 are loaded, effectively amplifying the neutron signal. Simultaneously, based on the increasing trend of the external source range neutron detector 3 count rate (before use) provided by the first three sets of loaded spent fuel assemblies 2 in Table 1 below, and considering the symmetry of the spent fuel arrangement within the core, it can be seen that after all six sets of spent fuel assemblies 2 on the core side closest to the detector are loaded, even without using the device described in this invention, the external detector count rate will not be less than an effective count rate of 2 cps. That is, after the first six sets of spent fuel assemblies 2 are loaded into the core, the signal amplification device 1 can be slowly removed from the core, and no blind spot will appear in the core. The above refueling sequence diagram is shown below. Figure 3 .

[0051] Table 1. Changes in the count rate of the external detectors before and after using the signal amplification device.

[0052]

[0053]

[0054] It should be noted that in the tests corresponding to the table above, in order to reflect the effect of the device thickness on the amplification of the neutron signal, the analysis results of devices with a thickness of 8cm and 16cm are given respectively.

[0055] Similarly, based on the above analysis, it can be deduced that using this signal amplification device 1 during the subsequent fuel loading phase of a large nuclear reactor can enable the reactor to switch to a non-startup neutron source fuel loading scheme as early as possible, reducing related risks. The application of this device also effectively avoids the problem of a time window for secondary neutron source loading, which places considerable pressure on technical management.

[0056] In summary, this invention provides a signal amplification device for counting neutron sources in reactors. By employing this signal amplification device, the thickness of the shielding water layer between the spent fuel assemblies and the external neutron detector is reduced during subsequent core loading cycles, increasing the number of neutrons reaching the detector. This allows the detector to effectively count neutrons during the loading process even after the core has been loaded with spent fuel assemblies that have not reached their minimum burnup level, without relying on the neutron source, thus ensuring effective monitoring of the entire loading process. For small nuclear reactors, with their small initial uranium loading and shallow spent fuel assembly burnup, it is difficult to eliminate the secondary neutron source without assistance. By placing the signal amplification device in the coolant water layer between the fuel assembly and the detector, the thickness of the water layer is reduced, and the neutron signal is enhanced, enabling the elimination of the secondary neutron source in subsequent cycles of small reactors, avoiding the risks of pollution and tritium emissions, and reducing costs. For large nuclear reactors, eliminating the secondary neutron source requires high spent fuel assembly burnup and is implemented late. The signal amplification device can increase the number of neutrons reaching the detector, allowing large reactors to eliminate the secondary neutron source earlier. This can mitigate risks such as damage to the secondary neutron source rod cladding and increased tritium levels, thereby reducing costs.

[0057] The above embodiments are merely illustrative of the principles and effects of this utility model and are not intended to limit the scope of this utility model. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this utility model. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this utility model should still be covered by the claims of this utility model.

Claims

1. A reactor structure for implementing a subsequent cycle without start-up of a neutron source, characterized by, The reactor comprises a reactor body and a signal amplification device (1) which is a hollow shell structure and is arranged between a fuel assembly (2) inside the reactor and a neutron detector (3) outside the reactor and on the neutron radiation path between the fuel assembly (2) and the neutron detector (3).

2. The reactor structure of claim 1, wherein, The signal amplification device (1) is arranged in a coolant water layer (4) of the reactor.

3. The reactor structure of claim 2, wherein, The contour of the hollow shell of the signal amplification device (1) matches the curvature of the reactor shell.

4. The reactor structure of claim 3, wherein, The hollow shell of the signal amplification device (1) is located in the circumferential direction of the reactor and covers all paths of neutrons in the fuel assembly (2) near the side of the neutron detector (3) to the sensitive volume section of the neutron detector (3).

5. The reactor structure of claim 3, wherein, The hollow shell of the signal amplification device (1) covers the neutron arrival paths between the two ends of the active section of the fuel assembly (2) corresponding to the two ends of the sensitive volume section of the neutron detector (3) in the cross section of the reactor.

6. The reactor structure of claim 3, wherein, The hollow shell of the signal amplification device (1) covers the neutron arrival paths between the two ends of the active section of the fuel assembly (2) corresponding to the two ends of the sensitive volume section of the neutron detector (3) in the longitudinal section of the reactor.

7. The reactor structure of claim 3, wherein, The thickness of the hollow shell of the signal amplification device (1) in the radial direction of the reactor is greater than the minimum required thickness.

8. The reactor structure of claim 3, wherein, The thickness of the hollow shell of the signal amplification device (1) is less than the thickness of the coolant water layer (4).

9. The reactor structure of claim 1, wherein, The outer side of the reactor shell further comprises a thermal insulation layer and a concrete layer, and the neutron detector (3) is arranged in the concrete layer.

10. The reactor structure of claim 9, wherein, The neutron detector (3) is arranged in the concrete layer near the side of the reactor shell.

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