Zinc concentration control method for zincification operation of main system of pressurized water reactor nuclear power unit

Abstract

The invention relates to the technical field of nuclear power plant chemistry, in particular to a zinc concentration control method for zinc adding operation of a main system of a pressurized water reactor nuclear power unit. The method comprises the following steps: injecting depleted zinc acetate into a main coolant system, and controlling the initial zinc adding rate for day; starting from initial zinc adding, regularly sampling and detecting the instantaneous value of the zinc concentration of the main coolant; if the detection results are all lower than the detection limit, triggering rate increasing logic; increasing the zinc adding rate step by step according to a preset increment until the zinc concentration in the main coolant reaches a detectable range; when the instantaneous value of the zinc concentration detected in a certain adjusting unit is higher than a detection limit, the zinc adding rate is gradually reduced by a preset decrement, so that the instantaneous value of the zinc concentration is finally stabilized to be within a target value range; when the instantaneous value of the zinc concentration is sampled and detected, the time weighted average value of the instantaneous value of the zinc concentration in a plurality of days is calculated, and if the time weighted average value is close to a target value, the zinc adding speed is reduced or zinc adding is stopped. The method is suitable for zinc concentration control of an in-operation unit, and risks are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear power plant chemistry, and particularly to a method for controlling zinc concentration during the operation of adding zinc to the main system of an operating pressurized water reactor nuclear power unit. Background Art

[0002] The technology of adding zinc to the main coolant system of a pressurized water reactor unit has become an important means to reduce the radiation field level and even the collective dose.

[0003] In the application of the zinc addition technology, the reduction effect of the unit's radiation field level is proportional to the cumulative exposure amount of zinc (μg / kg·month). That is, a high cumulative zinc exposure amount is more conducive to reducing the radiation field, but at the same time, it will increase the risks of core axial power shift (CIPS) and fuel fouling-induced local corrosion (CILC) caused by zinc addition.

[0004] When a new unit is first started up, the inside of the main system is in a "clean state", a stable oxide film has not yet formed on the material surface, and there are no corrosion products (such as metal ions like Fe, Ni, etc.) accumulated in the system for a long time. Therefore, for the zinc addition control of a new unit, it is necessary to focus on the rapid construction of the initial oxide film, and it is necessary to dynamically adjust the zinc injection rate to make it synergistically match with the coolant pH value, boric acid concentration, and temperature to form a uniform zinc oxide deposition layer.

[0005] However, a stable oxide film and corrosion product deposits already exist in the main system of an operating unit. The core goal of zinc addition control has changed to suppressing the continuous growth of the oxide film and reducing the release of corrosion products. Therefore, for the zinc addition operation of an operating unit that has run for several cycles, it is necessary to focus on the fuel and core risks, determine an appropriate target zinc concentration, and formulate an effective control method for the zinc in the main coolant to ensure the integrity of the fuel cladding and promote the smooth and safe implementation of the zinc addition operation for the operating unit. The complexity of zinc concentration control in the main system of an operating unit has increased significantly.

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

[0007] In summary, there is a lack of a special zinc addition control method for operating units in the prior art, and it is urgent to develop a dynamic regulation strategy for zinc concentration that adapts to its complex working conditions. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a zinc concentration control method for the zinc addition operation of the main system of an operating pressurized water reactor nuclear power unit. By determining the control parameters, index requirements, control process and requirements of zinc in the main system, reasonable control of the zinc in the primary coolant 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 the operating pressurized water reactor nuclear power unit to smoothly and safely implement the zinc addition operation.

[0009] The present invention provides a zinc concentration control method for the zinc addition operation of the main system of an operating pressurized water reactor nuclear power unit, including the following steps: Step 1: Confirm the preconditions for the unit to implement zinc addition; Step 2: Inject depleted zinc acetate into the primary coolant system, and control the initial zinc addition rate at 8 - 10 g / day; starting from the initial zinc addition, regularly sample and detect the instantaneous value of the zinc concentration in the primary coolant; During the first cycle after the initial zinc addition starts, the instantaneous value of the zinc concentration in the primary coolant is detected in real time. If the detection results are all lower than the detection limit, the rate increase logic is triggered; From the second cycle onwards, with a fixed time interval as the adjustment unit, the zinc addition rate is gradually increased step by step according to a preset increment until the zinc concentration in the primary coolant reaches the detectable range; the preset increment is 0.8 - 1.2 g / day; When the instantaneous value of the zinc concentration detected in a certain adjustment unit is higher than the detection limit, the zinc addition rate is gradually decreased step by step according to a preset decrement, so that the instantaneous value of the zinc concentration is finally stabilized within the target value range; While sampling and detecting the instantaneous value of the zinc concentration, calculate the time-weighted average value of the instantaneous values of the zinc concentration within several days starting from the zinc addition of the unit, and calculate it in a rolling manner. If it is close to the target value, reduce the zinc addition rate or stop zinc addition, and control the weighted average value of the zinc concentration within the target value range; The target value is 2 - 10 μg / kg.

[0010] In a specific embodiment of the present invention, the instantaneous value C of the zinc concentration 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 .

[0011] In a specific embodiment of the present invention, the first cycle is 2 weeks starting from the initial zinc addition, and the second cycle is the time cycle after the end of the first cycle. In 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.

[0012] In a specific embodiment of the present invention, the preset decrement is 0.8 - 1.2 g / day.

[0013] In a specific embodiment of the present invention, the sampling frequency in the first cycle is 2 - 3 times per day, and the sampling frequency in the second cycle is 1 time per day.

[0014] In a specific embodiment of the present invention, if the zinc concentration in the primary coolant cannot be detected again due to the change in the operating state of the unit, the original zinc addition rate is maintained, or at least the original zinc addition rate is maintained for one week before adjustment.

[0015] In a specific embodiment of the present invention, if during the above adjustment process, the zinc concentration in the primary coolant increases by 1 - 2 μg / kg per day, 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.

[0016] In a specific embodiment of the present invention, the time - weighted average zinc concentration is statistically calculated from the first day until 30 days are completed, and then the calculation for the next 30 - day period begins.

[0017] In a specific embodiment of the present invention, the 30 - day weighted average zinc concentration is denoted as C Zn-30天加权平均 , C Zn-30天加权平均 = (C Zn-瞬时1 ×t1 + C Zn-瞬时2 ×t2 + … + C Zn-瞬时n ×t n ) / (t1 + t2 + … + t n ); n is an integer between 1 and 30.

[0018] In a specific embodiment of the present invention, the pre - condition is that it is the time to start zinc addition operation and there is no sign of fouling - induced axial power shift in the core.

[0019] Compared with the prior art, a zinc concentration control method for zinc addition operation in the primary system of an in - service pressurized water reactor nuclear power unit of the present invention has the following beneficial effects: (1) For in - service units, a control method for zinc addition is formulated based on CIPS and CILC risk analysis, avoiding the risk of CIPS and CILC of the unit caused by too high zinc concentration control in the primary coolant during zinc addition operation, which affects the integrity of the fuel cladding; (2) A drug addition control method with an initial zinc addition rate of 8 - 10 g / day and an adjustment amount of 0.8 - 1.2 g / day is proposed. The adjustment amount is small and easy to operate, which helps to control the zinc concentration in the primary coolant more stably; (3)Simultaneously evaluate the instantaneous value of zinc concentration and the time-weighted average zinc concentration. In case of any significant change or approaching the limit value, the zinc addition amount shall be reduced for control, which helps to better control the zinc concentration during the zinc addition operation of the in-service unit and avoid the risks of CIPS and CILC of the unit caused by excessive zinc concentration control. Detailed implementation manners

[0020] To further understand the present invention, the implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the present invention.

[0021] The embodiment of the present invention discloses a zinc concentration control method for zinc addition operation in the primary system of an in-service pressurized water reactor nuclear power unit, including the following steps: Step 1: Confirm the preconditions for zinc addition in the unit; The preconditions include: First, the timing for starting zinc addition operation has been reached; the zinc addition timing is the effective full power operation days or the unit status such as the isolation of the shutdown cooling system required before the unit starts zinc addition operation.

[0022] Second, there is no sign of fouling-induced axial power shift (CIPS) in the reactor core.

[0023] Step 2: Inject depleted zinc acetate into the primary coolant system, and control the initial zinc addition rate at 8 - 10 g / day; preferably, it is 10 g / day; Since the initial zinc addition, detect the zinc concentration. The sampling frequency is 2 - 3 times / day in the first two months, and after the zinc concentration enters the limit range and stabilizes, the sampling frequency is: once a day. The sampling point should be upstream of the chemical volume purification bed for sampling to obtain a more representative zinc concentration of the primary coolant, which helps to implement more accurate monitoring and more precise control of the zinc concentration of the primary coolant.

[0024] The measured value of the sampling is the instantaneous value of the zinc concentration, represented by C Zn-瞬时 The limit requirement for C Zn-瞬时 is: (1 - 50%)C Zn-目标值 ≤C Zn-瞬时 ≤(1 + 50%)C Zn-目标值 .

[0025] During the first cycle after the initial zinc addition, continuously detect the zinc concentration of the primary coolant. If all the detection results are lower than the detection limit, trigger the rate increase logic; Since the second cycle, use a fixed time interval as the adjustment unit, and gradually increase the zinc addition rate step by step according to the preset increment until the zinc concentration in the primary coolant reaches the detectable range; the cycle for each level of increasing the zinc addition rate is 1 fixed time interval; The first period is 2 weeks starting from the initial zinc addition. 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 stabilizes. The fixed time interval is 1 week, and the preset increment is 1 g / day. In one adjustment unit, the daily zinc addition amount is equal. When the instantaneous value of the zinc concentration detected in a certain adjustment unit is higher than the detection limit, the zinc addition rate is gradually decreased in accordance with the preset decrement, so that the instantaneous value of the zinc concentration is finally stabilized within the limit range. The period for each level of reduction in the zinc addition rate is 1 fixed time interval. The preset decrement is 1 g / day. In one adjustment unit, the daily zinc addition amount is the same.

[0026] If the zinc concentration in the primary coolant cannot be detected again due to a change in the unit operation status, the original zinc addition rate is maintained, or at least the original zinc addition rate is maintained for one week before adjustment. If during the above adjustment process, the zinc concentration in the primary coolant increases rapidly, such as increasing by 1 - 2 μg / kg per day, or approaches the control upper limit, the zinc addition rate is decreased or zinc addition is stopped. The zinc addition rate is decreased in weekly cycles. In one cycle, the daily zinc addition amount is equal. The daily zinc addition amount in the next week is 1 g less than that in the previous week. During sampling detection, the time - weighted average value of the instantaneous zinc concentration within a certain number of days starting from the zinc addition to the unit is calculated. The weighted calculation period is at most 30 days. Calculations are performed in a rolling manner with a 30 - day cycle, and it is controlled within the target value range to avoid increasing the risks of CIPS and CILC due to excessive zinc concentration.

[0027] The 30 - day weighted average zinc concentration is denoted as C Zn-30天加权平均 and is controlled within the target value range through adjustment of the zinc addition rate to avoid increasing the risks of CIPS and CILC due to excessive zinc concentration.

[0028] The specific method is to start counting the time - weighted average zinc concentration from the first day until 30 days are calculated, and then start the calculation for the next 30 - day period, and so on in a cycle. If it approaches the target value, the zinc addition rate is decreased or zinc addition is stopped to control C Zn-30天加权平均 within the target value range and prevent it from exceeding the target value.

[0029] The standard for decreasing the zinc addition rate is to reduce it by 1 g / day per week. The target value C Zn-目标值 is 2 - 10 μg / kg.

[0030] C Zn-30天加权平均 =(C Zn-瞬时1 ×t1 + C Zn-瞬时2 ×t2 + … + C Zn-瞬时n ×t n) / (t1 + t2 + … + t n ). n is an integer between 1 and 30; The described C Zn-30天加权平均 is less than or equal to the target value C Zn-目标值 .

[0031] To further understand the present invention, the following describes in detail the zinc concentration control method for the in-service pressurized water reactor nuclear power unit's main system with zinc addition in operation in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0032] Embodiment 1 Determination of the parameters and index requirements of the primary coolant zinc: For an in-service pressurized water reactor nuclear power unit that has operated for several cycles, the target zinc concentration, zinc parameters, and index requirements are determined through core axial power offset (CIPS) and fuel fouling-induced local corrosion (CILC) risk analysis: 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 is the measured value of regular sampling.

[0033] 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 × t1 + C Zn-瞬时2 × t2 + … + C Zn-瞬时n × t n ) / (t1 + t2 + … + t n ). C Zn-30天加权平均 is the weighted average of the instantaneous zinc concentration every 30 days.

[0034] After the first fuel cycle with zinc addition, the zinc concentration target value can be adjusted accordingly according to the zinc addition operation situation of the unit and the CIPS and CILC risk situations.

[0035] The zinc concentration control method for the in-service pressurized water reactor nuclear power unit's main system with zinc addition in operation includes the following steps: Step 1: Judge that the timing to start zinc addition operation has been reached and there is no sign of fouling-induced axial power offset (CIPS) in the core; Step 2: After all the prerequisite conditions for the unit to start zinc addition are met, start injecting depleted zinc acetate into the primary coolant system, and control the initial zinc addition rate at 10 g / day; the 64 abundance of Zn in the depleted zinc acetate < 1% to reduce 64The new radiation source term introduced by the neutron activation of Zn to produce 65 Zn; After the unit starts to implement zinc addition, if zinc is not detected in the primary coolant within two weeks after the initial zinc addition begins, then starting from the 3rd week, the zinc addition rate will be increased by 1 g / day every week, that is: the zinc addition rate in the 3rd week is adjusted to 11 g / day; If zinc is still not detected in the 3rd week, the zinc addition rate in the 4th week is adjusted to 12 g / day, and so on.

[0036] Once zinc is detected in the primary coolant, the zinc addition rate will be gradually reduced at a rate of 1 g / day per week, so that the zinc concentration is finally stabilized within the instantaneous zinc concentration C Zn-瞬时 limit range.

[0037] The change in the operating state of the unit may cause the zinc concentration in the primary coolant to be undetectable again. If this occurs, maintain the zinc addition rate. If the zinc addition rate needs to be adjusted, the original zinc addition rate should be maintained for at least one week before adjustment. If the zinc concentration in the primary coolant increases rapidly at a rate of 1 - 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.

[0038] While sampling to detect the instantaneous value of the zinc concentration, start counting the time - weighted average zinc concentration from the first day until the calculation reaches 30 days, and then start the next 30 - day calculation, and so on in a cycle. When approaching the target value, reduce the zinc addition rate at a rate of 1 g / day per week or stop zinc addition to control C Zn-30天加权平均 within the target value range and prevent exceeding the target value.

[0039] After the zinc concentration returns to the target value range and shows a downward trend, resume zinc addition until the zinc concentration meets the requirements. During the unit shutdown process, zinc will return from the oxide film on the surface of the primary coolant system materials, causing the zinc concentration in the primary coolant to rise significantly. Therefore, stop zinc addition 1 day before the unit shutdown.

[0040] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0041] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those 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. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded 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; Step 2: Inject depleted zinc acetate into the main coolant system, and control the initial zinc addition rate at 8-10 g / day; starting from the initial zinc addition, regularly sample and test the instantaneous value of the zinc concentration of the main coolant; 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 detection results are all below the detection limit, the rate increase logic is triggered; From the second cycle, the zinc addition rate is gradually increased according to a preset increment with a fixed time interval as the adjustment unit until the zinc concentration in the main coolant reaches a detectable range; the preset increment is 0.8-1.2 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 reduction, 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 the instantaneous value of zinc concentration in several days from the start of zinc addition to the unit, and calculate it on a rolling basis. If it is close to the target value, reduce the zinc addition rate or stop adding zinc to control the weighted average value of zinc concentration within the target value range; The target value is 2 to 10 μg / kg.

2. 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 1, characterized in that: 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 .

3. 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 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 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 1, characterized in that: The preset reduction is 0.8~1.2g / day.

5. 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 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 a day.

6. 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 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 during the above adjustment process, the zinc concentration in the main coolant increases by 1~2μg / kg per day, 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 1g / day per week.

8. 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 1, characterized in that: The time-weighted average zinc concentration is calculated from the first day until 30 days are reached, 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.

10. 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 1, characterized in that: The prerequisite is that the timing of zinc addition operation is reached and there is no sign of axial power deviation caused by core fouling.