Method for eliminating response current delay effect of self-powered neutron detector in pressurized water reactor

Abstract

The invention relates to a method for eliminating the response current delay effect of a self-powered neutron detector in a pressurized water reactor, which comprises the following steps of: obtaining key parameters in response current calculation by using reactor core physical analysis software capable of accurately calculating the response current of the self-powered neutron detector; according to a response mechanism calculation formula of various components in response current, instant and delayed components are directly analyzed and separated according to the response current of the self-powered neutron detector transmitted from a pressurized water reactor core in real time, so that a real-time neutron flux density recovery value is obtained; the response current delay effect of the self-powered neutron detector in the pressurized water reactor is eliminated; the problem that the response current of the self-powered neutron detector in a transient reactor core state has a delay effect and cannot form corresponding instant response is solved, the neutron flux density recovery value for eliminating the delay effect can be obtained in real time according to the response current, and the method is suitable for various working conditions of reactor operation; the application obstacle of the SPND in a control and protection system is eliminated, and the method has a good engineering application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of self-powered neutron detectors, nuclear reactor in-core monitoring systems and nuclear reactor safe operation, and in particular to a method for eliminating the response current delay effect of a self-powered neutron detector in a pressurized water reactor. Background Art

[0002] The self-powered neutron detector (SPND) is an in-core fixed detector based on the activation method, which mainly consists of three parts: emitter, insulator and collector. Neutrons in the nuclear reactor core will react with the high neutron-sensitive emitter material to produce electrons, thereby forming an electric current.

[0003] Self-contained neutron detectors have the characteristics of small size, high neutron sensitivity, and no need for bias power supply. They are currently widely used as in-core neutron detectors in nuclear reactors such as heavy water reactors, VVER cores, and third-generation large commercial pressurized water reactors. They can monitor the neutron flux level in the core in real time, and realize real-time online monitoring of the power distribution of the reactor core, which can significantly improve the safety and economy of the core.

[0004] According to the time characteristics of the main component of the generated electrons, SPND can be divided into delayed type and instantaneous type. At present, delayed type SPND with a larger response current value is mostly used in advanced pressurized water reactors. However, the response current of delayed type SPND has a delay effect. During the process of the core undergoing transients, it is impossible to directly form a response current that can reflect the core power level, which limits the application of SPND in the core real-time control and protection system.

[0005] The existing methods that can deal with the response current delay effect of self-powered neutron detectors are mainly the following:

[0006] (1) Kalman filtering method. The essence of Kalman filtering is to predict and solve future information based on the original state equation according to the noise information and signals that have been observed in order to obtain accurate signals. After using the Kalman filtering method to process the vanadium SPND response current, the response characteristics of the vanadium SPND can be significantly improved to match the instantaneous cobalt SPND. However, the Kalman filtering method requires a priori assumptions about the covariance of the noise, which makes it difficult to apply to engineering practice.

[0007] (2)H ∞ Filtering method. ∞ The essence of the filtering method is to solve the problem based on the linear matrix inequality to design a matching filter. ∞ The filtering method processes the response current of the Rhodium SPND and minimizes the response delay to 1.4s, but the white noise is ignored in the state equation, resulting in excessive filter noise gain. To solve this problem, too many empirical adjustment parameters are introduced.

[0008] (3) Simple iterative method. A simple iterative method for compensating the rhodium SPND response current delay is used. The control differential equation is established according to the decay mechanism, and then a simple and flexible delay compensation iterative relationship is established by using a discretization method. The experimental results show that the delay of the compensated neutron flux response to step transients is only 0.9s; however, this method has not been used in actual complex working conditions.

[0009] (4) Deconvolution method. A deconvolution-based SPND real-time neutron flux reconstruction method first establishes a kinetic model to obtain the unit pulse response function h(t), and then establishes an iterative compensation relationship for delay compensation based on the convolution relationship I(t) = Φ(t)*h(t). It is proved that the compensation performance for step neutron flux is only 0.3s, and the compensation effect is good. However, this method has not been used in actual complex working conditions.

[0010] In summary, there are some methods at home and abroad that can handle the delay effect of SPND response current, which can reduce the delay effect of more than 100s to the order of 0.5s, and have achieved remarkable results. However, in actual application, these methods still have problems such as non-real-time, inaccurate, and unstable. It is necessary to propose a more accurate, stable, and reliable method to provide better technical support for the safe and stable operation of nuclear reactors. Summary of the invention

[0011] In order to overcome the problems existing in the prior art, the purpose of the present invention is to provide a method for eliminating the delay effect of the response current of a self-powered neutron detector in a pressurized water reactor. The method uses core physics analysis software that can accurately calculate the response current of the self-powered neutron detector to obtain key parameters in the response current calculation; uses the response mechanism calculation formula of various components in the response current, and directly analyzes and separates the prompt and delayed components based on the response current of the self-powered neutron detector transmitted in real time from the core of the nuclear reactor, so as to obtain a real-time neutron flux density recovery value. The method is suitable for various operating conditions of the reactor operation and realizes the elimination of the delay effect of the response current of the self-powered neutron detector in the pressurized water reactor.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] A method for eliminating the response current delay effect of a self-powered neutron detector in a pressurized water reactor comprises the following steps:

[0014] Step 1: Read the geometric dimensions, material layout information and state parameter information of the target pressurized water reactor core to be simulated, as well as the geometric structure and material information of the self-powered neutron detector placed in the central instrument measuring tube containing the self-powered neutron detector assembly in the core;

[0015] Step 2: Use the core physics analysis software that can accurately calculate the response current of the self-powered neutron detector to model and calculate the target core to obtain the small group constant library and SPND response characteristic parameters;

[0016] Step 3: During the operation of the target PWR, the core calculation program is used to perform core neutronics-thermal hydraulics-burnup coupling calculations to obtain the neutron flux density distribution of the entire core at the current moment and the SPND response characteristic parameters at the current moment; the current moment is marked as t0, and the next parameter update time is t n , change t0 to t n The time period is divided into n hour steps Δt i ,but;

[0017] t i =t i-1 +Δt i Formula (1)

[0018] Where: subscript i = 1, 2, ..., n; the SPND response current I(t0) at time t0 is obtained from the power plant;

[0019] Step 4: For t = t i At this time, it is known that t i-1 The neutron flux density φ(t i-1 ), SPND response current I(t i-1 ), obtained from the power plant i The SPND response current I(t i ),

[0020] Solve the burnup equation of the SPND emitter material to obtain t i The number density N of decay precursor nuclei that generate slow current at any moment dpni (t i ), where dpni represents the i-th decay precursor nucleus;

[0021] The SPND response current at any time can be expressed as the sum of the slow current and the instantaneous current:

[0022]

[0023] Where:

[0024] I(t i )——t i SPND response current at moment

[0025] I delay ——Slow-release current

[0026] I prompt ——Instantaneous current

[0027] q——charge constant, value is 1.602×10 -19 C

[0028] V 组件 ——Component volume

[0029] ε dpni ——The electron escape probability of the i-th decay precursor nucleus

[0030] λ dpni ——decay constant of the i-th decay precursor nucleus

[0031] S——Instantaneous sensitivity coefficient

[0032] a——The proportionality coefficient between the emitter flux density and the component flux density

[0033] V 发射体 ——Emissive volume

[0034] t i The number density of decay precursor nuclei N dpni (t i ) is substituted into the response current expression to obtain t i The neutron flux density recovery value φ(t i );

[0035] Step 5: Repeat step 4 to obtain the time from t0 to t n The neutron flux density recovery value φ(t i );

[0036] Step 6: Repeat steps 3 to 5, and from any time during the operation of the PWR, obtain the neutron flux density recovery value eliminating the delay effect in real time according to the response current.

[0037] Compared with the prior art, the present invention has the following outstanding advantages:

[0038] By using core physics analysis software that can accurately calculate the response current of the self-powered neutron detector, key parameters in the response current calculation are obtained; by using the response mechanism calculation formula of various components in the response current, the prompt and delayed components are directly analyzed and separated according to the response current of the self-powered neutron detector transmitted in real time from the nuclear reactor core, so as to obtain a real-time neutron flux density recovery value, which is suitable for various operating conditions of the reactor operation and realizes the elimination of the delay effect of the response current of the self-powered neutron detector in the pressurized water reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the flux recovery value, flux reference value and the error between them under stable core operation and variable power operation. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with specific implementation modes.

[0041] The present invention is a method for eliminating the response current delay effect of a self-powered neutron detector in a pressurized water reactor, and the specific steps are as follows:

[0042] Step 1: Read the geometric dimensions, material layout information and state parameter information of the pressurized water reactor core to be simulated, as well as the geometric structure and material information of the self-powered neutron detector placed in the central instrument measuring tube containing the self-powered neutron detector assembly in the core;

[0043] Step 2: Using the core physics analysis software that can accurately calculate the response current of the self-powered neutron detector, model and calculate the target core to obtain the small group constant library and SPND response characteristic parameters.

[0044] Through grid simulation calculation, the few group constants of different types of components are obtained. For the types of components equipped with SPND, it is also necessary to obtain the nuclear number density of the emitter material at different burnup depths, the homogenized absorption cross section of the emitter material, and the fine nuclide composition of the component. The few group constant library is generated by fitting using the few group parameter fitting program. At the same time, SPND simulation calculation is performed. According to the fine nuclide composition of the component at different burnup depths obtained by grid simulation calculation, the SPND response characteristic parameters under different state parameters are simulated and calculated;

[0045] Step 3: During the operation of the target nuclear reactor, the core calculation program is used to perform core neutronics-thermal hydraulics-burnup coupling calculations based on the small group constants obtained by grid calculations to obtain the neutron flux density distribution of the entire core at the current moment, and obtain the SPND response characteristic data at the current moment, including the nuclear number density of the emitter material, the single group absorption cross section of the emitter material, the proportionality coefficient of the component and SPND neutron flux density, the electron escape probability and the prompt sensitivity coefficient. This moment is marked as t0, and the next time the parameters are updated is t n , change t0 to t n The time period is divided into n hour steps Δt i ,but;

[0046] t i =t i-1 +Δt i Formula (1)

[0047] Where: subscript i = 1, 2, ..., n. Obviously, the neutron flux density φ(t0) at time t0 is known, and the SPND response current I(t0) at time t0 is obtained from the power plant.

[0048] Step 4: For t = t i At time i=1,2,...,n, it is known that ti-1 The neutron flux density φ(t i-1 )、SPND response current I(t i-1 ), obtained from the power plant i The SPND response current I(t i ), solve for t i =t i-1 +Δt i The neutron flux density φ(t i ). Taking the vanadium self-powered neutron detector as an example. According to the burnup process of the vanadium SPND emitter material, it is believed that from t0 to t n between, 51 The nuclear number density of V remains unchanged;

[0049] The burnup equation for the vanadium SPND emitter material is:

[0050]

[0051] in:

[0052] N V-50 (ti), N V-51 (ti), N V-52 (ti)——emitter material at time ti 50 V. 51 V. 52 The nuclear number density of V

[0053] ——Time t0 50 V. 51 Single-group microscopic homogenized absorption cross section of V

[0054] φ(t i-1 ),φ(t i )——t i-1 ,t i Neutron flux density at time

[0055] ——Emitter material at time t0 51 VNucleus number density

[0056] λ V-52 ——Nuclide 52 The decay constant of V

[0057] Solving the burnup equation for vanadium SPND emitter material yields t i Decay precursor nuclei that constantly generate slow currents 52 The nucleus number density of V is;

[0058]

[0059] The SPND response current at any time is expressed as the sum of the slow current and the instantaneous current;

[0060] I(t i )=I delay +I prompt =qλ V-52 N V-52 (t i )V 组件 ε V-52 +Sa·φ(t i )V 发射体

[0061] Formula (4) In the formula:

[0062] I(t i )——t i SPND response current at moment

[0063] I delay ——Slow-release current

[0064] I prompt ——Instantaneous current

[0065] q——charge constant, value is 1.602×10 -19 C

[0066] V 组件 ——Component volume

[0067] ε V-52 ——V-52 electron escape probability

[0068] S——Instantaneous sensitivity coefficient

[0069] a——The proportionality coefficient between the emitter flux density and the component flux density

[0070] V 发射体 ——Emissive volume

[0071] t i Time decay precursor 52 Substituting V nucleus density formula (3) into the response current expression formula (4), we get t i The neutron flux density recovery value of the component at the moment;

[0072]

[0073] in:

[0074]

[0075] Step 5: Repeat step 4 to obtain the time from t0 to t n The neutron flux density recovery value of each component at each moment betweeni );

[0076] Step 6: Repeating steps 3 to 5, the neutron flux density recovery value of the component that eliminates the delay effect can be obtained in real time based on the response current starting from any time during the operation of the pressurized water reactor.

[0077] To verify the effectiveness of the present invention, Figure 1 The relative error between the flux recovery value obtained by eliminating the delay effect using the present invention and the flux reference value obtained by the core physics analysis software is shown. The calculation results show that the flux recovery value after eliminating the delay effect calculated by the present invention has extremely high synchronization with the flux reference value, eliminating the delay effect, and the calculation accuracy is high, with a relative error within 4.5%.

[0078] The present invention solves the problem that the response current of the self-powered neutron detector has a delay effect and cannot form a corresponding instantaneous response under a transient core state. The neutron flux density recovery value that eliminates the delay effect can be obtained in real time according to the response current. The present invention is suitable for various operating conditions of the reactor, removes the obstacles to the application of SPND in the control and protection system, and has good engineering application prospects.

Claims

1. A method for eliminating the response current delay effect of a self-powered neutron detector in a pressurized water reactor, characterized in that: The steps include: Step 1: Read the geometric dimensions, material layout information and state parameter information of the target pressurized water reactor core to be simulated, as well as the geometric structure and material information of the self-powered neutron detector placed in the central instrument measuring tube containing the self-powered neutron detector assembly in the core; Step 2: Use the core physics analysis software that can accurately calculate the response current of the self-powered neutron detector to model and calculate the target core to obtain the small group constant library and SPND response characteristic parameters; Step 3: During the operation of the target PWR, the core calculation program is used to perform core neutronics-thermal hydraulics-burnup coupling calculations to obtain the neutron flux density distribution of the entire core at the current moment and the SPND response characteristic parameters at the current moment; the current moment is marked as t0, and the next parameter update time is t n , change t0 to t n The time period is divided into n hour steps Δt i ,but; t i =t i-1 +Δt i Formula (1) Where: subscript i = 1, 2, ..., n; the SPND response current I(t0) at time t0 is obtained from the power plant; Step 4: For t = t i At this time, it is known that t i-1 The neutron flux density φ(t i-1 )、SPND response current I(t i-1 ), obtained from the power plant i The SPND response current I(t i ), Solve the burnup equation of the SPND emitter material to obtain t i The number density N of decay precursor nuclei that generate slow current at any moment dpni (t i ), where dpni represents the i-th decay precursor nucleus; The SPND response current at any time is expressed as the sum of the slow current and the instantaneous current: Where: I(t i )——t i SPND response current at moment I delay ——Slow-release current I prompt ——Instantaneous current q——charge constant, value is 1.602×10 -19 C V 组件 ——Component volume ε dpni ——The electron escape probability of the i-th decay precursor nucleus λ dpni ——decay constant of the i-th decay precursor nucleus S——Instantaneous sensitivity coefficient a——The proportionality coefficient between the emitter flux density and the component flux density V 发射体 ——Emissive volume t i The number density of decay precursor nuclei N dpni (t i ) is substituted into the response current expression to obtain t i The neutron flux density recovery value φ(t i ); Step 5: Repeat step 4 to obtain the time from t0 to t n The neutron flux density recovery value φ(t i ); Step 6: Repeat steps 3 to 5, and obtain the neutron flux density recovery value eliminating the delay effect in real time according to the response current starting from any time during the operation of the PWR.

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