Detector background noise determination method and system based on fitting extrapolation

Abstract

The present invention relates to a detector background noise determination method and system based on fitting extrapolation. A current signal during lifting of control rods can be used to perform fitting and extrapolation data processing, so as to obtain a background noise current value suitable for dynamic rod worth measurement of each group of control rods, thereby improving the precision of a dynamic rod worth measurement test. Due to the use of a fitting extrapolation method, it is not necessary for a unit to perform an additional specific operation, and it is also not necessary to perform measurement every time a control rod is inserted, so that a key path time of a physics startup test is not increased, and an accurate background noise value during dynamic rod worth measurement of each group of control rods can be obtained.

Description

Method and system for determining detector background noise based on fitting extrapolation

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310921077.1, filed on July 25, 2023, entitled “Method and system for determining detector background noise based on fitting extrapolation,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the technical field related to nuclear reactor reactivity measurement, and in particular to a method and system for determining detector background noise based on fitting extrapolation. Background Art

[0004] According to nuclear safety regulations, guidelines, and industry standards, after a nuclear reactor is completed or reloaded, and before it is recommissioned for normal operation, it must undergo a series of physical startup tests to verify the consistency of reactor characteristics with the physical design and the rationality of safety analysis assumptions. The results of physical startup tests are crucial to the design and operation of nuclear reactors. By utilizing advanced testing methods and technologies while ensuring test accuracy and reliability, efficiently completing physical startup tests can shorten the time a nuclear reactor is out of production and improve the economic efficiency of its operation.

[0005] The dynamic rod value measurement method is a relatively advanced physical startup test technique. During this process, the control rod assembly to be tested is continuously inserted into the reactor core, introducing a large amount of negative reactivity. This causes the core neutron flux rate to drop to a very low level, and the external detector current level, which serves as the input signal for reactivity measurement, to drop by 1 to 3 orders of magnitude. Under these circumstances, the impact of detector background noise on the measurement results becomes significant. Therefore, accurately determining the background noise level and eliminating it during the test is key to successfully completing control rod value measurements using the dynamic rod value measurement method.

[0006] During their research, the inventors discovered that some methods and technologies used in the industry to determine background noise have the following limitations:

[0007] The background noise detection method for the partial dynamic rod value measurement process assumes that the background noise is constant. Once the background noise compensation value is determined, it will not be adjusted during the subsequent low power physics test (LPPT).

[0008] Some methods require maintaining control rod insertion for extended periods or requiring measurement with each rod insertion. Another approach involves inserting a high-value control rod into the core and keeping it inserted for approximately half an hour. The average power range detector signal during this period is used as the background noise compensation value. This approach still assumes that background noise remains constant over time. Furthermore, it prolongs the critical path for nuclear power plant startup, impacting the economic viability of dynamic rod value measurement technology.

[0009] Summary of the Invention

[0010] In response to the shortcomings of the existing technology, the present invention provides a method and system for determining the detector background noise based on fitting extrapolation, which does not increase the critical path time of the physical startup test and can obtain the accurate value of the background noise during the dynamic rod value measurement of each group of control rods.

[0011] A first aspect of the present invention provides a method for determining detector background noise based on fitting extrapolation, comprising the following steps:

[0012] During the dynamic rod value measurement process, the control rod group for background noise measurement is selected;

[0013] After the control rod group selected for background noise measurement is fully inserted into the reactor core, it is kept in this state. The detection time is set to a period during which the detector current maintains a linear change pattern, and a data set of the detector current variation over time within the set detection time is obtained.

[0014] Based on the acquired data set, the relationship between the detector current and time is obtained by fitting;

[0015] Based on the fitted relationship, the background noise current value during the measurement process of the control rod group to be tested is calculated according to the time point when the control rod group to be tested completes the rod insertion.

[0016] Preferably, the calculated background noise current value is used as the compensation current in the measurement experiment of the control rod group to be tested, so as to obtain the control rod value measurement result.

[0017] Preferably, selecting a control rod group for background noise measurement includes: selecting a control rod group with a predicted value greater than 1β eff The background noise measurement is performed on the control rod group of the

[0018] Preferably, selecting the control rod group for background noise measurement includes: selecting the control rod group with the largest predicted control rod value and the position closest to the power range detector for background noise measurement.

[0019] Preferably, the current data set of the external power range detector is acquired while the control rods are kept in the inserted state and the core is in a stable subcritical state.

[0020] Preferably, the detection time is set to about 15 minutes.

[0021] Preferably, fitting the relationship between the detector current and time according to the acquired data set includes: selecting a time period in which the detector current variation trend is close to linear, and using the least squares method to linearly fit the linear relationship between the detector current and time.

[0022] Preferably, the method for determining the time point at which rod insertion is completed for the control rod group to be tested is: completing the dynamic rod value measurement test process for all control rod groups according to the test procedure, and recording the time point at which rod insertion is completed for each control rod group to be tested.

[0023] The second aspect of the present invention provides a detector background noise determination system based on fitting extrapolation, comprising: a power range detector, a control rod group for inserting into the core, and a processor; the processor is configured to execute the detector background noise determination method based on fitting extrapolation described in the first aspect of the present invention.

[0024] A third aspect of the present invention provides a detector background noise determination system based on fitting and extrapolation, comprising:

[0025] The measurement control rod group selection module is used to select the control rod group for background noise measurement during the dynamic rod value measurement process;

[0026] The detector current acquisition module is used to select a control rod group for background noise measurement, keep it in the inserted state after it is fully inserted into the core, set a detection time based on the period of time during which the detector current maintains a linear change pattern, and obtain a data set of the detector current variation over time within the set detection time;

[0027] A fitting module is used to fit the relationship between the detector current and time according to the acquired data set;

[0028] The background noise calculation module is used to calculate the background noise current value during the measurement process of the control rod group to be tested based on the relationship obtained by fitting and the time point when the control rod group to be tested completes the rod insertion.

[0029] The present invention's detector background noise determination method and system based on fitting and extrapolation simply requires that individual control rod groups remain inserted for a set period of time after completing a measurement test, and then fits the relationship between background noise and time. The background noise during the dynamic rod value measurement conforms to this fitting relationship, i.e., it varies over time according to this fitting relationship. Based on this fitting relationship, extrapolation is performed to directly calculate the corresponding background noise during the measurement of other control rod groups based on their insertion times. This eliminates the need for additional measurements and operations, thus preserving the economic benefits of the dynamic rod value measurement technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application.

[0031] FIG1 is a flow chart of a method for determining background noise according to a specific embodiment of the present invention.

[0032] FIG2 shows the current variation of the power range detector during a low power physical startup test according to a specific embodiment of the present invention;

[0033] FIG3 is a detector current variation curve amplified to a background level according to a specific embodiment of the present invention;

[0034] FIG4 is a schematic diagram of the basic process of a dynamic stick value measurement test according to a specific embodiment of the present invention;

[0035] FIG5 is an enlarged trend diagram of the detector current change during the dynamic rod value measurement test according to a specific embodiment of the present invention;

[0036] FIG6 is a schematic diagram of obtaining a background noise value by extrapolating the detector current recorded during the control rod insertion period according to a specific embodiment of the present invention;

[0037] FIG7 shows the control rod value measurement results obtained without background noise compensation;

[0038] FIG8 shows a control rod value measurement result obtained by performing background noise compensation according to FIG6 in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0040] Background noise, also known as background noise, is generally generated by the gamma rays produced by the activation of the core structural materials and the reaction with the sensitive body of the detector to produce a signal, or it is the electrical noise generated by the detector and its cables. It is a signal in the detector signal that does not change with the reactivity of the core but shows the law of neutron dynamics.

[0041] The inventors discovered limitations in some industry-developed methods and techniques for determining background noise. To address this, the present invention provides a method and system for determining detector background noise based on fitting and extrapolation. This method uses current signals from control rods during their insertion period to perform fitting and extrapolation data processing, deriving background noise current values ​​applicable to each group of control rods during dynamic rod value measurements, thereby improving the accuracy of dynamic rod value measurement tests.

[0042] Generally, source range, intermediate range and power range detectors are set outside the nuclear power plant. The physical startup test generally uses the power range detector as the test input signal. The detectors involved in the background noise determination method and system in the present invention all refer to power range detectors.

[0043] FIG1 is a flow chart of a method for determining background noise according to a specific embodiment of the present invention.

[0044] As shown in FIG1 , the detector background noise determination method based on fitting and extrapolation in this embodiment includes the following steps:

[0045] Step S1, during the dynamic rod value measurement process, a control rod group is selected for background noise measurement.

[0046] Step S2: After the control rod group selected for background noise measurement is fully inserted into the core, it is kept in the inserted state. The detection time (T1, T2) is set to a time period in which the detector current maintains a linear change law. The data set (t i , I i ). Where T1 is the start time of the detection time, T2 is the end time of the detection time, t i To set any moment within the detection time period, I i t i The detector current obtained at the moment.

[0047] Step S3, according to the acquired data set (t i , I i ), the relationship between the detector current and time is obtained by fitting I(t)=F(t).

[0048] Step S4: Based on the fitted relationship and according to the time point t(k) when the kth control rod group Bank is completed with respect to the control rod insertion, the background noise current value I(k) during the measurement process of the control rod group Bank is calculated.

[0049] Step S5: Using the calculated background noise current value as the compensation current in the measurement experiment of the control rod group to be tested, and obtaining the control rod value measurement result.

[0050] In this embodiment, the background noise determination process measures the background noise of a group of control rod groups. After completing the measurement test, individual rod groups are simply inserted for a set period of time. A time-varying relationship between the background noise and the time of the measurement is fitted. The background noise during the dynamic rod value measurement conforms to this fitted relationship, i.e., it varies over time according to the fitted relationship. Based on this fitted relationship, the background noise corresponding to the measurement of other rod groups is directly calculated based on the insertion time of the other rod groups. This eliminates the need for additional measurements and operations, and does not affect the economic benefits of the dynamic rod value measurement technique. This method is highly adaptable and is applicable to situations where background noise levels decrease, remain constant, or even increase over time due to various factors.

[0051] In the following embodiments, the experimental process of the background noise determination method is as follows.

[0052] After a nuclear reactor is built or reloaded, a series of physical startup tests are required before it is put back into normal operation to verify the consistency of the reactor characteristics with the physical design and the rationality of the safety analysis assumptions.

[0053] Figure 2 shows the current variation of the power range detector during a low-power physical startup test, and Figure 3 shows the current variation curve of the power range detector when zoomed in to the background level. Background noise, also known as the noise floor, is shown on the vertical axis in Figure 2. The vertical axis displays a relatively large range, while Figure 3 limits the display range to the noise floor range, thereby illustrating the noise floor's changing trend.

[0054] As shown in Figures 2 and 3, the horizontal axis indicates the four test phases (time periods) of the physical start-up test, with the vertical axis indicating the current value of the power range detector. The process of each phase is as follows:

[0055] Stage 1: reaching critical process;

[0056] Phase 2: Determine the Doppler hotspot, reactivity instrument calibration process, and terminal critical boron concentration measurement test process;

[0057] Phase 3: Dynamic rod value measurement test process;

[0058] Phase 4: Isothermal temperature coefficient measurement test.

[0059] As shown in Figures 2 and 3, during Phase 1, before the reactor reaches criticality, the power range detector current is close to the background level; during Phase 3, during the dynamic rod value measurement test, when the rod value to be measured is large (more than 1β eff), when the rod group to be tested remains fully inserted into the core, the current of the power range detector quickly drops to the background level, and then changes in a nearly linear trend; during the entire low-power physical startup test, the background current level of the power range detector shows a downward trend, and the trends in different time periods are close.

[0060] Based on the variation of the power range detector current in FIG2 and FIG3 during the low power physical startup test, the present invention proposes to utilize the reactor in a stable deep subcritical state (not less than 1β eff ) The data set of the power range detector current variation over time recorded during the working condition (t i ,I i ), the detector background noise current compensation value during the dynamic rod value measurement test of different rod groups is determined by linear fitting, interpolation or extrapolation, and then used for data processing of each rod group value measurement to obtain accurate rod group value measurement results.

[0061] The above-mentioned current data of the power range detector used for fitting and extrapolating can be measured before reaching the critical value, during the dynamic rod value measurement or after the dynamic rod value measurement, preferably in a time period close to the dynamic rod value measurement test.

[0062] FIG4 is a schematic diagram of the basic process of a dynamic stick value measurement test according to a specific embodiment of the present invention.

[0063] As shown in Figure 4, the horizontal axis represents time, the first vertical axis represents the power range detector current, and the solid line curve is the detector current curve; the second vertical axis represents reactivity, and the dashed line curve is the reactivity curve over time calculated by the inverse dynamic method based on the time trend of the detector current. The basic process of dynamic rod value measurement is as follows:

[0064] Step A1, initial operating condition: all control rod groups are lifted to the top of the reactor, leaving only a small number of control rods of the first group inserted into the core to control core criticality. The length of the small number of control rods inserted in the first group can be within the range of 30 to 75 pcm.

[0065] In step A2, the first set of control rods is lifted to the top of the reactor, so that the core has positive reactivity corresponding to the control rod insertion amount in step A1, and the current signal of the power range detector begins to rise continuously, as marked A2 in FIG4 .

[0066] Step A3: When the current signal of the power range detector increases to a predetermined level, which may be about 50% of the Doppler heating point, the Nth group of control rods is continuously inserted to the bottom of the reactor.

[0067] During the insertion of the control rod to the bottom of the reactor, the detector current first continues to rise because the core still has positive reactivity before the rod is inserted to subcriticality; then it decreases rapidly as the control rod continues to introduce negative reactivity, as marked A3 in Figure 4.

[0068] Step A4: Analyze the data during the rod insertion period to obtain the control rod value measurement results of the Nth group of control rods.

[0069] In step A5, the Nth set of control rods is raised to the top of the reactor. The core has positive reactivity. During this period, the power range detector current signal begins to rise. However, since the power range detector current is close to the background level, the rising rate is low, as marked A5 in Figure 4.

[0070] In step A6, as the current signal level of the power range detector increases, the current rising rate of the power range detector also increases and approaches a stable doubling period, as indicated by A6 in FIG4 .

[0071] In step A7, when the current signal of the power range detector increases to a predetermined level, which may be 50% of the Doppler heating point, the N+1th group of control rods is continuously inserted, and measurement of the N+1th group of control rods is started, as indicated by A7 in FIG. 4 . Steps A3 to A6 are repeated until the control rod values ​​of all control rod groups are measured.

[0072] FIG5 is an enlarged trend diagram of the detector current change during the dynamic rod value measurement test of Example 1 of the present disclosure.

[0073] Corresponding to the dynamic rod value measurement process in Figure 4, the power range detector current change trend after the reactor enters subcriticality is shown in Figure 5. The horizontal axis in the figure is marked with time, the first vertical axis represents the power range detector current, and the solid line curve is the detector current curve; the second vertical axis represents reactivity, and the dotted line curve is the reactivity curve. During the dynamic rod value measurement test, the power range detector current change showed the following characteristics:

[0074] Step B1: During the rod insertion period, the core neutron flux rate is high and the current of the external power range detector is still significantly higher than the background level. However, as the reactor subcriticality gradually deepens, the current of the external power range detector decreases rapidly, as shown by mark B1 in Figure 5;

[0075] Step B2: Before and after the rod insertion is completed, the reactor remains at a relatively deep subcriticality, the core neutron fluence rate continues to decrease, and the current of the external power range detector continues to decrease. However, as the chain fission reaction gradually weakens, the core neutron fluence rate drops to a low level, the background noise contribution increases, and the rate of decrease of the external power range detector current slows down, as shown by mark B2 in Figure 5;

[0076] Step B3: As time passes, the chain fission reaction gradually disappears, and the current of the external power range detector changes in a nearly linear trend, as shown by the mark B3 in FIG5 ;

[0077] In step B4, as the rod group to be tested is withdrawn, the reactor re-enters the critical state and has a small amount of positive reactivity, and the current of the external power range detector begins to rise, as marked B4 in FIG5 .

[0078] Based on the dynamic rod value measurement test process in Figures 4 and 5 and the corresponding power range detector current change trend after the reactor enters subcriticality, the out-of-core power range detector current data set (t i , I i ), perform fitting, extrapolation or interpolation to obtain the detector background noise current value I(k) during the test of each rod group.

[0079] FIG6 is a schematic diagram of obtaining a background noise value by extrapolating the detector current recorded during the control rod insertion period according to a specific embodiment of the present invention.

[0080] As shown in Figure 1 and Figure 6, the steps for determining the background noise current value I(k) are as follows:

[0081] Step S1: In the dynamic rod value measurement process, a control rod group Bank is selected for background noise measurement.

[0082] In step S1, select the predicted control stick value greater than 1β eff The background noise measurement was performed using a rod group.

[0083] In this embodiment, the control rod group Bank selects a group of control rods with the largest value and closer to the external detector used for the test, so that after the group of control rods is inserted into the core, the detector current drops to the background level more quickly.

[0084] Specifically, a control rod group having the largest predicted control rod value and the position closest to the power range detector may be selected.

[0085] Step S2: After the control rod set Bank selected for background noise measurement is fully inserted into the core, it is kept in the inserted state. The detection time (T1, T2) is set according to the time period in which the detector current maintains a linear change law. The data set (t i , I i ).

[0086] In step S2, the power range detector current data used for fitting and extrapolation can be measured before reaching the critical point, during the dynamic rod worth measurement, or after the dynamic rod worth measurement. It is advisable to measure it during a time period close to the dynamic rod worth measurement test, so as to ensure that the change trend of the detector current during this time period is representative of the change trend during the entire dynamic rod worth measurement period.

[0087] Specifically, as shown in Figure 6, during the dynamic rod worth measurement, after the control rod group selected for background noise measurement is fully inserted into the core, it continues to remain inserted. The detection time (T1, T2) is set based on the time period during which the detector current shows a linear change pattern, and a data set of the detector current changing with time (t i , I i ) within the set detection time is obtained;

[0088] As an embodiment, in step S2, a data set of the power range detector current changing with time (t eff , I i ) recorded during the period when the reactor is in a stable deep subcritical (not less than 1β i ) condition is selected;

[0089] In another embodiment, with the control rods remaining inserted and the core in a stable subcritical state, a data set of the off-core power range detector current (t i , I i ) is obtained. Specifically, after the dynamic rod worth measurement of the control rod group Bank is completed, the control rod group Bank is kept inserted within the set detection time, and a data set of the detector current changing with time during the detection period (t i , I i ) is obtained.

[0090] Among them, the set detection time is about 15 minutes, for example, it can be between 13 minutes and 17 minutes.

[0091] Step S3, based on the obtained data set (t i , I i ), the relationship between the detector current and time changing with time, I(t) = F(t), is obtained by fitting.

[0092] In step S3, based on the obtained data set (t i , I i ), to obtain the relationship between the detector current and time changing with time, a time period T1 < t < T2 where the change trend of the detector current is close to linear can be selected, and the least squares method is used for linear fitting to obtain the linear relationship between the detector current and time, that is, the fitting relationship I(t) = F(t) is obtained.

[0093] Step S4: Based on the fitted relationship and according to the time point t(k) when the kth control rod group Bank is completed with respect to the control rod insertion, the background noise current value I(k) during the measurement process of the control rod group Bank is calculated.

[0094] In step S4, the method for determining the time point at which the rod insertion of other control rod groups to be tested is to complete the dynamic rod value measurement test process of all rod groups according to the test procedures, and record the time point t(k) at which the rod insertion of each group of control rods to be tested Bank(k) is completed.

[0095] Using the fitted relationship I(t) = F(t), linear interpolation and extrapolation are performed to obtain the fitting value corresponding to the time point t(k) when each group of test rods Bank(k) completes the insertion, that is, the final background noise current value I k =F(t(k)).

[0096] Step S5: Using the calculated background noise current value as the compensation current in the measurement experiment of the control rod group to be tested, and obtaining the control rod value measurement result.

[0097] In step S5, for the dynamic bar value measurement test of the bar to be tested Bank(k), I k The data is analyzed as a compensation current to obtain the rod value measurement results.

[0098] As shown in FIG6 , the detector current varies linearly with time, that is, it conforms to the linear relationship of I(t)=F(t), and exhibits a linear relationship between T1 and T2 of the first control rod group.

[0099] Figure 7 shows the control rod value measurement results obtained without background noise compensation. Figure 8 shows the control rod value measurement results obtained by implementing background noise compensation according to Figure 6 in a specific embodiment of the present invention.

[0100] In Figures 7 and 8, the dark curves are the measured values ​​of the control rod values, and the light curves are the estimated values ​​of the control rod values. Comparing Figures 7 and 8, the comparison results show that the control rod value measurement results obtained in Figure 8 after determining the background noise and implementing compensation according to the method of Figure 6 are consistent with the estimated values.

[0101] The background noise determination method of this embodiment uses the data collected during the basic process of dynamic rod value measurement to analyze and obtain the accurate value of the detector background noise signal.

[0102] This method requires only that individual rod groups remain inserted for approximately 15 minutes after completing the measurement test. No additional measurements or manipulation are required, thus preserving the economic effectiveness of dynamic rod value measurement technology. The background noise determination principle involved in this method is simple and intuitive, the data analysis process is straightforward, and the results are reliable. This method is highly adaptable and can be applied to situations where background noise levels decrease, remain constant, or even increase over time due to various factors.

[0103] The present invention also provides a detector background noise determination system based on fitting extrapolation, comprising: a power range detector, a control rod group for inserting into the core, and a processor; the processor is configured to execute the detector background noise determination method based on fitting extrapolation of the above embodiment.

[0104] In another embodiment, the present invention further provides a detector background noise determination system based on fitting extrapolation, comprising:

[0105] The measurement control rod group selection module is used to select the control rod group for background noise measurement during the dynamic rod value measurement process;

[0106] The detector current acquisition module is used to select a control rod group for background noise measurement, keep it in the inserted state after it is fully inserted into the core, set a detection time based on the period of time during which the detector current maintains a linear change pattern, and obtain a data set of the detector current variation over time within the set detection time;

[0107] A fitting module is used to fit the relationship between the detector current and time according to the acquired data set;

[0108] The background noise calculation module is used to calculate the background noise current value during the measurement process of the control rod group to be tested based on the relationship obtained by fitting and the time point when the control rod group to be tested completes the rod insertion.

[0109] The present invention's detector background noise determination method and system based on fitting and extrapolation simply requires that individual control rod groups remain inserted for a set period of time after completing a measurement test, and then fits the relationship between background noise and time. The background noise during the dynamic rod value measurement conforms to this fitting relationship, i.e., it varies over time according to this fitting relationship. Based on this fitting relationship, extrapolation is performed to directly calculate the corresponding background noise during the measurement of other control rod groups based on their insertion times. This eliminates the need for additional measurements and operations, thus preserving the economic benefits of the dynamic rod value measurement technology.

[0110] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for determining detector background noise based on fitting extrapolation, characterized in that: The steps include: During the dynamic rod value measurement process, the control rod group for background noise measurement is selected; After the control rod group selected for background noise measurement is completely inserted into the core, the control rod group continues to be inserted, and the detection time is set according to the time period in which the detector current maintains a linear change law, and a data set of the detector current changing with time within the set detection time is obtained; According to the acquired data set, fitting is performed to obtain the relationship between the detector current and time; Based on the fitted relationship, the background noise current value during the measurement process of the control rod group to be tested is calculated according to the time point when the control rod group to be tested completes the rod insertion.

2. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: The calculated background noise current value is used as the compensation current in the measurement experiment of the control rod group to be tested, and the control rod value measurement result is obtained.

3. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: The step of selecting a control rod group for background noise measurement includes: selecting a control rod group with a predicted value greater than 1β eff The control rod group is used for background noise measurement.

4. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: The selecting of the control rod group for background noise measurement includes: selecting the control rod group with the largest predicted control rod value and the closest position to the power range detector for background noise measurement.

5. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: With the control rods kept inserted and the core in a stable subcritical state, a current data set of the external power range detector is obtained.

6. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: The detection time is set to be about 15 minutes.

7. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: The fitting of the relationship between the detector current and time according to the acquired data set includes: selecting a time period in which the detector current variation trend is close to linear, and using the least squares method for linear fitting to obtain a linear relationship between the detector current and time.

8. The detector background noise determination method based on fitting extrapolation according to claim 1, characterized in that: The method for determining the time point at which the control rod group to be tested completes the rod insertion is: according to the test procedure, the dynamic rod value measurement test process of all control rod groups is completed, and the time point at which each control rod group to be tested completes the rod insertion is recorded.

9. A detector background noise determination system based on fitting extrapolation, characterized in that: include: power range detectors, control rod sets for insertion into the core, and processors; The processor is configured to execute the detector background noise determination method based on fitting extrapolation according to claim 1.

10. A detector background noise determination system based on fitting extrapolation, characterized in that: include: A control rod group selection module is used to select a control rod group for background noise measurement during dynamic rod value measurement; A detector current acquisition module is used to select a control rod group for background noise measurement and keep it in the inserted state after it is fully inserted into the core, set the detection time according to the time period in which the detector current keeps a linear change law, and obtain a data set of the detector current changing with time within the set detection time; A fitting module is used to fit the relationship between the detector current and time according to the acquired data set; The background noise calculation module is used to calculate the background noise current value during the measurement process of the control rod group to be tested based on the relationship obtained by fitting and according to the time point when the control rod group to be tested completes the rod insertion.

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