A zinc concentration control method for zinc addition operation in the main system of a pressurized water reactor nuclear power unit

Abstract

The present invention relates to the field of nuclear power plant chemical technology, and more particularly to a method for controlling zinc concentration in the main system of an operating pressurized water reactor nuclear power unit during zinc addition. The method comprises the following steps: injecting depleted zinc acetate into the main coolant system to control the initial zinc addition rate; starting from the initial zinc addition, periodically sampling and detecting the instantaneous zinc concentration of the main coolant; triggering rate-increasing logic if the test results are all below the detection limit; gradually increasing the zinc addition rate by preset increments until the zinc concentration in the main coolant reaches a detectable range; when the instantaneous zinc concentration detected in a regulating unit exceeds the detection limit, gradually reducing the zinc addition rate by preset decrements until the instantaneous zinc concentration eventually stabilizes within a target value range; while sampling and detecting the instantaneous zinc concentration, calculating the time-weighted average of the instantaneous zinc concentration values over several days; if the instantaneous zinc concentration approaches the target value, reducing the zinc addition rate or stopping zinc addition. The present invention is suitable for controlling zinc concentration in operating units to avoid risks.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology of nuclear power plants, and in particular to a method for controlling zinc concentration in a main system of a pressurized water reactor nuclear power unit during zinc addition operation. Background Art

[0002] Zinc addition technology for the primary coolant system of pressurized water reactor units has become an important means to reduce radiation field levels and even collective doses.

[0003] In the application of zinc dosing technology, the effect of reducing the radiation field level of the unit is proportional to the cumulative exposure to zinc (μg / kg·month). That is, a high cumulative zinc exposure is more conducive to reducing the radiation field, but at the same time it increases the risk of core axial power deviation (CIPS) and fuel fouling-induced localized corrosion (CILC) caused by zinc dosing.

[0004] When a new unit is first started up, the main system is in a "clean state"; a stable oxide film has not yet formed on the material surface, and there is no long-term accumulation of corrosion products (such as metal ions such as Fe and Ni) in the system. Therefore, zinc dosing control for new units must focus on the rapid formation of the initial oxide film. Dynamically adjust the zinc injection rate to coordinate with the coolant pH, boric acid concentration, and temperature to form a uniform zinc oxide deposition layer.

[0005] However, the main systems of operating units already have stable oxide films and corrosion product deposits. Therefore, the core objective of zinc dosing control has shifted to inhibiting the continued growth of oxide films and reducing the release of corrosion products. Therefore, for zinc dosing operations in operating units that have already run for several cycles, it is necessary to focus on fuel and core risks, determine appropriate target zinc concentrations, and develop effective methods for controlling primary coolant zinc to ensure fuel cladding integrity and facilitate the smooth and safe implementation of zinc dosing operations in operating units. The complexity of zinc concentration control in the main systems of operating units has increased significantly.

[0006] If the zinc concentration of an operating unit is controlled according to the zinc addition control method for a new unit, the zinc concentration in the main coolant will be too high, thereby increasing the risk of CIPS and CILC of the unit.

[0007] In summary, the existing technology lacks a zinc addition control method specifically for operating units, and there is an urgent need to develop a dynamic zinc concentration control strategy that is adapted to its complex operating conditions. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for controlling zinc concentration in the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation. By determining the control parameters, index requirements, and control process and requirements of the main system zinc, reasonable control of the main coolant zinc is achieved to effectively avoid the CIPS and CILC risks that may be caused by zinc addition, ensure the integrity of the fuel cladding, and help to smoothly and safely implement zinc addition operation in the operating pressurized water reactor nuclear power unit.

[0009] The present invention provides a method for controlling zinc concentration in a main system of a pressurized water reactor nuclear power unit during zinc addition operation, comprising the following steps:

[0010] Step 1: Confirm the prerequisites for zinc addition to the unit;

[0011] Step 2: Inject depleted zinc acetate into the main coolant system, with the initial zinc addition rate controlled at 8-10 g / day; starting from the initial zinc addition, regularly sample and test the instantaneous value of the main coolant zinc concentration;

[0012] In the first cycle after the initial zinc addition, the instantaneous value of the main coolant zinc concentration is detected in real time. If the test results are all below the detection limit, the rate increase logic is triggered;

[0013] Starting from the second cycle, the zinc addition rate is gradually increased by a preset increment at fixed time intervals until the zinc concentration in the main coolant reaches a detectable range; the preset increment is 0.8-1.2 g / day;

[0014] When the instantaneous value of zinc concentration detected in a certain regulating unit is higher than the detection limit, the zinc addition rate is gradually reduced by a preset decrement, so that the instantaneous value of zinc concentration is finally stabilized within the target value range;

[0015] While sampling and testing the instantaneous value of zinc concentration, calculate the time-weighted average value of zinc concentration over several days from the start of zinc addition to the unit, and calculate it on a rolling basis. If it approaches the target value, reduce the zinc addition rate or stop zinc addition to keep the weighted average value of zinc concentration within the target value range;

[0016] The target value is 2 to 10 μg / kg.

[0017] In one embodiment of the present invention, the instantaneous value of zinc concentration C Zn-瞬时 The stable range is: (1-50%)C Zn-目标值 ≤C Zn-瞬时 ≤(1+50%)C Zn-目标值 .

[0018] In a specific embodiment of the present invention, the first period is 2 weeks from the initial zinc addition, and the second period is the time period after the end of the first period. During the second period, the zinc concentration enters the limit range and tends to be stable; the fixed time interval is 1 week, and the preset increment is 1 g / day.

[0019] In a specific embodiment of the present invention, the preset reduction is 0.8-1.2 g / day.

[0020] In a specific embodiment of the present invention, the sampling frequency in the first period is 2 to 3 times per day, and the sampling frequency in the second period is once per day.

[0021] In one embodiment of the present invention, if the zinc concentration in the main coolant cannot be re-detected due to a change in the unit operating state, the original zinc addition rate is maintained or maintained for at least one week before adjustment.

[0022] In one embodiment of the present invention, if the zinc concentration in the main coolant increases by 1-2 μg / kg per day during the above adjustment process, the zinc addition rate is reduced or zinc addition is stopped until the zinc concentration returns to the target value; the standard for reducing the zinc addition rate is to reduce it by 1 g / day per week.

[0023] In one embodiment of the present invention, the time-weighted average zinc concentration is calculated starting from the first day until 30 days are completed, and then the calculation for the next 30 days begins.

[0024] In one embodiment of the present invention, the 30-day weighted average zinc concentration is expressed as C Zn-30天加权平均 ,

[0025] C Zn-30天加权平均 = (C Zn-瞬时1 ⅹt1+C Zn-瞬时2 ⅹt2+…+C Zn-瞬时n ×t n ) / (t1+ t2+…+ t n );

[0026] n is an integer between 1 and 30.

[0027] In a specific embodiment of the present invention, the prerequisite is that the timing for zinc addition operation is reached and there is no sign of axial power deviation caused by scaling of the core.

[0028] Compared with the prior art, the zinc concentration control method of the present invention for zinc addition operation in the main system of an operating pressurized water reactor nuclear power unit has the following beneficial effects:

[0029] (1) Based on the CIPS and CILC risk analysis, a zinc addition control method was developed for the operating units to avoid excessively high zinc concentration in the main coolant during zinc addition operation, which would lead to CIPS and CILC risks for the units and affect the integrity of the fuel cladding.

[0030] (2) A dosing control method with an initial zinc addition rate of 8-10 g / day and an adjustment amount of 0.8-1.2 gg / day was proposed. The adjustment amount is small and easy to operate, which helps to control the zinc concentration of the main coolant more stably.

[0031] (3) Simultaneously evaluate the instantaneous value of zinc concentration and the time-weighted average zinc concentration. If any of them changes significantly or approaches the limit, the zinc addition amount is reduced for control. This helps to better control the zinc concentration during the zinc addition operation of the operating unit and avoid the risk of CIPS and CILC of the unit caused by excessively high zinc concentration. DETAILED DESCRIPTION

[0032] In order to further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the present invention.

[0033] An embodiment of the present invention discloses a method for controlling zinc concentration in a main system of an operating pressurized water reactor nuclear power unit during zinc addition operation, comprising the following steps:

[0034] Step 1: Confirm the prerequisites for zinc addition to the unit;

[0035] The prerequisites include: first, the timing for starting zinc addition operation has been reached; the zinc addition timing refers to the unit status such as effective full-power operation days or cooling system isolation that needs to be achieved before the unit starts zinc addition operation.

[0036] Second, there is no sign of fouling-induced axial power deviation (CIPS) in the core.

[0037] Step 2: Injecting depleted zinc acetate into the main coolant system, with the initial zinc addition rate controlled at 8-10 g / day; preferably, 10 g / day;

[0038] Starting with the initial zinc addition, monitor the zinc concentration. Sampling frequency should be 2-3 times per day for the first two months. Once the zinc concentration stabilizes within the limit, sampling frequency should be increased to once per day. Sampling should ideally be conducted upstream of the chemical purification bed to obtain a more representative primary coolant zinc concentration, which facilitates more accurate monitoring and precise control of the primary coolant zinc concentration.

[0039] The measured value of the sample is the instantaneous value of zinc concentration, expressed as C Zn-瞬时 Indicates that C Zn-瞬时 The limit requirement is: (1-50%)CZn-目标值 ≤C Zn-瞬时 ≤(1+50%)C Zn-目标值 .

[0040] During the first cycle after the initial zinc addition, the main coolant zinc concentration is detected in real time. If all test results are below the detection limit, the rate increase logic is triggered;

[0041] From the second cycle onwards, the zinc addition rate is increased step by step according to the preset increments, with fixed time intervals as the adjustment unit, until the zinc concentration in the main coolant reaches the detectable range; the cycle of each step of zinc addition rate increase is one fixed time interval;

[0042] The first period is 2 weeks from the initial zinc addition, and the second period is the time period after the end of the first period. During the second period, the zinc concentration enters the limit range and tends to be stable; the fixed time interval is 1 week, and the preset increment is 1g / day; within one adjustment unit, the daily zinc addition amount is equal;

[0043] When the instantaneous value of zinc concentration detected in a certain regulating unit is higher than the detection limit, the zinc addition rate is gradually reduced by a preset decrement until the instantaneous value of zinc concentration is finally stabilized within the limit; the cycle of each step of zinc addition rate reduction is a fixed time interval;

[0044] The preset reduction is 1 g / day;

[0045] Within a conditioning unit, the daily zinc addition amount is the same.

[0046] If the zinc concentration in the main coolant cannot be re-detected due to a change in the unit's operating status, maintain the original zinc addition rate or maintain the original zinc addition rate for at least one week before making adjustments;

[0047] If the zinc concentration in the main coolant increases rapidly during the above adjustment process, such as increasing by 1~2μg / kg per day, or approaches the upper limit of control, the zinc addition rate should be reduced or stopped. The zinc addition rate is reduced on a weekly basis. Within a cycle, the daily zinc addition amount is equal; the daily zinc addition amount in the second week is 1g less than the daily addition amount in the previous week;

[0048] While sampling and testing, the time-weighted average value of the instantaneous zinc concentration over several days is calculated starting from the start of zinc addition to the unit. The weighted calculation is performed for up to 30 days, with 30 days as a cycle, and the calculation is carried out on a rolling basis to control it within the target value range to avoid increased CIPS and CILC risks due to excessively high zinc concentration.

[0049] The 30-day weighted average zinc concentration is expressed as C Zn-30天加权平均 By adjusting the zinc addition rate, it can be controlled within the target value range to avoid increasing the risk of CIPS and CILC due to excessive zinc concentration.

[0050] The specific method is to calculate the time-weighted average zinc concentration from the first day until the calculation is completed for 30 days, and then start the calculation for the next 30 days, and so on. If it is close to the target value, reduce the zinc addition rate or stop adding zinc. Zn-30天加权平均 Control within the target value range to prevent exceeding the target value.

[0051] The standard for reducing the zinc addition rate is to reduce it by 1g / day per week;

[0052] The target value C Zn-目标值 2~10μg / kg.

[0053] C Zn-30天加权平均 =(C Zn-瞬时1 ⅹt1+C Zn-瞬时2 ⅹt2+…+C Zn-瞬时n ×t n ) / (t1+ t2+…+ t n ). n is an integer between 1 and 30;

[0054] The C Zn-30天加权平均 Less than or equal to the target value C Zn-目标值 .

[0055] In order to further understand the present invention, the zinc concentration control method for zinc addition operation in the main system of an operating pressurized water reactor nuclear power unit provided by the present invention is described in detail below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0056] Example 1

[0057] Determination of parameters and index requirements of main coolant zinc:

[0058] For operating pressurized water reactor nuclear power units that have been running for several cycles, the target zinc concentration, zinc parameters and index requirements are determined through core axial power deviation (CIPS) and fuel fouling induced localized corrosion (CILC) risk analysis:

[0059] 1) Instantaneous zinc concentration (C Zn-瞬时 ) Limit requirement: (1-50%)C Zn-目标 ≤C Zn-瞬时 ≤(1+50%)C Zn-目标 . C Zn-瞬时 These are measured values sampled at regular intervals.

[0060] 2) 30-day weighted average zinc concentration (C Zn-30天加权平均 ) Limit requirement: less than or equal to the target zinc concentration C Zn-目标 . C Zn-30天加权平均 =(C Zn-瞬时1 ⅹt1+C Zn-瞬时2 ⅹt2+…+C Zn-瞬时n ×tn ) / (t1+ t2+…+ t n ). C Zn-30天加权平均 It is the weighted average of the instantaneous zinc concentration every 30 days.

[0061] For the fuel cycle after the first zinc dosing cycle, the zinc concentration target value can be adjusted accordingly based on the zinc dosing operation status of the unit and the CIPS and CILC risk conditions.

[0062] A method for controlling zinc concentration in a main system of a pressurized water reactor nuclear power unit during zinc addition operation comprises the following steps:

[0063] Step 1: Determine that the time has come to start zinc addition operation and there is no sign of scaling-induced axial power deviation (CIPS) in the core;

[0064] Step 2: After all the preconditions for the unit to start adding zinc are met, start injecting depleted zinc acetate into the main coolant system, and the initial zinc addition rate is controlled at 10g / day; the depleted zinc acetate 64 The abundance of Zn is less than 1%, which can reduce 64 Zn is produced by neutron activation 65 The new radiation source term introduced by Zn;

[0065] After the unit starts zinc dosing, if no zinc is detected in the main coolant within two weeks after the initial zinc dosing, the zinc dosing rate will be increased by 1g / day every week starting from the third week, that is, the zinc dosing rate in the third week will be adjusted to 11g / day;

[0066] If zinc is still not detected in the third week, the zinc addition rate in the fourth week will be adjusted to 12g / day, and so on.

[0067] Once zinc is detected in the main coolant, the zinc addition rate is gradually reduced at a rate of 1 g / day per week until the zinc concentration finally stabilizes to the instantaneous zinc concentration C Zn-瞬时 within the limit range.

[0068] Changes in the unit's operating status may result in the zinc concentration in the main coolant being undetectable. If this occurs, maintain the zinc addition rate. If the zinc addition rate needs to be adjusted, maintain the original zinc addition rate for at least one week before making any adjustments. If the zinc concentration in the main coolant increases rapidly at a rate of 1 to 2 μg / kg per day, reduce the zinc addition rate to prevent the zinc concentration from exceeding the instantaneous zinc concentration C. Zn-瞬时 Limit range.

[0069] While sampling and testing the instantaneous value of zinc concentration, calculate the time-weighted average zinc concentration from the first day until the calculation is completed for 30 days, then start the calculation for the next 30 days, and repeat this cycle. If the zinc concentration approaches the target value, reduce the zinc addition rate by 1g / day per week or stop adding zinc. Zn-30天加权平均Control within the target value range to prevent exceeding the target value.

[0070] After the zinc concentration returns to the target range and shows a downward trend, zinc addition is resumed until the zinc concentration meets the requirements. During unit shutdown, zinc will be released from the oxide film on the surface of the main coolant system materials, causing the main coolant zinc concentration to increase significantly. Therefore, zinc addition is stopped one day before the unit shutdown.

[0071] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0072] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling zinc concentration in a main system of a pressurized water reactor nuclear power unit during zinc addition operation, characterized in that: The following steps are involved: Step 1: Confirm the prerequisites for zinc addition to the unit; The prerequisites include: first, the timing for commencing zinc dosing has been reached; the timing for zinc dosing refers to the number of days of effective full-power operation or isolation of the cooling system required before the unit can begin zinc dosing; second, there is no sign of axial power excursion caused by core fouling; Step 2: Inject depleted zinc acetate into the main coolant system, with the initial zinc addition rate controlled at 8-10 g / day; starting from the initial zinc addition, regularly sample and test the instantaneous value of the main coolant zinc concentration; In the first cycle after the initial zinc addition, the instantaneous value of the main coolant zinc concentration is detected in real time. If the test results are all below the detection limit, the rate increase logic is triggered; Starting from the second cycle, the zinc addition rate is gradually increased by a preset increment at fixed time intervals, until the zinc concentration in the main coolant reaches a detectable range; the preset increment is 0.8 to 1.2 g / day; When the instantaneous value of zinc concentration detected in a certain regulating unit is higher than the detection limit, the zinc addition rate is gradually reduced by a preset decrement, so that the instantaneous value of zinc concentration is finally stabilized within the target value range; While sampling and testing the instantaneous value of zinc concentration, calculate the time-weighted average value of zinc concentration over several days from the start of zinc addition to the unit, and calculate it on a rolling basis. If it approaches the target value, reduce the zinc addition rate or stop zinc addition to keep the weighted average value of zinc concentration within the target value range; The target value is 2 to 10 μg / kg.

2. The zinc concentration control method for the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 1, characterized in that: The instantaneous value of the zinc concentration C Zn-瞬时 The stable range is: (1-50%)C Zn-目标值 ≤C Zn-瞬时 ≤(1+50%)C Zn-目标值 .

3. The zinc concentration control method for the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 1, characterized in that: The first cycle is 2 weeks from the initial zinc addition, and the second cycle is the time period after the end of the first cycle. During the second cycle, the zinc concentration enters the limit range and tends to be stable; the fixed time interval is 1 week, and the preset increment is 1 g / day.

4. The zinc concentration control method for the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 1, characterized in that: The preset reduction is 0.8-1.2 g / day.

5. The zinc concentration control method for the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 1, characterized in that: The sampling frequency in the first cycle is 2 to 3 times per day, and the sampling frequency in the second cycle is once per day.

6. The zinc concentration control method for the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 1, characterized in that: If the zinc concentration in the main coolant cannot be re-detected due to a change in the unit's operating status, maintain the original zinc addition rate or maintain the original zinc addition rate for at least one week before making adjustments.

7. The method for controlling zinc concentration in the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 6, characterized in that: If the zinc concentration in the main coolant increases by 1 to 2 μg / kg per day while maintaining the original zinc addition rate, reduce the zinc addition rate or stop adding zinc until the zinc concentration returns to the target value; the standard for reducing the zinc addition rate is to reduce it by 1 g / day per week.

8. The zinc concentration control method for the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 1, characterized in that: The time-weighted average zinc concentration is calculated from the first day until 30 days are completed, and then the calculation for the next 30 days begins.

9. The method for controlling zinc concentration in the main system of an operating pressurized water reactor nuclear power unit during zinc addition operation according to claim 8, characterized in that: The 30-day weighted average zinc concentration is expressed as C Zn-30天加权平均 , C Zn-30天加权平均 =(C Zn-瞬时1 ⅹt1+C Zn-瞬时2 ⅹt2+…+C Zn-瞬时n ×t n ) / (t1+t2+…+t n ); n is an integer between 1 and 30.