A method for measuring dynamic rod background current in a pressurized water reactor nuclear power plant

Abstract

The present invention belongs to the field of nuclear power plant reactor physics technology, and specifically relates to a method for measuring dynamic etched rod background current in a pressurized water reactor nuclear power plant. When performing an initial criticality test, a reactivity meter is connected to a power range channel. After the reactivity meter current stabilizes, this time is set as T1. Then, a dilution operation is started, and the dilution extrapolation countdown rate is continuously calculated. The dilution extrapolation countdown rate decreases continuously with the effect of dilution until the current value shows an obvious inflection point, and the reactivity meter current value begins to show a significant increase. The time after the current value shows an obvious inflection point is set as T2. The current value of any period between T1 and T2 is averaged to obtain the dynamic etched rod background current value, thereby obtaining the background current. The dynamic etched rod background current can be determined by this method. The method for measuring the background current is stable, reliable, simple, and can be widely used.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power plant reactor physics, and particularly relates to a method for measuring dynamic rod background current in a pressurized water reactor nuclear power plant. The method can be used to determine the dynamic rod background current. The method for measuring the background current is stable and reliable, simple, and can be promoted for use. Background Art

[0002] In the reactivity measurement of nuclear power plant reactors, the background current introduced by gamma rays emitted by fission products and activation products and the electrical background current introduced by circuit noise (the above two items are collectively referred to as background current) account for a significant proportion of the measured reactivity current, which has a great impact on the measurement of reactor reactivity and must be corrected in the dynamic rod reactivity measurement.

[0003] The current method for obtaining background current in nuclear power plants is to fully insert a set of control rods, introducing a reactivity of approximately -1000 pcm. After waiting approximately 30 minutes, the current is directly measured using a reactivity meter. This current is used as the background current for dynamic rod etching, and combined with the dynamic rod etching method, data processing is used to obtain control rod values. Due to the long 30-minute waiting time, the mid-range current value drops to a lower level. After the rods are withdrawn, it takes at least another 7 minutes to increase the flux to near the Doppler hot spot before the next set of rod values ​​can be measured. Reactor criticality testing and zero-power physics testing are the main tasks of nuclear power plant overhauls. Using traditional methods to obtain background current takes approximately 37 minutes of mainline time, equivalent to a reduction in revenue of approximately 250,000 yuan per unit per cycle. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring the dynamic rod background current in a pressurized water reactor nuclear power plant. By using this method, the dynamic rod background current value required for engineering purposes can be measured during the criticality process. This method can save about 37 minutes of main line overhaul time and increase the revenue of a million-kilowatt unit by about 250,000 yuan per unit per cycle.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for measuring dynamic etched rod background current in a pressurized water reactor nuclear power plant comprises the following steps: for a pressurized water reactor unit, when performing an initial criticality test, connecting a reactivity meter to a power range channel; after the reactivity meter current stabilizes, this time is set as T1; then, a dilution operation is started, and a dilution extrapolation countdown rate is continuously calculated. The dilution extrapolation countdown rate decreases continuously with the effect of dilution until a clear inflection point appears in the current value, and the reactivity meter current value begins to rise significantly; the time after the clear inflection point appears is set as T2; and the current values ​​in any period between T1 and T2 are averaged to obtain the dynamic etched rod background current value, thereby obtaining the background current.

[0007] When the dilution extrapolated countdown rate reaches 0.16, the current value shows an obvious inflection point.

[0008] The time when the dilution extrapolation countdown rate reaches 0.2 is set as T2.

[0009] The method for calculating the background current is shown in the following formula:

[0010]

[0011] I is the background current; ∑i is the sum of the background currents of the reactivity instrument during the selected time period; and n is the number of background currents of the selected reactivity instrument.

[0012] The beneficial effects achieved by the present invention are:

[0013] According to theoretical calculations, when the extrapolated dilution countdown rate (ICRR) is around 0.2, the core reactivity is close to -1000pcm, which is equivalent to the core reactivity when a control rod with a value of about -1000pcm is inserted into the bottom of the core when measuring the background current using the traditional method. Therefore, this method can select the dynamic rod reactivity instrument background current of any period from when the reactivity instrument is just connected to the power range to when the extrapolated dilution countdown rate (ICRR) is greater than 0.20, and calculate the average value to obtain the dynamic rod background current value.

[0014] The advantages of the present invention compared with the existing traditional method for measuring dynamic rod background current are:

[0015] 1. It reduces the waiting time for the reactivity meter current to stabilize when measuring background current using the traditional method, thus saving about 30 minutes of main line time for unit refueling and overhaul;

[0016] 2. The time required to wait for the reactor flux to rise to the Doppler heating point after the traditional method of lifting the rod is reduced by at least 7 minutes;

[0017] 3. Due to the saving of main line time, the units can be connected to the grid and generate electricity in advance, and the million-kilowatt units can increase the income by about RMB 250,000 per unit per cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] For a pressurized water reactor unit, when performing the initial criticality test, connect the reactivity meter to the power range channel. After the reactivity meter current stabilizes, this moment can be set as T1. Then the dilution operation begins, and the dilution extrapolated countdown rate (ICRR) is continuously calculated. The dilution extrapolated countdown rate (ICRR) decreases with the effect of dilution until the dilution extrapolated countdown rate (ICRR) is around 0.16. Figure 1 As shown in the figure, the current value shows a clear inflection point when the dilution extrapolated countdown rate (ICRR) is around 0.16, and the current value of the reactivity meter begins to rise significantly. We conservatively set the dilution extrapolated countdown rate (ICRR) of 0.2 as T2. This method selects the current value of any period from T1 to T2 and calculates the average value to obtain the dynamic rod background current value, which can be used to obtain the background current.

[0021] The method for calculating the background current is detailed in Formula 1:

[0022]

[0023] I is the background current (referring to the upper current or lower current or the sum of the upper and lower currents of the reactivity instrument);

[0024] ∑i is the total background current of the reactivity instrument during the selected time period;

[0025] n is the number of background currents of the selected reactivity instrument.

[0026] This method has been verified by multi-cycle startup data of multiple units, proving that the obtained background current can be applied to the units and the dynamic etching results meet the acceptance criteria.

[0027] Example: Taking the data of a certain cycle start of a unit as an example, the background current of three periods is selected for horizontal comparison. The first background current is the current of a period of time when the reactivity meter is just connected to the power range channel, and the upper background current I is obtained. up1 is 5.10E-10A, the lower background current I down1 The second background current is 8.82E-10A, which is the minimum current obtained by this method. The second background current is the current of the reactivity instrument when the dilution extrapolated countdown rate (ICRR) is 0.2, and the upper background current I is obtained. up2 is 5.17E-10A, and the lower background current I down2The third background current is measured by the traditional method, that is, after inserting the control rod with larger value into the bottom of the reactor and waiting for 30 minutes, the average current of the reactivity instrument over a period of time is selected to obtain the upper background current I up3 is 5.18E-10A, and the lower background current I down3 The background current of the three periods is compared in the following table:

[0028]

[0029] The maximum relative deviation between the background current obtained by this method and the background current obtained by the traditional method is only 1.54%.

[0030] The deviation between the control rod value measured by this method and the control rod value measured by the traditional method is shown in the following table:

[0031]

[0032]

[0033] The maximum relative deviation between the rod value obtained by this method and the rod value obtained by the traditional method is only 1.4%, and the relative deviation between the rod value measured by the traditional method and the rod value calculated by the new method and the theoretical value is less than 4%, indicating that the background current of the reactivity meter in any period of time from the time when the reactivity meter is just connected to the power range to the time when the dilution extrapolated countdown rate (ICRR) is greater than 0.20 can be used for dynamic rod data processing, thereby obtaining a more accurate rod value.

Claims

1. A method for measuring dynamic rod background current in a pressurized water reactor nuclear power plant, characterized by: For pressurized water reactor units, when performing the initial critical test, the reactivity meter is connected to the power range channel. After the reactivity meter current stabilizes, this moment is set as T1. Then the dilution operation is started, and the dilution extrapolation countdown rate is continuously calculated. The dilution extrapolation countdown rate decreases continuously with the effect of dilution until the current value has an obvious inflection point. The reactivity meter current value begins to show a significant increase. The moment after the current value has an obvious inflection point is set as T2. The current value of any period of time between T1 and T2 is selected to obtain the average value, and the dynamic etching rod background current value is obtained, and the background current can be obtained.

2. The method for measuring dynamic rod background current in a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The time when the dilution extrapolation countdown rate reaches 0.2 is set as T2.

3. The method for measuring dynamic rod background current in a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The method for calculating the background current is shown in the following formula: I is the background current; ∑i is the sum of the background current of the reactivity instrument during the selected time period; n is the number of background currents of the selected reactivity instrument.

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