阅读说明：本技术 一种适用于压水堆核电厂的自然循环冷却方法 (Natural circulation cooling method suitable for pressurized water reactor nuclear power plant ) 是由 程坤 冉旭 吴清 刘昌文 冷贵君 李峰 喻娜 陈宏霞 蔡容 习蒙蒙 陆雅哲 杨 于 2021-06-18 设计创作，主要内容包括：本发明公开了一种适用于压水堆核电厂的自然循环冷却方法,包括以下步骤：将主系统硼化至冷却堆硼浓度；维持主系统压力稳定,进行主系统热段降温；进行主系统降压；循环直至主系统热段温度降至设定值,主系统压力降至设定值；进行上封头流体降温；进行主系统降压；隔离安注箱,并主系统降压至最终压力值；将主系统冷却至冷停堆工况；本发明通过设定严格的主系统降温降压执行步骤和限制条件,防止主系统自然循环冷却过程中上封头流动死区流体的闪蒸产汽所导致的自然循环终止,确保了事故后反应堆能够被持续冷却至安全可控的冷停堆状态。(The invention discloses a natural circulation cooling method suitable for a pressurized water reactor nuclear power plant, which comprises the following steps: boronizing the primary system to a cooled heap boron concentration; maintaining the pressure of the main system stable, and performing the hot section cooling of the main system; carrying out pressure reduction on the main system; circulating until the temperature of the hot section of the main system is reduced to a set value, and the pressure of the main system is reduced to the set value; cooling the upper end socket fluid; carrying out pressure reduction on the main system; isolating the safety injection box, and reducing the pressure of the main system to a final pressure value; cooling the main system to a cold shutdown working condition; according to the invention, the strict main system cooling and depressurization execution steps and limiting conditions are set, so that the natural circulation termination caused by the flash evaporation and steam generation of the fluid in the flowing dead zone of the upper end enclosure in the natural circulation cooling process of the main system is prevented, and the reactor can be continuously cooled to a safe and controllable cold shutdown state after an accident.)

1. A natural circulation cooling method suitable for a pressurized water reactor nuclear power plant is characterized by comprising the following steps:

10. boronizing the primary system to a cooled heap boron concentration;

20. maintaining the pressure of the main system stable, and performing the hot section cooling of the main system;

30. carrying out pressure reduction on the main system;

40. step 20 and step 30 are circulated until the temperature of the hot section of the main system is reduced to a set value and the pressure of the main system is reduced to the set value;

50. cooling the upper end socket fluid;

60. carrying out pressure reduction on the main system;

70. isolating the safety injection box, and reducing the pressure of the main system to a final pressure value;

80. and cooling the main system to a cold shutdown working condition.

2. The natural circulation cooling method for a pressurized water reactor nuclear power plant according to claim 1, characterized in that in step 10, the reaching of the primary system to the cold shutdown boron concentration value is determined by sampling analysis.

3. The natural circulation cooling method for a pressurized water reactor nuclear power plant according to claim 1, characterized in that the step 40 comprises the following steps:

41. cooling the main system to a temperature of the hot section less than a first temperature;

42. the main system is depressurized to a pressure equal to the first pressure;

43. locking a safety injection signal;

44. maintaining the pressure of the main system at a first pressure, and cooling the main system until the temperature of the hot section is equal to a second temperature;

45. maintaining the supercooling degree of the main system, and reducing the pressure of the main system to be equal to the second pressure;

46. and maintaining the pressure of the main system at the second pressure, and cooling the main system to the temperature of the hot section equal to the third temperature.

4. The natural circulation cooling method for a pressurized water reactor nuclear power plant as recited in claim 3, wherein in step 50, the temperature of the main system is maintained at a third temperature, and the temperature of the head fluid is reduced to less than a fourth temperature.

5. The natural circulation cooling method for a pressurized water reactor nuclear power plant as recited in claim 4 in which the main system pressure is reduced to less than the third pressure by maintaining the main system temperature at the third temperature, maintaining the head fluid temperature at less than the fourth temperature, and at step 60.

6. The natural circulation cooling method for the pressurized water reactor nuclear power plant as claimed in claim 1, wherein in the steps 20 and 40, the temperature reduction rate of the main system is less than 14 ℃/h, the water level of the pressure stabilizer is at the zero load water level, the temperature and the pressure of the main system are within the limit of a natural circulation P-T diagram, and the narrow range water level of the steam generator is 34-50%.

7. The natural circulation cooling method for a pressurized water reactor nuclear power plant as claimed in claim 1, wherein in step 40, the main system cooling rate is less than 14 ℃/h, the pressurizer water level is at zero load water level, and the main system temperature pressure is within the limits of the natural circulation P-T diagram.

8. The natural circulation cooling method for a pressurized water reactor nuclear power plant according to claim 1, wherein the main system is depressurized by an auxiliary spray system, and if the auxiliary spray system is not available, the depressurization is performed by using a pressurizer safety valve.

9. The natural circulation cooling method for a pressurized water reactor nuclear power plant according to claim 5, characterized in that the first temperature is 284 ℃, the second temperature is 225 ℃, the third temperature is 177 ℃, the fourth temperature is 210 ℃, the supercooling degree is 70 ℃, the first pressure is 13.56MPa (a), the second pressure is 8.27MPa (a), the third pressure is 7MPa (a), and the final pressure value is 2.7MPa (a).

10. A method of cooling a pressurized water reactor nuclear power plant, comprising the steps of:

s1, if the reactor has an accident that the safety injection is not triggered or does not need to be triggered;

s2, if the main system main pump fails to start, executing natural circulation cooling;

s3, if the control body driving mechanism cooling fan fails to be started, executing a natural circulation cooling method suitable for a pressurized water reactor nuclear power plant according to any one of claims 1 to 9.

Technical Field

The invention relates to the field of pressurized water reactor nuclear power plants, in particular to a natural circulation cooling method suitable for a pressurized water reactor nuclear power plant.

Background

After the accident of 'Hualongyi' pressurized water reactor nuclear power plant which is not triggered or does not need to trigger safety injection occurs, the reactor is automatically and emergently stopped, and an operator needs to control and relieve the accident consequence according to the emergency accident regulation.

If the initial cause of the accident can not be repaired in the hot state of the reactor, the reactor needs to be cooled to a cold shutdown state for fault treatment. In this process, if the main system main pump, which is shut down, cannot be started again, the reactor main system needs to establish a natural circulation to cool the core.

In the natural circulation operation process of the main system, a high-temperature flow dead zone exists in the upper head area of the reactor pressure vessel, and a control rod driving mechanism cooling fan needs to be started to cool the flow dead zone of the upper head.

If the cooling fan of the control rod driving mechanism is partially or completely unavailable, the coolant in the high-temperature flow dead zone of the upper end enclosure is easy to flash and generate steam in the natural circulation cooling and depressurization process, the liquid level of the pressure vessel is possibly reduced to be lower than the upper surface of the heat pipe section, the natural circulation of a main system is interrupted, the waste heat of a reactor core is exhausted and failed, and the safety of the reactor is seriously threatened.

The existing emergency regulations of the pressurized water reactor nuclear power plant are not considered enough for the counter measures of the reactor natural circulation cooling under the condition that the cooling fan of the control rod driving mechanism cannot operate after the accident shutdown, and a special counter strategy is lacked to solve the above situations.

Disclosure of Invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a natural circulation cooling method suitable for a pressurized water reactor nuclear power plant.

A natural circulation cooling method suitable for a pressurized water reactor nuclear power plant comprises the following steps:

10. boronizing the primary system to a cooled heap boron concentration;

20. maintaining the pressure of the main system stable, and performing the hot section cooling of the main system;

30. carrying out pressure reduction on the main system;

40. step 20 and step 30 are circulated until the temperature of the hot section of the main system is reduced to a set value and the pressure of the main system is reduced to the set value;

50. cooling the upper end socket fluid;

60. carrying out pressure reduction on the main system;

70. isolating the safety injection box, and reducing the pressure of the main system to a final pressure value;

80. and cooling the main system to a cold shutdown working condition.

Specifically, in step 10, the primary system arrival cold shutdown boron concentration value is determined by sample analysis.

Specifically, step 40 specifically includes the following steps:

41. cooling the main system to a temperature of the hot section less than a first temperature;

42. the main system is depressurized to a pressure equal to the first pressure;

43. locking a safety injection signal;

44. maintaining the pressure of the main system at a first pressure, and cooling the main system until the temperature of the hot section is equal to a second temperature;

45. maintaining the supercooling degree of the main system, and reducing the pressure of the main system to be equal to the second pressure;

46. and maintaining the pressure of the main system at the second pressure, and cooling the main system to the temperature of the hot section equal to the third temperature.

Specifically, in step 50, the temperature of the main system is maintained at the third temperature, and the temperature of the head fluid is reduced to be lower than the fourth temperature.

Specifically, in step 60, the temperature of the main system is maintained at the third temperature, the temperature of the head fluid is maintained to be lower than the fourth temperature, and the pressure of the main system is reduced to be lower than the third pressure.

Preferably, in step 20 and step 40, the temperature reduction rate of the main system is less than 14 ℃/h, the water level of the voltage stabilizer is at the zero load water level, the temperature and pressure of the main system are within the limit of a natural circulation P-T diagram, and the narrow range water level of the steam generator is 34-50%.

Preferably, in step 40, the main system cooling rate is less than 14 ℃/h, the potentiostat water level is at the zero load water level, and the main system temperature pressure is within the natural cycle P-T map limits.

As an embodiment, the main system performs depressurization through the auxiliary spraying system, and if the auxiliary spraying system is unavailable, the depressurization is performed through the safety valve of the voltage stabilizer.

Preferably, the first temperature is 284 ℃, the second temperature is 225 ℃, the third temperature is 177 ℃, the fourth temperature is 210 ℃, the supercooling degree is 70 ℃, the first pressure is 13.56mpa (a), the second pressure is 8.27mpa (a), the third pressure is 7mpa (a), and the final pressure value is 2.7mpa (a).

A method of cooling a pressurized water reactor nuclear power plant comprising the steps of:

s1, if the reactor has an accident that the safety injection is not triggered or does not need to be triggered;

s2, if the main system main pump fails to start, executing natural circulation cooling;

and S3, if the control body driving mechanism cooling fan fails to be started, executing the natural circulation cooling method suitable for the pressurized water reactor nuclear power plant.

Compared with the prior art, the invention prevents the termination of natural circulation caused by the flash evaporation steam production of the fluid in the flowing dead zone of the upper end enclosure in the natural circulation cooling process of the main system by setting strict main system cooling and depressurization executing steps and limiting conditions, and ensures that the reactor can be continuously cooled to a safe and controllable cold shutdown state after an accident.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the principles of the invention.

Fig. 1 is a schematic flow diagram of a method for cooling a pressurized water reactor nuclear power plant according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the invention.

It should be noted that, for convenience of description, only the portions related to the present invention are shown in the drawings.

In the present invention, the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

A method of cooling a pressurized water reactor nuclear power plant comprising the steps of:

s1, if the reactor has an accident that the safety injection is not triggered or does not need to be triggered;

s2, if the main system main pump fails to start, executing natural circulation cooling;

and S3, if the control body driving mechanism cooling fan fails to be started, executing the natural circulation cooling method suitable for the pressurized water reactor nuclear power plant.

If an accident occurs in a pressurized water reactor nuclear power plant and the emergency shutdown condition occurs, the accident condition needs to be analyzed.

And if the safety injection system needs to be triggered in case of an accident, judging whether the safety injection system can work normally.

A safety injection system is a safety injection system/emergency reactor core cooling system and has the function of ensuring that enough reliable reactor core cooling is provided under the accident condition, so that the minimum of the surface of a reactor core fuel cladding is not smaller than that under the accident condition, when a heat sink loss event occurs, a reactor emergency shutdown is triggered by a coolant outlet temperature overhigh signal, a main circulating pump automatically stops running, the pressure of a reactor inlet main pipe is reduced at the moment, a reactor pool water is conveyed to the reactor coolant inlet main pipe by an emergency pump, and at least cooling flow in a reactor flows through the reactor core from top to bottom and carries away heat emitted by the reactor core.

An emergency core cooling system is one of the dedicated safety facilities in a pressurized water reactor nuclear power plant. Some nuclear power plants are provided with emergency boron adding devices. When the main steam pipeline is broken, a centrifugal charging pump or a high-pressure safety injection pump of a chemical and volume control system is used for injecting boron-containing water with boron concentration of 7000-21000 mu g/g into the reactor core from the emergency boron adding tank, negative reactivity is introduced into the reactor core, the reactor is prevented from being re-critical, and the reactor is kept in a safe shutdown state.

The safe injection system consists of a safe injection box, a high-pressure or medium-pressure safe injection subsystem and a low-pressure safe injection subsystem.

If the safety injection system cannot work normally, the reactor needs to be cooled in a natural circulation mode.

If the safety injection system can work normally, whether the safety injection system needs to be used or not needs to be judged, and if the safety injection system needs to be used, the reactor is cooled through the emergency reactor core cooling system.

If the safety injection system is judged not to be used for cooling, the reactor needs to be cooled in a natural circulation mode.

And trying to restart the main system main pump again before natural cooling is executed, and if the main system main pump fails to start, determining to perform natural circulation cooling.

In the process of executing natural circulation cooling, a control rod driving mechanism cooling fan needs to be started to cool the flow dead zone of the upper end enclosure.

If the cooling fan of the control rod driving mechanism can work normally, natural circulation cooling is performed normally.

If the cooling fan of the control rod driving mechanism cannot work normally, other cooling methods are needed to be used so as to avoid the flash evaporation steam production of the reactor upper head in the natural circulation cooling process under the condition that the cooling fan of the driving mechanism cannot work and eliminate the risk of stopping the natural circulation cooling.

Example one

A natural circulation cooling method suitable for a pressurized water reactor nuclear power plant comprises the following steps:

10. boronizing the primary system to a cooled heap boron concentration;

and determining that the main system reaches a cold stop reactor boron concentration value through sampling analysis, and setting the supply control of the reactor boron and water supply system into automatic control, namely automatically injecting boron and water with corresponding amount through the boron concentration value.

20. Maintaining the pressure of the main system stable, and performing the hot section cooling of the main system;

30. carrying out pressure reduction on the main system;

40. step 20 and step 30 are circulated until the temperature of the hot section of the main system is reduced to a set value and the pressure of the main system is reduced to the set value;

the temperature and the pressure in the main system are reduced and decompressed through the circulation of temperature reduction and decompression.

41. Cooling the main system to a temperature of the hot section less than a first temperature;

42. the main system is depressurized to a pressure equal to the first pressure;

43. locking a safety injection signal;

44. maintaining the pressure of the main system at a first pressure, and cooling the main system until the temperature of the hot section is equal to a second temperature;

45. maintaining the supercooling degree of the main system, and reducing the pressure of the main system to be equal to the second pressure;

46. and maintaining the pressure of the main system at the second pressure, and cooling the main system to the temperature of the hot section equal to the third temperature.

50. Maintaining the temperature of the main system at a third temperature, and cooling the upper end enclosure fluid to be lower than a fourth temperature;

the fluid of the upper end enclosure is cooled, so that the fluid of the flowing dead zone of the upper end enclosure in the natural circulation cooling process of the main system can be effectively prevented from generating flash evaporation and steam.

60. And maintaining the temperature of the main system at a third temperature, maintaining the temperature of the upper head fluid to be lower than a fourth temperature, and reducing the pressure of the main system to be lower than a third pressure. Carrying out pressure reduction on the main system;

and after the upper end socket fluid is cooled, continuously reducing the pressure of the main system.

70. Isolating the safety injection box, and reducing the pressure of the main system to a final pressure value;

80. and (5) putting in a waste heat discharge system, and continuously cooling the main system to the cold shutdown working condition.

The operation process related in the embodiment does not need to add new systems and equipment in the nuclear power plant, and only needs to use the existing related equipment of the nuclear power plant, and mainly comprises a temperature measuring device, a water level measuring device, a pressure measuring device, a chemical and volume control system, a reactor boron and water supply system, a normal waste heat discharge system and other related control systems of the nuclear power plant, so that the steam produced by the upper end socket of the reactor of the nuclear power plant under the non-operational condition of a cooling fan of a driving mechanism can be effectively avoided, the reactor of the nuclear power plant of. The invention has clear processing steps, simple and convenient operation, small operation burden on operators, effectively reduces the probability of misoperation,

example two

A specific example is provided below, which applies to example one.

Boronizing the primary system to a cooled heap boron concentration;

and determining that the main system reaches a cold stop reactor boron concentration value through sampling analysis, and setting the supply control of the reactor boron and water supply system into automatic control, namely automatically injecting boron and water with corresponding amount through the boron concentration value.

The temperature of the main system is reduced to the temperature of the hot section less than 284 ℃, and the pressure reduction process needs to be ensured:

the cooling rate of the main system is less than 14 ℃/h;

the water level of the voltage stabilizer is at zero load water level;

the temperature and pressure of the main system are within the limit value of a natural circulation P-T diagram;

the water level of the steam generator in the narrow range is 34-50%.

The main system is depressurized by an auxiliary spraying system or a safety valve, and the main system is depressurized to a pressure equal to 13.56MPa (a), wherein MPa (a) is expressed as absolute pressure.

And locking the safety injection signal to avoid the work of a safety injection system.

Maintaining the pressure of the main system at 13.56MPa (a), cooling the main system to a temperature of the hot section equal to 225 ℃, and ensuring that:

the cooling rate of the main system is less than 14 ℃/h;

the water level of the voltage stabilizer is at zero load water level;

the main system temperature pressure is within the limits of the natural cycle P-T diagram.

Maintaining the supercooling degree of the main system at 70 ℃, and reducing the pressure of the main system to be equal to 8.27MPa (a);

the pressure of the primary system was maintained at 8.27MPa (a), and the primary system was cooled to a hot-section temperature equal to 177 ℃.

Maintaining the temperature of the main system at 177 ℃, and cooling the upper end enclosure fluid to be less than 210 ℃;

the fluid of the upper end enclosure is cooled, so that the fluid of the flowing dead zone of the upper end enclosure in the natural circulation cooling process of the main system can be effectively prevented from generating flash evaporation and steam.

Maintaining the temperature of the main system at 177 ℃, maintaining the temperature of the upper head fluid to be less than 210 ℃, and reducing the pressure of the main system to be lower than 7MPa (a) through an auxiliary spraying system or a safety valve.

Isolating the safety injection box, and reducing the pressure of the main system to a final pressure value of 2.7MPa (a);

and (5) putting in a waste heat discharge system, and continuously cooling the main system to the cold shutdown working condition.

In addition, the main system performs pressure reduction through the auxiliary spraying system, and if the auxiliary spraying system is unavailable, the pressure reduction is performed through the safety valve of the pressure stabilizer.

EXAMPLE III

The difference between the first embodiment and the second embodiment is that the detection time of the cooling fan of the control rod drive mechanism is changed, so that the operation steps are changed integrally, and the specific steps are as follows:

if an accident occurs in a pressurized water reactor nuclear power plant and the emergency shutdown condition occurs, the accident condition needs to be analyzed.

And if the safety injection system needs to be triggered in case of an accident, judging whether the safety injection system can work normally.

If the safety injection system cannot work normally, the reactor needs to be cooled in a natural circulation mode.

If the safety injection system can work normally, whether the safety injection system needs to be used or not needs to be judged, and if the safety injection system needs to be used, the reactor is cooled through the emergency reactor core cooling system.

If the safety injection system is judged not to be used for cooling, the reactor needs to be cooled in a natural circulation mode.

And trying to restart the main system main pump again before natural cooling is executed, and if the main system main pump fails to start, determining to perform natural circulation cooling.

Boronizing the primary system to a cooled heap boron concentration;

and determining that the main system reaches a cold stop reactor boron concentration value through sampling analysis, and setting the supply control of the reactor boron and water supply system into automatic control, namely automatically injecting boron and water with corresponding amount through the boron concentration value.

The temperature of the main system is reduced to the temperature of the hot section less than 284 ℃, and the pressure reduction process needs to be ensured:

the cooling rate of the main system is less than 14 ℃/h;

the water level of the voltage stabilizer is at zero load water level;

the temperature and pressure of the main system are within the limit value of a natural circulation P-T diagram;

the water level of the steam generator in the narrow range is 34-50%.

The main system is depressurized by an auxiliary spraying system or a safety valve, and the main system is depressurized to a pressure equal to 13.56MPa (a), wherein MPa (a) is expressed as absolute pressure.

And locking the safety injection signal to avoid the work of a safety injection system.

Maintaining the main system stable at 13.56mpa (a):

in addition, the cooling process of the main system is monitored through instruments, sensors and systems of the reactor, so that the temperature of a thermocouple at the outlet of the reactor core is ensured to be reduced, the temperature of a hot section of the main system is reduced, and the supercooling degree of the outlet of the reactor core is ensured to be increased.

At the moment, a cooling fan of the control rod driving mechanism is required to be started to cool the flow dead zone of the upper end enclosure.

If the cooling fan of the control rod driving mechanism can work normally, natural circulation cooling is performed normally.

If the cooling fan of the control rod driving mechanism cannot work normally, other cooling methods are needed to be used so as to avoid the flash evaporation steam production of the reactor upper head in the natural circulation cooling process under the condition that the cooling fan of the driving mechanism cannot work and eliminate the risk of stopping the natural circulation cooling.

Maintaining the pressure of the main system at 13.56MPa (a), cooling the main system to a temperature of the hot section equal to 225 ℃, and ensuring that:

the cooling rate of the main system is less than 14 ℃/h;

the water level of the voltage stabilizer is at zero load water level;

the main system temperature pressure is within the limits of the natural cycle P-T diagram.

Maintaining the supercooling degree of the main system at 70 ℃, and reducing the pressure of the main system to be equal to 8.27MPa (a);

the pressure of the primary system was maintained at 8.27MPa (a), and the primary system was cooled to a hot-section temperature equal to 177 ℃.

Maintaining the temperature of the main system at 177 ℃, and cooling the upper end enclosure fluid to be less than 210 ℃;

the fluid of the upper end enclosure is cooled, so that the fluid of the flowing dead zone of the upper end enclosure in the natural circulation cooling process of the main system can be effectively prevented from generating flash evaporation and steam.

Maintaining the temperature of the main system at 177 ℃, maintaining the temperature of the upper head fluid to be less than 210 ℃, and reducing the pressure of the main system to be lower than 7MPa (a) through an auxiliary spraying system or a safety valve.

Isolating the safety injection box, and reducing the pressure of the main system to a final pressure value of 2.7MPa (a);

and (5) putting in a waste heat discharge system, and continuously cooling the main system to the cold shutdown working condition.

In the whole cooling process of the main system, the cooling process is monitored by the existing related equipment of the nuclear power plant (mainly comprising the main temperature, water level and pressure measuring devices of the nuclear power plant, a chemical and volume control system, a reactor boron and water supply system, a normal waste heat discharge system and other related control systems).

In the description herein, reference to the description of the terms "one embodiment/mode," "some embodiments/modes," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/mode or example is included in at least one embodiment/mode or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to be the same embodiment/mode or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/aspects or examples and features of the various embodiments/aspects or examples described in this specification can be combined and combined by one skilled in the art without conflicting therewith.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

It will be understood by those skilled in the art that the foregoing embodiments are merely for clarity of description and are not intended to limit the scope of the invention. It will be apparent to those skilled in the art that other variations or modifications may be made on the above invention and still be within the scope of the invention.