A method of measuring a temperature coefficient of a moderator

Abstract

This invention relates to the field of nuclear power plant core physics testing technology, specifically to a method for measuring the moderator temperature coefficient. The method includes: Step 1: Confirming measurement conditions, recording the average temperature of the moderator in the main system, calculating the thermal power, and measuring the boron concentration; Step 2: Manually adjusting the boron concentration in the reactor main system, and after the boron concentration in the main system is mixed, measuring the boron concentration and recording the average temperature of the moderator in the main system; Step 3: Calculating the introduced reactivity based on the change in boron concentration, and calculating the isothermal temperature coefficient and the moderator temperature coefficient; Step 4: After the measurement is completed, adjusting the average temperature of the moderator in the main system to restore it to the state before the test. This method provides stable measurement results and is simple and easy to implement. It allows for effective monitoring of the moderator temperature coefficient during the operation of the power plant unit, thus meeting the requirements for reactor core safety supervision.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant core physics testing technology, specifically to a method for measuring the temperature coefficient of a moderator. Background Technology

[0002] The moderator temperature coefficient (MTC) is the change in reactivity caused by a unit change in moderator temperature. A negative MTC is crucial for reactor regulation and operational safety; therefore, the fundamental design principles of pressurized water reactors (PWRs) require that the MTC be negative. During reactor operation, the negative feedback of the MTC plays a vital role in power control and stability. Therefore, monitoring the MTC during the operation of a PWR nuclear power plant is a very important task. According to current technical specifications, the MTC of an operating PWR unit must be measured at 300 ppm at the end of its service life.

[0003] During zero-power physics experiments, the moderator temperature coefficient can be calculated by measuring changes in reactivity using a reactivity meter while altering the moderator temperature. However, for reactors operating under power conditions, reactivity cannot be directly measured due to power feedback within the reactor core, thus the above method cannot be used to measure the moderator temperature coefficient. Summary of the Invention

[0004] This invention provides a method for measuring the temperature coefficient of a moderator, which solves the problem that the temperature coefficient of a moderator cannot be measured in reactors under power conditions in the prior art.

[0005] The technical solution of this invention:

[0006] This invention proposes a method for measuring the temperature coefficient of a moderator, the method comprising the following steps:

[0007] Step 1: Confirm the measurement conditions, record the average temperature of the moderator in the main system, the thermal power of the computer group, and measure the liquid boron concentration in the reactor main system and pressurizer;

[0008] Step 1.1: Confirm that the reactor is in xenon balance; within 2 hours before the test, ensure that the reactor power, average moderator temperature, unit thermal efficiency, and condenser cooling water temperature are stable.

[0009] Step 1.2: Change the control rod assembly from "automatic" to "manual" control mode and record the average temperature of the moderator in the reactor main system for 10 consecutive minutes;

[0010] Step 1.3: Perform a manual heat balance calculation to obtain the unit's accurate thermal power;

[0011] Step 1.4: Manually sample and analyze the boron concentration in the liquid phase of the reactor main system and pressurizer, and determine the stability of the boron concentration based on the sampling and analysis results;

[0012] Step 2: Manually adjust the boron concentration in the reactor main system. After the boron concentration in the main system is stirred and stabilized, measure the boron concentration and record the average temperature of the moderator in the main system.

[0013] Step 3: Measure the change in boron concentration of the coolant in the main system, calculate the introduced reactivity change according to formula (1), calculate the isothermal temperature coefficient according to formula (2), and calculate the moderator temperature coefficient according to formula (3).

[0014]

[0015] Where Δρ represents the reactivity change, Indicates the differential value of boron; ΔC B The change in boron concentration in the main system coolant;

[0016]

[0017] Where, α iso Δρ is the isothermal temperature coefficient; Δρ is the reactivity change; ΔT is the temperature coefficient. avg This represents the change in the average temperature of the moderator in the reactor main system caused by boron concentration adjustment.

[0018]

[0019] Where: α doppler The Doppler temperature coefficient; The temperature coefficient of the moderator; α iso It is the isothermal temperature coefficient;

[0020] Step 4: After the measurement is completed, adjust the average temperature of the moderator in the main system to return to the state before the test.

[0021] In some embodiments, step 1.1, confirming that the reactor should be in xenon balance, includes confirming whether the reactor is in xenon balance based on a power change of less than 2%FP within 48 hours.

[0022] In some embodiments, determining the stability of reactor power, average moderator temperature, unit thermal efficiency, and condenser cooling water temperature within 2 hours before the test in step 1.1 includes: reactor power variation less than 0.5%FP; no boron concentration dilution or boronization in the main reactor system; maintaining reactor power variation within ±0.3%FP; average moderator temperature in the main system stable within ±0.5°C of the reference temperature; stable unit thermal efficiency; and condenser cooling water temperature variation less than 0.5°C.

[0023] In some embodiments, the manual sampling analysis of the liquid boron concentration in the reactor main system and the pressurizer in step 1.4 is performed three times. The results of the manual sampling analysis should meet the following conditions: the deviation of the liquid boron concentration in the reactor main system and the pressurizer is less than 5 ppm, and the deviation of the three boron concentration analysis values ​​of the reactor main system is less than 5 ppm. If the boron concentration is stable, it indicates that there is fluctuation in the boron concentration in the reactor main system, and further stirring is required until the manual sampling analysis results that meet the requirements for boron concentration stability are met.

[0024] In some embodiments, before adjusting the boron concentration in step 2, the required reactivity change to be introduced by a 1°C change in the moderator can be calculated, and the amount of boron concentration to be adjusted can be estimated. The calculation method is as follows:

[0025] The design isothermal temperature coefficient is calculated as shown in formula (4);

[0026]

[0027] in: α is the isothermal temperature coefficient; doppler The Doppler temperature coefficient; To design the temperature coefficient of the moderator;

[0028] The reaction change required to introduce a 1°C change in the moderator is calculated as shown in formula (5);

[0029]

[0030] Where Δρ represents the reactive change, α iso This represents the isothermal temperature coefficient; ΔT is the temperature change of the moderator in the main system, which is 1℃ here.

[0031] The required change in boron concentration for the calculation method is shown in formula (6);

[0032]

[0033] in, To calculate the required change in boron concentration; The differential value of boron is represented by Δρ; Δρ represents the change in reactivity.

[0034] The amount of boron concentration adjustment for dilution or boration is calculated as shown in formula (7);

[0035]

[0036] Where V1 represents the amount of dilution or borylation; V0 represents the amount of water loaded into the reactor main system (t); C0 represents the boron concentration of the reactor main system before dilution; C1 represents the target boron concentration adjustment of the reactor main system; and C represents the boron concentration of the solution injected into the reactor main system, which is 0 ppm during dilution and the boron concentration of the injected concentrated boric acid during borylation.

[0037] In some embodiments, the standard for stabilizing and mixing the boron concentration in the main system in step 2 includes: the deviation of the boron concentration in the reactor main system and the pressurizer liquid phase is less than 5 ppm, and the deviation of the analytical values ​​of the three measurements of the boron concentration in the reactor main system is less than 5 ppm.

[0038] In some embodiments, one method for measuring the change in boron concentration in step 3 is as follows: perform three manual analyses on the boron concentration in the reactor main system before dilution and take the average value; perform three manual analyses on the boron concentration in the reactor main system after stirring and take the average value; the difference between the two is the change in boron concentration in the reactor main system.

[0039] In some embodiments, another method for calculating the change in boron concentration in step 3 is to calculate it by back-calculation using formula (7).

[0040] In some embodiments, step 3 measures the temperature coefficient of the moderator. The temperature coefficient of the moderator is combined with theoretical calculations and corrected for power, boron concentration, temperature and rod position to obtain the temperature coefficient of the moderator under standard conditions. The temperature coefficient of the moderator under standard conditions is used for comparison and analysis with the calculated value of the temperature coefficient of the moderator under a certain standard condition.

[0041] In some embodiments, step 4, adjusting the average temperature of the main system moderator to return to the pre-test level, includes: adjusting the average temperature of the main system moderator by adjusting the control rod assembly or the boron concentration of the reactor main system, so that the average temperature of the main system moderator is balanced with the reference temperature, and changing the control rod assembly from "manual" to "automatic" control mode.

[0042] The implementation of this invention has the following beneficial effects:

[0043] This invention provides a method for measuring the moderator temperature coefficient. The method provides stable measurement results and is simple and easy to implement. This method allows for effective monitoring of the moderator temperature coefficient during power plant unit operation, thus meeting reactor core safety monitoring requirements. It mainly has the following beneficial effects:

[0044] (1) This method is very time-efficient, completing a measurement within 2 hours. Currently, pressurized water reactor units generally use seawater cooling. With the rise and fall of tides, the condenser cooling water temperature fluctuates significantly, causing a noticeable change in the turbine unit's thermal efficiency throughout the day. The traditional method of measuring the moderator temperature coefficient by compensating for the decrease in reactivity caused by fuel consumption by the decrease in the average temperature of the moderator requires the unit to remain stable for more than 12 hours. However, the rise and fall of tides alter the unit's thermal efficiency, greatly affecting this method and even making it impossible to complete the measurement. This invention can quickly measure the moderator temperature coefficient by adjusting the boron concentration, effectively solving the problem of the influence of turbine unit thermal efficiency changes on the measurement.

[0045] (2) This method is not limited by reactor burnup and power. It can quickly and effectively measure the moderator temperature coefficient under any burnup condition. Even in the low-power stable operation stage, the moderator temperature coefficient can be effectively measured.

[0046] (3) During the daily operation of a pressurized water reactor unit, boron dilution of the reactor main system is required every day to compensate for the decrease in reactivity caused by burnup. After each dilution operation, relevant data can be actively collected to estimate the current moderator temperature coefficient and assist in the daily monitoring of the moderator temperature coefficient. Attached Figure Description

[0047] Figure 1 This is a flowchart of a method for measuring the temperature coefficient of a moderator according to the present invention. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] The method described above for measuring the moderator temperature coefficient during power operation of a pressurized water reactor nuclear power plant introduces a step reactivity by actively adjusting the boron concentration. The reactor, relying on its negative feedback self-stabilizing characteristics, automatically lowers / raises the average moderator temperature of the main system to compensate for this step reactivity. The temperature coefficient is measured by calculating the introduced step reactivity and the change in the average moderator temperature. This method yields relatively small and stable measurement results, is simple to operate, and takes little time. It is easy to implement during power operation and allows for convenient monitoring of the moderator temperature coefficient at any burnup point during reactor operation, thereby ensuring reactor core safety.

[0050] This invention proposes a method for measuring the temperature coefficient of a moderator, the method comprising the following steps:

[0051] Step 1: Confirm the measurement conditions, record the average temperature of the moderator in the main system, the thermal power of the computer group, and measure the liquid boron concentration in the reactor main system and pressurizer.

[0052] Step 1.1: Confirm that the reactor is in xenon balance, requiring the reactor power change to be less than 2%FP within 48 hours; within 2 hours before the test, ensure that the reactor power change is less than 0.5%FP, and that there is no boron concentration dilution or boronization in the main reactor system; maintain a stable reactor power level, with changes within ±0.3%FP; ensure the average temperature of the moderator in the main system is stable within ±0.5℃ of the reference temperature; ensure stable unit thermal efficiency, and that the condenser cooling water temperature change is less than 0.5℃.

[0053] Step 1.2: Change the control rod assembly from "automatic" to "manual" control mode and record the average temperature of the moderator in the reactor main system for 10 consecutive minutes;

[0054] Step 1.3: Perform a manual heat balance calculation to obtain the unit's accurate thermal power;

[0055] Step 1.4: Perform manual sampling and analysis of the liquid boron concentration in the reactor main system and pressurizer three times. The results of the manual sampling and analysis should meet the following conditions: the deviation of the liquid boron concentration in the reactor main system and pressurizer is less than 5 ppm, and the deviation of the three boron concentration analysis values ​​of the reactor main system is less than 5 ppm. If these conditions are met, the boron concentration is considered stable. Otherwise, it indicates that the boron concentration in the reactor main system is fluctuating, and further stirring is required until the results of the manual sampling and analysis meet the requirements for stable boron concentration.

[0056] Step 2: Manually adjust the boron concentration in the reactor main system. After the boron concentration in the main system is stirred and stabilized, the deviation of the boron concentration in the reactor main system and the pressurizer liquid phase should be less than 5 ppm. The boron concentration in the reactor main system should be measured three times, and the analytical value deviation of the three results should be less than 5 ppm. Also, measure the boron concentration and record the average temperature of the moderator in the main system.

[0057] Step 3: Measure the change in boron concentration of the coolant in the main system, calculate the introduced reactivity change according to formula (1), calculate the isothermal temperature coefficient according to formula (2), and calculate the moderator temperature coefficient according to formula (3).

[0058]

[0059] Where Δρ represents the reactivity change, Indicates the differential value of boron; ΔC B The change in boron concentration in the main system coolant;

[0060]

[0061] Where, α iso Δρ is the isothermal temperature coefficient; Δρ is the reactivity change; ΔT is the temperature coefficient. avg This represents the change in the average temperature of the moderator in the reactor main system caused by boron concentration adjustment.

[0062]

[0063] Where: α doppler The Doppler temperature coefficient; The temperature coefficient of the moderator; α iso It is the isothermal temperature coefficient;

[0064] Step 4: After the measurement is completed, adjust the boron concentration of the control rod assembly or the main reactor system to adjust the average temperature of the moderator in the main system, so that the average temperature of the moderator in the main system is balanced with the reference temperature, and change the control rod assembly from "manual" to "automatic" control mode.

[0065] This invention provides a method for measuring the temperature coefficient of a moderator. The method provides stable measurement results and is simple and easy to implement. This method can effectively monitor the temperature coefficient of the moderator during the operation of a power plant unit to meet the safety supervision requirements of the reactor core.

[0066] In some embodiments, before adjusting the boron concentration in step 2, the required reactivity change to be introduced by a 1°C change in the moderator can be calculated, and the amount of boron concentration to be adjusted can be estimated. The calculation method is as follows:

[0067] The design isothermal temperature coefficient is calculated as shown in formula (4);

[0068]

[0069] in: α is the isothermal temperature coefficient; doppler The Doppler temperature coefficient; To design the temperature coefficient of the moderator;

[0070] The reaction change required to introduce a 1°C change in the moderator is calculated as shown in formula (5);

[0071]

[0072] Where Δρ represents the reactive change, α iso This represents the isothermal temperature coefficient; ΔT is the temperature change of the moderator in the main system, which is 1℃ here.

[0073] The required change in boron concentration for the calculation method is shown in formula (6);

[0074]

[0075] in, To calculate the required change in boron concentration; Δρ represents the differential value of boron; Δρ represents the change in reactivity; the amount of boron concentration adjustment for dilution or boration is calculated as shown in formula (7);

[0076]

[0077] Where V1 represents the amount of dilution or borylation; V0 represents the amount of water loaded into the reactor main system (t); C0 represents the boron concentration of the reactor main system before dilution; C1 represents the target boron concentration adjustment of the reactor main system; and C represents the boron concentration of the solution injected into the reactor main system, which is 0 ppm during dilution and the boron concentration of the injected concentrated boric acid during borylation.

[0078] In some embodiments, step 3, measuring the change in boron concentration, involves: performing three manual analyses on the boron concentration in the reactor main system before dilution and taking the average value; performing three manual analyses on the boron concentration in the reactor main system after stirring and taking the average value; and the difference between the two analyses is the change in boron concentration in the reactor main system. This change in boron concentration can also be calculated by back-calculation using formula (7).

[0079] In some embodiments, step 3 measures the moderator temperature coefficient. The moderator temperature coefficient can be combined with theoretical calculations to correct for power, boron concentration, temperature, and rod position, thereby obtaining the moderator temperature coefficient under standard conditions. The moderator temperature coefficient under standard conditions can be used for comparison and analysis with the calculated value of the moderator temperature coefficient under a certain standard condition.

[0080] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for measuring the temperature coefficient of a moderator, characterized in that, The method includes the following steps: Step 1: Confirm the measurement conditions, record the average temperature of the moderator in the main system, the thermal power of the computer group, and measure the liquid boron concentration in the reactor main system and pressurizer; Step 1.1: Confirm that the reactor is in xenon balance; within 2 hours before the test, ensure that the reactor power, average moderator temperature, unit thermal efficiency, and condenser cooling water temperature are stable. Step 1.2: Change the control rod assembly from "automatic" to "manual" control mode and record the average temperature of the moderator in the reactor main system for 10 consecutive minutes; Step 1.3: Perform a manual heat balance calculation to obtain the unit's accurate thermal power; Step 1.4: Manually sample and analyze the boron concentration in the liquid phase of the reactor main system and pressurizer, and determine the stability of the boron concentration based on the sampling and analysis results; Step 2: Manually adjust the boron concentration in the reactor main system. After the boron concentration in the main system is stirred and stabilized, measure the boron concentration and record the average temperature of the moderator in the main system. Step 3: Measure the change in boron concentration of the coolant in the main system, calculate the introduced reactivity change according to formula (1), calculate the isothermal temperature coefficient according to formula (2), and calculate the moderator temperature coefficient according to formula (3); （1）； Among them Reactive changes Indicates the differential value of boron; The change in boron concentration in the main system coolant; （2）； in, It is the isothermal temperature coefficient; This is a reactive change; This represents the change in the average temperature of the moderator in the reactor main system caused by boron concentration adjustment. （3）； in: The Doppler temperature coefficient; The temperature coefficient of the moderator; It is the isothermal temperature coefficient; Step 4: After the measurement is completed, adjust the average temperature of the moderator in the main system to return to the state before the test.

2. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, Step 1.1, confirming that the reactor should be in xenon balance, includes confirming whether the reactor is in xenon balance based on the criterion that the power change is less than 2%FP within 48 hours.

3. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, In step 1.1, within 2 hours before the test, ensuring the stability of reactor power, average moderator temperature, unit thermal efficiency, and condenser cooling water temperature includes: reactor power variation less than 0.5%FP; no boron concentration dilution or boronization in the main reactor system; maintaining reactor power variation within ±0.3%FP; average moderator temperature in the main system stable within ±0.5℃ of the reference temperature; stable unit thermal efficiency; and condenser cooling water temperature variation less than 0.5℃.

4. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, In step 1.4, the liquid boron concentration of the reactor main system and the pressurizer is manually sampled and analyzed three times. The results of the manual sampling and analysis should meet the following conditions: the deviation of the liquid boron concentration of the reactor main system and the pressurizer is less than 5 ppm, and the deviation of the three boron concentration analysis values ​​of the reactor main system is less than 5 ppm. If these conditions are met, the boron concentration is considered stable. Otherwise, it indicates that the boron concentration of the reactor main system is fluctuating, and further stirring is required until the manual sampling and analysis results meet the requirements for stable boron concentration.

5. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, Before manually adjusting the boron concentration in step 2, the reactive change required to introduce a 1°C change in the moderator is calculated, and the amount of boron concentration to be adjusted is estimated. The calculation method is as follows: The design isothermal temperature coefficient is calculated as shown in formula (4); （4）； in: This is the theoretical isothermal temperature coefficient; The Doppler temperature coefficient; To theoretically design the temperature coefficient of the moderator; The reaction change required to introduce a 1°C change in the moderator is calculated as shown in formula (5); （5）； in For reactive changes, Indicates the isothermal temperature coefficient; This refers to the temperature change of the main system's moderator, which is 1°C in this case. The required change in boron concentration for the calculation method is shown in formula (6). （6）； in, To calculate the required change in boron concentration The differential value of boron; This is a reactive change; The amount of boron concentration adjustment for dilution or boration is calculated as shown in formula (7); （7） in, Indicates the amount of dilution or borylation; This indicates the amount of water loaded in the reactor main system (t). This indicates the boron concentration in the reactor main system before dilution; This indicates the target for boron concentration regulation in the reactor's main system; This indicates the boron concentration of the solution injected into the reactor main system; it is 0 ppm when diluted and the boron concentration of concentrated boric acid when borated.

6. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, The criteria for stabilizing and mixing the boron concentration in the main system in step 2 include: the deviation of the boron concentration in the reactor main system and the pressurizer liquid phase is less than 5 ppm, and the deviation of the analytical values ​​of the three measurements of the boron concentration in the reactor main system is less than 5 ppm.

7. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, One method for measuring the change in boron concentration in step 3 is as follows: perform three manual analyses on the boron concentration of the reactor main system before dilution and take the average value; perform three manual analyses on the boron concentration of the reactor main system after stirring and take the average value; the difference between the two is the change in boron concentration of the reactor main system.

8. The method for measuring the temperature coefficient of a moderator according to claim 5, characterized in that, Another method for calculating the change in boron concentration in step 3 is to use the formula (7).

9. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, Step 3 measures the temperature coefficient of the moderator. The temperature coefficient of the moderator is then combined with theoretical calculations and corrected for power, boron concentration, temperature, and rod position to obtain the temperature coefficient of the moderator under standard conditions. The temperature coefficient of the moderator under standard conditions is used for comparison and analysis with the calculated value of the temperature coefficient of the moderator under a certain standard condition.

10. The method for measuring the temperature coefficient of a moderator according to claim 1, characterized in that, Step 4, adjusting the average temperature of the main system moderator to return to the pre-test level, includes: adjusting the average temperature of the main system moderator by adjusting the control rod group or the boron concentration of the reactor main system, so that the average temperature of the main system moderator is balanced with the reference temperature, and changing the control rod group from "manual" to "automatic" control mode.

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