Evaluation method for oxidation purification effect of primary loop of nuclear power plant

Abstract

The invention belongs to the field of source item control during shutdown of a nuclear power plant, and discloses a method for evaluating the oxidation purification effect of a primary loop of the nuclear power plant. According to the method, a specific activity model of nuclide changing along with time after a loop oxidation peak appears is established, and then a theoretical lower limit purification curve and an expected upper limit purification curve of the nuclide specific activity are obtained according to the expected upper limit and the theoretical lower limit of the continuous specific activity release rate after the peak value appears after the nuclide is oxidized. And whether deposition or additional release occurs in the process is judged by comparing the actually measured nuclide specific activity value with the relative position of the curve. And the duration of oxidation purification is decided through the nuclide specific activity expectation upper limit purification curve. And by comparing the relative position relationship between the actually measured nuclide specific activity value before the oxidation purification is finished and the calculated value of the deposition-free purification model curve at the moment, the overall purification effect evaluation of the oxidation purification is given.

Description

Technical Field

[0001] The invention belongs to the field of source term control during shutdown of a nuclear power plant, and in particular relates to a method for evaluating the oxidation purification effect of a primary circuit of a nuclear power plant. Background Art

[0002] During the down-stream cooling and depressurization period of the reactor overhaul, when the primary coolant reaches 80°C, hydrogen peroxide will be injected into the primary coolant to make the dissolved oxygen in the primary coolant greater than 1 ppm, so that the corrosion products on the primary surface are quickly dissolved and released into the coolant under the action of dissolved oxygen and removed through the purification system of the down-stream loop. At the same time, a relatively stable oxide film is formed on the primary surface to reduce the subsequent continuous release of corrosion products on the primary surface.

[0003] When hydrogen peroxide is added to the primary circuit, corrosion products rapidly dissolve and release in large quantities, forming a corrosion product peak in the primary circuit within approximately half an hour. The release of corrosion products from the primary circuit surface then transitions to a continuous, small-scale release. In some cases, two other scenarios can occur during this period: First, corrosion products from the primary circuit deposit within the primary circuit piping, increasing the piping dose rate; second, an additional release of corrosion products occurs at a certain stage of the oxidation purification process, significantly exceeding the small, continuous release. Promptly identifying the deposition and additional release of corrosion products and accurately estimating the specific activity of corrosion products at a given time are crucial for correctly evaluating the effectiveness of oxidation purification and determining its end point. The duration of oxidation purification directly impacts the economic benefits of a nuclear power plant.

[0004] After the oxidation peak of the primary circuit corrosion products, the change trend of their specific activity in the primary circuit is related to the morphology of the corrosion products, the sustained release rate, the downstream purification flow rate, the purification efficiency of the purification unit, the purification time, the half-life of the corrosion products, and whether deposition occurs.

[0005] Oxidation purification during overhaul has a significant impact on removing corrosion products from the primary circuit surface, controlling the overhaul's collective dose, critical path duration, and economic benefits. The purification trend is usually determined by analyzing the segmented slope of the curve showing the measured specific activity of corrosion products versus purification time. In the later stages of oxidation purification, when the absolute value of the slope is small (i.e., the specific activity curve is relatively flat), the end time of oxidation purification is determined by the rate of decrease of the specific activity per hour. This method lacks a clear standard for determining the slope and relies primarily on the experience of the staff. Furthermore, the end time of oxidation purification can only be determined near the end of oxidation, and cannot be predicted in the early or middle stages of oxidation purification. It is also impossible to promptly identify and evaluate the impact of abnormalities (deposition or additional release) in the early or middle stages on the final results. At the same time, there is no clear standard for determining whether the specific activity value of corrosion products in the primary circuit coolant is within a reasonable range at the end of oxidation purification. Summary of the Invention

[0006] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for evaluating the oxidation purification effect of a nuclear power plant primary circuit comprises the following steps:

[0009] (1) Establish a model for estimating nuclide specific activity, as shown below:

[0010]

[0011] in,

[0012] A n,mode : The specific activity of the nuclide at time t under ideal conditions, that is, when no deposition and additional release occur, MBq / t;

[0013] A0: The peak specific activity of the nuclide actually measured after oxidation, MBq / t;

[0014] A Δ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s);

[0015] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0016] t: purification time, s;

[0017] (2) draw the purification curve;

[0018] (3) Compare the relative positions of the measured values ​​and the purification curves to analyze abnormalities in the oxidation purification process;

[0019] (4) Correct the purification curve when abnormal conditions of deposition or extra release exist;

[0020] (5) Determine the duration of oxidation purification;

[0021] (6) Evaluate the oxidation purification effect.

[0022] Furthermore, the purification curve drawn in step (2) is as follows: the theoretical lower limit value and the expected upper limit value of the specific activity release rate of the nuclide after the peak value of oxidation are calculated, and the nuclide specific activity estimation model is substituted to obtain the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity.

[0023] Furthermore, the abnormal situation analysis of step (3) is as follows: comparing the relative positions of the measured value of the nuclide specific activity with the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if the measured value is less than the theoretical lower limit corresponding to the time, deposition occurs; if the measured value is greater than the expected upper limit corresponding to the time, additional release occurs.

[0024] Furthermore, the oxidation purification time length of step (5) is determined as follows: the oxidation purification time length is determined according to the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if deposition or additional release occurs during the oxidation purification process, the oxidation purification time length is determined according to the revised expected upper limit purification curve obtained in step (4).

[0025] Furthermore, the evaluation of the oxidation purification effect in step (6) is as follows: comparing the relative positions of the measured value of the nuclide specific activity before the end of the oxidation purification with the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if the theoretical lower limit corresponding to the time is ≤ the measured value ≤ the expected upper limit corresponding to the time, the oxidation purification effect meets expectations.

[0026] Furthermore, the nuclide in step (1) is Co-58.

[0027] Furthermore, the nuclide equivalent attenuation coefficient in step (1) is obtained by the following relationship:

[0028]

[0029] in,

[0030] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0031] M w : Total mass of coolant in the primary circuit and purification circuit, t;

[0032] λ n : decay constant of the nuclide, s-1;

[0033] F RCV : primary circuit coolant discharge purification flow rate, t / s;

[0034] P urifnRCV : Removal factor of the purification system, dimensionless.

[0035] Furthermore, the theoretical lower limit of the specific activity release rate of the nuclide after the peak of oxidation in step (2) is A Δ,min , A Δ,min = 0; the expected upper limit of the specific activity release rate of the nuclide after the peak of oxidation is A Δ,max ,

[0036] Furthermore, the correction of the purification curve in step (4) comprises the following steps:

[0037] S1. When deposition occurs, the nuclide specific activity prediction model is corrected by the deposition factor; when additional release occurs, the purification curve of the nuclide between the two measurement points where the additional release occurs is corrected by the sustained specific activity release rate A. Δ Correction, then according to A Δ The calculated value of the next measurement point is obtained from the corrected curve, and the specific activity peak value A0 of the purification curve after two measurement points is corrected with this calculated value;

[0038] S2. Based on the corrected curve obtained in step S1, the abnormal situation analysis of the subsequent measured values ​​in step (3) is performed;

[0039] S3. Repeat steps S1 and S2 until there are no abnormalities.

[0040] Furthermore, in step (4), when the purification curve is corrected and deposition occurs, the correction steps are:

[0041] A′ n =η·A n,mode

[0042] in,

[0043] A′ n : specific activity of the nuclide at time t after sedimentation correction, MBq / t;

[0044] η: sedimentation factor, dimensionless;

[0045] Deposition mainly occurs in the initial short period of time after the oxidation peak. When deposition occurs between the n-1th measurement and the nth measurement after the peak, the deposition factor η is determined by the following formula:

[0046]

[0047] in,

[0048] A n,measure : The nth measured value of specific activity after the nuclide peak appears, MBq / t;

[0049] A n,mode : The calculated value of the nuclide at the same time for the nth measurement, MBq / t.

[0050] Furthermore, in step (4), when the purification curve is corrected and additional release occurs, the correction steps are:

[0051] When the additional release occurs between the n-1th measurement and the nth measurement after the peak, the corrected A Δ ' is determined by the following formula:

[0052]

[0053] in,

[0054] A Δ ′: specific activity release rate after correction for additional release of nuclides, MBq / (t·s);

[0055] A n,measure : The nth measured value of specific activity after the nuclide peak appears, MBq / t;

[0056] A n―1,measure : The measured value of the specific activity at the n-1th time after the nuclide peak appears, MBq / t;

[0057] t Δ : the time interval between the n-1th measurement and the nth measurement, s;

[0058] A Δ ′ is substituted into the nuclide specific activity prediction model, and the expected upper limit value A corresponding to the n-1th measured value is used. n―1,max By replacing A0 in the nuclide specific activity prediction model with t′, we can obtain the additional release-corrected nuclide specific activity at each moment between the n-1th measurement and the nth measurement, which is recorded as A′. n ′; Then, when calculating the nuclide specific activity after the nth measurement point, A in the nuclide specific activity prediction model Δ The expected upper limit value A of the specific activity release rate of the nuclide after the peak of oxidation is still used. Δ,max , A0 uses the predicted upper limit value A″ at the nth measurement point n,max Replacement;

[0059] Additional release of the corrected A′ between the n-1th measurement and the nth measurement n ′, is determined by the following formula:

[0060]

[0061] in,

[0062] A′ n ′: specific activity at time t′ after additional release correction between the n-1th measurement point and the nth measurement point, MBq / t;

[0063] A n―1,max : the expected upper limit value corresponding to the n-1th measurement point, MBq / t;

[0064] A Δ′: specific activity release rate after correction for additional release of nuclides, MBq / (t·s);

[0065] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0066] t′: purification time starting from the n-1th measurement point, s;

[0067] Nuclide specific activity A′ after the nth measurement point n ″, is determined by the following formula:

[0068]

[0069] in,

[0070] A″ n,max : the expected upper limit of specific activity after additional release correction at the nth measurement point, MBq / t; A Δ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s);

[0071] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0072] t″: Purification time starting from the nth measurement point, s.

[0073] Furthermore, in the correction of the purification curve in step (4), when additional release occurs, the theoretical lower limit purification curve of the nuclide specific activity is not corrected.

[0074] Furthermore, the oxidation purification time is determined in step (5): the hourly decrease in nuclide specific activity is calculated based on the expected upper limit purification curve of the nuclide specific activity or the revised expected upper limit purification curve. When the hourly decrease in nuclide specific activity is ≤530MBq / t, the oxidation purification ends.

[0075] The implementation of the present invention has the following beneficial effects:

[0076] The present invention establishes a specific activity model of nuclides that changes with time after a loop oxidation peak occurs, and then calculates the nuclide specific activity value at each moment and draws a trend curve by calculating the nuclide equivalent attenuation coefficient and the expected upper limit and theoretical lower limit of the specific activity release rate of the nuclides after the oxidation peak occurs. By comparing the relative position of the measured nuclide specific activity value and the curve, it is judged whether the process meets expectations (within the range of the two curves), or whether deposition (the measured value is below the theoretical lower limit purification curve) or additional release (the measured value is above the expected upper limit purification curve) has occurred. The duration of oxidation purification is determined by the expected upper limit purification curve of the nuclide specific activity (when deposition or additional release occurs, the duration of oxidation purification is determined by the revised expected upper limit purification curve of the nuclide specific activity). By comparing the relative position relationship between the measured nuclide specific activity value before the end of oxidation purification and the calculated value of the purification model curve without deposition at that moment, the overall purification effect evaluation of oxidation purification is given. If it is between the expected upper limit and the theoretical lower limit, it means that the expectation is met; if it is outside the expected upper limit and the theoretical lower limit, it means that the expectation is not met. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 These are the theoretical lower limit purification curve and the expected upper limit purification curve of the specific activity of the nuclide Co-58 after oxidation purification.

[0078] Figure 2 Comparison between the measured and estimated values ​​of Co-58 specific activity.

[0079] Figure 3 Comparison between the measured and estimated Co-58 specific activity values ​​after correction for the deposition factor at point "d1".

[0080] Figure 4 Comparison between the measured and estimated values ​​of Co-58 specific activity after correction for the “d1” and “d2” deposition factors.

[0081] Figure 5 Comparison between the measured and estimated values ​​of Co-58 specific activity after correction for the deposition factors from "d1" to "d5".

[0082] Figure 6 The measured and estimated values ​​of Co-58 specific activity after correction for the deposition factors from "d1" to "d5" and the additional release correction on "d13" are shown.

[0083] Figure 7 The figure is a flow chart of the method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to the present invention. DETAILED DESCRIPTION

[0084] The present invention will be described in further detail below with reference to the Examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the Examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0085] Unless otherwise specified, all reagents used in the examples can be purchased from the market.

[0086] A method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant, such as Figure 7 As shown, it is mainly implemented in the following steps:

[0087] (1) Establish a model for estimating nuclide specific activity, as shown below:

[0088]

[0089] in,

[0090] A n,mode : The specific activity of the nuclide at time t under ideal conditions, that is, when no deposition and additional release occur, MBq / t;

[0091] A0: The peak specific activity of the nuclide actually measured after oxidation, MBq / t;

[0092] A Δ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s);

[0093] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0094] t: purification time, s.

[0095] Specifically, the establishment of the nuclide specific activity prediction model includes the following steps:

[0096] 1) In view of the characteristics of continuous release of radionuclides in the primary coolant after the oxidation peak, the differential equation of the coolant radionuclides during the continuous purification period after the oxidation peak is listed as follows:

[0097] dA n,mode =(A Δ ―λ eq ·A n,mode )·dt

[0098] in:

[0099] A n,mode : specific activity of the nuclide at time t under ideal conditions (no deposition and additional release), MBq / t;

[0100] AΔ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s);

[0101] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0102] t: purification time, s.

[0103] 2) Integrate the above equation and substitute the initial conditions. When t=0, A n,mode =A0, the above nuclide specific activity estimation model can be obtained.

[0104] (2) Draw the purification curve:

[0105] 1) Calculate the equivalent attenuation coefficient. The nuclide equivalent attenuation coefficient is calculated using the following relationship:

[0106]

[0107] in:

[0108] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0109] M w : Total mass of coolant in the primary circuit and purification circuit, t;

[0110] λ n : decay constant of the nuclide, s -1 ;

[0111] F RCV : primary circuit coolant discharge purification flow rate, t / s;

[0112] P urifnRCV : Removal factor of the purification system, dimensionless.

[0113] 2) The theoretical lower limit of the specific activity release rate of the nuclide after the peak of oxidation is determined. Δ,min and the expected upper limit A Δ,max The calculation is as follows:

[0114] A Δ,min =0 means no sustained release, A Δ,max Determined by the following formula:

[0115]

[0116] in:

[0117] A 平衡 : The equilibrium value of the specific activity of the nuclide when the oxidation purification time is infinite, MBq / t.

[0118] The specific activity equilibrium value A of the nuclide 平衡 Take 1% of the oxidation peak A0 of the nuclide, that is:

[0119] A 平衡 =0.01·A0

[0120] in:

[0121] A0: The peak specific activity of the nuclide actually measured after oxidation, MBq / t.

[0122] 3) Substitute the equivalent attenuation coefficient and the theoretical lower limit and expected upper limit of the specific activity release rate of the nuclide after the peak of oxidation into the nuclide specific activity prediction model to obtain the theoretical lower limit purification curve of the nuclide specific activity (A n,min -t curve) and the expected upper limit purification curve (A n,max -t curve).

[0123] (3) Compare the relative positions of the measured values ​​and the purification curves to analyze abnormalities in the oxidation purification process:

[0124] Determine whether deposition or additional release occurs. Compare the measured specific activity of the nuclide at time t to see if it is within the expected range (i.e. the measured value is within A n,min With A n,max If the measured value is within the expected range, it is considered that no abnormality has occurred during this stage; if the measured value is outside the expected range, it is considered that deposition or additional release has occurred.

[0125] (4) When there is an abnormal situation of deposition or extra release, the purification curve is corrected, specifically including the following steps:

[0126] S1. Correction steps:

[0127] 1) When the measured value n,min When , it is determined that deposition has occurred. At this time, the nuclide specific activity estimation model is corrected for deposition:

[0128]

[0129] in:

[0130] A′ n : specific activity of the nuclide at time t after sedimentation correction, MBq / t;

[0131] η: Sedimentation factor, dimensionless.

[0132] Deposition mainly occurs in the initial short period of time after the oxidation peak. Assuming that deposition occurs between the n-1th measurement and the nth measurement after the peak, the deposition factor η is determined by the following formula: ​

[0133]

[0134] in:

[0135] A n,measure : The nth measured value of specific activity after the nuclide peak appears, MBq / t;

[0136] A n,mode : The calculated value of the nuclide at the same time for the nth measurement, MBq / t.

[0137] 2) When the measured value>A n,max When the additional release occurs, it is determined that the additional release occurs. At this time, the purification curve of the nuclide between the two measurement points where the additional release occurs is subjected to the sustained specific activity release rate A. Δ Correction, then according to A Δ The calculated value of the next measurement point is obtained from the corrected curve, and the specific activity peak value A0 of the purification curve after two measurement points is corrected with the calculated value.

[0138] Assuming that the additional release occurs between the n-1th measurement and the nth measurement after the peak, the corrected A Δ ' is determined by the following formula:

[0139]

[0140] in,

[0141] A Δ ′: specific activity release rate after correction for additional release of nuclides, MBq / (t·s);

[0142] A n,measure : The nth measured value of specific activity after the nuclide peak appears, MBq / t;

[0143] A n―1,measure : The measured value of the specific activity at the n-1th time after the nuclide peak appears, MBq / t;

[0144] t Δ : the time interval between the n-1th measurement and the nth measurement, s;

[0145] A Δ ′ is substituted into the nuclide specific activity prediction model, and the expected upper limit value A corresponding to the n-1th measured value is used. n―1,max By replacing A0 in the nuclide specific activity prediction model with t′, we can obtain the additional release-corrected nuclide specific activity at each moment between the n-1th measurement and the nth measurement, which is recorded as A′. n ′; Then, when calculating the nuclide specific activity after the nth measurement point, A in the nuclide specific activity prediction model ΔThe expected upper limit value A of the specific activity release rate of the nuclide after the peak of oxidation is still used. Δ,max , A0 uses the predicted upper limit value A′ at the nth measurement point n ' ,max Replacement;

[0146] Additional release of the corrected A′ between the n-1th measurement and the nth measurement n ′, is determined by the following formula:

[0147]

[0148] in,

[0149] A′ n ′: specific activity at time t′ after additional release correction between the n-1th measurement point and the nth measurement point, MBq / t;

[0150] A n―1,max : the expected upper limit value corresponding to the n-1th measurement point, MBq / t;

[0151] A Δ ′: specific activity release rate after correction for additional release of nuclides, MBq / (t·s);

[0152] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0153] t′: purification time starting from the n-1th measurement point, s;

[0154] Nuclide specific activity A′ after the nth measurement point n ″, is determined by the following formula:

[0155]

[0156] in,

[0157] A″ n,max : the expected upper limit of specific activity after additional release correction at the nth measurement point, MBq / t;

[0158] A Δ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s);

[0159] λ eq : Nuclide equivalent attenuation coefficient, s -1 ;

[0160] t″: Purification time starting from the nth measurement point, s.

[0161] S2. Based on the corrected curve obtained in step S1, the subsequent measured values ​​are analyzed for abnormal conditions in step (3);

[0162] S3. Repeat steps S1 and S2 until there are no more abnormalities.

[0163] In carrying out step (4) or repeating step (4), do not n,min Additional release correction is performed because A Δ,min A value of 0 means no sustained release or excess release at all.

[0164] (5) Determine the duration of oxidation purification:

[0165] The oxidation purification time is determined based on the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if deposition or additional release occurs during the oxidation purification process, the oxidation purification time is determined based on the revised expected upper limit purification curve obtained in step (4).

[0166] The deactivation of the last main pump during an oxidation cleanup phase marks the end of the process. Therefore, determining the duration of an oxidation cleanup is equivalent to determining when to deactivate the last main pump. Provided that the radiochemical criteria for deactivating the last main pump are met, the decision to deactivate the last main pump can be made when the hourly decrease in the primary coolant specific activity is ≤530 MBq / t. Specifically, the hourly decrease in specific activity is calculated based on the expected upper limit of the decontamination curve or a revised expected upper limit of the specific activity curve. The end of oxidation cleanup is determined when the hourly decrease in specific activity is ≤530 MBq / t.

[0167] (6) Evaluation of oxidation purification effect:

[0168] By comparing the measured value of the radionuclide specific activity in the first circuit before the last main pump is shut down to see whether it is within the theoretical lower limit of the ideal model and the expected upper limit, an overall evaluation of the oxidation purification effect is given.

[0169] Specifically, the relative positions of the measured value of the nuclide specific activity before the end of the oxidation purification are compared with the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity obtained in step (2). If the theoretical lower limit corresponding to the time is ≤ the measured value ≤ the expected upper limit corresponding to the time, the oxidation purification effect meets expectations.

[0170] Example 1

[0171] Before oxidation of the primary coolant in a nuclear power plant during an overhaul (at 18:10 on the 23rd of a certain month), the actual measured nuclide Co-58 was 21335 MBq / t. After oxidation (at 18:35 on the 23rd of a certain month), the actual measured peak value of the nuclide Co-58 was 142000 MBq / t, that is, A0 = 142000 MBq / t.

[0172] According to the data in Table 1, the equivalent attenuation coefficient λ of Co-58 nuclide is calculated using the relationship between the equivalent attenuation coefficient of nuclide eq =4.06×10 -5 s -1 ; Further according to A Δ,max The expression is calculated to be A Δ,max =5.77E-02MBq / (ts).

[0173] Table 1 Values ​​of relevant parameters of the primary coolant nuclide specific activity variation trend model

[0174]

[0175]

[0176] λ eq The values ​​of A0 are substituted into the nuclide specific activity prediction model of the present invention, and A Δ =A Δ,max and A Δ =A Δ,min , and obtain the theoretical lower limit purification curve of Co-58 specific activity (A n,min -t curve) and the expected upper limit purification curve (A n,max -t curve), see Figure 1 .

[0177] Comparison of Co-58 specific activity values ​​measured at different times and Figure 1 The theoretical lower limit and expected upper limit at each moment are shown in Table 2.

[0178] Table 2: Measured and estimated Co-58 specific activity data (MBq / t)

[0179] Measurement date and time: 18:20:00 18:35:00 18:50:00 19:05:00 19:20:00 19:35:00 19:50:00 21:05:00 <![CDATA[A n,max ]]> 21335 142000 136897 131979 127240 122673 118272 98549 <![CDATA[A n,measure ]]> 21335 142000 130000 121000 115000 110000 102000 85500 <![CDATA[A n,min ]]> 21335 142000 136846 131878 127091 122478 118032 98110 Measurement date and time: 21:20:00 22:05:00 0:05:00 4:05:00 6:05:00 8:05:00 12:05:00 16:05:00 <![CDATA[A n,max ]]> 95023 85195 63744 35913 27080 20509 11984 7266 <![CDATA[A n,measure ]]> 82900 74100 54000 29100 21800 16700 15400 8940 <![CDATA[A n,min ]]> 94549 84622 62954 34842 25921 19284 10673 5907 Measurement date and time: 17:05:00 18:05:00 19:05:00 20:05:00 22:05:00 23:05:00 \ \ <![CDATA[A n,max ]]> 6462 5769 5171 4655 3826 3495 \ \ <![CDATA[A n,measure ]]> 7790 6808 5910 5230 3970 \ \ <![CDATA[A n,min ]]> 5095 4394 3790 3269 2432 2098 \ \

[0180] In order to more intuitively compare the measured values ​​with the estimated values, the data in Table 2 are made into a curve graph, as shown in Figure 2 shown.

[0181] (1) Evaluation of oxidation purification effect during the process

[0182] from Figure 2As can be seen, the measured value "d1" is below the two estimated curves, which indicates that deposition occurred from the peak to the time corresponding to point "d1". In order to accurately determine whether deposition continued or additional release occurred in the subsequent process, the two estimated curves were corrected by the deposition factor. According to the above deposition factor relationship, the deposition factor was calculated to be 0.95. The specific activity calculation formula of the estimated curve after point d1 is A' n,min,1 =0.95A n,min , A′ n,max,1 =0.95A n,max ,get Figure 3 .

[0183] from Figure 3 It can be seen that point "d2" is still below the two trend lines of the purification model, indicating that deposition is still occurring from the peak to point "d2". Similarly, it can be judged that deposition is also occurring from "d3", "d4" to "d5" (short-term deposition after the peak is basically inevitable). The same method as point "d1" is used. Figure 3 The estimated curve is corrected for deposition, and the Figure 4 .

[0184] After the estimated curve is corrected by sedimentation factors according to "d1" to "d5", we can get Figure 5 , it can be seen that the next 7 data from "d5" are well in line with the purification curve. Only one data at 12:05 is above the model curve, which indicates that additional release of corrosion products occurred in the short period between 08:05 and 12:05.

[0185] Using A Δ 'The expression is calculated to get A Δ '=5.59E-01MBq / (ts), A Δ Substitute ′ into the nuclide specific activity prediction model,

[0186]

[0187] A′ n,max,5 is the expected upper limit value corresponding to the 12th measurement point calculated based on the expected upper limit purification curve after correction of "d5" above, t' is the purification time starting from the 12th measurement point, and the corrected specific activity A" between the 12th and 13th measurement points is obtained. n The expected upper limit purification curve of this section is as follows Figure 6 As shown in paragraphs d12 to d13 of

[0188] Calculate the expected upper limit of the 13th measurement point based on the corrected curve and record it as A″ n,max, t″ is the purification time starting from the 13th measurement point, and the expected upper limit purification curve calculation formula after the 13th measurement point is:

[0189]

[0190] Among them A Δ Take 5.77E-02MBq / (ts), the curve is as follows Figure 6 As shown, it can be seen that the measured values ​​of the following 6 measurement points are in good agreement with the estimated values.

[0191] (2) Determine the duration of oxidation purification

[0192] In actual measurements during oxidation purification at nuclear power plants, the oxidation peak and the first few sets of measurement data after the peak are all given at the same time after data processing. Therefore, when estimating the duration of oxidation purification, the correction of the first few sets of data after the peak is taken into account. The estimated curve is corrected for the deposition factor according to "d1" to "d5". Using the corrected estimation model, the nuclide specific activity at the 23rd hour is calculated to be A n,max =5762MBq / t, A at 24 hours n,max =5164MBq / t, A at 25 hours n,max =4649MBq / t. The 24th hour saw a decrease of 598MBq / t compared to the 23rd hour, and the 25th hour saw a decrease of 515MBq / t compared to the 24th hour, meeting the standard of an hourly decrease in radionuclide specific activity of 530MBq / t. Therefore, a 25-hour oxidation decontamination period was planned.

[0193] During the purification process, because the data points "d12" and "d13" (see Figure 6 ) during the period, the revised estimation model was used to calculate that the 26th hour was A n,max =5701MBq / t, A at 27 hours n,max =5112MBq / t, A at 28 hours n,max =4604MBq / t. The 27th hour saw a decrease of 589MBq / t compared to the 26th hour, and the 28th hour saw a decrease of 508MBq / t compared to the 27th hour. It was expected that by the 28th hour, the standard hourly reduction in radionuclide specific activity of 530MBq / t would be achieved. Therefore, on the afternoon of the 24th, the nuclear power plant decided to extend the oxidation cleanup period to 28 hours.

[0194] (3) Overall effect evaluation

[0195] The last set of measurement data of the nuclear power plant was measured at 22:05, and the measured value was 3970MBq / t, which is within the expected upper limit of Co-58 specific activity (A n,max)3826MBq / t and the theoretical lower limit specific activity of Co-58 (A n,min )2432MBq / t, so it is believed that the purification operation as a whole did not fully meet the expectations, but the measured value only deviated from the expected value by less than 5%.

[0196] It can be understood that the above embodiments only express the preferred implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, all of which fall within the scope of protection of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should fall within the scope of coverage of the claims of the present invention.

Claims

1. A method for evaluating the oxidation purification effect of a nuclear power plant primary circuit, characterized in that: The following steps are involved: (1) Establish a model for estimating nuclide specific activity, as shown below: in, A n,mode : The specific activity of the nuclide at time t under ideal conditions, that is, when no deposition and additional release occur, MBq / t; A0: The peak specific activity of the nuclide actually measured after oxidation, MBq / t; A Δ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s); λ eq : Nuclide equivalent attenuation coefficient, s -1 ; t: purification time, s; (2) draw the purification curve; (3) Compare the relative positions of the measured values ​​and the purification curves to analyze abnormalities in the oxidation purification process; (4) Correct the purification curve when abnormal conditions of deposition or extra release exist; (5) Determine the duration of oxidation purification; (6) Evaluate the oxidation purification effect.

2. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1, characterized in that: The step (2) of drawing the purification curve comprises: calculating the theoretical lower limit value and the expected upper limit value of the specific activity release rate of the nuclide after the peak value of the oxidation of the nuclide is reached, substituting them into the nuclide specific activity estimation model to obtain the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity; Or / and the abnormal situation analysis of step (3) is as follows: comparing the relative positions of the measured value of the nuclide specific activity with the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if the measured value is less than the theoretical lower limit corresponding to the time, deposition occurs; if the measured value is greater than the expected upper limit corresponding to the time, additional release occurs; Or / and the oxidation purification time length of step (5) is determined as follows: the oxidation purification time length is determined according to the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if deposition or additional release occurs during the oxidation purification process, the oxidation purification time length is determined according to the revised expected upper limit purification curve obtained in step (4); Or / and the evaluation of the oxidation purification effect of the step (6) is: comparing the relative positions of the measured value of the nuclide specific activity before the end of the oxidation purification with the theoretical lower limit purification curve and the expected upper limit purification curve of the nuclide specific activity obtained in step (2); if the theoretical lower limit corresponding to the time is ≤ the measured value ≤ the expected upper limit corresponding to the time, the oxidation purification effect meets expectations.

3. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1 or 2, characterized in that: The nuclide in step (1) is Co-58.

4. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1 or 2, characterized in that: The nuclide equivalent attenuation coefficient in step (1) is obtained by the following relationship: in, λ eq : Nuclide equivalent attenuation coefficient, s -1 ; M w : Total mass of coolant in the primary circuit and purification circuit, t; λ n : decay constant of the nuclide, s -1 ; F RCV : primary circuit coolant discharge purification flow rate, t / s; P urifnRCV : Removal factor of the purification system, dimensionless.

5. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 2, characterized in that: The theoretical lower limit of the specific activity release rate of the nuclide in step (2) after the peak of oxidation is A Δ,min , A Δ,min = 0; the expected upper limit of the specific activity release rate of the nuclide after the peak of oxidation is A Δ,max , 6. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1 or 2, characterized in that: The correction of the purification curve in step (4) comprises the following steps: S1. When deposition occurs, the nuclide specific activity prediction model is corrected by the deposition factor; when additional release occurs, the purification curve of the nuclide between the two measurement points where the additional release occurs is corrected by the sustained specific activity release rate A. Δ Correction, then according to A Δ The calculated value of the next measurement point is obtained from the corrected curve, and the specific activity peak value A0 of the purification curve after two measurement points is corrected with this calculated value; S2. Based on the corrected curve obtained in step S1, the abnormal situation analysis of the subsequent measured values ​​in step (3) is performed; S3. Repeat steps S1 and S2 until there are no abnormalities.

7. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1 or 2, characterized in that: In step (4), when the purification curve is corrected and deposition occurs, the correction steps are: A′ n =η·A n,mode in, A′ n : specific activity of the nuclide at time t after sedimentation correction, MBq / t; η: sedimentation factor, dimensionless; Deposition mainly occurs in the initial short period of time after the oxidation peak. When deposition occurs between the n-1th measurement and the nth measurement after the peak, the deposition factor η is determined by the following formula: in, A n,measure : The nth measured value of specific activity after the nuclide peak appears, MBq / t; A n,mode : The calculated value of the nuclide at the same time for the nth measurement, MBq / t.

8. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1 or 2, characterized in that: In step (4), when the additional release occurs, the correction steps for the purification curve are: When the additional release occurs between the n-1th measurement and the nth measurement after the peak, the corrected A Δ ' is determined by the following formula: in, A Δ ′: specific activity release rate after correction for additional release of nuclides, MBq / (t·s); A n,measure : The nth measured value of specific activity after the nuclide peak appears, MBq / t; A n―1,measure : The measured value of the specific activity at the n-1th time after the nuclide peak appears, MBq / t; t Δ : the time interval between the n-1th measurement and the nth measurement, s; A Δ ′ is substituted into the nuclide specific activity prediction model, and the expected upper limit value A corresponding to the n-1th measured value is used. n―1,max By replacing A0 in the nuclide specific activity prediction model with t′, we can obtain the additional release-corrected nuclide specific activity at each moment between the n-1th measurement and the nth measurement, which is recorded as A′. n ′; Then, when calculating the nuclide specific activity after the nth measurement point, A in the nuclide specific activity prediction model Δ The expected upper limit value A of the specific activity release rate of the nuclide after the peak of oxidation is still used. Δ,max , A0 uses the predicted upper limit value A″ at the nth measurement point n,max Replacement; Additional release of the corrected A′ between the n-1th measurement and the nth measurement n ′, is determined by the following formula: in, A′ n ′: specific activity at time t′ after additional release correction between the n-1th measurement point and the nth measurement point, MBq / t; A n―1,max : the expected upper limit value corresponding to the n-1th measurement point, MBq / t; A Δ ′: specific activity release rate after correction for additional release of nuclides, MBq / (t·s); λ eq : Nuclide equivalent attenuation coefficient, s -1 ; t′: purification time starting from the n-1th measurement point, s; Nuclide specific activity A′ after the nth measurement point n ″, is determined by the following formula: in, A″ n,max : the expected upper limit of specific activity after additional release correction at the nth measurement point, MBq / t; A Δ : the specific activity release rate of the nuclide after the peak of oxidation, MBq / (t·s); λ eq : Nuclide equivalent attenuation coefficient, s -1 ; t″: Purification time starting from the nth measurement point, s.

9. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 1 or 2, characterized in that: In the correction of the purification curve in step (4), when additional release occurs, the theoretical lower limit purification curve of the nuclide specific activity is not corrected.

10. The method for evaluating the oxidation purification effect of the primary circuit of a nuclear power plant according to claim 2, characterized in that: The decision-making oxidation purification time in step (5) is: the hourly decrease in nuclide specific activity is calculated based on the expected upper limit purification curve of the nuclide specific activity or the revised expected upper limit purification curve. When the hourly decrease in nuclide specific activity is ≤530MBq / t, the oxidation purification ends.

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