Radiation field data correction method based on region gamma and neutron measured value

Abstract

The embodiment of the invention provides a radiation field data correction method based on a region gamma and neutron measured value, and the method comprises the steps: carrying out the theoretical calculation of a radiation field, and calculating a gamma-ray source item, a primary shielding gamma-ray source item and a primary shielding neutron source item which are decayed from N-16 radionuclide in a coolant pipeline in a region of interest during normal operation; establishing an equipment model in the region, and establishing a geometric model according to equipment and materials arranged in the region; carrying out transport calculation on gamma rays and neutrons in a radioactive source item in the whole region by using a set calculation mode, calculating by using an Fmesh counting card, and obtaining a gamma radiation field and a neutron radiation field in the region during normal operation in the region by using the size of a grid and the size of a detection device; and according to the measured values of the plurality of detection devices arranged in the region and the theoretical values of the radiation fields of the corresponding monitoring points, a least square method is utilized to solve a correction coefficient, all theoretical radiation field data is corrected, and a corrected region radiation field is obtained.

Description

Technical Field

[0001] The invention relates to the field of radiation protection technology, in particular to a radiation field data correction method based on regional gamma and neutron measured values. Background Art

[0002] In order to understand the size of the radiation field in the entire area during normal operation and after shutdown, the Monte Carlo transport calculation of the radioactive source term can be performed through modeling to obtain the theoretical radiation field of a certain area. However, since the Monte Carlo transport calculation is time-consuming and takes a long time, up to several months, the calculation result can only be used as a reference database and cannot reflect the actual radiation field that is changing all the time. In addition, detection devices are set up in the area to measure the dose rate at the location in real time, but due to the limitations of space and other conditions, it is impossible to set up an infinite number of detection devices to measure the regional radiation field. Therefore, in order to understand the regional radiation field under the current operating conditions, the current limited number of actual measurement values ​​can be used to use a mathematical method to correct the theoretically calculated radiation field so that the radiation field data is closer to the actual data. Summary of the invention

[0003] In view of the above-mentioned problems existing in the prior art, an embodiment of the present invention provides a radiation field data correction method based on the regional γ and neutron measured values. Based on the regional γ and neutron measured values, the theoretically calculated radiation field is corrected to provide support for obtaining a more accurate radiation field.

[0004] The embodiment of the present invention provides a radiation field data correction method based on regional gamma and neutron measured values, comprising:

[0005] Step 1: Perform theoretical calculation of the radiation field, which specifically includes:

[0006] Perform source term calculation to calculate the radioactive source term in the area of ​​interest during normal operation, wherein the source term at least includes a gamma ray source term generated by the decay of N-16 radioactive nuclides in the coolant pipeline, a primary shielding gamma ray source term, and a primary shielding neutron source term;

[0007] Establish equipment models in the area, and establish geometric models based on the equipment and materials arranged in the area to prepare for the transport of gamma rays and neutrons in the area;

[0008] Carry out transport calculations within the region, including using the set calculation method to calculate the transport of gamma rays and neutrons in the radioactive source term within the entire region. The calculation uses an Fmesh counting card, and the mesh size is equivalent to the size of the detection device, thereby obtaining the gamma radiation field and neutron radiation field within the region when the region is operating normally;

[0009] Step 2: Perform radiation field correction, including using the least squares method to calculate the correction coefficient based on the measured values ​​of multiple detection devices set up in the area and the theoretical values ​​of the radiation field at the corresponding monitoring points, and correcting all theoretical radiation field data to obtain the corrected regional radiation field.

[0010] In some embodiments of the present invention, the gamma-ray source term includes a gamma-ray source within the stack and a gamma-ray source within the coolant.

[0011] In some embodiments of the present invention, gamma rays from a gamma ray source within the stack pass through the fuel cladding, the pressure vessel, and the primary shield to reach the outer surface of the primary shield. The gamma ray source term on the outer surface of the primary shield can be calculated using source term calculation software.

[0012] In some embodiments of the present invention, the gamma-ray source in the coolant includes a gamma-ray source in the coolant pipe and a gamma-ray source on the primary side of the evaporator;

[0013] The source term calculation software was used to calculate the specific activity of N-16 radioactivity at different locations in the coolant pipe when operating at full power;

[0014] Among them, when N-16 decays, it emits 6.13MeV and 7.11MeV gamma photons in a ratio of 67:5, based on which the N-16 decay gamma ray source terms at different positions in the coolant pipeline are obtained.

[0015] In some embodiments of the present invention, neutrons in the stack pass through the fuel cladding, the pressure vessel, the primary shield and finally reach the outer surface of the primary shield. The neutron source term of the outer surface of the primary shield can be calculated using source term calculation software.

[0016] In some embodiments of the present invention, the source card of MCNP is established by using N-16 decay gamma ray source terms at different positions in the coolant pipeline, shielding the outer surface gamma ray source term once and shielding the neutron source term once;

[0017] Use the Fmesh card to divide the regional space into small grids, calculate the radiation field in the region, and obtain the radiation field intensity R N-16 -xyz,R γ -xyz,R n -xyz;

[0018] Finally, the γ radiation field in the area under full power normal operation is obtained as (R N-16 -xyz+R γ -xyz), the neutron radiation field is R n -xyz.

[0019] In some embodiments of the present invention, the radiation field at different powers is obtained by multiplying the value of the neutron radiation field by a power proportional factor.

[0020] Compared with the prior art, the radiation field data correction method based on regional γ and neutron measured values ​​provided by the embodiment of the present invention has the beneficial effect that it uses the least squares method based on regional γ and neutron measured values ​​to correct the theoretically calculated radiation field, providing support for obtaining a more accurate radiation field. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A calculation flow chart of a radiation field data correction method based on regional gamma and neutron measured values ​​provided in an embodiment of the present invention;

[0022] Figure 2 The radiation field data after correction for a certain section of the Z axis and the theoretical radiation field data diagram in the radiation field data correction method based on regional gamma and neutron measured values ​​provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0024] Various aspects and features of the present application are described herein with reference to the accompanying drawings.

[0025] These and other characteristics of the present application will become apparent from the following description of a preferred form of embodiment given as a non-limiting example with reference to the accompanying drawings.

[0026] It should also be understood that, although the present application has been described with reference to some specific examples, those skilled in the art will be able to realize many other equivalent forms of the present application that have the features described in the claims and are therefore within the scope of protection defined thereby.

[0027] The above and other aspects, features and advantages of the present application will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings.

[0028] Specific embodiments of the present application are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments applied for are merely examples of the present application, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to determine the true intent based on the user's historical operations and to avoid unnecessary or redundant details that make the present application unclear. Therefore, the specific structural and functional details applied for herein are not intended to be limiting, but are merely used as the basis and representative basis for the claims to teach those skilled in the art to use the present application in a variety of ways with substantially any suitable detailed structure.

[0029] This specification may use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," all of which may refer to one or more of the same or different embodiments according to the present application.

[0030] The embodiment of the present invention provides a radiation field data correction method based on regional gamma and neutron measured values, comprising:

[0031] Step 1: Perform theoretical calculation of the radiation field, which specifically includes:

[0032] Perform source term calculation to calculate the main radioactive source terms in the area of ​​concern during normal operation, wherein the source terms at least include the gamma ray source term generated by the decay of N-16 radioactive nuclides in the coolant pipeline, the primary shielding gamma ray source term, and the primary shielding neutron source term;

[0033] Establish equipment models in the area, and establish geometric models based on the equipment and materials arranged in the area to prepare for the transport of gamma rays and neutrons in the area;

[0034] Carry out transport calculations within the region, including using the set calculation method to calculate the transport of gamma rays and neutrons in the radioactive source term within the entire region. The calculation uses an Fmesh counting card, and the mesh size is equivalent to the size of the detection device, thereby obtaining the gamma radiation field and neutron radiation field within the region when the region is operating normally;

[0035] Step 2: Perform radiation field correction, including using the least squares method to calculate the correction coefficient based on the measured values ​​of multiple detection devices set up in the area and the theoretical values ​​of the radiation field at the corresponding monitoring points, and correcting all theoretical radiation field data to obtain the corrected regional radiation field.

[0036] In some embodiments of the present invention, the gamma-ray source term includes a gamma-ray source within the stack and a gamma-ray source within the coolant.

[0037] The gamma rays from the gamma-ray source in the reactor pass through the fuel cladding, pressure vessel, primary shielding and reach the outer surface of the primary shielding. The gamma-ray source term on the outer surface of the primary shielding can be calculated using the source term calculation software.

[0038] The gamma ray source in the coolant includes a gamma ray source in the coolant pipe and a gamma ray source on the primary side of the evaporator;

[0039] The source term calculation software was used to calculate the radioactive specific activity of N-16 at different positions in the coolant pipeline when operating at full power. Among them, N-16 emits 6.13MeV and 7.11MeV gamma photons in a ratio of 67:5 when it decays, and the gamma ray source terms of N-16 decay at different positions in the coolant pipeline are obtained based on this.

[0040] In this embodiment, neutrons in the stack pass through the fuel cladding, the pressure vessel, the primary shield and finally reach the outer surface of the primary shield. The neutron source term of the outer surface of the primary shield can be calculated using the source term calculation software.

[0041] The source card of MCNP is established by using the N-16 decay γ-ray source term at different positions in the coolant pipe, shielding the outer surface γ-ray source term once and shielding the neutron source term once;

[0042] Use the Fmesh card to divide the regional space into small grids, calculate the radiation field in the region, and obtain the radiation field intensity R N-16 -xyz,R γ -xyz,R n -xyz;

[0043] Finally, the γ radiation field in the area under full power normal operation is obtained as (R N-16 -xyz+R γ -xyz), the neutron radiation field is R n -xyz.

[0044] The radiation field at different powers is obtained by multiplying the value of the neutron radiation field by the power proportional factor.

[0045] In order to facilitate the understanding of the above technical solution, the following is a description with reference to the accompanying drawings and examples, as follows:

[0046] This method is mainly carried out according to the following process: Figure 1 As shown below, the calculation of regional γ radiation field correction during normal operation is taken as an example:

[0047] Source Term Calculation

[0048] (1) γ-ray source

[0049] The gamma-ray sources include the gamma-ray sources in the reactor and the gamma-ray sources in the coolant. The gamma-rays in the reactor pass through the fuel cladding, pressure vessel, and primary shield to reach the outer surface of the primary shield. The gamma-ray source term of the outer surface of the primary shield can be calculated using the source term calculation software. The gamma-ray sources in the coolant are mainly the gamma-ray sources in the coolant pipes and the gamma-ray sources on the primary side of the evaporator. The source term calculation software is used to calculate the specific activity of N-16 radioactivity at different positions in the coolant pipes when operating at full power. When N-16 decays, it emits 6.13MeV and 7.11MeV gamma photons in a ratio of 67:5. Based on this, the gamma-ray source terms of N-16 decay at different positions in the coolant pipes can be obtained.

[0050] (2) Neutron source term

[0051] Similar to the gamma-ray source inside the reactor, the neutrons inside the reactor pass through the fuel cladding, pressure vessel, primary shielding and finally reach the outer surface of the primary shielding. The neutron source term on the outer surface of the primary shielding can be calculated using the source term calculation software.

[0052] Build models of various equipment in the cabin

[0053] According to the equipment and materials arranged in the area, a geometric model is established to prepare for particle transport calculations.

[0054] Carry out transport calculations within the region

[0055] The N-16 decay γ-ray source items at different positions in the coolant pipeline are used to shield the outer surface γ-ray source items once and the neutron source items once. The source card of MCNP is established, and the regional space is divided into small grids using the Fmesh card. The radiation field in the area is calculated to obtain the radiation field intensities R N-16-xyz, Rγ-xyz, and R n-xyz.

[0056] Finally, the gamma radiation field in the area under full power normal operation is (R N-16-xyz+Rγ-xyz), and the neutron radiation field is R n-xyz. The radiation field under different powers can be obtained by multiplying this value by the power proportional factor.

[0057] 4) Data correction

[0058] The main purpose of the correction algorithm is to correct the radiation field calculation data based on the actual monitoring data, reduce the errors caused by the calculation conditions and calculation process, and make the final data used for analysis closer to the actual data.

[0059] Correction algorithm:

[0060] When making corrections, you need to understand the relevant methods, the characteristics of the Monte Carlo theory for calculating the radiation field, the relevant data interpolation simulation methods, and the characteristics of the measured values:

[0061] The characteristics of Monte Carlo theory for calculating radiation fields are as follows:

[0062] 1): The results of theoretical calculations are credible.

[0063] 2): The data trend of theoretical calculation is consistent with the data trend of actual radiation field.

[0064] 3): The radiation field distribution trend at different power levels is consistent and proportional to the power level.

[0065] 4): Monte Carlo theory calculation can calculate the radiation field gamma ray dose rate and neutron dose rate , unit: μGy / h.

[0066] There are many related data interpolation simulation methods, such as Kriging interpolation and least squares method. The least squares method is a mathematical method for estimating system parameters with the goal of minimizing the sum of squared errors. The least squares method can be used to easily obtain unknown data so that the sum of squared errors between the obtained data and the actual data is minimized. Taking the univariate linear model as an example, the variables x and y satisfy a linear relationship, that is,

[0067] y=ax+b(1)

[0068] We can use N sets of known (x i ,y i ), according to the idea of ​​least squares method, find a set of a and b so that the total error square sum σ 2 Minimum.

[0069]

[0070] Thus, using formula 1) and x, the variable y can be simulated.

[0071] The characteristics of the measured values ​​are as follows: Taking the γ field as an example, ionization chamber detection devices, GM tube counters, etc. are generally used for detection. The detection principle of the ionization chamber detection device is: the detection device is filled with a certain amount of gas, and the γ rays pass through the gas in the sensitive volume, ionizing or exciting the gas molecules to generate charged particles. The generated charged particles are all collected under the external electric field to generate current signals. When the energy is E and the injection rate is When a parallel gamma-ray beam with an emission area of ​​S irradiates the ionization chamber, the average energy W deposited by each photon in the sensitive body of the ionization chamber is assumed to be all converted into the ionization energy of the sensitive gas in the ionization chamber, and the generated charges are all collected by the electrodes, the current output by the ionization chamber is as follows:

[0072]

[0073] Where I is the current output by the ionization chamber, in A, W is the average energy deposited by each photon in the sensitive body of the ionization chamber, S is the emission area, e is the electron charge, μ en / ρ is the mass energy absorption coefficient of the gamma ray with energy E, E is the gamma ray energy, w is the ionization energy of the sensitive gas, is the gamma-ray dose rate at the spatial location, in μGy / h. From formula (3), it can be seen that the ionization chamber output current I is related to the gamma-ray dose rate The ionization chamber detector can convert the current I into the gamma ray dose rate by using the sensitivity (A / (μGy / h) parameter obtained by simulation through its software. This value can be read directly on the detection device and represents the actual measured value in the area.

[0074] According to the above characteristics, the gamma-ray dose rate of the detection device measured value and Monte Carlo simulation value We can use the least squares method to perform linear fitting. We can obtain the radiation field trend through a Monte Carlo simulation (i.e., obtain x in formula (1)), and then use the actual measurement value of the detection device (y in formula (2) i ) and its corresponding theoretical simulation value (x in formula (2) i ), using the least square method (formula (2)), a and b in formula (1) are obtained, so as to estimate the actual radiation field based on the theoretically calculated radiation field and the measured values ​​of some detection points. The above correction method for the neutron radiation field is similar. The above correction method has been applied in similar directions, such as "Research on the method of core power distribution reconstruction based on off-core counting", and it has been proved to be reliable.

[0075] When the correction algorithm is actually implemented, (1) considering the computational characteristics of Monte Carlo calculation, if the error at some positions is too large or the calculation does not converge, resulting in a large error between the theoretical value and the measured value of the point, then the point cannot contribute to the data correction; therefore, an error threshold is set. The setting of the threshold is usually based on empirical estimates during the calculation. For radiation field calculation, the error between the theoretical value and the monitored value generally does not exceed one order of magnitude. Therefore, the maximum error threshold can be set to 10. If the theoretical calculated value differs from the measured value by more than 10 times, the point will not participate in the data correction calculation.

[0076] (2) Using formula (2), according to the minimum sum of statistical variance, the least square method is used to obtain the correction coefficients a and b. Here, it is assumed that there are 8 γ detection devices in the area for measuring the γ absorbed dose rate in the area. The actual measured values ​​and the theoretical values ​​of this point are shown in Table 1. It is calculated that a and b are 5.026 and -0.505 respectively.

[0077] (3) Calculate the correction result of the entire radiation field.

[0078] Finally, the correction result of the entire radiation field can be obtained by the results calculated in 2) and the theoretical calculation results of the radiation field, such as Figure 2 As shown, a section of data along the Z axis is taken.

[0079] Table 1

[0080] x(theoretical calculated value)(uGy / h) y(monitoring value)(uGy / h) 1.70E+00 8.13E+00 1.78E+00 1.06E+01 2.17E+01 1.01E+02 2.23E+01 1.19E+02 5.31E-01 2.52E+00 5.18E-01 1.93E+00 1.90E+00 4.37E+00 1.98E+00 1.19E+01

[0081] It can be seen from the above technical scheme that the radiation field data correction method based on the actual measured values ​​of regional γ and neutrons provided in the above embodiment of the present invention, based on the actual measured values ​​of regional γ and neutrons, uses the least squares method to correct the theoretically calculated radiation field, thereby providing support for obtaining a more accurate radiation field.

[0082] The above embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present invention.

Claims

1. A radiation field data correction method based on regional gamma and neutron measured values, characterized in that: include: Step 1: Perform theoretical calculation of the radiation field, which specifically includes: Perform source term calculation to calculate the radioactive source term in the area of ​​interest during normal operation, wherein the source term at least includes the gamma ray source term generated by the decay of N-16 radioactive nuclides in the coolant pipeline, the primary shielding gamma ray source term, and the primary shielding neutron source term; Establish equipment models in the area, and establish geometric models based on the equipment and materials arranged in the area to prepare for the transport of gamma rays and neutrons in the area; Carry out transport calculations within the region, including using the set calculation method to calculate the transport of gamma rays and neutrons in the radioactive source term within the entire region. The calculation uses an Fmesh counting card, and the mesh size is equivalent to the size of the detection device, thereby obtaining the gamma radiation field and neutron radiation field within the region when the region is operating normally; Step 2: Perform radiation field correction, including using the least squares method to calculate the correction coefficient based on the measured values ​​of multiple detection devices set up in the area and the theoretical values ​​of the radiation field at the corresponding monitoring points, and correcting all theoretical radiation field data to obtain the corrected regional radiation field.

2. The radiation field data correction method based on regional gamma and neutron measured values ​​according to claim 1 is characterized in that: The gamma-ray source term includes a gamma-ray source in the stack and a gamma-ray source in the coolant.

3. The radiation field data correction method based on regional gamma and neutron measured values ​​according to claim 2 is characterized in that: The gamma rays from the gamma-ray source in the reactor pass through the fuel cladding, pressure vessel, primary shielding and reach the outer surface of the primary shielding. The gamma-ray source term on the outer surface of the primary shielding can be calculated using the source term calculation software.

4. The radiation field data correction method based on regional gamma and neutron measured values ​​according to claim 3 is characterized in that: The gamma ray source in the coolant includes a gamma ray source in the coolant pipe and a gamma ray source on the primary side of the evaporator; The source term calculation software was used to calculate the specific activity of N-16 radioactivity at different locations in the coolant pipe when operating at full power; Among them, when N-16 decays, it emits 6.13MeV and 7.11MeV gamma photons in a ratio of 67:5, based on which the N-16 decay gamma ray source terms at different positions in the coolant pipeline are obtained.

5. The radiation field data correction method based on regional gamma and neutron measured values ​​according to claim 4 is characterized in that: The neutrons in the reactor pass through the fuel cladding, pressure vessel, primary shield and finally reach the outer surface of the primary shield. The neutron source term on the outer surface of the primary shield can be calculated using the source term calculation software.

6. The radiation field data correction method based on regional gamma and neutron measured values ​​according to claim 5 is characterized in that: The source card of MCNP is established by using the N-16 decay γ-ray source term at different positions in the coolant pipe, shielding the outer surface γ-ray source term once and shielding the neutron source term once; Use the Fmesh card to divide the regional space into small grids, calculate the radiation field in the region, and obtain the radiation field intensity R N-16 -xyz,R γ -xyz,R n -xyz; Finally, the γ radiation field in the area under full power normal operation is obtained as (R N-16 -xyz+R γ -xyz), the neutron radiation field is R n -xyz.

7. The radiation field data correction method based on regional gamma and neutron measured values ​​according to claim 6 is characterized in that: The radiation field at different powers is obtained by multiplying the value of the neutron radiation field by the power proportional factor.

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