Dynamic control rod reactivity measurement method

Abstract

A method for measuring the dynamic control rod reactivity of a reactor using a fission chamber as an external measuring instrument, the method comprising: maintaining the reactor in a critical state with a set output by inserting a set of reference control rods into the reactor core to a first depth; fully inserting the set of reference control rods into the reactor core from the first depth at a maximum permissible speed, and immediately fully withdrawing the set of reference control rods from the reactor core at a maximum permissible speed; measuring a first signal of the external measuring instrument from before the insertion of the set of reference control rods to after the withdrawal of the set of reference control rods; and determining the static control capability of the set of reference control rods by adding a measurement of the reactor's remaining control capability to a first static reactivity of the reactor calculated using the first signal of the external measuring instrument.

Description

Technical Field

[0001] This invention relates to a method for measuring the responsiveness of a dynamic control rod. Background Technology

[0002] As disclosed in Korean Patent Publication No. 10-0598037 and Korean Patent Publication No. 10-1604100, in the dynamic control rod reactivity measurement method of light water reactor, the prerequisite for the test is that the number of neutrons incident on the external measuring instrument corresponds linearly to the signal of the external measuring instrument.

[0003] When an uncompensated ionization chamber is used as an external measurement instrument, the current (or voltage) signal generated by the external measurement instrument meets these conditions, so the control rod to be measured can be inserted into or pulled out of the core at maximum speed. After removing the background signal from the signal obtained from the external measurement instrument at this time, the dynamic reactivity of the reactor can be obtained using the signal during the external measurement. The final static reactivity of the reactor can be obtained by applying the dynamic to static covnersion factor (DSCF) to the obtained dynamic reactivity.

[0004] However, recently, when low-sensitivity fission chambers are used as external measurement instruments, it has been confirmed that the number of neutrons incident on the external measurement instrument does not maintain linearity with the signal of the external measurement instrument at low outputs within the test range.

[0005] The fission chamber can provide both a pulse signal representing the number of pulses per unit time and a continuous voltage signal, corresponding to the reactor's reactivity. It has been confirmed that at high reactor outputs within the test range, the pulse signal loses its linearity due to the overlap of these pulses (two or three pulses are identified as one pulse), and at low reactor outputs, the voltage signal loses its linearity due to disturbances and noise. In particular, since the voltage signal of the fission chamber is obtained using the variance between the pulse current distribution and the average current value, linearity cannot be mathematically guaranteed at low outputs. Furthermore, methods for interlocking the pulse and voltage signals of the fission chamber can be considered, but the evaluation results vary depending on how the region for maintaining linearity is selected, and further research is needed because the voltage signal post-processing method lacks a mathematical context.

[0006] Therefore, when using a fission chamber as an external measurement instrument in a reactor, a dynamic control rod reactivity measurement method needs to be implemented within a range that ensures the linearity between the number of neutrons incident on the fission chamber and the number of pulses per unit time. Summary of the Invention

[0007] Technical issues

[0008] This invention aims to provide a dynamic control rod reactivity measurement method in a reactor that uses a fission chamber as an external measuring instrument, which has the advantage of having the static control capability of a safe measurement control rod.

[0009] Technical solution

[0010] An exemplary embodiment of the present invention provides a method for measuring the dynamic control rod reactivity of a reactor using a fission chamber as an external measuring instrument. The method includes: maintaining the reactor in a critical state with a set output by inserting a reference control rod bank into the reactor core to a first depth; fully inserting the reference control rod bank into the reactor core from the first depth at a maximum permissible speed, and immediately fully withdrawing the reference control rod bank from the reactor core at a maximum permissible speed; measuring a first signal of the external measuring instrument from before the insertion of the reference control rod bank to after the withdrawal of the reference control rod bank; and determining the static control capability of the reference control rod bank by adding a measurement of the reactor's remaining control capability to a first static reactivity of the reactor calculated using the first signal of the external measuring instrument.

[0011] The method may further include: when the reactor has a set output, maintaining the reactor in a critical state with a set output by inserting a test control rod assembly into the core to a second depth; fully inserting the test control rod assembly into the core from the second depth at the maximum permissible speed, and immediately fully withdrawing the test control rod assembly from the core at the maximum permissible speed, and measuring a second signal from an external measuring instrument from before the insertion of the test control rod assembly to after the withdrawal of the test control rod assembly; and determining the static control capability of the test control rod assembly by adding a measurement of the reactor's remaining control capability to a second static reactivity of the reactor calculated using the second signal from the external measuring instrument.

[0012] The second depth can be deeper than the first depth.

[0013] The reactor's set output can be an output of pulses of the first signal measured by an off-site measuring instrument that do not overlap with each other.

[0014] The reactor's set output can be 10. 5 cps.

[0015] The remaining control capability of the reactor can be measured from 50 pcm to 80 pcm.

[0016] Beneficial effects

[0017] According to an exemplary embodiment, a method for measuring the reactivity of dynamic control rods in a reactor, which uses a fission chamber as an off-core measuring instrument, can be provided, which can safely measure the static control capability of the control rods. Attached Figure Description

[0018] Figure 1This is a flowchart illustrating a dynamic control rod reactivity measurement method according to an exemplary embodiment.

[0019] Figure 2 This is a graph used to illustrate a dynamic control rod reactivity measurement method according to an exemplary embodiment. Specific Implementation

[0021] In the following description, the invention will be further explained with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention. As will be understood by those skilled in the art, the illustrated exemplary embodiments can be modified in various ways without departing from the spirit or scope of the invention.

[0022] Furthermore, unless explicitly stated otherwise, the term “comprising” and its variations (such as “including”, “having”) shall be understood to imply the inclusion of the mentioned elements without excluding any other elements.

[0023] Before nuclear fuel is loaded into the reactor core, the control capabilities of the control rods need to be measured to confirm the suitability of the nuclear design report used in the reactor safety analysis. Within the core, there are multiple control rods that perform this function when it is necessary to adjust heat output or axial output distribution, or when it is necessary to completely terminate the nuclear reaction in the core for various reasons. These multiple control rods do not operate individually, but are managed in multiple control rod groups (e.g., 6 or 10) depending on the reactor size. A control rod group includes 4 or 8 control rod assemblies, and a control rod assembly can include 4 or 12 individual control rods.

[0024] In the following text, the dynamic control rod responsiveness measurement method may refer to measuring the responsiveness of a group of control rods, rather than measuring the responsiveness of individual control rods.

[0025] In the following text, reference will be made to Figure 1 and Figure 2 The following describes a dynamic control rod reactivity measurement method according to an exemplary embodiment. This exemplary embodiment's dynamic control rod reactivity measurement method is for reactors using a fission chamber as an external measuring instrument, but is not limited thereto.

[0026] Figure 1 This is a flowchart illustrating a dynamic control rod reactivity measurement method according to an exemplary embodiment. Figure 2 This is a graph used to illustrate the dynamic control rod reactivity measurement method according to an exemplary embodiment. Figure 2 The x-axis of (a), (b), and (c) represents time, respectively. Figure 2 The y-axis of (a) represents the position of the control rods, which is the depth at which the control rods are inserted into the core. Figure 2 The y-axis of (b) represents the cps as the reactor output, and Figure 2 The y-axis of (c) is the pcm representing the dynamic reactivity of the reactor.

[0027] Reference Figure 1 and Figure 2 The reference control rod assembly (rod assembly A5) is inserted into the core to a first depth to maintain the reactor in a critical state with a set output (S100).

[0028] Specifically, the reference control rod assembly (rod assembly A5) is inserted into the subcritical core with a dynamic reactivity of 60 pcm to a first depth of approximately 20 cm to 40 cm, thereby reaching the control rod position at 350 cm, thus maintaining the reactor at a dynamic reactivity of 10 pcm. 5 The critical state of CPS's set output. At this point, 10 is the set output of the reactor. 5 CPS is the maximum output of pulses in the fission chamber, which serves as an external measuring instrument, where the pulses do not overlap. In other words, the reactor's set output is 10. 5 cps is the maximum output of the pulse signal of the off-site measuring instrument where the pulses do not overlap.

[0029] Then, the reference control rod assembly (rod assembly A5) is fully inserted into the core from the first depth at the maximum permissible speed, and immediately pulled out of the core at the maximum permissible speed. The first signal of the external measuring instrument is measured from before the insertion of the reference control rod assembly to after the removal of the reference control rod assembly (S200).

[0030] Specifically, without withdrawing the reference control rod assembly (rod assembly A5) from the first insertion depth, the reference control rod assembly (rod assembly A5) is fully inserted into the reactor core from the control rod position of 350 cm, which is the initial insertion depth, at the maximum permissible speed, and immediately withdrawn from the reactor core to the control rod position of 375 cm at the maximum permissible speed. At this time, from 1 minute before the insertion of the reference control rod assembly (rod assembly A5) to 1 minute after the withdrawal of the reference control rod assembly (rod assembly A5), the first signal, which is the pulse signal of the off-core measuring instrument, is measured.

[0031] On the other hand, Korean Patent Publication No. 10-0598037, as a relevant document, discloses that after the control rod assembly is completely pulled out from the first depth, the control rod assembly is fully inserted into the reactor core at the maximum permissible speed and then pulled out from the reactor core, thereby allowing the control rods to be inserted and removed when the output of the reactor core fluctuates.

[0032] Next, the static control capability of the reference control rod group (rod group A5) is determined by adding the reactor’s first static reactivity calculated using the first signal from the off-site measuring instrument to the reactor’s remaining control capability measurement value (S300).

[0033] Specifically, the density-to-response conversion factor (DRCF) and the dynamic-to-static conversion factor (DSCF) are generated by inputting the control rod position from the insertion height of the reference control rod group (rod group A5) to the control rod position when the control rod is fully inserted into the RAST-K code. The first static reactivity of the reactor is then calculated by inputting the generated DSCF and DRCF, the first signal measured by the external measuring instrument, and the control rod position at the insertion height of the reference control rod group (rod group A5) into the setting computer code.

[0034] On the other hand, Korean Patent Publication No. 10-0598037, as a relevant document, discloses that DSCF and DRCF can be calculated in advance. However, in the dynamic control rod reactivity measurement method according to the exemplary embodiment, since the control rod height corresponding to 60 pcm (i.e., reactivity that maintains the critical state of the reactor) may be different for each control rod group in the field, DSCF and DRCF need to be generated each time.

[0035] Furthermore, since the external measurement instrument, which serves as the fission chamber, only utilizes pulse signals based on neutron number and uranium reaction, the external measurement instrument does not require a background signal compensation algorithm, and can be improved by not applying the background signal compensation algorithm in the setting computer code.

[0036] By using it as a measure of residual control capability ( Figure 2 The final static control capability of the reference control rod group (group A5) is determined by adding 60 pcm of the control capability measurement value of section (A) of (c) to the first static reactivity of the reactor calculated in the setup computer code. Then, the final static control capability of the reference control rod group (group A5) is compared with the static control capability of the reference control rod group in the nuclear design report.

[0037] Meanwhile, the remaining control capability measurement can be between 50 pcm and 80 pcm.

[0038] On the other hand, Korean Patent Publication No. 10-0598037, as a related document, discloses calculating the final static control capability of the control rod assembly in the setting computer code. However, in the dynamic control rod reactivity measurement method according to an exemplary embodiment, it is determined by adding 60 pcm, which is the remaining control capability measurement value, to the first static reactivity of the reactor calculated in the setting computer code.

[0039] Next, when the reactor has a set output, the first test control rod group (rod group R1) is inserted into the core to a second depth to keep the reactor in a critical state with a set output.

[0040] Specifically, because the reference control rod assembly (rod assembly A5) is completely removed from the core, 60 pcm of positive reactivity is added to the core, thus increasing the cps exponent as a reactor output. When the reactor reaches 10... 5 When setting the CPS output, the first test control rod group (rod group R1) is inserted into the core to a second depth deeper than the first depth of the reference control rod group (rod group A5), thereby reaching the control rod position of 340 cm, and with a 10 5 The set output of the CPS is maintained at the critical state for approximately 100 seconds. When the reactor remains in the critical state, the control rods, serving as the insertion position for the first test control rod group (rod group R1), are positioned at a compensation of 60 pcm, and the slow-emission neutron cluster of the reactor is sufficient to stop fluctuations after 100 seconds. Furthermore, because the reactor maintains a set output of 10 pcm, the pulses of the pulse signal from the external measuring instrument do not overlap. 5 cps does not cause linearity problems in pulse signals measured by off-pile measuring instruments.

[0041] Then, the first test control rod group (rod group R1) is fully inserted into the core from the second depth at the maximum permissible speed, and immediately pulled out of the core at the maximum permissible speed. The second signal of the external measuring instrument is measured from before the insertion of the first test control rod group (rod group R1) to after the removal of the first test control rod group.

[0042] Specifically, without removing the first test control rod group (rod group R1) from the second depth, the first test control rod group (rod group R1) is fully inserted into the reactor core at the maximum permissible speed from the control rod position of 340 cm, which is the initial insertion depth of the second depth, and is immediately fully pulled out of the reactor core to the control rod position of 375 cm at the maximum permissible speed. At this time, from 1 minute before the insertion of the first test control rod group (rod group R1) to 1 minute after the extraction of the first test control rod group (rod group R1), a second signal, which is the pulse signal of the off-core measuring instrument, is measured.

[0043] Next, the static control capability of the first test control rod group (rod group R1) is determined by adding the reactor's remaining control capability measurement value to the reactor's second static reactivity calculated using the second signal from the off-site measuring instrument (S300).

[0044] Specifically, the density response conversion factor (DRCF) and dynamic-to-static conversion factor (DSCF) are generated by inputting the control rod position from the insertion height of the first test control rod group (rod group R1) to the control rod position when the control rod is fully inserted into the RAST-K code. By inputting the generated DSCF and DRCF, the measured second signal from the off-core measuring instrument, and the control rod position as the insertion height of the first test control rod group (rod group R1) into the setting computer code, the second static reactivity of the reactor is calculated.

[0045] By using it as a measure of residual control capability ( Figure 2 The final static control capability of the first test control rod group (rod group R1) is determined by adding 60 pcm of the control capability measurement value of part (A) of (c) to the second static reactivity of the reactor calculated in the setting computer code. Then, the final static control capability of the first test control rod group (rod group R1) is compared with the static control capability of the first test control rod group in the nuclear design report.

[0046] Next, the same method as that used for the first test control rod group (R1) described above is applied to the second test control rod group (R2) to determine the final static control capability of the second test control rod group (R2) and compare it with the static control capability of the second test control rod group in the nuclear design report.

[0047] Specifically, when the reactor reaches 10 5 When setting the output of CPS, the reactor is maintained at a depth of 10 cm by inserting the second test control rod group (rod group R2) into the reactor core to a third depth, deeper than the second depth of the first test control rod group (rod group R1), reaching a control rod position of 320 cm. 5 The critical state of the cps is set, and then the complete insertion and removal of the second test control rod group (rod group R2) is performed in the same way as the first test control rod group (rod group R1) as described above. The final static control capability of the second test control rod group (rod group R2) is determined and compared with the static control capability of the second test control rod group in the nuclear design report.

[0048] As described above, in the dynamic control rod reactivity measurement method according to the exemplary embodiment, the time point at which the control rod is completely withdrawn is not the starting point, but rather the time point at which the portion of the control rod to be measured is inserted into the reactor core is used as the measurement starting point. In the existing method and process disclosed in Korean Patent Publication No. 10-0598037, which is a related document, the control rod is inserted when the reactor output fluctuates. However, in the new process of the dynamic control rod reactivity measurement method according to the exemplary embodiment, the measurement always begins at the reactor's critical time point.

[0049] The control capability from the point when the control rods are completely withdrawn to the critical time point is considered the residual control capability. The reactivity calculated from the pulse signals of the external measuring instruments is strictly speaking dynamic reactivity, but reactivity below approximately 120 pcm shows about a 1% deviation in the dynamic to static reactivity value. Therefore, when the reactivity calculator produces a reactivity between 20 pcm and 70 pcm, even if it is dynamic reactivity, it is considered static reactivity. Thus, the reactivity up to the point where the control rod assembly is partially inserted into the core is the same as the residual control capability (each time at...). Figure 2 (c) (A) part confirmed).

[0050] At the reactor site where dynamic control rod reactivity measurement methods will be implemented, the actual insertion position of the test control rod assembly may not match the insertion position calculated according to the design. Because the critical boron concentration of the reactor varies and the control capability of the reference control rod assembly is determined to be between 60 pcm and 70 pcm, the insertion position of the test control rod assembly will not match the calculated value when the control capability of the reference control rod assembly changes to 60 pcm, 65 pcm, 70 pcm, etc. In particular, the insertion position will change accordingly when the control capability of the test control rod assembly differs from the design value.

[0051] Therefore, in the dynamic control rod reactivity measurement method according to the exemplary embodiment, at the reactor site, various transition analyses are performed from the insertion position of the control rod assembly to full insertion to generate DSCF and DRCF, and then the DSCF and DRCF are substituted into the measurement data to evaluate the static control capability of the control rod assembly.

[0052] The basic process for generating DSCF and DRCF is the same as that disclosed in Korean Patent Publication No. 10-0598037, which is a related document. However, in that related document, the starting point for analysis is the state in which the control rod assembly is completely pulled out while the reactor output fluctuates, while in the dynamic control rod reactivity measurement method according to the exemplary embodiment, the starting point for analysis is the state in which the reactor is in a critical state while the control rod assembly is partially inserted into the core.

[0053] Therefore, regarding the signal increase data of the off-site measuring instrument one minute before the control rod group is inserted at maximum speed, as per Korean Patent Publication No. 10-0598037, which is a relevant document, when generating DSCF and DRCF, it is necessary to perform a complete simulation of continuously moving the reference control rod group, the first test control rod group, and the second test control rod group sequentially. However, in the dynamic control rod reactivity measurement method according to the exemplary embodiment, the test is performed at the reactor critical point, so the DSCF and DRCF of the reference control rod group (rod group A5), the first test control rod group (rod group R1), and the second test control rod group (rod group R2) can be simulated and processed independently, and only one of them is simulated and processed at a time. Therefore, at the reactor site, whether measuring the static control capability of the first test control rod group (rod group R1) or the second test control rod group (rod group R2), for each control rod group, DSCF and DRCF can be generated immediately corresponding to a given insertion position without affecting other control rod groups.

[0054] Since the dynamic control rod reactivity measurement method according to the exemplary embodiment requires immediate generation and utilization of DSCF and DRCF in response to test adjustments at the reactor site, RAST-K and INVERSE 2.0 code as the setup computer code can be used sequentially. However, the entire operation can be automated, and from the user's perspective, it appears superficially no different from executing only INVERSE 1.0 code as the existing setup computer code, but the internal processing differs in the computational flow due to the design and analysis being performed on-site.

[0055] As described above, the dynamic control rod reactivity measurement method according to the exemplary embodiment can measure the dynamic control rod control capability of a reactor that uses the fission chamber as an off-core measuring instrument.

[0056] Furthermore, the dynamic control rod reactivity measurement method according to the exemplary embodiment performs a complete insertion and removal of the control rod assembly without altering the reactor's output in a critical state, thereby safely measuring the control capability of the control rods compared to prior literature on nuclear reactor output fluctuations.

[0057] Furthermore, according to the exemplary embodiment, the dynamic control rod reactivity measurement method ensures that, under the critical state of the reactor, the reactor's set output is at 10% of the maximum output condition where the pulses of the pulse signal from the off-site measuring instrument in the fission chamber do not overlap and always maintain linearity. 5 Performing a complete plugging and unplugging of the control rod group under CPS minimizes the chance of disturbances entering the segment, aiming for excellent evaluation results.

[0058] Furthermore, since the dynamic control rod reactivity measurement method according to the exemplary embodiment can utilize dynamic control rod reactivity technology within the range of ensuring the linearity of the pulse signal of the off-site measuring instrument, the test time can be shortened by 7 hours compared with the conventional boron dilution method and control rod exchange method. Therefore, when the dynamic control rod reactivity measurement method according to the exemplary embodiment is applied to 6 units utilizing the fission chamber, an effect of increasing power generation can be expected over 5 technology life cycles.

[0059] Although exemplary embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. That is to say, any modifications and alterations made by those skilled in the art using the basic concept of the present invention as defined in the claims fall within the scope of the present invention.

[0060] Explanation of reference numerals in the attached figures

[0061] Reference control rod assembly (rod assembly A5)

[0062] First test control rod group (rod group R1)

[0063] Second test control rod group (rod group R2)

Claims

1. A method for measuring the reactivity of dynamic control rods in a reactor that uses a fission chamber as an external measuring instrument, the method comprising: The reactor is maintained in a critical state with a set output by inserting a set of reference control rods into the core to a first depth. The reference control rod assembly is fully inserted into the reactor core from the first depth at the maximum permissible speed, and immediately pulled out of the reactor core at the maximum permissible speed. The first signal of the off-core measuring instrument is measured from before the insertion of the reference control rod assembly until after the removal of the reference control rod assembly. as well as The static control capability of the reference control rod group is determined by adding the measured value of the reactor's remaining control capability to the first static reactivity of the reactor calculated using the first signal from the off-site measuring instrument.

2. The method of claim 1, further comprising: When the reactor has the set output, the reactor is maintained in the critical state with the set output by inserting the test control rod assembly into the core to a second depth; The test control rod assembly is fully inserted into the reactor core from the second depth at the maximum permissible speed, and immediately pulled out of the reactor core at the maximum permissible speed. The second signal of the off-core measuring instrument is measured from before the insertion of the test control rod assembly until after the removal of the test control rod assembly. as well as The static control capability of the test control rod assembly is determined by adding the measured value of the reactor's remaining control capability to the second static reactivity of the reactor calculated using the second signal from the off-pile measuring instrument.

3. The method of claim 2, wherein, The second depth is deeper than the first depth.

4. The method of claim 1, wherein, The set output of the reactor is the output of pulses of the first signal measured by the off-pile measuring instrument that do not overlap with each other.

5. The method of claim 4, wherein, The set output of the reactor is 10 5 cps.

6. The method of claim 1, wherein, The reactor's remaining control capability was measured to be between 50 pcm and 80 pcm.

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