A radiation field data correction method based on regional gamma and neutron measured values

Abstract

The embodiment of the present application provides a radiation field data correction method based on regional gamma and neutron measured values, comprising: performing radiation field theoretical calculation, calculating N-16 radionuclide decayed gamma ray source term in the coolant pipe in the region of interest, primary shielding gamma ray source term and primary shielding neutron source term during normal operation; establishing a device model in the region, establishing a geometric model according to the devices and materials arranged in the region; using a set calculation method to perform transport calculation of gamma rays and neutrons in the radioactive source term in the entire region, calculating using Fmesh counting cards, the grid size is equivalent to the size of the detection device, obtaining the gamma radiation field and neutron radiation field in the region during normal operation in the region; according to the measured values of the plurality of detection devices arranged in the region and the radiation field theoretical values of the corresponding monitoring points, using the least square method, the correction coefficient is obtained, all the theoretical radiation field data is corrected, and the corrected regional radiation field is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of radiation protection, in particular to a radiation field data correction method based on regional gamma and neutron measured values. BACKGROUND

[0002] In order to understand the radiation field size in the whole region during normal operation and after shutdown, the theoretical radiation field of a region can be obtained by modeling and performing Monte Carlo transport calculation of radioactive source terms. However, the Monte Carlo transport calculation is time-consuming and the calculation result can only be used as a reference database and cannot reflect the actual radiation field which is changing at any time. In addition, it is impossible to set an infinite number of detection devices to measure the regional radiation field due to the limitations of space and other conditions. Therefore, in order to understand the regional radiation field under the current operation condition, the theoretical calculated radiation field can be corrected by using a mathematical method based on the current limited actual measurement values, so that the radiation field data is closer to the actual data. SUMMARY

[0003] In view of the above problems existing in the prior art, the embodiments of the present application provide a radiation field data correction method based on regional gamma and neutron measured values, which corrects the theoretically calculated radiation field based on regional gamma and neutron measured values, and provides support for obtaining a more accurate radiation field.

[0004] The embodiments of the present application provide a radiation field data correction method based on regional gamma and neutron measured values, which comprises the following steps:

[0005] Step 1: performing radiation field theoretical calculation, which specifically comprises:

[0006] performing source term calculation to calculate the radioactive source terms in the region of interest during normal operation, wherein the source terms at least include the gamma ray source term of N-16 radionuclide decay in the coolant pipe, the primary shielding gamma ray source term and the primary shielding neutron source term;

[0007] establishing a device model in the region, specifically establishing a geometric model according to the devices and materials arranged in the region to prepare for the transport of gamma rays and neutrons in the region;

[0008] performing transport calculation in the region, including performing transport calculation of gamma rays and neutrons in the radioactive source terms in the whole region by using a set calculation method, and using Fmesh counting cards with a grid size comparable to the size of the detection device to obtain the gamma radiation field and the neutron radiation field in the region during normal operation, respectively;

[0009] Step 2: Perform radiation field correction, including according to the measured values of a plurality of detection devices arranged in the region and the theoretical values of the radiation field of the corresponding monitoring points, using the least square method, the correction coefficient is obtained, and all the theoretical radiation field data is corrected to obtain the corrected regional radiation field.

[0010] In some embodiments of the application, the gamma ray source term includes a gamma ray source in the reactor and a gamma ray source in the coolant.

[0011] In some embodiments of the application, the gamma ray source in the reactor passes through the fuel cladding, the pressure vessel and the primary shielding to reach the outer surface of the primary shielding, and the source term calculation software can calculate the gamma ray source term of the outer surface of the primary shielding.

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

[0013] The N-16 radioactivity specific activity at different positions in the coolant pipe during full power operation is calculated by the source term calculation software.

[0014] Wherein, N-16 emits 6.13 MeV and 7.11 MeV gamma photons at a ratio of 67:5 during decay, and accordingly the N-16 decay gamma ray source term at different positions in the coolant pipe is obtained.

[0015] In some embodiments of the application, the neutrons in the reactor pass through the fuel cladding, the pressure vessel and the primary shielding to finally reach the outer surface of the primary shielding, and the source term calculation software can calculate the neutron source term of the outer surface of the primary shielding.

[0016] In some embodiments of the application, the source card of MCNP is established by using the N-16 decay gamma ray source term at different positions in the coolant pipe, the gamma ray source term of the outer surface of the primary shielding and the neutron source term of the primary shielding.

[0017] The region space is divided into small grids by using Fmesh card, and the radiation field in the region is calculated to obtain the radiation field intensity R N-16 -xyz, R γ -xyz, R n -xyz;

[0018] Finally, the gamma radiation field of the region during normal operation at full power is (R N-16 -xyz+R γ -xyz), and the neutron radiation field is R n -xyz.

[0019] In some embodiments of the application, the value of the neutron radiation field under different power is multiplied by the power scaling factor to obtain the neutron radiation field under different power.

[0020] Compared with the prior art, the radiation field data correction method based on regional gamma and neutron measured values provided by the embodiment of the application has the beneficial effect that the least square method is used to correct the theoretically calculated radiation field based on the regional gamma and neutron measured values, thereby providing support for obtaining a more accurate radiation field. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A calculation flowchart of the radiation field data correction method based on regional gamma and neutron measured values provided by the embodiment of the application is shown in the figure.

[0022] Figure 2 A figure of the modified radiation field data and the theoretical radiation field data of a certain segment of the Z axis in the radiation field data correction method based on regional gamma and neutron measured values provided by the embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0023] In order for those skilled in the art to better understand the technical solutions of the application, the application will be described in detail below with reference to the drawings and specific embodiments.

[0024] The various aspects and features of the 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 the preferred forms given, by way of non-limiting example, with reference to the annexed drawings.

[0026] It is also to be understood that even though numerous specific details of the application are set out herein, various other equivalent forms of the application which do not depart from the spirit and essential characteristics of the application can likewise be made by persons skilled in the art and it is recognized that such forms would be within the scope of the application as defined by the claims.

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

[0028] Specific embodiments of the application are described herein with reference to the accompanying drawings. However, it is to be understood that the embodiments described are merely examples of the application and that the application can be implemented in many ways. Well-known and / or redundant functions and structures are not described in detail in order to avoid obscuring the application by unnecessary detail, to discern true intent, and to avoid obscuring the application. Therefore, specific structural and functional details disclosed herein are not to be interpreted in a limiting manner, but merely as a basis for the claims and representative basis for teaching one skilled in the art to most suitably employ the application.

[0029] The specification can use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," which can refer to one or more embodiments according to the present application.

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

[0031] Step 1: performing radiation field theoretical calculation, which specifically comprises:

[0032] Performing source term calculation, calculating the main radioactive source term in the region of interest during normal operation, wherein the source term at least includes the gamma ray source term of N-16 radionuclide decay in the coolant pipe, the primary shielding gamma ray source term and the primary shielding neutron source term;

[0033] Establishing a device model in the region, specifically establishing a geometric model according to the devices and materials arranged in the region, preparing for the transport of gamma rays and neutrons in the region;

[0034] Performing transport calculation in the region, including performing transport calculation of gamma rays and neutrons in the radioactive source term in the entire region by using a set calculation method, and using Fmesh counting cards with a grid size comparable to the size of the detection device, and then obtaining the gamma radiation field and the neutron radiation field in the region during normal operation in the region respectively;

[0035] Step 2: performing radiation field correction, including using the least square method to obtain correction coefficients according to the measured values of the plurality of detection devices arranged in the region and the radiation field theoretical values of the corresponding monitoring points, correcting all the theoretical radiation field data to obtain the corrected regional radiation field.

[0036] In some embodiments of the present application, the gamma ray source term includes the in-pile gamma ray source and the gamma ray source in the coolant.

[0037] The gamma rays of the in-pile gamma ray source pass through the fuel cladding, the pressure vessel and the primary shielding to reach the outer surface of the primary shielding, and the source term calculation software can calculate the gamma ray source term of the outer surface of the primary shielding.

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

[0039] The source term calculation software is used to calculate the N-16 specific activity at different positions in the coolant pipe during full power operation; wherein N-16 emits 6.13MeV and 7.11MeV gamma photons at a ratio of 67:5 during decay, and accordingly the N-16 decay gamma ray source term at different positions in the coolant pipe is obtained.

[0040] In the embodiment, the neutrons in the reactor pass through the fuel cladding, the pressure vessel and the primary shield to reach the outer surface of the primary shield, and the source term calculation software can calculate the neutron source term of the outer surface of the primary shield.

[0041] The source cards of MCNP are established by using the N-16 decay gamma ray source terms at different positions in the coolant pipe, the gamma ray source term of the outer surface of the primary shield and the neutron source term of the primary shield.

[0042] The region space is divided into small grids by using the Fmesh card, and the radiation field calculation in the region is performed to obtain the radiation field intensity R N-16 -xyz, R γ -xyz, R n -xyz;

[0043] Finally, the gamma radiation field of the region during normal operation at full power is R N-16 -xyz+R γ -xyz, and the neutron radiation field is R n -xyz.

[0044] The value of the neutron radiation field at different powers is multiplied by a power scaling factor to obtain the neutron radiation field.

[0045] In order to facilitate the understanding of the above technical solutions, the following will be described in conjunction with the drawings and examples in the specification, as follows:

[0046] The method mainly proceeds according to the following flow, as shown in Figure 1 The following takes the correction calculation of the gamma radiation field of the region during normal operation as an example:

[0047] Source term calculation

[0048] (1) Gamma ray source

[0049] The gamma ray source includes the gamma ray source in the reactor and the gamma ray source in the coolant. The gamma ray in the reactor passes through the fuel cladding, the pressure vessel and the primary shield to reach the outer surface of the primary shield, and the source term calculation software can calculate the gamma ray source term of the outer surface of the primary shield. The gamma ray source in the coolant mainly includes the gamma ray source in the coolant pipe and the gamma ray source on the primary side of the evaporator. The source term calculation software is used to calculate the N-16 specific activity at different positions in the coolant pipe during full power operation. When N-16 decays, it emits 6.13 MeV and 7.11 MeV gamma photons at a ratio of 67:5, and accordingly the N-16 decay gamma ray source term at different positions in the coolant pipe can be obtained.

[0050] (2) Neutron source term

[0051] Similar to the gamma source in the reactor core, the neutrons in the reactor core pass through the fuel cladding, the pressure vessel and the primary shield to the outside surface of the primary shield. The source term of the outside surface of the primary shield can be calculated by the source term calculation software.

[0052] Establishing the model of the equipment in the cabin

[0053] According to the equipment and materials arranged in the area, the geometric model is established. It is prepared for the transport calculation of particles.

[0054] Transport calculation in the area

[0055] Using the N-16 decay gamma source term at different positions in the coolant pipe, the gamma source term and the neutron source term of the outside surface of the primary shield, the source card of MCNP is established, and the space of the area is divided into small grids by using the Fmesh card. The radiation field calculation in the area is carried out, and the radiation field intensity R N-16-xyz, Rγ-xyz and Rn-xyz is obtained.

[0056] Finally, the gamma radiation field of the area during normal operation at full power is (R N-16-xyz+Rγ-xyz), and the neutron radiation field is Rn-xyz. The radiation field at different power levels can be obtained by multiplying the power scaling factor by this value.

[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 the calculation process, and make the final data used for analysis closer to the actual data.

[0059] Correction algorithm:

[0060] In order to correct, it is necessary to understand the relevant methods, to understand the characteristics of Monte Carlo theory calculation of radiation field, related data interpolation simulation methods and the characteristics of measured values:

[0061] The characteristics of Monte Carlo theory calculation of radiation field are as follows:

[0062] 1): The results of theoretical calculation are reliable.

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

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

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

[0066] There are various data interpolation simulation methods, such as Kriging interpolation method and least square method. The least square method is a mathematical method for system parameter estimation with the minimum error square sum as the target. The unknown data can be obtained by using the least square method, and the error square sum between the obtained data and the actual data is minimum. Taking a linear model as an example, the variables x and y satisfy a linear relationship, that is

[0067] y = ax + b (1)

[0068] We can obtain a set of a and b by using N sets of known (x i , y i ) according to the idea of the least square method, so that the total error square sum σ 2 is minimum.

[0069]

[0070] Thus, the variable y is simulated by using formula (1) and x.

[0071] The characteristics of the measured values are as follows: taking a γ field as an example, the ionization chamber detection device, GM tube counter and the like are generally used for detection. The detection principle of the ionization chamber detection device is as follows: the inside of the detection device is filled with a certain amount of gas, the γ rays pass through the gas in the sensitive volume, the gas molecules are ionized or excited, the charged particles are generated, the charged particles generated are all collected under an applied electric field, and an electric current signal is generated. When a parallel γ ray beam with an energy E, an emission area S and an injection rate is irradiated on the ionization chamber, the energy W deposited in the ionization chamber sensitive volume by each photon on average, it is assumed that all the energy is converted into the ionization energy of the ionization chamber sensitive gas, and the generated electric charge is all collected by the electrode, and the electric current output by the ionization chamber is as follows:

[0072]

[0073] Wherein, I is the electric current output by the ionization chamber, the unit is A, W is the energy deposited in the ionization chamber sensitive volume by each photon on average, S is the emission area, e is the electronic charge, μ en / ρ is the mass energy absorption coefficient of the γ rays with the energy E, E is the energy of the γ rays, w is the ionization energy of the sensitive gas, is the γ ray dose rate of the spatial position point, the unit is μGy / h. As can be seen from formula (3), the electric current I output by the ionization chamber is proportional to the γ ray dose rate . The ionization chamber detection device can convert the electric current I into the γ ray dose rate by using the sensitivity (A / (μGy / h) parameter obtained by simulation through the software thereof. The value can be directly read on the detection device, and represents the actual measured value in the region.

[0074] Based on the above characteristics, the gamma-ray dose rate is calculated using both the measured values ​​from the detection device and the Monte Carlo simulation values. We can use the least squares method for linear fitting. We can obtain the radiation field trend through a Monte Carlo simulation (i.e., obtain x in formula (1)), and then obtain the actual measured value (y in formula (2)) through the detection device. i ) and its corresponding theoretical simulation value (x in formula (2) i Using the least squares method (formula (2)), we obtain a and b in formula (1), and thus estimate the actual radiation field based on the theoretically calculated radiation field and the measured values ​​of some detection points. The correction of the neutron radiation field is similar. The above correction method has been applied in similar fields, such as "Research on Core Power Distribution Reconstruction Method Based on External Counting", which has proven to be reliable.

[0075] In the actual implementation of the correction algorithm, (1) considering the computational characteristics of Monte Carlo calculation, if the error at certain locations is too large or the calculation does not converge, the error between the theoretical value and the measured value at that point will be too large, and that point will not be able to contribute to the data correction; therefore, an error threshold is set. The threshold is usually set based on empirical estimation during the calculation. In terms of radiation field calculation, the error between the theoretical value and the monitored value is generally no more than 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, then that point will not participate in the data correction calculation.

[0076] (2) Using formula (2), based on the minimum statistical variance, the correction coefficients a and b are obtained by the least squares method. 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 ​​at this point are shown in Table 1. The calculated values ​​of a and b are 5.026 and -0.505, respectively.

[0077] (3) Calculate the correction results for the entire radiation field.

[0078] Finally, the corrected result of the entire radiation field can be obtained from the results calculated in 2) and the theoretical calculation results of the radiation field, such as... Figure 2 As shown, a segment of data along the Z-axis was taken.

[0079] Table 1

[0080] x (theoretically calculated value) (uGy / h) y (monitored 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] As can be seen from the above technical solutions, the radiation field data correction method based on the measured values ​​of regional γ and neutrons provided by the above embodiments of the present invention corrects the theoretically calculated radiation field based on the measured values ​​of regional γ and neutrons using the least squares method, thus providing support for obtaining a more accurate radiation field.

[0082] The above examples are only exemplary embodiments of the present application, and are not intended to limit the present application, and the protection scope of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present application within the spirit and protection scope of the present application, and such modifications or equivalent replacements are also considered to fall within the protection scope of the present application.

Claims

1. A method of radiation field data correction based on area gamma and neutron real-time measurements, characterized in that, The method comprises the following steps: Step 1: performing radiation field theoretical calculation, which specifically comprises: performing source term calculation to calculate radioactive source terms in the region of interest during normal operation, wherein the source terms at least include a gamma ray source term of N-16 radionuclide decay in the coolant pipe, a primary shielding gamma ray source term, and a primary shielding neutron source term; establishing a device model in the region, specifically establishing a geometric model according to the devices and materials arranged in the region, to prepare for the transport of gamma rays and neutrons in the region; performing transport calculation in the region, including performing transport calculation of gamma rays and neutrons in the entire region in the radioactive source terms by using a set calculation method, and calculating by using Fmesh counting cards with a grid size comparable to the size of the detection device, to obtain the gamma radiation field and the neutron radiation field in the region during normal operation in the region, respectively; Step 2: performing radiation field correction, including using the least square method to obtain correction coefficients according to the measured values of the plurality of detection devices arranged in the region and the theoretical values of the radiation field of the corresponding monitoring points, and correcting all theoretical radiation field data to obtain the corrected regional radiation field; the method of using the least square method to obtain correction coefficients according to the measured values of the plurality of detection devices arranged in the region and the theoretical values of the radiation field of the corresponding monitoring points comprises: in the linear model, the variables x and y satisfy a linear relationship, that is, y = ax + b (1) By N groups of known (x i , y i ), according to the idea of least squares, a group of a and b is obtained, so that the total error square sum σ 2 is minimum; so as to simulate the variable y by using formula (1) and x; in the gamma field, ionization chamber detection devices and GM tube counters are used for detection; when parallel gamma ray beams irradiate on the ionization chamber, the average energy W deposited by each photon in the ionization chamber sensitive body, if all the energy is converted into ionization energy of the ionization chamber sensitive gas, and all the generated electric charges are collected by the electrode, then the current output by the ionization chamber is as follows: Wherein, I is the current output by the ionization chamber, unit A, W is the energy deposited by each photon in the ionization chamber sensitive volume, S is the emission area, e is the electronic charge, μ en / ρ is the mass energy absorption coefficient of the γ-ray with energy E, E is the energy of the γ-ray, w is the ionization energy of the sensitive gas, is the γ-ray dose rate of the spatial position point, unit μGy / h; From equation (3) it is known that the ionization chamber output current I is proportional to the gamma-ray dose rate ; the ionization chamber detection device converts the current I into a gamma-ray dose rate D by means of the sensitivity parameter obtained by simulation This value can be read directly on the detection device and represents the actual measurement in the area. an error threshold is set, and for radiation field calculation, the error threshold is set to be at most 10; if the theoretical calculation value and the measured value differ by more than 10 times, the point does not participate in data correction calculation; the correction coefficients a and b are obtained by using formula (2) according to the statistical variance and the minimum. the correction results of the entire radiation field are obtained through the calculation results and the radiation field theoretical calculation results.

2. The radiation field data correction method based on regional gamma and neutron measured values according to claim 1, wherein the gamma ray source terms comprise in-core gamma ray sources and coolant internal gamma ray sources.

3. The radiation field data correction method based on regional gamma and neutron measured values according to claim 2, wherein the gamma rays of the in-core gamma ray sources pass through the fuel cladding, the pressure vessel and the primary shielding to reach the outer surface of the primary shielding, and the source term calculation software can calculate the primary shielding outer surface gamma ray source term.

4. The radiation field data correction method based on regional gamma and neutron measured values according to claim 3, wherein the coolant internal gamma ray sources comprise coolant pipe internal gamma ray sources and evaporator primary side gamma ray sources; the N-16 specific activity at different positions in the coolant pipe during full power operation is calculated by using the source term calculation software. ​ ​ ​ Wherein, N-16 decay emits 6.13 MeV and 7.11 MeV gamma photons in the proportion of 67:5, and accordingly the N-16 decay gamma ray source term at different positions in the coolant pipe is obtained.

5. The method of claim 4, wherein the method is characterized in that, The neutrons in the reactor pass through the fuel cladding, the pressure vessel and the primary shield to finally reach the outer surface of the primary shield, and the source term calculation software can calculate the neutron source term of the outer surface of the primary shield.

6. The method of claim 5, wherein the method is characterized in that, The source cards of MCNP are established by using the N-16 decay gamma ray source term at different positions in the coolant pipe, the gamma ray source term of the outer surface of the primary shield and the neutron source term of the primary shield. The area space is divided into small grids by Fmesh card, and the radiation field calculation in the area is carried out to obtain the radiation field intensity R N-16 -xyz, R γ -xyz, R n -xyz; Finally, the gamma radiation field of the full-power normal operation region is R N-16 -xyz+R γ -xyz, and the neutron radiation field is R n -xyz.

7. The method of claim 6, wherein the method is characterized in that, The value of the neutron radiation field at different powers is multiplied by the power scaling factor to obtain the value of the neutron radiation field.

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