A method for measuring the value of subcritical regulator rods in heavy water reactors

Abstract

The present invention belongs to the technical field of nuclear reactor physical testing, and specifically relates to a method for measuring the value of regulating rods under subcriticality of a heavy water reactor. The method comprises the following steps: Step 1: Calculation of the regulating rod correction factor is completed before the test begins; Step 2: The reactor is detoxified and reaches criticality according to the normal startup and criticality steps until the reactor enters the second stage of criticality, after the startup instrument exits and the off-core ionization chamber test is completed, all regulating rods are pulled out of the core during the criticality period; Step 3: After the start of any multiplication operation, the RRS ionization chamber signal is continuously monitored, and the detoxification is stopped at a certain moment before the ionization chamber signal approaches but does not reach the target power of the power multiplication operation; Step 4: Fitting the ICRR linear relationship intended for regulating rod value measurement; Step 5: Inserting 21 regulating rods in sequence; Step 6: Calculating the 1 / M corresponding to the corrected signal i Step 7: Use the ICRR linear relationship Y=aX+b fitted in step 4 to extrapolate and calculate the value of 1 / M in step 6 i The corresponding value R i Step 8: Calculate the values ​​of the 21 regulating rods. The present invention eliminates the need to measure the reactivity of the LZC water level and eliminates the need to adjust the LZC water level range by detoxification or addition of toxins. This reduces testing time, shortens overhaul periods, and reduces radioactive waste generation.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear reactor physical testing, and in particular relates to a method for measuring the value of a subcritical regulating rod of a heavy water reactor. Background Art

[0002] The unique design and operation of heavy water reactors (HWRs) are widely utilized both domestically and internationally to produce high-specific-activity cobalt-60 radioactive sources. During each outage and overhaul, new cobalt regulator rods are replaced. Upon startup, the newly inserted regulator rods are measured to verify that their neutronic properties are consistent with the design. Traditionally, regulator rod measurement tests are conducted on a post-critical zero-power platform. These tests include three sub-projects: liquid zone control (LZC) value measurement, single regulator rod value measurement, and rod group value measurement. By inserting or removing regulator rods during criticality, the reactivity value of the measured regulator rods is calculated based on the water level changes in the LZC. Therefore, before measuring the regulator rod value, the LZC water level must be measured. The entire test process requires frequent detoxification and addition of poisons to adjust the LZC water level range, involving extensive operational operations and the consumption of poisons and purification resins. The test is lengthy and occurs during the unit's overhaul critical path, impacting the unit's safe and economical operation. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for measuring the value of subcritical regulating rods in heavy water reactors, which avoids frequent poisoning and detoxification operations, saves a large amount of resin, significantly reduces the generation of radioactive waste, and improves the economy and safety of unit operation.

[0004] The technical solution of the present invention is as follows: A method for measuring the value of a subcritical regulator rod of a heavy water reactor comprises the following steps:

[0005] Step 1: Complete the calculation of the adjustment rod correction factor before the test begins;

[0006] Step 2: The reactor is detoxified and criticalized according to normal startup and criticality procedures until the reactor enters the second stage of criticality. That is, after the startup instrument is removed and the external ionization chamber test is completed, all the regulating rods are pulled out of the core during the criticality period.

[0007] Step 3: After any power doubling operation begins, continuously monitor the RRS ionization chamber signal and stop the detoxification at a certain moment when the ionization chamber signal approaches but does not reach the target power of the power doubling operation;

[0008] Step 4: Use the least squares method to fit the ICRR linear relationship to be used to adjust the value measurement of the stick;

[0009] Step 5: Insert the 21 adjustment rods in sequence according to the designed insertion order;

[0010] Step 6: Calculate 1 / M corresponding to the corrected signal i value, i is the corresponding adjustment rod number, i = 1, ..., 21;

[0011] Step 7: Use the ICRR linear relationship Y = aX + b fitted in step 4 to extrapolate and calculate the 1 / M in step 6 i The corresponding value R i ;

[0012] Step 8: Calculate the value of each of the 21 adjustment rods.

[0013] The step 4 includes:

[0014] Step 41: Based on the most recent moderator poison concentration sampling and analysis data, the continuously collected purge flow rate, and the purge duration, calculate the continuously changing poison concentration in the core over a period of time until the detoxification is stopped, and the corresponding core subcriticality, which is recorded as X j , j corresponds to different moments, and the core subcriticality at the moment of stopping detoxification is recorded as X0;

[0015] Step 42: Collect the signals of the three RRS off-pile ionization chambers in the same period as step 41, and select the ionization chamber signal with the best linearity by observation and comparison, which is recorded as Y j ;

[0016] Step 43: The two sets of data points (X j , Y j ) is fitted with the least squares method, and the data points that deviate from the fitted curve by more than d% are removed using the linear relationship obtained by fitting. The least squares fitting is performed again using the retained data points. The above process is iterated until all data points are accepted, thereby obtaining the final ICRR linear relationship Y = aX + b.

[0017] The step 5 includes waiting for the RRS ionization chamber signal to stabilize after each adjustment rod is inserted, collecting the stabilized ionization chamber signal, and correcting the signal using the correction factor corresponding to the inserted adjustment rod calculated in step 1.

[0018] The step 8 includes inserting the regulating rods into the core in the order in which the regulating rods are inserted first into the core. i -X0, the rest of the adjustment sticks are valued at R i m -R i m-1 , m is the insertion order corresponding to the adjustment rod, m = 2,…, 21.

[0019] The adjustment rod correction factor C in step 1 is iThe calculation process is as follows: the flux value S of the RRS ionization chamber outside the pile corresponding to the core state when the regulating rod i is at the top and at the bottom of the pile is simulated respectively. o With S i , then the spatial correction factor C of the adjustment rod i is i =S o / S i .

[0020] The correction in step 5 is as follows: Assume that the regulating rod i is inserted into the core and the RRS ionization chamber signal after stabilization is S i,b , then the corrected signal S i,c =S i,b ×C i .

[0021] In step 7, 1 / M i Substitute Y in Y=aX+b and solve X(R i ), R i =(1 / M i -b) / a.

[0022] The beneficial effects of the present invention are as follows: the application of the present invention does not require the reactivity of the LZC water level to be measured first, nor does it require the LZC water level interval to be adjusted by detoxification or addition of poisons, which can reduce the test time, shorten the overhaul period, and reduce the amount of radioactive waste generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 To adjust the spatial effect of the rod;

[0024] Figure 2 Fitting the linear relationship of ICRR;

[0025] Figure 3 The present invention provides a flow chart of a method for measuring the value of a heavy water reactor subcritical regulator rod. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The criticality of a heavy water reactor is achieved by dilution, i.e., the moderator purification system is used to continuously remove neutron poisons (mainly Gd). This method makes full use of the characteristics of the heavy water reactor itself and the good linear relationship between the signal of the RRS ionization chamber of the reactor control system and the subcriticality of the core during the criticality process. The spatial effect in the RRS ionization chamber signal introduced by the action of the regulating rod is eliminated by applying a spatial correction factor (see Figure 1 ), and then use the pre-fitted linear relationship between the countdown rate 1 / M and the subcriticality (ICRR) to measure the value of the adjustment rod group.

[0028] A method for measuring the value of a heavy water reactor subcritical regulator rod comprises the following steps:

[0029] Step 1: Complete the calculation of the adjustment rod correction factor before the test begins

[0030] When calculating the regulating rod space correction factor, given that the value of the regulating rod is generally small, it is necessary to comprehensively and accurately consider all factors that may affect reactivity under the test conditions when defining the core state, including: a) core power level b) core burnup distribution c) Gd concentration in the moderator d) B concentration in the moderator e) LZC average water level f) moderator temperature g) coolant temperature h) moderator liquid level i) moderator heavy water purity j) coolant heavy water purity. When using the core program to simulate the test state, starting from the instantaneous core state before shutdown, the reactor is simulated from full power to ~1×10 -7 The transient process of FP is simulated, and then the long-term shutdown condition is simulated. Finally, starting from the long-term shutdown state, the core state under different rod states during the test condition is simulated to obtain the flux at different channels of the RRS ionization chamber outside the pile, and then the regulating rod correction factor C is calculated. i (i is the number of the adjustment rod, i=1,…,21) for use during testing.

[0031] Adjustment rod correction factor C i The calculation process is as follows:

[0032] Taking the regulating rod i as an example, the flux value S of the RRS ionization chamber outside the pile corresponding to the core state when the regulating rod i is at the top and at the bottom of the pile is simulated respectively. o With S i , then the spatial correction factor C of the adjustment rod i is i =S o / S i .

[0033] Step 2: The reactor is detoxified and criticalized according to the normal startup and criticality steps until the reactor enters the second stage of criticality, that is, after the startup instrument is withdrawn and the external ionization chamber test is completed, all the regulating rods are pulled out of the core during the criticality period. Considering that the core of the heavy water reactor is closer to the critical state in the second stage of criticality, the RRS ionization chamber signal is higher (the reactor power reaches 10 -6 FP even 10 -5 FP), ICRR linearity is better, so the adjustment rod value measurement test is chosen to be carried out at this stage.

[0034] Step 3: After any power doubling operation begins, continuously monitor the RRS ionization chamber signal. Stop the detoxification when the ionization chamber signal approaches but does not reach the target power of the power doubling operation, that is, when the power deviation EP is about to become 0.

[0035] During the test, after the power doubler operation, the reactor power deviation (EP) is monitored in real time. EP represents the difference between the current power and the target power. When EP = 0, it means that the current power represented by the ionization chamber signal has reached the target power of the doubler operation. Detoxification is terminated when EP approaches but does not equal 0. The specific EP value at which detoxification is terminated can be determined by the physics test personnel and is not strictly limited.

[0036] Step 4: Use the least squares method to fit the ICRR linear relationship to be used to adjust the stick value measurement.

[0037] Specific operations include:

[0038] Step 41: Based on the most recent moderator poison concentration sampling and analysis data, the continuously collected purge flow rate and the purge duration, calculate the continuously changing poison concentration in the core over a period of time (until the detoxification is stopped), and the corresponding core subcriticality, which is recorded as X j , j corresponds to different moments. The core subcriticality at the moment of stopping detoxification is recorded as X0.

[0039] Step 42: Collect the signals of the three RRS off-pile ionization chambers in the same period as step 41, and select the ionization chamber signal with the best linearity by observation and comparison, which is recorded as Y j .

[0040] Step 43: The two sets of data points (X j , Y j ) is used to perform a least squares fit. The linear relationship obtained by fitting is used to remove data points that deviate from the fitting curve by more than d% (e.g., d = 0.3, d can be determined based on the quality and number of actual data points). The least squares fit is then performed again using the remaining data points. The above process is iterated until all data points are accepted, thereby obtaining the final ICRR linear relationship Y = aX + b, see Figure 2 .

[0041] Y=aX+b is a linear relationship, which can be regarded as an equation. a and b are the fitted coefficients and are known parameters; X and Y are unknown quantities, X is the independent variable, and Y is the dependent variable.

[0042] Step 5: Insert all 21 adjustment rods in the designed insertion sequence. After each rod is inserted, wait for the RRS ionization chamber signal to stabilize. Collect the stabilized ionization chamber signal and correct it using the correction factor corresponding to the inserted adjustment rod calculated in Step 1.

[0043] The corrections are as follows:

[0044] Assuming that the regulating rod i is inserted into the core, the RRS ionization chamber signal after stabilization is Si,b , then the corrected signal S i,c =S i,b ×C i .

[0045] Step 6: Calculate 1 / M corresponding to the corrected signal i value (i is the corresponding adjustment rod number, i=1,...,21).

[0046] In the field of reactor physics, the ICRR linear relationship is also called the "1 / M extrapolation curve", so the value obtained by processing the measured signal is usually expressed as 1 / M, but it can also be expressed as 1 / S i,c replace.

[0047] 1 / M i =1 / S i,c .

[0048] Step 7: Use the ICRR linear relationship Y = aX + b fitted in step 4 to extrapolate and calculate the 1 / M in step 6 i The corresponding value R i .

[0049] R i =(1 / M i -b) / a.

[0050] Step 8: Calculate the value of each of the 21 adjustment rods.

[0051] According to the order in which the regulating rods are inserted into the core, the value of the regulating rod inserted first is R i -X0, the rest of the adjustment sticks are valued at R i m -R i m-1 , m is the insertion order corresponding to the adjustment rod, m = 2,…, 21.

[0052] The economic benefit analysis is as follows:

[0053] Assuming that the full insertion process of a single regulating rod into the reactor core (including waiting for the ionization chamber signal to stabilize) takes 2 minutes, the total time required to insert all 21 regulating rods is 42 minutes, or less than 1 hour, with detoxification operations suspended during the test. Assuming that the operation of lifting all regulating rods out of the reactor also takes up criticality time, detoxification operations must also be suspended during this period from the perspective of reactivity management. Therefore, the delay in achieving criticality due to the suspension of detoxification for the regulating rod value measurement test is estimated to be less than 2 hours. Compared with current practices, the new method will no longer require separate LZC water level value measurement. Single-rod and rod group value measurement tests can be completed simultaneously, which is expected to save more than 12 hours of overhaul mainline time. In addition, compared with current testing practices, the new method avoids frequent poisoning and detoxification operations, saves a large amount of resin, and significantly reduces the generation of radioactive waste, with extremely significant economic benefits.

Claims

1. A method for measuring the value of a heavy water reactor subcritical regulator rod, characterized in that: The steps include: Step 1: Complete the calculation of the adjustment rod correction factor before the test begins; Step 2: The reactor is detoxified and criticalized according to normal startup and criticality procedures until the reactor enters the second stage of criticality. That is, after the startup instrument is removed and the external ionization chamber test is completed, all the regulating rods are pulled out of the core during the criticality period. Step 3: After any power doubling operation begins, continuously monitor the RRS ionization chamber signal and stop the detoxification at a certain moment when the ionization chamber signal approaches but does not reach the target power of the power doubling operation; Step 4: Use the least squares method to fit the ICRR linear relationship to be used to adjust the value measurement of the stick; The step 4 includes: Step 41: Based on the most recent moderator poison concentration sampling and analysis data, the continuously collected purge flow rate, and the purge duration, calculate the continuously changing poison concentration in the core over a period of time until the detoxification is stopped, and the corresponding core subcriticality, which is recorded as X j , j corresponds to different moments, and the core subcriticality at the moment of stopping detoxification is recorded as X0; Step 42: Collect the signals of the three RRS off-pile ionization chambers in the same period as step 41, and select the ionization chamber signal with the best linearity by observation and comparison, which is recorded as Y j ; Step 43: The two sets of data points (X j , Y j ) Perform a least squares fit, use the linear relationship obtained by fitting to remove data points that deviate from the fitting curve by more than d%, and use the retained data points to perform the least squares fit again. Iterate the above process until all data points are accepted, thereby obtaining the final ICRR linear relationship Y = aX + b; Step 5: Insert the 21 adjustment rods in sequence according to the designed insertion order; Step 6: Calculate 1 / M corresponding to the corrected signal i value, i is the corresponding adjustment rod number, i=1,…,21; Step 7: Use the ICRR linear relationship Y=aX+b fitted in step 4 to extrapolate and calculate the 1 / M in step 6 i The corresponding value R i ; Step 8: Calculate the value of each of the 21 adjustment rods.

2. The method for measuring the value of a heavy water reactor subcritical regulator rod according to claim 1, wherein: The step 5 includes waiting for the RRS ionization chamber signal to stabilize after each adjustment rod is inserted, collecting the stabilized ionization chamber signal, and correcting the signal using the correction factor corresponding to the inserted adjustment rod calculated in step 1.

3. The method for measuring the value of a heavy water reactor subcritical regulator rod according to claim 1, wherein: The step 8 includes inserting the regulating rods into the core in the order in which the regulating rods are inserted first into the core. i -X0, the rest of the adjustment sticks are valued at R i m -R i m-1 , m is the insertion order corresponding to the adjustment rod, m=2,…,21.

4. The method for measuring the value of a heavy water reactor subcritical regulator rod according to claim 1, wherein: The adjustment rod correction factor C in step 1 is i The calculation process is as follows: the flux value S of the RRS ionization chamber outside the pile corresponding to the core state when the regulating rod i is at the top and at the bottom of the pile is simulated respectively. o With S i , then the spatial correction factor C of the adjustment rod i is i =S o / S i .

5. The method for measuring the value of a heavy water reactor subcritical regulator rod according to claim 1, wherein: The correction in step 5 is as follows: Assume that the regulating rod i is inserted into the core and the RRS ionization chamber signal after stabilization is S i,b , then the corrected signal S i,c =S i,b ×C i .

6. The method for measuring the value of a heavy water reactor subcritical regulator rod according to claim 1, wherein: In step 7, in the ICRR linear relationship Y=aX+b, a and b are the fitted coefficients, X and Y are unknown quantities, and 1 / M i Substitute Y into Y=aX+b and solve for X(R i ), R i =(1 / M i -b) / a.

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