Implementation method of secondary neutron source assembly in first cycle of reactor

Abstract

The invention provides an implementation method of a secondary neutron source assembly in a first cycle of a reactor. The method comprises the following steps: performing irradiation activation on the secondary neutron source assembly to be activated; according to the structure of the first reactor, determining the arrangement position of the activated secondary neutron source assembly in the core of the first reactor; determining reactor entering time of the activated secondary neutron source assembly based on the correlation time of the secondary neutron source assembly; and loading the activated secondary neutron source assembly to a predetermined arrangement position in the first reactor core according to the in-reactor time. The secondary neutron source assembly to be activated is subjected to irradiation activation, the arrangement position and the reactor entering time of the secondary neutron source assembly in the reactor core are determined according to the structure and time requirements of the reactor, and finally the activated secondary neutron source assembly is loaded into the reactor core. The problems that the supply of a primary neutron source is limited, the cost is high, and a neutron detector is difficult to detect the neutron fluence rate level in a reactor core after the reactor is shut down for a long time are solved.

Description

Technical Field

[0001] This application relates to the technical field of nuclear power reactors, and particularly to an implementation method of a secondary neutron source assembly in the first cycle of a reactor. Background Art

[0002] During the refueling and startup processes of a nuclear power plant reactor, to ensure critical safety, the entire process needs to be under the effective supervision of neutron detectors. However, before the initial operation of the reactor or after a long-term shutdown, there are very few neutrons in the core during the refueling and startup processes, and the off-core detectors may not be able to detect the neutron fluence rate level in the core. To solve this problem, neutron source assemblies are usually installed in the core. The neutrons generated by these neutron source assemblies can produce a sufficient number of neutrons after subcritical multiplication, so that the neutron detectors can detect the neutron level in the reactor.

[0003] Nuclear power plant reactors usually use two types of neutron sources, namely primary neutron sources (252Cf) and secondary neutron sources (Sb-Be). Primary neutron sources are expensive and have a long half-life, and are generally only used in the first cycle of the reactor. Secondary neutron sources are cheap and have a short half-life, and need to be irradiated and activated in the reactor in advance for use in subsequent cycles. Summary of the Invention

[0004] This application provides an implementation method of a secondary neutron source assembly in the first cycle of a reactor to solve the problems of high cost and inconvenient use of primary neutron source assemblies.

[0005] The technical solution adopted by this application to solve its technical problems is as follows:

[0006] This application provides an implementation method of a secondary neutron source assembly in the first cycle of a reactor. The steps of the method include:

[0007] S1: Irradiate and activate the secondary neutron source assembly to be activated;

[0008] S2: Determine the arrangement position of the activated secondary neutron source assembly in the core of the first reactor according to the structure of the first reactor;

[0009] S3: Determine the time for the activated secondary neutron source assembly to enter the reactor based on the relevant time of the secondary neutron source assembly;

[0010] S4: Load the activated secondary neutron source assembly into the predetermined arrangement position in the core of the first reactor according to the time for entering the reactor.

[0011] In one embodiment, the step S1 includes:

[0012] Place the secondary neutron source assembly to be activated in the second reactor core for irradiation activation;

[0013] Alternatively, place the secondary neutron source assembly to be activated in a preset irradiation device for irradiation activation.

[0014] In one embodiment, the second reactor core includes a primary neutron source assembly and a secondary neutron source assembly; the step of placing the secondary neutron source assembly in the second reactor core for irradiation activation includes: replacing the secondary neutron source assembly to the position of the primary neutron source assembly in the second reactor core for irradiation activation;

[0015] The method further includes:

[0016] Place a plugging flow restrictor assembly at the corresponding position in the first reactor core according to the placement position of the primary neutron source assembly in the second reactor core.

[0017] In one embodiment, the structure of the first reactor includes the layout position of the core, the layout position of the control rod assembly, and the layout position of the RPN source range detector;

[0018] The step S2 includes:

[0019] S2-1: Obtain the position outside the control rod assembly according to the layout position of the control rod assembly;

[0020] S2-2: Obtain the outer ring position of the core according to the layout position of the core;

[0021] S2-3: Determine the preliminary position for arranging the secondary neutron source assembly according to the position outside the control rod assembly and the outer ring position of the core;

[0022] S2-4: Determine the final position of the secondary neutron source assembly according to the preliminary position and the RPN source range detector position.

[0023] In one embodiment, when the secondary neutron source assembly is placed in the second reactor core for irradiation activation, the relevant time of the secondary neutron source assembly includes: the time to unload the activated secondary neutron source in the second reactor, the time to transport the activated secondary neutron source assembly, the preset allowable interval time, and the decay period time of the secondary neutron source assembly;

[0024] The step S3 includes:

[0025] Based on the time to unload the activated secondary neutron source in the second reactor, the time to transport the activated secondary neutron source assembly, the preset allowable interval time, and the decay period time of the secondary neutron source assembly, determine the time for the activated secondary neutron source assembly to enter the reactor.

[0026] In one embodiment, the decay time of the secondary neutron source assembly includes the available time of the secondary neutron source after the second reactor stops irradiation. The method further includes:

[0027] Calculating the source strength of the secondary neutron source assembly to obtain the available time of the secondary neutron source after it stops irradiation in the second reactor.

[0028] In one embodiment, the calculating the source strength of the secondary neutron source assembly to obtain the available time of the secondary neutron source after it stops irradiation in the second reactor includes:

[0029] Obtaining reactor parameters and calculating the source strength of the secondary neutron source assembly according to the reactor parameters;

[0030] Calculating the count rate of the RPN source range detector according to the source strength of the secondary neutron source assembly;

[0031] Judging whether the count rate meets a preset minimum supervision requirement. If it meets, determining the available time of the secondary neutron source after it stops irradiation.

[0032] In one embodiment, the obtaining reactor parameters and calculating the source strength of the secondary neutron source assembly includes:

[0033] Obtaining reactor parameters and substituting the reactor parameters into the saturation activity formula to obtain the saturation activity of 124Sb;

[0034] Obtaining the sum of the absolute intensities of the effective γ-rays emitted by the preset 124Sb and substituting the saturation activity of 124Sb into the effective γ-ray source strength formula to obtain the source strength of the effective γ-rays;

[0035] Substituting the source strength of the effective γ-rays into the neutron source strength formula to obtain the neutron source strength of the secondary neutron source.

[0036] In one embodiment, the obtaining the sum of the absolute intensities of the effective γ-rays emitted by the preset 124Sb and substituting the saturation activity of 124Sb into the effective γ-ray source strength formula to obtain the source strength of the effective γ-rays includes:

[0037] Based on the neutron source strength of the secondary neutron source, using a Monte Carlo program to calculate the count rate measured by the RPN source range detector after the secondary neutron source assembly is in place at a specific position in the reactor core.

[0038] In one embodiment, the reactor parameters include the number of 123Sb atoms in the reactor, the neutron fluence rate, the cross-section of 123Sb reacting with neutrons to generate 124Sb, the decay constant of 124Sb, and the irradiation time;

[0039] The saturation activity formula includes:

[0040] A(t) = ΦσN 123Sb (1 - e -λt )

[0041] Wherein, A(t) is the saturation activity of 124Sb, Φ is the neutron fluence rate, σ is the cross-section for the reaction of 123Sb with neutrons to generate 124Sb, N 123Sb is the number of atoms of 123Sb, λ is the decay constant of 124Sb, and t is the irradiation time;

[0042] The formula for the effective γ-ray source strength includes:

[0043] S γ = A(t) × I γ

[0044] Wherein, S γ is the effective γ-ray source strength, A(t) is the saturation activity of 124Sb, and I γ is the sum of the absolute intensities of the effective γ-rays emitted by 124Sb;

[0045] The formula for the neutron source strength includes:

[0046] S n = Sn γ × S γ-n

[0047] Wherein, Sn is the neutron source strength, S γ is the effective γ-ray source strength, and S γ-n is the γ-n conversion factor.

[0048] Implementing the present application has the following beneficial effects: The present invention irradiates and activates the secondary neutron source assembly to be activated, determines its arrangement position and insertion time into the reactor core according to the structure and time requirements of the reactor, and finally loads the activated secondary neutron source assembly into the reactor core to obtain a neutron source solution that can effectively replace the primary neutron source and provide a sufficient neutron count rate in the first cycle of the reactor. This method solves the problems of limited supply and high cost of the primary neutron source, and the difficulty of the neutron detector to detect the neutron fluence rate level in the reactor core after a long-term reactor shutdown. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The following will further illustrate the present application in conjunction with the drawings. In the drawings:

[0050] Figure 1 is a schematic flow chart of the implementation method of the secondary neutron source assembly in the first cycle of the reactor provided by the present application;

[0051] Figure 2It is a schematic diagram of the position of the primary neutron source component in the second reactor core where the secondary neutron source component of this application is replaced;

[0052] Figure 3 It is the layout position of the activated secondary neutron source component of this application in the first reactor core;

[0053] Figure 4 It is a schematic diagram of the change curve of the 124Sb activity of this application with irradiation and decay time. Specific Embodiments

[0054] The following further details this application in conjunction with the accompanying drawings through specific embodiments. Similar components in different embodiments use related similar component numbers. In the following embodiments, many detailed descriptions are provided to enable a better understanding of this application. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to this application are not shown or described in the specification to avoid overwhelming the core part of this application with excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the descriptions in the specification and the general technical knowledge in the art.

[0055] It should be noted that for the primary neutron source: Usually, the primary neutron source of a reactor uses the californium source 252Cf (californium) that can spontaneously fission to generate neutrons. The half-life of 252Cf (californium) is 2.6 years. Each fission emits an average of 3.8 neutrons, and the average neutron energy is about 2 MeV. The design document of the first reactor requires using 3 groups of primary neutron sources in the first cycle.

[0056] Currently, only some countries in the world have the ability to commercially produce 252Cf (californium) raw materials. Moreover, the primary neutron source is expensive, and the primary neutron source can only be used for one cycle.

[0057] For the secondary neutron source: Usually, the secondary neutron source of a reactor consists of Sb - Be pellets stacked in a stainless steel cladding. The secondary neutron source does not produce neutrons initially and only becomes a neutron source after being irradiated by neutrons in the reactor: 123Sb (antimony) reacts with neutrons to form 124Sb (antimony), 124Sb (antimony) decays and releases γ - rays, and 9Be (beryllium) reacts with γ - rays to emit neutrons.

[0058] As Figure 1 shown, this application provides an implementation method of the secondary neutron source component in the first cycle of the reactor. The steps of the method include:

[0059] S1: Irradiate and activate the secondary neutron source assemblies to be activated.

[0060] Select the secondary neutron source assemblies to be activated. These assemblies are usually made of neutron source materials such as Sb-Be (antimony-beryllium). Then, send these assemblies to the determined irradiation unit for irradiation activation. The irradiation process needs to strictly control the irradiation dose and time to ensure that the secondary neutron source assemblies can reach the expected activation level. After irradiation, conduct necessary inspections and tests on the assemblies to verify their activation effects.

[0061] S2: Determine the arrangement positions of the activated secondary neutron source assemblies in the core of the first reactor according to the structure of the first reactor.

[0062] Based on the structural characteristics and design requirements of the first reactor, formulate an arrangement plan for the secondary neutron source assemblies in the core. The arrangement positions need to consider the radiation range of the neutron source, the neutron flux distribution in the core, and the safety operation requirements of the reactor. Through simulation analysis and optimized design, determine the optimal arrangement positions to ensure that the neutron source assemblies can fully play their roles.

[0063] S3: Determine the time for the activated secondary neutron source assemblies to be loaded into the reactor based on the relevant time of the secondary neutron source assemblies.

[0064] After determining the arrangement positions, it is necessary to determine the time for loading them into the reactor according to the relevant time factors of the secondary neutron source assemblies (such as half-life, post-irradiation cooling time, etc.). The selection of the loading time needs to ensure that the neutron source assemblies reach the optimal activation state before the reactor starts, and at the same time avoid adverse effects on the reactor operation caused by loading too early or too late. Through precise calculations and predictions, determine the optimal loading time window.

[0065] S4: Load the activated secondary neutron source assemblies into the pre-determined arrangement positions in the core of the first reactor according to the loading time.

[0066] According to the determined loading time, load the activated secondary neutron source assemblies into the pre-determined arrangement positions in the core of the first reactor. The loading process needs to strictly comply with the operating procedures and safety requirements to ensure that the assemblies can be accurately and stably installed in the designated positions. After loading, conduct necessary inspections and tests on the reactor to verify the installation effects of the neutron source assemblies and their impacts on the reactor operation.

[0067] The present application activates the secondary neutron source assembly by irradiation and arranges it reasonably in the reactor core, thereby effectively improving the monitoring capability of the neutron detector and ensuring that the reactor can accurately and reliably monitor the neutron injection rate level in the initial stage of startup. Compared with the primary neutron source, the secondary neutron source assembly has the advantages of low cost, easy acquisition and reusability, so the method of the present invention can significantly reduce the operating cost of the reactor. In addition, reasonable neutron source layout and pile entry time selection can also help enhance the safety and stability of the reactor and reduce the operating risks caused by insufficient neutrons. At the same time, by optimizing the layout and pile entry time of the neutron source assembly, it can be ensured that the reactor can quickly and smoothly reach a critical state during the startup process, thereby improving the operating efficiency of the reactor. In summary, the present invention provides an efficient, safe and economical solution for the first cycle operation of the reactor.

[0068] Further, step S1 includes:

[0069] placing the secondary neutron source assembly to be activated in the core of the second reactor for irradiation activation;

[0070] Alternatively, the secondary neutron source assembly to be activated is placed in a preset irradiation device for irradiation activation.

[0071] like Figure 2 As shown, further, the second reactor core includes a primary neutron source assembly and a secondary neutron source assembly; placing the secondary neutron source assembly in the second reactor core for irradiation activation includes:

[0072] Replacing the secondary neutron source assembly to the position of the primary neutron source assembly of the second reactor core for irradiation activation;

[0073] The method also includes:

[0074] According to the placement position of the primary neutron source assembly of the second reactor core, a matching choke assembly is placed at a corresponding position of the first reactor core.

[0075] In one embodiment, irradiation activation is performed in the second reactor core: a reactor that is already in operation or about to be in operation (referred to as the second reactor) is selected as the irradiation source. In the second reactor core, according to actual needs, the secondary neutron source assembly to be activated can be replaced in the position of the primary neutron source assembly for irradiation. This method utilizes the neutron radiation generated during the operation of the reactor, does not require additional irradiation equipment, and reduces costs.

[0076] In another embodiment, irradiation activation is performed in a preset irradiation device: a special irradiation device may be selected for irradiation activation, which generally has a controllable irradiation environment and dose, and can ensure that the secondary neutron source assembly reaches the expected activation level.

[0077] To ensure the integrity of the reactor core and the safety of the neutron source assembly, a plugging and flow-blocking plug assembly can be placed at the pre-determined layout position of the secondary neutron source assembly in the first reactor core. Among them, the position of the secondary source neutrons in the first reactor core is the corresponding position according to the placement position of the primary source neutrons in the second reactor core, or the position of the plugging and flow-blocking plug assembly is determined according to the structural characteristics of the first reactor. These plug assemblies are used to temporarily seal the layout position to prevent the coolant or other media in the core from flowing in, while maintaining the stability of the core structure.

[0078] As Figure 3 shown, further, the structure of the first reactor includes the layout position of the core, the layout position of the control rod assembly, and the layout position of the RPN source range detector;

[0079] Step S2 includes:

[0080] S2-1: Obtain the position outside the control rod assembly according to the layout position of the control rod assembly;

[0081] S2-2: Obtain the outer ring position of the core according to the layout position of the core;

[0082] S2-3: Determine the preliminary position for arranging the secondary neutron source assembly according to the position outside the control rod assembly and the outer ring position of the core;

[0083] S2-4: Determine the final position of the secondary neutron source assembly according to the preliminary position and the position of the RPN source range detector.

[0084] In one embodiment, according to the known layout position of the control rod assembly, the interfering area is excluded to ensure the safe placement of the secondary neutron source assembly. Secondly, the outer ring position of the core is clarified to avoid placing the secondary neutron source assembly in an area where the neutron detector may respond excessively. Then, after excluding the control rod assembly position and the outer ring position of the core, the layout position located inside the core and at a certain distance from the above areas is preliminarily determined. Finally, combining the preliminary position and the layout position of the RPN (reactor protection nuclear instrumentation system) source range detector, the final position of the secondary neutron source assembly is further adjusted and determined to ensure that the detector can accurately respond to the neutron level of the fuel assembly, while avoiding a large amount of absorption or reflection of neutrons by the substances in the reactor. As Figure 2 shown in the preferred embodiment of the present invention, 3 groups of activated secondary neutron source assemblies are carefully arranged at the G2, B9, and J14 positions of the core. These positions not only correspond to the positions of the primary neutron source assemblies in the original design, but also perfectly avoid the control rod assemblies, are not placed in the outermost ring of the core, and at the same time ensure the effectiveness of the RPN source range detector and the consistent symmetry of counting.

[0085] Further, when the secondary neutron source assembly is placed in the second reactor core for irradiation activation, the relevant times of the secondary neutron source assembly include: the time for discharging the activated secondary neutron source in the second reactor, the time for transporting the activated secondary neutron source assembly, the preset allowable interval time, and the decay time of the secondary neutron source assembly;

[0086] Step S3 includes:

[0087] Based on the time for discharging the activated secondary neutron source in the second reactor, the time for transporting the activated secondary neutron source assembly, the preset allowable interval time, and the decay time of the secondary neutron source assembly, determine the time for the activated secondary neutron source assembly to enter the reactor.

[0088] In one embodiment, the refueling time of the first reactor is set as A. The discharging time of the irradiated and activated secondary neutron source assembly in the operating unit is B. The time taken for transporting radioactive materials is 3 months. The time A should be within the interval [B + 3, B + 10]. Otherwise, a state of no available source will occur. Among them, 10 months is the preset allowable interval time.

[0089] Further, the decay time of the secondary neutron source assembly includes the available time of the secondary neutron source after the second reactor stops irradiation. The method further includes:

[0090] Calculate the source strength of the secondary neutron source assembly to obtain the available time of the secondary neutron source after it stops irradiation in the second reactor.

[0091] Further, calculating the source strength of the secondary neutron source assembly to obtain the available time of the secondary neutron source after it stops irradiation in the second reactor includes:

[0092] Obtain the reactor parameters and calculate the source strength of the secondary neutron source assembly according to the reactor parameters;

[0093] Calculate the count rate of the RPN source range detector according to the source strength of the secondary neutron source assembly;

[0094] Judge whether the count rate meets the preset minimum supervision requirement. If it meets, determine the available time of the secondary neutron source after it stops irradiation.

[0095] It should be noted that the preset minimum supervision requirement includes that the count rate of the RPN source range detector is at least 2 cps (counts 2 times per second). Through the above steps, it is ensured that the secondary neutron source assembly can still provide sufficient neutron source strength after the reactor shuts down, so as to maintain the effective supervision of the RPN system, while prolonging the service life of the assembly and improving the safety and economy of the reactor.

[0096] Further, obtaining the reactor parameters and calculating the source strength package of the secondary neutron source assembly includes:

[0097] Obtain the reactor parameters and substitute the reactor parameters into the saturation activity formula to obtain the saturation activity of 124Sb (antimony-124);

[0098] Obtain the sum of the absolute intensities of the effective γ-rays emitted by the preset 124Sb, and substitute the saturation activity of 124Sb into the effective γ-ray source strength formula to obtain the effective γ-ray source strength;

[0099] Substitute the effective γ-ray source strength into the neutron source strength formula to obtain the neutron source strength of the secondary neutron source.

[0100] Furthermore, the reactor parameters include the number of 123Sb atoms in the reactor, the neutron fluence rate, the cross-section for the reaction of 123Sb with neutrons to generate 124Sb, the decay constant of 124Sb, and the irradiation time;

[0101] The saturation activity formula includes:

[0102] A(t) = ΦσN 123Sb (1 - e -λt )

[0103] where A(t) is the saturation activity of 124Sb, Φ is the neutron fluence rate, σ is the cross-section for the reaction of 123Sb with neutrons to generate 124Sb, N 123Sb is the number of 123Sb atoms, λ is the decay constant of 124Sb, and t is the irradiation time;

[0104] The effective γ-ray source strength formula includes:

[0105] S γ = A(t) × I γ , where S γ is the effective γ-ray source strength, A(t) is the saturation activity of 124Sb, and Ⅰγ is the sum of the absolute intensities of the effective γ-rays emitted by 124Sb;

[0106] The neutron source strength formula includes:

[0107] S n = S γ × S γ-n

[0108] where Sn is the neutron source strength, S γ is the effective γ-ray source strength, and S γ-n is the γ-n conversion factor.

[0109] It should be noted that the reaction equations involved in the generation of neutrons by the secondary neutron source are as follows:

[0110]

[0111] It should be noted that in reaction formula (1): Antimony-123 absorbs a neutron and transforms into Antimony-124. In reaction formula (2): Antimony-124 undergoes beta decay, transforms into Tellurium-124, and simultaneously releases a beta particle and a gamma photon. In reaction formula (3): Beryllium-9 undergoes a photonuclear reaction after absorbing a gamma photon, transforms into Beryllium-8 and releases a neutron.

[0112] Assume that 123Sb in the secondary neutron source pellet is irradiated in the reactor core at a constant neutron fluence rate. The rate of change of the number of radioactive nuclide 124Sb atoms at a certain moment t is:

[0113]

[0114] In the formula, P is the production rate of 124Sb; D is the decay rate of 124Sb; Φ is the irradiation neutron fluence rate; λ is the decay constant of 124Sb; Na is the number of 123Sb atoms; σ is the cross-section of the reaction of 123Sb with neutrons to generate 124Sb.

[0115] Using the initial condition (at t = 0, N = 0), the activity of 124Sb in the secondary neutron source at the moment of stopping irradiation t can be obtained as:

[0116] A(t) = N a σΦ(1 - e -λt ) (5)

[0117] It can be seen that after a sufficiently long irradiation time, the activity of 124Sb will reach saturation. According to formula (5), the calculation formula for the saturation activity of 124Sb is:

[0118] A = N a σΦ (6) where, Na is the number of 123Sb atoms, σ is the cross-section of the reaction of 123Sb with neutrons to generate 124Sb. Φ is the irradiation neutron fluence rate.

[0119] According to the calculation formula for the saturation activity of 124Sb, the saturation activity of the secondary neutron source is proportional to the neutron fluence rate in the reactor core, and the neutron fluence rate in the core is usually proportional to the reactor power.

[0120] As Figure 4 shown, according to formula (5), an example of the curve of the activity of 124Sb changing with the irradiation time in the reactor core can be obtained (the abscissa is the number of half-lives of 124Sb, and the half-life of 124Sb is known to be 60.2 d), as Figure 4 shown by the blue solid line in the figure. After the reactor shuts down, 124Sb only decreases due to decay and does not increase due to irradiation. Therefore, the curve of the activity of 124Sb changing with the decay time is as Figure 4 shown by the green dashed line.

[0121] In a specific embodiment, calculating the source strength of the secondary neutron source assembly and determining its available time after stopping irradiation in the second reactor includes the following steps:

[0122] First step, calculate the saturation activity of \(^{124}Sb\): By simulating the neutron fluence rate spectrum of the secondary neutron source Sb-Be pellet and the nuclear reaction rate of \(^{123}Sb(n,\gamma)^{124}Sb\) through a Monte Carlo program, an equivalent microscopic cross-section \(\sigma\) of a group of \(^{123}Sb(n,\gamma)^{124}Sb\) nuclear reactions is obtained. The neutron fluence rate \(\varPhi\) is calculated through core nuclear design software. The saturation activity is \(A = N\) a \(\sigma\varPhi\).

[0123] Second step, calculate the effective gamma-ray source strength: The energy of the gamma-ray required for the \((\gamma,xn)\) reaction of \(Be-9\) is at least 1.6654 MeV. By referring to the nuclear database, it is known that the sum of the absolute intensities of the effective gamma-rays emitted by \(^{124}Sb\) is 53.58%. The effective gamma-ray source strength \(S_{\gamma}\) is: \(S_{\gamma}=A(t)\times0.5358\). Use the Monte Carlo method to perform photon transport calculations to obtain the effective gamma fluence rate spectrum inside the Sb-Be pellet.

[0124] Third step, calculate the neutron source strength: Using the effective gamma fluence rate spectrum obtained in the second step and the microscopic cross-section of the \(^{9}Be(\gamma,xn)\) reaction, calculate the reaction rate of the \(^{9}Be(\gamma,xn)\) nuclear reaction.

[0125] The neutron source strength \(S_{n}\) of the secondary neutron source is \(S\) n \(=S\) γ \(\times S\) γ-n , where \(S_{n}\) is the neutron source strength, \(S\) γ is the effective gamma-ray source strength, \(S\) γ-n is the \(\gamma - n\) conversion factor.

[0126] Fourth step, calculate the count rate of the RPN detector. According to the neutron source strength \(S_{n}\) obtained in the third step, use a Monte Carlo program to calculate the count rate of the RPN source range detector. If the count rate is greater than 2 cps, then the available time of the secondary neutron source after stopping irradiation is the time that satisfies this condition. After obtaining five half-lives according to the above steps, the activity of \(^{124}Sb\) is about 3.15% of the initial saturation activity. To ensure that the count rate is still greater than 2 cps even after the activity decreases after five half-lives, the above calculations need to be performed. If the refueling progress is delayed by more than 300 days, the activity of \(^{124}Sb\) will be lower than the level required to maintain 2 cps, affecting the effective supervision of the RPN detector. That is to say, the available time of the Sb-Be secondary neutron source after stopping irradiation is 300 days to ensure that the count rate of the RPN source range detector is greater than 2 cps.

[0127] During the transfer process, the activated secondary neutron source is unloaded and stored in the reactor spent fuel pool; transferred from the reactor spent fuel pool to the first reactor spent fuel pool for storage; and transferred from the first reactor spent fuel pool to the first reactor core.

[0128] Implementing this application has the following beneficial effects:

[0129] 1. Provide a method that enables the startup of the Hualong One reactor even without using the primary neutron source. The project of replacing the primary neutron source with the secondary neutron source in the first cycle of the Hualong One can solve the problem of the shortage of neutron sources.

[0130] 2. Compared with the primary neutron source scheme in the first cycle, this project can not only maintain the same safety level but also save high procurement costs, having economic advantages.

[0131] 3. The primary neutron source is no longer used after one cycle and will be disposed of as radioactive waste. The secondary neutron source is originally to be used in the subsequent cycles of the reactor. This project activates it in advance for the first cycle and cancels the primary neutron source. Therefore, this project can reduce the generation of radioactive waste and is beneficial to ecological environment protection.

[0132] It is understood that the above embodiments only represent the preferred implementation modes of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent; it should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, by freely combining the above technical features and making several deformations and improvements, these all fall within the protection scope of the present invention; therefore, all equivalent transformations and modifications made to the scope of the claims of the present invention shall fall within the scope covered by the claims of the present invention.

Claims

1. A method for implementing a secondary neutron source assembly in the first cycle of a reactor, characterized in that: The steps of the method include: S1: irradiating and activating the secondary neutron source assembly to be activated; S2: determining, according to the structure of the first reactor, the arrangement position of the activated secondary neutron source assembly in the core of the first reactor; S3: Determining the time for the activated secondary neutron source assembly to enter the stack based on the correlation time of the secondary neutron source assembly; S4: loading the activated secondary neutron source assembly into a predetermined arrangement position in the first reactor core according to the loading time.

2. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 1, characterized in that: The step S1 comprises: placing the secondary neutron source assembly to be activated in the second reactor core for irradiation activation; Alternatively, the secondary neutron source assembly to be activated is placed in a preset irradiation device for irradiation activation.

3. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 2, characterized in that: The second reactor core includes a primary neutron source assembly and a secondary neutron source assembly; placing the secondary neutron source assembly in the second reactor core for irradiation activation includes: replacing the secondary neutron source assembly to the position of the primary neutron source assembly of the second reactor core for irradiation activation; The method further comprises: According to the placement position of the primary neutron source assembly of the second reactor core, a matching choke assembly is placed at a corresponding position of the first reactor core.

4. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 1, characterized in that: The structure of the first reactor includes the arrangement position of the core, the arrangement position of the control rod assembly and the arrangement position of the RPN source range detector; The step S2 comprises: S2-1: acquiring a position outside the control rod assembly according to the arrangement position of the control rod assembly; S2-2: acquiring the outer ring position of the core according to the arrangement position of the core; S2-3: determining a preliminary position for arranging a secondary neutron source assembly according to a position outside the control rod assembly and an outer ring position of the core; S2-4: Determine the final position of the secondary neutron source assembly based on the preliminary position and the RPN source range detector position.

5. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 3, characterized in that: When the secondary neutron source assembly is placed in the core of the second reactor for irradiation activation, the relevant time of the secondary neutron source assembly includes: the time of unloading the activated secondary neutron source in the second reactor, the time of transporting the activated secondary neutron source assembly, the preset allowable interval time and the decay time of the secondary neutron source assembly; The step S3 comprises: The time for the activated secondary neutron source assembly to enter the reactor is determined based on the time for unloading the activated secondary neutron source in the second reactor, the time for transporting the activated secondary neutron source assembly, the preset allowable interval time and the decay time of the secondary neutron source assembly.

6. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 5, characterized in that: The decay time of the secondary neutron source assembly includes the available time of the secondary neutron source after the second reactor stops irradiating, and the method further includes: The source intensity of the secondary neutron source assembly is calculated to obtain the available time of the secondary neutron source after irradiation in the second reactor is stopped.

7. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 6, characterized in that: The calculating of the source intensity of the secondary neutron source assembly to obtain the available time of the secondary neutron source after stopping irradiation in the second reactor comprises: Acquiring reactor parameters, and calculating the source strength of the secondary neutron source assembly according to the reactor parameters; The count rate of the RPN source range detector is calculated according to the source intensity of the secondary neutron source assembly; it is determined whether the count rate meets the preset minimum supervision requirement, and if so, the available time of the secondary neutron source after stopping irradiation is determined.

8. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 7, characterized in that: The reactor parameters are obtained, and the secondary neutron source component source intensity package is calculated according to the reactor parameters: Acquiring reactor parameters, and substituting the reactor parameters into a saturation activity formula to obtain the saturation activity of 124Sb; Obtaining the sum of the absolute intensities of the effective gamma rays emitted by the preset 124Sb, and substituting the saturation activity of the 124Sb into the effective gamma ray source intensity formula to obtain the effective gamma ray source intensity; The effective gamma-ray source intensity is substituted into the neutron source intensity formula to obtain the neutron source intensity of the secondary neutron source.

9. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 8, characterized in that: The sum of the absolute intensities of the effective gamma rays emitted by the preset 124Sb is obtained, and the saturation activity of the 124Sb is substituted into the formula of the effective gamma ray source intensity to obtain the effective gamma ray source intensity, including: Based on the neutron source intensity of the secondary neutron source, a Monte Carlo program is used to calculate the count rate measured by the RPN source range detector after the secondary neutron source assembly is in place at a specific position in the core.

10. The method for implementing the secondary neutron source assembly in the first cycle of a reactor according to claim 9, characterized in that: The reactor parameters include the number of 123Sb atoms in the reactor, the neutron injection rate, the cross section of 123Sb reacting with neutrons to generate 124Sb, the decay constant of 124Sb and the irradiation time; The saturation activity formula includes: A(t)=ΦσN 123Sb (1-e -λt ) Where A(t) is the saturation activity of 124Sb, Φ is the neutron injection rate, σ is the cross section of the reaction between 123Sb and neutrons to generate 124Sb, and N 123Sb is the atomic number of 123Sb, λ is the decay constant of 124Sb, and t is the irradiation time; The effective gamma ray source intensity formula includes: S γ =A(t)×I γ Among them, S γ is the effective γ-ray source intensity, A(t) is the saturation activity of 124Sb, I γ It is the sum of the absolute intensities of the effective gamma rays emitted by 124Sb; The neutron source strength formula includes: S n =S γ ×S γ-n Among them, Sn is the neutron source strength, S γ is the effective γ-ray source intensity, S γ-n is the γ-n conversion factor.

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