Method for reconstructing reactor core power distribution based on out-of-core nuclear measurement system

Abstract

The invention discloses a method for reconstructing power distribution of a reactor core based on an ex-core nuclear measurement system, which comprises the following steps: firstly, obtaining correlation coefficients among fuel assemblies of the reactor core through reactor core transport calculation, and establishing a power correlation matrix; secondly, obtaining a response function of the out-of-pile nuclear measurement system through reactor core transport calculation, and establishing an out-of-pile nuclear measurement system response matrix; and finally, on the basis of the out-of-core nuclear measurement system signal acquired in real time, performing online calculation to obtain the power distribution of the reactor core fuel assembly under the corresponding working condition. Wherein the detector response function is obtained through transport calculation of a fixed source mode, and the power correlation matrix needs to be subjected to transport calculation of a characteristic value mode and transport calculation of the fixed source mode step by step. According to the invention, by considering the mutual influence among the fuel assemblies, the strong'underdetermined 'problem of in-pile information loss when inversion is carried out on the power distribution of the reactor core assembly only by relying on an out-of-pile detector is avoided, and high-precision inversion of the power distribution of the reactor core fuel assemblies can be carried out only based on information provided by an out-of-pile nuclear measurement system. And the precision requirement of on-line monitoring of the reactor core power distribution is met.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear reactor core operation and safety technology, and in particular relates to a method for reconstructing core power distribution based on an off-core nuclear measurement system. Background Art

[0002] Reactor core monitoring plays a very important role in reactor startup, operation and safety protection, and is an indispensable key system in the reactor. In order to enhance the operator's understanding of the reactor interior, the international community has developed reactor core online monitoring technology in recent years to provide operators with three-dimensional real-time information on the core power distribution. Online monitoring of the reactor's three-dimensional power distribution is an effective means to fully tap the economic benefits of nuclear energy while ensuring the safety of reactor operation.

[0003] The current mainstream online core monitoring systems at home and abroad are mainly aimed at commercial pressurized water reactors with fixed or movable in-core detectors. Due to the compact core space of future advanced reactors, it is difficult to set up in-core neutron detectors, so the mature technical route of the existing online core monitoring system of pressurized water reactors cannot be adopted. The deployment location of the out-of-core detector is not restricted by the structure of the active area, the operating environment is relatively good and the maintenance is relatively simple. Online core monitoring based on the out-of-core nuclear measurement system has become the current development trend in the field of online core monitoring of reactors. However, since the neutrons from the fuel area are absorbed or scattered by the in-core fuel, moderator, structural materials, etc., the out-of-core detectors are not sensitive enough to the changes in the in-core state. When relying solely on the out-of-core detectors to invert the power distribution of the core components, the problem of missing in-core information is faced. Therefore, the present invention aims to propose a method for reconstructing the core power distribution based on the out-of-core nuclear measurement system. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a method for reconstructing the core power distribution based on the extra-core nuclear measurement system. The method establishes the correlation between the core fuel assemblies and applies it to the extra-core detector response function, combining the extra-core nuclear measurement system signals collected during actual reactor operation, to achieve high-precision and high-efficiency core power distribution reconstruction calculation.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for reconstructing core power distribution based on an off-core nuclear measurement system comprises the following steps:

[0007] Step 1: Obtain the correlation coefficients between the fuel assemblies in the core through core transport calculation and establish the power correlation matrix F;

[0008] Step 2: Obtain the response function of the out-of-core nuclear measurement system through core transport calculation and establish the response matrix C of the out-of-core nuclear measurement system;

[0009] Step 3: Collect the real-time measurement signal D of the detector of the out-of-core nuclear measurement system, and calculate online to obtain the power distribution R = D·C of the core fuel assembly under the corresponding working conditions -1 ·F -1 .

[0010] Furthermore, the step 1 comprises the following steps:

[0011] Step 1.1: Solve for fuel zone i (i=1,2,…,N f , N f The average number of neutrons released per fission is N=1,2,…,N t , N t Indicates the number of nuclides:

[0012]

[0013] Where:

[0014] (v∑ f ) i,N ——Neutron production cross section of nuclide No. N in fuel zone i

[0015] (vΣ f ) i,N ——Fission cross section of the Nth nuclide in fuel zone i

[0016] Step 1.2: Perform eigenvalue mode transport calculation to obtain the source strength S of fuel zone i i :

[0017]

[0018] Where:

[0019] (vΣ f ) i ——Neutron production cross section of fuel zone i

[0020] ——Neutron injection rate in fuel zone i

[0021] Step 1.3: Take fuel zone i as source and source strength as S i Carry out transport calculations in the fixed source mode to obtain the fission reaction rate x of fuel zone k generated by fuel zone i i,k (k=1,2,…,N f ):

[0022]

[0023] Where:

[0024] (vΣf ) k ——Fission cross section of fuel zone k

[0025] ——Neutron injection rate in fuel zone k

[0026] Step 1.4: Calculate the power correlation coefficient f from formula (4): i,k , we can establish the power correlation matrix F = (f i,k ):

[0027]

[0028] Where:

[0029] x i,k ——the fission reaction rate of fuel zone k produced by fuel zone i

[0030] ——The average number of neutrons released per fission in fuel zone i

[0031] V i ——Volume of fuel zone i

[0032] V k ——The volume of the fuel zone k.

[0033] Furthermore, the step 2 is specifically: performing a conjugate transport calculation or a forward transport calculation in a fixed source mode to obtain the response coefficient c of the out-of-core nuclear measurement system i,j (j=1,2,…,N d , N d represents the number of off-core nuclear measurement systems), the off-core nuclear measurement system response matrix C can be established. i,j ):

[0034]

[0035] Where:

[0036] V i ——Volume of fuel zone i

[0037] χ i ——Fission neutron spectrum of fuel region i

[0038] ——Conjugate neutron flux rate of fuel zone i generated by detector j in the ex-core nuclear measurement system

[0039] ∑ j —— Neutron response cross section of detector j in the out-of-core nuclear measurement system

[0040] ——neutron flux rate of detector j in the ex-core nuclear measurement system generated by fuel zone i

[0041] Furthermore, the ex-core nuclear measurement system includes a plurality of ex-core detectors arranged at preset positions outside the core active area, and the ex-core detectors are combined to form a complete ex-core nuclear measurement system for a nuclear reactor. Usually, the number of detectors is less than the number of fuel zones, and the established detector response matrix is ​​not a square matrix, so the symbol C -1 It represents the optimal pseudo-inverse matrix of the detector response matrix based on least squares.

[0042] Compared with the prior art, the present invention has the following advantages: The present invention proposes a method for reconstructing the core power distribution based on the off-core nuclear measurement system, which reconstructs the core power distribution by establishing the correlation between the core fuel assemblies and applying it to the off-core detector response function. The present invention avoids the strong "underdetermination" problem of missing in-core information when only relying on off-core detectors to invert the power distribution of the core assemblies by considering the mutual influence between the fuel assemblies, and effectively improves the accuracy of the core power distribution reconstruction calculation while meeting the calculation speed requirements of online monitoring, especially the calculation accuracy of the power of the fuel assemblies inside the core far away from the detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The present invention is a flow chart of a method for reconstructing core power distribution based on an off-core nuclear measurement system.

[0044] Figure 2 A simplified schematic diagram of a nuclear reactor core.

[0045] Figure 3 Schematic diagram of the layout of the nuclear reactor's extracore nuclear measurement system, where (a) shows six detectors arranged outside the axial shielding layer and on the axial extension line of the active area, and (b) shows six detectors arranged outside the radial shielding layer and in the middle of the active area.

[0046] Figure 4 Schematic diagram of the reconstruction error of nuclear reactor core power distribution, where (a) does not consider power correlation, and (b) considers power correlation.

[0047] In the above figures: 1: reflection layer; 2: shielding layer; 3: active area; 4: out-of-pile neutron detector. DETAILED DESCRIPTION

[0048] The structure of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0049] like Figure 2 The figure shows a simplified schematic diagram of the core of a nuclear reactor, which is mainly composed of an active area 3, a reflector 1, and a shield 2. The core active area consists of 30 fuel assemblies and is less than 1m in size. 3 , compact structure.

[0050] like Figure 3 As shown, the arrangement scheme of the ex-pile nuclear measurement system for reconstructing the power distribution of the nuclear reactor core includes 12 ex-pile neutron detectors 4: D1-D6 are arranged outside the axial shielding layer and on the axial extension line of the active area; D7-D12 are arranged outside the radial shielding layer and in the middle of the active area.

[0051] right Figure 2 The nuclear reactor shown is based on Figure 3 The external nuclear measurement system shown in the figure uses the present invention to perform power distribution reconstruction calculation on the core, such as Figure 1 As shown, the specific steps are:

[0052] Step 1: Obtain the correlation coefficient f between the fuel assemblies in the core through core transport calculation i,k (i, k = 1, 2, ..., 30), establish the power correlation matrix F, specifically:

[0053] (1.1) Solve for the average number of neutrons released per fission in fuel zone i N=1,2,…,N t , N t Indicates the number of nuclides:

[0054]

[0055] Where:

[0056] (vΣ f ) i,N ——Neutron production cross section of nuclide No. N in fuel zone i

[0057] (Σ f ) i,N ——Fission cross section of the Nth nuclide in fuel zone i

[0058] (1.2) Carry out the transport calculation of the eigenvalue model to obtain the source strength S of fuel zone i i :

[0059]

[0060] Where:

[0061] (vΣ f ) i ——Neutron production cross section of fuel zone i

[0062] ——Neutron injection rate in fuel zone i

[0063] (1.3) Take fuel zone i as source and source strength as S i Carry out transport calculations in the fixed source mode to obtain the fission reaction rate x of fuel zone k generated by fuel zone ii,k :

[0064]

[0065] Where:

[0066] (Σ f ) k ——Fission cross section of fuel zone k

[0067] ——Neutron injection rate in fuel zone k

[0068] (1.4) The power correlation coefficient f is obtained from formula (4): i,k , we can establish the power correlation matrix F = (f i,k ):

[0069]

[0070] Where:

[0071] x i,k ——the fission reaction rate of fuel zone k produced by fuel zone i

[0072] ——The average number of neutrons released per fission in fuel zone i

[0073] V i ——Volume of fuel zone i

[0074] V k ——The volume of the fuel zone k

[0075] Step 2: Obtain the response function c of the out-of-core nuclear measurement system through core transport calculation i,j (j=1,2,…,12), establish the response matrix C of the out-of-core nuclear measurement system, specifically:

[0076] Perform conjugate transport calculation or forward transport calculation in fixed source mode to obtain the response coefficient c of the out-of-pile nuclear measurement system i,j , then the response matrix of the out-of-core nuclear measurement system C can be established. i,j ):

[0077]

[0078] Where:

[0079] V i ——Volume of fuel zone i

[0080] χ i ——Fission neutron spectrum of fuel region i

[0081] ——Conjugate neutron flux rate of fuel zone i generated by detector j in the ex-core nuclear measurement system

[0082] ∑ j —— Neutron response cross section of detector j in the out-of-core nuclear measurement system ——neutron flux rate of detector j in the ex-core nuclear measurement system generated by fuel zone i

[0083] Step 3: Collect the real-time measurement signal D of the off-core nuclear measurement system, and calculate online to obtain the core fuel assembly power distribution R = D·C under the corresponding working conditions -1 ·F -1 .

[0084] The results are as follows Figure 4 As shown, compared with the calculation results without considering power correlation, considering power correlation reduces the maximum error of reconstruction calculation from 4.99% to 0.66%, and the reconstruction error of the inner ring component is significantly reduced, with high calculation accuracy.

Claims

1. A method for reconstructing core power distribution based on an off-core nuclear measurement system, characterized in that: The steps include: Step 1: Obtain the correlation coefficients between the fuel assemblies in the core through core transport calculation and establish the power correlation matrix F; Step 2: Obtain the response function of the out-of-core nuclear measurement system through core transport calculation and establish the response matrix C of the out-of-core nuclear measurement system; Step 3: Collect the real-time measurement signal D of the off-core nuclear measurement system, and calculate online to obtain the core fuel assembly power distribution R = D·C under the corresponding working conditions -1 ·F -1 .

2. The method for reconstructing core power distribution based on an off-core nuclear measurement system according to claim 1, characterized in that: Step 1 includes the following steps: Step 1.1: Calculate the average number of neutrons released per fission in fuel zone i Where: v∑ f ) i,N ——Neutron production cross section of nuclide No. N in fuel zone i (∑ f ) i,N ——Fission cross section of the Nth nuclide in fuel zone i i=1,2,…,N f , N f Indicates the number of fuel zones N=1,2,…,N t , N t Indicates the number of nuclides Step 1.2: Perform eigenvalue mode transport calculation to obtain the source strength S of fuel zone i i : Where: (v∑ f ) i ——Neutron production cross section of fuel zone i ——Neutron injection rate in fuel zone i Step 1.3: Take fuel zone i as source and source strength as S i Carry out transport calculations in the fixed source mode to obtain the fission reaction rate x of fuel zone k generated by fuel zone i i,k ,k=1,2,…,N f : Where: (∑ f ) k ——Fission cross section of fuel zone k ——Neutron injection rate in fuel zone k Step 1.4: Calculate the power correlation coefficient f from formula (4): i,k , and then establish the power correlation matrix F = (f i,k ): Where: x i,k ——the fission reaction rate of fuel zone k produced by fuel zone i ——The average number of neutrons released per fission in fuel zone i V i ——Volume of fuel zone i V k ——The volume of the fuel zone k.

3. The method for reconstructing core power distribution based on an off-core nuclear measurement system according to claim 1, characterized in that: Step 2 is as follows: Perform conjugate transport calculation or forward transport calculation in fixed source mode to obtain the response coefficient c of the out-of-pile nuclear measurement system i,j j=1,2,…,N d , N d represents the number of the out-of-core nuclear measurement system, and then establishes the out-of-core nuclear measurement system response matrix C = (c i,j ): Where: V i ——Volume of fuel zone i χ i ——Fission neutron spectrum of fuel region i ——Conjugate neutron flux rate of fuel zone i generated by detector j in the ex-core nuclear measurement system ∑x——neutron response cross section of detector j in the out-of-core nuclear measurement system ——The neutron flux rate of detector j in the extra-core nuclear measurement system generated by fuel zone i.

4. The method for reconstructing core power distribution based on an off-core nuclear measurement system according to claim 1, characterized in that: The ex-core nuclear measurement system includes a plurality of ex-core detectors arranged at preset positions outside the core active area, and the ex-core detectors are combined to form a complete ex-core nuclear measurement system for a nuclear reactor.

5. The method for reconstructing core power distribution based on an off-core nuclear measurement system according to claim 4, characterized in that: The number of detectors is less than the number of fuel zones, and the detector response matrix established is not a square matrix, so the symbol C -1 It represents the optimal pseudo-inverse matrix of the detector response matrix based on least squares.

6. The method for reconstructing core power distribution based on an off-core nuclear measurement system according to claim 4, characterized in that: The out-of-core nuclear measurement system includes six detectors arranged on the outside of the axial shielding layer and on the axial extension line of the active area, and six detectors arranged on the outside of the radial shielding layer and in the middle of the active area.

Images