阅读说明：本技术 一种核电厂二回路停运期间的湿保养法 (Wet maintenance method for nuclear power plant during two-loop shutdown ) 是由 聂雪超 姜磊 钟铁 赵东波 李河洋 吴旭东 侯涛 苗丽 孟宪波 范赏 于 2020-05-26 设计创作，主要内容包括：本发明公开了一种核电站二回路停运期间的湿保养方法,包括步骤：前期准备、确定保养液的目标浓度、确定保养液的加入量及添加时长、加入保养液、加保养液后的循环、化学取样分析、充入氮气、进入保养状态和定期监测保养液浓度；本发明向二回路设备中通入具有强还原性和吸水性的联氨溶液,制造还原环境,降低了设备金属表面的电位,从而达到对二回路进行保养的目的；本发明结合机组设计特点,明确了保养范围、确定了保养方式和监测手段,本发明所述的湿保养方法覆盖了二回路的全部设备；本发明的实施例中,经过三门核电的几次验证,取得了显著的效果,明显地缩短了启动冲洗的时间。(The invention discloses a wet maintenance method for a nuclear power station secondary circuit during shutdown, which comprises the following steps: preparing at an early stage, determining the target concentration of the maintenance liquid, determining the addition amount and the addition duration of the maintenance liquid, adding the maintenance liquid, circulating after adding the maintenance liquid, chemically sampling and analyzing, filling nitrogen, entering a maintenance state and periodically monitoring the concentration of the maintenance liquid; in the invention, hydrazine solution with strong reducibility and water absorbability is introduced into the secondary loop equipment to produce a reducing environment, so that the potential of the metal surface of the equipment is reduced, and the aim of maintaining the secondary loop is fulfilled; the invention combines the design characteristics of the unit, defines the maintenance range, determines the maintenance mode and the monitoring means, and covers all equipment of the two loops by the wet maintenance method; in the embodiment of the invention, after several times of verification of three-door nuclear power, a remarkable effect is obtained, and the time for starting flushing is obviously shortened.)

1. A wet maintenance method for a nuclear power station secondary circuit during shutdown comprises the following steps:

preparing in an early stage, and ensuring that the system is stopped for more than 7 days before wet maintenance;

determining the target concentration of the maintenance solution, wherein the concentration of the maintenance solution = 50 (ppm) maintenance weeks for the condensed water and water supply system (3) but not more than 600ppm, and for the steam generator system (4), the concentration of the maintenance solution is more than or equal to 25ppm, the pH (25 ℃) is more than 9.50, and the maintenance solution is hydrazine solution with the concentration of 32%;

step three, determining the adding amount and the adding time of the maintenance liquid,

method for calculating addition amount of maintenance liquid

In the formula: v_nThe volume (L) of the maintenance liquid to be added,

m is the water charging mass (kg) of the system to be added with the medicine,

C₁-target concentration of hydrazine (ppm) in the system to be dosed,

C₀-the current concentration (ppm) of hydrazine in the system to be dosed,

C_nthe purity/content (ppm) of hydrazine to be added,

rho is the density (kg/L) of the hydrazine solution to be added, and takes the value of 1;

method for calculating pumping time of maintenance liquid

In the formula: t-the running time (min) of dosing the dosing pump into the system to be dosed,

V_n-the amount (L) of hydrazine to be added,

q is the flow (L/h) of a dosing metering pump in the system to be dosed;

adding maintenance liquid, determining the addition amount and the addition duration of the maintenance liquid according to the target concentration of the maintenance liquid, starting a dosing pump (2), and enabling the maintenance liquid to flow out of a maintenance liquid storage tank pump (1) and enter the system through a dosing port (5) arranged in the system;

circulating after adding the maintenance liquid, wherein the system needs to circularly operate for a period of time after the maintenance liquid is added, the circulation of the condensed water and water supply system (3) is not less than 8 hours, and the circulation of the steam generator system (4) is not less than 32 hours;

sixthly, carrying out chemical sampling analysis, sampling at each sampling point (6) after the subsequent circulation of the system is finished, carrying out chemical analysis sampling, monitoring the concentration of the maintenance solution, and repeating the step III to the step VI if the concentration of the maintenance solution does not reach the target concentration;

seventhly, filling nitrogen, detecting that the concentration of the maintenance liquid reaches a target concentration after chemical analysis sampling, filling nitrogen to the upper parts of a water tank of a deaerator (37) and the maintenance liquid of a steam generator (41), and maintaining the pressure of the nitrogen to be 10 KPa-30 KPa;

step eight, entering a maintenance state, detecting that the concentration of the maintenance liquid reaches a target concentration after chemical analysis and sampling, stopping circulation, and entering the maintenance state;

and ninthly, monitoring the concentration of the maintenance liquid periodically, after the maintenance liquid enters a maintenance state, detecting the concentration of the maintenance liquid periodically, if the concentration of the maintenance liquid is in a stable state, prolonging the sampling frequency, and if the concentration of the maintenance liquid is unstable, executing the current monitoring period.

2. The method of claim 1, wherein the method comprises the steps of: the maintenance range of the maintenance method comprises a condensate and water supply system (3), a steam generator (4) and connecting pipelines between devices.

3. The method of claim 1, wherein the method comprises the steps of: the condensate pump (32), main feedwater pump (38), and steam generator recirculation pump (42) remain operational during the performance of the service.

4. The method of claim 1, wherein the method comprises the steps of: and during the maintenance period, the condenser (31) enters water to a high liquid level, the large circulation of the condenser (31), the condensate pump (32), the low-pressure heater, the deaerator (37), the high-pressure heater and the condenser (31) is maintained, and the water feeding of the steam generator (41) is up to 82% -95% of the liquid level.

5. The method of claim 1, wherein the method comprises the steps of: the dosing point (5) is arranged at an emergency water replenishing pipeline of the condenser (31) and an outlet of a steam generator recirculation pump (42).

6. The method of claim 1, wherein the method comprises the steps of: the condensate and feed water system (3) is analyzed for maintenance fluid concentration at a weekly frequency, and if the results stabilize for 3 consecutive weeks, the measurement frequency is adjusted to once a month.

7. The method of claim 1, wherein the method comprises the steps of: for the steam generator system (4), the frequency of the three times a week is analyzed, and the measured frequency can be adjusted after the result is stable.

8. A method of wet maintenance during shutdown of a secondary circuit in a nuclear power plant as recited in claim 1, wherein: for the steam generator system (4), the steam generator recirculation pump (42) is started for not less than 12h before each sampling.

9. The method of claim 1, wherein the method comprises the steps of: and sampling points for chemical sampling analysis are arranged on a recycling pipeline exhaust valve for selecting an outlet (36) of a 4# low-pressure heater, an outlet of a deaerator (37) and an outlet of a 7# high-pressure heater (310) and a steam generator (41).

10. The method of claim 1, wherein the method comprises the steps of: after the concentration of the maintenance liquid reaches the target concentration, the steam generator system (4) enters a maintenance state, and simultaneously drains the condensed water and a condenser (31) in the water supply system (3) and introduces hot air.

Technical Field

The invention relates to the field of equipment maintenance of a secondary circuit of a nuclear power plant, in particular to a wet maintenance method during shutdown of the secondary circuit of the nuclear power plant.

Background

The two-loop system of the nuclear power plant mainly comprises a saturated steam turbine, a generator, a condenser (or called condenser), a condensate pump, a low-pressure heater, a deaerator, a water feed pump, a high-pressure heater, an intermediate steam-water separation reheater, a corresponding instrument, a valve and a pipeline. The main function of the second loop is to form a closed thermodynamic cycle, and the steam generated by the nuclear steam supply system is sent to a steam turbine to do work, and the steam turbine drives a generator to convert mechanical energy into electric energy; is a steam and power conversion system. The main working principle of the two loops is as follows: the condensed water in the second loop absorbs heat and then is changed into water vapor, and the water vapor pushes a steam turbine to do work so as to convert the heat energy into the kinetic energy of the steam turbine; the steam turbine further drives the generator to generate electricity, and the water vapor after energy conversion is converted back into condensed water again, so that a thermodynamic cycle is completed.

The secondary loop equipment of the nuclear power plant is mostly made of carbon steel, and oxygen absorption corrosion is easy to occur. When the ambient humidity is below 40%, the carbon steel equipment hardly generates corrosion behavior, because a thin oxidation film is generated on the metal surface in a dry environment, and the corrosion can be effectively prevented. Above the critical value of 60%, the corrosion rate of carbon steel in air increases sharply, because the essence of atmospheric corrosion is the electrochemical corrosion process under the liquid film, and when the humidity is above the critical value of 60%, the liquid film starts to form, the speed of oxygen passing through the liquid film to reach the metal surface changes, the thinner the liquid film, the faster the diffusion, the faster the reaction speed, and the corrosion is accelerated.

During the shutdown of the unit, if the equipment is not maintained, the corrosion of the equipment is increased, a part of corrosion products can be removed by the circular flushing before the unit is started, but a part of corrosion products enter the evaporator, and the long-term stable operation of the unit is influenced. Migration of iron to steam generators has been a concern in the industry. A study in 2008 showed that around 20% of the iron migration occurred during the start-up period. At the same time, because the corrosion products delivered to the steam generator during start-up are more oxidizing than those delivered during power operation, these oxidizing corrosion products will increase the risk of corrosion cracking of the steam generator heat transfer tubes. On the other hand, if the equipment is not maintained, the washing progress after the unit is started is influenced, and the 'shortest overhaul period' of the power station is challenged.

The utility model discloses a utility model patent with publication number CN206345918U, which discloses an anti-corrosion device for the pipeline of the important service water system of the nuclear power station, the utility model makes the pipeline become a protected cathode by arranging sacrificial anodes at the two sides of the pipeline, thereby effectively slowing down the corrosion and damage of seawater to the pipeline, prolonging the service life of the pipeline and saving the maintenance and management cost of the pipeline; however, the sacrificial anode method, in addition to requiring separate sacrificial anode equipment, results in lower current efficiency due to its own self-corrosion consumption, and is difficult and expensive to replace with spent anodes.

To date, there are no published papers, patents and standards for two-circuit equipment maintenance methods in nuclear power plants.

Disclosure of Invention

The present invention is to solve the above problems and to provide a wet maintenance method for a nuclear power plant during a shutdown period of a secondary circuit, which can prevent corrosion of the surface of the equipment.

A wet maintenance method for a nuclear power station secondary circuit during shutdown comprises the following steps:

preparing in an early stage, and ensuring that the system is stopped for more than 7 days before wet maintenance;

determining the target concentration of the maintenance liquid in the system, wherein the concentration of the maintenance liquid = 50 maintenance weeks (ppm) but not more than 600ppm for the condensate and water supply system, and the concentration of the maintenance liquid is more than or equal to 25ppm for the steam generator, and the pH (25 ℃) is more than 9.50;

step three, calculating the adding amount of the maintenance liquid and the pumping time,

method for calculating addition amount of maintenance liquid

In the formula: v_nThe volume (L) of the maintenance liquid to be added,

m is the water charging mass (kg) of the system to be added with the medicine,

C₁-target concentration of hydrazine (ppm) in the system to be dosed,

C₀-the current concentration (ppm) of hydrazine in the system to be dosed,

C_nthe purity/content (ppm) of hydrazine to be added,

rho is the density (kg/L) of the hydrazine solution to be added, and takes the value of 1;

method for calculating pumping time of maintenance liquid

In the formula: t-the running time (min) of dosing the dosing pump into the system to be dosed,

V_n-the amount (L) of hydrazine to be added,

q is the flow (L/h) of a dosing metering pump in the system to be dosed;

adding maintenance liquid, determining the addition amount and the addition duration of the maintenance liquid according to the target concentration of the maintenance liquid, starting a dosing pump, and pumping the maintenance liquid out of a storage tank and into the system through a dosing port arranged in the system;

circulating after adding the maintenance liquid, wherein the system needs to circularly operate for a period of time after the maintenance liquid is added, the circulation of a condensed water system is not less than 8 hours, and the circulation of a steam generator system is not less than 32 hours;

sixthly, performing chemical analysis sampling, after the subsequent circulation of the system is finished, sampling at each sampling point to perform chemical analysis sampling, monitoring the concentration of the maintenance solution, and repeating the step three to the step six if the concentration of the maintenance solution does not reach the target concentration;

seventhly, filling nitrogen for protection, detecting that the concentration of the maintenance liquid reaches a target concentration after chemical analysis and sampling, filling nitrogen to the upper parts of the deaerator water tank and the steam generator maintenance liquid, and maintaining the nitrogen pressure at 10 KPa-30 KPa;

step eight, entering a maintenance state, detecting that the concentration of the maintenance liquid reaches a target concentration after chemical analysis and sampling, and stopping circulation;

and ninthly, monitoring the concentration of the maintenance liquid periodically, after the maintenance liquid enters a maintenance state, detecting the concentration of the maintenance liquid periodically, if the concentration of the maintenance liquid is in a stable state, prolonging the sampling frequency, and if the concentration of the maintenance liquid is unstable, executing the current monitoring period.

Preferably, the maintenance range of the maintenance method is 1, 2, 3, 4# low-pressure heater water side, deaerator, 6, 7# high-pressure heater water side, steam generator and connecting pipeline between devices.

Preferably, the maintenance solution is concentrated hydrazine solution with the concentration of 32%.

Preferably, the condensate pump, the main feedwater pump, and the steam generator recirculation pump remain operational during the performance of the service.

Preferably, the condenser is filled with water to a high liquid level during the maintenance period, the large circulation of the condenser, the condensate pump, the low-pressure heater, the deaerator, the high-pressure heater and the condenser is maintained, and the water feeding of the steam generator is up to 82% -95% of the liquid level.

Preferably, the dosing point is arranged at the outlet of an emergency water replenishing pipeline of the condenser and a recirculation pump of the steam generator.

Preferably, for both the condensate and the feedwater system, the hydrazine concentration is analyzed at a weekly frequency, and if the results stabilize for 3 consecutive weeks, the measurement frequency is adjusted to once a month.

Preferably, for a steam generator system, the analysis is performed at a frequency of three times a week, and the measurement frequency can be adjusted after the results have stabilized.

Preferably, for a steam generator system, the steam generator recirculation pump is started for no less than 12 hours before each sampling.

Preferably, sampling points for chemical sampling analysis are arranged at an outlet of a selected 4# low-pressure heater, a deaerator, a 7# high-pressure heater and a steam generator recirculation pipeline exhaust valve.

Preferably, after the concentration of the condensate and the maintenance solution of the water supply system reaches the target concentration, the condenser is drained and hot air is introduced.

The beneficial effects of the invention include:

1) the implementation of the invention is that when the system is stopped for more than 7 days, the condensate pump, the main water feed pump and the steam generator recirculation pump equipment keep running, and the system does not drain water, hydrazine solution with strong reducibility and water absorbability is introduced into the two-loop equipment to produce a reducing environment, and the potential of the metal surface of the equipment is reduced, thereby achieving the purpose of maintaining the two loops;

2) the invention combines the design characteristics of the unit, defines the maintenance range, determines the maintenance mode and the monitoring means, and covers all equipment of the two loops by the wet maintenance method;

3) in the embodiment of the invention, after several times of verification of three-door nuclear power, a remarkable effect is obtained, and the time for starting flushing is obviously shortened.

Drawings

FIG. 1 is a flow chart of a wet maintenance method during a nuclear power plant secondary loop outage;

FIG. 2 is a system diagram of a wet maintenance method during a nuclear power plant two-circuit outage.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

The embodiment of the invention is a moisture preservation method for a two-loop shutdown period formed by combining the design characteristics of a system and selecting an optimal maintenance technology on the basis of application practice and experience summary of the unit No. 1 and No. 2 of a three-door nuclear power plant during the previous shutdown period so as to minimize equipment corrosion during the system shutdown period.

Fig. 2 is a system schematic diagram of a wet maintenance method during the shutdown of a secondary loop of a nuclear power plant, and referring to fig. 2, the maintenance system comprises a maintenance liquid storage tank 1 for storing a maintenance liquid, a dosing pump 2 for adding the maintenance liquid into the system, a condensate and water supply system 3 for circulating water in the secondary loop, a steam generator system 4, a dosing point 5 and a sampling point 6; the condensate and water supply system 3 comprises a condenser 31, a condensate pump 32, a # 1 low-pressure heater 33, a # 2 low-pressure heater 34, a # 3 low-pressure heater 35, a # 4 low-pressure heater 36, a deaerator 37, a main water supply pump 38, a # 6 high-pressure heater 39 and a # 7 high-pressure heater 310; the steam generator system 4 comprises a steam generator 41 and a steam generator recirculation pump 42.

Fig. 1 is a flowchart of a wet maintenance method during shutdown of a secondary circuit of a nuclear power plant, and as shown in fig. 1, the steps of the wet maintenance method during shutdown of the secondary circuit of the nuclear power plant include:

preparing in an early stage, and ensuring that the system is stopped for more than 7 days before wet maintenance; the condensate pump 32, main feedwater pump 38, and steam generator recirculation pump 42 remain operational during the performance of the service; and during the maintenance period, the condenser 31 is fed with water to a high liquid level, the large circulation of the condenser 31, the condensate pump 32, the low-pressure heater, the deaerator 37, the high-pressure heater and the condenser 31 is maintained, and the water feeding of the steam generator 41 is kept to be 82% -95% of the liquid level.

Determining the target concentration of the maintenance solution, wherein the concentration of the maintenance solution is = 50 (ppm) maintenance weeks for the condensed water and water supply system 2 but not more than 600ppm, the concentration of the maintenance solution is more than or equal to 25ppm for the steam generator system 3, the pH value (25 ℃) is more than 9.50, and the maintenance solution is a concentrated hydrazine solution with the concentration of 32%.

Step three, determining the adding amount and the adding time of the maintenance liquid,

method for calculating addition amount of maintenance liquid

In the formula:V_nthe volume (L) of the maintenance liquid to be added,

m is the water charging mass (kg) of the system to be added with the medicine,

C₁-target concentration of hydrazine (ppm) in the system to be dosed,

C₀-the current concentration (ppm) of hydrazine in the system to be dosed,

C_nthe purity/content (ppm) of hydrazine to be added,

rho is the density (kg/L) of the hydrazine solution to be added, and takes the value of 1;

method for calculating pumping time of maintenance liquid

In the formula: t-the running time (min) of dosing the dosing pump into the system to be dosed,

V_n-the amount (L) of hydrazine to be added,

q is the flow (L/h) of a dosing metering pump in the system to be dosed;

adding maintenance liquid, determining the addition amount and the addition duration of the maintenance liquid according to the target concentration of the maintenance liquid, starting a dosing pump 2, pumping the maintenance liquid out of a maintenance liquid storage tank 1, and entering the system through a dosing port 4 arranged in the system; the dosing point 4 is arranged at the outlet of the emergency water replenishing pipeline of the condenser 31 and the recirculation pump 42 of the steam generator.

Circulating after adding the maintenance liquid, wherein the system needs to circularly operate for a period of time after the maintenance liquid is added, the circulation of condensed water and a water supply system is not less than 8 hours, and the circulation of a steam generator system is not less than 32 hours;

sixthly, carrying out chemical sampling analysis, after the subsequent circulation of the system is finished, sampling at each sampling point 5 to carry out chemical analysis sampling, monitoring the concentration of the maintenance solution, and repeating the step three to the step six if the concentration of the maintenance solution does not reach the target concentration;

seventhly, filling nitrogen, detecting that the concentration of the maintenance liquid reaches a target concentration after chemical analysis sampling, filling nitrogen to the water tank of the deaerator 37 and the upper part of the maintenance liquid of the steam generator 41, and maintaining the nitrogen pressure at 10 KPa-30 KPa;

step eight, entering a maintenance state, detecting that the concentration of the maintenance liquid reaches a target concentration after chemical analysis and sampling, and closing the medicine adding pump 2;

and ninthly, monitoring the concentration of the maintenance liquid periodically, after the maintenance liquid enters a maintenance state, detecting the concentration of the maintenance liquid periodically, if the concentration of the maintenance liquid is in a stable state, prolonging the sampling frequency, and if the concentration of the maintenance liquid is unstable, executing the current monitoring period.

The maintenance range of the maintenance method is the connecting pipelines between the condensate and water supply system 3, the evaporative crystallization system 4 and the equipment.

For the condensate and feedwater system 3, the monitoring period of the chemical sampling is such that the hydrazine concentration is analyzed at a frequency of once a week, and if the results are stable for 3 consecutive weeks, the measurement frequency is adjusted to once a month.

For the steam generator system 4, the frequency of the measurement can be adjusted after the results have stabilized, as the analysis is performed at a frequency of three times a week.

For the steam generator system 4, the steam generator recirculation pump cycle was started no less than 12h before each sampling.

And the sampling point 5 for chemical sampling analysis is arranged at the outlet of the selected 4# low-pressure heater 36, the outlet of the deaerator 37 and the outlet of the 7# high-pressure heater 310 and the steam generator recirculation pipeline exhaust valve.

When the concentration of the treating liquid in the condensate and water supply system 3 reaches the target concentration, the steam generator system 4 enters a maintenance state and simultaneously discharges the condensate and the condenser 31 in the water supply system 3 to perform hot air ventilation.

The embodiment of the invention counts the starting and flushing conditions of the secondary circuit of the three-door nuclear power calendar, the data are shown in the table 1,

TABLE 1 statistics of high flush times and turbidity peaks during the start-up of three-door calendar secondary loop

During the period of 101 overhaul, the equipment is not maintained, so that the turbidity peak value of washing water is far higher than that of the washing water in the past, the difficulty of adjusting the quality of condensed water after washing is increased, and the time for adjusting the quality of the condensed water is prolonged.

The above description is only a preferred embodiment of the present invention and should not be taken as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention should be included in the scope of the present invention/appended claims.