A method for predicting residual wall thickness of a control rod assembly cladding of a nuclear power plant

Abstract

The purpose of this invention is to provide a method for predicting the remaining wall thickness of the control rod assembly cladding in nuclear power plants. This method can quickly, efficiently, and comprehensively quantify the wear degree of all control rods without the risk of contamination. The above-mentioned technical objective of this invention is achieved through the following technical solution: It includes the following steps: S01, Cladding wall thickness data acquisition step: acquiring the wall thickness data of the control rod cladding before and after each cycle in several completed cycles at core location L; S02, Wear rate determination step at core location L: using the difference in cladding wall thickness ΔX of the control rod before and after one cycle at core location L as the wear rate C at that core location. L S03. Initial cladding wall thickness acquisition steps: Obtain the initial cladding wall thickness value X1 of the control rod before it enters the cycle at core position L; S04. Remaining cladding wall thickness calculation steps: The remaining cladding wall thickness X2 of the control rod inserted at core position L after the cycle is X1 = X1 - C L *Number of loops.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant control rod assembly technology, specifically to a method for predicting the remaining wall thickness of the cladding of nuclear power plant control rod assemblies. Background Technology

[0002] In nuclear power plants, the primary function of control rod assemblies is to provide reactivity control for the reactor core. They compensate for changes in core reactivity caused by variations in power, coolant temperature, or boron concentration, and provide normal and rapid shutdown capabilities, making them crucial components for ensuring safe reactor operation. During nuclear power plant operation, friction between control rods and components such as guide tubes can cause wear on the control rod cladding. Severe wear can lead to extreme situations such as control rod breakage or even fracture. Control rod breakage poses a significant threat to the safe operation of the reactor and, in severe cases, can cause a nuclear accident.

[0003] Control rods are located at multiple positions within the reactor core. Wear of the control rod cladding is a common and unavoidable phenomenon in nuclear power plants. The only way to determine whether replacement or relocation is necessary is through periodic inspections of the control rod cladding wear. Chinese patent application CN201910665024.1 discloses a method for measuring the wear of control rod guide clips based on image recognition technology, including the following steps: calibrating the detection range, image acquisition, image processing, measurement calculation, and result display. After calibrating the detection range, image acquisition begins. A camera is placed in the water tank containing the control rod to capture an image. After acquiring the image of the control rod, image processing is performed, including image filtering, image template recognition and positioning, and contour fitting. The processed image is clearer. Measurement calculations are then performed on the image, and the measurement results are directly plotted onto the image, visually displaying the wear location and value, thus determining the degree of wear of the control rod. However, this method has the following drawbacks: the process of measuring the wear of the control rods is complicated, the detection efficiency is low, it is impossible to quickly and quantitatively grasp the wear of each control rod, and it is impossible to adjust the position and layout of the control rods in a timely manner, thus causing the control rods to break. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the remaining wall thickness of the cladding of control rod assemblies in nuclear power plants, which can quickly, efficiently, and comprehensively quantify the wear degree of all control rods.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0006] A method for predicting the remaining wall thickness of the control rod assembly cladding in a nuclear power plant includes the following steps: S01, cladding wall thickness data acquisition step: acquiring the wall thickness data of the control rod cladding before and after each cycle in several completed cycles at core location L; S02, wear rate determination step at core location L: using the difference ΔX in the cladding wall thickness of the control rod before and after one cycle at core location L as the wear rate C at that core location. L S03. Initial cladding wall thickness acquisition steps: Obtain the initial cladding wall thickness value X1 of the control rod before it enters the cycle at core position L; S04. Remaining cladding wall thickness calculation steps: The remaining cladding wall thickness X2 of the control rod inserted at core position L after the cycle is X1 = X1 - C L *Number of loops.

[0007] Therefore, using the existing cladding wall thickness data before and after a control rod cycle, the difference in cladding wall thickness ΔX before and after one cycle is used as the wear rate C at core location L. L Then, by utilizing the initial wall thickness X1-C of the casing L *The number of cycles determines the remaining cladding wall thickness X2 of the control rods after several cycles at core location L. Workers can then use this remaining wall thickness X2 to assess the wear level of the control rods and decide whether to replace the mating position or replace the control rods altogether. Obtaining the remaining wall thickness X2 does not require direct measurement; it can be easily calculated using a pre-established formula. This method provides a fast, efficient, and comprehensive quantitative assessment of the wear level of all control rods, without any risk of contamination.

[0008] Preferably, step S02 includes the following: when all control rods inserted in all cycles with cladding wall thickness data records at core location L are the same, the largest cladding wall thickness difference ΔX in all cycles is recorded as ΔX. max Wear rate C L For ΔX max .

[0009] Preferably, step S02 includes the following: Let ΔX be the total thickness of the casing wall worn by the control rod from the first cycle to the nth cycle. n Then the average wall thickness worn per cycle is C. n =ΔX n / n, the largest C among several loops n Let it be C nmax ; will C nmax With ΔX max The maximum value is taken as the wear rate C at core location L. L .

[0010] Preferably, step S02 includes the following: Let C1 be the thickness of the casing wall worn by the control rod during the first cycle. m =ΔX n -(n-1)*C1, where C is the largest value among several iterations. m Let it be C mmax , will C mmax With C nmax ΔX max The maximum value is taken as the wear rate C at core location L. L .

[0011] Preferably, step S02 includes the following: C L1 =ΔX max +T*A,C L2 =X n =(ΔX) n +T*A) / n,C L3 =C m =ΔX n -(n-1)*C1+T*A, C L =max[C L1 C L2 C L3 ], where A represents the error value of each measured shell wall thickness data, and T represents the number of times the measured shell wall thickness data is used.

[0012] Preferably, step S02 includes the following: when the control rods inserted at core position L intervals are different, the wall thickness difference ΔX before and after each cycle of control rods is recorded. R Choose the largest wall thickness difference ΔX R Let it be ΔX Rmax , will ΔX Rmax +T*A represents the wear rate C at core location L. L .

[0013] Preferably, step S02 includes the following: when the core position L is the same control bar for several consecutive cycles, and the remaining intervals are different control bars, the wear rate when the same control bar is used consecutively is denoted as C. L4 C L4 =max[C L1 C L2 C L3 The wear rate of different control rods during the remaining cycle is denoted as C. L5 C L5 =ΔX Rmax +T*A, C L =max[C L4 C L5].

[0014] Preferably, step S02 includes the following: when the control rod inserted at the core position L has undergone n cycles but no wall thickness data has been recorded, the wear rate C... L The value is (A+B) / n, where A represents the error value of each measured shell wall thickness data, which is manually set; B represents a threshold set manually during the control rod shell inspection process. During the inspection process, values ​​less than the threshold of B are not recorded, and only wear values ​​with wear depth greater than B are recorded.

[0015] Preferably, step S03 includes the following: if the control rod is a new control rod that has not been circulated, the initial wall thickness value X1 of the casing is the original wall thickness value designed; if the control rod has been circulated and the casing wall thickness after the last circulation is recorded, it is X1. m If the control rod has already been cycled and the cladding wall thickness after the most recent cycle is not recorded, but the cladding wall thickness data after the i-th cycle is recorded, then the initial cladding wall thickness value X1 is Xi minus the wear rate at the core location of each cycle after the i-th cycle minus A; if the control rod cladding wall thickness data is not recorded, then X1 = original wall thickness - AB, where B represents a threshold manually set during the control rod cladding inspection process. During the inspection process, thresholds smaller than B are not recorded, and only wear values ​​with wear depths greater than B are recorded.

[0016] Preferably, step S04 includes the following: when the control rod has been cycled at different core locations, the remaining cladding wall thickness X2 is equal to X1 minus the wear rate of each cycled core location multiplied by the number of cycles of the control rod at that core location.

[0017] In summary, the embodiments of the present invention have the following beneficial effects:

[0018] 1. By utilizing the recorded control rod cladding wall thickness data, the wear rate at each core location can be obtained. The remaining cladding wall thickness of the control rods can be calculated simply, and the remaining cladding wall thickness of the control rods after subsequent cycles at different core locations can be predicted. This reduces the number and amount of manual measurements, enabling rapid, efficient, and comprehensive quantitative acquisition of the wear degree of all control rods, thus reducing the risk of contamination.

[0019] 2. Based on the different insertion methods of control rods at different core locations, the wear rate of each core location under different insertion methods is obtained, making the wear rate more accurate and adaptable to different control rod insertion methods.

[0020] 3. Once the core wear rate is established across the entire core, the initial wall thickness data of the control rod cladding, which was not recorded, can be obtained through simple calculations, and the data is easy to acquire.

[0021] 4. The wear rate and initial cladding wall thickness both take into account measurement errors, providing a more conservative estimate of the wear of the control rods and ensuring the safe operation of the nuclear power plant.

[0022] 5. Select the calculation method with the highest wear rate at the core location to more conservatively estimate the wear of the control rods and ensure the safe operation of the nuclear power plant. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating this embodiment. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings.

[0025] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0026] Example 1: As is known in the prior art, control rods are installed at different locations within the reactor core, and the wear rate varies at different locations and even within the same location across different cycles. Previously, to prevent control rods from failing before reaching their expected lifespan, the wear level of the control rods was checked during major overhauls, and their arrangement was rearranged accordingly. For example, control rods located in areas with high wear rates were placed in areas with low wear rates, thereby slowing down the wear rate of those control rods, preventing premature failure and reaching their service life, reducing replacement costs, and saving maintenance time.

[0027] In the past, during nuclear power plant maintenance, the cladding wall thickness data after control rod cycles was manually measured and recorded. Using this existing data, a mathematical model was established. The wear degree of the control rod is equal to the remaining cladding wall thickness x2 after several cycles. Remaining cladding wall thickness x2 = Initial cladding wall thickness x1 - Wall thickness worn during cycles. The wall thickness worn during cycles = Wear amount per cycle at the corresponding core location * Number of cycles of the control rod at that location. The total wear amount of the control rod after cycling through multiple core locations is the sum of the wear amounts at each core location, i.e., the wear rate at each core location multiplied by the number of cycles at that core location, summed sequentially. First, it is necessary to know the wear amount per cycle at the corresponding core location, i.e., the wear rate C at each core location. L Let the core position where the control rod is located be L, and obtain the wear rate C at core position L. L The steps are as follows:

[0028] S01. Steps for obtaining cladding wall thickness data: Obtain the wall thickness data of the control rod cladding before and after each cycle in the several completed cycles at core location L.

[0029] After obtaining the wall thickness data, proceed to step S02. The wear amount of the control rod at core location L in each cycle = control rod cladding wall thickness before the cycle - control rod cladding wall thickness after the cycle. That is, the difference in control rod cladding wall thickness before and after one cycle is taken as the wear rate C of core location L in that cycle. L .

[0030] However, due to the complexity of control rod insertion at the core location, the control rods inserted at different cycles within the same core location may be the same or different. Different insertion methods result in different recorded wall thickness data, and consequently, different wear rates. Therefore, the wear rate for each core location needs to be calculated in conjunction with the corresponding insertion method, based on the wear rate calculation for each method. Considering the possible control rod insertion methods at the core location, a more comprehensive and conservative calculation of the wear rate C at the core location is proposed. L .

[0031] The following prediction calculations are performed for various interpolation methods.

[0032] For mating method 1, when the same control rod is cyclically mated at core position L, the wear rate can be obtained in the following three ways:

[0033] (1) The largest difference in shell wall thickness before and after all cycles, ΔX, is denoted as ΔX. max ΔX max The wear rate is derived from the difference in wall thickness.

[0034] (2) Let ΔXn be the total wall thickness of the casing worn by the control rod from the first cycle to the nth cycle. Then the average wall thickness worn per cycle is C. n =ΔX n / n, the largest C among several loops n Let it be C nmax C nmax The wear rate is obtained by calculating the average wear amount.

[0035] (3) Let ΔXn be the total thickness of the casing worn by the control rod from the first cycle to the nth cycle, and C1 be the thickness of the casing worn by the control rod in the first cycle. m =ΔX n -(n-1)*C1, where C is the largest value among several iterations. m Let it be C mmax C mmaxThis represents the wear rate obtained by using extreme values. Where (n-1)*C1 represents the wear amount in the (n-1)th cycle, and ΔX... n -(n-1)*C1 represents the total wear amount of the nth cycle minus the total wear amount of the (n-1)th cycle, which is the wear amount of the nth cycle alone. The reason for choosing the wear amount C1 from the first cycle is that the wear experienced by the control rod in the initial first cycle is relatively pure and therefore representative. Simultaneously, the wear amount of the final cycle can also be used as C1. If there is no data recorded for the initial and final cycles, the wear amounts of the second, third, and subsequent cycles can also be selected.

[0036] Furthermore, since the wall thickness data recorded for the control rods are all obtained through manual measurement, a certain measurement error exists. To minimize the impact of measurement error and maximize the estimation of control rod wear, the error value A must be considered for each wall thickness measurement. The error value A represents the error present in the measurement of each obtained cladding wall thickness data point, and its magnitude is determined by the operator. The number of measurements used in deriving the wear rate corresponds to the number of times A is added, i.e., adding T*A, where T represents the number of times the measured cladding wall thickness data was used.

[0037] Therefore, the wear rate in methods (1), (2), and (3) above should be as follows:

[0038] The wear rate of type (1) is denoted as C. L1 C L1 =ΔX max +T*A;

[0039] The wear rate of type (2) is denoted as C. L2 C L2 =C n =(ΔX) n +T*A) / n;

[0040] The wear rate of type (3) is denoted as C. L3 C L3 =C m =ΔX n -(n-1)*C1+T*A.

[0041] In summary, the highest wear rate among the three methods should be selected as the wear rate C for mating method 1. L That is, the wear rate C L =max[C L1 C L2 C L3 ].

[0042] Insertion method 2: When the control bars inserted in the cycle at core position L intervals are different:

[0043] Record the wall thickness difference ΔX after a single cycle of different control rods. R Choose the largest wall thickness difference ΔX R Let it be ΔX Rmax After considering measurement errors, the wear rate C at core position L corresponding to mating method 2 is... L =ΔX Rmax +T*A.

[0044] Interlocking method 3: When the core position L is the same control rod for several consecutive cycles, and the remaining intervals are different control rods:

[0045] (1) The wear rate of the same control rod is calculated in the same way as that of mating method 1. There are three calculation methods, and the wear rate is denoted as C. L4 C L4 =max[C L1 C L2 C L3 ];

[0046] (2) The wear rate of the control rod under different residual cycles is denoted as C. L5 The calculation method is the same as that for mating method 2, and the wear rate is denoted as C. L5 =ΔX Rmax +T*A.

[0047] In summary, the wear rate C at core location L obtained by mating method 3 is... L =max[C L4 C L5 ].

[0048] Insertion method 4: When the control rod inserted at position L in the core passes through n cycles but no wall thickness data is recorded:

[0049] The wear rate is estimated using the measurement error value A and the wear limit value B of the casing wall thickness. Wear rate C L The formula is: (A+B) / n. Where A represents the error value of each measured shell wall thickness data, which is manually set; B represents a threshold set manually during the control rod shell inspection process. During the inspection process, values ​​less than the threshold of B are not recorded, and only wear values ​​with wear depths greater than B are recorded.

[0050] In summary, based on different mating methods, there are four corresponding wear rates C at core location L. L The above method for calculating wear rates applies to all core locations.

[0051] The wear rate C at core location L is obtained. LThen, in step S03, the initial wall thickness X1 of the cladding before the control rod enters a certain cycle is obtained. Depending on whether the control rod has participated in the cycle and whether wall thickness data has been recorded after the cycle, the initial wall thickness X1 of the cladding can be obtained in the following ways:

[0052] 1. If the control rod is a new control rod that has not been circulated, the initial wall thickness value of the casing X1 is the original wall thickness value designed;

[0053] 2. If the control rod has been cycled, and the casing wall thickness after the most recent cycle is recorded, it is X. m Then, the initial wall thickness of the casing before the control rod enters the next cycle is X1 = X m -A;

[0054] 3. If the control rods have been cycled and the cladding wall thickness after the most recent cycle has not been recorded, but the cladding wall thickness data Xi after the i-th cycle has been recorded, then the initial cladding wall thickness value X1 is Xi minus the wear rate of the core location in each cycle after the i-th cycle minus A.

[0055] 4. If the control rod casing wall thickness data is not recorded, then X1 = original wall thickness - AB.

[0056] After obtaining the initial cladding wall thickness X1 before the control rod enters the cycle, proceed to step S04, the remaining cladding wall thickness calculation step: The remaining cladding wall thickness X2 of the control rod inserted at the core position L after the cycle is X1 - C. L *Number of cycles. This represents the wear amount of the control rod at a core location L. Furthermore, depending on the actual operation of the nuclear power plant, a control rod may be located at different core locations during different cycles. Therefore, when the control rod has undergone cycles at different core locations, the remaining cladding wall thickness X2 equals X1 minus the wear rate at each cycled core location multiplied by the number of cycles the control rod has undergone at that core location. In other words, by subtracting the wear amount at different core locations from the initial wall thickness before cycling, the wear amount at each core location is the wear rate at that core location multiplied by the number of cycles the control rod has undergone at that core location.

[0057] The wear level is determined by multiplying the remaining cladding wall thickness of each control rod by two values, and the corresponding control rod positions are rearranged accordingly. Control rods with severe wear are promptly replaced with those in core areas with lower wear rates to mitigate control rod wear.

[0058] The remaining wall thickness X2 after a cycle can be calculated for control rods at any location in the reactor core using the above method. This eliminates the need for manual measurement of the wall thickness of each control rod, allowing for a more convenient and comprehensive quantitative understanding of control rod wear. Based on the predicted remaining wall thickness X2, control rods can be rearranged or replaced to slow down wear, balance their overall lifespan, prevent premature replacements that would consume overhaul time, and significantly reduce the workload for staff.

Claims

1. A method for predicting the remaining wall thickness of the cladding of a control rod assembly in a nuclear power plant, characterized in that, The process includes the following steps: S01, Cladding wall thickness data acquisition step: Acquire the cladding wall thickness data of the control rods before and after each cycle in the several completed cycles at core location L; S02, Wear rate determination step at core location L: Use the difference in cladding wall thickness ΔX between the control rods before and after one cycle at core location L as the wear rate at that core location. ; S03. Initial Cladding Wall Thickness Acquisition Steps: Obtain the initial cladding wall thickness value before the control rod enters the cycle at core position L. S04. Calculation steps for remaining cladding wall thickness: The remaining cladding wall thickness after the cycle is calculated based on the control rod inserted at position L in the core. In step S02, when all the control rods inserted in all cycles with cladding wall thickness data records at core location L are the same, the wear rate... The calculation methods include the following three approaches: Method 1: Denote the largest difference in shell wall thickness ΔX in all cycles as... Wear rate for ; Method 2: Let the total wear of the casing wall thickness of the control rod from the first cycle to the nth cycle be... The average wall thickness worn per cycle is The largest in several loops Recorded as ;Will and The maximum value is taken as the wear rate at core location L. ; Method 3: Record the thickness of the casing wall worn by the control rod during the first cycle as... , The largest in several loops Recorded as , Will and , The maximum value is taken as the wear rate at core location L. ; The wear rates of Method 1, Method 2, and Method 3 are denoted as follows: , , ,in, , , The final wear rate , where A represents the error value present in each measured shell wall thickness data during measurement, and T represents the number of times the measured shell wall thickness data is used; When the control rods inserted at core position L intervals are different, record the wall thickness difference before and after each cycle of control rod insertion. Choose the largest wall thickness difference. Recorded as ,Will The wear rate at core location L .

2. The method for predicting the remaining wall thickness of the cladding of a nuclear power plant control rod assembly according to claim 1, characterized in that, Step S02 includes the following: when the core position L is the same control rod for several consecutive cycles, and the remaining intervals are different control rods, the wear rate when the same control rod is used consecutively is recorded as follows: , The wear rate of different control rods during the remaining cycle is denoted as . , , .

3. The method for predicting the remaining wall thickness of the cladding of a nuclear power plant control rod assembly according to claim 1, characterized in that, Step S02 includes the following: when the control rod inserted at the core position L has undergone n cycles but no wall thickness data has been recorded, the wear rate... for: Where A represents the error value of each measured shell wall thickness data, which is manually set; B represents a threshold set manually during the control rod shell inspection process. Wear values ​​less than B are not recorded during the inspection process, only wear values ​​with wear depth greater than B are recorded.

4. The method for predicting the remaining wall thickness of the cladding of a nuclear power plant control rod assembly according to claim 2, characterized in that, Step S03 includes the following: if the control rod is a new control rod that has not been circulated, the initial wall thickness of the casing. The original wall thickness value for the design; If the control rod has already cycled, and the casing wall thickness after the last cycle is recorded, then... The initial wall thickness of the casing before the control rod enters the next cycle is then determined. ; If the control rod has been looped, and the cladding wall thickness after the most recent loop was not recorded, but the cladding wall thickness data after the i-th loop was recorded. Then the initial wall thickness of the shell is for Subtract the wear rate at the core location in each subsequent cycle (after the i-th cycle) and then subtract A; if the control rod cladding wall thickness data is unrecorded, then... =Original wall thickness - AB, where B represents a threshold set manually during the control rod cladding inspection process. Wear values ​​less than B are not recorded during the inspection; only wear values ​​with a wear depth greater than B are recorded.

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