Passive start-up simulation method and device for zero-power reactor

Abstract

The embodiment of the invention relates to the field of nuclear reactor testing, in particular to a passive starting simulation method and device of a zero-power reactor. According to the passive start simulation method and device of the zero-power reactor, the performance parameters and the physical parameters of the zero-power reactor are obtained, the Monte Carlo calculation model of the zero-power reactor is constructed according to the obtained parameters, and passive start of the Monte Carlo calculation model is started, so that the passive start simulation of the zero-power reactor is realized. According to the method, the process that a reactor is physically started only through spontaneous fission of nuclear fuel or multiplication of neutrons generated by reaction under the condition that a critical device does not have an external neutron source can be simulated, and the actual neutron density function in the reactor in the starting process can be determined in the simulation process so as to represent the change condition of the neutron level in the reactor; therefore, the scientificity and safety of the zero-power reactor design can be safely verified at low cost, and the understanding of operators on the passive start-up physical process can be deepened.

Description

Technical Field

[0001] The embodiments of this application relate to the field of nuclear reactor testing, and in particular to a passive start-up simulation method and apparatus for a zero-power reactor. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] A zero-power reactor is a nuclear reactor operating at extremely low power, primarily used for nuclear physics research and reactor design verification. Conventional research on zero-power reactors typically relies on an external neutron source for safe and controlled startup. While this standard operating procedure ensures the accuracy and repeatability of experiments, it cannot fully verify the reactor's inherent safety characteristics when all external support is lost. Therefore, research is needed on passive startup scenarios, i.e., physically starting the reactor without using an additional neutron source, to further verify the reactor design. Summary of the Invention

[0004] A brief overview of this application is provided below to offer a basic understanding of certain aspects thereof. It should be understood that this overview is not an exhaustive summary of the application. It is not intended to identify key or essential parts of the application, nor is it intended to limit its scope. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0005] This application provides a passive startup simulation method for a zero-power reactor, comprising the following steps: S10: determining the critical load, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor; S20: determining the actual geometry, fuel nuclear material, and reactivity control method of the zero-power reactor, and determining a Monte Carlo simulation model of the zero-power reactor based on the actual geometry, fuel nuclear material, and reactivity control method; S30: determining the backup reactivity of the Monte Carlo simulation model based on the critical load, nuclear fuel element, pellet value, and neutron kinetic parameters determined in step S10, and the Monte Carlo simulation model determined in step S20, and determining the in-reactor neutron level inflection point time of the Monte Carlo simulation model based on the backup reactivity; S40: determining the in-reactor neutron level inflection point time based on the in-reactor neutron level inflection point time. S10: Determine the maximum startup time probability density function of the Monte Carlo computational model at the specified time point; S50: Repeat steps S30-S40 to obtain the maximum startup time probability density function set corresponding to different backup reactivity; S60: Initiate the passive startup of the Monte Carlo computational model, determine the current core load of the Monte Carlo computational model, and determine the backup reactivity of the Monte Carlo computational model based on the current core load; S70: Determine the probability density function of the maximum startup time of this startup based on the backup reactivity of the Monte Carlo computational model; S80: Determine the maximum startup time of the Monte Carlo computational model for this startup based on the probability density function of this startup; S90: Determine the actual neutron density function of this startup based on the neutron dynamics parameters determined in step S10 and the maximum startup time determined in step S80.

[0006] This application, in another aspect, provides a passive start-up simulation device for a zero-power reactor, comprising: a zero-power reactor performance parameter determination module configured to determine the critical load, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor; a zero-power reactor physical parameter determination module configured to determine the actual geometry, fuel nuclear materials, and reactivity control method of the zero-power reactor; and a controller configured to determine a Monte Carlo calculation model of the zero-power reactor based on the actual geometry, fuel nuclear materials, and reactivity control method; determine the backup reactivity of the Monte Carlo calculation model based on the critical load, nuclear fuel elements, pellet value, neutron kinetic parameters, and the Monte Carlo calculation model; and determine the Monte Carlo calculation model based on the backup reactivity. The calculation process involves determining the time of the in-core neutron level inflection point in the Monte Carlo computational model; based on the time of the in-core neutron level inflection point, determining the probability density function of the maximum startup time for the Monte Carlo computational model; obtaining the set of maximum startup time probability density functions corresponding to different backup reactivity levels; initiating a passive startup of the Monte Carlo computational model, determining the current core load of the Monte Carlo computational model, and determining the backup reactivity of the Monte Carlo computational model based on the current core load; determining the probability density function of the maximum startup time for this startup based on the backup reactivity of the Monte Carlo computational model; determining the maximum startup time of the Monte Carlo computational model for this startup based on the probability density function of this startup; and determining the actual neutron density function for this startup based on the neutron dynamics parameters and the maximum startup time.

[0007] The passive startup simulation method for zero-power reactors provided in this application simulates the process of a critical device physically starting up without an external neutron source, relying solely on the spontaneous fission or reaction-generated neutrons from the nuclear fuel itself. This simulation allows for the determination of the actual neutron density function within the reactor during startup, characterizing the changes in neutron levels. This enables safe and low-cost verification of the scientific validity and safety of the zero-power reactor design. Furthermore, it provides researchers, students, and operators with opportunities to simulate the passive startup process, deepening their understanding of the physical processes involved.

[0008] The passive startup simulation device for zero-power reactors provided in the embodiments of this application acquires the performance parameters and physical parameters of the zero-power reactor, and constructs a Monte Carlo calculation model based on the acquired parameters to reproduce the neutron density change during the simulated passive startup process, thereby eliminating the need for actual startup tests and improving the efficiency and safety of reactor research and development design. Attached Figure Description

[0009] To further illustrate the above and other advantages and features of this application, the specific embodiments of this application will be described in more detail below with reference to the accompanying drawings. The drawings, together with the following detailed description, are included in and form a part of this specification. Elements having the same function and structure are indicated by the same reference numerals. It should be understood that these drawings only depict typical examples of this application and should not be considered as limiting the scope of this application.

[0010] Figure 1 This is a schematic diagram of the simulation results of the passive startup process of a zero-power reactor obtained according to the method provided in the embodiments of this application. Detailed Implementation

[0011] Exemplary embodiments of this application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0012] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the equipment structure and / or processing steps closely related to the solution according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0013] The following disclosure provides several different implementations or examples for carrying out this application. To simplify the disclosure of this application, specific examples of components and methods are described below. Of course, these are merely examples and are not intended to limit this application. In the description of the embodiments of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0014] Currently, when conducting passive start-up verification of zero-power reactors, the low reactor power level and correspondingly low neutron flux during the initial start-up significantly increase the requirements for detector sensitivity and external background noise. This can prevent the monitoring system from capturing the reactor's critical state in a timely and accurate manner, hindering operators' judgment of the actual core condition and potentially posing a criticality risk. There is currently no method to improve the safety of the passive start-up process for zero-power reactors.

[0015] To address the aforementioned problems, embodiments of this application provide a passive startup simulation method for a zero-power reactor, comprising the following steps: S10: determining the critical load, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor; S20: determining the actual geometry, fuel nuclear material, and reactivity control method of the zero-power reactor, and determining a Monte Carlo simulation model of the zero-power reactor based on the actual geometry, fuel nuclear material, and reactivity control method; S30: determining the backup reactivity of the Monte Carlo simulation model based on the critical load, nuclear fuel element, pellet value, and neutron kinetic parameters determined in step S10, and the Monte Carlo simulation model determined in step S20, and determining the in-pile neutron level inflection point time of the Monte Carlo simulation model based on the backup reactivity; S40: determining the in-pile neutron level inflection point time based on the in-pile neutron kinetic parameters; S50: Repeat steps S30-S40 to obtain the maximum startup time probability density function set corresponding to different backup reactivity; S60: Initiate the passive startup of the Monte Carlo computational model, determine the current core load of the Monte Carlo computational model, and determine the backup reactivity of the Monte Carlo computational model based on the current core load; S70: Determine the probability density function of the maximum startup time of this startup based on the backup reactivity of the Monte Carlo computational model; S80: Determine the maximum startup time of the Monte Carlo computational model for this startup based on the probability density function of this startup; S90: Determine the actual neutron density function of this startup based on the neutron dynamics parameters determined in step S10 and the maximum startup time determined in step S80.

[0016] The passive startup simulation method for zero-power reactors provided in this application simulates the process of a critical device physically starting up without an external neutron source, relying solely on the spontaneous fission or reaction-generated neutrons from the nuclear fuel itself. This simulation allows for the determination of the actual neutron density function within the reactor during startup, characterizing the changes in neutron levels. This enables safe and low-cost verification of the scientific validity and safety of the zero-power reactor design. Furthermore, it provides researchers, students, and operators with opportunities to simulate the passive startup process, deepening their understanding of the physical processes involved.

[0017] In some embodiments, step S90 further includes: S91: determining the ideal neutron density function for this startup based on the neutron dynamics parameters determined in step S10 and the maximum startup time determined in step S80; S92: determining the error function of the ideal neutron density function based on the passive startup in step S60; S93: determining the actual neutron density function for this startup based on the error function. Determining the actual neutron density function for this startup through the above steps better reflects the changes in in-core neutron density levels during actual zero-power reactor operation, allowing the simulation results to more accurately reflect the actual physical scenario.

[0018] Figure 1 This is a schematic diagram illustrating the simulation results of the passive startup process of a zero-power reactor obtained according to the method provided in the embodiments of this application. In some embodiments, such as... Figure 1 As shown, the black straight line represents the ideal neutron density change during this startup, the orange curve represents the actual neutron density change during this startup, and the time corresponding to the intersection of the dashed lines is the time of the in-reactor neutron level inflection point determined by step S91, denoted as . The corresponding neutron count rate is denoted as .

[0019] In some embodiments, in step S91, the time of the in-pile neutron level inflection point can be determined based on the maximum startup time. The time to reach the inflection point of the neutron level in the reactor refers to the time when the predetermined neutron count rate is reached. The time.

[0020] In some embodiments, in step S92, when the neutron count is less than When the error function uses a Poisson distribution; when the neutron count is greater than... When the error function is normal, a normal distribution is used.

[0021] In some embodiments, such as Figure 1 As shown, the passive boot process can be simulated in the following manner: As the dividing point, an exponential function is used for fitting. Neutron fluence rate over the previous time period; determined using point pile equations. The growth trend of neutron flux rate over the subsequent time period was determined, and the point pile equations were solved based on the neutron dynamics parameters determined in step S10.

[0022] In some embodiments, step S93 further includes: S931: a sampling error function to determine the error of the ideal neutron density function at each moment; S932: superimposing the error onto the ideal neutron density function to determine the actual neutron density function for this startup. By superimposing the sampled error values ​​onto the ideal neutron density function, the random errors or uncertainties present in the actual operation of a zero-power reactor can be simulated, and the physical laws can be reflected more accurately.

[0023] In some embodiments, step S70 further includes: S71: determining the position of the backup reactivity in the maximum startup time probability density function set in step S50 based on the backup reactivity of the current startup in the Monte Carlo calculation model; S72: determining the probability density function of the maximum startup time for this startup based on the position. By determining the maximum startup time probability density function corresponding to the backup reactivity in this startup from the maximum startup time probability density function set corresponding to different backup reactivity, it is beneficial to correct the probability density function of the maximum startup time, making it more consistent with the operating rules of a real zero-power reactor and reducing errors.

[0024] In some embodiments, step S72 further includes: S721: determining the first maximum start-up time and the second maximum start-up time closest to the location, wherein the location lies between the first maximum start-up time and the second maximum start-up time; S722: determining the maximum start-up time corresponding to the location based on the first maximum start-up time and the second maximum start-up time; S723: determining the probability density function of the maximum start-up time for this startup based on the maximum start-up time. By determining the adjacent maximum start-up time data of the location, and then determining the maximum start-up time corresponding to the location, the range of the probability density function of the maximum start-up time for this startup can be limited, making it more consistent with the operating rules of a real zero-power reactor.

[0025] In some embodiments, in step S722, interpolation is used to determine the maximum startup time corresponding to the location based on the first maximum startup time and the second maximum startup time. Using interpolation makes the maximum startup time more closely approximate the actual value.

[0026] In some embodiments, in step S722, the smaller difference between the first maximum startup time and the second maximum startup time and the backup responsiveness of the current startup can be selected to determine the maximum startup time corresponding to the location.

[0027] In some embodiments, step S723 further includes: S7231: adjusting the probability density function corresponding to the maximum startup time based on the maximum startup time; S7232: determining the probability density function of the maximum startup time for this startup based on the adjusted probability density function. This helps to correct the probability density function of the maximum startup time, making it more consistent with the operating characteristics of a real zero-power reactor and reducing errors.

[0028] In some embodiments, in step S7231, the probability density function corresponding to the adjusted maximum startup time is determined using the following relationship. ;in, This represents the adjusted probability density function. Indicates the first maximum startup time. Indicates the second maximum startup time. This indicates the maximum startup time at the current location. Indicates confirmation and closest The function, where t represents time. Let represent the coefficients of the polynomial, i represent the degree of the polynomial, and k represent the maximum degree of the polynomial used in the polynomial fitting. Using polynomial fitting yields the probability density function corresponding to the maximum start-up time, which, compared to linear fitting, can reflect complex nonlinear trends.

[0029] In some embodiments, in step S7231, the adjusted probability density function is the probability density function of the maximum startup time for this startup.

[0030] In some embodiments, in step S10, the critical load, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor are set to predetermined values ​​according to actual needs. For example, a criticality experiment can be conducted on a prototype zero-power reactor to measure the critical load, nuclear fuel element value, pellet value, and neutron kinetic parameters, so that the subsequently constructed Monte Carlo calculation model is closer to reality.

[0031] In some embodiments, step S30 may further include the following steps: S31: Determine a predetermined core loading configuration based on the critical loading, nuclear fuel element value, pellet value, and neutron dynamics parameters (e.g., measurements from criticality experiments conducted on a prototype zero-power reactor) determined in step S10; S32: Determine the backup reactivity under the predetermined core loading configuration using a Monte Carlo model; S33: Based on the backup reactivity determined in step S32, simulate the neutron density changes and the timing of the neutron level inflection point during the passive startup process for the corresponding core loading configuration in a predetermined manner (e.g., Monte Carlo direct simulation). The neutron density changes under the predetermined core loading configuration can be obtained in the above manner.

[0032] In some embodiments, step S40 may further include the following steps: S41: fitting a probability density function of the time of the in-pile neutron level inflection point; S42: determining the maximum startup time based on the probability density function of the time of the in-pile neutron level inflection point determined in step S41; S43: determining the probability density function of the maximum startup time based on the probability density function of the time of the in-pile neutron level inflection point determined in step S41 and the maximum startup time.

[0033] In some embodiments, in step S42, the probability density function of the time of the neutron level inflection point in the reactor can be integrated, and the time when the difference between the integrated probability density function value and the probability density function value corresponding to the initial time reaches 99% can be set as the maximum start time.

[0034] In some embodiments, in step S43, a database can be constructed based on the probability density function of the time of the in-pile neutron level inflection point and the maximum startup time as a data source for interpolation in step S722.

[0035] In some embodiments, in step S50, the core loading mode predetermined in step S30 is set to multiple modes, and steps S30-S40 are repeated to obtain multiple neutron density change samples and time samples of neutron level inflection points in the reactor core under different backup reactive core loading modes, thereby increasing the data source of the maximum start-up time probability density function set and making the maximum start-up time probability density function more consistent with the operation law of zero-power reactor.

[0036] In some embodiments, in step S80, the probability density function of the maximum startup time determined in step S70 can be sampled to determine the maximum startup time for this startup.

[0037] Another embodiment of this application provides a passive start-up simulation device for a zero-power reactor, comprising: a zero-power reactor performance parameter determination module configured to determine the critical load, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor; a zero-power reactor physical parameter determination module configured to determine the actual geometry, fuel nuclear materials, and reactivity control mode of the zero-power reactor; and a controller configured to determine a Monte Carlo calculation model of the zero-power reactor based on the actual geometry, fuel nuclear materials, and reactivity control mode; determine the backup reactivity of the Monte Carlo calculation model based on the critical load, nuclear fuel elements, pellet value, neutron kinetic parameters, and the Monte Carlo calculation model; and determine the Monte Carlo calculation model's backup reactivity based on the backup reactivity. The Monte Carlo computational model is used to determine the in-core neutron level inflection point time; based on the in-core neutron level inflection point time, the maximum startup time probability density function of the Monte Carlo computational model is determined; and the maximum startup time probability density function set corresponding to different backup reactivity is obtained; a passive startup of the Monte Carlo computational model is initiated, the current core load of the Monte Carlo computational model is determined, and the backup reactivity of the Monte Carlo computational model is determined based on the current core load; based on the backup reactivity of the Monte Carlo computational model for this startup, the probability density function of the maximum startup time for this startup is determined; based on the probability density function of this startup, the maximum startup time of the Monte Carlo computational model for this startup is determined; and based on the neutron dynamics parameters and the maximum startup time, the actual neutron density function for this startup is determined.

[0038] The passive startup simulation device for zero-power reactors provided in the embodiments of this application acquires the performance parameters and physical parameters of the zero-power reactor, and constructs a Monte Carlo calculation model based on the acquired parameters to reproduce the neutron density change during the simulated passive startup process, thereby eliminating the need for actual startup tests and improving the efficiency and safety of reactor research and development design.

[0039] Regarding the embodiments of this application, it should also be noted that, without conflict, the embodiments of this application and the features in the embodiments can be combined with each other to obtain new embodiments.

[0040] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. The scope of protection of this application shall be determined by the scope of the claims.

Claims

1. A passive start-up simulation method for a zero-power reactor, characterized in that, It includes the following steps: S10: Determine the critical loading, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor; S20: Determine the actual geometric dimensions, fuel and nuclear materials, and reactivity control method of the zero-power reactor; and determine the Monte Carlo calculation model of the zero-power reactor based on the actual geometric dimensions, fuel and nuclear materials, and reactivity control method of the zero-power reactor. S30: Based on the critical loading, nuclear fuel elements, pellet value, and neutron dynamics parameters determined in step S10, and the Monte Carlo calculation model determined in step S20, determine the backup reactivity of the Monte Carlo calculation model, and based on the backup reactivity, determine the time of the in-pile neutron level inflection point of the Monte Carlo calculation model. S40: Determine the maximum startup time probability density function of the Monte Carlo computation model based on the time of the in-pile neutron level inflection point; S50: Repeat steps S30-S40 to obtain the maximum start-up time probability density function set corresponding to different backup responsiveness; S60: Initiate the passive startup of the Monte Carlo computing model, determine the current core load of the Monte Carlo computing model, and determine the backup reactivity of the Monte Carlo computing model based on the current core load; S70: Determine the probability density function of the maximum startup time for this startup based on the backup responsiveness of the current startup in the Monte Carlo calculation model; S80: Determine the maximum startup time of the Monte Carlo computation model for this startup based on the probability density function of this startup; S90: Based on the neutron dynamics parameters determined in step S10 and the maximum start-up time determined in step S80, determine the actual neutron density function for this start-up.

2. The method according to claim 1, characterized in that, Step S90 also includes: S91: Determine the ideal neutron density function for this startup based on the neutron dynamics parameters determined in step S10 and the maximum startup time determined in step S80. S92: Determine the error function of the ideal neutron density function according to the passive initiation described in step S60; S93: Determine the actual neutron density function for this startup based on the error function.

3. The method according to claim 2, characterized in that, Step S93 also includes: S931: Sample the error function to determine the error of the ideal neutron density function at each time step; S932: The error is superimposed on the ideal neutron density function to determine the actual neutron density function for this startup.

4. The method according to claim 1, characterized in that, Step S70 also includes: S71: Based on the backup responsiveness of the current startup of the Monte Carlo calculation model, determine the position of the backup responsiveness in the maximum startup time probability density function set in step S50; S72: Based on the location, determine the probability density function of the maximum startup time for this startup.

5. The method according to claim 4, characterized in that, Step S72 also includes: S721: Based on the location, determine the first maximum startup time and the second maximum startup time that are closest to the location, wherein the location is located between the first maximum startup time and the second maximum startup time; S722: Determine the maximum startup time corresponding to the position based on the first maximum startup time and the second maximum startup time; S723: Determine the probability density function of the maximum startup time for this startup based on the maximum startup time.

6. The method according to claim 5, characterized in that, In step S722, an interpolation method is used to determine the maximum startup time corresponding to the position based on the first maximum startup time and the second maximum startup time.

7. The method according to claim 6, characterized in that, Step S723 also includes: S7231: Adjust the probability density function corresponding to the maximum startup time according to the maximum startup time; S7232: Determine the probability density function of the maximum startup time for this startup based on the adjusted probability density function.

8. The method according to claim 7, characterized in that, In step S7231, the probability density function corresponding to the adjusted maximum startup time is determined using the following relationship. ； in, This represents the adjusted probability density function. This indicates the first maximum startup time. This indicates the second maximum startup time. This indicates the maximum startup time at the current location. Indicates confirmation and closest The function, where t represents time. Let represent the coefficients of the polynomial, i represent the degree of the polynomial, and k represent the maximum degree of the polynomial used in the polynomial fitting.

9. The method according to claim 8, characterized in that, In step S7231, the adjusted probability density function is the probability density function of the maximum startup time for this startup.

10. A passive start-up simulation device for a zero-power reactor, characterized in that, It includes: A zero-power reactor performance parameter determination module is configured to determine the critical loading, nuclear fuel element value, pellet value, and neutron kinetic parameters of the zero-power reactor. The zero-power reactor physical parameter determination module is configured with the actual geometric dimensions, fuel nuclear materials, and reactivity control method of the zero-power reactor. A controller configured to determine a Monte Carlo calculation model of the zero-power reactor based on the actual geometry, fuel nuclear materials, and reactivity control method of the zero-power reactor; Based on the critical loading, nuclear fuel elements, pellet value, and neutron kinetic parameters, as well as the Monte Carlo calculation model, the backup reactivity of the Monte Carlo calculation model is determined. Based on the backup reactivity, the timing of the in-pile neutron level inflection point of the Monte Carlo computational model is determined; Based on the time of the in-pile neutron level inflection point, the maximum startup time probability density function of the Monte Carlo computational model is determined; and the set of maximum startup time probability density functions corresponding to different backup reactivity is obtained. Initiate the passive startup of the Monte Carlo computing model, determine the current core load of the Monte Carlo computing model, and determine the backup reactivity of the Monte Carlo computing model based on the current core load. Based on the backup responsiveness of this startup in the Monte Carlo computational model, determine the probability density function of the maximum startup time for this startup; Based on the probability density function of this startup, determine the maximum startup time of the Monte Carlo computation model for this startup; Based on the neutron dynamics parameters and the maximum start-up time, the actual neutron density function for this start-up is determined.

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