Chemical control method for nuclear power plant during starting two-loop flushing
阅读说明：本技术 一种核电厂启动二回路冲洗期间的化学控制方法 (Chemical control method for nuclear power plant during starting two-loop flushing ) 是由 姜磊 聂雪超 钟铁 吴旭东 侯涛 苗丽 孟宪波 范赏 谭东斌 王孝宇 于 2020-06-10 设计创作，主要内容包括：一种核电厂启动二回路冲洗期间的化学控制方法,用向冲洗水中加入添加剂来降低冲洗期间设备的腐蚀速率,所述添加剂的添加方式为：联用间断加药和连续加药的加药方式；并且在加药过程中采样进行浓度分析,并根据添加剂浓度来调整所述添加剂的加药量及加药时间。本发明规定了一套完整的二回路系统冲洗期间的化学控制方法,明确了药品在不同阶段的加药浓度及监测手段,以抑制冲洗过程中的设备腐蚀,提高冲洗效果,缩短冲洗工期。(A method of chemical control during a startup two-loop flush of a nuclear power plant by adding an additive to the flush water to reduce the rate of corrosion of equipment during the flush, the additive being added by: the intermittent dosing and the continuous dosing modes are combined; and sampling in the dosing process for concentration analysis, and adjusting the dosing amount and the dosing time of the additive according to the concentration of the additive. The invention provides a set of complete chemical control method during the flushing of the two-loop system, and defines the dosing concentration and monitoring means of the medicine at different stages so as to inhibit the corrosion of equipment in the flushing process, improve the flushing effect and shorten the flushing period.)
1. A method of chemical control during a startup two-circuit flush of a nuclear power plant, characterized by adding an additive to the flush water to reduce the corrosion rate of equipment during the flush, the additive being added in a manner that: the intermittent dosing and the continuous dosing modes are combined; and sampling is carried out during the operation period of intermittent dosing and continuous dosing for concentration analysis, and the dosing amount and the dosing time of the additive are adjusted according to the concentration of the additive.
2. The method of claim 1, wherein the intermittent dosing is used before the condensate polishing system is put into operation; the continuous dosing is used in the condenser charging and discharging stage or after the condensate polishing system is put into operation.
3. The method of claim 2, wherein the formula for calculating the dosage of the intermittent dosing is as follows:
；
in the formula:
Vn: the amount of additive to be added, unit: l;
m: the water charge of the medicine adding system is treated, and the unit is as follows: kg;
C1: target concentration of additive in the system to be dosed, unit: ppm;
C0: target concentration of additive in tape dosing system, unit: ppm;
Cn: purity/content of additive to be added, unit: ppm;
ρ: density of the additive to be added, unit: kg/L;
the formula for calculating the dosing time of the intermittent dosing is as follows:
；
in the formula:
t: the operating time of the dosing pump in the system to be dosed, unit: min;
Vn: the amount of additive to be added, unit: l;
q: flow rate of a dosing pump in a to-be-dosed system, unit: l/h.
4. The method of claim 2, wherein the continuous dosing is calculated by the formula:
；
in the formula:
C12: target concentration of additive in the system to be dosed, unit: ppm;
C2: purity/content of additive to be added, unit: ppm;
Q2: flow rate of the dosing pump, unit: l/h;
Q1: the system drainage/condensate fine treatment purification flow rate, unit: l/h.
5. A method of chemical control during a nuclear plant startup two-circuit flush according to any of claims 3 or 4, characterized in that the target concentration of the additive is: before vacuumizing or before fine treatment of the condenser: 5-10 ppm; after the condenser is vacuumized or after the fine treatment is put into operation: 1 to 2 ppm.
6. The method of claim 5, wherein the additive is prepared by using a hydrazine solution prepared from a hydrazine stock solution, and the formula of the hydrazine solution is as follows:
in the formula:
m0: the mass of hydrazine stock solution to be added, unit: kg;
c: the mass percentage of hydrazine in the hydrazine stock solution is as follows: percent;
v: preparing a target volume of hydrazine solution, unit: m is3；
C10: target concentration of hydrazine solution in the hydrazine solution tank, unit: percent;
ρ1: density of hydrazine solution, unit: kg/m3。
7. The method of claim 5, wherein the concentration analysis is sampled at a frequency of: before vacuumizing or before fine treatment of the condenser: the sampling frequency is more than or equal to 1 time/24 h; after the condenser is vacuumized or after the fine treatment is put into operation: the sampling frequency is more than or equal to 1 time/12 h.
8. The method of claim 2, wherein the point of intermittent dosing is located at an emergency feedwater line of the condenser; the continuous dosing point is arranged at the outlet of the condensate polishing treatment.
Technical Field
The invention belongs to the technical field of nuclear power engineering construction and debugging, and particularly relates to a chemical control method for a nuclear power plant during starting of a two-loop flushing period.
Background
Before the two loops are started, the nuclear power plant needs to flush system pipelines and equipment so as to remove foreign matters, impurities and corrosion products introduced into the system equipment in the processes of manufacturing, installing and debugging the equipment, ensure that the water quality of downstream users (steam generators) reaches the standard requirements as soon as possible, maintain good water chemical environment of the steam generators and inhibit or delay the corrosion of the steam generators.
The two-loop system equipment is made of carbon steel, oxygen absorption corrosion is easy to occur, oxygen is a depolarizer, corrosion potential is formed in a saturated dissolved oxygen humid environment, equipment corrosion is caused, and the reaction mechanism is as follows:
anode:；
cathode:；
and (3) total reaction:；
the two-loop flushing in the starting stage of most of domestic nuclear power plants adopts the mode of integral water inlet and circulating flushing, no medicine is added during flushing, the corrosion of equipment pipelines can not be effectively inhibited in the environment of saturated dissolved oxygen neutral flushing water, and the flushing time is prolonged. According to the actual verification result on site, during the system flushing, the system turbidity is flushed to 1ppm and then the charging and discharging are stopped, no medicine is added in the period, after 8 hours, the system turbidity is measured again, the system turbidity is increased to about 2ppm, the charging and discharging are required to be performed again, the flushing water consumption is increased, and the influence is caused on the flushing period of the two loops; even if hydrazine is used as an additive, the hydrazine solution is relatively coarse and shallow in application, the addition amount of the hydrazine solution is not clear and standardized along with the change of flushing flow in the flushing process of the two-loop system, the use standard of the hydrazine is unclear, and the inactivation effect on system pipeline equipment is poor.
Disclosure of Invention
In view of the above problems, the present invention provides a chemical control method for a nuclear power plant during starting two-loop flushing, which specifies a complete set of chemical control method for a two-loop system during flushing, and defines the dosing concentration and monitoring means of drugs at different stages to inhibit equipment corrosion during flushing, improve flushing effect, and shorten flushing period.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method of chemical control during a startup two-loop flush of a nuclear power plant by adding an additive to the flush water to reduce the rate of corrosion of equipment during the flush, the additive being added by: the intermittent dosing and the continuous dosing modes are combined; and sampling for concentration analysis in the intermittent dosing and continuous dosing processes, and adjusting the dosing amount and the dosing time of the additive according to the concentration of the additive.
As a further preferred aspect of the present invention, the intermittent dosing is used before the condensate polishing system is put into operation; the continuous dosing is used in the condenser charging and discharging stage or after the condensate polishing system is put into operation.
As a further preferred aspect of the present invention, the formula for calculating the dosage of the intermittent dosing is as follows:
Vn: the amount of additive to be added, unit: l;
m: the water charge of the medicine adding system is treated, and the unit is as follows: kg;
C1: target concentration of additive in the system to be dosed, unit: ppm;
C0: target concentration of additive in tape dosing system, unit: ppm;
Cn: purity/content of additive to be added, unit: ppm;
ρ: density of the additive to be added, unit: kg/L;
the formula for calculating the dosing time of the intermittent dosing is as follows:
；
t: the operating time of the dosing pump in the system to be dosed, unit: min;
Vn: the amount of additive to be added, unit: l;
q: flow rate of a dosing pump in a to-be-dosed system, unit: l/h.
As a further preferred aspect of the present invention, the calculation formula of the continuous dosing is:
；
C12: target concentration of additive in the system to be dosed, unit: ppm;
C2: need to addPurity/content of additive, unit: ppm;
Q2: flow rate of the dosing pump, unit: l/h;
Q1: the system drainage/condensate fine treatment purification flow rate, unit: l/h.
As a further preferred aspect of the present invention, the target concentrations of the additives are: before vacuumizing or before fine treatment of the condenser: 5-10 ppm; after the condenser is vacuumized or after the fine treatment is put into operation: 1 to 2 ppm.
As a further preferred aspect of the present invention, the additive is prepared by using a hydrazine solution prepared from a hydrazine stock solution, and the formula of the hydrazine solution is as follows:
；
m0: the mass of hydrazine stock solution to be added, unit: kg;
the mass percentage of hydrazine in the hydrazine stock solution C is as follows: percent;
v: preparing a target volume of hydrazine solution, unit: m is3；
C10: target concentration of hydrazine solution in the hydrazine solution tank, unit: percent;
ρ1: density of hydrazine solution, unit: kg/m3。
As a further preferred aspect of the present invention, the sampling frequency of the concentration analysis is: before vacuumizing or before fine treatment of the condenser: the sampling frequency is more than or equal to 1 time/24 h; after the condenser is vacuumized or after the fine treatment is put into operation: the sampling frequency is more than or equal to 1 time/12 h.
As a further preferred aspect of the present invention, the dosing point for intermittently dosing is disposed at an emergency water replenishing pipeline of the condenser; the continuous dosing point is arranged at the outlet of the condensate polishing treatment.
In conclusion, the invention has the following beneficial effects:
1. the invention selects the optimal control strategy according to different working conditions, and has clear order and proper control.
2. The invention has clear indexes and strict process control, and ensures that the control strategy is effectively implemented.
3. By using the flushing method, the flushing period of the two loops is shortened to 5 days from the previous one week, the effect is remarkable, and the consumption of the desalted water can be reduced by 1000-2000t by one flushing.
4. The index is excellent:
by adopting the flushing mode of the invention, in the practical production and application process:
(1) after the machine No. 1 is charged, the chemical control mode is used in the flushing period, and the quality of the sewage reaches the WANO-CPI median requirement after ten days of commercial transportation and is recorded by domestic power stations at the fastest speed;
(2) after 101 overhaul is started, the chemical control mode is used in the flushing period, the quality of the sewage is always maintained below the WANO-CPI median level, and the same-row power station can reach the standard after about 7 days of purification time after full power;
(3) after the machine No. 2 is charged, the chemical control mode is used in the flushing period, twenty days after commercial transportation, the sewage quality reaches the WANO-CPI median requirement, and the average level is obviously improved compared with the average level of about 3 months in China.
Drawings
FIG. 1 is a flow chart of the chemical control during a two-circuit flush of the present invention.
FIG. 2 is a schematic diagram of a two-circuit flush according to the present invention.
Detailed Description
First, medicine selection
In the washing process, hydrazine solution is added as an additive.
The hydrazine is added into the washing water, on one hand, the removal rate of corrosion products and foreign matters on the inner surface is increased by using the oxidation-reduction reaction of the hydrazine and the iron oxide, and on the other hand, the pH value of the washing water is improved, and the reducibility of the washing water is maintained, so that the removal rate of organic matters is increased, and the corrosion rate of equipment during washing is reduced.
Second, preparation of additive (medicine)
The hydrazine stock solution is prepared into a certain diluted hydrazine solution, and the preparation formula is as follows:
in the formula:
m0: the mass of hydrazine stock solution needs to be added, kg;
c: mass percent of hydrazine in hydrazine stock solution;
v: target volume, m, of hydrazine solution3；
C10: target concentration,%, of the hydrazine solution in the hydrazine solution tank;
ρ1the density of hydrazine solution in kg/m3。
Third, target concentration
Before vacuumizing or before fine treatment of the condenser: 5-10 ppm;
after the condenser is vacuumized or after the fine treatment is put into operation: 1 to 2 ppm.
Fourthly, the medicine adding mode and the medicine adding point are selected
1. Discontinuously adding medicine: before the condensate polishing system is put into operation, the dosing point is the emergency water replenishing pipeline of the condenser;
2. continuously adding medicine: and in the condenser filling and discharging stage or after the condensate polishing system is put into operation, the dosing point is a condensate polishing outlet.
During the operation of the two-loop motor set, the method comprises a phase of filling and discharging the condenser, a phase of putting the condensate polishing system into operation for purifying the cleaning water and a phase of flushing the qualified cleaning water by circulating flow in the two-loop system. When the condenser is charged and discharged, the cleaning water is in a state of discharging and replenishing, and the hydrazine amount to be added is calculated according to the water discharge amount for continuous replenishment when the hydrazine in the water quality reaches the target concentration; when the condensate polishing system is put into operation, the concentration of hydrazine in the cleaning water is greatly reduced under the operation of the condensate polishing system, and the hydrazine to be added needs to be calculated according to the flow of the cleaning water for continuous replenishment. In the two states, hydrazine addition is in a continuous dosing stage. When the washing water is circularly flushed in the two-loop system, the consumption of the hydrazine only exists in the condition of the redox reaction of the hydrazine and the iron oxide, the consumption of the hydrazine is low in the state, the adding amount of the hydrazine is calculated according to the actual hydrazine concentration of the washing water obtained by detection, and the hydrazine is periodically supplemented, and the stage is an intermittent dosing stage. Therefore, according to the working mode of the two-loop system during flushing, the invention adopts specific dosing measures for the cleaning states at different stages, and has clear indexes and strictly controllable process, thereby ensuring the effective implementation of the control strategy.
Fifthly, calculating the dosing amount and the dosing time
1. Discontinuously adding medicine:
(1) dosage of medicine
In the formula:
Vn: the amount of additive to be added, L;
m: the water content of the drug adding system is kg;
C1: the target concentration of the additive in the system to be dosed is ppm;
C0: target concentration of additive in the dosing system, ppm;
Cn: purity/content of additive to be added, ppm;
ρ: density of additive to be added, kg/L.
(2) Time of adding medicine
In the formula:
t: the operation time of a dosing pump in a system to be dosed is min;
Vn: the amount of additive to be added, L;
q: the flow rate of a medicine adding pump in a system to be added with medicine is L/h;
60: and the time units of min and h are converted into coefficients.
2. Continuous dosing
In the formula:
C12: the target concentration of the additive in the system to be dosed is ppm;
C2: purity/content of additive to be added, ppm;
Q2: the flow rate of the dosing pump is L/h;
Q1: and (3) the system drainage/condensed water fine treatment purification flow is L/h.
Sixthly, sampling analysis
During the continuous operation of the dosing pump, the analysis frequency is not less than 1 time/24 h;
during the period that the dosing pump is not continuously operated, the analysis frequency is not less than 1 time/12 h.
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