Introduction method for reaching critical reactivity by first start of reactor without external neutron source

Abstract

Some embodiments of the invention disclose a reactor first start-up critical reactivity introduction method without an external neutron source, and the method comprises the following steps: starting from a reactor core in a shutdown standby state, introducing positive reactivity meeting a large reactivity introduction stage condition for several times until the reactor core is in a state with a first critical degree; introducing positive reactivity meeting conditions of a small reactivity introduction stage into the reactor core, waiting for a preset time to judge whether the reactor external source range detector displays an effective count or not, continuing to introduce the positive reactivity meeting the conditions of the small reactivity introduction stage into the reactor core if the effective count is not displayed, and stopping introducing the second reactivity if the effective count is displayed, if the effective count does not continuously rise, extrapolating to a critical value by adopting a countdown rate method; otherwise, introducing negative reactivity into the reactor core by adopting a power stabilization method to maintain the reactor core criticality. According to the method, an external neutron source and a high-cost high-sensitivity detector are not needed, and the purpose that the reactor is started for the first time to reach the critical value can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear power, in particular to a method for introducing reactivity for first startup of a reactor to criticality without an external neutron source. BACKGROUND

[0002] In order to improve the neutron flux level under subcriticality of the core of a conventional pressurized water reactor, so that the out-of-core nuclear measurement system can effectively supervise the change of the neutron flux in the reactor, an external neutron source is generally needed in the first startup. The commonly used external primary neutron source is a californium source, and the neutrons come from spontaneous fission of californium-252. The californium-252 primary neutron source material has unfavorable factors in terms of supply stability and price.

[0003] It is found through research that, in addition to californium-252 that can spontaneously fission to generate neutrons, the fuel loaded in the core also has the ability of spontaneous fission, and the main contribution is uranium-238. The neutrons generated by spontaneous fission of uranium-238 and other nuclides can also achieve the purpose of the reactor startup to criticality without an external neutron source in the core. However, the spontaneous source intensity of the fuel is lower than that of the californium source, and the out-of-core range detector may not be able to obtain effective counts during the process of reaching criticality. In order to realize the first startup without an external neutron source, a high-sensitivity detector is added to the VVER core in related technologies, which requires the development of a high-sensitivity detector for a specific reactor, and the cost is high. SUMMARY

[0004] The present application provides a method for introducing reactivity for first startup of a reactor to criticality without an external neutron source, which can achieve the purpose of the reactor startup to criticality without using an external neutron source and a high-sensitivity detector with high cost.

[0005] The present application provides a method for introducing reactivity for first startup of a reactor to criticality without an external neutron source, which can achieve the purpose of the reactor startup to criticality without using an external neutron source and a high-sensitivity detector with high cost.

[0006] The method comprises the following steps:

[0007] If the effective count is displayed, it is judged whether the effective count is continuously increasing; if not, the count-down rate method is used to extrapolate the criticality; if continuously increasing, the power stabilization method is used to introduce negative reactivity into the core to maintain the core criticality.

[0008] In some embodiments, the first criticality is not less than 1500 pcm and not greater than 2500 pcm.

[0009] In some embodiments, the method further comprises:

[0010] determining an effective delayed neutron fraction;

[0011] determining the first reactivity according to the effective delayed neutron fraction and a preset core shutdown protection signal setting value.

[0012] In some embodiments, the step of determining the effective delayed neutron fraction comprises:

[0013] determining the effective delayed neutron fraction according to a correction amount set according to the difference between the delayed neutron and the prompt neutron energy and the delayed neutron fraction of different groups in the collective lump at the beginning of the core life.

[0014] In some embodiments, the step of determining the first reactivity according to the effective delayed neutron fraction and a preset core shutdown protection signal setting value comprises:

[0015] determining the core reactivity corresponding to the short period protection signal setting value of the core according to the preset core shutdown protection signal setting value, the prompt neutron lifetime, the correction amount set according to the difference between the delayed neutron and the prompt neutron energy, the delayed neutron fraction of different groups in the collective lump at the beginning of the core life, and the delayed neutron precursor decay constant of different groups in the collective lump at the beginning of the core life.

[0016] determining the first reactivity according to the effective delayed neutron fraction and the core reactivity corresponding to the short period protection signal setting value of the core.

[0017] In some embodiments, the step of determining the first reactivity according to the effective delayed neutron fraction and the core reactivity corresponding to the short period protection signal setting value of the core comprises:

[0018] determining the minimum value of the effective delayed neutron fraction and the core reactivity corresponding to the short period protection signal setting value of the core;

[0019] determining that the first reactivity is less than the minimum value.

[0020] In some embodiments, the method further comprises determining the second reactivity.

[0021] wherein the determining the second reactivity comprises:

[0022] determining a core reactivity corresponding to the cycle limit in the core startup procedure according to the prompt neutron lifetime, the cycle limit in the core startup procedure, a correction amount set according to a difference between the energy of the delayed neutron and the energy of the prompt neutron, a delayed neutron fraction of different groups in the initial lumped parameter in the core life, and a delayed neutron precursor decay constant of different groups in the initial lumped parameter in the core life;

[0023] determining the second reactivity according to the core reactivity corresponding to the cycle limit in the core startup procedure.

[0024] In some embodiments, the determining the second reactivity according to the core reactivity corresponding to the cycle limit in the core startup procedure comprises:

[0025] determining a half of the core reactivity corresponding to the cycle limit in the core startup procedure;

[0026] determining that the second reactivity is less than a half of the core reactivity corresponding to the cycle limit in the core startup procedure.

[0027] In some embodiments, the effective count is greater than 0.5 cps.

[0028] In some embodiments, the method further comprises determining the preset time.

[0029] wherein the determining the preset time comprises:

[0030] determining a core cycle corresponding to the core having the second reactivity;

[0031] determining the preset time according to the core cycle corresponding to the core having the second reactivity, a minimum effective count of the source range detector, a sensitivity of the source range detector, and a neutron fluence rate at a position of the source range detector in a sensitive interval of the source range detector when a core effective multiplication factor is 0.99.

[0032] In the above embodiment, a method for introducing reactivity to reach criticality in the first start-up of a reactor without an external neutron source is provided, which starts from the state that the core of the reactor is in a shutdown standby state, introduces positive reactivity, i.e., first reactivity, which meets the condition of a large reactivity introduction stage, in batches until the core is in a state with a first criticality, then introduces positive reactivity, i.e., second reactivity, which meets the condition of a small reactivity introduction stage, to the core, waits for a preset time to determine whether the out-of-pile source range detector shows valid counts, if no valid counts are shown, continues to introduce positive reactivity, which meets the condition of a small reactivity introduction stage, to the core, and if valid counts are shown, stops introducing the second reactivity, and determines whether the valid counts continue to rise; if not, extrapolates to reach criticality by using the count-down rate method; and if so, introduces negative reactivity to the core to maintain the core criticality by using the power stabilization method. In this way, the method in the embodiment of the present application can achieve the purpose of reaching criticality in the first start-up of a reactor without using an external neutron source and a high-sensitivity detector with high cost. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 An exemplary flow chart is shown to illustrate a method for introducing reactivity to reach criticality in the first start-up of a reactor without an external neutron source according to some embodiments;

[0034] Figure 2 An exemplary diagram is shown to illustrate the process from subcriticality to the out-of-pile source range detector having valid counts in the small reactivity introduction stage. DETAILED DESCRIPTION

[0035] In order to make the purpose and implementation of the present application clearer, the exemplary implementation of the present application will be described clearly and completely below in conjunction with the drawings in the exemplary embodiments of the present application. Obviously, the described exemplary embodiments are only some of the embodiments of the present application, but not all of the embodiments.

[0036] It should be noted that the brief description of the terms in the present application is only for the convenience of understanding the implementation described next, and is not intended to limit the implementation of the present application. Unless otherwise specified, these terms should be understood according to their ordinary and general meanings.

[0037] The terms "first", "second", "third", etc. in the specification and claims and the above drawings are used to distinguish similar or similar objects or entities, and do not necessarily mean to limit the specific order or sequence, unless otherwise specified. It should be understood that the terms used in this way can be interchanged under appropriate circumstances.

[0038] The terms “comprising” and “having”, and any variations thereof, are intended to cover but not exclude inclusion, for example, a product or device that includes a range of components is not necessarily limited to all of the components that are clearly listed, but may include other components that are not clearly listed or that are inherent to such product or device.

[0039] To address the aforementioned technical problems, this application provides a method for introducing reactivity to achieve criticality during the initial startup of a reactor without an external neutron source. This method begins with the reactor core in a shutdown / standby state, introducing positive reactivity in stages to meet the conditions for the large reactivity introduction stage (i.e., the first reactivity) until the core reaches a state with the first criticality. Then, positive reactivity meeting the conditions for the small reactivity introduction stage (i.e., the second reactivity) is introduced into the core. A preset time is waited to determine if an external source range detector displays a valid count. If no valid count is displayed, positive reactivity meeting the conditions for the small reactivity introduction stage is continued to be introduced into the core. If a valid count is displayed, the introduction of the second reactivity is stopped, and it is determined whether the valid count continues to increase. If it does not continue to increase, the count rate method is used to extrapolate to criticality. If it continues to increase, a power stabilization method is used to introduce negative reactivity into the core to maintain core criticality. Thus, the method in this application does not require an external neutron source or a costly, high-sensitivity detector to achieve the goal of achieving criticality during the initial startup of the reactor.

[0040] Figure 1 An exemplary flowchart illustrates a method for introducing critical reactivity during the initial startup of a reactor without an external neutron source, according to some embodiments. The method includes steps S100-S300.

[0041] S100. Starting from the reactor core being in a shut-down standby state, first reactive substances are repeatedly introduced into the reactor core. Until the core is at the first critical degree ρ T The state; wherein, in two consecutive introductions of the first reactive energy into the core. The first critical value ρ is obtained by waiting for a preset time. T It is less than the second criticality corresponding to the core being in a standby state and greater than 0 pcm.

[0042] In this embodiment, step S100 is also referred to as the high reactivity introduction stage. Starting from the reactor core being in a shutdown standby state, positive reactivity (i.e., the first reactivity) is introduced into the reactor core in stages until the reactor core reaches a theoretically calculated subcriticality (i.e., the first criticality ρ). T When the reactor core reaches a certain state, the introduction of positive reactivity is stopped. A preset time is waited between two consecutive introductions of positive reactivity into the core.

[0043] In some embodiments, the first critical degree ρT not less than 1500 pcm and not more than 2500 pcm. The first criticality degree p T is in pcm. The first criticality degree needs to be less than the subcriticality of the reactor core in the shutdown standby state, and greater than 0 pcm. The smaller the first criticality degree, the higher the accuracy requirement of the theoretical calculation, and the larger the first criticality degree, the longer the start-up time. Therefore, in consideration of the efficiency and safety, the first criticality degree p T is determined to be not less than 1500 pcm and not more than 2500 pcm.

[0044] In some embodiments, the method further comprises determining a first reactivity . Specifically, the method comprises:

[0045] determining an effective delayed neutron fraction; and determining the first reactivity eff based on the effective delayed neutron fraction b

[0046] In some embodiments, the step of determining the effective delayed neutron fraction comprises:

[0047] determining the effective delayed neutron fraction b eff based on a correction amount set according to the difference between the energy of the delayed neutron and the energy of the prompt neutron and the delayed neutron fractions of different groups of the initial collective neutrons in the core lifetime.

[0048] Specifically, the effective delayed neutron fraction can be determined according to the following formula (1):

[0049]

[0050] In formula (1), b eff is the effective delayed neutron fraction of the core, i.e., the effective delayed neutron fraction of the initial core lifetime, which is a dimensionless quantity; I is a correction amount set according to the difference between the energy of the delayed neutron and the energy of the prompt neutron, which is a dimensionless quantity, and is generally taken as 0.97 for a general nuclear power plant; b i is the collective delayed neutron fraction b i of the six groups of the initial collective neutrons in the core lifetime, i.e., the delayed neutron fractions of different groups of the initial collective neutrons in the core lifetime, which is a dimensionless quantity.

[0051] In some embodiments, the step of determining the first reactivity eff based on the effective delayed neutron fraction b and the preset core shutdown protection signal setting value comprises:

[0052] Based on the preset core shutdown protection signal setting value, the transient neutron lifetime, the correction amount set for the difference between the delayed neutron and transient neutron energies, the proportion of delayed neutrons in different groups in the initial core lifetime lumped set, and the decay constants of the delayed neutron precursor nuclei in different groups in the initial core lifetime lumped set, the core reactivity corresponding to the short-period protection signal setting value of the core is determined.

[0053] Specifically, the decay constants λ of six delayed neutron precursor nuclear groups are known. i Delayed neutron share β i And the transient neutron lifetime l, i = 1 to 6. According to the reactivity equation, i.e., Formula 2, the relationship between the core period and the reactivity of the core can be obtained:

[0054]

[0055] Where ρ represents the reactivity of the reactor core, measured in pcm; l represents the transient neutron lifetime, measured in seconds; T represents the core period, measured in seconds; I is a dimensionless correction factor for the energy difference between delayed and transient neutrons; β i The six delayed neutron fractions β are lumped together at the beginning of the reactor core's lifespan. i (i = 1 to 6), representing the proportion of delayed neutrons from different groups in the initial lumped core lifetime, which is a dimensionless quantity; λ i This represents the decay constant of the i-th group of delayed neutron precursor nuclei, i.e., the decay constants of different groups of delayed neutron precursor nuclei in the initial lumped core lifetime, expressed in seconds (s). -1 ).

[0056] The preset short-cycle protection signal setting value T for the reactor core is known. a According to formula (2), the core reactivity ρ corresponding to the short-period protection signal setting value of the core can be calculated. a Thus, we obtain formula (3).

[0057]

[0058] Where, ρ a This represents the core reactivity corresponding to the short-period protection signal setting value of the reactor core, in pcm; l represents the transient neutron lifetime, in seconds; T a This represents the preset short-period protection signal setting value for the reactor core, in seconds; I is the correction amount for the energy difference between delayed neutrons and instantaneous neutrons, which is a dimensionless quantity; β i The six delayed neutron fractions β are lumped together at the beginning of the reactor core's lifespan. i (i = 1 to 6), representing the proportion of delayed neutrons from different groups in the initial lumped core lifetime, which is a dimensionless quantity; λ iThis represents the decay constant of the i-th group of delayed neutron precursor nuclei, i.e., the decay constants of different groups of delayed neutron precursor nuclei in the initial lumped core lifetime, expressed in seconds (s). -1 Therefore, based on the preset core shutdown protection signal setting value, the transient neutron lifetime, the correction amount set for the difference between the delayed neutron and transient neutron energies, the proportion of delayed neutrons in different groups in the initial core lifetime lumped set, and the decay constants of the delayed neutron precursor nuclei in different groups in the initial core lifetime lumped set, the core reactivity corresponding to the short-period protection signal setting value of the core can be determined based on formula (3).

[0059] According to the effective delayed neutron fraction β eff The core reactivity ρ corresponding to the short-period protection signal setting value of the core. a Determine the first reactivity

[0060] In some embodiments, the effective delayed neutron fraction β eff The core reactivity ρ corresponding to the short-period protection signal setting value of the core. a Determine the first reactivity The steps include:

[0061] Determine the effective delayed neutron fraction β eff Half of the core reactivity ρ corresponds to the short-cycle protection signal setting value of the core. a The minimum value in; determine the first reactivity It is less than the minimum value.

[0062] In this embodiment, the first reactive power introduced into the reactor core in step S100 is... Requires less than half of the effective delayed neutron fraction β eff The core reactivity ρ corresponding to the short-period protection signal setting value of the core a The minimum value between, i.e. From the moment the reactor core is shut down, no more than [amount] can be introduced into the reactor core at a time. The positive reactivity is such that after each introduction, a preset time is waited until the core is in a state that has reached the first criticality according to theoretical calculations.

[0063] In this embodiment of the application, the preset time mentioned in step S100 is the same as the preset time mentioned in step S200. The specific steps for determining the preset time are described below.

[0064] S200, To the point where the first critical degree ρ is present T Introducing a second reactive power into the reactor core in a state of flux. After waiting for a preset time, it is judged whether the out-of-pile source range detector displays valid counts; if not, the step of introducing the second reactivity is re-executed.

[0065] In the embodiment, the process of step S200 is also called a small reactivity introduction phase. The second reactivity is different from the first reactivity. Starting from the state that the core has the first criticality ρ T calculated theoretically, the positive reactivity, i.e., the second reactivity is introduced into the core, and after waiting for a preset time, it is judged whether the source range detector displays valid counts; if not, the second reactivity is continuously introduced.After waiting for a preset time, it is judged whether the out-of-pile source range detector displays valid counts; if not, the second reactivity is continuously introduced. After waiting for a preset time, it is judged whether the out-of-pile source range detector displays valid counts; if yes, step S300 is executed.

[0066] In some embodiments, the method further includes determining the second reactivity Vρ S . Specifically, the process includes:

[0067] According to the prompt neutron lifetime, the period limit in the core startup procedure, the correction amount set according to the difference between the energy of the delayed neutron and the prompt neutron, the delayed neutron fraction of different groups in the initial lumped parameter of the core lifetime, and the delayed neutron precursor decay constant of different groups in the initial lumped parameter of the core lifetime, the core reactivity corresponding to the period limit in the core startup procedure is determined.

[0068] Specifically, the period limit corresponding to the core short period alarm signal is T b , and according to formula (2), the core reactivity ρ b corresponding to the period limit in the core startup procedure can be calculated, i.e., formula (4) is obtained.

[0069]

[0070] wherein, ρ b is the core reactivity corresponding to the period limit in the core startup procedure, with the unit of pcm; l represents the prompt neutron lifetime, with the unit of second; T b represents the period limit in the core startup procedure, i.e., the period limit corresponding to the core short period alarm signal, with the unit of second; I is the correction amount set according to the difference between the energy of the delayed neutron and the prompt neutron, which is a dimensionless quantity; β i is the delayed neutron fraction β i of the six groups in the initial lumped parameter of the core lifetime, i.e., the delayed neutron fraction of different groups in the initial lumped parameter of the core lifetime, which is a dimensionless quantity; λ irepresents the i-th group delayed neutron precursor decay constant, i.e. the collective delayed neutron precursor decay constant of different groups at the beginning of the core life, with the unit of per second (s -1 Therefore, according to the prompt neutron life, the cycle limit value in the core startup procedure, the correction amount set according to the difference between the energy of the delayed neutron and the prompt neutron, the delayed neutron share of the collective delayed neutron of different groups at the beginning of the core life, and the delayed neutron precursor decay constant of different groups at the beginning of the core life, the core reactivity corresponding to the cycle limit value in the core startup procedure can be determined by using formula (4).

[0071] According to the core reactivity corresponding to the cycle limit value in the core startup procedure, the second reactivity Vp b is determined. S

[0072] In some embodiments, the step of determining the second reactivity Vp S according to the core reactivity corresponding to the cycle limit value in the core startup procedure includes: determining half of the core reactivity corresponding to the cycle limit value in the core startup procedure; and determining the second reactivity Vp S to be less than half of the core reactivity corresponding to the cycle limit value in the core startup procedure. In this embodiment, the single introduced second reactivity Vp S in step S200 is not greater than half of the core reactivity corresponding to the cycle limit value in the core startup procedure, i.e. the second reactivity Vp L < p b / 2.

[0073] Figure 2 An exemplary diagram showing the effective counting process of the subcritical to excore source range detector in the small reactivity introduction stage is shown. Figure 2 The change of the reactivity and the nuclear power from subcritical to supercritical to the minimum detectable power level, i.e. when the excore source range detector has effective counting, is shown over time.

[0074] In some embodiments, the effective counting is greater than 0.5 cps. In this embodiment, the effective counting of the excore source range detector is at least greater than 0.5 cps according to the standard.

[0075] In some embodiments, the method further includes: determining the preset time; and wherein the step of determining the preset time includes: determining the core period corresponding to the second reactivity Vp S . Specifically, the second reactivity Vp S is taken as the reactivity p of the core in formula (2), i.e. the core period T corresponding to the second reactivity Vp S can be obtained. ​

[0076] According to the core period corresponding to the core having the second reactivity Vρ S , the minimum effective count of the source range detector, the source range detector sensitivity, and the neutron fluence rate at the source range detector position in the source range detector sensitive interval when the core effective multiplication factor is 0.99, the preset time is determined. Specifically, the preset time can be determined according to formula (5):

[0077]

[0078] wherein t is the preset time, the unit is second; T(Vρ S ) represents the core period corresponding to the core having the second reactivity Vρ S ; N represents the minimum effective count of the source range detector, the unit is cps; S represents the source range detector sensitivity, the unit is cps / (n·cm -2 ·s -1 ); Φ 0.99 represents the neutron fluence rate at the source range detector position in the source range detector sensitive interval when the core effective multiplication factor is 0.99, the unit is n·cm -2 ·s -1 .

[0079] In the embodiment, the preset time is the time for the neutron fluence rate at the position of the ex-core source range detector when the core effective multiplication factor is 0.99 to be multiplied to the effective count obtained by the source range detector.

[0080] S300, if the effective count is displayed, it is judged whether the effective count is continuously rising; if not, the inverse counting rate method is used to extrapolate to reach criticality; if continuously rising, the power stabilization method is used to introduce negative reactivity to the core to maintain the core criticality.

[0081] In the embodiment, after the ex-core source range detector displays the effective count for the first time, the introduction of the second reactivity to the core is stopped, because the ex-core source range detector has the effective count at this time, which can guide the process of reaching criticality, it is judged whether the effective count is continuously rising; if not, the inverse counting rate method is used to extrapolate to reach criticality; if continuously rising, the power stabilization method is used to introduce negative reactivity to the core to maintain the core criticality.

[0082] The method of the embodiment of the application cancels the use of the primary neutron source assembly, reduces the production of radioactive waste and its disposal cost, and saves the procurement cost of the primary source. In addition, no high-sensitivity detector is needed in the starting process, which reduces the cost. The method in the embodiment of the application can significantly improve the economy of the power plant, is conducive to environmental protection, and can avoid dependence on imported primary neutron sources, significantly improving the independence of nuclear power reactors in China.

[0083] In the above embodiment, the method for first starting up the reactor to critical reactivity is introduced, which starts from the state that the reactor core is in the shutdown standby state, introduces the positive reactivity, i.e., the first reactivity, which meets the condition of the large reactivity introduction stage, in batches until the core is in the state with the first criticality; then, the positive reactivity, i.e., the second reactivity, which meets the condition of the small reactivity introduction stage, is introduced to the core, and a preset time is waited to determine whether the out-of-core source range detector displays effective counts; if no effective counts are displayed, the positive reactivity, which meets the condition of the small reactivity introduction stage, is continuously introduced to the core; if effective counts are displayed, the introduction of the second reactivity is stopped, and it is determined whether the effective counts continue to rise; if the effective counts do not continue to rise, the count-down rate method is used to extrapolate the criticality; if the effective counts continue to rise, the power stabilization method is used to introduce the negative reactivity to the core to maintain the criticality of the core. In this way, the method in the embodiment of the present application can achieve the purpose of first starting up the reactor to critical reactivity without using the external neutron source and the high-sensitivity detector with high cost.

[0084] Those skilled in the art can easily understand that the above advantageous modes can be freely combined and superimposed without conflict. The above is only a preferred embodiment of the present application and does not limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only a preferred embodiment of the present application, and it should be pointed out that, for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, which should be regarded as the protection scope of the present application.

Claims

1. A method for introducing a first start-up of a reactor to critical reactivity without an external neutron source, characterized in that, The method comprises the following steps: introducing first reactivity into a reactor core multiple times from a shutdown standby state of the reactor core until the reactor core is in a state with a first criticality; wherein a preset time is waited between adjacent two times of introducing the first reactivity into the reactor core, and the first criticality is smaller than a second criticality corresponding to the shutdown standby state of the reactor core and greater than 0 pcm; introducing second reactivity into the reactor core in the state with the first criticality, and judging whether an out-of-core source range detector displays effective counts after waiting for a preset time; if the effective counts are not displayed, the step of introducing the second reactivity is repeatedly executed; if the effective counts are displayed, judging whether the effective counts continue to rise; if the effective counts do not continue to rise, a count-down rate method is used to extrapolate the criticality; if the effective counts continue to rise, a power stabilization method is used to introduce negative reactivity into the reactor core to maintain the criticality of the reactor core.

2. The method of claim 1, wherein, The first criticality is not less than 1500 pcm and not greater than 2500 pcm.

3. The method of claim 1, wherein, The method further comprises the following steps: determining an effective delayed neutron fraction; determining the first reactivity according to the effective delayed neutron fraction and a preset shutdown protection signal setting value of the reactor core.

4. The method of claim 3, wherein, The step of determining the effective delayed neutron fraction comprises the following steps: determining the effective delayed neutron fraction according to a correction amount set according to a difference between delayed neutron energy and prompt neutron energy and delayed neutron fractions of different groups in a core life initial lumped parameter.

5. The method of claim 3, wherein, The step of determining the first reactivity according to the effective delayed neutron fraction and the preset shutdown protection signal setting value of the reactor core comprises the following steps: determining a short period protection signal setting value corresponding to the reactor core reactivity of the reactor core according to the preset shutdown protection signal setting value of the reactor core, a prompt neutron lifetime, the correction amount set according to the difference between the delayed neutron energy and the prompt neutron energy, the delayed neutron fractions of different groups in the core life initial lumped parameter, and delayed neutron precursor decay constants of different groups in the core life initial lumped parameter; determining the first reactivity according to the effective delayed neutron fraction and the short period protection signal setting value corresponding to the reactor core reactivity of the reactor core.

6. The method of claim 5, wherein, The step of determining the first reactivity according to the effective delayed neutron fraction and the short period protection signal setting value corresponding to the reactor core reactivity of the reactor core comprises the following steps: determining a minimum value of a half of the effective delayed neutron fraction and the short period protection signal setting value corresponding to the reactor core reactivity; determining that the first reactivity is smaller than the minimum value.

7. The method of claim 1, wherein, The method further comprises the following steps: determining the second reactivity; The step of determining the second reactivity comprises the following steps: determining a reactor core reactivity corresponding to a cycle limit value in a reactor core startup procedure according to a prompt neutron lifetime, the cycle limit value in the reactor core startup procedure, the correction amount set according to the difference between the delayed neutron energy and the prompt neutron energy, the delayed neutron fractions of different groups in the core life initial lumped parameter, and the delayed neutron precursor decay constants of different groups in the core life initial lumped parameter; determining the second reactivity according to the reactor core reactivity corresponding to the cycle limit value in the reactor core startup procedure.

8. The method of claim 7, wherein, The step of determining the second reactivity according to the reactor core reactivity corresponding to the cycle limit value in the reactor core startup procedure comprises the following steps: determining that the second reactivity is less than half of the core reactivity corresponding to the cycle limit in the core startup procedure. determining that the second reactivity is less than half of the core reactivity corresponding to the cycle limit in the core startup procedure.

9. The method of claim 1, wherein, The effective count is greater than 0.5 cps.

10. The method of claim 1, wherein, Further comprising: determining the preset time; wherein the step of determining the preset time comprises: determining a core cycle corresponding to the second reactivity of the core; determining the preset time according to the core cycle corresponding to the second reactivity of the core, the minimum effective count of the source range detector, the source range detector sensitivity, and the neutron fluence rate in the source range detector sensitive interval at the source range detector position when the core effective multiplication factor is 0.99.

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